Speciation of mercury by ICP-MS after on-line capillary cryofocussing and ambient temperature multicapillary gas chromatography

An automated, small and easily mountable/demountable accessory based on a constant temperature multicapillary GC is proposed for time-resolved introduction of gaseous mercury species into an ICP-MS. The fast, narrow-band injection was achieved by cryofocussing (280 °C) of dimethyl-, methylethyl- and diethylmercury in an 11 cm capillary housed in a steel tube prior to desorption of the species (within 3–5 s) by rapid-pulse high intensity current. The highest chromatographic resolution was achieved at ambient column temperatures; isothermal separations at higher temperatures offered increased sensitivity and speed of analysis controlled by the data acquisition rate of a quadrupole MS. The compatibility of the operating variables with the ICP ionization conditions (argon at 50–300 ml as the carrier gas) and negligible peak broadening on the column and in the ICP-MS interface allow the sensitive (limit of detection 0.15 pg) isotope-selective speciation of mercury in biological and sediment samples.