Effectiveness of in-needle extraction device for liquid samples

Abstract

In this work in-needle technique as the method for liquid samples preparation which faces with the problem of high flow resistance produced by a sorbent layer is considered. The influence of parameters (needle size, sorbent particle size and length of sorbent layer) of in-needle device on the flow rate was examined. Acceptable sampling conditions were selected on the basis of experiments and their chemometric evaluation. Darcy law was used to describe flow velocity through sorbent in the needle. Kozeny–Carman model and Brinkman model led to results significantly different from those obtained experimentally. Baaren model gave the most realistic results. Diameter of grain, porosity and a constant termed C were taken into account in this model. Incorporation of an additional parameter – “constant C” provides the completion of the model and allows predicting effectively the permeability of the extraction system. The so-called “constant C” is not constant but characteristic for a given system.The range for geometrical characteristics of the sorbent has been determined, where the extraction system works properly. To estimate suitability of a given extraction system, a new parameter PIN expressing the geometry of the system was proposed. The usefulness of the range of PIN parameter was confirmed experimentally. This tool might be used in designing and preparation of a number of in-needle devices having similar ability of liquid transportation.