Filtration membranes 0.22 μm

Myoglobin from equine skeletal muscle (95–100% purity, lyophilized powder), N-acetyl-D-glucosamine (≥99% purity), D-glucose (≥99.5% purity), D-glucosamine hydrochloride (≥99% purity), potassium phosphate monobasic and dibasic, sodium azide, HPLC-grade solvents (acetonitrile, methanol, formic acid, trifluoroacetic acid), glucosone (2-keto-D-glucose; ≥98.0% purity; M_W 178.14 Da), glyoxal (ethanedial; 40% in H₂O; M_W 58.04 Da), methylglyoxal (2-oxopropanal; 40% in H₂O; M_W 72.06 Da), diacetyl (butane-2,3-dione; ≥95.0% purity; M_W 86.09 Da), 1,2-diaminobenzene, DTPA and Thioflavin T were purchased from Sigma-Aldrich (St. Louis, MO). 3-deoxyglucosone (3-Deoxy-D-erythro-hexosulose; ≥95% purity; M_W 162.14 Da) was obtained from Cayman Chemical (Ann Arbor, MI). SPE tC-18 Sep-Pak Vac 6 cc columns were obtained from Waters (Milford, MA). Filtration membranes (0.22 μm) were from Millipore (Billerica, MA). 3,5 dimethoxy-4-hydroxycinnamic acid (sinapinic acid), ProMix3 (mass spectrometry protein standards) were obtained from LaserBiolabs. Standard ion calibration solution (Pierce LTQ) for electrospray ionization in positive mode was purchased from Thermo Scientific (Rockford, IL, USA). Milli-Q purified distilled water for buffers and reagents preparations were purchased from Waters Millipore (Milford, MA, USA). All the reagents and chemicals used in the study were of analytical grade.