Study on the retention equation in hydrophilic interaction liquid chromatography

Hydrophilic interaction liquid chromatography (HILIC) is an effective technique for separating polar compounds. But its retention equation has not been studied systematically yet. In this study, an appropriate retention equation was established by using eight nucleosides as model analytes and by comparing four retention models on six different HILIC columns. As a result, retention equation Ink = a + b x InC(B) + cxC(B) could be quantitatively described the retention factors with good accuracy in HILIC mode. Based on this equation, the retention times of eight nucleosides under the conditions by other mobile phase can be predicted on each column. All of the predicted relative errors of retention times were smaller than 5%. The established retention model was also successfully applied to predict retention times of the real Traditional Chinese Medicine-Carthaus tinctorius L. sample.     

An efficient enantioselective method for asymmetric Michael addition of nitroalkanes to alpha,beta-unsaturated aldehydes

The addition of nitroalkanes to alpha,beta-unsaturated aldehydes under the catalysis of (S)-2-(diphenyl(trimethylsilyloxy)methyl)pyrrolidine and lithium acetate as additive afforded gamma-nitroaldehydes in good yield and up to 97% ee.     

Two-dimensional LC-MS analysis of components in Swertia franchetiana Smith

An off-line 2-D-LC approach was developed for the separation and identification of components in extracts of Swertia franchetiana Smith, which is a traditional Chinese medicine. An octadecylsilica column was used for further separation of fractions from a cyano column with UV and MS detection. In this method, a longer column was used in the second dimension to improve the separation ability, and "on-column focusing" was adopted to reduce sample loss and pollution on concentrating the fractions from the first dimension. More than 118 and 575 components were detected in the chloroform and n-butanol extracts by this method, respectively. In contrast, only 20 and 95 peaks were detected by the one-dimensional method. Most of the additionally detected compounds were of low-abundance components. Many compounds can be preliminarily identified according to their UV and mass spectra in the two-dimensional method. The obtained results not only demonstrated the powerful resolution of 2-D-LC, but also led to in-depth comprehension of the UV and mass spectra of complex samples.     

Application of chromatography in purification and structural analysis of natural polysaccharides: A review

Polysaccharides are widely distributed in natural sources from monocytic microorganisms to higher animals, and are found in a variety of biological activities in recent decades. Natural polysaccharides have the characteristics of large molecular weight, diverse composition, and complex structure, so their purification and structural analysis are difficult issues in research. Chromatography as a powerful separation technique, plays an irreplaceable role in the separation and structural analysis of natural polysaccharides, especially in the purification of polysaccharides, the separation of hydrolysates, and the analysis of monosaccharide composition. The separation mechanisms and application of different chromatographic methods in the studies of polysaccharides were summarized in this review. Moreover, the advantages and drawbacks of various chromatography methods were discussed as well.     

Novel reversed-phase high-performance liquid chromatography stationary phase with oligo(ethylene glycol) "click" to silica

Oligo(ethylene glycol) (OEG) covalently bonded silica was prepared by using click chemistry and employed as a stationary phase for reversed-phase high-performance liquid chromatography. The column efficiency and effect of organic modifier content on retention were investigated. The separation selectivity was also studied with phenyl compounds and an actual sample of natural products. The results indicated that the stationary phase possessed good separation efficiency and separation selectivity in RP-HPLC mode. Moreover, the stationary phase showed good complementary separation selectivity to the C18 stationary phase. The OEG stationary phase had "clustering" function for "homologous component" in the separation of natural products.     

Separation analysis of macrolide antibiotics with good performance on a positively charged C18HCE column

The separation of basic macrolide antibiotics suffers from peak tailing and poor efficiency on traditional silica‐based reversed‐phase liquid chromatography columns. In this work, a C18HCE column with positively charged surface was applied to the separation of macrolides. Compared with an Acquity BEH C18 column, the C18HCE column exhibited superior performance in the aspect of peak shape and separation efficiency. The screening of mobile phase additives including formic acid, acetic acid and ammonium formate indicated that formic acid was preferable for providing symmetrical peak shapes. Moreover, the influence of formic acid content was investigated. Analysis speed and mass spectrometry compatibility were also taken into account when optimizing the separation conditions for liquid chromatography coupled with tandem mass spectrometry. The developed method was successfully utilized for the determination of macrolide residues in a honey sample. Azithromycin was chosen as the internal standard for the quantitation of spiramycin and tilmicosin, while roxithromycin was used for erythromycin, tylosin, clarithromycin, josamycin and acetylisovaleryltylosin. Good correlation coefficients (r² > 0.9938) for all macrolides were obtained. The intra‐day and inter‐day recoveries were 73.7–134.7% and 80.7–119.7% with relative standard deviations of 2.5–8.0% and 3.9–16.1%, respectively. Outstanding sensitivity with limits of quantitation (S/N ≥ 10) of 0.02–1 μg/kg and limits of detection (S/N ≥ 3) of 0.01–0.5 μg/kg were achieved.     

基于高效液相色谱定量指纹图谱和液相色谱-质谱联用定量的酸枣仁提取物质量考察

酸枣仁具有显著的改善睡眠和抗焦虑等作用,其提取物在助眠类功能食品开发中应用前景广阔。但目前市场上酸枣仁提取物质量参差不齐,缺乏统一标准,企业在使用时面临较大的质量风险,因此亟须建立一种准确、全面的内控质量评价方法。针对酸枣仁提取物中黄酮和皂苷两类主要活性成分紫外响应差异巨大且水提物中皂苷成分含量低的问题,该研究建立了酸枣仁水提物HPLC定量指纹图谱方法,共标定了8个共有峰。通过对照品指认、文献比对以及高效液相色谱-四极杆飞行时间质谱数据解析,8个共有峰均为黄酮类化合物,该方法可同时实现7种黄酮成分的半定量对比分析和斯皮诺素的含量测定;采用超高效液相色谱-三重四极杆质谱,在正离子模式下,以多反应监测扫描方式可实现酸枣仁皂苷A和B的含量测定;最终以雷达图展现上述10种成分的半定量和定量数据。应用上述方法,该研究对比分析了实验室自制的3批酸枣仁水提物和15家供应商的15批提取物样品。结果显示,实验室自制的3批酸枣仁水提物虽然原料来自不同饮片企业,但总体差异性不大,而不同厂家提供的酸枣仁提取物样品成分含量差异巨大,提示不同厂家存在辅料稀释、理枣仁掺假和醇提或纯化富集等情况。该法为企业制定内控质量标准和筛选合格供应商提供了依据。     

Identification of phenolics and nucleoside derivatives in Gastrodia elata by HPLC-UV-MS

An HPLC-UV-MS method for simultaneous identification of predominant phenolics and minor nucleoside derivatives in Gastrodia elata was developed, which was based on their UV and MS characteristics summarized through a series of homemade reference standard experiments. Phenolics showed characteristic UV lambda(max) at 267 nm, [M + NH(4)](+) base peak in positive mode and [M-H](-) base peak in negative mode while nucleosides exhibited UV lambda(max) at 255 nm, [M + H](+), [M-H + 2H(2)O](-) or [M-H + CH(3)COOH](-). Phenolics conjugates mainly underwent the consecutive loss of gastrodin residue (-268 U) and the combined loss of H(2)O and CO(2 )from the citric acid unit under negative MS/MS conditions whereas nucleosides simply lost the ribose (-132 U) under positive MS/MS conditions. According to these characteristics, a special pattern under MS/MS conditions and reported compound data for G. elata in the literature, not only 15 phenolics were identified but also 6 nucleoside derivatives were identified. Among these compounds, seven phenolics and three nucleoside derivatives have not been reported yet from G. elata.     

Selective separation of flavonoid glycosides in Dalbergia odorifera by matrix solid-phase dispersion using titania

Dalbergia odorifera contains high concentrations of flavonoid aglycones and trace flavonoid glycosides. In this study, trace flavonoid glycosides were separated from D. odorifera by titania with matrix solid-phase dispersion (MSPD). Before the MSPD experiment, four standards, including two isoflavone glycosides (genistin and formononetin-8-C-apiosyl (1-6)-glucoside) and their aglycones (genistein and formononetin), were used to compare their retention on a titania column. The effect of acetonitrile concentration and pH on their retention was investigated and a conclusion was drawn that high acetonitrile concentration and pH lead to the greatest difference in the retention of flavonoid as glycosides and aglycones. Besides hydrophilic interaction and ligand-exchange interaction may exist between sugar moiety of flavonoid glycoside and titania, so that flavonoid glycosides have stronger retention than that of aglycones. Based on the chromatographic rule of flavonoid as glycosides and aglycones on the titania column, the MSPD method was optimized to elute high concentration flavonoid aglycones first with 90% acetonitrile and 10% water containing 100 mM ammonium acetate buffer, and then to elute trace flavonoid glycosides with 20% acetonitrile and 80% water containing 1% trifluoroacetate (TFA). Isolated flavonoid glycosides were further analyzed by UPLC-MS/MS, and their fragmentation in MS(2) showed they are C-glycosyl flavonoids.