Semi quantitative detection of signature peptides in body fluids by liquid chromatography tandem mass spectrometry (LC–MS/MS)

This study covers a modified semi-quantitative approach to detecting signature peptides for body fluid identification. A liquid chromatography tandem mass spectrometer normally used for toxicology was adapted to detect target ion transitions for five semen or saliva specific peptides. Peptide concentrations were measured based on a mixture of synthetic peptide standards. Samples were processed using a three-hour trypsin digestion and Microcon membrane filtration. This method generates PCR compatible DNA and peptide fractions that can be typed without any further treatment. Preliminary validation tests covered stains on different substrates, semen/saliva mixtures, limit of detection, and repeatability. All signature peptides were present at different concentrations, varied amongst donors, and were tissue specific. Saliva peptides were detected at lower concentrations and had a higher limit of detection (LOD). Semen peptides had higher concentrations and were detected even as a minor component in a mixture. All semen peptides and all, but one, saliva peptides were detected on the various substrates. Semen peptide concentrations had relative standard deviations (RSDs) lower than 20%, indicating high repeatability, different from saliva where higher RSDs were observed. DNA fractions did not show signs of degradation or PCR inhibition.