Determination of highly concentrated Na, K, Mg and Ca in dialysis solution with flow injection on-line 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 with on-line sample volume reduction using stream splitting to obtain precise dilution factors: a series of split and confluence points are traversed by the injected sample zone. At each split point, the sample volume is reduced and at each confluence point dilution occurs to an extent governed by the relative flow rates in the two merging streams. Using various configurations of the manifold and by changing the flow rate of the carrier stream, dilution factors ranging from 10 to 10 000 are obtained. Normally, to achieve high dilution factors the carrier flow rate must be reduced. However, the dilution performance depends critically on the carrier flow rate; when the latter is low, the throughput is correspondingly reduced as well. In this work, it is shown that a reasonably high dilution factor is achievable when using relatively high carrier flow rates. Higher carrier flow rate provides precise dilution factors with the use of peristaltic pumps. To combine precise performance with high sample throughput, the dilution range, using this method, is recommended at 10-3000. To demonstrate the performance of this 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 precision of approximately 2% (RSD n = 11). The automated results were checked with a conventional manual dilution method and the results between the two methods were comparable and with no significant difference found at the 95% level (t-test) for analyte concentration range from 64 000 to 450 mg l−1.