Quantification of Etoposide and Etoposide Phosphate in Human Plasma by Micellar Electrokinetic Chromatography and Near-Field Thermal Lens Detection

A method employing micellar electrokinetic chromatography in combination with near-field thermal lens detection (NF-TLD) was developed for the rapid simultaneous determination of etoposide phosphate and etoposide in human blood plasma, taking teniposide as internal standard. The method developed allows the baseline separation of the solutes of interest from each other and from potential interfering matrix constituents within 4 min. The NF-TLD device employed permits detection of solutes absorbing electromagnetic radiation at λ = 257 nm in fused-silica capillaries with 75-μm i.d. via the near-field thermal lens effect with LODs of 100 μg L-1 for etoposide phosphate and 170 μg L-1 for etoposide. Comparison of the performance of this detector to the performance of a commercial absorption spectrometric detector working at λ = 257 nm showed a substantial improvement in detection limits (up to 60-fold improvement) for the near-field thermal lens detector.