Die gebruik van dialise in vloei-inspuitanalise

Abstract

The growth in analytical chemistry and in particular analytical biochemistry during the last decade, highlighted the necessity for automatic analytical systems. The majority of automated systems are flow-injection analytical systems. These systems operate according to a process 1n which the concentration of the analcite ls measured continuously in a stream of liquid. In this context successive samples pass through the same path (length of tubing) in the analyser while reagents are being added at strategic points. The mixing and incubation of the sample and reagents takes place while the sample solution is on its way towards flow-through cuvette, where the signal is continuously monitored and recorded. With the use of this method it is possible to analyse a large number of samples with high accuracy, in a very big space of time. Some of the advantages of this system is the use of small sample volumes (microlitres), small amounts of reagents are used and as demonstrated by this research is also possible to determine three different elements simultaneously in one sample. This method can be used on a wide variety of samples. Biological samples can also be analysed with success; however, a large number of interferences can complicate the analysis of biological samples. The removal of these interferences can be time consuming and expensive. By this method, on the other hand, interferences are removed simultaneously with the determination by means of dialysis. The dialysis process also acts as diluter and separator of total and free ions to be determined. Dialysis in conjunction with flow-injection analysis has not been investigated by many researchers. In this project we took a closer look at the parameters affecting dialysis. Different types of membranes and different lengths were also investigated. Through this investigation it became clear· that dialysis is not only theoretically a useful addition to flow-injection analytical systems, but it also creates great opportunities for analysis in practise. In the first instance the dialysis system Was used for the simultaneous determination of total and free calcium in milk by atomic absorption spectroscopy (AAS) and spectrophotometry respectively. Secondly the total and free calcium as well as in milk were determined simultaneously. The calcium was determined in the same way as in the first approach, while the chlorite was determined by a flow-through chloride selective electrode. In the third instance the dialysis system was used for the indirect determination of sulphate, making use of an indirect barium determination. Through this study it became clear that dialysis as part of a flow-injection analytical system can be utilized in the analysis of biological samples, without any additional treatment of samples.