Determination of inorganic and total mercury in seafood samples by a new ultrasound-assisted extraction system and cold vapor atomic fluorescence spectrometry

Application of two ultrasonic frequencies in the sample preparation process can not only speed up the extraction rate, but can also effectively improve the extraction efficiency of Hg, especially that of organic Hg. Based on the findings, in this paper we constructed a fast and efficient sample extraction device by the combination of an ultrasonic bath and an ultrasonic probe. Factors such as frequency of ultrasound, extraction agents and sonication time were studied in detail. Compared with an ultrasonic probe at 20 kHz or an ultrasonic bath at 40 kHz, the extraction efficiency of organic Hg species by the combination of the two was improved by at least 40% under the same conditions. Moreover, L-cysteine was chosen to weaken the C Hg bond of methyl-mercury. Under the optimized conditions, inorganic Hg and total Hg in fish samples were completely extracted in only 60 s. The detection limits (3 sigma) of inorganic Hg and total mercury in aqueous solutions are 0.0086 mu g L-1 and 0.0072 mu g L-1, respectively. The relative standard deviations for 11 replicate determinations of 1 mu g L-1 Hg were obtained as 2.4% and 3.1% for inorganic Hg and total Hg. The accuracy of the method is verified through analysis of certified reference materials (CRM) and the proposed method has been applied satisfactorily to the determination of inorganic Hg and total Hg in several biological samples, such as squid, penaeus and ling fish.