Fang-Qiu Guo

Simultaneous separation and determination of active components in Cordyceps sinensis and Cordyceps militarris by LC/ESI-MS.

A simple and rapid isocratic LC/MS coupled with electrospray ionization (ESI) method for simultaneous separation and determination of adenine, hypoxanthine, adenosine and cordycepin in Cordyceps sinensis (Cs) and its substitutes was developed. 2-Chloroadenosine was used as internal standard for this assay. The optimum separation for these analytes was achieved using the mixture of water, methanol and formic acid (85:14:1, v/v/v) as a mobile phase and a 2.0 x 150 mm Shimadzu VP-ODS column. Selective ion monitoring (SIM) mode ([M+H]+ at m/z 136, 137, 268, 252 and 302) was used for quantitative analysis of above four active components. The regression equations were liner in the range of 1.4-140.0 microg ml(-1) for adenine, 0.6-117.5 microg ml(-1) for hypoxanthine, 0.5-128.5 microg ml(-1) for adenosine and 0.5-131.5 microg ml(-1) for cordycepin. The limits of quantitation (LOQ) and detection (LOD) were, respectively 1.4 and 0.5 microg ml(-1) for adenine, 0.6 and 0.2 microg ml(-1) for hypoxanthine, 0.5 and 0.1 microg ml(-1) for adenosine and cordycepin. The recoveries of four constituents were from 93.5 to 107.0%. The nucleoside contents of various types of natural Cs and its substitutes were determined and compared with this developed method.

Determination of the volatile chemical constituents of Notoptergium incium by gas chromatography-mass spectrometry and iterative or non-iterative chemometrics resolution methods.

The qualitative and quantitative determination of the chemical constitutes in traditional Chinese medicine (TCM) is an important task, which builds the foundation of the theory of pharmacological activity. The hyphenated chromatography instruments combined with the related chemometric methods provide powerful tools for the resolution of such complex systems. The familiar chemometrics methods can be roughly divided into two different kinds, the iterative one such as orthogonal projection approach (OPA) and non-iterative one representing by evolving window orthogonal projection (EWOP). One can use different kinds of methods according to overlapping condition, and then the measured data matrix can be resolved into pure concentration profiles and mass spectra of the chemical components with relative high efficiency and acceptable accuracy. One kind of TCM, named Notoptergium incium (NI) was analyzed by gas chromatography-mass spectrometry (GC-MS) and resolved by above chemometric approach. Experiment results show the efficiency and convenience of the proposed approach. 65 of the 98 separated constituents in essential oil, accounting for 92.13%, were identified by mass spectroscopy (MS).

Development of the chromatographic fingerprint of Scutellaria barbata D. Don by GC–MS combined with Chemometrics methods

Gas chromatography fingerprint of Scutellaria barbata D. Don (SB) from different origins was studied by gas chromatography-mass spectrometry (GC-MS) and related Chemometrics methods. The constituents of essential oil of Scutellaria barbata D. Don (SB) and its two adulterants Oldenlandia diffusa (OD) and Lobelia chinensis Lour (LCL) were analyzed and compared, 50, 36 and 38 components were identified from SB, OD and LCL, respectively, there were 16 and 18 common components between SB and OD, SB and LCL. Nine different samples collected from different producing areas of SB were studied. The relative standard deviations (RSDs) of retention time and peak area of each component were less than 0.2% and 6%, respectively. The number of common peaks was up to 52 and the un-common peak area was less than 10%. The similarity and difference among SB and its adulterants were also evaluated by correlation coefficient similarity analysis and principal component analysis, the result showed that developed fingerprint characterize the SB from different producing areas and it is useful and feasible for the discrimination of its adulterants.

Comparison of quantitative structure-retention relationship models on four stationary phases with different polarity for a diverse set of flavor compounds

A quantitative structure-retention relationship study was performed for 656 flavor compounds with highly structural diversity on four stationary phases of different polarities, using topological, constitutional, quantum chemical and geometrical descriptors. Statistical methods were employed to find an informative subset that can accurately predict the gas chromatographic retention indices (RIs). Multivariable linear regression (MLR) was used to map the descriptors to the RIs. The stability and validity of models have been tested by internal and external validation, and good stability and predictive ability were obtained. The resulting QSRR models were well-correlated, with the square of correlation coefficients for cross validation, Q², values of 0.9595, 0.9528, 0.9595 and 0.9223 on stationary phase OV101, DB5, OV17 and C20M, respectively. The molecular properties known to be relevant for GC retention index, such as molecular size, branching, electron density distribution and hydrogen bond effect were well covered by generated descriptors. The descriptors used in models on four stationary phases were compared, and some reasonable explanations about gas chromatographic retention mechanism were obtained. The model may be useful for the prediction of flavor compounds while experimental data is unavailable.

QSRR Study on Flavor Compounds of Diverse Structures on Different Columns with the Help of New Chemometric Methods

A quantitative structure–retention relationship study was performed for 286 flavor compounds with highly structural diversity on different stationary phases of different polarities. Firstly, the structure–retention relationship was statistically explored using constitutional, topological, molecular properties, charge descriptors and quantum chemical descriptors. Some recently developed chemometric methods, such as the ones for robust analysis and variable selection were firstly employed to predict accurately the gas chromatographic retention indices. The stability and validity of models have been tested by internal and external validation, and good robustness and predictive ability were obtained. The resulting QSRR models were well correlated, with the square of correlation coefficient for cross validation, Q2, values of 0.9847, 0.9838, 0.9745 and 0.9646 on stationary phase DB5, OV101, OV17 and C20M, respectively. The molecular properties known to be relevant for GC retention index, such as molecular size, branching, electron density distribution and hydrogen bond effect were well covered by generated descriptors. The descriptors used in models on four stationary phases were compared, and some reasonable explanations about gas chromatographic retention mechanism were obtained. The developed model may be useful for the prediction of flavor compounds while experimental data are unavailable.