Results identified that guidelines are needed on sample preparation protocol when analysing canned food as a drained product or solid/liquid composite.
The JRC organised the proficiency test (PT) for the determination of some heavy metals (trace elements) by 127 laboratories from 36 countries.
The European Union Reference Laboratory on Heavy Metals (EURL-HM) did the tests for the National Reference Laboratories (NRL).
Non-compliant test item
Results presented the determination of total arsenic (As), cadmium (Cd), lead (Pb), mercury (Hg), tin (Sn) and inorganic arsenic (iAs) mass fractions in peas in brine in glass jars.
They revealed most labs lacked guidance documents for analysis of canned food and two different sample preparation approaches (drained product or solid/liquid composite) were used by labs from the same country.
The test item was not compliant with the maximum levels (ML) in Regulation (EC) No 1881/2006 for total Cd in vegetables and fruits, both in the drained product and in the solid / liquid composite, and for total Sn in canned foods in the drained product.
Seventy-two labs declared the test item non-compliant but 32 reported it complied and could be consumed while 19 did not answer the question.
The regulation sets maximum levels of 200 mg kg−1 for tin in canned foods; 0.2 mg kg−1 for lead in legume vegetables, cereals and pulses; and 0.05 mg kg−1 for cadmium in vegetables and fruits.
From the participating labs 67 (54%) analysed the drained product and 56 the solid/liquid composite.
Total As values were reported by 52 labs for the drained product and 51 for the solid / liquid composite, total Cd by 66 and 54, total Pb by 64 and 55, total Sn by 50 and 46 and iAs by 19 and 22 labs respectively.
Two labs decided to analyse the drained product and the brine separately and report the results for solid / liquid composite using mathematical approaches.
Sample prep strategy and other results
The majority of labs answered a questionnaire showing sample preparation strategy is based on common sense, about what is intended for consumption and what is not.
Only Spain, among EU countries, has a protocol that processed food, canned in its natural liquid or in sauces, should be drained before analysis and only for processed canned fruits the liquid should be included.
For the total As mass fraction the performance of those analysing the drained product was better than those looking at the solid / liquid composite (92 vs. 82%).
For the iAs mass fraction 84% of labs analysing the drained product got satisfactory performance as did 74% of those analysing the solid / liquid composite.
For the total Sn mass fraction, 96 participants gave results. The majority (74 and 78%) performed satisfactorily for analysis of the drained product and solid/liquid composite respectively.
“In the case of total Sn and iAs there is room for improvement, regarding not only the performance but also the number of laboratories carrying out the analyses (only 33% of the participants reported values for iAs),” said the researchers.
Only two participants reported values lower than 0.002 mg kg−1 found by two expert labs for the drained product and four for the solid liquid composite.
“The experience acquired in previous PTs in which total mercury was covered, tells us that there is a tendency to overestimation of total mercury in food and feed matrices. Laboratory contamination has been attributed to be the most likely cause for that overestimation,” said the researchers.
Source: Trends in Anal. Chem. 85 (2016) 57-66
“Determination of toxic trace elements in canned vegetables. The importance of sample preparation”
Authors: Yiannis Fiamegos, Mitja Vahcic, Håkan Emteborg, James Snell, Georg Raber, Fernando Cordeiro, Piotr Robouch, Beatriz de la Calle