Proficiency testing schemes for Cadmium in cocoa powder analysis for Colombian laboratories

Carlos España, Gustavo Gómez, Katherin Holguín, Johanna Abella, Diego A. Ahumada

Abstract

This paper shows the experience in the operation of a proficiency test for the analysis of Cadmium in Cocoa. Due to the limited number of analytical laboratories participating, this proficiency test was developed with two reference materials (RMs), which were prepared from cocoa beans. The certified value for Cadmium in the two RMs (low and high concentration levels of Cadmium) was based on the agreement of results of at least two methods: ICP-MS and GF-AAS conducted at the National Metrology Institute of Colombia. The homogeneity and stability studies were performed according to guide ISO 35. In the first study, it was found an uncertainty associated to homogeneity between bottles of 0.06 % for low concentration level and 0.89 % for the high concentration level. Stability contribution was estimated by 0.24 % in accelerated conditions and 0.47 % in the long-term conditions. On the other hand, the assigned value was 0.202 ± 0.018 mg/kg by low concentration of the RM and 2.32 ± 0.15 mg/kg by the second one. The proficiency testing scheme counted with the participation of 10 laboratories with unsatisfactory results only for one participant. Following this scheme, some tools for improvement were identified such as the use of both internal and subrogate quality control standards for measurement, among others.

Keywords

Cadmium analysis, Cocoa powder, Proficiency testing schemes, Technical competence, Colombian laboratories

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IMEKO-TC10-2020-017.pdf

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IMEKO TC

TC10 - Measurement for Diagnostics, Optimization and Control

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