2.7 HPLC analysis
The above-mentioned supernatants were thawed at room temperature. After proper dilution, the filtered samples were analyzed on an Agilent 1260 HPLC system (Agilent Technologies, The Netherlands), using an Agilent TC-C18 column (150 mm x 4.6 mm; Agilent Technologies), maintaining at 25 °C with UV detection at 238 nm. The flow rate was 0.8 mL/min using 1% HPLC grade methanol (pH adjusted to 2 with phosphoric acid) as the mobile phase. The injection volume was 10 μL. The AA-2G concentration was calculated on the basis of peak area of the standard samples.