Abstract

In this paper the capillary cold trap (CCT) is presented as a novel sample introduction and separation system for microwave-induced plasma detection. The method is based on cryogenic trapping and gas chromatographic separation carried out within the same capillary. The device, which comprises a derivatization step, on-line gas phase extraction, preconcentration and analyte separation, is semi-automated and all operational parameters are adjustable via an in-house developed control unit, regulating the selected parameters throughout the analysis process. Detection was carried out using a 2.45 GHz microwave-induced argon discharge sustained in a TM₀₁₀ Beenakker cavity and emission lines were recorded by means of a ST6-UV CCD camera provided by the Santa Barbara Instrument Group. The detection limits achieved were 6.0, 0.95 and 1.25 ng L⁻¹ for dimethylmercury, methylmercury and inorganic mercury, respectively. A complete chromatogram could be obtained within 3 min, resulting in the duration of one whole analysis cycle of about 15 min. The proposed method was validated by the analysis of a reference material (BCR 710) and applied to mercury speciation in different sample matrices such as oyster, tuna fish and sediments after microwave-assisted extraction. The total mercury concentration in real samples was in the range of 0.2–11 mg kg⁻¹, of which up to 75% corresponded to organic mercury species.