Comparison of three coupled gas chromatographic detectors (MS, MIP-AES, ICP-TOFMS) for organolead speciation analysis

An automatic unit for the screening of rainwater is used for the determination of organolead compounds using different detectors coupled to a gas chromatograph. A systematic overview is given of the advantages and disadvantages of several detectors (electron ionization mass spectrometry, EI-MS; microwave induced plasma atomic emission spectrometry, MIP-AES; and inductively coupled plasma time-of-flight mass spectrometry, ICP-TOFMS, for the speciation of organolead compounds on the basis of sensitivity, selectivity and reliability. C60 fullerene and RP-C18 were used as sorbent materials for these compounds. The primary assets of the fullerene sorbent, as compared to C18 sorbent, are high sensitivity and selectivity resulting from efficient adsorption due to large surface area and interstitial volume. Among the detection systems, GC/ ICP-TOFMS is the most sensitive, with absolute detection limits of approximately 15 fg of organolead compounds (as lead) using 5-mL sample volumes. Except for diethyllead, similar sensitivities were obtained by MIP-AES. GC/MS is intrinsically the most specific option, because the species are detected directly from molecular information. The precision is similar for all detectors. The screening of rainwater from different locations showed that samples collected in countries in which leaded gasolines are now banned contain organolead species at concentrations below 2 pg/ mL, levels that can be detected only for sample volumes of 25 mL and using MIP-AES or ICP-TOFMS as detectors, their determination being impossible by GC/MS.