<title>Gradient microbore liquid chromatography with dual-wavelength absorbance detection: tunable analyzers for remote chemical monitoring</title>

Abstract

On-column sampling, preconcentration and gradient separation using microbore liquid chromatography ((mu) LC) will be described. Both thermal gradient (TG) and transient mobile phase gradient (TMPG) elution methods have been developed and evaluated. A previously developed dual- wavelength absorbance detector is incorporated in the analyzer, thus providing real-time correction for adverse refractive index (RI) effects that normally hinder remote single fiber optic absorbance measurements. An absorbance detection limit of 3 X 10-4 AU is routinely achieved and chromatographic baseline conditions remain stable even during very steep gradients, in which the solvent RI changes rapidly with time. Sampling and preconcentrating analytes by a factor of 1000 is illustrated and is shown to be ideally suited for trace analysis of water samples. The result is a tunable analyzer that provides rapid characterization of samples typically not amenable to selective analyzer monitoring due to their high degree of complexity or due to low concentrations of analytes of interest. TG-(mu) LC, is quite simple, requiring a single pump; while TMPG-(mu) LC, incorporating a single pump and two injection valves, offers more selectivity than TG-(mu) LC. Both gradient techniques offer preconcentration and rapid, optimized separation conditions, giving an improvement over isocratic separations that employ a single mobile phase.