Ultrasound‐assisted dual‐cloud point extraction with high‐performance liquid chromatography‐hydride generation atomic fluorescence spectrometry for mercury speciation analysis in environmental water and soil samples

Abstract A method for simultaneous preconcentration and determination of mercury species in water and soil samples was established using high‐performance liquid chromatography with hydride generation atomic fluorescence spectrometry after ultrasound‐assisted dual‐cloud point extraction. The extraction process was divided into two steps. In the first cloud point extraction, inorganic mercury and methylmercury formed chelates with sodium diethyldithiocarbamate and were extracted into Triton X‐114 micelles. In the second stage, a displacement reaction between sodium diethyldithiocarbamate‐inorganic mercury/methylmercury and l ‐cysteine occurred, and the analytes entered the l ‐cysteine aqueous solution under ultrasonication. This aqueous solution was directly introduced to the high‐performance liquid chromatography with hydride generation atomic fluorescence spectrometry and the detection was completed within 6 min. Under the optimum experimental conditions, the linear range was 0.10–5.0 μg/L ( r ≥0.9993) for inorganic mercury and methylmercury, and the enhancement factors were 15.7 for inorganic mercury and 6.35 for methylmercury. The limits of detection for inorganic mercury and methylmercury were 0.004 and 0.016 μg/L, respectively. The approach was successfully applied to the determination of trace inorganic mercury and methylmercury in water and soil samples with good recoveries (85.3–110%). This method solved the problem of peak fusion of the two analytes and was successfully applied to the speciation analysis of mercury.