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Pilot Study of Routine Monitoring of Sampling Precision in the Sampling of Bulk Foods


A number of analyte/matrices combinations were used in developing the concept of routine quality control of sampling (QCSAM). Namely:
Canned tuna - mercury, zinc.
Coleslaw - nitrogen (Kjeldahl method), sodium.
Bottled water - magnesium, nitrate (TON), additional data on calcium, sodium and potassium.
Animal feed - nitrogen (Dumas method), manganese, additional data on phosphorus, calcium, sodium, aluminium, copper, iron, magnesium, zinc and sulphur.
Butter - moisture, calcium, magnesium, phosphorus.

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Sampling is the most important initial stage in any analytical process, but the concept of sampling variability is often neglected. In order to arrive at a correct decision on compliance against quality specifications, control authorities need information on the total variance associated with any results gained. The total variance is made up of two major contributions: one from sampling and one from the measurement of the samples. Any result of a measurement is accompanied by a degree of uncertainty, and it is incumbent upon the analyst to estimate the magnitude of this uncertainty and ensure that it is appropriately small. Laboratories can check that they meet 'fit-for-purpose' requirements by implementing a program of quality assurance measures. Laboratories routinely employ ongoing quality control procedures and record the outcome on quality control charts.

The measures, put in place by a laboratory to monitor uncertainty only conveys part of the story, however. There is another important aspect. If the laboratory sample was not representative of a bulk consignment of goods, even the best analytical result could be misleading. Often the laboratory has no control over this as a third party submits the samples. Ideally then there should be some level of control in enforcement situations where sampling should have been undertaken in accordance with a sampling plan. Even so, there will be variation in the composition of the product throughout a batch and, consequently, variation in the composition of samples collected according to the plan. In order to make a reliable assessment of the quality of a consignment the user needs to know the uncertainty introduced by this sampling variation as well as the measurement uncertainty.
The aim of this research is to develop a proposal for an inexpensive and widely applicable method for assessing uncertainty associated with sampling from bulk foods that would be suitable for use in a quality control style. The project aims to assist in ensuring fitness-for-purpose of food surveillance programs and to provide a basis for long-term assessment of sampling precision. The estimates of sampling precision should allow end users of analytical data to estimate the combined uncertainty of results, a prerequisite to interpreting data correctly.

<p>Find more about this project and other FSA food safety-related projects at the <a href="; target="_blank">Food

Standards Agency Research webpage</a>.

ADAS Consulting Ltd
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