Flow system device for the on-line determination of total mercury in seawater

The instrumental set-up for the on-line sampling, digestion and quantification of total mercury in seawater is described. Based on a flow system and cold vapour atomic absorption spectrometry (CVAAS) detection limit was improved by a gold amalgam preconcentration to 0.5 ng l(-1). The manifold design was optimized by the variation of the gas flow, length of reaction coils, shape and material of the gas-liquid separator and flow rate of the reductant. A calibration following the equations p=0.039c+0.0813 (p, peak area; c, concentration) and a correlation coefficient of r=0.9996 was obtained. The relative standard deviation of three measurements of 0.5 ng l(-1) Hg(2+) was 3.8%. The long-time (12 h) reproducibility was 6.2% RSD (n=25) of 0.5 ng l(-1) Hg(2+). With a recovery rate >90% mercury can be determined after on-line UV digestion. For a complete analysis, 6 min is required. The technique is fast, simple to handle and robust. The apparatus is designed for the use on research vessels under sea conditions.