Patent ID: 7537704

Claim:
A method for determining the concentration of asymmetric dimethylarginine (ADMA) simultaneously with arginine and symmetric dimethylarginine (SDMA) in biological samples by using HPLC-MS-MS, comprising the steps of preparing a sample including only addition of a solution of isotope-marked internal standards ( 13 C 6 -arginine and D 6 -ADMA) and addition of a mixture of acetonitrile/propionic acid/trifluoroacetic acid for precipitation of high-molecular proteins, whereby quantity and composition are realized by adjusting the sample composition to the composition of the mobile phase in the HPLC separation, without requiring derivatization or extraction of the analytes, separating chromatographically the analytes occurring on a silica normal phase HPLC column by using a mobile phase of water/acetonitrile/propionic acid/trifluoroacetic acid, wherein the volume ratio of water to acetonitril is from about 2 to 98 to 30 to 70, the volume fraction of trifluoroacetic acid is about 0.01 to 0.5, the volume fraction of propionic acid is about 10 to 100 times higher than that of trifluoroacetic acid, and the optimized composition of the mobile phase is composed of water/acetonitrile/propionic acid/trifluoroacetic acid with about 10/90/1/0.025 parts per volume, and the detection and quantification occurs by a tandem mass spectrometry, wherein the fragmentation is about 175.2 m/z→70.1 m/z for arginine, about 181.2 m/z→74.1 m/z for 13 C 6 -arginine, about 203.2 m/z→172.1 m/z for SDMA, about 203.2 m/z→46.1 m/z for ADMA, and about 209.2 m/z→70.1 m/z for D 6 -ADMA.