Ag11 hc 4mm guard column

Citrate concentration was analysed by ion chromatography (IC) with suppressed conductivity detection (ICS-5000+ ion chromatographic system; AS-AP autosampler; ATC-3 trap column installed between pump and injection valve; IonPac 4x250 mm AS11-HC ion-exchange analytical column coupled with a AG11-HC 4mm guard column; anion self-regenerating suppressor ASRS 300 (4mm) in auto suppression recycle mode; Dionex, Thermo Fischer Scientific, USA). Ten µL sample was injected. Separation was performed with NaOH in laboratory grade I water as eluent, with a flow rate of 1.5 mL min -1 and constant temperature of 30°C, with the following gradient: E1 (NaOH 1mM) and E2 (NaOH 60mM); 0-15 min 20% E1 80% H2O, 15-25 min 15% E2 85% H2O, 25-35 min 30% E2 70% H2O, 35-45 min 60% E2 40% H2O. An external standard of citrate (Sigma Aldrich, citric acid, ACS reagent, ≥ 99.5%) was used for identification (retention time) and quantification after the construction of a calibration curve (R 2 =0.99). Seven standards with the following concentrations were used: 2.60. 5.20, 26, 52, 130, 260, 520 µmol L -1 . Limit of quantification was 0.014 µmol L -1 .