DETERMINATION OF HIGHLY CONCENTRATED NA, K, MG AND CA IN DIALYSIS SOLUTION WITH FLOW-INJECTION ONLINE DILUTION AND FLAME ATOMIC-ABSORPTION SPECTROMETRY

An on-line flow injection dilution method for flame atomic absorption spectrometry was developed. This method is based on the cascade method of dilution. The method combines the technology of merging streams wi th on-line sample volume reduction using stream splitting to obtain pr ecise dilution factors: a series of split and confluence points are tr aversed by the injected sample zone. At each split point, the sample v olume is reduced and at each confluence point dilution occurs to an ex tent governed by the relative how rates in the two merging streams. Us ing various configurations of the manifold and by changing the flow ra te of the carrier stream, dilution factors ranging from 10 to 10 000 a re obtained. Normally, to achieve high dilution factors the carrier ho w rate must be reduced. However, the dilution performance depends crit ically on the carrier flow rate; when the latter is low, the throughpu t is correspondingly reduced as well. In this work, it is shown that a reasonably high dilution factor is achievable when using relatively h igh carrier flow rates. Higher carrier flow rate provides precise dilu tion factors with the use of peristaltic pumps. To combine precise per formance with high sample throughput, the dilution range, using this m ethod, is recommended at 10-3000. To demonstrate the performance of th is manifold, high concentrations of Na, K, Mg and Ca were measured in a dialysis solution. Using a 1000-fold dilution, the sample throughput for a fully automated analysis was 70 measurements per hour, with a p recision of approximately 2% (RSD n=11). The automated results were ch ecked with a conventional manual dilution method and the results betwe en the two methods were comparable and with no significant difference found at the 95% level (t-test) for analyte concentration range from 6 4 000 to 450 mg l(-1).