## 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, V A 22304

Prepared under

EPA Scientific and Technical Support Contract EP

- C

- 12

- 008



## January 1 6 , 201 3Collision Cell MDL Study Results i 1/1 6 /201 3 

## Table of Contents

Background

................................ ................................ ................................ ................................ ................... 1 Page

Study Implementation

................................ ................................ ................................ ................................ ... 1

Derivation of Detection and Quantitation Limits

................................ ................................ .......................... 2

Pooled MDLs

................................ ................................ ................................ ................................ ............ 3

Pooled MLs

................................ ................................ ................................ ................................ ............... 4

Summary of Study Results

................................ ................................ ................................ ............................ 4

Synthetic FGD Matrix

................................ ................................ ................................ ............................... 4

Reagent Wate r

................................ ................................ ................................ ................................ ........... 4

CSC Recommendations

................................ ................................ ................................ ................................ 5

References

................................ ................................ ................................ ................................ ..................... 5Collision Cell MDL Study Results 1 1/1 6 /201 3 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) Engineering and Analysis Division (EAD), within the Office of Water (OW) has d eveloped a draft procedure for the use of a collision 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 electric generating facilities (Reference 1) . The collision cell accessory has the potential to reduce interferences 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 target analytes .

The focus of the present study wa s to characterize method detection limits (MDLs) and minimum levels (ML s ) 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 we re arsenic, cadmium, chromium, lead, selenium and thallium.

The p rimary goals of this study we re 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 a n ML for each target analyte to supp ort EAD’s efforts to regulate discharges from FGD systems.

Secondary goals we re 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 a ssist in designing and implementing 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 three qualified laboratories, and pro viding study coordination and implementation support. D etails of the study are described in a formal study plan reviewed and approved by EAD (Reference 2 ).

CSC issued purchase orders to three laboratories (two commercial and one utility) to perform MDL

s tudies 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

. After completion of the MDL studies by those four laboratories, CSC and EAD worked with the commerci al laboratory that developed the collision cell procedure for EAD t o obtain an additional set of MDL data in the FGD matrix.

The f ive laboratories were:

**•** Agriculture and Priority Pollutants Laboratories, Inc. (APPL)

- commercial

**•** Hampton Roads Sanitation D istrict (HRSD)

- utility

**•** Southwest Research Institute (SwRI)

- com m ercial

**•** Perkin Elmer (PE)

- instrument vendor

**•** TestAmerica Laboratories

- Denver

- commercial, and developer of the draft procedureCollision Cell MDL Study Results 2 1/1 6 /201 3 CSC provided each of the f ive 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 dates to establish due dates for the study results.

This synthetic matrix was prepared at twice the nominal 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 participati ng in the MDL study diluted this solution by a factor o f

two to create the reference matrix for its FGD MDL study aliquots.

The first four laborator ies provided their own reagent water for use as the clean reference matrix for their

MDL study aliquots. The fifth laboratory was not tasked with performing an MDL study in reagent

water ; this laboratory only performed an MDL study in the FGD matrix.

CSC and EAD held a kick

- off conference call with the first four laboratories on August 28, 2012. CSC

and E AD responded to several rounds of follow

- up questions after the call. Answer s to all questions from laboratory participants were routed to all laboratories via email as quickly as practical, in order to keep

the study on schedule. CSC also worked with th e standards vendor and all of the laboratories to refine the available information on the background levels of some of the target analytes that were found in the synthetic matrix, so that each laboratory could adjust the concentrations of these analytes sp iked into the MDL study aliquots. CSC and EAD held a conference call with the fifth laboratory on November 3, 2012, to discuss their participation and share the information about the background levels in the synthetic FGD matrix that had been provided to the other four laboratories earlier.

As data were delivered to CSC, the results were reviewed in two stages. The first stage was to review each laboratory’s electronic data deliverable (an Excel file) with the results for each target analyte in each

matr ix. 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 closer examination of the raw data and QC results supporting the MDL sample results. The results from 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 deve lopment, some deviations from the draft procedure’s QC limits were anticipated. Examples include the QC limits for the internal standards employed in the procedure. The draft QC limits for samples specified internal standard responses of 60

- 125% of the response s in the

calibration blank , and some responses were above and below those limits

. No gross deviations occurred,

and a ny minor deviations were noted, but were not a priori grounds for exclusion of the results from the study data set. The data fro m the MDL study samples may be used by EAD to refine the QC specifications for the final procedure at a later date.

Th e remainder of this document describes the results of the study, including CSC’s derivation of pooled

MDLs and MLs for ICP/MS collision c ell analyses of the synthetic FGD matrix and reagent water using

the results from all the laboratories. CSC’s recommendations for the uses of the results are provided at

the end of the document.

Derivation of Detection and Quantitation Limits

CSC combin ed the data from all the 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

.Collision Cell MDL Study Results 3 1/1 6 /201 3 The maximum MDL was simply the highest MDL value for the analyte reported by any of the five laboratories in the study. CSC rounded the maximum MDLs to two significant figures (i.e., two decimal places for values less than 1, and one decimal place for val ues 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 negativ e integer. This rounding approach is described in EAD’s formal definition

of the ML (Reference 3) and is designed to facilitate preparation of calibration standards at practical

concentrations.

As noted above, all five laboratories provided MDL data for the FGD matrix, and the first four

laboratories were tasked to provide MDL data for the reagent water matrix. 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 analyt es was calculated from the aggregated results from all four laboratories. Each laboratory prepared and analyzed seven MDL study aliquots of the synthetic FGD

matrix and seven more aliquots of reagent water . Each laboratory reported the results for each a liquot, 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 � = 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 replicates (in concentration units) for laboratory i, and

m = the number of laboratories (5 f or the FGD matrix and 4 for reagent water )

The pooled MDL was calculated using the formula:

where:

t

m = the 99 th percentile t

- statistic for the total number of MDL replicates combined across all laboratories, minus the number of laboratories. For the FGD matrix, with five laboratories,

t

m = 2.457, and for the reagent water matrix, with four laboratories, t

m = 2.492.

The pooled MDL values were rounded to two significant figure s for the purposes of this report. 1 n ) x x (

s n

1 i 2

i

**−**

**−**

**=** 

# ∑

**=**



### m s m

1 i 2

i

w 

# s **∑**

**=** 

### =

m w pooled 

### t x s MDL **=**Collision Cell MDL Study Results 4 1/1 6 /201 3 Pooled MLs

The pooled ML was derived by multiplying the pooled with in

- lab oratory standard deviation , s w , from the pooled MDL calculation, by 10:

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

Summary of Study Results

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

Synthetic FGD Matrix

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 different version of the synthetic FGD matrix ; these values are included above simply for reference . TestAmerica did not determine the MDL for chromium at that time because of problems with the background concentration of this metal in the FGD matrix used

at that time.

Reagent Water

As part of the overall study design, the first four laboratories also determined MDLs in reagent water. The goal of that effort was to illustrate the capabilities of the collision cell procedure in a clean reference

matrix with no interferences. The tabl e below summarizes the results from those four laboratories. 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. Because the current draft procedure document does not include MDLs determined in reagent water, that column has been omitted. Summary of Method Detection Limits and Minimum Levels in the Synthetic Flue Gas Desulfurizat ion Matrix (in μg/L , 5 labs)

Matrix Analyte Maximum

MDL Maximum

ML Pooled MDL Pooled

ML Current Procedure

MDL

FGD Arsenic 0.80 2 0.35 1 0.61

FGD Cadmium 0.19 0.5 0.08 0.2 0.59

FGD Chromium 0.32 1 0.13 0.5 NA

FGD Lead 0.31 1 0.14 0.5 0.36

FGD Selenium 1.1 5 0.44 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 , 4 labs )

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 0.05 

### 10 x s ML

w pooled 

### =Collision Cell MDL Study Results 5 1/1 6 /201 3 CSC Recommendations

T he primary goals of this study were to o btain MDL data from at least three laboratories that reflect the capabilities of the draft EAD ICP/MS collision cell procedure in FGD wastewaters, and u se th os e MDL data to derive an ML for each target analyte

.

CSC calculated b oth pooled and maximum values for the MDLs and MLs for the target analytes. The pooled MDL and ML values provide a more accurate estimate of method sensitivity than the maximum

values. By their very nature, the pooled limits are somewhat like an average of what was observed in the study. Some laboratories in this MDL study achieved MDLs above the pooled value and some

laboratories achieved MDLs below the pooled value. Results from laboratories with ICP/MS collision cell experience using the procedure in the future would be ex pected to follow the same pattern ; some laboratories with some laboratories achieving MDLs above the pooled values and others below the pooled

values.

For the purpose of developing effluent limitations guidelines and standards for discharges of FGD

wastew ater, CSC recommends that EAD use the maximum MDL and maximum ML values for the FGD

matrix. The maximum values are the “worst

- case” results for each of the target analytes from the MDL study, meaning that the other laboratories in the study were able to a chieve better sensitivity. The data from this study illustrates that all of the laboratories in this study (which were all identified as well

operated laboratories with experienced staff and operating the appropriate analytical instrumentation)

could achi eve MDL values at least that low, and the maximum ML values represent the corresponding quantitation limits from the study.

EAD’s secondary goals for this MDL 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. To address these 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 pr ocedure, along with the maximum MDL and maximum ML values for the FGD matrix. Supporting text in the procedure and the tables can explain that the pooled values are indicative of the MDLs and MLs that may be achieved using the procedure, based on a study i nvolving five laboratories.

References

1. Draft FGD ICP/MS Collision Cell Procedure for Trace Element Analysis in Flue Gas Desulfurization
Wastewaters, June 2012.

2. Study Plan for Developing Method Detection Limits and Minimum Levels of Quantitation fo r 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.