5975c ms system

GC-MS was performed on an Agilent 7890A gas chromatograph with a 5975 C MS system. An HP-5 (25-m by 320-μm by 0.25-μm-inside-diameter [i.d.]) fused silica capillary column (Agilent J&W Scientific, Folsom, CA) was used with the open split interface. The injector, transfer line, and ion source temperatures were maintained at 220, 220, and 250°C, respectively. Oven temperature was programmed at 70°C for 0.2 min and increased at 10°C/min to 270°C, where it was sustained for 5 min, and further increased at 40°C/min to 310°C, where it was held for 11 min. The MS was operated in the electron impact ionization mode at 70 eV. Mass data were acquired in full scan mode from m/z 40 to 600 with an acquisition rate of 20 spectra per second. To detect retention time shifts and enable Kovats retention index (RI) calculation, a standard alkane series mixture (C₁₀ to C₄₀) was injected periodically during the sample analysis. RIs are relative retention times normalized to n-alkanes eluted adjacently. The injector port temperature was held at 250°C, and the helium gas flow rate was set to 1 ml/min at an initial oven temperature of 50°C. The oven temperature was increased at 10°C/min to 310°C for 11 min, and mass data were acquired in full scan mode from m/z 40 to 600 with an acquisition rate of 20 spectra per second.

General parameters (glucose, ethanol, glycerol, acetic acid, malic acid, lactic acid, and succinic acid) were determined by high-performance liquid chromatography (HPLC, 1200 series, Agilent Technologies, Inc., Palo Alto, CA, United States) as described by Duan et al. (2015) . The system was equipped with an HPX-87H Aminex ion-exchange column (300 mm × 7.8 mm, Bio-Rad Laboratories, Hercules, CA, United States) with 5 mM sulfuric acid as the mobile phase. The volatile compounds of the wines were determined by headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS) as previously described (Zhang et al., 2011 (link); Xu et al., 2015 (link)). An Agilent 6890A equipped with a 5975C MS system and an HP-INNOWAX column (60 m × 0.25 mm × 0.25 μm) was used in this system. The aroma compounds were identified by a comparison of the retention indices (RI) of reference standards and mass spectra that matched in the NIST 08 MS database. The quantification was applied with the calibration curves of aroma standards as described by Xu et al. (2015) (link). Analyses were performed in triplicate. Significant differences of metabolites among the treatments were identified using one-way analysis of variance (ANOVA) followed by Duncan’s test (p < 0.05) (SPSS 17.0, SPSS Inc., Chicago, IL, United States).