An improved method for the determination of S-Carboxymethyl-L-cysteine in biological fluids with precolumn derivatization and on-line clean-up

In order to follow levels of S-Carboxymethyl-L-cysteine in biological fluids for a period as long as three half-lives after drug administration during pharmacokinetic studies, an improved method for its determination had to be developed. Like the previous one, this method uses a protein precipitation step followed by an O-Phthalaldehyde derivatization step and then an HPLC on-line clean-up. This latter was obtained by means of a switching valve system, including a Nucleosil CN 5 μm (3 cm × 4.6 mm i.d.) precolumn and a Spherisorb ODS 5 μm (15 cm×4.6 mm i.d.) analytical column. The sensitivity limit was improved to 0.1 μg/ml in plasma samples and 0.2 μg/ml in urine samples.