Reference Materials as a Tool for the Analysis of Mycotoxins in Food and Feed
Reference materials (RMs) are materials (organic solutions or food or feed matrices) containing a known or certified mycotoxin content. RMs should be used by analysts as internal (standards, secondary reference materials) or external (certified reference materials) criteria for quality assurance. RMs are key tools to show traceability in analytical work in comparing the measured value of the unknown sample to the assigned or certified value of RM. Hence, De Bievre, in the editorial section of Accred Qual Assur, 2000, 5: 307, pointed out the importance for analysts to combine their own measurements’ uncertainty to the one delivered by the RM supplier; moreover, the supplier should be able to demonstrate its own traceability when assigning or certifying a value to the RM it manufactured.
Characteristics of Reference Materials
The following reference materials for mycotoxins in food or feed can be distinguished:
Pure mycotoxin standards, which are mostly commercially available at reasonable cost, taking into account the minute concentration needed for establishing calibration curves. They are sold as lyophilised film or powder, or they are already prepared in organic aqueous solutions as working solutions for establishment of calibration curves. Attention should be drawn to the purchaser that the amount indicated on the vial may be approximate, so that checking of standard stock solutions should always be done whenever possible by spectrophotometry before use.
Certified reference materials (CRMs), whose elaboration and measurement of the mycotoxin content are carried out by a specialised laboratory or institution that recruits laboratory experts or known analysts specialising in mycotoxin analysis. Mycotoxin contents of CRMs are specified together with uncertainty interval as determined in the course of the interlaboratory study. In addition to the accurate determination of mycotoxin contents, stability of the analyte in materials and sample-to-sample homogeneity within a batch are studied. CRMs are distributed along with a certificate. 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), is specialised in the production, characterisation and commercialisation of such certified reference materials.
Naturally contaminated or spiked materials, with mycotoxin contents measured by use of a reference method or compared with the content of a certified material analysed in the same conditions. Another method is to use the remaining batches of contaminated materials distributed to laboratories in the course of a proficiency test. In such cases, the co-ordinator will have assigned a value to the material from the overall mean obtained by the laboratories participating.
Manufacturers of RMs should follow the series of ISO Guides 30-32, 34-35 for elaboration and certification of high-quality RMs, and users will find in the ISO Guide 33 a detailed description of reference materials, which is also valuable in the mycotoxin field.
Availability of CRMs for Mycotoxins in Food and Feed
IRMM ( www.irmm.jrc.be ) markets the following CRMs (values of contaminated materials are given below without their uncertainty interval; please refer to the accompanying technical reports):
- Aflatoxin B1 in defatted peanut meal: blank (< 3 µg/kg) and one contaminated material 206 µg of aflatoxin B1/kg)
- Aflatoxin B1 in compound feed: blank (< 1 µg/kg) and one contaminated material (9.3 µg of aflatoxins/kg)
- Aflatoxin M1 in milk powder: blank (< 0.05 µg/kg) and three contaminated materials (0.09, 0.31 and 0;76 µg/kg)
- Deoxynivalenol in maize: blank (< 0.05 µg/kg) and one contaminated material (0.43 µg of deoxynivalenol/kg)
- Deoxynivalenol in wheat flour: blank (< 0.05 µg/kg) and one contaminated material (0.67 µg of deoxynivalenol/kg)
- Ochratoxin A in wheat: blank (< 0.6 µg/kg) and one contaminated material (8.2 µg of ochratoxin A/kg)
CRMs for aflatoxins B&G in peanut butter: blank (< 0.5 µg/kg) and contaminated material (10 µg of aflatoxins/kg);and aflatoxin B1 in defatted peanut meal: contaminated material (43.3 µg of aflatoxin B1/kg) are no longer available. IRMM has just launched a new production and certification campaign for these CRMs. Two European projects funded in the 5th Framework Programme for Research and Technological Development of the EU deal with the preparation and certification of certified reference materials for trichothecenes (contract N° SMT4-CT96-2047) and zearalenone (project’s acronym: ZONMAIZE N° SMT4-CT98-2228).
As manufacturing of CRMs is a long and expensive process, there is a very limited choice of matrix-mycotoxin combination. So, there is a crucial need for having another method to obtain other reference materials, even if not considered "certified" materials: providers of proficiency testing were asked to supply to laboratories their remaining batches of materials whose mycotoxin levels would be derived from the overall mean obtained by participants in the proficiency tests. In that case, the provider should carefully scrutinise statistics of proficiency trials to ascertain (not certify) the mycotoxin contents of materials distributed in the course of proficiency testing. FAPAS® - Food Analysis Performance Assessment Scheme (UK) ( ptg.csl.gov.uk/fapas.cfm ), the well-known proficiency supplier, already sells to analysts such materials for mycotoxins in food or feed.
References
Zschunke A., The role of reference materials, Accred Qual Assur, 5, 441-445 (2000).
Parkany M., Klich H., Rasberry S., REMCO, the ISO Council Committee on Reference Materials its first 25 years, Accred Qual Assur, 6, 226-235 (2000).
Van Egmond HP., Mycotoxins: regulations, quality assurance and reference materials, Food Addit Contamin, 12 (3), 321-330 (1995).