Food Standards Agency
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This research project aims to compare extraction methods used to measure nitrate residues levels in lettuce and spinach to determine the accuracy of the analytical results.
Study Duration : February 2001–October 2001
Contractor : ADAS Laboratories
It is important that the Food Standards Agency has confidence in the results generated by the UK nitrate monitoring programme, to support negotiations within the European Union and to provide evidence for the UK derogation on nitrate levels in lettuce and spinach. Concerns over the consistency of analytical results obtained when homogeneous sub-samples were sent to a number of laboratories, coupled with rather poor overall FAPAS results for nitrate, led the Agency to commission an investigation of nitrate extraction methods.
This study will be performed by undertaking a literature search of methodology, liaising with laboratories currently participating in the UK nitrate monitoring programme, selection of the most suitable analytical method, in-house validation and ruggedness testing of the method and organisation of a collaborative trial.
This work has led to the following main observations and recommendations.
Laboratories currently involved in the UK nitrate monitoring programme use a variety of extraction techniques. However, all claim they comply with EC method performance criteria requirements.
Current procedures for the receipt of samples by UK monitoring laboratories did not appear to lead to any significant risk of changes in nitrate level. It was decided that considerable care needs to be taken when homogenising bulk samples of lettuce or spinach in order to distribute the nitrate uniformly and so a procedure is recommended.
Laboratories may choose to incorporate a solid phase clean-up stage into the analytical procedure without risk of loss of nitrate, but under the conditions adopted in the project, this step appeared unnecessary. It was considered advisable to avoid using the alternative Carrez reagent clean-up option as this could lead to small losses of nitrate. Due to a high bias observed, chromatographic detection was preferred to colorimetric detection.
This project developed a method based on BS EN 12014-2: 1997, involving hot water extraction, and this was shown to fully meet EC method performance criteria both in-house and in full collaborative trial conditions. This extraction procedure should be incorporated into the future Code of Good Practice.
The final report is available from the Agency's Information Centre.
To obtain a copy, please contact the Enquiry Desk, Information Services, Food Standards Agency (tel: 020 7276 8181/8182 or email: infocentre@foodstandards.gsi.gov.uk )
It is described in full in Food Standards Agency Bulletin on Methods of Analysis and Sampling of Foodstuffs No 16 (January 2001).
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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