Measurement of platinum in plasma and urine by direct current plasma atomic emission spectrometry

Abstract

The measurement of Pt in biological fluids has been developed using a d.c. plasma emission spectrometer. The analyses were validated by standard additions and spectral overlay procedures using a dynamic wavelength scanner and showed no background or spectral interferences. The detection limits were 0.2, 0.04 and 0.02 µg ml^–1 for plasma, urine and ultrafiltrate, respectively, and the assay was linear up to 20 µg ml^–1. The recovery of Pt added to plasma and urine averaged 100%(n= 66) and the precision over the range 1–5 µg ml^–1 was 4.6–7.1% within batch and 2.8–6.6% between batch. Comparison with an electrothermal atomisation atomic absorption procedure (x) gave highly significant correlations (P < 0.001) for urine (y= 0.967x– 0.011, r=+0.98, n= 23) and plasma (y= 1.088x+ 0.03, r=+0.971, n= 68).

Free Pt levels in vitro declined logarithmically with a t_½ of 165 min. The initial ultrafilterable (free) Pt accounted for 93–97% of the total plasma Pt levels. Recovery of cisplatin from ultrafiltered aqueous solutions was 95 ± 8% at a Pt concentration of 1.3 µg ml^–1.

Cisplatin infusion over 8 h was carried out in nine patients and up to 30% of the dose was excreted in urine within 3 d. Total Pt levels in plasma were maximal at the end of infusion with mean values ± 1 SD of 2.53 ± 0.19 (n= 4) and 1.58 ± 0.38 µg ml^–1(n= 5) with doses of 100 and 50 mg m^–2, respectively. Nine hours after completion of the infusion, the total Pt was 75 ± 11% of the peak level and thereafter declined with a t_½ of 81 ± 11 h.