COMPARISON OF ETHANOL PLASMA-PROTEIN PRECIPITATION WITH PLASMA ULTRAFILTRATION AND TRICHLOROACETIC-ACID PROTEIN PRECIPITATION FOR THE MEASUREMENT OF UNBOUND PLATINUM CONCENTRATIONS

Sample preparation for the measurement of non-protein-bound platinum w as evaluated by precipitation of plasma proteins with cold ethanol. Th e method was compared with the routinely used plasma ultrafiltration a nd with trichloroacetic acid (TCA) protein precipitation. After incuba tion of human plasma samples with cisplatin or carboplatin, unbound pl atinum concentrations were determined applying Amicon Diaflo ultrafilt ration membranes and Millipore ultra-free-MC filters. For protein prec ipitation, 1 ml of cold (-20 degrees C) pure ethanol was added to 0.5 ml of human plasma and the supernatant was collected after 2 h, or 0.5 ml of cold 20% TCA was added to 0.5 mi of plasma. Platinum was analyz ed by atomic absorption spectrophotometry (AAS). There was no signific ant difference between the ethanol and ultrafiltration methods in the unbound platinum concentration. The protien content in the supernatant (1.00 +/- 0.20%) was slightly higher than that in the Amicon (0.58 +/ - 0.05%) and Millipore (0.55 +/- 0.04%) ultrafiltrates. On average, th e TCA and ethanol method seemed to be equally appropriate. The ethanol precipitation method is concluded to be simple, convenient, and repro ducible and has negligible costs.