Urea free and more efficient sample preparation method for mass spectrometry based protein identification via combining the formic acid-assisted chemical cleavage and trypsin digestion

Pipette-tip solid-phase extraction coupled with matrix-assisted laser desorption/ionization mass spectrometry enables rapid and high-throughput analysis of antidepressants in rat serum

Therapeutic drug monitoring is essential for ensuring the efficacy and safety of medications. This study introduces a streamlined approach that combines pipette-tip solid-phase extraction (PT-SPE) with matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), facilitating rapid and high-throughput monitoring of drug concentrations. As a demonstration, this method was applied to the extraction and quantification of antidepressants in serum. Utilizing Zip-Tip C18, the method enabled the extraction of antidepressants from complex biological matrices in less than 2 min, with the subsequent MALDI-MS analysis yielding results in just 1 min. Optimal extraction recoveries were achieved using a sampling solution at pH 9.0 and a 10 μL ethanol desorption solution containing 0.1% phosphoric acid. For MALDI analysis, 2,5-dihydroxybenzoic acid was identified as the most effective matrix for producing the highest signal intensity. The quantification strategy exhibited robust linearities (R2 ≥ 0.997) and satisfactory limits of quantification, ranging from 0.05 to 0.5 μg/mL for a suite of antidepressants. The application for monitoring dynamic concentration changes of antidepressants in rat serum emphasized the method's efficacy. This strategy offers the advantages of high throughput, minimal sample usage, environmental sustainability, and simplicity, providing ideas and a reference basis for the subsequent development of methods for therapeutic drug monitoring.

Removal of Copper in Microdroplets by Ovomucoid Hydrolysates Bound to Reverse-Phase Chromatography Media Within Pipette Tips

Ovomucoid (OVM) is a protein found in chicken egg white. When it is hydrolyzed by a protease, subtilisin A from Bacillus licheniformis, it possesses Cu²⁺-chelating activity. In the present work, we demonstrate that the resulting OVM hydrolysates bind to reverse-phase chromatography media in pipette tips and can be applied to remove Cu²⁺ within microdroplets. 1.4 nmol of purified OVM was digested in the presence of 17 pmol of subtilisin A at 55 °C for 3 h. The OVM hydrolysates efficiently removed 2.1 and 2.4 nmol of Cu²⁺ in the droplets by binding to the C4 and C18 chromatography media, respectively. Conversely, 0.6 and 1.0 nmol of Cu²⁺ were removed by the non-digested OVM bound to the C4 and C18 media, respectively. The removal ratio of Cu²⁺ increased as more OVM was digested by subtilisin A. The digested OVM polypeptides were stained with Cu²⁺ after they were separated by non-denaturing electrophoresis. These results indicate that OVM hydrolysates bound to chromatography media in a pipette tip can be applied to remove Cu²⁺ within microdroplets of biological samples.

Optimization of carbamylation conditions and study on the effects on the product ions of carbamylation and dual modification of the peptide by Q-TOF MS

Modified peptides fragmented by collision-induced dissociation can offer additional sequence information, which is beneficial for the de novo sequencing of peptides. Here, the model peptide VQGESNDLK was carbamylated. The optimal conditions were as follows: temperature of 90℃, pH of 7, and the time of 60 min. Then, we studied the b- and y-series ions of the native, carbamylated, and dual-modified peptides. The results were as follows. The short carbamylated peptides (≤10 amino acid residues) produced more b-series ions (including b₁ ion). The long carbamylated peptides (>10 amino acid residues) produced additional b₁ ion but fewer y-series ions (especially in the high-mass region). The short dual-modified peptides produced more b-series ions (including b₁ ion) and more y-series ions, and their peptide sequence coverage was almost 100%. The long dual-modified peptides produce b₁ ion and more y-series ions, and their peptide sequence coverage was nearly above 90%. Therefore, both carbamylation and the dual modification method could be used to identify the N-terminal amino acid, and the dual modification method was also excellent for the de novo sequencing of the tryptic peptides.