Optimisation of parameters for determination of rubidium in spent CAPD fluids by flame and electrothermal atomic absorption spectrometry

Abstract

An analytical procedure is reported for the determination of rubidium in spent continuous ambulatory peritoneal dialysis (CAPD) fluids by flame and electrothermal atomic absorption spectrometry (FAAS, ETAAS). Samples of spent CAPD fluids were collected as 5 ml aliquots in polyethylene tubes and stored in a freezer at −20°C. Before analysis, samples were equilibrated to room temperature and analysed within 8 h. A total of 2 mg ml −1 of caesium was added to each sample and standard solution to overcome interferences from ionisation. An air–acetylene flame was applied in FAAS determinations. Analysis was performed against aqueous standards. The calibration graph was linear from 30.0 up to 5000 μg l −1 Rb, while the limit of detection (3 s) was found to be 20.0 μg l −1 rubidium. Good repeatability of measurement (RSD 1%) was obtained. Parameters were also optimised for determination of rubidium in spent CAPD fluids by ETAAS. Ten-fold diluted samples (3.5% nitric acid) were analysed applying standard addition calibration. The calibration graph was linear from 2.0 up to 30.0 μg l −1 rubidium, while the limit of detection (3 s) was found to be 1.0 μg l −1 rubidium (sample volume 10 μl). Good repeatability of measurement (RSD 5%) was obtained. The results of direct determination by FAAS and ETAAS were compared to those obtained after acid digestion of samples in Parr bombs. The accuracy of the procedure for direct determination was checked by spiking samples. In 73% of samples analysed, the differences between the results obtained by the two techniques, either for direct determinations of samples or for samples digested in a Parr bomb did not exceed ±10%.