Improved method for plasma ADMA, SDMA, and arginine quantification by field-amplified sample injection capillary...

Here, we describe an easy field-amplified sample injection capillary electrophoresis method with UV detection for the separation and detection of free plasma arginine and dimethylated arginines. The analytes were baseline-separated within 22 min by using 50 mmol/L Tris phosphate pH 2.3 as running buffer. The plasma samples were treated with acetonitrile/ammonia for protein elimination, the supernatants were dried, re-swollen in water and directly injected in the capillary without complex cleanup by solid phase extraction and/or tedious sample derivatization procedures. Due to the stacking effects of the electrokinetic injection, it was possible to operate a consistent on-line pre-concentration of the analytes before running the electrophoresis. This procedure allowed to reach a detection limit in the real sample of 10 nmol/L for dimethylated arginines and 20 nmol/L for arginine, thus improving about threefold our previous method, that required a more complicated pre-analytical procedure to concentrate samples. The recovery of plasma ADMA was 99-104% and inter-day CV was less than 3%. The assay performance was evaluated measuring the levels of arginine and its dimethyl derivatives in 50 subjects. The statistical tests for the methods comparison suggest that the data obtained by our new method and by our previous CE assay are similar.