R. Toniolo et al., A SIMPLE PROCEDURE FOR THE CHROMATOGRAPHIC ANALYSIS OF NANOLITER SAMPLES, Fresenius' journal of analytical chemistry, 360(2), 1998, pp. 260-262
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.