Sm. Wilbert et al., Quantitative analysis of a synthetic peptide, NR58-3.14.3, in serum by LC-MS with inclusion of a diastereomer as internal standard, ANALYT BIOC, 278(1), 2000, pp. 14-21
A method for quantifying an intramolecularly linked all-D-amino acid peptid
e, NR58-3.14.3, in rat serum by LC-MS using selected ion monitoring with in
clusion of a diastereomer as internal standard was developed. The reproduci
ble quantitation of multiply charged compounds by LC-MS using single ion or
selective reaction monitoring is often a challenge as the intensity ratio
of the ions in a series of different charge states can vary. Good precision
was obtained in the selected ion monitoring mode by integrating the summed
ion currents of the singly, doubly, and triply charged molecular ions. Sin
ce stable isotope analogs are costly and integration of residual unlabeled
material can be of concern, a diastereomer of NR58-3.14.3, NR58-3.14.5, was
used as internal standard. The diastereomers mere indistinguishable by ele
ctrospray MS, but fully separated by reversed-phase LC. Consequently, inter
ference due to isotopic impurities or coelution was not encountered. The ca
libration plot was linear throughout a concentration range of 0.2 to 200.0
mu g/ml (r(2) = 0.9996). Intraday precision of the standards analyzed was l
ess than 12% RSD over the calibration range and the accuracy within +/-11%
RE. Serum pharmacokinetics were in good agreement with the pharmacokinetic
profiles of small, ionic, and polar molecules. (C) 2000 Academic Press.