An automatic Flow System of Rapid on-Line Digestion and Pre-Concentration for In-Field Determination of Trace Total Mercury in Seawater

Abstract

An automatic flow system of rapid on-line sampling, digestion, and pre-concentration for in-field determination of total mercury in seawater has been developed. In this system, both UV radiator and bromine monochloride (1%, v/v) were used to make the sample digestion rapid and reliable. And, the active gold columns were used for the effective preconcentration of mercury. Double loops connected to an 8-way valve were adopted to quantitate the volume of samples and reductant, respectively. With the hyphenation of the flow system and cold vapor atomic fluorescence spectrometry (CVAFS), the detection limit for total mercury was as low as 0.04 ng/L. The manifold parameters, including the carrier gas flow, digestion time, purging time, and reagent flow rates, were optimized. The calibration curve (p = 0.0566C+0.0174, n = 8, R 2 = 0.9994) was obtained within the range of 0.18-200 ng/L. The relative standard deviation (RSD) was 1.9% (n = 12), evaluated from 12 successive measurements of a real seawater sample at 5.2 ng/L mercury level. The recovery ranged from 99.4% to 109%. The analysis speed of the system was 6.5 min per sample. Furthermore, the proposed method was applied to in-field analysis of sixteen real seawater samples for total mercury. The samples were also analyzed with US EPA method (EPA, 1631) in the laboratory. The correlation coefficient between the results obtained with the two methods was 0.9762.