Quantification of NC100668, a new tracer for imaging of venous thromboembolism, in human plasma using reversed-phase liquid chromatography coupled with electrospray ionization ion-trap mass spectrometry.

NC100668 is being developed as a new tracer for radiopharmaceutical imaging of venous thromboembolism. NC100668 consists of a targeting peptide of 13 amino acids with a (99m)Tc-binding chelator linked to the C-terminal amino acid. The present report describes a method for quantification of NC100668 in human citrated plasma. The method is based on solid-phase extraction followed by reversed-phase liquid chromatography using a gradient of water and acetonitrile with 0.1% formic acid. The chromatographic system was coupled on-line with an electrospray mass spectrometer. The analyses were performed by selective ion monitoring of the [M+2H]2+ and the [M+3H]3+ ions of NC100668 and an internal standard which was identical to NC100668 except for not being iodinated in the tyrosine residue. The limit of quantification of the method was 2ng NC100668/ml plasma. The calibration curve ranged from 2 to 250 ng NC100668/ml plasma and was fitted to a linear equation with a weighing factor of 1/y2 and found to be highly reproducible. The total precision of the method, expressed as the relative standard error of the mean, was 23.2, 8.8 and 14.7% for the low, medium and high control samples, respectively. The accuracy of the method was 108.5, 100.0 and 105.0% for the low, medium and high control samples, respectively. NC100668 was stable in human plasma during at least three freeze/thaw cycles, during 30 h on dry ice and up to 3 months when stored in a -20 degrees C freezer.