Date of Award

Summer 8-2023

Document Type


Degree Name

Master of Science (MS)


Forensic Science



First Advisor or Mentor

Marta Concheiro-Guisan

Second Reader

Mechthild Prinz

Third Advisor

Ana de Castro


Oral fluid is a biological sample of increasing interest in clinical and forensic toxicology. This matrix is easy to obtain, it shows a low biohazard risk, and it reflects recent drug exposure. However, the interpretation of its quantitative values is limited, due to the high inter- and intraindividual variability. The investigation of normalization factors in this biological matrix may improve the interpretation value of oral fluid. This study investigated the potential of two signature peptides from the submaxillary gland androgen-regulated protein 3B (SMR3B) as normalization factors in oral fluid. SMR3B was digested in trypsin and the signature peptides SMR3B-1 and 2 were determined by liquid chromatography tandem mass spectrometry (LC-MSMS). To quantify, an isotope-labeled synthetic peptide (SMR3B-2iso) was acquired and optimized in the LC-MSMS. SMR3B-1 quantifier MRM transition was m/z 1034.8>614.9, for SMR3B-2 was m/z 711.0>614.4, and for SMR3B-2iso was m/z 713.4>438.3. The LC-MSMS method linearity for SMR3B-1 and 2 was from 0.5 to 50 nmol/mL. SMR3B-2iso had a process efficiency of 76.1% with a CV of 17.6% across 10 distinct oral fluid sources. The method was applied to 107 samples from 18 authentic oral fluid donors. SMR3B-1 and 2 were detected in about 50% of the samples, with concentrations between 0.5-22.4 nmol/mL. No differences were observed due to gender nor age. Statistical significance (p<0.05) was observed in peptide concentrations between time-of-day sampling (morning and evening). Due to the scarcity of these peptides in oral fluid, they are not good candidates for normalization factors.

Available for download on Thursday, August 14, 2025