At the end of 2023, Test Veritas embarked on a new project with the aim of developing a method to prepare a stable and homogenous Test Material for the metal-contaminated table salt matrix for international Proficiency Testing. Various salts, by type and origin, contaminated with metals (Lead and Cadmium) were tested.
The reasons behind the choice of matrix-analyte combination
The project was part of a larger project concerning metal contaminations in solid matrices, a topic considered to be of great interest. Salt as a matrix and Lead and Cadmium as analytes were chosen following the publication of new European regulations 2021/1323 (EU) e 2021/1317 (EU) where new maximum levels for the presence of Cadmium and Lead in various foodstuffs were implemented, also introducing salt among the regulated matrices.
This has led to a growing market interest in metal-contaminated salt, primarily from European national reference bodies.
The need was to give testing laboratories the opportunity to verify the performance of analytical methods they had developed or were developing.
Project Phases
The project was divided into several phases:
- Study of available literature, purchase of matrices and analysis of negative matrices → in order to familiarise oneself with the matrix and the analytes to be processed. Numerous studies on analytical salt activities from different countries were viewed in order to identify all the information needed to evaluate the parameters to be set for the Proficiency Test.
- Spiking tests → Various procedures were tested until the most suitable one was identified, in order to obtain an homogenisable sample. The amount of Lead and Cadmium to be spiked to the matrix was estimated based on the legal limits imposed by regulations 2021/1323 (EU) and 2021/1317 (EU), literature studies and based on the detection limits of the analytical laboratories.
- Identification of potential accredited laboratories to invite to the study → Through an in-depth study of the market and the databases available to our company, several laboratories accredited for the matrix-analysis combination under study were identified. Among all these, two types of laboratories were chosen to which to send the request for participation in the study in question:
- European National Reference Laboratories for Metals
- Italian laboratories (private and public) accredited for metals in food
31 of the interviewed laboratories decided to join the project of which 20 were public institutions (15 different countries, INTRA and EXTRA EU).
- Collection of analytical requirements reported by the 31 participating laboratories
- Large-scale production of the Test Material, organisation of the PT and shipment of samples → It was also decided to provide within the PT both a spiked sample (for the limits of interest indicated by the laboratories involved in the study) and a sample of salt incurred (naturally contaminated with concentrations far below the legal limits), so as to provide the laboratories with an additional assessment of their analytical capabilities for concentrations normally found in products placed on the market.
- Processing of participants’ results → The laboratories had about one month to fill in and send in the response forms available in the Confidential Area of the Trieste Project. 30 out of 31 laboratories sent their results.
- Issuing the Final Report
Analysis of results
The results obtained were consistent with expectations regarding the added concentrations of Cadmium and Lead in the Test Materials provided:
- TM naturally contaminated with Lead: assigned value 51.34 μg/kg, quantified by 21 laboratories.
- TM spiked, Cadmium: assigned value 460,52 μg/kg, spiked during production 500,00 μg/kg. Out of 28 quantitative data received, 96%t obtained a satisfactory evaluation in terms of z-score. Only one laboratory made an error in the analysis, providing a concentration value twice as high as the calculated assigned value. This negatively affected its evaluation and it was judged ineligible, receiving an ‘action’ signal.
- TM spiked, Lead: assigned value 920,68 μg/kg, added during production 1 ppm (= 1000,00 μg/kg). This is very similar to what was done for cadmium. Out of 27 quantitative data received, 88.89% of the participants received a satisfactory z-score. Two laboratories provided results such that they received an unsatisfactory evaluation and a ‘warning’ signal, while it is interesting to note that the same laboratory that had provided a concentration value twice as high as the calculated assigned value in the cadmium analyses also made the same mistake in this case, receiving a negative evaluation and a second ‘action’ signal.
Laboratories that have received unsatisfactory evaluations will have to identify the causes that led to these evaluations. The purpose of the proposed interlaboratory circuit is to allow a large group of laboratories pioneering the implementation of a specific analytical test to have a comparison, possibly allowing them to revise the method they have developed.
Thanks to the procedures drawn up during this project and the results obtained from the interlaboratory circuit, it was possible to include the PT for Salt Metals in the Trieste Project 2025-2026 commercial programme!
Would you be interested in participating in new research projects in the future? Contact us on info@testveritas.com and let us know which matrix-analyte combinations you are interested in!
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