3. Results and discussion
3.1. Correlation between DART-MS and HPLC-ELSD
As DART-MS is an analysis method without chromatographic separation, the selectivity should be investigated. The product ion spectra of GA standard substance and the loading solution were obtained by DART-MS with Product Ion Scan mode taking m/z 426 as the precursor ion. The similarity between these two spectra showed an evidence of the selectivity. Correspondingly, similar product ion spectra were also obtained from GB standard sub- stance and the loading solution, taking m/z 442 as the precursor ion.
On the other hand, ionization matrix effect is considered as one of the major drawbacks of DART-MS technique [8,15], and sample dilution is a frequently used method for reducing matrix effect. In this research, it was found that the DART-MS response intensity of the effluent sample was much lower than the standard substance solution. Therefore, the commonly used quantitation method based on calibration curve was not applied. However, in the loading pro- cess, only a very small part of the substances was adsorbed from the loading solution onto the adsorbent. Therefore, the matrixes of the loading solution and the effluent samples were nearly the same, which means the extents of ionization suppression were nearly the same. Based on the discussion above, Equation 1 was used to cal- culate the concentrations of ginkgolides and the matrix effect was negligible in this study.
3. Results and discussion3.1. Correlation between DART-MS and HPLC-ELSD As DART-MS is an analysis method without chromatographic separation, the selectivity should be investigated. The product ion spectra of GA standard substance and the loading solution were obtained by DART-MS with Product Ion Scan mode taking m/z 426 as the precursor ion. The similarity between these two spectra showed an evidence of the selectivity. Correspondingly, similar product ion spectra were also obtained from GB standard sub- stance and the loading solution, taking m/z 442 as the precursor ion.On the other hand, ionization matrix effect is considered as one of the major drawbacks of DART-MS technique [8,15], and sample dilution is a frequently used method for reducing matrix effect. In this research, it was found that the DART-MS response intensity of the effluent sample was much lower than the standard substance solution. Therefore, the commonly used quantitation method based on calibration curve was not applied. However, in the loading pro- cess, only a very small part of the substances was adsorbed from the loading solution onto the adsorbent. Therefore, the matrixes of the loading solution and the effluent samples were nearly the same, which means the extents of ionization suppression were nearly the same. Based on the discussion above, Equation 1 was used to cal- culate the concentrations of ginkgolides and the matrix effect was negligible in this study.
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