Analytical characterization of a method for mercury determination in food using cold vapour capacitively coupled plasma microtorch optical emission spectrometry – compliance with European legislation requirements

Abstract

This paper presents the analytical characterization of a highly sensitive and inexpensive method for Hg determination in food based on cold vapour capacitively coupled plasma microtorch optical emission spectrometry. The novelty of the work lies in combining the on-line preconcentration of Hg cold vapour on a gold filament microcollector with a low-power (20 W) and low Ar consumption (200 mL min⁻¹) microtorch to increase the sensitivity of the method. The method involves microwave assisted digestion of the lyophilized samples in a HNO₃–H₂O₂ mixture, conventional chemical cold vapour generation using the SnCl₂–HCl system, on-line preconcentration on a gold filament and emission measurement at 253.652 nm using a low-resolution microspectrometer. The figures of merit were discussed in relation with the demands in the Decisions 2007/333/EC, 2011/836/EC and 2002/657/EC on the determination of toxic elements in food. The detection and quantification limits were 0.005 μg kg⁻¹ and 0.015 μg kg⁻¹ allowing the use of the method for Hg determination in foods such as chicken meat, bread, rice, vegetables and fruits. For concentrations in the range 0.57–25.2 μg kg⁻¹ the precision was 0.7–9.0%, below the maximum standard uncertainty set in the above mentioned legislation. Recovery of 97.9 ± 4.6% and trueness in the range (−7.7)–(+4.7%) in the analysis of five certified reference materials were found to be satisfactory, since the found concentrations fall within the ±10% bound of the target value. The proposed method developed using miniaturized instrumentation is cost-effective and enables us to achieve Hg determination in food complying with European legislation. The system has analytical potential for the future and prototyping perspectives.