Direct analysis of un-derivatized asymmetric dimethylarginine (ADMA) and l-arginine from plasma using mixed-mode ion-exchange liquid chromatography–tandem mass spectrometry

A high-throughput analytical method was developed for the measurement of asymmetric dimethylarginine (ADMA) and l-arginine (ARG) from plasma using LC/MS/MS. The sample preparation was simple and only required microfiltration prior to analysis. ADMA and ARG were assayed using mixed-mode ion-exchange chromatography which allowed for the retention of the un-derivatized compounds. The need for chromatographic separation of ADMA from symmetric dimethylarginine (SDMA) was avoided by using an ADMA specific product ion. As a result, the analytical method only required a total run time of 2 min. The method was validated by linearity, with r2 ≥ 0.995 for both compounds, and accuracy, with no more than 7% deviation from the theoretical value. The estimated limit of detection and limit of quantification were suitable for clinical evaluations. The mean values of plasma ADMA and ARG taken from healthy volunteers (n = 15) were 0.66 ± 0.12 and 87 ± 35 μM, respectively; the mean molar ratio of ARG to ADMA was 142 ± 81.