Alkaline extraction for mercury determination in fish samples by CV - MIP AES as an alternative to conventional sample preparation methods.

Abstract

Aquatic animals are capable of absorbing inorganic elements from soil, sediment and water, such as mercury (Hg) among others, which is biomagnified, and due to human intake, represents a potential risk of toxicity. Its presence is studied in foods of aquatic origin to guarantee the safety of the products consumed by the population. In this work, we present the development of a method for mercury determination in fish samples by CV-MIP AES after alkaline extraction with tetramethylammonium hydroxide. Fresh fish samples and certificate reference material of mussel tissue and dogfish liver were evaluated for the extraction optimisation. The method consisted in adding 3.5 mL of TMAH 25% w w−1 in water to 0.6 g of sample (dried and milled), homogenising by using a vortex and letting it stand overnight. The resulting suspension was neutralised and acidified with HNO3 and volume was completed up to 20.0 mL with purified water. The determination was performed by CV-MIP AES using NaBH4 2% w v-1 in NaOH 0.5 % v v-1. Limit of detection (3s) and limit of quantification (10s) were 0.0029 mg kg-1 and 0.0096 mg kg-1 respectively; linear range 1.3 – 10.4 µg L-1 and precision of repeatability 13.3 %. Trueness was assessed by comparison of the mean value obtained using the two reference materials by means of a Student´s t-test. Fish samples were analysed by the proposed method and by the most common acidic microwave assisted digestion method. The results obtained were statistically equivalent at the 95% significance level. The proposed method could be postulated as an easy to handle, environmentally friendly alternative to the classic methods that use acidic digestion.