Liquid chromatographic determination of oxaliplatin in blood using post-column derivatization in a microwave field followed by photometric detection

Oxaliplatin ([(1R,2R)-1,2-cyclohexanediamine-N,N′]oxalato(2-)-O,O′-platinum) is the first platinum drug with significant activity for metastatic colon cancer. The analysis of oxaliplatin has previously almost exclusively been based on the determination of the platinum content in plasma or ultrafiltrate using flameless atomic absorption spectroscopy (FAAS) or inductively coupled plasma mass spectrometry (ICPMS). A new method for quantitative determination of the free fraction of the intact drug in blood ultrafiltrate is presented here. Blood was ultrafiltrated centripetally at 4 °C and the ultrafiltrate was analyzed by liquid chromatography. Oxaliplatin was separated on a Hypercarb column using a mobile phase of methanol/succinic acid buffer pH 7.0 (9/1, v/v). Post-column derivatization was performed by adding N,N-diethyldithiocarbamate in methanol and with microwave heating of a Teflon tubing. The derivative was quantified by photometric detection at 344 nm. The coefficient of variation of standard blood samples was 4.9 and 2.5% at 0.100 and 1.00 μg/ml, respectively. The limit of quantitation was 0.04 μg/ml.