A simple procedure for the chromatographic analysis of nanoliter samples

A simple method for the analysis of nanoliter droplets is proposed, which is profitable when larger samples cannot be collected as, for instance, in the case of several biological fluids and particularly in clinical chemistry. A glass capillary associated to a micromanipulator is used to collect submicroliter volumes which are partially transferred into transparent polymeric tubings with known internal diameters (120-178 mu m), where the volumes sampled are measured by meniscus collimations with a collimator microscope at suitable magnification. Both ends of these tubings are preliminarily equipped with ferrules and fittings. so as to make them suitable: for connection as the loop to a conventional high-pressure injection valve. The reliability of this procedure has been tested for the analysis of Na+, K+ and Ca2+ present in minute synthetic standard samples (10-200 nL) by a conventional ion-chromatographic instrumentation. Relative standard deviations in peak area measurements (5-6%) are discussed in terms of the whole approximation affecting volume measurements, which depends on both the inconstancy of the inner diameter of the polymeric tubings employed and the uncertainty characterizing meniscus collimations. The proposed procedure can be easily extended to the determination of any organic or inorganic species present in very small samples, provided that their detection can be achieved by any chromatographic approach or. more generally, by flow injection analysis.