Fast and Precise Quantification of L-Homoarginine in Human Plasma by HILIC-Isotope Dilution-MS-MS

Lowered plasma concentrations of the endogenous amino acid l-homoarginine have been recently identified as an independent risk factor for cardiovascular and all-cause mortality in patients referred for coronary angiography in the LURIC study. To support further investigations into this matter, we describe here a fast and easy LC-MS-MS method for the detection of l-homoarginine in human plasma. The sample preparation consisted only of the addition of the stable isotope-labeled internal standard d (4)-l-homoarginine and protein precipitation. The analytes were separated isocratically on an HILIC silica column. Detection took place by tandem mass spectrometry. The calibration function was linear in the range of 0.1-10 mu mol L-1. The intra-day precision was better than 2 % RSD and the inter-day precision better than 4 % RSD in plasma. The accuracy was always better than 5 % deviation. The method was matrix independent owing to the usage of the analogous stable isotope-labeled internal standard.