Quantitative analysis of [Dmt1]DALDA in ovine plasma by capillary liquid chromatography-nanospray ion-trap mass spectrometry

The synthetic opioid peptide analog Dmt-D-Arg-Phe-Lys-NH2 ([Dmt1]DALDA; Dmt=2′,6′-dimethyltyrosine) is a highly potent and selective mu opioid-receptor agonist. A very sensitive and robust capillary liquid chromatography/nanospray ion-trap (IT) mass spectrometry method has been developed to quantify [Dmt1]DALDA in ovine plasma, using deuterated [Dmt1]DALDA as the internal standard. The standard MS/MS spectra of d0- and d5-[Dmt1]DALDA were obtained, and the collision energy was experimentally optimized to 25%. The product ion [M+2H-NH3]2+ (m/z 312.2) was used to identify and to quantify the synthetic opioid peptide analog in ovine plasma samples. The MS/MS detection sensitivity for [Dmt1]DALDA was 625 amol. A calibration curve was constructed, and quantitative analysis was performed on a series of ovine plasma samples.