## Results of the ICP/MS Collision Cell Method Detection Limit Studies in the Synthetic Flue Gas Desulfurization Matrix

Prepared for

Marion Kelly and Lemuel Walker U.S. Environmental Protection Agency Office of Water Office of Science and Technology Engineering and Analysis Division (4303T) 1200 Pennsylvania Avenue, NW Washington, DC 20460

Prepared by

CSC 6101 Stevenson Avenue Alexandria, VA 22304

Prepared under

EPA Scientific and Technical Support Contract EP-C-12-008



## October 18, 2012Collision Cell MDL Study Results i 10/18/2012 

## Table of Contents

Page Background .................................................................................................................... ............................... 1 Study Implementation .......................................................................................................... ......................... 1

Derivation of Detection and Quantitation Limits................................................................................ .......... 2

Pooled MDLs ................................................................................................................... ......................... 3

Pooled MLs .................................................................................................................... ........................... 3 Summary of St udy Results ...................................................................................................... ...................... 4 Synthetic FGD Matrix .......................................................................................................... ..................... 4 Reagent Water ................................................................................................................. .......................... 4

CSC Recomme ndations ........................................................................................................... ..................... 5

References .................................................................................................................... ................................. 5Collision Cell MDL Study Results 1 10/18/2012 Results of the ICP/MS Collision Cell Method Detection Limit Studies in the Synthetic Flue Gas Desulfurization Matrix

Background

The U.S. Environmental Protection Agency (EPA) E ngineering and Analysis Division (EAD), within the Office of Water (OW) has developed a draft procedur e for the use of a collisi on cell accessory with an inductively coupled plasma and mass spectrometer (ICP/MS) in the analysis of effluent samples from flue gas desulfurization (FGD) processes at steam electri c generating facilities (Reference 1). The collision cell accessory has the potential to reduce interferenc es in ICP/MS analyses from non-target analytes present in typical wastewaters from this industry, thus allowing more accurate and precise measurement of the concentrations of the analytes EP A expects to be subject to regulation.

The focus of the present study was to characterize method detection limits (MDLs) and minimum levels (MLs) of quantitation for the target analytes in both reagent water and in a synthetic matrix that is designed to mimic the composition of FGD wastewaters. The target analytes for this study were arsenic, cadmium, chromium, lead, selenium and thallium.

The primary goals of this study were to:

 Obtain MDL data, from at least three laboratories, that reflect the capabilities of the draft EAD ICP/MS collision cell procedure in FGD wastewaters, and

 Use the MDL data to derive an ML for each targ et analyte to support EAD’s efforts to regulate discharges from FGD systems.

Secondary goals were to:

 Obtain MDL data from laboratories using ICP/MS instrumentation and collision cell accessories other than those used in the initial development of the procedure,

 Obtain laboratory feedback regarding the draft procedure itself, including information about modifications to the operating conditions that may be needed for specific ICP/MS instrumentation or collision cell accessories.

Study Implementation

EPA tasked CSC to assist in designing and implemen ting this study. CSC supported the effort by procuring a sufficient quantity of a synthetic matrix designed to mimic the composition of FGD wastewaters, procuring MDL study services from th ree qualified laboratories, and providing study coordination and implementation support. Details of the study are described in a formal study plan reviewed and approved by EAD (Reference 2).

CSC issued purchase orders to three laboratories (t wo commercial and one u tility) to perform MDL studies as outlined in 40 CFR Part 136 Appendix B. EAD worked with an instrument vendor to obtain similar MDL data from the vendor’s in-house laboratory. The four laboratories were:

 Agriculture and Priority Pollutants La boratories, Inc. (APPL) - commercial

 Hampton Roads Sanitation District (HRSD) - utility

 Southwest Research Institute (SwRI) - commercial

 Perkin Elmer (PE) - instrument vendor

CSC provided each of the four laboratories with one 500-mL volume of the synthetic FGD matrix described in the study plan. CSC tracked each shipment of the solution, confirmed condition upon receipt by each laboratory, and used the receipt dat es to establish due dates for the study results.Collision Cell MDL Study Results 2 10/18/2012 This synthetic matrix was prepared at twice the nomi nal concentrations of the constituents described in the draft collision cell procedure so that it could be used to support another EAD study of the collision cell instrumentation. Each laboratory participating in the MDL study diluted this solution by a factor of two to create the reference matrix for its FGD MDL study aliquots. Each laboratory provided its own reagent water for use as the clean refere nce matrix for its MDL study aliquots.

CSC and EAD held a kick-off conference call with all of the laboratories on August 28, 2012. CSC and EAD responded to several rounds of follow-up questions after the call. Answers to all questions from laboratory participants were routed to all laboratori es via email as quickly as practical, in order to keep the study on schedule. CSC also worked with the sta ndards vendor and all of the laboratories to refine the available information on the background levels of so me of the target analytes that were found in the synthetic matrix, so that each laborat ory could adjust the concentrations of these analytes spiked into the MDL study aliquots.

As data were delivered to CSC, the results were review ed in two stages. The first stage was to review the electronic data deliverable (an Excel file) from each la boratory with the results for each target analyte in each matrix. CSC confirmed the standard deviations calculated by the laboratories for each analyte and the resulting MDL values. No calculation errors occurred.

The second stage of the review process involved a clo ser examination of the raw data and QC results supporting the MDL sample results. The results fro m each laboratory were reviewed against the QC specifications in the laboratory statement of work and the study plan. Because the draft collision cell procedure is still under development, some deviations from the draf t procedure’s QC limits were anticipated. Examples include the QC limits for the in ternal standards employed in the procedure. The draft QC limits for samples specified internal sta ndard responses of 60 - 125% of the responses in the calibration blank, and some responses were above and below those limits. No gross deviations occurred, and any minor deviations were noted, but were not a priori grounds for exclusion of the results from the study data set. The data from the MDL study sam ples may be used by EAD to refine the QC specifications for the final procedure at a later date.

The remainder of this document d escribes the results of the study, including CSC’s derivation of pooled MDLs and MLs for ICP/MS collision cell analyses of the synthetic FGD matrix and reagent water using the results from all four laboratories. CSC’s recomme ndations for the uses of the results are provided at the end of the document.

Derivation of Detection and Quantitation Limits

CSC combined the data from all four laboratories and calculated the following limits:

 the maximum MDL for each analyte

 the maximum ML for each analyte

 the pooled MDL for each analyte

 the pooled ML for each analyte.

The maximum MDL was simply the highest MDL va lue for the analyte reported by any of the laboratories in the study. CSC rounded the maximu m MDLs to two significant figures (i.e., two decimal places for values less than 1, and one deci mal place for values between 1 and 10).

The maximum ML is derived from that maximum MDL value by multiplying standard deviation of the results from that laboratory by 10 and rounding the result to the nearest value of 1, 2, or 5 times 10 n

, where n is a positive or negative integer. This roundi ng approach is described in EAD’s formal definition of the ML (Reference 3) and is designed to facilita te preparation of calibration standards at practical concentrations.Collision Cell MDL Study Results 3 10/18/2012 The derivations of the pooled MDLs and pooled MLs are described in detail below.

Pooled MDLs

The pooled MDL for each of the six target analytes w as calculated from the aggregated results from all four laboratories. Each laboratory prepared and an alyzed seven MDL study aliquots of the synthetic FGD matrix and seven more aliquots of reagent water. Each laboratory reported the results for each aliquot, along with their calculated single-laboratory MDL value for each matrix.

For each matrix, CSC confirmed the reported standard deviations of the seven MDL replicates (in concentration units) for each analyte in each laboratory using the formula:

where: s = standard deviation

x i = result for MDL aliquot i (in concentration units)

x ത = the mean of all seven MDL aliquots

As noted above, there were no calculation errors. CSC then calculated the pooled within-laboratory standard deviation, s w , for each analyte and matrix using the formula:

where:

s i = the standard deviation of the seven MDL repli cates (in concentration units) for laboratory i, and m = the number of laboratories (4 in this study)

The pooled MDL was calculated using the formula:

where: 2.49 = the 99 th percentile t -statistic with 24 degrees of freedom (i .e., the total number of MDL replicates combined across all laboratories, minus the number of laboratories).

The pooled MDL values were rounded to two significant figures.

Pooled MLs

The pooled ML was derived from the pooled MDL by multiplying s w , the pooled within-laboratory standard deviation, s w , from the pooled MDL calculation, by 10:

The pooled ML was then rounded to the number nearest value of 1, 2 or 5 times 10 n , where n is a positive or negative integer. 

### 10 x s ML
w pooled 

###  1 n ) x x (

s n

1 i 2 i





 

# 





### m s m

1 i 2
i

w 

# s 

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### 

49

. 2 x s MDL
w pooled 

### Collision Cell MDL Study Results 4 10/18/2012 Summary of Study Results

The tables below summarize the resu lts of the method detection limit (MDL) studies conducted in the synthetic flue gas desulfurization (FGD) matrix and reagent water.

Synthetic FGD Matrix

In some instances, the ML rounds down to 1, 2, or 5, and in other cases, it rounds up. For example the cadmium MDL of 0.11 would yield an unrounded ML value of 0.3368, which rounds down to 0.2, rather than up to 0.5, because it is below 0.35, wh ich is the mid-point between 0.2 and 0.5.

The values for the current procedure MDL are those that TestAmerica determined in 2009, using an earlier version of the collision cell procedure and a di fferent version of the synthetic FGD matrix; these values are included above simply for reference. T estAmerica did not determine the MDL for chromium at that time because of problems with the background c oncentration of this metal in the FGD matrix used at that time.

Reagent Water

As part of the overall study design, the laboratories al so determined MDLs in reagent water. The goal of that effort was to illustrate the cap abilities of the collision cell procedure in a clean reference matrix with no interferences. The table below su mmarizes the results from all four labor atories. In all instances, the reagent water values are below the corresponding FGD values, illustrating the potential effects of the FGD matrix interferences on method sensitivity. B ecause the current draft procedure document does not include MDLs determined in reagent wa ter, that column has been omitted. Summary of Method Detection Limits and Minimum Levels in the Synthetic Flue Gas Desulfurization Matrix (in μg/L)

Matrix Analyte Maximum MDL Maximum ML Pooled MDL Pooled ML Current Procedure MDL FGD Arsenic 0.52 2 0.24 1 0.61 FGD Cadmium 0.11 0.2 0.05 0.2 0.59 FGD Chromium 0.17 0.5 0.08 0.2 NA FGD Lead 0.31 1 0.13 0.5 0.36 FGD Selenium 1.1 5 0.49 2 0.31 FGD Thallium 0.07 0.2 0.04 0.2 0.23

Summary of Method Detection Limits and Minimum Levels in Reagent Water (in μg/L) Matrix Analyte Maximum MDL Maximum ML Pooled MDL Pooled ML

RW Arsenic 0.07 0.2 0.04 0.2 RW Cadmium 0.02 0.1 0.01 0.05 RW Chromium 0.05 0.2 0.03 0.1 RW Lead 0.13 0.5 0.05 0.2 RW Selenium 0.8 2 0.32 1 RW Thallium 0.02 0.05 0.01 0.05Collision Cell MDL Study Results 5 10/18/2012 CSC Recommendations

As noted at the outset, the primary goals of this study were to:

 Obtain MDL data, from at least three laboratories, that reflect the capabilities of the draft EAD ICP/MS collision cell procedure in FGD wastewaters, and

 Use the MDL data to derive an ML for each targ et analyte to support EAD’s efforts to regulate discharges from FGD systems.

Both of these primary goals were achieved.

CSC recommends that EAD use the maximum MDL a nd maximum ML values for the FGD matrix to support the regulatory effort. The maximum values ar e the “worst-case” results from the study, and the other laboratories in the study were able to achieve better sensitivity. The data from this study illustrates that all of the laboratories could achieve MDL valu es at least that low, and the maximum ML values represent the corresponding quantitation limits from the st udy. For arsenic and selenium, the metals of greatest concern to EAD, those maximum values are:

Analyte Maximum MDL (μg/L) Maximum ML (μg/L) Arsenic 0.52 2 Selenium 1.1 5

However, EAD’s secondary goals for this study and the related method performance study being conducted separately by TestAmerica include gathering data that may be used to revise and improve the collision cell procedure itself. Such revisions are likely to include adding example performance data to the tables at the end of the procedure document; su ch performance data may be used by laboratories and others in evaluating the utility of the pr ocedure for various aqueous matrix types.

Given those secondary goals, CSC recommends that EAD include the pooled MDL and pooled ML values for both the FGD and reagent water matrices in the revised procedure, along with the maximum MDL and maximum ML values for the FGD matrix.

By their nature, the pooled limits are somewhat like an average of what was observed in the study. Some laboratories had MDLs above the pooled value and some laboratories had MDLs below the pooled value. Results from laboratories with ICP/MS collision cell e xperience using the procedure in the future would be expected to follow the same pattern. Their in -house MDLs might be above or below the pooled values. However, as long as the MDLs were adequate to support whatever decision was to be made by using the procedure, that laboratory’s performance of the method would be considered acceptable.

The pooled MDL and ML values provide a more ac curate estimate of method sensitivity than the maximum values. Supporting text in the procedure and the tables can explain that the pooled values are indicative of the MDLs and MLs that may be achieve d using the procedure, based on a study involving four laboratories. The text would further clarify that the example limits are not requirements that a given laboratory must meet, or that the example limits are to be used as QC limits.

References

1. Draft FGD ICP/MS Collision Cell Procedure for Tra ce Element Analysis in Fl ue Gas Desulfurization Wastewaters, June 2012. 2. Study Plan for Developing Method Detection Limits and Minimum Levels of Quantitation for Selected Analytes Using EAD’s Draft Collision Cell ICP/MS Procedure , July 24, 2012. 3. Federal Register
, Guidelines Establishing Test Procedures for the Analysis of Pollutants; Measurement of Mercury in Water (EPA Method 1631, Revision B); Final Rule, 64 FR 30417, June 8, 1999.