Problems related to determination of trace elements in spent continuous ambulatory peritoneal dialysis fluids by electrothermal atomic absorption spectrometry

Critical parameters which influence the direct determination of trace eleme nts in spent continuous ambulatory peritoneal dialysis (CAPD) fluids by ele ctrothermal atomic absorption spectrometry (ETAAS) were investigated. Sampl es were collected after CAPD fluid exchange in 5.0 ml polyethylene cups and stored at -20 degrees C. Daily spent CAPD fluids were frozen immediately, while nightly spent CAPD fluids were frozen 2-3 h after the morning exchang e. Before analysis samples were equilibrated to room temperature and analys ed within 8 h. It was found experimentally that some samples which were not frozen immediately leaked out of the pyrolytically coated graphite tube be fore the drying step. In order to keep the sample in the graphite tube and to obtain reproducible measurements of copper, aluminium and iron, samples were diluted before analysis 1+1 with 32% v/v nitric acid. The standard add ition method was used in the calibration procedure. The results of direct E TAAS determinations for copper agreed well (+/-5-10%) with those obtained a fter acid digestion of CAPD fluids in Parr bomb. The procedure for direct d etermination of all three elements was validated with spiked samples. (C) 1 999 Elsevier Science B.V. All rights reserved.