### i March 2007 

# Solutions to Analytical Chemistry

Problems with Clean Water Act Methods

March 2007

### ii March 2007 

## Solutions to Analytical Chemistry Problems

with Clean Water Act Methods

Prepared by

Analytical Methods Staff Engineering and Analysis Division Office of Science Technology

Office of Water U. S. Environmental Protection Agency Washington, DC

EPA 821-R-07-002

March 2007

### iii March 2007 

### Disclaimer

This technical document recommends ways to document and resolve analytical chemistry problems encountered in the analysis of wastewater sa mples. This advice is not a substitute for the Clean Water Act (CWA) or EPA regulations, nor is this doc ument a regulation. The advice in this document does not alter any otherwise applicable statutory or regulatory requirements and does not, and may not, impose legally binding requirements on EPA, States, Tribes, or the regulated community.

Our advice may not apply to your case-specific circumstances. EPA, State and other decision makers retain the discretion to adopt other appro aches on a case-by-case basis where appropriate, or when

additional information is available to them. It is recommended that commercial laboratories convey analytical problems to their customers and permitte es communicate problems to their regulatory authority and regional EPA water program offices.

Staff of the Engineering and Analytical Support Branch within the Engineering and Analysis

Division of the EPA Office of Water have reviewed this document. Mention of trade names or commercial products does not constitute e ndorsement or recommendation for use.

### iv March 2007 

### Foreword

“ Solutions to Analytical Chemistry Problems with Clean Water Act Methods “ is an update of the

document titled “G uidance on Evaluation, Resolution, and Documentation of Analytical Problems Associated with Compliance Monitoring”, which was published in 1993. The 1993 document has been

referred to as the A Pumpkin Book @ because of its pumpkin-colored cover. The material and technical advice in the Pumpkin Book, and this document are b ased on questions and situations directed to EPA’s Clean Water Act chemists by the EPA regions, stat e agencies and other users of our methods. The questions and situations discussed in this documen t concern analytical challenges encountered in the conduct of compliance monitoring under the Clean Water Act (CWA) for chemical pollutants.

The purpose of this document is to recommend ways to document the existence of a matrix or analytical problem with a CWA sample analysis, and m itigate these problems.

This document is organized as follows:

Chapter 1 Introduction Chapter 2 Sampling Requirements Chapter 3 Flexibility to Modify an Analytical Method Chapter 4 Data Required to Document Matrix Interference Chapter 5 Case Histories of Reports of Matrix Interferences Chapter 6 Solutions to Matrix Interference Problems Chapter 7 Review of Data from Analysis of Samples Chapter 8 When a Matrix Interference Is Demonstrated Chapter 9 Sources of Additional Help

EPA's Engineering and Analysis Division (EAD) is solely responsible for the content of this document. Comments and suggestions should be directed to:

CWA Analytical Methods Staff Engineering and Analysis Division (4303T) Office of Science and Technology U.S. Environmental Protection Agency 1200 Pennsylvania Avenue, N.W. Washington, DC 20460

E-mail: OSTCWAMethods@epa.gov

### v March 2007 

### Table of Contents

Disclaimer

............................................................................................................................... ......iii

Foreword

............................................................................................................................... ........ iv Chapter 1 Introduction ................................................................................................................. 1 Pollutants Regulated Under the Clean Water Act....................................................................... 1 Analytical Methods Approved U nder the Clean Water Act ....................................................... 1 Scope of This Document......................................................................................................... .... 2 Chapter 2 Sampling Requirements ............................................................................................. 4 Sample Collection.............................................................................................................. ......... 4 NPDES Sampling Requirements ............................................................................................ 4 Pretreatment Program Sampling Requirements...................................................................... 5 Trace Metals Sampling Guidance........................................................................................... 5 Compositing Samples for Volatiles ........................................................................................ 5 Sample Preservation and Holding Times.................................................................................... 5 Chapter 3 Flexibility to Mo dify an Analytical Method ............................................................. 7 Balancing Flexibility and Performance ...................................................................................... 7 EPA's Alternate Test Procedure (ATP) Program........................................................................ 7 Flexibility in the EPA Methods ................................................................................................. . 8 Demonstrating Equivalency of a Method Modification ............................................................. 9

Initial Demonstration of Method Performance ....................................................................... 9 Application of a Method Modifi cation to a Sample Matrix ................................................. 10 Suggested QC Acceptance Criteria for Crit eria Not Stated in Approved Methods.............. 10 Intractable Samples............................................................................................................ ....... 10 Chapter 4 How to Document Matrix Interference .................................................................. 11 Chapter 5 Reports of Matrix Interferences .............................................................................. 15

Case Histories ................................................................................................................. .......... 16 Chapter 6 Solutions to Matrix Interferences ............................................................................ 20 Solving Matrix Problems ........................................................................................................ .. 20 Solutions Applicable to Nearly All Analytes............................................................................ 20

Selective Reaction and/or Rem oval of the Interferent.......................................................... 20 Method of Standard Additions (MSA) ................................................................................. 20 Solutions Applicable to Classical Pollutants ............................................................................ 21

Oil and Grease................................................................................................................. ...... 21 Cyanide ........................................................................................................................ ......... 21 Solutions Applicable to Metals Pollutants................................................................................ 24

Clean Room ..................................................................................................................... ..... 24

General Matrix Interferences ................................................................................................ 25

Chromium VI.................................................................................................................... .... 25 Mercury........................................................................................................................ ......... 25 Solutions Applicable to Organic Pollutants.............................................................................. 25

Volatiles ...................................................................................................................... .......... 25

Semivolatiles.................................................................................................................. ....... 26 Determination of Phenol as a Specific Example....................................................................... 27

### vi March 2007 

### Chapter 7 Review of Data from Analysis of Samples .............................................................. 29 Standardized Quality Control ................................................................................................... 29 Provision of QC Data........................................................................................................... ..... 30

Review of Data from the 600- and 1600-Series Methods......................................................... 30 Chapter 8 When a Matrix Interference Is Demonstrated ....................................................... 41 Poor Recovery or Precision of the Matrix Spikes..................................................................... 41 Inability to Meet the Met hod Detection Limit (MDL) ............................................................. 41

Allowance for a Matrix Interference......................................................................................... 42 Chapter 9 Sources of Additonal Help and Information .......................................................... 43

Web Sites ...................................................................................................................... ............ 43

Method Indices................................................................................................................. ......... 43

Office of Water CD-ROMs....................................................................................................... 4 3

Water Docket ................................................................................................................... ......... 44 Federal Register ............................................................................................................... ......... 44 Code of Federal Regulations.................................................................................................... . 44 Approval of an Alternate Test Procedure ................................................................................. 45 Sources for Supporting Documents .......................................................................................... 46

Appendices 

### A) Text of October 26, 1984 Preamble, pp. 7-11 B) Text of Preamble to March 12, 2007 Methods Update Rule (Note flexibility only applies to 40 CFR Part 136 methods) C) Recommended Approved Modifications to EPA Method 625

### 1 March 2007 

## Chapter 1

Introduction

Pollutants Regulated Under the Clean Water Act

The Federal Water Pollution Control Act (FWPCA ) Amendments of 1972, later amended as the Clean Water Act (CWA), classifies each pollutant as a “conventional pollutant,” “toxic pollutant,” or “non-conventional pollutant.” The fi ve “conventional pollutants” are codified at Title 40, Part 401.16 of

the Code of Federal Regulations (40 CFR Part 401.16). (For information on how to access the CFR, see Chapter 9 of this document). The five conventional pollutants are:

$ biological oxygen demand (BOD)
$ total suspended solids (TSS)
$ fecal coliform
$ pH
$ oil and grease

There are 65 “toxic pollutants” listed at 40 CFR Part 401.15 and this group of pollutants has been further refined to a list of 126 “priority pollutants” at 40 CFR Part 423, Appendix A. The priority pollutants can be subdivided into:

$ cyanide
$ asbestos
$ 13 metals pollutants
$ 25 pesticide/PCB pollutants
$ 86 non-pesticide/non-PCB organic pollutants

By definition, all pollutants other than “conve ntional pollutants” or “toxic pollutants” are “nonconventional pollutants.” Examples of non-conventional pollutants are:

$ toxicity (acute or chronic)
$ chemical oxygen demand (COD)
$ metals and organic compounds not on the priority pollutant list
$ radioactivity
$ color

Analytical Methods Approved Under the Clean Water Act

CWA Section 304(h) requires EPA to publish test procedures (analytical methods) appropriate for the measurement of pollutants. These methods are commonly known as the “304(h) methods”.

CWA Section 402 establishes a National Pollutant Discharge Elimination System (NPDES) to control the discharge of pollutants to surface wate rs of the U.S. NPDES is implemented through regulations at 40 CFR Parts 100 - 135 and the effluent guidelines and pretreatment regulations at 40 CFR Parts 400 - 500. The CWA prohibits any discharger of a pollutant except in compliance with the Act, including Section 402. EPA regulations implemen ting Section 402 generally require facilities that discharge wastewater directly to surface waters of th e U.S. to obtain an NPDES permit. The regulations refer to the facility or person that discharges pollu tants as “discharger,” “permittee,” or “applicant”.

### 2 March 2007 Facilities that discharge wa stewater to a publicly owned treatment works (POTW) are known as indirect dischargers and subject to pretreatment requirements. EPA’s pretreatment program regulations are found at 40 CFR Part 403. The term “discharger” will be used in this document to mean a discharger, permittee, applicant, or other entity regulated under EPA's wa stewater regulations. Under the regulations, each discharger is required to monitor its effluent for co mpliance with any and all relevant Federal and State discharge limitations, and use the 304(h) methods to demonstrate compliance with NPDES and pretreatment program limitations. Regulatory author ities have accepted primacy for implementing the Clean Water Act and with that responsibility have au thority to be more restrictive than the federal regulations.

The 304(h) methods are published or incorporat ed by reference at 40 CFR Part 136 or 40 CFR Parts 405 – 500 and are commonly known as the “Part 136 methods.” For many analytes, these methods include methods published by EPA, by the U.S. Geological Survey (USGS), by voluntary consensus standards bodies such as ASTM International (former ly known as the American Society for Testing and Materials International), and by manufactu rers of instruments and testing devices.

The Part 136 methods include me thods approved for use in all of EPA's wastewater and ambient water programs (e.g., methods for gene ral use). Methods approved for general use are listed in tables at 40 CFR Part 136.3(a), including:

$ Table IA - List of approved biological methods
$ Table IB - List of approved inorganic test procedures
$ Table IC - List of approved test procedures for non-pesticide organic compounds
$ Table ID - List of approved test procedures for pesticides
$ Table IE - List of approved radiological test procedures
$ Table IF - List of approved methods for pharmaceutical pollutants
$ Table IG – Test methods for pesticide active ingredients
$ Table IH – List of approved microbiological methods for ambient water

Methods approved for use in a single industrial category are published in tables at 40 CFR Part 136 or at 40 CFR Parts 405 - 500. If the methods are not published in tables at 40 CFR Part 136, they are not approved for general use, and may only be used for discharges from the industrial category for which they are approved. These special category methods ar e for uses when the nature of the discharge from a particular industry poses unique analytical challenges, or when the pollutants to be regulated are specific to that industry. For example, methods approved fo r use in the Pharmaceuticals industrial category are listed in Table IF at 40 CFR Part 136, while met hods approved for use in the Pesticides Manufacturing industrial category are listed in Table 7 at 40 CFR Part 455.

At present, there are 75 pollutants listed in Tabl e IB, including common inorganic anions, metals, and many of the conventional polluta nts named above. To simplify discu ssions in the remainder of this document, the term “classical pollutant” will re fer to all the pollutants listed in Table IB, except the metals (i.e., the conventional pollu tants listed in Table IB and all other non-metals in the table).

Scope of This Document

We presume that you have knowledge of, and access to the relevant Part 136 analytical methods. These methods cover a wide range of pollutants and analytical technologies. The method descriptions range from a few pages for simple tests to lengthy an d detailed documents covering hundreds of analytes. Many of these methods and accompanying documents are available on various CD-ROM products or at the Office of Science and Technology (OST) web si te at www.epa.gov/waterscience/methods. Methods from other organizations are often available from those organizations for a fee (see Chapter 9.)

### 3 March 2007 Our goal is to address a broad range of analytical problems and sample types. As a result, some

level of detail was sacrificed and some situations ha ve not been addressed in this document. However, the approaches to resolve matrix in terferences that are described in this document may be applied to issues not specifically addressed in this publication. States and EPA have laboratories with experts to answer some questions regarding analytical problems.

This document does not cover analyses of oil and grease, metals requiring the use of “clean” sampling and analysis techniques, whole-effluent toxicity (WET), biological (microbiological), or radiological pollutants. EPA has provided guida nce for some of these categories, including:

$ Analytical Method Guidance for EPA Method 1664A Implementation and Use (40 CFR Part 136), EPA 821-R-00-003, February 2000, (Oil & Grease)

$ Guidance for Implementation and Use of EPA Method 1631B (40 CFR Part 136) , EPA 821-R-01- 023, March 2001, (Mercury)

$ Method 1669: Sampling Ambient Water for Trace Metals at EPA Water Quality Criteria Levels , EPA 821-R-96-011, July 1996,

$ Guidance on Establishing Trace Metal Clean Rooms in Existing Facilities, EPA 821-B-95-001, January, 1996,

$ Trace Metal Cleanroom , prepared by the Research Triangle Institute, RTI/6302/04/02 F,

$ Evaluating Field Techniques for Collecting E ffluent Samples for Trace Metals Analysis, EPA-821-R98-008, June 1998,

$ Guidance on the Documentation and Evaluation of Tra ce Metals Data Collected for Clean Water Act Compliance Monitoring, EPA 821-B-96-004, July, 1996,

$ Water Quality-Based Permitting for Trace Metals Fact Sheet, April 1996 (no EPA number)

,

$ Method Guidance and Recommendations for Whole Efflu ent Toxicity (WET) Testing (40 CFR Part 136) (EPA 821-B-00-004, July 2000; the “WET Methods guidance”), and

$ Understanding and Accounting for Method Variability in Whole Effluent Toxicity Applications Under the National Pollutant Discharge Elimination System Program (June, 2000).

Guidance for microbiological methods can be found in Section 9000 of Standard Methods for Examination of Water and Wastewater

.

Guidance for radiochemistry me asurements can be found in the Multi-Agency Radiological Laboratory Analytical Protocols Manual (EPA 402-B-04-001A to C (in three volumes); the “MARLAP Manual”) published in Volume 69, page 77228 of the Federal Register (69 FR 77228) on December 27,

2004.

The documents listed above are available from the sources in Chapter 9.

### 4 March 2007 

## Chapter 2

Sampling Requirements

Sample Collection

The collection of the sample can have significan t effects on the overall analytical process. In addition, to ensure some degree of consistency a nd representativeness, EPA requires that a sample for compliance monitoring be collected in a prescribed f ashion. Sampling requirements for the NPDES and pretreatment programs are spelled out in Parts 122 and 403 of Title 40 of the CFR.

Even when the analyst or other laboratory pers onnel are not responsible for collecting the sample, it is important for them to understand EPA’s sampli ng requirements in order to provide acceptable and cost-effective analytical results (e.g., there may be littl e point in analyzing an improperly collected sample if the results may not be used for compliance mon itoring). Ideally, laboratory personnel will have ready access to the relevant sections of the CFR. However, recognizing that this is not always practical, a reasonable level of detail is provided below.

NPDES Sampling Requirements

The sampling requirements under NPDES are given at 40 CFR Part 122, as part of the requirements for applying for an NPDES discharge perm it. The requirements are broken out by type of industry and discharge. For example:

$ 40 CFR Part 122.21(g)(7) provides the requirements for sampling existing manufacturing, commercial, mining, and silvicultural dischargers,

$ 40 CFR Part 122.21(h)(4)(i) provides the require ments for sampling manufacturing, commercial, mining and silvicultural facilities that discharge only non-process wastewater.

$ 40 CFR Part 122.21(j)(4)(viii) provides the requi rements for sampling new and existing publicly owned treatment works (POTWs).

Although many of the other permit application requi rements differ among these types of dischargers, they have in common the requirements for collecting grab samples for certain pollutants and how composite samples for other pollutants must be collected, namely:

“ Grab samples must be used for pH, temp erature, cyanide, total phenols, residual chlorine, oil and grease, fecal coliform, feca l streptococcus, E. coli, Enterococci, and volatile organics, unless specified otherwise at 40 CFR Part 136. For all other pollutants, a 24-hour composite sample, using a minimum of four (4) grab samples, must be used unless specified otherwise at 40 CFR Part 136.”

Providing acceptable data for NPDES compliance samp les requires that the sample be collected in the required fashion. Therefore, laboratory personnel should recognize that grab samples are required for the 12 pollutants listed above and 24-hour composite samples are to be used for all other pollutants monitored under an NPDES permit.

### 5 March 2007 Pretreatment Program Sampling Requirements

Sampling requirements for the pretreatment program are found at 40 CFR Part 403, specifically at 40 CFR Part 403.7(b)(2)(iii), 40 CFR Part 403(b)(2)(iv), 40 CFR Part 403.12(b)(5)(iii), and 40 CFR Part 403, Appendix E. Similar to NPDES program require ments, these sections list the pollutants for which grab sampling is required. Appendix E to Part 403 gives details on the collection of grab and composite samples for the pretreatment program.

Trace Metals Sampling Guidance

Sampling for trace metals presents a unique challe nge to avoid sample contamination. EPA has guidelines for sampling ambient water for trace metals (See Chapter 9).

Compositing Samples for Volatiles

As specified in 40 CR 122.21 and noted above, samp les to be analyzed for volatile organics must be collected as grab samples and not with an automa ted compositing device. This stands to reason, since the compositing equipment is at least partially open to the atmosphere and volatil e contaminants could be lost from the equipment during the lengthy sample collection period. While using grab samples for volatiles preserves the integrity of the individual sample, it raises the overall analytical cost when multiple samples of the same discharge have to be collected and analyzed.

EPA has studied the differences between the analysis of individual grab samples, and analysis of a composite sample prepared at the laboratory from grab samples collected in the field. The study was not conclusive so the EPA has not recommended VOA compositing procedures.

Sample Preservation and Holding Times

Sample preservation and holding time requirements are listed by analyte or analyte group in Table II at 40 CFR Part 136, and are detailed in the analytical methods. The information listed in Table II is often generic, as it applies to a large group of analyt es, e.g., metals. The information in the methods is often more specific because preservation and holdi ng times generally are studied as a part of method development. However, in some cases, there are f ootnotes in the table for specific analytes that provide additional information or requirements that are critical to compliance monitoring. The footnotes to Table II at 40 CFR Part 136 often are quite deta iled and address, but are not limited to:

• Sample containers,

• Sample holding times,

• Sample preservation, including instances in which the sample must be held for a shorter time than the stated holding time if the shorter time is necessary to mainta in sample stability,

• Department of Transportation (DOT) shipping requirements,

• Interferences specific to certain parameters; e.g., interferences specific to cyanide.

Because the footnotes may change with each update to Part 136, the current version of the CFR

should be consulted for the latest information. The order of precedence for the sample preservation and holding time requirements is:

$ Table II with footnotes,
$ The individual method

### 6 March 2007 Conflicts between these requirements can arise, particul arly if new methods are brought into use and the generic requirements in Table II are inadvertently not revised. If you discover a potential conflict between the holding time requirements in Table II and in a method, please notify the Engineering and Analysis Division at the e-mail address given in Chapter 9, and your permitting authority or your client.

### 7 March 2007 

## Chapter 3

Flexibility to Modify an Analytical Method

Balancing Flexibility and Performance

EPA provides analysts with the flexibility to d eal with interferences, or otherwise improve method performance. This flexibility dates back to the in ception of EPA’s wastewater method approval program. In December 1979, when EPA proposed the majority of the test methods for organic pollutants, the Agency requested comments on the relationship between flexibility in methods and the approach to quality control. After reviewing those comments, EPA deci ded to allow limited flexibility in both the sample preparation and analysis portions of its methods. The major flexibility options are discussed in the preamble of the October 26, 1984 final rule promulga ting the organic methods at 40 CFR Part 136. That discussion, which is reproduced in the appendix of th is document, specifically cites the ability to change chromatographic conditions such as co lumn packings and detectors and changes to sample concentration procedures. The preamble also states that:

“However, the primary objective underlying th is flexibility is to enhance precision and accuracy for each analysis. Flexibility shoul d not be permitted if the altered technique would be less precise or less accurate than the standard approved analytical method. Thus, a corollary of increased flexibility was an increased need for a rigorous and unambiguous quality control procedure.”

All of the EPA methods approved at 40 CFR 136 since 1984 have incorporated a rigorous and standardized approach to quality control. If unsur e, the permittee should contact the regulatory authority with questions and guidance on what constitutes allowable flexibility.

EPA's Alternate Test Procedure (ATP) Program

In addition to balancing limite d flexibility in the methods against a more rigorous quality control procedure, EPA included a process for obtaining appr oval of an alternate test procedure (ATP) on a nationwide basis or on a site- or discharge-specific basis (40 CFR Parts 136.4 and 136.5).

The ATP program is intended to encourage deve lopment of new or improved analytical methods and to give analysts options for reso lving analytical problems that may be unique to specific wastewaters. If you want to use a method other than those specified at 40 CFR Part136, you should apply to the Engineering and Analysis Division for approval of a nationwide ATP, or to the State or Regional EPA authority for approval of a limited-use ATP e.g. an approval for method changes from those listed in 40 CFR Part 136 which are granted to a specifi c site/facility as opposed to all permittees.

As part of the ATP program, EPA developed prot ocols to assist applicants seeking EPA approval of alternate test procedures or new methods for use in monitoring wastewater, ambient water, and drinking water. There are protocols for organic and inorgani c contaminants, and microbiological contaminants. The changes instituted in 1999 made the process simpler. These protocols are available at www.epa.gov/waterscience/methods . (EPA 821-B-98-002 Protocol for EPA Approval of Alternate Test Procedures for Organic and Inorganic Analytes in Wastewater and Drinking Water March 1999)

### 8 March 2007 Flexibility in the EPA Methods

As noted above, flexibility is permitted in many EPA analytical methods. For example, the methods for organic pollutants published at 40 CFR Part 136, Appendix A note that the analyst is permitted to “improve separations or lower the costs of analyses” provided that the results obtained are as or more accurate than the results obtained using the unmodified method. Recent EPA methods for other analytes may also include speci fic allowances for flexibility.

The flexibility to make changes in approved methods without prior approval from EPA is

described at 40 CFR Part 136.6. The full text of Part 136.6 is reproduced in the appendix of this document. It is strongly recommended that analysts consult the full text of 40 CFR Part 136.6 before undertaking method modifications. Briefly, Part 136 .6 (b)(1) describes allowable method modifications, including:

$ Changes between automated and manual discrete instrumentation,
$ Changes between automated and manual sample preparations such as digestions, distillations, and extractions (provided that the temperatures and/or exposure times are maintain same as manual method to achieve same performance),
$ Changes in the calibration range (provided that th e modified range covers any relevant regulatory limit),
$ Changes in equipment such as using similar equipm ent from a vendor other than that mentioned in the method,
$ Changes in equipment operating parameters such as minor changes in the monitoring wavelength of a colorimeter or modifying the temperature program for a specific GC column,
$ Changes to chromatographic columns, including th e use of a capillary (open tubular) GC column with EPA Methods 601-613, 624, 625, and 1624B, and
$ Increases in purge-and-trap sample volumes,
$ Adjusting sample sizes or changing extraction so lvents to optimize method performance in meeting regulatory requirements.

Such changes are only allowed if the modified met hod produces equivalent performance for the analyte(s) of interest, and the equivalent pe rformance is documented. Part 136. 6 provides detailed requirements for

both the demonstration and documentation of the performance of a modified method.

Note: The allowance for modifications does not apply to a method for a method-defined analyte or a change that would result in measurement of a di fferent form or species of an analyte (e.g., a change to a metals digestion or total cyanide di stillation). It also does not apply to changes in sample preservation and/or holding time.

In addition to the flexibility provided by the ATP program and in the analytical methods, EPA suggests that regulatory authorities allow flexibility in the spirit of method improvement. Because it is not possible to address all matrix interferences in all wastewaters, it may be necessary to tailor a method modification to a specific matrix interference probl em. For example, the solid-phase and continuous liquid/liquid extraction have been shown to be eff ective in reducing emulsions formed with separatory funnel extraction, and microwave and bomb digesti ons have been shown to be more effective in solubilizing some metals than minera l acid digestions. The spirit of allowing a method modification is that the change results in improved method performance such as accuracy (e.g. recovery) a lower detection limits, or better precision.

### 9 March 2007 Demonstrating Equivalency of a Method Modification

Your objective in modifying a method should be to make it more specific for a given pollutant, more sensitive, more accurate, or to improve the method in some other way without compromising the performance of the method for the intended use. Such improvements could include reducing the overall cost of the analysis, or reducing the volumes of wastes produced by the analysis. However, some laboratories have interpreted the provision to modify a method solely as a means of increasing the speed of analysis, thus reducing the analysis time, or taking other “shortcuts” to reduce cost. This is not EPA’s approach.

EPA has addressed this issue by:

1. providing limited flexibility within the met hods, so that improvements can be made, and 2. requiring the analyst to demonstrate that the results produced by a modification will be equal or superior to results produced by the unmodified method.

The yardsticks by which this perform ance is to be measured are pr ecision and recovery, but can be extended to include detection limit, chromatographi c resolution, mass spectral resolution, and other measures of method performance. For compliance analyses, clearly note that the method is modified and communicate the modifications to the regulatory authority. If in doubt contact your local regulatory authority.

Initial Demonstration of Method Performance

To prove the modification is appropriate, the laboratory should first perform an initial precision and recovery test (IPR) with the unmodified method, and record the results. The initial demonstration provides validation of the performance of a method by a specific laboratory. The procedure is described in

detail in Section 8 or 9 of the 600-series and 1600- Series wastewater methods and also is in ASTM International methods and other methods systems. Fo r some methods systems, the IPR may be termed an “initial demonstration of method performance” or “in itial demonstration of capability” (IDC). A typical test consists of an analysis of four or more rep licate volumes of reagent water, or other appropriate reference matrix, spiked with the pollutants of interest at the concentration specified in the method or at 5–

10 times the detection limit of the method. The fi nal demonstration should be done in the actual

wastewater matrix of concern.

For each analyte, the precision of analysis of the replicates, as determined by the standard deviation or relative standard deviation (RSD) of the measurements, should be less than the standard deviation or RSD specified in quality control (QC) accep tance criteria in the method. Similarly, for each analyte, the average percent recovery of the measureme nts should fall within the range of percent recovery specified in the method. If either the precision or r ecovery test is failed, the test is repeated until the laboratory is able to meet preci sion and recovery requirements.

Include a minimum of one blank in the initial demonstration, and the concentration of the analyte(s) in the blank should be less than the level(s) specified in the method.

If you modify a method, repeat the initial demonstration with the modification as an integral part of the method, until the QC acceptance criteria in the method for precision and recovery and for the blank are met. Otherwise, the modification is not permitted. Maintain records that document that the initial demonstration was performed on the modified method and those requirements for precision and recovery

and the blank were met.

### 10 March 2007 Application of a Method Modification to a Sample Matrix

In addition to the initial demonstration in a refe rence matrix such as reagent water, the method modification is applied to the specific discharge or sample matrix to which the modified method will be applied in monitoring. The modified method is tested by spiking the analytes of interest into duplicate aliquots of the sample matrix at a concentration of 5 - 10 times the background concentration of the pollutant in the sample, 1 - 5 times the quantitation lim it, or 1 -5 times the regulatory limit, whichever is greatest. The recoveries of the analytes from these ma trix spike/matrix spike duplicate (MS/MSD) tests are compared to the QC acceptance limits in the origin al method. Likewise, the relative percent difference (RPD) of the MS/MSD results is calculated and comp ared to the QC limits for RPD in the approved method. The modification is acceptable if the rec overy and RPD meet the respective limits. Methods from some sources may use terms other than MS/MSD for these QC samples, but the concept and use

remain the same.

Suggested QC Acceptance Criteria for Cr iteria Not Stated in Approved Methods

Many of the older methods listed in the tables at 40 CFR Part 136 do not contain standardized QC or QC acceptance criteria. To fill this gap, EPA pr oposed standardized QC tests and analyte-specific QC acceptance criteria for all 75 contaminants in Table IB at 40 CFR Part 136 in a “Streamlining Initiative” in 1997. The initiative was proposed on March 28, 1997 (62 FR 14975) and a correction was published on June 26, 1997 (62 FR 34573). The QC acceptance cr iteria published in the Streamlining Initiative were developed from interlaboratory data or from single-laboratory data with an allowance for interlaboratory variability (see Section III.B.2 of the proposal at 62 FR 14983). Although that initiative was not completed, EPA remains committed to the intent of th is initiative. EPA suggests use of the QC tests and QC acceptance criteria in the Streamlining In itiative as a starting point for evaluating method modifications when the approved method is absent of such tests and criteria.

Intractable Samples

Method flexibility permits pollutant identities and c oncentrations to be determined in nearly all wastewaters, but EPA recognizes that there may be a few intractable sample matrices that do not yield readily to extensive analytical efforts. Please let EPA or your regulatory authority know about modifications that you have made that have worked or not worked with difficult matrices. Reporting to the permitting authority that “the sample couldn't be an alyzed” is not sufficient and will not be accepted as justification for a claim of matrix interference. S ee Chapter 4 for the information that will document a matrix interference and Chapter 8 for possible relief when a matrix interference is shown.

### 11 March 2007 

## Chapter 4

How to Document Matrix Interference

This chapter outlines the analytical data and other information that the EPA recommends be provided to evaluate a discharger's claim that a co mplex matrix precludes measurement of a pollutant. Generally, the data are the same as data gathered by EPA in developing the Agency's regulations.

Because different analytical techniques provide different data (e.g., gas chromatography/mass spectrometry (GC/MS) procedures produce plots of mass intensities while colorimetric procedures do not), the specific form of the data will differ according to the method. The following items describe the minimum data that should be develope d to support a claim of compliance.

1. The identity of the method used for the measurement.

In order to support a claim of a matrix interference, the analyst should, of course, use a method that is approved for the pollutant of interest for NPDES co mpliance monitoring. Therefore, the most basic information an analyst should submit is the iden tity of the method used for the measurement e.g., separatory funnel or continuous liquid/liquid extraction. This information should include the source of the method (e.g., EPA, Standard Methods , or ASTM), the method number, complete with any letter suffixes or “point” designations (e.g., 1613B or 350. 1), and the date of issue of the method (for EPA methods) or the edition of the method compilation (e.g., Standard Methods , 18th edition). The tables

at 40 CFR Part 136 illustrate the level of deta il required to unambiguously identify a particular

method. The date of an EPA method revision or the edition from which a Standard Method is drawn

are often critical because not all EPA method revisi ons are approved at 40 CFR Part 136 and different

editions of Standard Methods may use different letter suffixes fo r the same technique as methods are added or removed from the manual (e.g., SM 4500-S -2 E in the 18th edition is the iodometric method, but in the 19th and 20th editions, the iodometric method is SM 4500-S -2 F).

2. A detailed narrative discussing the problems wi th the analysis, corrective actions taken, and the changes made to the approved method identified.

The discharger should describe the reasons for th e change to the approved method, the supporting logic behind the technical approach to the change, and the result of the change.

Many compliance monitoring analyses are performed by contract laboratories on behalf of the discharger. However, the responsibility for provi ding the information to EPA rests with the discharger. The discharger should, therefore, impre ss upon its contract laboratory the need for detailed technical communication of problems experienced a nd solutions attempted. The narrative should be authored by an analyst and written in terms that another analyst can understand.

3. A summary level report or data reporting form s giving the pollutants for which analyses were

conducted and the concentrations detected. Fo r the pollutants that were not detected, the detection limits or estimated detection limits should be provided.

Such results should be provided for each field sample analyzed, including any dilutions and reanalyses. If not specified in the approved met hod, the means for estimating the detection limit of each pollutant should be provided in the narrative. If the laboratory uses “flags” in its data reporting, the definition of each flag should be provided with the data.

### 12 March 2007 4. A summary of all quality control resu lts required by the approved method.

These results include, but are not limited to the following:

• Instrument tuning, if applicable

• Calibration

• Calibration verification

• Initial precision and recovery test, as described in Chapter 3

• Ongoing demonstration of laboratory capability (i.e., ongoing precision and recovery, laboratory control sample, laboratory fortified blank)

• Matrix spike/matrix spike duplicate (MS/MSD) or equivalent spiked sample matrices

• Surrogate recovery, if applicable

• Labeled compound recovery (isotope dilution methods)

• Blank results

5. Raw data that will allow an independent revie wer to validate (reconstruct) each determination and calculation performed by the laboratory.

This validation would consist of tracing the instru ment output (peak height, area, or other signal intensity) to the final result reported. The raw data are method specific and may include any of the following:

• Sample numbers or other identifiers used by the both the discharger and the laboratory

• Extraction or digestion date

• Analysis date and time

• Sequence of analyses or run log

• Sample volume

• Extract volume prior to each cleanup step

• Extract volume after each cleanup step

• Final extract volume prior to injection

• Digestion volume

• Titration volume

• Percent solids or percent moisture

• Dilution data, differentiating between dilution of a sample and dilution of an extract or digestate

• Instrument and operating conditions

• GC and/or GC/MS operating conditions , including detailed information on

-columns used for determination and confirma tion (column length and diameter, stationary phase, solid support, film thickness, etc.) -analysis conditions (temperature program, flow rate, etc.) -detector (type, operating conditions, etc.)

• Chromatograms, extracted ion current profil es, bar graph spectra, library search results

• Quantitation reports, data system outputs, and othe r data to link the raw data to the results reported. (Where these data are edited manually , explanations of why manual intervention was necessary should be included.)

• Direct instrument readouts; i.e., strip charts, printe r tapes, etc., and other data to support the final

results

• Laboratory bench sheets and copies of all pertinen t logbook pages for all sample preparation and cleanup steps, and for all other parts of the determination

### 13 March 2007 The raw data required should be provided not only for the analysis of samples, but also for all calibrations, calibration verificati ons, blanks, matrix spikes and duplicates, and other QC analyses required by the approved method. Da ta should be organized so that an analyst can clearly understand how the analyses were performed.

6. Example calculations that will allow the data reviewer to determine how the laboratory used the

raw data to arrive at the final results.

Useful examples include both detected compounds a nd undetected compounds. If the laboratory or the method employs a standardized reporting level for unde tected compounds, this should be made clear in the example, as should adjustments for sample volum e, dry weight reporting (solids only), dilutions,

etc.

7. Possible submission of raw data in electronic format.

For GC/MS and other instruments involving data system s, the discharger should be prepared to submit

raw data in electronic format or curre nt permanent format upon request by EPA.

8. The names, titles, addresses, and telephone num bers of the analysts that performed the analyses and of the quality control officer that assured and will attest to the results.

If a contract laboratory collected the data, it is th e discharger's responsibility to see that the contract laboratory met all of the requirements in the met hods and that the pertinent data listed above are provided.

9. Describe attempts to minimize interference.

It is important that the laboratory describe all atte mpts to eliminate or minimize the interference, e.g., use of simple dilution or use of a totally differe nt 40 CFR Part 136 method that still allows reliable measurements at the permit level.

10. Document modifications.

The lab should also lists how any modifications ma de were demonstrated by the supporting data to give equivalent performance over the reference method as written.

### 15 March 2007 

## Chapter 5

Reports of Matrix Interferences

Chapter 4 described the kind of information that in the EPA’s view should be provided to demonstrate that a matrix problem precluded measure ment of a pollutant regulated under a NPDES permit limitation. This chapter provides case histories of selected reports of matrix interference problems submitted by dischargers regulated under the Organic Chemicals, Plastics, and Synthetic Fibers (OCPSF)

rule. Additional details of matrix interferences reported by dischargers and others, and how to overcome these interferences, are given in Chapter 6 of this document.

In the early 1990s, the Engineering and Analysis Division (EAD) of EPA reviewed data provided by at least 15 dischargers regulated under the categor ical pretreatment standards for the OCPSF industry. In each instance, the discharger reported that the facility's wastewater could not be monitored for compliance with the pretreatment standards because of interferences. EAD was asked by either the Region or State permitting authority to review these reports of matrix interferences. Over the years, dischargers have reported similar matrix interfere nces in other industrial categories and many of the documents cited in this document were develope d by EPA to address these reports.

EAD's review focused on each facility's reported in ability to determine the organic analytes in its wastewater because of interferences. This chapter presents six case histories of EAD's review of data submitted by dischargers reporting interference pr oblems and provides further detail as to how these dischargers might resolve matrix interference probl ems. None of the dischargers nor any of the

laboratories involved are identified in this document.

Prior to EAD reviewing the data, each of the permitting authorities was provided with:

• A draft checklist of laboratory data required to s upport a claim that the discharger was unable to measure pollutants due to matrix problem s. That draft checklist resembled the Data Required to Document a Matrix Interference in Chapter 4 of this document.

• Draft guidance for analysts attempting to identify and quantify pollutants in wastewaters discharged from plants manufacturing organic chemicals, plastics, and synthetic fibers. That draft guidance was ultimately incorporated into the 1993 “Pumpkin” book.

• Draft guidance for permit writers and others review ing data from the analysis of organic compounds determined using the 600- and 1600-Series methods, similar to that found in Chapter 7 of this

document.

It was EAD's intention that these draft documents be provided to the dischargers and in turn to their laboratories, as needed. However, the review revealed that the States and Regions had either not provided the draft documents or had not followed them. In general, EAD's review of the reports submitted by the dischargers revealed the following:

• In nearly all instances where data were submitted, the dischargers and/or their contract laboratories used incorrect analytical methods or did not follow the procedures required in 40 CFR Part 136.

• In other instances, the dischargers and/or their c ontract laboratories did not submit data necessary to

document that the methods were followed.

### 16 March 2007 • Finally, the dischargers and/or their contract laboratories did not submit documentation regarding the nature of interferences and the attempts (if any) to resolve these interferences.

Case Histories

Case #1: This discharger used a contract laboratory for its analytical work. Information submitted by the laboratory revealed inconsistencies with the stated analytical methods.

The discharger allowed the laboratory to either:

(1) Use methods other than the 40 CFR Part 136 methods, or (2) Modify methods 624 and 625.

At the time the data were evaluated by EAD, alternative methods were allowed under the ATP program described at 40 CFR Part 136.4 and 136.5, but required prior approval from EPA. Otherwise,

alternative methods were not allowed. EAD found no reference to the approval of the laboratory’s

modified methods.

If Methods 624 and 625 were modified under the spirit of the 40 CFR Part 136.6, the laboratory

did not document these modifications and did not demonstrate their equi valence. Modifications that the laboratory made to Methods 624 and 625 included:

• Combining acid and base/neutral fractions for samples analyzed by Method 625,

• Using a fused-silica capillary column for the anal ysis of acid and base/neutral fractions (since approved by EPA Appendix B and C)

• Using alternative internal standards,

• Using alternative surrogates,

• Using higher detection limits,

• Using fewer matrix spike compounds, and

• Using matrix spike amounts inconsistent with regul atory compliance, background, or method-specified

levels.

The October 26, 1984 preamble to the 40 CFR Part 136 methods states that a method is considered to be equivalent, if its performance has been demons trated to meet or exceed the specifications in the original method. None of the submitted data provided any evidence supporting method equivalence.

The use of multiple internal standards and a fu sed-silica capillary column for the base/neutral and acid fractions represent improvements. EPA has provided letters recommending approving of these modifications. 40 CFR Part 136.6 explicitly allows for changes to the chromatogr aphic column and use of

alternative internal standards and surro gates without prior approval from EPA.

However, at that time EPA did not accept combini ng fractions, higher det ection limits, alternative matrix spike compounds, and matrix spike amounts inconsistent with background or regulatory compliance levels represent improvements. It was de termined also at that time these changes degrade method performance and are therefore in violation of bot h the spirit and letter of the flexibility permitted in the 600- and 1600-Series 40 CFR Part 136 organic methods.

The matrix spike compounds and spiking levels used by the laboratory appeared to have been from Office of Solid Waste (OSW) SW-846 methods or from Superfund Contract Laboratory Program (CLP)

methods. The 600- and 1600-Series wastewater methods require the matrix spike compounds to be the

### 17 March 2007 compounds regulated in the discharge (e.g., 40 CFR Pa rt 136, Appendix A: Method 624, Section 8.3) and require that the spike levels be at:

(1) The regulatory compliance level, (2) 1–5 times the background level of the analyte in the sample, or (3) The level specified in the method (e.g., Method 624, Section 8.3.1).

The compounds spiked were not those regulated, and the sp ikes were not at the levels required. Therefore, the results were not useful in demonstrating pe rformance of the method for the problem analytes.

The matrix spike was performed on a diluted sa mple. Had the matrix spike been performed as specified in Method 624 or 625, the spike would likely have failed the specifications in the method and the associated sample result could not have been repor ted for regulatory compliance purposes. This should have triggered cleanup procedures, the use of altern ative methods, or modification of Method 624 or 625 to improve method performance.

The QC specifications for matrix spike recovery used by the laboratory were not the specifications given in Methods 624 and 625. The specifications in the wastewater methods (40 CFR Part 136, Appendix A: Method 624, Table 5; and Method 625, Table 6) must be used for compliance monitoring. While tighter specifications from a documented source may be acceptable if met, use of wider limits without documentation is not acceptable.

The detection limits reported for semivolatiles were , for the most part, twice the minimum levels given in Method 625 and were approximately 10–20 times the method detection limits (MDLs) given in Method 625. No explanation for the increased detecti on limits was given, nor could the limits be derived from the data provided.

The laboratory made no attempt to clean up the samples using pH change, gel permeation chromatography, or the other tec hniques described in the 600- and 1600-Series methods or in the draft guidance provided by EPA.

Even with the increased and explicit allowance fo r flexibility provided at 40 CFR Part 136.6, the majority of the modifications made by this labor atory did not improve performance; did not see the analytes at the regulatory limits, and thus the modifications were not acceptable.

EAD has since recommended (Appendix C) allowing several acceptable modifications to EPA Method 625 for environmental permitting and complia nce monitoring under the EPA’s CWA program.

Case #2: Information provided with data submitted by this discharger was insufficient for a detailed

review.

Despite the general lack of data, it appeared the discharger submitted samples to a contract laboratory for analyses by a GC/MS method which failed to produce useful results. The discharger and/or the laboratory attributed the problems to large con centrations of acetone in the discharge, though this problem could not be confirmed from the information pr ovided. The analytical contractor proposed to the discharger that Methods 601 and 602 be used for the volatiles analysis in an attempt to overcome the interference problems. Both of these methods are approved at Part 136 methods and they are more

sensitive and more selective than a GC/MS method. Therefore, the regulated analytes should be measurable in the presence of a large concentration of acetone. The discharger ignored the laboratory's

### 18 March 2007 proposal and submitted a report of matr ix interferences. EPA reported that the approach proposed by the laboratory was workable and appropriate , and should have been attempted.

Case #3: This discharger used several contract labor atories for analyses. The reports from these laboratories consisted of summary reporting fo rms showing detection limits that were 10–50 times greater than the MDLs in Methods 624 and 625.

There were no QC results, no details of how th e analyses were performed, and no documentation of interference problems or steps taken to ove rcome interference problems, and therefore, no

documentation that an interference existed. The la boratory may have chosen to dilute samples for convenience. The discharger and its laboratory should ha ve provided the data listed in Chapter 4 of this document, and attempted to solve interference problems using the techniques discussed in Chapter 6 of this

document.

Case #4: This discharger submitted a report from one contract laboratory that contained insufficient information for evaluation; and two letters from a second contract laboratory describing a problem with 4,6-dinitro- o -cresol.

The report provided by the first laboratory indicated no results for spikes of the OCPSF-regulated analytes into samples, no details of how the analy ses were performed, what interference problems were encountered, or what steps were taken to overcome inte rference problems. In addition, it appeared that the contract laboratory combined acid and base/neutral extracts, thus exacerbating interference effects.

The letters from the second laboratory describing the problem with 4,6-dinitro- o -cresol asked for suggestions on how to determine this compound in the presence of interferences. Chapter 6 of this document provides general sugges tions for overcoming matrix interference problems and specific suggestions for determination of phenol. The specifi c suggestions for determin ation of phenol can be applied to 4,6-dinitro- o -cresol.

Other reports by the contract laboratory showed high detection limits for the substituted phenols because of a huge quantity of phenol in the sample. The analytical laboratory should have used the procedures for determination of phenol deta iled in the Chapter 6 of this document.

Case #5: This discharger submitted letters and repor ts from several contract laboratories.

Data items that were present and are required fo r a thorough review were instrument tunes, run chronologies, chromatograms, calibration data, calibra tion verification data, results for blanks, quantitation reports for samples, and matrix spike data run agains t the QC limits for Methods 624 and 625. The initial precision and recovery (IPR) data that dem onstrate method equivalence were missing.

The semivolatile matrix spike data were inconsis tent. Results of analysis of unspiked samples

indicated that some of the acids and base/neutrals we re not detected, yet results for the spiked samples showed large concentrations of some analyt es that were not spiked into the samples.

The volatiles matrix spike had been diluted by a factor of 200 and spiked after dilution. Diluting and spiking will not show matrix interferences, and thus these data are of no value in evaluating the undiluted sample results.

### 19 March 2007 Cases #6: Several dischargers simply submitted summary reports from their laboratories.

None of the materials contained the information required in Chapter 4 of this document, and none contained explanations of the nature of the interfe rences found or descriptions of attempts to overcome

these interferences. These facilities should have followed the guidan ce in Chapters 4 and 6 of this document, and reviewed the data produced using the da ta review guidance provided in Chapter 7 of this

document.

### 20 March 2007 

## Chapter 6

Solutions to Matrix Interferences

Solving Matrix Problems

The inability to measure the concentration of a pollu tant in a specific wastewater is often attributed to a “matrix problem.” Matrix problems are caused by substances in the water that interfere in some way in the analysis. These substances can be suspended ma terials, dissolved salts, polymeric materials, and highly acidic or caustic waters. Examples of soluti ons to matrix problems are described below and given in references in this chapter. The examples are not intended to be exhaustive, but rather representative enough to help the analyst understand how to ove rcome typical matrix interference problems.

In addition to the information below and in the guidance documents referenced in this document,

the means to overcome matrix interferences can often be found in the technical literature and in sets of methods and individual methods publis hed by other EPA Offices and by other organizations, most notably Standard Methods for the Examination of Water and Wastewater (Standard Methods) and methods published by ASTM International. Both of these method sets contain extensive means for overcoming matrix interference problems, and Standard Methods and ASTM methods should be consulted before contacting EPA for a solution to a matrix interference problem.

Solutions Applicable to Nearly All Analytes

Selective Reaction and/or Removal of the Interferent

The best solution to a matrix interference problem caused by a particular substance is to first identify the substance, then selectively remove it from th e sample or from the sample extract or digestate. Selective removal can be accomplished by reaction with another substance that will not interfere or by physical separation from the analyte of interest by adsorption on an ion exchange or chromatographic column. The selective reaction/removal technique is described in some of th e suggested solutions to matrix interference problems below, and is described in further detail in Standard Methods and ASTM

methods.

Method of Standard Additions (MSA)

A common means of resolving matrix interferences th at can be applied to nearly all analytes in all

matrices is the “method of standard additions” (MSA). MSA for metals is described in Methods for Chemical Analysis of Water and Wastes (MCAWW Revised March 1983, NTIS PB 84-128677). MSA for organics is described in ASTM Standard D 5788. Also, instrument manufacturers may provide MSA procedures in instruction manuals and/or application notes. In MSA, increasing concentrations, typically at factors of 2, 4, and 8 times the concentration of th e analyte in the sample, ar e added to separate aliquots of the sample. The aliquots are analyzed and a regressi on or plot of response versus concentration is used

to determine the concentration of the analyte in the sample.

### 21 March 2007 Solutions Applicable to Classical Pollutants

Oil and Grease

Oil and grease is the pollutant for which the most matrix interferences have been reported to EPA, and nearly all of the reports have been about the form ation of emulsions in the extraction of oil and grease. EPA has published advice on these problems in Analytical Method Guidance for EPA Method 1664A Implementation and Use, EPA 821-R-00-003, February 2000 (see Chapter 9).

Cyanide

Next to oil and grease, cyanide is the pollutant for which the most matrix interferences have been reported to EPA. Cyanide chemistry is very comple x, and resolving matrix interferences with cyanides may involve considerable investigation. Fortunately, companies that work with cyanides are usually very familiar with the cyanide chemistry used in their products/processes a nd wastewaters, and have addressed cyanide interference issues. Sugg ested means for mitigating or overcoming cyanide interferences are presented in Section 4500-CN

- of Standard Methods for the Examination of Water and Wastewater , in ASTM D2036, Standard Test Methods for Cyanides in Water , and in OIA Method 1677, approved for use

at 40 CFR Part 136. Standard Method 4500-CN

- and ASTM D2036 devote larg e sections to overcoming cyanide interferences.

The most common interfering species in the determin ation of cyanides is sulfur, primarily in the

form of sulfide. Footnotes to Table II at 40 CF R Part 136.3 address cyanide interferences other than sulfide, including:

$ sulfur,
$ sulfite,
$ oxidants (including chlorine and hypochlorite),
$ thiocyanate,
$ aldehydes, and
$ carbonate.

The footnotes also address the preservatives that may be used and how to deal with particulate matter in the sample. The following text is based on foot notes to Table II at 40 CFR Part 136.3 and input from

ASTM:



### “Add a reducing agent only if an oxidant (e.g., chlorine) is present. Reducing agents shown to be effective are sodium thiosulfate (Na 2 

### S 2 

### O 3 

### ), ascorbic acid, sodium arsenite (NaAsO 2 

### ), or sodium borohydride (NaBH 4 

### ). However, some of these agents have been shown to produce a positive or negative cyanide bias, depending on other substances in the samp le and the analytical method used. Therefore, do not add an excess of reduc ing agent. Methods recommending ascorbic acid (e.g., EPA Method 335.4) specify adding ascorbic ac id crystals, 0.1 - 0.6 g, until a drop of sample produces no color on potassium iodide (KI) starch paper, then adding 0.06 g (60 mg) for each liter of sample volume. If NaBH 4 

### or NaAsO 2 

### is used, 25 mg/L NaBH 4 

### or 100 mg/L NaAsO 2 

### will reduce more than 50 mg/L of chlorine (see method “Kelada-01" and/or Standard Method 4500-

CN

– 

### for more information). After adding reducing agent, test the sa mple using KI paper, a test strip (e.g. for chlorine, SenSafeTM Total Chlo rine Water Check 480010) moistened with acetate buffer solution (see Standard Method 4500-Cl.C.3e), or a chlorine/oxidant test method (e.g., EPA Method 330.4 or 330.5), to make sure all oxidant is removed. If oxidant remains, add more

### 22 March 2007 

### reducing agent. Whatever agent is used, it should be tested to a ssure that cyanide results are not affected adversely.

6 

### Sample collection and preservation: Collect a volume of sample appropr iate to the analytical method in a bottle of the material specified. If the sample can be analyzed within 48 hours and sulfide is not present, adjust the pH to >12 with sodi um hydroxide solution (e.g., 5 % w/v), refrigerate as specified, and analyz e within 48 hours. Otherwise, to extend the holding time to 14 days and mitigate interferences, treat the sample immediately using any or all of the following techniques, as necessary, followed by adjustment of the sample pH to >12 and refrigeration as specified. There may be interferences that ar e not mitigated by approved procedures. Any procedure for removal or suppression of an interference may be employed, provided the laboratory demonstrates that it more accurately meas ures cyanide. Particulate cyanide (e.g., ferric ferrocyanide) or a strong cyanide complex (e.g., c obalt cyanide) are more accurately measured if the laboratory holds the sample at room temper ature and pH >12 for a mi nimum of 4 hours prior to analysis.

(1) Sulfur: To remove elemental sulfur (S 8 

### ), filter the sample immediately. If the

filtration time will excee d 15 minutes, use a larger filt er or a method that requires a smaller sample volume (e.g., EPA Method 335.4 or Lachat Method 01). Adjust the pH of the filtrate to 12-13 with NaOH, refrigerate the filter and filtrate, and ship or transport to the laboratory. In th e laboratory, extract the filter with 100 mL

of 5% NaOH solution for a minimum of 2 hours. Filter the extr act and discard the

solids. Combine the 5% NaOH-extracted filt rate with the initial filtrate, lower the pH to approximately 12 with concentrat ed hydrochloric or sulfuric acid, and analyze the combined filtrate. Because the detection limit for cyanide will be increased by dilution by the filtrate from the solids, test the sample with and without the solids procedure if a low dete ction limit for cyanide is necessary. Do not use the solids procedure if a higher cyanide concen tration is obtained without it. Alternatively, analyze the filtrates from the sample and the solids separately,
add the amounts determined (in Φ g or mg), and divide by the original sample volume to obtain the cyanide concentration.

(2) Sulfide: If the sample contains sulfide as determined by lead acetate paper, or if sulfide is known or suspected to be pr esent, immediately conduct one of the volatilization treatments or the precipitati on treatment as follows: Volatilization - Headspace expelling. In a fume hood or we ll-ventilated area, tr ansfer 0.75 liter of sample to a 4.4-L collapsible containe r (e.g., CubitainerTM) . Acidify with concentrated hydrochloric acid to pH < 2. Cap the container and shake vigorously for 30 seconds. Remove the cap and expel the headspace into the fume hood or open area by collapsing the container wit hout expelling the sample. Refill the headspace by expanding the container. Repeat expelling a total of five headspace volumes. Adjust the pH to >12, refrigerate, and ship or transport to the laboratory. Scaling to a smaller or larger sample volume must maintain the air to sample volume ratio. A larger volume of air will result in too great a loss of cyanide (> 10%). Dynamic stripping: In a fume hood or well-ventilate d area, transfer 0.75 liter of sample to a container of th e material specified and acidify with

### 23 March 2007 

### concentrated hydrochloric acid to pH < 2. Using a calibrated air sampling pump or flowmeter, purge the aci dified sample into the fu me hood or open area through a fritted glass aerator at a flow rate of 2.25 L/min for 4 minutes. Adjust the pH to 12 - 13, refrigerate, and ship or transport to the laboratory. Scaling to a smaller or larger sample volume must maintain the air to sample volume ratio. A larger volume of air will result in too great a loss of cyanide (> 10%). Precipitation: If the sample contains particulate matter that would be removed by filtration, filter the sample prior to treatment to assure th at cyanide associated with the particulate

matter is included in the measurement. Ship or transport the filter to the laboratory. In the laboratory, extract th e filter with 100 mL of 5% NaOH solution

for a minimum of 2 hours. Fi lter the extract and discard the solids. Combine the

5% NaOH-extracted filtrate with the initia l filtrate, lower the pH to approximately 12 with concentrated hydrochloric or sulfuric acid, and analyze the combined

filtrate. Because the detection limit fo r cyanide will be increased by dilution by the filtrate from the solids, test the sample with and w ithout the solids procedure if a low detection limit for cyanide is necessar y. Do not use the solids procedure if a higher cyanide concentration is obtained without it. Alternatively, analyze the filtrates from the sample and the solids separately, add the amounts determined (in

Φ g or mg), and divide by the original sample volume to obtain the cyanide

concentration. For removal of sulfide by precipit ation, raise the pH of the sample to >12 with NaOH solution, then add a pproximately 1 mg of powdered cadmium chloride for each mL of sample. For example, add approximately 500 mg to a 500-mL sample. Cap and shake the contai ner to mix. Allow the precipitate to settle and test the sample with lead a cetate paper. If necessary, add cadmium chloride but avoid adding an excess. Finally, filter through 0.45 micron filter. Cool the sample as specified and ship or transport the filtrate and filter to the laboratory. In the laboratory, extract the filter with 100 mL of 5% NaOH solution

for a minimum of 2 hours. Fi lter the extract and discard the solids. Combine the

5% NaOH-extracted filtrate with the initia l filtrate, lower the pH to approximately 12 with concentrated hydrochloric or sulfuric acid, and analyze the combined

filtrate. Because the detection limit fo r cyanide will be increased by dilution by the filtrate form the solids, test the sample with and without the solids procedure if a low detection limit for cyanide is necessar y. Do not use the solids procedure if a higher cyanide concentration is obtained without it. Alternatively, analyze the filtrates from the sample and the solids separately, add the amounts determined (in

Φ g or mg), and divide by the original sample volume to obtain the cyanide concentration. If a ligand-exchange method is used (e.g., ASTM D6888), it may be necessary to increase the ligand-exchange reagent to offset any excess of

cadmium chloride

(3) Sulfite, thiosulfate, or thiocyanate: If thiocyanate is known or suspected to be present, use UV digestion with a glas s coil (Method Kelada-01) or ligand exchange (Method OIA-1677) to preclude cyan ide loss or positive in terference. If sulfite and thiosulfate are present there is no way to accurately determine cyanide if heat is applied. In these situations a non-distillation method such as D6888-04, or method OI-1677 may be used.

### 24 March 2007 

### (4) Aldehyde: If formaldehyde, acetalde hyde, or another water-soluble aldehyde is known or suspected to be present, tr eat the sample with 20 mL of 3.5% ethylenediamine solution pe r liter of sample.

(5) Carbonate: Carbonate interference is evidenced by noticeable effervescence upon

acidification in the distillati on flask, a reduction in the pH of the absorber solution, and incomplete cyanide spike recovery. When significant carbonate is present, adjust the
pH to ∃ 12 using calcium hydroxide instead of sodi um hydroxide. Allow the precipitate to settle and decant or filter the sample prior to analysis (als o see Standard Method 4500-CN.B.3.d)”.

Solutions Applicable to Metals Pollutants

In environmental testing, samples analyzed for me tals are digested with strong mineral acid(s), or the metal is chelated and extracted, follo wed by determination of the metals by:

$ flame atomic absorption spectrophotometry (FLAA),
$ graphite furnace atomic absorption spectrophotometry (GFAA),
$ cold-vapor atomic absorption spectrophotometry (CVAA),
$ hydride generation atomic absorption spectrophotometry (HGAA),
$ direct-current plasma atomic absorption spectrophotometry (DCPAA),
$ inductively coupled plasma/optical emission spectrometry or mass spectrometry (ICP/OES and ICPMS),
$ atomic fluorescence spectrophotometry (AF)
$ or colorimetric, titrimetric, voltammetric, or gravimetric techniques.

The full list of techniques approved for metals analys is is listed in Table IB at 40 CFR Part 136.

The most commonly used of these techniques for determination of metals in wastewater are GFAA, HGAA, and ICP-MS. HGAA is only approved at 40 CFR Part 136 for arsenic and selenium. CVAA is used exclusively for determination of me rcury. The introduction of EPA Method 1631, an atomic fluorescence method, has caused a shift in tec hnology because of the ability to measure to lower levels than CVAA, and with fewer interferences.

Clean Room

Although not strictly a matrix interference problem , contamination of metals samples, particularly at or near ambient water quality criteria (WQC) leve ls, can be a significant problem in sampling and in some laboratories. The problem is particularly common for mercury, which is a volatile metal and, therefore, can be transported throughout a building through heating, ventilating, and air conditioning systems. However, clean room techniques have be en successful at eliminating contamination sources for many other metals, including lead and zinc.

To mitigate laboratory contamination problems with mercury and othe r metals, EPA published Guidance on Establishing Trace Metal Clean Rooms In Existing Facilities , EPA-821-B-96-001, April,

1995 and Trace Metal Cleanroom, RTI/6302/04-02F, Research Triangle Institute, October, 1995. These guidance documents detail how the laboratory can modi fy existing facilities to reduce contamination to the lowest levels and, thereby, prevent contam ination from interfering in the analysis.

### 25 March 2007 General Matrix Interferences

Matrix interferences in metals determinations by AA, ICP, and other techniques result in a decrease or increase in the signal (response) from what the signal would be if the interference were not present. For analysis of environmental samples, th e most common forms of matrix interference are caused by dissolved materials in the sample digestate. These interferents cha nge the characteristics of the solution that is injected into the instrument.

One means of resolving matrix problems with me tals is use of MSA, described in the section on MSA above. Another means of overcoming matrix inte rferences from dissolved materials is to match the blank and the matrix containing the standard used for instrument calibration with the characteristics of the sample or digestate. Matrix matching can involve matching the pH, acid concentration, and dissolved

solids content of the blank and standards. If chela tion is used, or if the sample contains significant concentrations of organic compounds, the standards and blank should be chelated and/or otherwise matched to contain the organic compounds also.

Chromium VI

Although chromium VI (also known as “hexav alent chromium,” and colloquially known as “chrome 6") can be considered a metal pollutant, it h as historically been treated as a classical pollutant because it is usually determined using classical we t-chemistry techniques. Interferences in the

determination of chromium VI ha ve been overcome by use of ion chromatography with methods such as

EPA Method 218.6.

Mercury

The dual amalgam purge-and-trap and fluor escence system in EPA Method 1631 is less susceptible to matrix interferences, particularly at lo w levels, than cold vapor atomic absorption and other mercury analysis techniques. Therefore, if a matrix interference is encountered in the determination of mercury, EPA Method 1631 should be used. Generall y, use of this method will resolve most matrix interferences. Recommended approaches for addressi ng any remaining interferences can be found in Chapter 3 of EPA's Guidance for Implementation and Use of EPA Method 1631B, EPA 821-R-01-023, March 2001, which specifically addresses matrix interfere nces in the determination of mercury. This guidance is applicable to subsequent versions of the method, e.g. 1631E.

Solutions Applicable to Organic Pollutants

Many of these solutions focus on the pollutants regulated under the OCPSF rule, but are applicable to pollutants in other effluent guidelines as well.

Volatiles - The 304(h) methods for volatiles include Me thods 601, 602, 603, 624, and 1624.

1. Use of Selective GC Detectors

The effluent limits in the OCPSF regulation and an y other industry regulations involving volatiles are all greater than 10 μg/L (10 ppb). The selective GC detectors in Methods 601 and 602 cover all OCPSF volatile pollutants regulated, and allow detection at levels well below the effluent limits in the OCPSF regulation. The specificity provided by th e electrolytic conductivity detector and by the photoionization detector allows detection of the halo genated and aromatic analytes, respectively, in complex matrices.

### 26 March 2007 2. Micro-extraction and Gas Chromatography with Selective Detectors

The selective GC detectors in Methods 601 and 602 provide sensitivity that is 10–100 times greater than that required to detect the volatile analytes of interest. Some of this sensitivity can be used to substitute micro-extraction in place of purge-and-trap. The advantage of micro-extraction is that the pH of the water can be adjusted to attempt to keep the interferences in the water while the analytes of

interest are extracted. 1

3. Sample Dilution

Methods 601 and 602 can achieve me thod detection limits of less than 1 μg/L (ppb) for all volatile analytes in the OCPSF regulation, and of less than 0.1 μg/L (ppb) for many of these analytes. The added sensitivity of the selective GC detectors can be used to overcome matrix problems by diluting the sample by a factor of 10–100. Even with this d ilution, the pollutants can be detected at the levels required, and the effects of the interfe rences will be reduced or eliminated.

4. Isotope Dilution

Method 1624 employs stable, isotopically labeled analogs of the pollutants as internal standards in the analysis. The use of these labeled compounds frequently permits the pollutant to be determined in the presence of interferences because the unique spectrum of the labeled compound can be located in the presence of these interferences, and the pollutant can then be located by reference to the labeled compound.

Semivolatiles

1. Use of Selective GC Detectors

Methods 604 through 612 employ gas chromatogr aphy with selective detectors and high-performance liquid chromatography with an ultraviolet (UV) or el ectrochemical detector to detect pollutants in the presence of interferences. In addition, Method 6 04 employs derivatization and a halogen-specific detector for the determination of phenols. As w ith volatiles, the added sensitivity of the selective detectors permits the sample to be diluted by a factor of 10–100 while allowing detection of the analytes at the effluent limits specified in the OCPSF regulation.

2. pH Change

A very powerful means of separating the pollutants of in terest from interferences is to adjust the pH of the sample to keep the interferences in solution wh ile allowing the pollutants to be extracted in an organic solvent. For example, neutral pollutants can be extracted at either low or high pH. Therefore, if the main interferences are acidic, the pH can be adjusted to >13 and the acidic interferences will

remain in the water in ionic form while the neutra l pollutants are extracted using an organic solvent.

Phenol and 2,4-dimethylphenol can be extracted at high pH (11–13) using continuous liquid/liquid extractors, as described in Method 1625. This perm its phenol and 2,4-dimethylphenol to be extracted in the presence of other, stronger acids. 2 Continuous liquid-liquid extraction at low pH is also an

1 Rhodes, J.W., and Nulton, C.P., J. Env. Sci. and Health , vol. A15, no. 5, (1980).

2 Jackson, C.B. et. al., J. Env. Sci. and Health , vol. A15, no. 5, (1980).

### 27 March 2007 effective means of extracting phenols and overcomi ng poor recovery “matrix interferences” caused by separatory funnel extraction.

In a manner analogous to the pH change described above, the extract from the primary extraction can be back-extracted with water of the opposite pH to remove other interferences. To keep the organic pollutants in the extract, the water used for back-extraction can be saturated with salt (sodium sulfate and/or sodium chloride). Aqueous solutions containing 2% of each of these salts have been shown to be effective in keeping the polluta nts of interest in the extract.

3. Gel-permeation (Size-exclusion) Chromatography (GPC)

This technique is described in Revision C of Method 1625. The same technique is used in the Superfund Contract Laboratory Program (CLP) methods and SW-846 method 3640, and has been shown to be effective for removing lipids and high -molecular-weight interferences that can degrade GC and mass spectrometer performance.

4. Solid-phase Extraction (SPE)

Although SPE has not been fully evaluated as a cl eanup technique, SPE may be effective as a cleanup for acidic, basic and neutral organic species. It has been shown to be effective in removing interferences from extracts containing pesticides 3 and in its use for the extraction of pollutants from drinking water in EPA Method 525. Method 525 is the drinking water analog to method 625. The principle has been extensively used to remove inte rferences in HPLC by adding a short C18 or other appropriate column as a guard column in front of the HPLC analytical column.

5. Florisil, Alumina, and Silica Gel Chromatography

These adsorbents are effective in separating neut ral species from polar interferences. For polar analytes of interest, the adsorbent should be evaluate d to determine if the analyte will be recovered. The level of activation of the adsorbent plays a major role in this recovery process. Techniques can be found in SW-846 methods 3610, 3620 and 3630.

6. Isotope Dilution

Method 1625 permits determinati on of pollutants in the presence of interferences in semivolatile samples in the same way d escribed above for volatiles. In addition, the wide range of recovery of the labeled analogs permitted in the method allows good quantitation of the pollutant when interferences reduce the efficiency of the extraction.

Determination of Phenol as a Specific Example

Phenol is a commonly occurring pollutant in OCPSF wastewaters. The protocols below are suggested as approaches to the determination of phenol in a comp lex sample matrix. After a protocol has been found to be effective, the laboratory must demonstrate th at the modification has equivalent performance to the original method. This demonstration involves the test s described in Chapter 3 of this document. The QC acceptance criteria in the approved method must be met before proceeding with analysis of a sample for compliance monitoring.

3 Tessari, J.D., 12th Annual EPA Conference on Analysis of Pollutants in the Environment, Norfolk, Virginia, May

1989.

### 28 March 2007 1. Base/neutral extraction, acid back extraction, and isotope dilution GC/MS (based on Method 1625)

1.1 Measure 1.0 L of well-mixed sample into a gr aduated cylinder and spike with labeled phenol per

Section 10 of Method 1625. Stir and equilibrate per this method. Quantitatively transfer the sample to a continuous liquid/liquid extractor. Ad just the pH of the sample to 11–13 and extract with methylene chloride as described in the method.

1.2 Remove the extract from the extractor and place in a 1–2 L separatory funnel. Back-extract the extract sequentially three times with 500-mL porti ons of salt-saturated reagent water (pH <2), discarding the reagent water after each back-extraction.

1.3 Concentrate the extract to 10 mL and clean up using gel-permeation chromatography (GPC) per

Section 10 of Method 1625.

1.4 After GPC, concentrate the extract to 0.5 mL and analyze by isotope dilution GC/MS, as described

in Method 1625.

1.5 Calculate the recovery of labeled phenol and compare to the performance specifications in Method

1625.

2. Dilution, acid extraction, back-extraction with base, derivatization, silica gel cleanup, and gas chromatography with an electrolytic co nductivity detector (based on Method 604)

2.1 Measure two 100-mL aliquots of well-mixed sample into 1000-mL graduated cylinders. Spike one of the aliquots with phenol at the level specified in Section 8 of Method 604. This aliquot serves as the matrix spike sample. Dilute both aliquots to 1.0 L with reagent water. Adjust the pH of each aliquot to less than 2 with HCl.

2.2 Pour each aliquot into a separate 1–2 L separatory funnel and sequentially extract three times with methylene chloride per Method 604. Discard the aqueous phase and return the extract to the separatory funnel. It is recommended that the use of continuous liquid-liquid extraction in place of separatory funnel extraction be used. The recoveries of the analyte of interest are usually better.

2.3 Back-extract the extract sequentially three time s with salt-saturated reagent water, discarding the reagent water after each back extraction.

2.4 Concentrate, derivatize, and clean up the extract per Method 604.

2.5 Analyze using the electrolytic conductivity det ector. This detector is less susceptible to interferences than the electron capture detector used in Method 604. Newer models have sensitivity nearly equivalent to the electron capture detector.

2.6 Calculate the recovery of phenol in the matrix spike aliquot and compare this recovery to the specifications in Method 604.

### 29 March 2007 

## Chapter 7

Review of Data from Analysis of Samples

This chapter describes how a responsible part y should review data submitted for compliance monitoring under the National Pollutant Discharge E limination System (NPDES ) and data submitted to

EPA and State authorities under the Clean Water Act. Th is data should be maintained on file in an organized fashion available for inspection. The 19 93 Pumpkin Book focused on the review of data for organic compounds regulated under the OCPSF Rule th at was collected with the 600-series and 1600- Series wastewater methods. Although this revision of the Pumpkin Book now includes references to EPA documents for review of other data, the data from th e 600- and 1600-Series methods has been described in this chapter so that the data reviewer can see deta ils of the information reviewed. EPA uses these data reviews in data gathering to support development of effluent guidelines and st andards under Sections 301, 304, 307, 308, 402, and 501 of the Clean Water Act and for other purposes. The principles of data review described in this Chapter would also be applicable to data from the 500-series drinking water methods, the SW-846 (RCRA) methods, and any method that contains the standardized quality control elements that are contained in these methods; e.g., recent ASTM International Committee D19 (Water) methods.

The following example is technically detailed and is intended for data reviewers familiar with the EPA methods and similar analytical methods. Review ers unfamiliar with these methods should review the methods and the supporting background materials provi ded in the preamble to the promulgation of the

600- and 1600-Series methods for a full understandi ng of the philosophy behind these documents.

Standardized Quality Control

In developing methods for the determination of organic pollutants in wastewater, EPA sought scientific and technical advice from many sources, includi ng EPA's Science Advisory Board, scientists at EPA's environmental research laboratories, scientists in industry and academia, and scientists, managers, and legal staff. The result of discussions held among these groups was the standardized quality assurance and quality control (QA/QC) approach that is an integr al Part of the 600- and 1600-Series methods. This QA/QC takes the form of performance specifications for each method and contains the following elements:

• Purity and traceability of reference standards

• Number of calibration points

• Linearity of calibration

• Calibration verification

• Method detection limit (MDL) and minimum level of quantitation

• Initial precision and recovery

• Analysis of blanks

• Recovery of analytes spiked into the sample matrix (e .g., an matrix spike or laboratory-fortified matrix aliquot) or recovery of labeled compounds spiked into samples

• Statements of data quality for recovery of sp ikes of analytes or labeled compounds into samples

• Ongoing precision and recovery

• Statements of data quality for the laboratory

In reviewing data submitted for compliance, th e permit writer or other individual or organization has the authority and responsibility to assure that the test data submitted contain the elements listed above. Otherwise, the data may be considered unacceptable for compliance monitoring.

### 30 March 2007 Provision of QC Data

Dischargers and other organizations submitting t est data under CWA or other acts may use their own laboratories or contract the testing to laboratories that meet the requirements specified in the methods. The permit writer may require that the supporting QA/Q C data described above be submitted with results or that it be on record at the discharger's facility or at the testing laboratory.

EPA strongly recommends that the supporting QA/QC data be submitted along with the analytical results, so that the quality of the data can be evalua ted directly, and so that these supporting data are not lost between the time of submission of the analytical r esults and the time that the QA/QC data are required.

In many of its early analytical programs, EPA relied upon laboratories to maintain records of QA/QC data. This practice was cumbersome for the laboratories, because many of the QA/QC data were common to the analytical results for a variety of c lients. Retrieving these data from the laboratory to resolve questions of permit compliance was time-cons uming for the discharger and the permit writer. More importantly, this practice occasionally resulte d in unscrupulous laboratories failing to perform the necessary QA/QC testing, or performing the QA/QC testing “after the fact” to satisfy an audit or data submission request. In particular, many laboratories di d not perform the initial precision and recovery test (the “start-up” test) prior to practice of the method and did not perform a spike of the analytes into the sample matrix to prove that the method would work on a particular sample. Therefore, while the data provided by those laboratories may have been comp liant, there was no way to prove the data was acceptable for compliance purposes.

When collecting data for the development of a regulation, EPA requires that supporting QA/QC data be provided along with the results for the sample analyses. If an individual or organization submits analytical results for inclusion into EPA's regula tions, EPA similarly requires submission of the QA/QC data. Sample results are evaluated relative to the QA/QC specifications in the method, and those results that pass the QA/QC requirements are included for consideration. Submission of QA/QC data at the time of submission of analytical results is essential to timely and effective evaluation of permit compliance

issues.

Review of Data from the 600- and 1600-Series Methods

Details of the data review process depend to a great extent upon the specific analytical methods being employed for compliance monitoring. Even fo r data from the same methods, there are probably as many specific approaches as there are reviewers. However, given the standardized QA/QC requirements of the 600- and 1600-Series EPA methods, a number of basic concepts apply. The following sections provide the basic details for reviewing data submitted and provide some of EPA's rationale for the QA/QC

tests.

1. Purity and Traceability of Reference Standards

The accuracy of any non-absolute empirical measu rement is dependent on the reference for that measurement. In determining pollutants in water or other sample matrices, the analytical instrument and analytical process should be calibrated with a known reference material. The 600- and 1600- Series analytical methods, as well as other EPA methods , require that the standards used for calibration and other purposes be of known purity and traceable to a reliable reference source.

The ultimate source for reference ma terials is National Institute for Standards and Technology (NIST). Dischargers and their supporting laboratories subm itting analytical data should be able to prove

### 31 March 2007 traceability of the reference standards used in the analysis to EPA or NIST. The proof of this traceability is a written certification from the supplier of the standard.

Documentation of the purity and traceability of the st andards need not be provided with every sample analysis. Rather, it should be maintained on file at the laboratory and provided on request. When analyses are conducted in a contract laboratory, su ch documentation ought to be provided to the discharger the first time that a laboratory is em ployed for specific analyses and then updated as

needed.

2. Number of Calibration Points

The 600-series methods specify a minimum of three calibration points. The lowest of these points is required to be near the MDL. The highest is require d to be near the upper linear range of the analytical system, and the third point is approximately mi dway between the two. Some methods, such as Methods 1624 and 1625, require calibration at five sp ecific concentrations for nearly all analytes, and three or four specific concentrations for the re maining analytes for which the methods are not as

sensitive.

The lowest calibration point should be below the ac tion level and the high st andard should still be within the calibration range of the instrument.

The flexibility in selecting the levels of the calibration points in the 600-series methods has led to a wide variety of calibration ranges as each laborator y may determine its own calibration range. Some laboratories may establish a relatively narrow calibra tion range, for instance a five-fold concentration range such as 10 to 50 μg/L (ppb), because it makes it simpler to meet the linearity specifications of the 600-series methods. Other laboratories may choose wider calibration ranges, e.g., 10 to 200 μg/L (ppb), in order to minimize the number of samples that should be diluted and reanalyzed because the concentration of one or more analytes exceeds the calibration range.

The data reviewer will need to make certain that all measurements are within the calibration range of the instrument. Samples with an alyte concentrations above the ca libration range should have been diluted and reanalyzed. The diluted sample results need only apply to those an alytes that were out of the calibration range in the initial analysis. In othe r words, it is acceptable to use results for different analytes from different levels of dilution within the same sample. Some flexibility may be exercised in acceptance of data that are only slightly above (<10% ) the calibration range. Such data are generally acceptable as calculated.

If data from an analysis of the diluted sample are not provided, limited use shoul d be made of the data that are above the calibration range (>10%). Th e response of the analytical instrument to concentrations of analytes will eventually level o ff at concentrations above the calibration range. While it is not possible to specify at what con centration this will occur from the calibration data provided, it is generally safe to assume that the re ported concentration above the calibrated range is a lower limit of the actual concentration. Therefore, if concentration above the calibration range is also above a regulatory limit, it is highly likely that the act ual concentration would also be above that limit.

### 32 March 2007 3. Linearity of Calibration

The relationship between the response of an analytical instrument to the concentration or amount of an analyte introduced into the instrument is refe rred to as the “calibration curve.” An analytical instrument can be said to be calibrated in any in stance in which an instrumental response can be related to a single concentration of an analyte. The response factor (GC/MS methods) or calibration factor (GC, HPLC methods) is the ratio of the r esponse of the instrument to the concentration (or amount) of analyte introduced into the instrument. The response factor and calibration factor concepts are used in many methods for organic contaminants , while methods for metals and some other analytes may employ different concepts such as linear regressions.

While the shape of calibration curves can be m odeled by quadratic equa tions or higher order mathematical functions, most analytical methods focus on a calibration range where the response is essentially a linear function of the concentration of th e analyte. An advantage of linear calibration is that the response factor or calibration factor represen ts the slope of the calibration line and is relatively constant, simplifying the calculations and data interpretation. Whicheve r approach is used, all the 600- and 1600-Series methods specify some criterion for de termining linearity of calibration. When this criterion is met, the calibration is sufficiently linear to permit the laboratory to use an average response factor or calibration factor, and it is assumed that the calibration is a straight line that passes through the zero/zero calibration point. Linearity is determ ined by calculating the relative standard deviation (RSD) of the response factor or calibration factor for each analyte and comparing this RSD to the limit specified in the method. If the RSD does not exceed the specification, linearity is assumed.

In the 600- and 1600-Series methods, the linearity specification varies from method to method, depending on the quantitation technique. Th e typical limits on the RSD are as follows:

$ 15% for the gas chromatography (GC) and high-performance liquid chromatography (HPLC)

methods
$ 20% for analytes determined by the internal st andard technique in the gas chromatography/mass spectrometry (GC/MS) methods (624, 625, 1624, and 1625)
$ 20% for analytes determined by isotope dilution in Methods 1613, 1624, and 1625
$ 15% for mercury determined by atomic fluorescence in Method 1631

Metals methods that employ a linear regression specify a criterion for the correlation coefficient, r,

such as 0.995.

If the calibration is not linear, as determined by the RSD of th e response factor or calibration factor, a

calibration curve should be used. This means that a regression line or other mathematical function should be employed to relate the instrument r esponse to the concentration. However, properly maintained and operated lab instrumentation should have no difficulty in meeting linearity specifications for 600- and 1600-Series methods. Linear regression emphasizes the importance of higher concentration standards and that the corre lation coefficient is little impacted by poor performance of calibration standards with low concentrations.

For determination of nearly all of the organi c analytes using the 600- and 1600-Series methods,

calibration curves are linear over a concentration ra nge of 20–100 times the nominal concentration, depending on the detector being employed. Whatev er calibration range is used, the laboratory should provide the RSD results by which one can judge lin earity, even in instances where the laboratory is using a calibration curve. In instances where the la boratory employs a curve ra ther than an average

### 33 March 2007 response or calibration factor, the data reviewer s hould review each calibration point to assure that the response increases as the concentration increases. If it does not, the instrument is not operating properly, or the calibration curve is out of the range of that instrument, and data are not considered

usable.

4. Calibration Verification

Calibration verification involves the analysis of a single standard, typically in the middle of the calibration range, at the beginning of each analytical shift. The concentration of each analyte in this standard is determined using the initial calibration data and compared to specifications in the method. If the results are within the specifications, the labor atory is allowed to proceed with analyses without recalibrating and to use the multi-point calibration da ta to quantify sample results. It is also recommended that a calibration verification at the action level is periodically analyzed.

Specifications for calibration verification are gene rally given as a range of concentrations, as a recovery range, or as a percentage difference from the test concentration. For the 600-series semivolatile GC and HPLC methods, the difference must be within

 15%. For Method 625, the

difference must be within

 20%. The GC and GC/MS methods for volatiles and the 1600-Series methods specify a range of concentrations or r ecoveries for each analyte. These ranges are based on interlaboratory method validation studies.

If calibration cannot be verified, the laboratory may ei ther recalibrate the instrument or prepare a fresh calibration standard and make a second attempt to ve rify calibration. If calibration cannot be verified with a fresh calibration standard, the instrument shoul d be recalibrated. If calibration is not verified, subsequent data are considered to be in valid until the instrument is recalibrated.

5. Method Detection Limit or Minimum Level

Although this requirement is not explicitly stated in EPA wastewater methods (e.g., 600 and 1600- Series methods) we recommend use of the met hod detection limit (MDL) concept to establish detection capabilities. Detailed procedures for determ ining the MDL are provided at 40 CFR Part 136, Appendix B. Although exact frequencies vary by me thod, most methods require that, at a minimum, laboratories conduct an MDL study as part of their initial demonstration of capability and whenever a modification is made to the method that might affect the detection limit and am ends thereafter. Data reviewers should consult the methods used for speci fic requirements, or the requirements of their customers, auditors, etc.

The Minimum Level (ML) is used as a quantitation le vel, and is defined in most of the 1600-Series

methods as the lowest level at which the entire an alytical system gives a recognizable signal and acceptable calibration point. Therefore, each 1600- Series method specifies that the calibration range for each analyte encompass the method-specified ML.

Many of the EPA wastewater methods provide speci fic requirements regarding reporting results that are below the ML or the method-specified quan titation limit when these data will be used for compliance monitoring. Since these requirements va ry slightly, data reviewers should consult the specific method for details.

If the sample results are above the ML, but are belo w the facility’s regulatory compliance level, then the laboratory should report the results to indicate that the pollutant has been detected but is compliant with a facility’s permit, assuming all QC criteria ar e met. If sample results are above the regulatory

### 34 March 2007 compliance level, the data reviewer may wish to ev aluate the laboratory QC sample results to verify that the reported concentration is not attributable to analytical bias. In addition, the data reviewer

should evaluate all blank results to determine if the level of pollutant detected may be attributable to

contamination.

6. Initial Precision and Recovery

Part 136 methods require this Initial Precision Recovery (IPR) test before use of a method. It is sometimes termed the “start-up test.” The labor atory should demonstrate that it can meet the specifications in the method for the recovery of analyt es spiked into a reference matrix (reagent water). EPA’s experience has been that laboratories that ha ve difficulty passing the start-up test have such marginal performance that they will have difficu lty in the routine practice of the method.

The start-up test consists of spiking the analytes of interest into reagent water and analyzing four aliquots. The mean concentration and the standard deviation of the concentration are calculated for each analyte and compared to the specifications in each method. If the mean and standard deviation are within the limits, the laboratory may use the me thod to analyze field samples. For some methods, a repeat test is allowed because of the larg e number of analytes being tested simultaneously.

If start-up test data fail to meet the specifications in the method, none of the data produced by that laboratory using that method should be considered usab le. As with the documentation of the purity of the standards, the start-up test data need not be s ubmitted with each set of sample results, but should be submitted the first time a laboratory is employed for analyses, and updated as changes to the method necessitate (see below) in order to allow the data reviewer to determine the adequacy of the laboratory’s performance.

If the laboratory did not perform the start-up tests, th e data should not be considered usable, unless all other QC criteria have been met and the laborator y has submitted IPR (and associated instrument QC) data that were generated after-the-fact on the same instrument. If these conditions are met, then the data reviewer may consider the data to be acceptable for most purposes.

Note: Discussion of this alternative should not in any way be construed as EPA approval of the practice of performing IPR analyses after the anal ysis of field samples. Rather, EPA regards the demonstration of laboratory capability pr ior to sample analysis as an essential QC component. This suggestion provides a tool to permitting authorities when data have already been collected without the required IPR samp les. Once the missing IPR data has been identified as a problem, all responsible parties should implement corrective action necessary to ensure that it is not repeated.

It is important to remember that if a change is made to a method, the start-up test will need to be repeated with the change as an integral part of the method. Such changes may involve alternative extraction, concentration, or cleanup processes; alte rnative GC columns, GC conditions, or detectors; or other steps designed to address a particular matrix problem. If the start-up test is not repeated when these steps are modified or added, then laboratory data produced by the modified method should not be

considered reliable and thus should not be used. Many laboratories report the configuration of their GCs (instrument number, column, detector) as a part of their report header. If a configuration change is made and new IPR data are not supplied, EPA recommends requesting the new IPR data from the laboratory.

### 35 March 2007 7. Analysis of Blanks

Blanks should be analyzed on a routine basis, wh en any part of the analytical process has been changed, and when contamination of the analytical system is suspected. Most recent EPA methods require that a blank be prepared and analyzed with each batch (set) of samples. The size of a batch is usually limited to a maximum of 20 field samples. In practice, this means that on each day that a laboratory prepare samples, they should also prep are a blank, even if fewer than 20 samples are prepared. The purpose of analyzing a blank with each set of samples is to determine the extent of possible contamination of the samples while in the laboratory. If the blank is handled by the same analysts in the same way as the samples and the bl ank shows no contamination, it is likely that the samples will not have been contaminated. Analyz ing a blank when the anal ytical process has been changed is consistent with requiring a repeat of th e start-up tests, because the change introduces a new possibility for contamination of samples through the use of the new materials or procedures.

Contamination in the laboratory is a common problem, though there are many opinions on what

constitutes contamination. In more recent EPA me thods, a concentration above the minimum level of quantitation of the method is a cause for concern. In reality, it is not unusual to find low levels of common laboratory solvents, phthalates, and othe r ubiquitous compounds in laboratory blanks.

Controlling laboratory contamination is an importa nt aspect of each laboratory's quality assurance plan. The laboratory should maintain records, ty pically in the form of control charts, of blank contaminants. These records should prompt correctiv e action by the laboratory, including reanalysis of any affected samples, when concentration of an an alyte in a blank rises above a historical level. The reviewer in evaluating sample results may request co ntrol charts; however, they are not required in

EPA methods and are not routinel y submitted with sample data.

Unfortunately, by the time that results have been f ound to be contaminated, it is usually too late for corrective action. Therefore, the reviewer has several options in making use of the sample data. First, if a contaminant is present in a blank, but not presen t in a sample, then there is little need for concern about the sample result, though it may be useful to occasionally review the raw data for samples

without the contaminant to ensure that the labor atory did not edit the results for this compound.

The second approach deals with inst ances where the contamin ant is also reported in a sample. Some general guidance will help determine the degree to wh ich the contaminant is affecting sample results:

• If the sample contains the contaminant at levels of at least 10 times that in the blank, then the likely contribution to the sample from the contamin ant in the laboratory environment is at most 10%. Since most of the methods in question are no more accurate than that level, the possible contamination is negligible.

• If the sample contains the contaminant at levels of at least 5 times but less than 10 times the blank result, the compound is probably present in the sample, but the numerical result should be considered an upper limit of the true concentration.

• If the sample contains the contaminant at levels be low 5 times the level in the blank, there is no adequate means by which to judge whether or not the sample result is attributable to laboratory contamination. The results for that compound in that sample should be considered unacceptable for compliance monitoring.

### 36 March 2007 There are two difficulties in evaluating sample results relative to blank contamination. First, the

reviewer should be able to associat e the samples with the correct bla nks. For analysis of volatiles by purge-and-trap techniques, where no sample extrac tion is required, the blanks and samples are associated by analysis date and time, and specific to the instrument as well. For methods involving the extraction of organic compounds from the samples, th e blanks and samples are primarily associated by the date on which they were extracted, and by th e batch of samples and associated lab equipment (glassware, reagents, cleanup media).

The second difficulty involves samples that have been diluted. Dilution of a sample with reagent water or dilution of an extract with solvent repr esents an additional potentia l source of contamination

that will not be reflected in the results for the blan k unless the blank was similarly diluted. Therefore, in applying the 10-times rule, the concentration of the sample is compared to the blank result multiplied by the dilution factor of the sample or sample extract. For instance, if 12 ppb of a contaminant are found in the blank, and the associated sample extract was diluted by a factor of 6 relative to the extract from the blank prior to analysis , then the sample result would have to be greater than 12x6x10, or 720 ppb, to be acceptable. Between 360 ppb a nd 720 ppb, the sample result would best be considered an upper limit of the actual c oncentration. Below 360 ppb, the sample result is not acceptable for compliance monitoring.

In general, practitioners of analytical methods do not subtract the concentration of the analyte in the blank from the concentration of the analyte in the sample to determine the true concentration of the analyte in the sample. Experience indicates that this practice is not reliable. The obvious problem occurs when the blank concentration is higher than that in the sample, and subtraction would yield a negative concentration. Using the 10-times rule above provides a more appropriate means of evaluating the results and does not require that the re viewer alter the results reported by the laboratory.

8. Ongoing Precision and Recovery

The 1600-Series methods require that an “ongoing prec ision and recovery” (OPR) sample be analyzed with each sample set, and the results of this OPR sample should meet the acc eptance criteria in the method prior to the analysis of blanks and samples. Most other methods approved at 40 CFR Part 136 contain a similar requirement, but may use different terminology, such as a laboratory control sample (LCS), laboratory fortified blank (LFB), or QC check sample. For this purposes of this discussion, all such samples are referred to as OPR samples.

The OPR samples are used to ensure that laborator y performance is in control during analysis of the associated batch of field samples. The data reviewer should determine if the OPR sample has been run with each sample set and if all criteria have been met. For methods that do not require sample digestion or extraction, such as volatile analyses by Method 1624, the OPR analysis is associated with the samples on the basis of the analysis date and time and the specific GC/MS system. For other analyses, such as semivolatile an alyses by Method 1625, OPR resu lts are associated with samples extracted (or digested) at the same time as the OPR. In addition to defining sample batches by date and time of extraction or analysis, each method specifies a maximum batch size (generally no more than 10 or 20 samples) that can be associated with a single OPR. The reviewer should verify that OPR samples were run at the proper frequency.

Because of the large number of compounds being t ested simultaneously in the 600- and 1600-Series methods, there is a small probability that the OPR analysis will occasionally fail to meet the specifications. While the laboratory is supposed to correct any problems and analyze another OPR aliquot, it may still be possible to utilize the data associated with an OPR aliquot that does not meet all

### 37 March 2007 of the method specifications. The following guide lines may be useful to data reviewers when evaluating the usability of data:

• If the concentration of an analyte in the OPR is above the method specifications, but that compound is not detected in an associated sample , then it is unlikely that the sample result is affected by the failure in the OPR.

• If the concentration of the analyte in the OPR is above method specifications and the analyte is detected in the sample, then the numerical result may represent an upper limit of the true concentration, and data users should be cautione d when using the data for enforcement purposes.

• If the concentration in the OPR is below the method specifications, and that analyte is detected in an associated sample, then the sample result is likely a lower limit of the true concentration for that analyte.

• If the concentration of the analyte in the OPR is below method specification and that analyte is not detected in the associated sample, then the sa mple data are suspect and are not usable for regulatory compliance purposes because the analys is does not demonstrate the absence of the analyte.

If the OPR sample was not run, there is no way to veri fy that the laboratory pr ocesses were in control. In such cases, a data reviewer may be able to u tilize the field sample data by examining labeled compound or matrix spike recovery results, the IPR results, OPR results from previous and subsequent batches, and any available historical data from bot h the laboratory and the sample site. If the matrix spike or labeled compound results associated with the sample batch do not meet the performance criteria in the methods, then the results for that set of samples cannot be considered usable.

If the laboratory’s IPR results and the matrix spik e or labeled compound results associated with the sample batch in question meet a ll applicable performance criteria in the methods, then the data reviewer may be reasonably confident that laborat ory performance was in control during field sample analysis. This level of confidence may be furthe r increased if there is a strong history of both laboratory performance with the method and method pe rformance with the sample matrix in question, as indicated by additional OPR and matrix spike data collected from the laboratory and samples from

the same site.

Note: The preceding discussion of maximizing use of failed OPR data is not an EPA endorsement of the practice of proceeding with uncontrolled laborat ory analyses. Rather, laboratories failing to meet OPR specifications should identify and co rrect the problem and re-analyze affected samples whenever possible. This preceding discu ssion is provided only to describe a tool for permitting authorities when re-analysis is not possible due to sample holding times, insufficient sample volumes, or other reasons.

9. Recovery of Analyte Spiked into the Sample Matrix or Recovery of Labeled Compound Spiked into Samples

The majority of the 600- and 1600-Series methods we re developed to analyze effluent samples, and may not be appropriate for in-process samples. While many of the methods were tested using effluents from a wide variety of industries, samples from some sources may not yield acceptable results. It is, therefore, important to evaluate method perfo rmance in the sample matrix of interest.

### 38 March 2007 The non-isotope dilution wastewater methods require a spike of the analytes of interest into a second aliquot of the sample for analysis with the sample . The purpose of spiking the sample (often termed a “matrix spike (MS)”) is to determine if the method is applicable to the sample in question. Most of these wastewater methods also require that laborator ies prepare and analyze a duplicate aliquot of the matrix spike (often called a “matrix spike duplicate (MSD)”), or a duplicate aliquot of an unspiked field sample (usually called a “duplicate”). Ge nerally, one matrix spike/matrix spike duplicate (MS/MSD) pair or one MS and one duplicate sample is required for every 10 or 20 field samples, depending on the requirements of the specific method being used.

In evaluating method performance in the sample matrix, data reviewers should examine both the precision and accuracy of the analysis. Precision is evaluated by comparing the relative percent difference (RPD) of results obtained from the MS/MSD pair or from the duplicate and its corresponding field sample. Accuracy is assessed by examining the recovery of compounds in the matrix spike sample (and if applicable, the matrix spike duplicate sample). In evaluating matrix spike results, the data reviewer should verify that:

• The unspiked sample has been analyzed.

• The spiked sample has been analyzed, and that the analytes were spiked at an appropriate concentration (generally 5 - 10 times the background concentration of the analyte in the sample or 1 - 5 times the regulatory compliance limit, whicheve r is greater). If the analytes are spiked too high or too low, it is not usually possible to differe ntiate recovery of the spiked concentration from recovery of the analyte in the unspiked sample.

• The recovery of the spike is within the range specified.

If the RPD and recoveries of the MS/MSD or MS and duplicate samples are within the limits specified in the method, the method is judged to be applicable to that sample matrix. If, however, the RPD or recoveries in these samples are not within the range specified, either the method does not work on the sample, or the sample preparation process which includes sample collection is out of control.

If the method is not appropriate for the sample matrix , changes to the method or use of an alternative method would be needed. Matrix spike results are necessary in evaluating a modified method. If the analytical process is out of control, the laborator y should take immediate corrective action before any more samples are analyzed.

To separate indications of method performance from those of laboratory performance, the laboratory should prepare and analyze a quality control check standard (laboratory control sample) or an OPR sample, as described in Items 4 and 8 of this chapter. If the results for either of these analyses are not within the range specified , the analytical system or process should be repaired. After verifying the performance of the repaired system and pro cesses through successful analysis of calibration verification and OPR samples, the sample and sp iked sample analysis should be repeated. If recoveries and RPD of the repeated matrix spik e and duplicate analyses are within the ranges specified, the analytical process is judged to be in co ntrol. If, however, the repeated analysis results are still outside the specified ranges, then sample results generally are not useful for regulatory compliance purposes because the matrix spike and d uplicate results indicate that the method is not applicable to the sample.

In rare cases, it may be possible to make use of su ch data while efforts are being made to identify a method that works on the matrix in question. The following guidelines may be applicable as a temporary measure in such circumstances:

### 39 March 2007 • If the recovery of the matrix spike and duplicate are above the method specifications, but the regulated analyte was not detected in the associated sample or was detected below the regulatory compliance limit, it is unlikely that the sample resu lt was affected by the failu re in the matrix spike

because the factors that caused th e analysis to over-estimate the co ncentration in the spiked sample would not likely have resulted in an under-estimate in the unspiked sample. In other words, it is likely that the sampled effluent is in co mpliance with the permit limit in such cases.

• If the recovery of the matrix spike and duplicate are below method specifications, but the regulated analyte was detected above the regulatory compliance limit in an associated sample, the sample result may represent the lower limit of the true concen tration for that pollutant and it is likely that

true concentration in the effluent is in violation of the permit limit.

• If the recovery of the matrix spike and duplicate are above the method specifications and the regulated pollutant was detected in an associ ated sample, the sample result may represent the upper limit of the true concentration and the data cannot be considered useable for regulatory compliance purposes.

• If the recovery of the matrix spike and duplicate are below the method specifications and the regulated pollutant was either not detected or was detected below the regulatory compliance limit, the sample result may represent a lower limit of th e true concentration and cannot be considered usable for regulatory compliance purposes.

Note: The preceding discussion of maximizing use of failed matrix spike or duplicate data is not an EPA endorsement of the practice of using methods that do not work on the sample matrix. The preceding discussion is provided only to describe a tool for permitting authorities for use in evaluating compliance monitoring results pending the permittees’ successful identification and use of an alternate method or method modifications such as those described in Chapter 6 of this document.

For isotope dilution analyses, data evaluation is simpler because isotopically labeled analogs of the pollutants are spiked into every sample. If recove ry of a labeled compound spiked into a sample is not within the range specified in the method, and results of analysis of the ongoing precision and recovery

standard are within the respective limits, sample results would be considered invalid. When labeledcompound recoveries are outside of method specificati ons, the problem may be related to the sample matrix. The isotope dilution methods specify that , in these instances, the sample should be diluted with reagent water and reanalyzed. If the labele d compound recoveries meet the method specifications after dilution of the sample, the sa mple results are acceptable, although the sensitivity of the analysis will be decreased by the dilution.

For some sample matrices, even dilution will not r esolve the problem, and for other matrices, the loss of sensitivity precludes use of the results for dete rmining compliance. In these instances, additional steps need to be taken to achieve acceptable results.

Steps that may be taken when the results of ma trix-spike or labeled-compound recoveries are not within the limits specified in the methods are descr ibed in Chapter 6 of this document. These steps include suggestions for more extensive extraction and cleanup procedures, for sample dilution, and for other measures to overcome matrix interference problems.

### 40 March 2007 10. Control limits for Recovery of Spiked Analytes or Labeled Compounds in Samples

The 600- and 1600-Series methods specify that after the analyses of five spiked samples, control limit is constructed for each analyte. The control limits for each analyte is computed as the mean percent recovery plus and minus two times th e standard deviation of percent recovery for each analyte. The laboratory should then update their control limits af ter each five to ten subsequent spiked sample analyses.

For non-isotope dilution results, the control limits can be used to estimate the true value of a reported

result and to construct confidence bounds around the r esult. For example, if the result reported for analysis of phenol is 25 μg/L (ppb), and the statement of data quality for phenol is 70%

 + 30% (i.e., the mean recovery is 70% and the sta ndard deviation of the recovery is 15%), the true value for phenol will be in the range of 28–43 μg /L (ppb), with 95% confidence. This range is derived as follows:

Lower limit = [(25 ÷ 0.7) – (25 x 0.3)] = {35.7 – 7.5] = 28 ug/L (ppb)

Upper limit = [(25 ÷ 0.7) + (25 x 0.3)] = {35.7 + 7.5] = 43 ug/L (ppb)

Many laboratories do not maintain or provide cont rol limits with sample results, in which case a data reviewer should contact the laboratory to determine if the control limits are being maintained for each analyte. If necessary, the reviewer can construct a control limits from individual data points if the laboratory has records of recoveries for matrix spikes.

Statements of data quality for isotope dilution me thods are based on the recoveries of the labeled compounds. Using an isotope dilution method, the sa mple result has already been corrected for the recovery of the labeled analog of the compound. Th erefore, for a reported result for phenol of 25 μg/L where the standard deviation of the labeled phenol rec overy is 15%, the true value for phenol will be in the range of 17–32 μg/L, with 95% confidence, derived as follows:

Lower limit = [25 – (25 x 0.3)] = 17 μg/L (ppb)

Upper limit = [25 + (25 x 0.3)] = 32 μg/L (ppb)

The lack of control limits does not invalidate r esults, but makes some compliance decisions more difficult. If the laboratory does not maintain contro l limits there may be increased concern about both specific sample results and the laborat ory's overall quality assurance program.

11. Contol limits for the Laboratory (Methods 1624 and 1625)

In addition to statements of data quality for results of analyses of the labeled compounds spiked into the samples, Methods 1624 and 1625 require that control limits be constructed from the initial and ongoing precision and recovery data. The purpose of the control limits is to assess laboratory performance in the practice of the method, as co mpared to the assessment of method performance made from the labeled compound results for the sampl es. Ideally, the two limits would be the same. Any difference is attributable to either random error or sample matrix effects.

If the laboratory is practicing isotope dilution met hods, the data reviewer should review the control chart for the laboratory. If the laboratory does not make these statements available for the reviewer, they may be requested. If the laboratory still does not make them available, it does not necessarily invalidate any data, but indicates that the labor atory may not be following the method as written.41March 2007Chapter 8When a Matrix Interference Is DemonstratedThe preceding chapters describe how to overcome matrix interference problems and case histories of matrix interference problems thatwere mitigated. This chapter describeshelpthat may be available when all attempts atovercoming matrix interference problems have beenexhausted.Poor Recovery or Precision of Matrix SpikesThe most common indication of a matrix problem will be recoveryor precision of the matrix spike and matrix spike duplicate (MS/MSD)outside of the QC acceptance criteria inthe method or QC acceptance criteria suggested in the Streamlining Initiative (see Chapter 4 of thisdocument). Once a matrix interference is demonstrated to be the cause of a laboratory's inability to meet the QC acceptance criteria, the laboratoryshould document the interference and attempt to overcome it using the procedures suggested in the analytical method, in Chapter6 of thisdocument, and other techniques in the test method or technical literature.If an allowance for matrix effects is warranted or appropriatewithout a demonstration that a matrix interference exists and without anattempt to overcome the matrix interference, such an allowance provides a disincentive for addressing interferences that may beovercome using theprocedures recommended in this document and in the method. The discharger should be familiar with its wastewater and thus ableto find solutionsto matrix interference problems. However, a site-specific orfacility-specific allowance may be warranted after all efforts toremove theinterference(s) have been exhausted,and should be handled on a case-by-case basis by the regulatory/control authority.Inability to Meet the Method Detection Limit (MDL)Another common indication of a matrix interference is that measurements cannot be made at lowlevels because interferences arepresent atthese levels.Statements of the performance in EPA methods, including estimates of MDLs, are estimates based on the Agency's evaluation of amethodin various performance studies, and the method may not achieveall of the stated performance characteristics in all possible sample matrices. TheScope and Application section of most modernmethods approved for use in EPA's wastewater programs states: “The detection limitand minimumlevel of quantitation in this method usuallyare dependent on the level of interferences rather than instrumental limitations.”Therefore, the MDLand minimum level of quantitation (ML) should be treated as “presumptive” performance characteristics. These characteristics may varydepending on the sample matrix and on the concentration of interest. The MDL issue has not been resolved and may change.The MDL procedure at 40 CFR Part 136, Appendix B allows determination of an MDL in a matrix other than reagent water (see theScopeand Application section of the MDL procedure). A permit could specify a different detection or quantitation limit when a discharger demonstrates42March 2007that a different limit is appropriate for its effluent based on the presumptive statement at the beginning of most modern EPA methods, andstatements in the MDL procedure. After the discharger demonstrates that the approved test method cannot achieve the presumptive detection orquantitation limit on an effluent-specific basis, the dischargerand regulatory authority should work cooperatively to establish the permit limit usinga procedure such as the procedure given at 40 CFR Part132, Appendix F, Procedure 8. This procedure, titledWater Quality-based EffluentLimitations Below the Quantification Levelallows a discharger to establish an effluent-specific ML.Although EPA has provided the procedure above to develop an effluent-specific ML, EPA recommends that the discharger attempt toachieve the MDL and ML stated in the approved method by usingthe interference-reducing procedures given in this document and the analyticalmethod. Prior to allowing the adjustment of a permit limit because the discharger reports it is unable to achieve the MDL andML the appropriatemethod approved at 40 CFR Part 136, the regulatory authority should review the steps taken by the discharger to reduce interferences to ensure thatall reasonable efforts have been made toachieve the permit limit. It is critical that the permittee be able to measure and accurately report results ator above their permit limit and the achievement of method specified MDLs or MLs is of less importance.Allowance for a Matrix InterferenceBecause every situation is different, EPA has not adopted a rigidprotocol for obtaining data that demonstrate that a matrix interferenceexists, nor can a hard-and-fast rule be developed to state theconditions under which an allowance for a matrix interference should be granted. Afterall attempts at resolving the matrix interference are unsuccessful,the most common analytical solution to a matrix interference problem is to dilutethe sample with reagent water until the precision and recovery are within normal levels. No more than the minimum amount of dilution should beused. The effect of this dilution will be to raise the MDL andML and may necessitate development of an effluent-specific MDLand ML. Shouldthis situation arise, EPA suggests that the regulatory/controlauthority solicit and evaluate the following information to demonstrate that anallowance for matrix interferences in the form ofan effluent-specific MDL and ML may be appropriate:•MDL, IPR, and blank data demonstrating that the laboratory can perform the method;•Field, equipment, and reagent blank datademonstrating that the sampling and analysis systems are free from contamination at the levelsrequired for reliable determination of the pollutant;•MS/MSD data (where applicable) demonstrating that a potential matrix interference exists because the recovery and or precisionis not withinthe QC acceptance criteria of the method;•Confirmation of the out-of-specification MS/MSDrecovery or precision by a second laboratory;•Identification of the potential interferent(s);•Steps taken to attempt to mitigate the interference (e.g., sample, extract, or digestate concentration; sample dilution; use ofa larger sample size;use of cleanup procedures; use of pH change prior to extraction;use of a greater amount of a removal reagent; use of techniques to selectivelyremove the interferent; etc.); and•Calculation of an effluent-specific MDL using the procedure at 40 CFR Part 136, Appendix B, and calculation of an ML using theproceduregiven at 40 CFR Part 132, Appendix F, Procedure 8;•Other methods approved for NPDES compliance which utilize different approaches were tried.43March 2007Once the regulatory/control authority receives these data, the authority would make adetermination that an effluent-specificMDL and MLare appropriate.Chapter 9Sources of Additional Help and InformationFollowing are several sources of information and EPA contacts related to the issues addressed in this document. Please visitthe websites(listed below), and/or obtain a copy of the EPA CD-ROMs for reference information on analytical methods and topics discussed inthis guidance.Web SitesEPA’s home pagehttp://www.epa.govEPA’s Office of Science and Technology’swater science analytical methods pageshttp://www.epa.gov/ost/methodsorhttp://www.epa.gov/waterscience/methodsEffluent Guidelineshttp://www.epa.gov/ost/guideMethod IndicesEPA Region 1 Libraryhttp://www.epa.gov/epahome/index/EPA Information Sourceshttp://www.epa.gov/epahome/index/key.htmNational Environmental Methods Index(NEMI)http://www.nemi.govOffice of Water CD-ROMsSelected Office of Water Methods and Guidance, Version 5(EPA 821-C-04-001; September 2004)44March 2007Water DocketThe Water Docket contains copies of materials that support ourrules under the Safe Drinking Water Act (SDWA) and Clean WaterAct(CWA). These materials includeFederal Registernotices, references cited in these notices; health criteria, analytical methods, treatmenttechnology, and economic impact and environmental assessment data; development documents, public comments, and other backgroundinformation.US Environmental Protection AgencyEPA Docket Center (EPA/DC)Public Reading RoomRoom B102, EPA West Building1301 Constitution Avenue, NWWashington, DC 20460The Docket is open to the public on all Federal government workdays from 8:30 a.m. until 4:30 p.m. A reasonable fee may be charged forphotocopying. On-line Docket searches may be performed athttp://www.epa.gov/ow/docket.html.Federal RegisterTheFederal Registerpage is athttp://www.gpoaccess.gov/fr/index.html. All issues of theFederal Registerfrom 1994 to the present areonline.Federal Registernotices prior to 1994 may be found at a library or through a search service. Search instructions for theFederal Registerare at the Government Printing Office (GPO) web site athttp://www.gpoaccess.gov.Code of Federal RegulationsAll issues from 1996 to the present are on line. The Code of Federal Regulations (CFR) is athttp://www.gpoaccess.gov/cfr/index.html.CFRs prior to 1996 may be found ata library or through a search service.45March 2007Approval of an Alternate Test Procedure or Questions Specifically Related to this GuidanceProcedure for nationwide use (see the regulations at 40 CFR Parts 136.4 and 136.5)Analytical Methods Staff (4303T)U.S. EPAAriel Rios Building1200 Pennsylvania Avenue, N.W.Washington, DC 20460email: OSTCWAMethods@epa.govProcedure for use on a specific discharge (see the regulations at 40 CFR Parts 136.4 and 136.5)46March 2007Sources for Supporting DocumentsNote:These sources are documents referenced in this document. Fora more comprehensive list of guidance and other documents, see EPA'swaterscience, yosemite, and other websites, or performan online search for the document by title or subject.Table 9-1 Sources for Supporting DocumentsSubjectTitle of GuidanceDocument numberDateSourceMethods UpdateRuleGuidelines Establishing Test Proceduresfor the Analysis of Pollutants Under theClean Water Act; National PrimaryDrinking Water Regulations; and NationalSecondary Drinking Water Regulations;Analysis and Sampling Procedures; FinalRuleEPA 821-F-06-005 March 12, 2007 72 FR 11200http://www.epa.gov/waterscience/methods/update2003/index.htmlClean spacesguidanceGuidance on Establishing Trace Metal CleanRooms in Existing FacilitiesEPA 821B96001 January 1996http://yosemite.epa.gov/water/owrccatalog.nsfCleanroom guidanceTrace Metal Cleanroom, prepared by theResearch Triangle InstituteRTI/6302/04/02 F October 1995 Research TriangleInstituteMercury; Method1631 guidanceMethod 1631, Revision E: Mercury in Water byOxidation, Purge and Trap and Cold VaporAtomic Fluorescence SpectrometryEPA 821-R-02-019 August 2002 http://www.epa.gov/waterscience/methods/1631guid.pdfMethods, wastewaterand drinking waterEPA Methods and Guidance for Analysis ofWaterEPA 821-C-99-004 June 1999 NTIS1PB99-500209Methods, historicalMethods for Chemical Analysis of Water andWastes(MCAWW)EPA 600/4-79-020 March 1983 NTIS1PB84-128677Methods andguidanceSelected Office of Water Methods and Guidance,Version 5EPA 821-C-04-001 September 2004Metals samplingtechniquesevaluationEvaluating Field Techniques for CollectingEffluent Samples for Trace Metals AnalysisEPA-821-R-98-008 June 1998http://yosemite.epa.gov/water/owrccatalog.nsf47March 2007Table 9-1 Sources for Supporting DocumentsSubjectTitle of GuidanceDocument numberDateSourceMetals samplingvideoOffice of Water Methods and Guidance, Version2.0 - Suite(video and CD-ROM; includesmethods on CD-ROM EPA 821-C-99-004)2002 NTIS1PB2002-500076,includes video andmethods on CD-ROMsMetals dataevaluation guidanceGuidance on the Documentation and Evaluationof Trace Metals Data Collected for Clean WaterAct Compliance MonitoringEPA 821-B-96-004 July 1996 http://yosemite.epa.gov/water/owrccatalog.nsfMethod flexibilityStreamlining Initiative – Guide to MethodFlexbility and Approval of EPA Water MethodsEPA-821-D-96-006 December 1996 http://epa.gov/waterscience/methods/guide/flex.htmlOil and grease;Method 1664guidanceAnalytical Method Guidance for EPA Method1664A Implementation and Use (40 CFR Part136)EPA 821-R-00-003 February 2000 http://www.epa.gov/waterscience/methods/1664guide.pdfRadiochemistrymethod guidanceMulti-Agency Radiological LaboratoryAnalytical Protocols Manual(MARLAPManual)(EPA 402-B-04-001A to C (in threevolumes)December 2004 69 FR 77228Sampling guidanceMethod 1669: Sampling Ambient Water forTrace Metals at EPA Water Quality CriteriaLevelsEPA 821-R-96-011 July 1996Whole-effluenttoxicity (WET)testing guidanceMethod Guidance and Recommendations forWhole Effluent Toxicity (WET) Testing (40 CFRPart 136)EPA 821-B-00-004 July 2000 http://www.epa.gov/waterscience/WETWhole-effluenttoxicity (WET)variability guidanceUnderstanding and Accounting for MethodVariability in Whole Effluent ToxicityApplications Under the National PollutantDischarge Elimination System ProgramEPA 833-R-00-003 June 2000 http://www.epa.gov/waterscience/WET1National Technical Information Service,http://www.ntis.gov

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# Solutions to Analytical Chemistry

Problems with Clean Water Act Methods

March 2007