Improved method for analysis of cysteinyldopa in human serum

Abstract

5‐S‐l‐Cysteinyl‐l‐dopa is a well‐known pigment intermediate and analysis of its serum concentration is well suited for evaluation of treatment and follow‐up of stage III and IV malignant melanoma. A simplified analytical method is described using organic extraction followed by clean‐up on a boronate gel to capture the compound containing vicinal hydroxyls. Weak acid solution elutes the 5‐S‐cysteinyldopa suitable for high‐performance liquid chromatography (HPLC). The absolute recoveries of cysteinyldopa and its diastereomer 5‐S‐D‐cysteinyl‐l‐dopa (used as an internal standard) were 81.5±2.8% and 81.3±2.7%, respectively, and use of the internal standard for the whole procedure gave an analytical recovery of 101±0.8%. The limit of quantitation was 1.5 nmol/L and the imprecision of the method was <5.0% over the analytical range 1.5–500 nmol/L. The method is cheap and easy to perform and compares well with other described techniques. The use of the method is illustrated by results obtained during treatment of a patient with metastatic malignant melanoma.

• Boronate affinity gel
• 5‐S‐D‐cysteinyl‐l‐dopa
• 5‐S‐L‐cysteinyl‐l‐dopa
• high‐performance liquid chromatography