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Listen to this siteWednesday 2 August 2006
This research project investigates the key factors that lead to poor performance in the determination of the chloride content of food and to produce recommendations for achieving good analytical performance for such measurements.
Study Duration : October 2000 to October 2002.
Contractor : Rhondda Cynon Taff County Borough Council's laboratory [Analytical Services (South Wales)]. Following premature closure of that laboratory before completion of the project the report was prepared by Expert Services (South Wales).
The determination of chloride in food is, in theory, relatively easy, with the existence of several methods for extracting chloride from food as well as for analysis of chloride in solution. The overall performance of laboratories in the FAPAS® series requiring the determination of salt or chloride has historically been poor, with an unacceptable proportion of laboratories failing to achieve an acceptable z-score.
Having identified a particularly low proportion of laboratories achieving satisfactory performance in Series I Round 17, FAPAS® sought additional information regarding methodology. However, its conclusions were not robust as the FAPAS® Advisory Committee considered that the sample that had been circulated to laboratories for methodology testing, a fish paste with no added salt, was inappropriate.
The proportion of laboratories achieving satisfactory performance in Series X round 16 was also particularly low, with some visual indication of possible bimodality to the data. Investigation by FAPAS® confirmed bimodality. Since the FAPAS® report presented limited information as to the extraction and quantification methods employed, no conclusive reason has been identified for this problem.
A number of possibilities exist for poor performance in the determination of chloride content, including heterogeneous samples; difficulties in extracting the chloride from the sample; difficulties with the actual determination of the chloride and difficulties with expression of results.
This project set out to investigate FAPAS® performance and analytical methodology to try to identify the probable cause or causes of poor performance and to give guidance as to how performance can be improved.
A detailed review of participants in FAPAS® Series I Round 26 and Series X Round 16 was conducted, with the co-operation of the FAPAS® Secretariat, in order to obtain details of the methods used for extraction and quantification of chloride. These data were analysed to find patterns or relationships that may relate to the variability in results reported in the original FAPAS® series.
Following the review a programme of experimental work was conducted to test hypotheses for poor results arising from the response to the survey.
A report was prepared presenting the conclusions of the research and making recommendations for achieving good analytical performance for chloride.
This project set out to investigate FAPAS
performance and analytical methodology to try to identify the probable cause or causes of poor performance and to give guidance as to how performance can be improved.
The project findings showed that:
In order to achieve good analytical performance for chloride the following recommendations are made:
The above recommendations are in addition to normal good practice, such as the correct use of properly calibrated volumetric ware, the use of accurately standardised volumetric and standard solutions traceable to national standards, the validation of methods using certified reference materials of a similar matrix to samples, and, in particular, care to report results in the form expected or required by the end user (for example, not as sodium chloride when chloride is required).
In order for proficiency test schemes to assess the performance of participants accurately, the following additional recommendations are made:
Final report is available from the FSA Library and Information centre. To obtain a copy, please contact the Enquiry Desk, Dr. Elsie Widdowson Library and Information Services, Food Standards Agency (020 7276 8181/8182 or at library&info@foodstandards.gsi.gov.uk ).
Contact
: For any enquiries concerning this research project, please contact the relevant programme contact or email
science@foodstandards.gsi.gov.uk
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