Communication Speciation of mercury by ICP-MS after on-line capillary cryofocussing and ambient temperature multicapillary gas chromatography Andrzej Wasik, b Isaac Rodriguez Pereiro, c Christian Dietz, d Joanna Szpunar a and Ryszard Oobi ´ nski *a a CNRS, EP132, Helioparc, 2, av. Pr. Angot, F-64000 Pau, France. E-mail: Ryszard.Lobinski@univ-pau.fr b Politechnika Gda´ nska, Department of Analytical Chemistry, Chemical Faculty, ul. G. Narutowicza 11/12, 80-952 Gda´ nsk, Poland c Universidad de Santiago de Compostela, Department of Analytical Chemistry, 15706 Santiago, Spain d Universidad de Madrid, Department of Analytical Chemistry, 28040 Madrid, Spain Received 3rd August 1998, Accepted 25th August 1998 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 varia- bles 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. Introduction Because of the different toxicities of methylmercury (MeHg + ) and labile inorganic mercury (Hg 2+ ), and the notoriety of the Minamata accident, 1 there has been a surge of interest in the species selective analysis of mercury since the work of Westöö et al. 2 Particular attention has been paid to techniques allowing the determination of MeHg + and Hg 2+ within one analytical run, which has led to the development of a number of procedures based on the coupling of gas chromatography of hydride or ethyl derivatives of MeHg + and Hg 2+ with atomic absorption (AAS), 3–6 fluorescence (AFS), 7,8 plasma source emission (MIPAES) 9,10 and mass (ICP-MS) 11–13 spectrometry. The increasing availability of ICP-MS in recent years has resulted in a number of studies on the gas chromatographic sample introduction of organometallic compounds into the ICP plasma with a view to trace element environmental speciation analysis (for a review see ref. 14). Besides the conventional capillary GC, 12,13 the use of a silanized quartz tube packed with a chromatographic sorbent which had been cooled with liquid nitrogen, 2196 °C, and heated electrically 11 in order to desorb the analytes, has been the most popular. Both these approaches suffer from several drawbacks. The use of capillary GC entails the need for a regular (rather bulky) chromatographic oven with temperature gradient pro- gramming. The sample should be injected in a volatile organic solvent which interferes with more volatile analytes (Me 2 Hg and MeEtHg) and limits the amount of extract that can be analysed to 1 ml (of 1 ml) available, thus negatively affecting the experimental detection limits. On the level of the interface the huge difference between the carrier (column) gas flow (1 ml min 21 ) and the flow required to ‘punch’ the plasma (1 l min 21 ) results in a sample dilution effect and the vulnerability of the interface to cold spots and dead volumes. This increases the complexity of the interface in terms of the precision of machining and the need for heating. The packed column thermal desorption systems offer a better compatibility in terms of flow rates (80–150 ml min 21 ). However, the system has a high dead volume itself, and the inertness of the packing is limited, which may induce dismutation reactions which require silanization of the packing. 15 Desorption of analytes requires temperature programming of the column heating and takes 5–20 min. The paper uses multicapillary GC 16–18 as a basis to develop a small-size accessory for speciation analysis of mercury by ICP- MS that combines the advantages of sample introduction by capillary and packed column GC and eliminates their draw- backs. The fully automated device integrates a derivatization– gas-phase extraction step of MeHg + and Hg 2+ from a sample, cryofocussing of the derivatized species and their separation on a multicapillary column, of which the outlet is inserted in an ICP-MS sample injector. Experimental Instrumentation The injection–separation module used is shown schematically in Fig. 1(a) and (b). Ethylated mercury species were purged with a stream of nitrogen through a 30 cm Nafion tube (1/16B od) (Permapure, Toms River, NJ) to the capillary cryotrap. The latter was made of a fused silica capillary (11 cm 3 0.53 mm id) coated with a 5 mm CP-Sil 8 CB layer (Chrompack, Middelburg, The Netherlands) housed in a 1 mm id stainless steel tube which was housed in a 16 mm id brass tube. Electrical contacts were put on the stainless steel tube to enable its connection to a transformer 100 VA/5 V and a current of ca. 20 A passed through it. The maximum heating rate of 300 °C s 21 could be achieved, and reduced, if necessary, by the dedicated electron- ics. A thermocouple measuring the actual trap temperature was soldered in the middle of the stainless steel tube. Nitrogen, pre- cooled to a desired temperature in liquid nitrogen, was passed between the stainless steel and the brass tube, which enabled the trap to cool down to 2150 °C. A six-way heated GC injection valve (Valco, Schenkon, Switzerland) with an electronically Anal. Commun., 1998, 35, 331–335 331