Acetonitrile

Ultra-pure water and LC–MS grade solvents were used for protein digestion and MS experiments. De-staining buffer: 100 mM NH₄HCO₃ (Merck, Darmstadt, Germany), acetonitrile (Merck, Darmstadt, Germany), 1:1 v/v; reduction buffer: 10 mM dithiothreitol (Sigma-Aldrich, Saint Louis, USA) in 100 mM NH₄HCO₃ (Merck, Darmstadt, Germany), alkylation buffer: 55 mM iodoacetamide (Sigma-Aldrich, Saint Louis, USA) in 100 mM NH₄HCO₃ (Merck, Darmstadt, Germany), trypsin solution: 13 ng/μL trypsin (Promega, Madison, WI, USA) in 10 mM NH₄HCO₃ (Merck, Darmstadt, Germany) containing 10% (v/v) acetonitrile (Merck, Darmstadt, Germany); Pierce C18 pipette tips (Thermo-Scientific, Waltham, USA), elution buffer: 10 mg/mL of α-cyano-4-hydroxycinnamic acid (Bruker, Billerica, MA, USA) in acetonitrile: 0.1% TFA (Merck, Darmstadt, Germany) in H₂O 7:3 v/v.

All solutions were prepared using water from an Arium water purification system (resistivity > 18 MΩ cm, Sartorius, Göttingen, Germany). LC-MS grade chemicals were employed for analysis, namely acetonitrile (Merck, Darmstadt, Germany), formic acid (Merck, Darmstadt, Germany), and ammonium bicarbonate (Fluka, Buchs, Switzerland). Mixtures of acetonitrile, water, and aqueous ammonium bicarbonate (pH 7.4; 100 mM) were used to prepare the mobile phase, being filtered through 0.45 μm Millipore (Billerica, MA) HVHP filters and degassed for 15 min in an ultrasonic bath prior to use.
High purity (≥99%) analytical standards of tranexamic acid (TXA, Scheme 1) and the corresponding isotopically labeled internal standard ¹³C₂,¹⁵N,trans-tranexamic acid (TXA-IS) were supplied by Toronto Research Chemicals (Toronto, Canada). Individual stock solutions of TXA and IS were prepared on a weight basis in water at a concentration of 1 mg mL⁻¹ and stored at −20 °C. A working standard solution of TXA was prepared in water at 10 µg mL⁻¹ to perform ionization studies. For quantification assays, working standard solutions of TXA (30, 60, 90, 150, 300, 450, 600 ng mL⁻¹) were prepared in mobile phase by dilution of appropriate amounts of intermediate solutions at 20 and 1.5 μg mL⁻¹. The internal standard TXA-IS was added at a final concentration of 300 ng mL⁻¹.

The preparation of 50% acetonitrile was done by diluting 5 mL of 100% acetonitrile (Merck, Germany) stock solution with 5 mL of HPLC grade water then 0.1% TFA was prepared by diluting 10% TFA stock solution (Merck, Germany) with 49.5 mL of HPLC grade water (Merck, Germany). Finally, elution buffer, 75% ACN / 0.1% TFA was prepared by adding 7.5 mL of 100% acetonitrile stock solution, 0.1 mL of 10% TFA stock solution and 2.4 mL of HPLC grade water. Oasis columns were placed in 15 mL tube, 1 mL of 50% ACN was added and let it flow, 1 mL of 0.1% TFA was added to equilibrate column, let it flow. The equilibration step was repeated 3 times. The protein samples were added into column and slowly let it flow by gravity. Then 1 mL of 0.1% TFA was added and let it flow. Then, oasis columns were taken and placed in the new clean 15 mL tubes, peptide was eluted by adding 1 mL elution buffer, 75% ACN / 0.1% TFA, let it flow by gravity. The samples were taken to evaporate at speed vacumm centrifuge cincentrator machine (Meditop, Thailand), then kept samples in − 80 °C until further analysis.

The solvent used for VOCs standard solutions was methanol (Fisher Chemical, Loughborough, UK, 99.99%), and the highest quality possible of pure compounds were used: benzene (Sigma-Aldrich, MO, USA, >99.9%), toluene (Sigma-Aldrich, WI, USA, 99.5%), styrene (Sigma-Aldrich, MO, USA >99%), naphthalene (Sigma-Aldrich, MO, USA, 99.9%), furfural (Fluka, Switzerland, >99%), furan (Aldrich, MO, USA, ≥99%), isoprene (Aldrich, MO, USA, 99%), 2-butenal (Aldrich, MO, USA, ≥99.5%), phenol (Sigma-Aldrich, Switzerland, 99%), 2-furyl methyl ketone (Aldrich, MO, USA, 99%). The solvent used for aldehydes with low molecular weight solutions was acetonitrile (Sigma-Aldrich, MO, USA, 99.9%), and the derivatives compounds of 2,4-DNPH were: formaldehyde-2,4-DNPH (Supelco, PA, USA, 99.9%), acetaldehyde-2,4-DNPH (Supelco, PA, USA, 99.9%), and acrolein-2,4-DNPH (solution in acetonitrile, Aldrich, PA, USA, 99.9%).

Isophthalic acid, benzoic acid, L-alanine, 1,3-phenylene diisothiocyanate, phenyl isothiocyanate, acetonitrile for reaction, and acetonitrile for spectroscopy were purchased from Sigma Aldrich Co. and used directly without purification. acetonitrile-D₃ and dimethyl sulfoxide-D₆ were purchased from Cambridge Isotope Laboratories Inc. All other starting materials were obtained from Sinopharm Chemical Reagent Ltd.