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 / Approximate level(mg/kg)
As / 50
Cd / 2
Cr / 5
Pb / 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 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
Event / Time / Responsible PartyPreparation of sample / June to August 2006 / HKGL
Homogeneity study / August 2006 / HKGL
Submission of proposal to APLAC PT Committee for approval / September 2006 / 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 HKGL & APLAC Proficiency Committee / Apr 2007 / HKGL/HKAS
Distribution of final report / May 2007 / HKAS
7. 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
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 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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