AQA 16-18 Chromium VI in Soil

25 Pages·2017·0.69 MB·English

by  National Measurement Institute

Proficiency Test Report
AQA 16-18
Chromium VI in Soil

March 2017

ACKNOWLEDGMENTS

This study was conducted by the National Measurement Institute (NMI). Support funding was
provided by the Australian Government Department of Industry, Innovation and Science.
I would like to thank the management and staff of the participating laboratories for supporting
the study. It is only through widespread participation that we can provide an effective service
to laboratories.
The assistance of the following NMI staff members in the planning, conduct and reporting of
the study is acknowledged.

Luminita Antin
Dr Andrew Evans

Paul Armishaw
Manager, Chemical Proficiency Testing
P O Box 138
North Ryde 1670
Phone: [phone]
Fax: [phone]
[email protected]
H

Accredited for compliance with ISO/IEC 17043

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AQA 16-18 Chromium VI in Soil
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AQA 16-18 Chromium VI in Soil
TABLE OF CONTENTS
1 SUMMARY 4
2 INTRODUCTION 5
2.1 NMI Proficiency Testing Program 5
2.2 Study Aims 5
2.3 Study Conduct 5
3 STUDY INFORMATION 5
3.1 Selection of Matrix and Analyte 5
3.2 Participation 5
3.3 Test Material Specification 6
3.4 Laboratory Code 6
3.5 Sample Preparation, Analysis and Homogeneity Testing 6
3.6 Stability of Analytes 6
3.7 Sample Storage, Dispatch and Receipt 6
3.8 Instructions to Participants 6
3.9 Interim Report 6
4 PARTICIPANT LABORATORY INFORMATION 7
4.1 Test Method Summaries 7
4.2 Basis of Participants’ Measurement Uncertainty Estimates 7
5 PRESENTATION OF RESULTS AND STATISTICAL ANALYSIS 8
5.1 Results Summary 8
6 TABLES AND FIGURES 10
7 DISCUSSION OF RESULTS 12
7.1 Assigned Value 12
7.2 Measurement Uncertainty Reported by Participants 12
7.3 Analytical Methods for Cr(VI) in Soil 12
7.4 Participants’ Analytical Methods 13
7.5 Problems Identified by Participants 18
8 REFERENCE MATERIALS AND CERTIFIED REFERENCE MATERIALS 20
9 REFERENCES 21
APPENDIX 1 - SAMPLE PREPARATION, ANALYSIS AND HOMOGENEITY TESTING 23

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AQA 16-18 Chromium VI in Soil
1 SUMMARY
This report presents the results of the proficiency test AQA 16-18, Chromium (VI) in soil.
One sample was prepared. Sample S1 was contaminated biosoil: the Cr(VI) in this sample
was incurred.
Twelve laboratories registered to participate and eleven submitted results.
This was the first study conducted by NMI for Cr(VI) in soil and the first for many
participants in which they could check the methods used for Cr(VI) measurements. The study
was a pilot round and no performance assessment was made.
The outcomes of the study were assessed against the aims as follows:
i. assess the variability of measurements of Cr(VI) in soil;
No agreement was found between the reported results for Cr(VI).
ii. evaluate the laboratories methods in the extraction and measurement of Cr(VI) in soil.
Although most participants used the same extraction and measurement technique most of the
produced results were not compatible.

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AQA 16-18 Chromium VI in Soil
2 INTRODUCTION
2.1 NMI Proficiency Testing Program
The National Measurement Institute (NMI) is responsible for Australia’s national
measurement infrastructure providing a wide range of services, including a chemical
proficiency testing program.
Proficiency testing (PT) “is evaluation of participant performance against pre-established
criteria by means of interlaboratory comparison.”1 NMI PT studies target chemical testing in
areas of high public significance such as trade, environment and food safety. NMI offers
studies in:
 inorganic analytes in soil, water, food and pharmaceuticals;
 pesticide residues in fruit and vegetables, soil and water;
 petroleum hydrocarbons in soil and water;
 allergens in food;
 controlled drug assay; and
 folic acid in flour.
AQA 16-18 is the 20th NMI proficiency study of inorganic analytes in soil and the first
involving measurement of Cr(VI).
2.2 Study Aims
The aims of the study were to:
 assess the variability of measurements of Cr(VI) in soil;
 evaluate the laboratories’ methods used in determination of Cr(VI) in soil.
2.3 Study Conduct
The conduct of NMI proficiency tests is described in the NMI Chemical Proficiency Testing
Study Protocol.2 The statistical methods used are described in the NMI Chemical Proficiency
Statistical Manual.3 These documents have been prepared with reference to ISO Standard
170431 and The International Harmonized Protocol for Proficiency Testing of (Chemical)
Analytical Laboratories.4
NMI is accredited by National Association of Testing Authorities, Australia (NATA) to
ISO/IEC 17043 as a provider of proficiency testing schemes.
Participants were asked to use the same extraction method (USEPA3060A) but the choice of
the measurement technique was left to them.
3 STUDY INFORMATION
3.1 Selection of Matrix and Analyte
The test and the test level was selected from those for which an ecological investigation level
is published in the National Environment Protection (Assessment of Site Contamination)
Measure (NEPM) Schedule B(1) Guidelines on the Investigation Levels for Soil and
Groundwater, promulgated by the National Environmental Protection Council (NEPC).5
3.2 Participation
Twelve laboratories participated and eleven submitted results. Laboratory 4 submitted the
result for Cr(VI) after the interim report was issued. This result was still included in the final
report as participants’ performance was not assessed in this study.
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AQA 16-18 Chromium VI in Soil
The timetable of the study was:
Invitation issued: 05 December 2016
Samples dispatched: 13 December 2016
Results due: 20 January 2017
Interim report issued: 01 February 2017
3.3 Test Material Specification
One sample was provided for analysis:
Sample S1 was 15 g of dried biosoil from a water treatment station, submitted to NMI for
Cr(VI) analysis; Cr(VI) in this sample was incurred.
3.4 Laboratory Code
All participant laboratories were assigned a confidential code number.
3.5 Sample Preparation, Analysis and Homogeneity Testing
Three samples were randomly selected from the 20 prepared for a partial homogeneity test.
The same preparation procedure was followed as in previous studies for soil matrix. The test
samples from the previous studies using this procedure were demonstrated to be sufficiently
homogeneous for evaluation of participants’ performance.6
The preparation, analysis and homogeneity testing of the study sample are described in
Appendix 1.
3.6 Stability of Analytes
No stability study was carried out in the present study. The Cr(VI) stability in the sample was
assumed based on exisiting literature.7
3.7 Sample Storage, Dispatch and Receipt
The test samples were stored at ambient temperature prior to dispatch.
The samples were dispatched by courier on 13 December 2017.
A description of the test sample with instructions and a form to confirm the receipt of the test
sample, were sent with the samples.
An Excel spreadsheet for the electronic reporting of results was e-mailed to participants.
3.8 Instructions to Participants
Participants were instructed as follows:
 Quantitatively analyse the samples using the USEPA method 3060A or equivalent
methods.
 The concentration of Cr(VI) in this sample is above 0.5 mg/kg level.
 Report the result for Cr(VI) as you would report to a client.
 Report the expanded measurement uncertainty associated with your analytical result
(eg 5.0 ± 0.5 mg/kg). Report the basis of your uncertainty estimates (i.e. control
charts, proficiency testing).
 Please send us all the requested details regarding the test method.
 Return the completed results sheet by 20 January 2017.
3.9 Interim Report
An interim report was emailed to participants on 01 February 2017.
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AQA 16-18 Chromium VI in Soil
4 PARTICIPANT LABORATORY INFORMATION
4.1 Test Method Summaries
Summaries of the test methods and participants’ comments are transcribed in Table 5.
4.2 Basis of Participants’ Measurement Uncertainty Estimates
Participants were requested to provide information about the basis of their uncertainty
estimates (Table 1).
Table 1 Basis of Uncertainty Estimate
Lab. Information Sources for MU Estimation Guide Document for
Approach to Estimating MU
Code Estimating MU
Precisiona Method Biasa
Top Down - precision and
1 estimates of the method and Control Sample-RM Recoveries of SS NATA Technical Note 33
laboratory bias
Standard deviation of replicate
2 Control Sample-CRM CRM NATA Technical Note 33
analyses multiplied by 2 or 3
Control Sample
4 Duplicate Analysis
Instrument calibration
Standard deviation of replicate
5 Duplicate Analysis Instrument Calibration Eurachem/CITAC Guide
analyses multiplied by 2 or 3
Top Down - precision and
Duplicate Analysis
6 estimates of the method and Instrument Calibration Nordtest Report TR537
Instrument calibration
laboratory bias
Top Down - precision and
Control Sample-RM
7 estimates of the method and NATA Technical Note 33
Instrument calibration
laboratory bias
Top Down - precision and Control Samples
9 estimates of the method and Duplicate Analysis Recoveries of SS Eurachem/CITAC Guide
laboratory bias
Top Down - precision and
10 estimates of the method and Control Sample-RM Recoveries of SS NATA Technical Note 33
laboratory bias
CRM
Top Down - precision and
Laboratory bias from
11 estimates of the method and Control Sample-RM NATA Technical Note 33
PT studies
laboratory bias
Instrument calibration
a RM = Reference Material, CRM = Certified Reference Material, SS = Spiked samples.
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AQA 16-18 Chromium VI in Soil
5 PRESENTATION OF RESULTS AND STATISTICAL ANALYSIS
5.1 Results Summary
Participant results are listed in Table 2 with the resultant summary statistics: robust average,
median, maximum, minimum, robust standard deviation (SD ) and robust coefficient of
rob
variation (CV ). Bar charts of the results are presented in Figure 2.
rob
An example chart with an interpretation guide is shown in Figure 1.

Independent estimates of analyte concentration with
associated uncertainties (coverage factor is 2).

Md = Median (of participants’ results)
H.V. = Value from NMI homogeneity testing
Histogram of distribution of results
R.A. = Robust Average.
around the assigned value
(illustrates participant consensus). Uncertainties R.V. = Reference Value (if applicable).
reported by
participants. S = Spike (if applicable)

Figure 1 Guide to Presentation of Results
5.2 Assigned Value
The assigned value is defined as: ‘the value attributed to a particular property of a proficiency
test item.’1 In this study no assigned value was set for Cr(VI) in soil because the reported
results were too variable.
5.3 Robust Average
The robust averages and associated expanded measurement uncertainties were calculated
using the procedure described in ‘Statistical methods for use in proficiency testing by
interlaboratory comparisons, ISO13528:2015(E)’.8
5.4 Robust Between-Laboratory Coefficient of Variation
The robust between-laboratory coefficient of variation (CV) is a measure of the variability of
participants’ results and was calculated using the procedure described in ISO13528:2015(E).8
5.5 Target Standard Deviation
The target standard deviation (σ) is used in the calculation of z-scores and provides scaling for
laboratory deviation from the assigned value.
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AQA 16-18 Chromium VI in Soil