Final Report

Final Report
Report No.: 4
Program No.: WAT-CL-0001
Program Name: Residual chlorine in water
Date: March 12, 2013
Acknowledgement
PQP should acknowledge the technical assistance provided by East Azerbaijan Water &
Wastewater Laboratory for this program which was included technical advice in different
stages of this program including design, execution and evaluation of participants results.
PQP Proficiency testing
Apt. 9- 3rd floor- No. 20- 6th St.- Ghaem Magham Farahani St., Tehran- Iran, Postal Code:
1586844137
Tel.: +98(21)88546426-7, Fax: +98(21)88546443, Email: info@qualitypioneers.ir

Report No.: 4
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Report No.: 4
Table of Contents
1. Introduction ....................................................................................................................... 5
2- Test Materials ....................................................................................................................... 5
2-1- Preparation of samples ................................................................................................. 5
2-2- Samples homogeneity .................................................................................................. 5
2-3- Samples Stability .......................................................................................................... 5
2-4- Distribution .................................................................................................................... 5
3- Statistical design of the program ....................................................................................... 5
4- Features of the program ...................................................................................................... 6
4-1- Number of Participants ................................................................................................. 6
4-2- Supplied samples .......................................................................................................... 6
4-3- Parameters .................................................................................................................... 6
4-4- Participants instruction ................................................................................................ 6
4-5- Confidentiality ............................................................................................................... 6
4-6- Appeals .......................................................................................................................... 6
5- Summary of results ............................................................................................................. 7
6- Statistical evaluation of results .......................................................................................... 7
6-1- General........................................................................................................................... 7
6-2- Calculation of assigned value ...................................................................................... 7
6-3- Standard deviation for proficiency assessment (SDPA) ............................................ 7
6-4- Measurement uncertainty of the assigned value (u x ) ................................................. 7
6-5- Purpose of performance scoring ................................................................................. 7
6-6- z-scores ......................................................................................................................... 8
7- PQP and technical advisor comments ............................................................................... 8
7-1- Metrological Traceability of Assigned Values ............................................................. 8
7-2- Methodology summary ................................................................................................. 8
7-3- Overall performance ..................................................................................................... 9
8- References ........................................................................................................................... 9
Appendix A- Results and data analysis .................................................................................10
Appendix B- Homogeneity and stability testing ...................................................................14
B-1- Homogeneity testing ...................................................................................................14
B-2- Stability testing ............................................................................................................15
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Report No.: 4
Appendix C- Documents .....................................................................................................16
C-1- Instructions to participants .........................................................................................16
C-2- Results Sheet ...............................................................................................................17
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Report No.: 4
1. Introduction
This report is a summary of the results of participating laboratories in proficiency testing
program residual chlorine in water round no. 1. The aim of this program is to enable
laboratories to monitor and improve the quality of their routine analytical measurements, for the
benefit of their customers. It also enables laboratories to demonstrate to customers, regulators
and accreditation bodies the validity of their analytical measurements.
Participation in PQP proficiency testing provides independent evidence of laboratory
performance for both laboratory management and customers.
This proficiency testing was performed by Pasargad Quality Pioneers (PQP) in February, 2013.
The program coordinator was Ms. Bahar Hosseinzadeh. This report was authorized by Mr.
Hamidreza Dehnad, PQP proficiency testing technical manager on March 12, 2013
Signature:
2- Test Materials
2-1- Preparation of samples
The test material was prepared by ERA Company. The samples distributed to the participants
were Certified Reference Materials with ERA code 696 Lot No. S193-696.
2-2- Samples homogeneity
Certified reference materials with the same lot number were supplied to the participants. ERA is
a reference material producer and has been accredited by A2LA according to ISO/IEC Guide
34: 2009, Certificate no. 1539.03 so it can be concluded that the samples are considered to be
adequately homogenous therefore any results later identified as outliers could not be attributed
to sample variability.
2-3- Samples Stability
Certified reference materials with the same lot number were supplied to the participants. ERA is
a reference material producer and has been accredited by A2LA according to ISO/IEC Guide
34: 2009, Certificate no. 1539.03. In the material certificate of analysis the expiry date is defined
as July 31, 2016 so it can be concluded that the samples are considered to be adequately
stable therefore any results later identified as outliers could not be attributed to sample
instability.
2-4- Distribution
The dispatch date was February 12, 2013. Each laboratory received 1 x 2mL sample together
with a covering letter, participants instruction and a result sheet.
3- Statistical design of the program
Participating laboratories were each supplied 1 x 2mL sample labeled “Sample 1 (WAT-CL-
0001)”. One result was reported for all tests. For each statistically analysed test, robust
statistical procedures were used to generate the z-scores and summary statistics for each test.
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The assigned value (X) and the standard deviation of proficiency assessment ( ) has been
determined according to the criteria given in clause 6 of this report.
4- Features of the program
4-1- Number of Participants
A total of 6 laboratories received samples. A total of 6 laboratories returned results for inclusion
in this report.
4-2- Supplied samples
Participating laboratories were each supplied 1 x 2mL sample labeled “Sample 1 (WAT-CL-
0001)”.
4-3- Parameters
The following determinations were to be performed on the samples:
Free residual chlorine
Total residual chlorine
4-4- Participants instruction
Laboratories were requested to perform the tests according to the “Instructions to Participants"
and to record their results on the accompanying "Results Sheet”, all of which were distributed to
participants with the samples (Appendix C).
The methods used by each participant are summarized in Appendix A.
4-5- Confidentiality
Each laboratory was randomly allocated a unique code number for the program to enable
confidentiality of results. Reference to each laboratory in this report is made by its code number.
National Water and Wastewater Engineering Company as a regulatory authority has requested
PQP to directly provide the proficiency testing results to them so the performance of the affected
participants i.e. laboratories of water and wastewater companies in this program has also been
reported to National Water and Wastewater Engineering Company.
4-6- Appeals
The participants are able to appeal against the evaluation of their performance in this program
through the program coordinator. In one week period after receiving the appeal, PQP sends a
letter to the participant to acknowledge the receipt of the appeal and ensure the participant that
their appeal will be handled in a timely manner.
The participant will be notified of the results after the actions are confirmed with a response
letter.
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Report No.: 4
5- Summary of results
Results for this proficiency test are summarized as follows:
Test
Free residual
chlorine
Total residual
chlorine
No. of
Results
Assigned
Value
(mg/L)
SDPA 1
( )
Expanded
uncertainty of
the assigned
value (U x )
No. of
satisfactory
scores
( )
Satisfactory
(%)
6 0.78 0.085 5.80% 3 50.0
1 0.78 0.061 5.80% 1 100.0
6- Statistical evaluation of results
6-1- General
The object of the statistical procedure employed is to obtain a simple and transparent result,
which the participant and other interested parties can readily appreciate. The procedure follows
that recommended in ISO 13528: 2005, Statistical methods for use in proficiency testing by
interlaboratory comparisons.
6-2- Calculation of assigned value
The assigned value is the value selected as being the best estimate of the ‘true value’ for the
parameter under test.
Since the material used in this proficiency test is a certified reference material (CRM), its
certified reference value is used as the assigned value X.
6-3- Standard deviation for proficiency assessment (SDPA)
The standard deviation used to assess the proficiency of participants in this round of scheme
is calculated using fixed acceptance criteria specified in US NELAC 2 proficiency testing
requirements.
6-4- Measurement uncertainty of the assigned value (u x )
The uncertainty of the assigned value is derived from the information on uncertainty provided on
the certificate on analysis.
6-5- Purpose of performance scoring
Once the assigned value for the parameters under test has been established, participant
laboratories are assessed on the difference between their result and the assigned value, with
this difference being represented by a performance score, normally the z-score. The
advantages of a z-score are:
- Results can be expressed in a form that is relatively easy to interpret and understand
1 Standard Deviation of Proficiency Assessment
2 National Environmental Laboratory Accreditation Conference
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Report No.: 4
- Results can be summarized in graphical or tabular form to depict overall performance
- A performance score allows participants to directly compare their own result with others
- If consistent statistical values are applied, a performance score enables participants to
monitor and trend their own performance over time.
6-6- z-scores
Z-score of the participants is calculated using the following formula:
In which:
x: participant result
µ: assigned value
SDPA: Standard deviation for proficiency assessment
For the purposes of performance assessment for a single round, z scores are interpreted as
follows:
Z-Score
Interpretation
Satisfactory Result
Questionable result
Unsatisfactory result
7- PQP and technical advisor comments
7-1- Metrological Traceability of Assigned Values
The assigned value is a certified value reported in the material COA 3 (ERA Catalog No. 696).
ERA standards or their stock solutions are analysed against the applicable NIST 4 SRM 5 listed in
the certificate so it can be assumed that the assigned value is metrologically traceable. All
gravimetric and volumetric measurements related to its manufacture are traceable to NIST
through an unbroken chain of comparisons.
7-2- Methodology summary
Participants’ methods are tabulated according to the information supplied by the participants.
Free residual chlorine
Method
Number of
results
% of total Sat. (%)
Colorimetry 5 83.3 60
Titration 1 16.7 0
3 Certificate of Analysis
4 National Institute of Standards and Technology
5 Standard Reference Materials
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Total residual chlorine
Method
Number of
results
% of total Sat. (%)
Colorimetry 1 100.0 100
7-3- Overall performance
Colorimetry method is a suitable method for analyzing residual chlorine. Calibration of the
instrument before analysis is very important in this method.
8- References
1- ISO/IEC 17025: 2005, general requirements for the competence of testing and
calibration laboratories.
2- ISO/IEC 17043: 2010, Conformity assessment — General requirements for proficiency
testing
3- ISO 13528: 2005, Statistical methods for use in proficiency testing by interlaboratory
comparisons
4- PR-14- rev. 00, PQP Performance evaluation Procedure
5- PR-15- rev. 00, PQP Homogeneity and stability Procedure
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Frequency
Report No.: 4
Appendix A- Results and data analysis
Free residual chlorine
Lab. Code Method Result (mg/L) Z-score
Data Statistics
4 Colorimetry 0.60 -2.12
13 Titration 0.50 -3.29
14 Colorimetry 0.49 -3.41
33 Colorimetry 0.78 0.00
34 Colorimetry 0.90 1.41
35 Colorimetry 0.63 -1.76
Number of results 6
Number of excluded results* 0
Assigned value 0.78
Uncertainty of assigned 0.02
value
SDPA 0.085
* The influence of outliers on summary statistics has been minimized by the use of robust
statistical methods but obvious blunders, such as those with incorrect units, decimal point
errors, and results for a different proficiency test item are removed from the data set and treated
separately. These results are not the subject to outlier tests or robust statistical methods.
2.5
Histogram of participants Z-scores for Free
Residual Chlorine
2
1.5
1
0.5
0
-4 -3 -2 -1 0 1 2 More
Z-scores
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Z-score
Report No.: 4
4
3
2
1
0
-1
14 13 4 35 33 34
-2
-3
-4
Lab No.
Methodology Summary
Method
Number of
results
% of total Sat. (%)
Colorimetry 5 83.3 60
Titration 1 16.7 0
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Frequency
Report No.: 4
Total residual chlorine
Lab. Code Method Result (mg/L) Z-score
34 Colorimetry 0.9 1.98
Data Statistics
Number of results 1
Number of excluded 0
results*
Assigned value 0.78
Uncertainty of assigned 0.02
value
SDPA 0.061
* The influence of outliers on summary statistics has been minimized by the use of robust
statistical methods but obvious blunders, such as those with incorrect units, decimal point
errors, and results for a different proficiency test item are removed from the data set and treated
separately. These results are not the subject to outlier tests or robust statistical methods.
1.2
Histogram of participants Z-scores for Total
Residual Chlorine
1
0.8
0.6
0.4
0.2
0
1 2 More
Z-scores
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Z-score
Report No.: 4
4
3
2
1
0
-1
34
-2
-3
-4
Lab No.
Methodology Summary
Method
Number of
results
% of total Sat. (%)
Colorimetry 1 100.0 100
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Appendix B- Homogeneity and stability testing
B-1- Homogeneity testing
Certified reference materials with the same lot number were supplied to the participants. ERA is
a reference material producer and has been accredited by A2LA according to ISO/IEC Guide
34: 2009, Certificate no. 1539.03 so it can be concluded that the samples are considered to be
adequately homogenous therefore any results later identified as outliers could not be attributed
to sample variability.
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B-2- Stability testing
Certified reference materials with the same lot number were supplied to the participants. ERA is
a reference material producer and has been accredited by A2LA according to ISO/IEC Guide
34: 2009, Certificate no. 1539.03. In the material certificate of analysis the expiry date is defined
as July 31, 2016 so it can be concluded that the samples are considered to be adequately
stable therefore any results later identified as outliers could not be attributed to sample
instability.
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Appendix C- Documents
C-1- Instructions to participants
Sample WAT-CL-0001 Preparation Instruction
Materials Supplied:
WAT-CL-0001
- One 2 mL screw-cap vial labeled as
Sample 1 (WAT-CL-0001)
Sample 1 (WAT-CL-0001)
-
Preparation:
1- Add 100-200 mL of organic/chlorine-free
water to a clean 1000 mL class A volumetric
flask.
2- Carefully snap the top off of the Residual
Chlorine ampule.
3- Using a clean, dry, class A pipet,
volumetrically pipet 1.0 mL of the concentrate
into the 1000 mL volumetric flask.
4- Dilute the flask to final volume with
organic/chlorine-free water.
5- Cap the flask and mix well.
6- Immediately analyze the diluted sample by
your normal procedures.
7- Report your results as mg/L for the diluted
sample
1.0 mL
mg/L
A
A
100-200 mL
1000 mL
1000 mL
Remarks:
1- The result should be reported in the results
sheet form and the test method should be
specified.
2- The laboratory should calculate and report
the expanded measurement uncertainty with
95% confidence interval (coverage factor
k=2). It should be noted that the reported
value of uncertainty won’t be used for
performance evaluation of your laboratory.
3- The sample can be stored at room
temperature.
4- This concentrate is not preserved.
k=2
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Report No.: 4
C-2- Results Sheet
Residual chlorine in water proficiency testing program- Round 1
WAT-CL-0001 :(Program No.)
(Laboratory Code)
Parameter Result Unit
(±MU)
Method
Free Residual
Chlorine
mg/L
Total Residual
Chlorine
mg/L
(Signature)
(Date)
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