Signal-to-noise ratios for coupled gas chromatography–atomic absorption spectrometry using quartz tube atomizers

Abstract

A study of coupled gas chromatography–atomic absorption spectrometry (GC–AAS) was undertaken in an effort to identify the operating conditions and quartz tube (QT) atomizer dimensions yielding optimum signal-to-noise (S/N) ratios. Tetramethyllead (TML) and tetraethyllead (TEL) were chosen as test analytes and separated by temperature-programmed GC using a wide-bore capillary column. The noise level was dependent only on the limiting aperture in the optical train, defined by either the design of the spectrometer system or, at conditions maximizing the S/N ratios, by the dimensions of the QT atomizer. The atomizer dimensions also affected the signal magnitude, as did the gas flow rate and composition and the standard deviation of the (assumed) Gaussian peak, s_G, eluting from the GC system. A physical model describing the S/N ratio in terms of these operating variables was developed and verified experimentally for TML and TEL using five QT atomizer configurations. The S/N ratios were shown, both experimentally and theoretically, to improve using chromatographic conditions that minimize s_G. Optimum QT atomizer dimensions for a range of operating conditions are tabulated.