HPLC determinations of enantiomeric ratios

[Determination of gypenoside XLVI and LVI in Gynostemma pentaphyllum from Fujian by ultra-high performance liquid chromatography-charged aerosol detector]

Gynostemma pentaphyllum (Thunb.) Makino contains dammarane-type triterpenoid saponins, similar to ginseng, with a host of pharmacological activities. However, its planting resources and chemical composition are quite complex. The chemical constituents of Gynostemma pentaphyllum vary drastically among different origins and varieties. Thus, the corresponding quality control methods also need to be different. Currently, limited information is available about the quality control of Gynostemma pentaphyllum from Fujian. A new method based on ultra-high performance liquid chromatography-charged aerosol detection (UHPLC-CAD) was established for the determination of gypenoside XLVI and LVI in Gynostemma pentaphyllum. The major components of Gynostemma pentaphyllum were characterized using UHPLC-quadrupole time-of-flight-mass spectrometry (UHPLC-Q-TOF/MS) combined with UHPLC-CAD. The results revealed gypenoside XLVI, LVI, and their corresponding malonyl-containing acidic saponins as the main components. However, malonylgypenoside XLVI and LVI can easily remove their malonyl group and convert to gypenoside XLVI and LVI during the application of Gynostemma pentaphyllum. In this study, the samples were pretreated using alkali hydrolysis to transform the acid saponins completely, and the final contents of gypenoside XLVI and LVI were determined via UHPLC-CAD. The optimal alkaline hydrolysis, extraction, and liquid chromatography conditions were established. First, the alkaline hydrolysis conditions were optimized. The effects of the volume of ammonia and reaction time on the contents of gypenoside XLVI, LVI, malonylgypenoside XLVI, and LVI were examined. Malonylgypenoside XLVI and LVI could be transformed completely to gypenoside XLVI and LVI by standing for 24 h in an ethanol-water-ammonia (50∶46∶4, v/v/v) mixture. Furthermore, the extraction conditions were optimized. Next, effects of the different solvents, extraction time, and solid-liquid ratio on the extraction rates of gypenoside XLVI and LVI were investigated. The extraction method for Gynostemma pentaphyllum powder using the ethanol-water-ammonia (50∶46∶4, v/v/v) and a solid-liquid ratio of 1∶150 (g∶mL) for 30 min was established. Finally, a prepared test solution was separated on a Waters ACQUITY UPLC BEH C18 chromatographic column (100 mm×2.1 mm, 1.7 μm). Acetonitrile and 0.1% (v/v) formic acid aqueous solution were used as the mobile phases for gradient elution. The flow rate was set to 0.5 mL/min and column temperature was maintained at 40 ℃. The separation was detected using a charged aerosol detector. Results indicated that the logarithm of the mass concentrations of gypenoside XLVI and LVI had a linear relationship with the logarithm of the peak area in the range of 9.94-318.00 μg/mL and 12.78-409.00 μg/mL, respectively. The correlation coefficients (r) were 0.9993 and 0.9995, respectively. The limit of detection (LOD) and the limit of quantification (LOQ) of gypenoside XLVI were 1.58 μg/mL and 6.36 μg/mL, respectively. The LOD and LOQ of gypenoside LVI were 2.05 μg/mL and 8.18 μg/mL, respectively. The relative standard deviations (RSDs) of precision, repeatability, and 24 h stability were less than 2.0% (n=6). The spiked recoveries of gypenoside XLVI were 100.2%-107.2% and the RSD value was 2.4%. The spiked recoveries of gypenoside LVI were 97.9%-104.2% and the RSD value was 2.6%. The results of 16 batches of Gynostemma pentaphyllum samples indicated that the gypenoside XLVI content was 0.57%-2.57%, and gypenoside LVI content was 0.66%-2.99%. Hence, this method has high sensitivity and good reproducibility. Therefore, it can be used for quality research and quality control of Gynostemma pentaphyllum from Fujian.

Automated solubility and crystallization analysis of non-UV active compounds: integration of evaporative light scattering detection (ELSD) and robotic sampling

The integration of high-performance liquid chromatography-evaporative light scattering detection with robotic sampling allows for the acquisition of reliable and data-rich solubility and crystallization profiles of minimally- or non-UV active compounds in an automated manner.

Review of operating principle and applications of the charged aerosol detector

Recently a new detection method, based upon aerosol charging (the charged aerosol detector (CAD)) has been introduced as an alternative to evaporative light-scattering detector (ELSD), chemiluminescent nitrogen detector and refractive index detector for detection of non-ultraviolet and weakly ultraviolet active compounds and for UV-absorbing compounds in the absence of standards. The content of this review article includes description of operation principle, advantages and disadvantages of CAD system, and short reports of selected applications of this detector. The main advantages of CAD detector are unique performance characteristics: better sensitivity than ELSD system, a dynamic range of up to 4 orders of magnitude, ease of use and constancy of response factors. Both detectors are mass dependent and the response generated does not depend on the spectral or physicochemical properties of the analyte. This attractive feature of a detection technique generating universal response factors is the potential use of a single, universal standard for calibration against which all other compounds or impurities can be qualified. CAD also has the same limitation as ELSD, namely, the response is affected by mobile-phase composition. This problem has been resolved by using inverse gradient compensation as is done for high pressure liquid chromatography and supercritical fluid chromatography. CAD has been applied for the analysis of structurally diverse compounds used in the pharmaceutical, chemical, food, and consumer products industries and in life science research. They include nonvolatile and semivolatile neutral, acidic, basic, and zwitterionic compounds, both polar and nonpolar (e.g. lipids, proteins, steroids, polymers, carbohydrates, peptides).

Comparison of ultraviolet detection, evaporative light scattering detection and charged aerosol detection methods for liquid-chromatographic determination of anti-diabetic drugs

Recently, charged aerosol detection (CAD), a new kind of universal detection method, has been widely employed in the HPLC system. In the present study, four kinds of anti-diabetic drug standards, glipizide, gliclazide, glibenclamide and glimepiride were determined by ultraviolet (UV) detection, evaporative light scattering detection (ELSD) and the aforementioned CAD. The results were compared with reference to linearity, accuracy, precision and limit of detection (LOD). All of the experiments were performed on a reverse phase column with water and acetonitrile as the mobile phase. Separations were achieved under the same chromatographic conditions for each detection method. As a result, CAD generated nearly uniform responses compared with UV detection and ELSD. It showed the best accuracy and LOD among 3 detectors and had similar precision with UV detection at higher concentrations while UV detection showed a better precision at lower concentrations than did CAD or ELSD. The LOD of CAD, in fact, can be up to two times higher than that of ELSD. The UV and ELSD linearity was satisfactory at R(2)>0.99, though in the case of CAD, a log-log transformation was needed. The proposed methods were also applied to the real anti-diabetic drugs and diabetes-related dietary supplements.