Determination of Trace Lead in Fish Sauces by ID-ICP-MS After Mg(OH)2 Coprecipitation

A method of isotope dilution coupled with inductively coupled plasma mass spectrometry (ID-ICP-MS) after Mg(OH)₂ coprecipitation was employed to determine trace lead (Pb) in fish sauces. The pH values and the amounts of Mg²⁺ in the coprecipitation system and the amounts of isotopically enriched ²⁰⁶Pb reagent added in the measurement were optimized. Results showed that a recovery by adding standard was 92.0% with a relative standard deviation (RSD) of 0.39%. The detection limit estimated with the calculated method used in the study was 7.65 ng g^?1. Through the Mg(OH)₂ coprecipitation, more than 80% of matrix ions such as K⁺, Na⁺, and Ca²⁺ in the samples were effectively removed, and the trace Pb in fish sauces was largely enriched. The concentrations of Pb measured in 12 fish sauces ranged from 0.068 to 0.299 μg g^?1, which was completely within the Pb limit (0.50 μg g^?1), a hygienic standard for aquatic flavorings set in China (GB 10133-2005). It has been well demonstrated that the method of ID-ICP-MS coupled with Mg(OH)₂ coprecipitation is suitable for determining trace Pb in fish sauces containing high levels of salt matrices.