Quality Assurance for the Analysis of Mycotoxins in Food and Feed
There have been 40 years of very active development in mycotoxin analysis, which has produced numerous well-characterised or validated analytical methods as well as well-trained analysts. High-quality and high-performance mycotoxin analysis continues to be required by bodies in charge of risk assessment and regulatory implementation, for monitoring programmes, for control of agricultural imports and exports of food and feed, and for trade. The analyst is responsible for producing reliable analytical data, and there are a certain number of ground rules and tools to help in this:
Methods of Analysis
For regulatory or any official purposes or in case of dispute, the analyst should preferably use a method of reference. A reference or an official method is one chosen by a public authority, an official or trade body/association, or even by a reference laboratory.
When the analyst is involved in surveillance or monitoring, trade exchanges, or commodity controls, where there is no reference method, they should opt for a standardised or published validated method. A standardised method is a method usually validated by an interlaboratory exercise, written in a standardised format and adopted by a standardisation body. For mycotoxins in foodstuffs, the more active standardisation bodies are AOAC, IUPAC, CEN, IDF, etc., including national standardisation associations. The working group 5 Biotoxins of CEN-European Committee of Normalisation (CEN/TC 275 WG 5) is in charge of selecting published validated methods for mycotoxins and formatting them as CEN standards after obtaining consensus from national experts of State Members of the European Union. Several methods were recently validated through interlaboratory trials in the course of EU-funded projects in the 4th and 5th framework programmes and the corresponding analytical protocols were adopted as working documents to be normalised as CEN standards. In addition, the AOAC-Association of Official Analytical Chemists publishes yearly the AOACâ Official Methods of Analysis book, containing a large number of analytical methods for mycotoxins that were validated following the recommendation of the AOAC.
An analytical method should be well characterised and validated in-house, but it should also be validated through an interlaboratory trial according to ISO 5725, 1994 (Accuracy - trueness and precision - of measurement methods and results) or following the Harmonised IUPAC protocol (Thompson & Wood, 1993, J AOAC Int 76(4), 926-940).
Alternative and Confirmatory Methods
In cases where numerous analyses are to be carried out, the reference or official method might be considered too time-consuming or laborious for the analyst. Therefore, as an alternative, commercialised kits can be used. These are immunoassay-based methods, usually more rapid and simple. An example of this type of assay is the Enzyme Linked Immunosorbent Assays (ELISA). A major disadvantage of using ELISA is that false-positives are frequently produced, leading to problematic interpretation of results. Therefore, the analytical values produced by these assays need to be confirmed by the use of a reference or confirmatory method, to identify the mycotoxin and the quantity present in the sample.
Reference Materials
Reference materials are invaluable tools for the analyst. The use of reference materials provides the most accurate means for assessing the reliability and reproducibility of the data obtained. In the analytical field, reference materials are mainly used for establishing calibration curves, to check the linearity of the method and for generating control charts as an internal indicator of quality assurance. Reference materials correspond to matrices containing a known or certified mycotoxin content of pure mycotoxin standard solutions or naturally contaminated or spiked materials. Mycotoxin contents are measured by either a reference laboratory or certified through an interlaboratory trial, carried out with expert laboratories. The results are submitted for statistical analysis, which includes the calculation of uncertainty on mean values. The Institute for Reference Materials and Measurements (IRMM, ex-BCR Bureau Communautaire de Reference), funded by the European Union as a Joint Research Centre, located in Geel (Belgium), specialises in the production, characterisation and commercialisation of certified reference materials.
Proficiency Tests
Proficiency testing was first designed to allow analysts to compare their analytical results with those obtained by their colleagues in other laboratories. A proficiency test is an interlaboratory exercise, where participants receive similar samples from a co-ordinator to be analysed in the same conditions as participants would carry out their routine analysis. The main purpose of proficiency testing is to study the performance of laboratories for a given analyte. Calculation of their z-scores, corresponds to the ratio of the bias estimate between laboratory results and assigned value (perhaps the overall mean of the interlaboratory study) of the distributed samples to the standard deviation for reproducibility. The ISO CEI guide 43, 1997, describes how to organise proficiency testing. Proficiency testing is a predictable tool for external quality assurance for a given laboratory and a means of monitoring quality control. Participation in proficiency tests is strongly recommended by accreditation bodies, if not obligatory. Many national and international proficiency test programmes exist for mycotoxins.
Quality Assurance and Accreditation
Through the years, each country or professional body elaborates its own quality assurance scheme, including laboratory accreditation. A huge effort is currently being made to harmonise such schemes, particularly throughout the European Union within the EA (European Co-operation for Accreditation), in order to be able to examine the performance of an analytical laboratory regardless of the country it belongs to. The new EN ISO CEI 17025 guide (General requirements for the competence of testing and calibration laboratories) used for the accreditation of laboratories is now one of the main harmonised tools for accreditation bodies, and most countries have accreditation programmes for mycotoxins in food and feed.