3. Results and discussion
3.1. Stability of AA in meta-phosphoric acid
The results of our study show that the stability of AA in juice samples using 2.5% meta-phosphoric acid (final concentration of meta-phosphoric acid was 1.25%) was significantly less than with 10% meta-phosphoric acid (meta-phosphoric acid final concentration of 5%). The concentration of AA in juice samples (n = 6) decreased from 252.7 to 232.2 mg/L (8%) in 1 h. In the same time, the concentration of AA in tablet samples dissolved in 2.5% meta-phosphoric acid (n = 6) decreased from 62.5 to 46.5 mg/tablet (26%). Juice or tablet samples dissolved in 10% meta-phosphoric acid were more stable. However, after 24 h, at least 97.3% of AA was still present in juice or tablet samples. Based on these results, 10% meta-phosphoric acid was used for sample preparations (final concentration of meta-phosphoric acid was 5% or 10% for juices and tablets, respectively).
3.2. Analytical characteristics
In this paper, HPLC and UPLC methods for vitamin C determination were compared. AA and DTT were eluted from an HPLC system in 4.01 and 13.06 min, respectively. Using UPLC system, retention times of AA and DTT were 1.56 and 3.30 min, respectively (Fig. 1). Using UPLC method, the total time of analysis was 2.5 times shorter than with HPLC and solvent consumption decreased from 12 to 1.2 mL/min.
3. Results and discussion
3.1. Stability of AA in meta-phosphoric acid
The results of our study show that the stability of AA in juice samples using 2.5% meta-phosphoric acid (final concentration of meta-phosphoric acid was 1.25%) was significantly less than with 10% meta-phosphoric acid (meta-phosphoric acid final concentration of 5%). The concentration of AA in juice samples (n = 6) decreased from 252.7 to 232.2 mg/L (8%) in 1 h. In the same time, the concentration of AA in tablet samples dissolved in 2.5% meta-phosphoric acid (n = 6) decreased from 62.5 to 46.5 mg/tablet (26%). Juice or tablet samples dissolved in 10% meta-phosphoric acid were more stable. However, after 24 h, at least 97.3% of AA was still present in juice or tablet samples. Based on these results, 10% meta-phosphoric acid was used for sample preparations (final concentration of meta-phosphoric acid was 5% or 10% for juices and tablets, respectively).
3.2. Analytical characteristics
In this paper, HPLC and UPLC methods for vitamin C determination were compared. AA and DTT were eluted from an HPLC system in 4.01 and 13.06 min, respectively. Using UPLC system, retention times of AA and DTT were 1.56 and 3.30 min, respectively (Fig. 1). Using UPLC method, the total time of analysis was 2.5 times shorter than with HPLC and solvent consumption decreased from 12 to 1.2 mL/min.
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