Problems related to determination of trace elements in spent continuous ambulatory peritoneal dialysis fluids by...

Critical parameters which influence the direct determination of trace elements in spent continuous ambulatory peritoneal dialysis (CAPD) fluids by electrothermal atomic absorption spectrometry (ETAAS) were investigated. Samples 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 exchange. Before analysis samples were equilibrated to room temperature and analysed within 8 h. It was found experimentally that some samples which were not frozen immediately leaked out of the pyrolytically coated graphite tube before 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 addition method was used in the calibration procedure. The results of direct ETAAS determinations for copper agreed well (+/-5-10%) with those obtained after acid digestion of CAPD fluids in Parr bomb. The procedure for direct determination of all three elements was validated with spiked samples.