GL/2006/PT-1
Proficiency Testing Programme Proposal
Determination of Heavy Metals in Seawater Shrimp
1.
Nature and purpose of the programme:
Heavy metals are contaminants that may be present in food due to contamination from the
environment, industrial activities or food processing. Excess intake of these metals from food
could cause adverse health effect and hence their respective maximum levels in foodstuffs
have been set by national health authorities. As such, heavy metals contents in foods are being
analysed routinely by testing laboratories worldwide. The main purpose of this proficiency
testing programme is to evaluate the performance of laboratories that provide such testing.
This proficiency testing programme proposed will be organised by the Government
Laboratory (HKGL) with Hong Kong Accreditation Service (HKAS) as the collaborator under
the auspices of Asia-Pacific Laboratory Accreditation Cooperation (APLAC).
2.
Procedure for selection of programme participants, or criteria to be met before
participation is allowed:
APLAC members as well as non APLAC members (i.e. EA and IAAC members, and
non-affiliated accreditation bodies) will be invited to participate in this programme.
Invitations will be sent to all APLAC members and other accreditation bodies when this
proposal is approved by the APLAC Proficiency Testing Committee.
3.
Name and address of the collaborators involved in the provision of the programme
HKAS is responsible for inviting participants, and dispatching samples, result sheets and
reports to participating accreditation bodies. HKGL prepares the samples, performs
homogeneity and stability tests, assigns confidential code numbers, collects the test results
from participating laboratories, conducts statistical analysis of data and prepares the interim
and final reports.
4.
The number and identity of expected participants in the programme
Participating accreditation bodies will be asked to nominate laboratories to participate and
indicate whether the nominated laboratories are accredited for the test method used or not.
Preference will be given to laboratories that are accredited for the test. A restriction on the
number of participating laboratories from each accreditation body may need to be imposed.
The number of laboratories will be limited to 100.
5.
Sample
Sample Selection and Preliminary Processing:
About 10 kg of shrimp samples would be purchased from local market. After washing with
water to remove foreign matters and dirt, the samples would be freeze dried. The dried shrimp
samples were then powdered, sieved and thoroughly mixed. About 10 g of powder would be
packed into clean and air-tight amber bottles, then disinfected by -irradiation at a dose of
about 10 kGy.
Heavy metal
As
Cd
Cr
Pb
Approximate level
(mg/kg)
50
2
5
0.1
Homogeneity Test and Stability Monitoring
Not less than ten samples will be taken randomly from the prepared powder sample and
analyzed using validated methodology in duplicate for homogeneity tests by HKGL. The
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sampling and analytical procedures will be in accordance with the recommendation stipulated
in APLAC PT002 Testing Interlaboratory Comparisons and guidelines in ILAC G13:2000.
Regularly, at least three samples will be chosen randomly (on a monthly basis) and analyzed
in triplicate for monitoring the stability of the analytes until the deadline for return of test
results from participants.
Testing Methodology
Each participating laboratory will be given one sample containing about 10 g of dried shrimp
powder. The laboratories will be required to determine the quantity of total arsenic, cadmium,
chromium and lead in the samples according to their accredited methods, validated methods
and/or in-house methods. Analysis should be conducted in triplicate and test results and other
details should be reported in the result sheets provided.
6.
Information supplied to the participants and the time schedule for the various phases of
the programme
Invitation of Participants
HKAS is responsible for inviting the participants in September 2006. Deadline for returning
the nomination form to HKAS is in November 2006.
Sample preparation
The sample containing arsenic, cadmium, chromium and lead at appropriate levels will be
prepared by the HKGL around June to August 2006.
Homogeneity study and Stability monitoring
Homogeneity study will commence around August 2006 after the completion of sample
preparation. Stability study will commence around November 2006 and extend to March
2007, the deadline for submission of test data from the participating laboratories.
Dispatch of Samples and Instructions to Accreditation Bodies and Laboratories
Test samples together with sample receipt form, instructions to accreditation bodies and
laboratories will be dispatched to participating accreditation bodies around November 2006.
Upon receipt of the sample pack from HKAS, a participating accreditation body should check
the samples for damage during transportation and then complete and return the receipt
acknowledgement form to HKAS. The samples, instructions and results sheets should be
distributed to the participating laboratories as soon as possible. Laboratories have about four
weeks to analyze the samples and are required to report the test results as well as their
measurement uncertainties and accreditation status of the test method(s).
Collection of results
Participating laboratories should submit the result sheets to HKGL via email by the end of
January 2007.
Statistical Analysis of Data
Each laboratory shall report three sets of test data for statistics data treatment. The
performance of each laboratory can then be assessed by calculating the z-score which will be
presented in tabular form as well as histograms. The analysis will be conducted once all data
have been collected in January 2007.
Reporting
HKGL shall prepare an interim report before the end of February 2007. Draft final report will
then be prepared and be submitted to APLAC Proficiency Committee for review before 31
March 2007. After obtaining approval from the Committee, copies of the final report will be
forwarded to participating accreditation bodies for distribution to the participating
laboratories.
Proposed schedule
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7.
Event
Time
Responsible Party
Preparation of sample
June to August 2006
HKGL
Homogeneity study
August 2006
HKGL
Submission of proposal to APLAC PT
September 2006
Committee for approval
HKAS
Invitation of participants
September 2006
HKAS
Dispatch of samples
November 2006
HKAS
Stability study
Nov 2006– Mar 2007
HKGL
Collection of results
Jan 2007
HKGL
Statistical analysis of data
Feb 2007
HKGL
Interim report
Feb 2007
HKGL
Preparation of draft report
Mar 2007
HKGL
Approval of draft report by PTAB of
Apr 2007
HKGL & APLAC Proficiency Committee
HKGL/HKAS
Distribution of final report
HKAS
May 2007
The proposed initial and target dates of the programme, including the dates on which
testing will be carried out by participants
Initial date:
September 2006
Target date:
May 2007
Dates on which testing is to be carried out by participants:
November – December 2006
8.
Information on methods or procedures which participants may need to use to perform
the tests or measurement
Participating laboratories are free to use their accredited methods, validated methods or
in-house methods whenever appropriate. Participating laboratories are requested to provide an
outline of the methods/procedures that being used in the test.
9.
An outline of the statistical analysis to be used, including the determination of assigned
values
Each laboratory shall report three sets of test data. Robust statistics will be used to eliminate
the effect of outliers and calculate the consensus mean and standard deviation as stipulated in
ISO 13528.
10.
A description of the data or information to be returned to participants
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The performance of each laboratory is assessed by using z-score which will be presented in
tabular form as well as histograms. The HKGL shall prepare an interim report once the
preliminary data analysis is completed. After obtaining comments from the participating
laboratories and/or accreditation bodies, a draft final report will be prepared and be submitted
to the APLAC PT Committee for review. Once the approval from the Committee is obtained,
electronic copy of the final report will be forwarded to participating accreditation bodies for
distribution to the participating laboratories.
11.
The basis of performance evaluation techniques
The performance of each laboratory is assessed by calculating the z-score which will be
presented in tabular form as well as histograms.
The z-score is commonly interpreted as follows:
(a) z  2
Satisfactory
(b)
2 < z < 3
Questionable
(c)
z  3
Unsatisfactory
Laboratories having a |z| score larger than 3 shall investigate their results.
Laboratories having a z-score in the range 2 < z < 3 are encouraged to review their results.
12.
A description of the extent to which test results, and the conclusion that will be based on
the outcome of the programme are to be made public
The information on the identities and results of the laboratories will be kept confidential to the
accreditation bodies and the organizers. Each laboratory will be assigned with a unique
identification code. This unique code will be used in the report. The identity of the
participating laboratories will not be disclosed. If the laboratories submit their results through
their accreditation bodies, their results may be disclosed to and released through their
accreditation bodies.
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