A SIMPLE PROCEDURE FOR THE CHROMATOGRAPHIC ANALYSIS OF NANOLITER SAMPLES

A simple method for the analysis of nanoliter droplets is proposed, wh ich is profitable when larger samples cannot be collected as, for inst ance, in the case of several biological fluids and particularly in cli nical 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 collima tions with a collimator microscope at suitable magnification. Both end s of these tubings are preliminarily equipped with ferrules and fittin gs. so as to make them suitable: for connection as the loop to a conve ntional high-pressure injection valve. The reliability of this procedu re has been tested for the analysis of Na+, K+ and Ca2+ present in min ute synthetic standard samples (10-200 nL) by a conventional ion-chrom atographic 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 o f the inner diameter of the polymeric tubings employed and the uncerta inty characterizing meniscus collimations. The proposed procedure can be easily extended to the determination of any organic or inorganic sp ecies present in very small samples, provided that their detection can be achieved by any chromatographic approach or. more generally, by fl ow injection analysis.