Electrothermal vaporization for sample introduction into a gas sampling glow discharge time-of-flight mass spectrometer

An electrothermal vaporizer (ETV) has been coupled with a helium-supported gas sampling glow discharge (GSGD) time-of-flight mass spectrometer (TOFMS) for the analysis of small volumes of aqueous solutions. Both the cation (metal) and anion (halide) could both be measured with this source owing to the high ionization potential of the discharge gas. Inorganic halides were transported more effectively than were the nitrate, sulfate, or acetate salts of copper and zinc. The transport efficiency of the non-halides was improved through the use of ammonium chloride and mineral acids as matrix modifiers. Detection limits (3σ) in the range of 5–120 pg and a linear dynamic range of three orders of magnitude were measured for six elements with the use of boxcar averagers. Precision was 3.8% R.S.D. for a series of 15 replicate injections of zinc chloride; isotope ratio precision (64Zn+/66Zn+) was 1.8% R.S.D. and limited by counting statistics. Comparable precision was obtained for measurement of both peak heights and integrated peak areas. Speciation of iron was accomplished by employing a modulated GSGD to sequentially collect atomic and molecular mass spectra. The different volatilities from the ETV permitted ferrocene to be temporally resolved from ferrous chloride.