Agilent lc msd tof mass spectrometer

All data were acquired and reference mass corrected via a dual-spray ESI source in positive mode. Spectra were generated using an electrospray ionization source on an Agilent LC/MSD-TOF mass spectrometer coupled to an Agilent 1100 LC system (Agilent, Palo Alto, CA). Mass spectrometry was performed on a sample prepared in water with direct sample injection in acetonitrile in water containing 0.04 % (v/v) formic acid according to the manufacturer's instructions. Raw spectra were deconvoluted using MASSHUNTER software (Agilent, Palo Alto, CA).

Because of the detection limit of 500 Da for the MS/MS method, the UF fractions with MW <1,000 Da from different aged cheeses were also subjected to HPLC-electrospray ionization (ESI)-time-of-flight (TOF)-MS to help identify these peptides (Martin et al., 2008) . Peptides in the fractions of MW <1,000 Da were identified based on theoretical molar mass of the selected peptides, the detected mass, and elemental composition analysis.
The fractions of MW <1,000 Da were subjected to HPLC-ESI-TOF MS using a Vydac-C 8 column (3 μm, 2.1 × 250 mm) on an Agilent 1200 HPLC connected to an Agilent LC/MSD TOF mass spectrometer (Agilent) with electrospray ionization in positive ion mode. Forty microliters of each fraction was injected. A linear gradient elution was performed at a flow rate of 0.25 mL/min with 98% DI water, 2% acetonitrile, and 0.1% formic acid to 90% acetonitrile, 10% DI water, and 0.1% formic acid over 25 min. The lists of peptide masses were generated in Agilent MassHunter Qualitative Analysis using the Find Compound by Molecular Feature. Features were restricted to m/z 200 to 3,000 with no charge state limitation over the retention time of 3.1 to 15.5 min when peaks were eluted by the gradient. Peptides were identified by mass and elemental composition analysis.