Quantification of Arginine and Dimethylated Arginines in Human Plasma by Field-Amplified Sample Injection Capillary Electrophoresis UV Detection

We report a capillary electrophoresis method by field-amplified sample injection (FASI) for the separation and detection of free plasma arginine and dimethylated arginines. Protein elimination from plasma was performed by acetonitrile/ammonia precipitation. Supernatants were dried, reswollen in water, and directly injected on capillary without complex cleanup by solid-phase extraction and/or tedious sample derivatization procedures. Analytes were baseline-separated within 22 min by using 50 mmol/L Tris phosphate pH 2.3 as running buffer. Due to the stacking effects of electrokinetic injection, it is possible to perform a considerable on-line preconcentration of the analytes before running the electrophoresis. This procedure allows to reach a detection limit in real sample of 10 nmol/L for dimethylated arginines and 20 nmol/L for arginine. Recovery of plasma ADMA was 99–104 % and inter-day CV was less than 3 %.