Optical studies into the SPLITS effect: New insights into controlling sampling errors in turbid solutions for analytical instruments

摘要

This study into the SPLITS {Sampling Partitioning (Liquid) Irregularities in Turbid Solutionsjeffect is part of the Aqua-STEW (Water Quality Surveillance Techniques for Early Warning by Tensiographic Sensors) 5th Framework European project. The paper reports new experimental measurements into this effect using the fibre drop analyser. Capillary hydrodynamic fractionation has been previously been observed, but the drop analyser technique provides improved experimental characterisation of the effect. A description of the optical tensiograph system used is given with details of the five strategies designed to minimize this SPLITS effect. It has been observed that the sampling of the solution by a stepper-pump to the instrument drophead, leads to irregular concentrations in the delivery tubing and thence the drophead. The measured tensiotrace variations in successive microlitre samples delivered from the capillary have provided an insightful experimental approach for the study of this important effect. It has been found that the best approach for the minimization of these unwanted concentration irregularities is using high-speed aspiration. The paper ends with discussion on the general relevance of this SPLITS effect to other chemical techniques that must sample turbid solutions and analyses the specific issues posed for on-line water monitoring systems.