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 99mTc-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 2 ng 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 °C freezer.