A high-performance liquid chromatography coupled with tandem mass spectrometry method for determination of ascorbic acid and its isomer, erythorbic acid was developed. The separation was performed on Aminex HPX-87H column using isocratic elution with 0,1 % formic acid in water. Quantification was done using ESI ionization in negative mode with m/z 174,9 as a precursor ion and m/z 115 as a product ion for both acids. In order to avoid false positive results, the product ion m/z 87 was also recorded at each measurement and was used as a confirmation. The stability of standards, linearity, limits of detection and instrument repeatability were studied. The standards were found to degrade very quickly at room temperature. Because of that, TCEP was used as a reducing agent. The linear range was from the limit of detection to 2000 ppb while the limits of detection were 69 ppb and 61 ppb for ascorbic and erythorbic acid, respectively. RSD of measurements was below 10 %. The studied parameters were within the acceptable ranges which lead to the reliable determination of ascorbic and erythorbic acid. The method was evaluated on different real samples: effervescent and ordinary tablets and on juices. The results for tablets deviated from the value on the label by a maximum of ±10 %. The tablets were found to be homogeneous with good homogeneity both within and between tablets. The concentration of erythorbic acid was below the limit of detection in all the analyzed samples which is very important due to its low activity compared to ascorbic acid.
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