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

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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 t½ 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 t½ of 81 ± 11 h.

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