On-line preconcentration of mercury using an integrated column/gas-liquid separator (PCGLS) and cold vapour atomic absorption spectrometry

Abstract

A novel flow injection (FI) method for the determination of mercury at ng l⁻¹ levels was developed, using on-line solid phase extraction and cold vapour atomic absorption spectrometry (CVAAS). The pyrrolidine dithiocarbamate mercury complex Hg(PDC)₂, is adsorbed and reduced to elemental mercury, and the generated vapour is separated in a newly specifically designed and constructed unified and combined preconcentration column/gas-liquid separator (PCGLS). The lower of the two sections of PCGLS is a preconcentration column packed with polytetrafluoroethylene (PTFE) turnings for the retention of Hg(PDC)₂ and subsequent on-column reduction of mercury by SnCl₂. Mercury vapour is generated within the column and expelled from the reaction mixture by passing nitrogen through the PCGLS. The upper section of the PCGLS is a headspace for receiving mercury vapour and separating it from humidity residues before entering the absorption cell. The use of strong inorganic acids or volatile organic solvents as eluents is avoided, because the elution step is eliminated. The excellent performance of PTFE as packing material and the compact design of the PCGLS results in higher sensitivity and sampling frequency and to a more functional and simple manifold. An enrichment factor of 32, a detection limit of c_L = 6 ng l⁻¹, a sampling frequency of 30 h⁻¹ were obtained at sample flow rate of 11.5 ml min⁻¹, for 60 s preconcentration time. The precision, expressed as relative standard deviation, at 0.6 µg l⁻¹ Hg(II), was s_r = 2.1%. The proposed method overcomes the common interferences including those from volatile organic solvents and has been successfully applied to the determination of inorganic mercury in natural waters, and total mercury in urine and mussel samples after digestion.