Separation of dansylated amino acid enantiomers by chiral ligand-exchange CE with a zinc(II) L-arginine complex as the selecting system

A facile chiral ligand-exchange capillary electrophoretic method has been explored for the enantioseparation and UV detection of dansyl-amino acids with Zn(II) L-arginine complex as a chiral selecting system. Successful enantioseparation of 17 pairs of amino acid enantiomers has been achieved with a buffer of 100 mM boric acid, 5 mM ammonium acetate, 3 mM ZnSO4 and 6 mM L-Arg at pH 8.0, of which 10 pairs were fully resolved with resolution in between 1.59 and 4.21. This new method was shown to be applicable to the separation of some mixed pairs of amino acids and to the quantitative analysis of some real samples such as rice vinegars, with a linear range between 0.8 and 150 microg/mL, correlation coefficient above 0.99 and recovery in between 90.1 and 112.4%. It was found that amino acids with low resistance side chain(s), low tendency to form intramolecular hydrogen bond or high tendency to form intermolecular hydrogen bonds are more easily enantioseparated than those with extra carboxyl and/or phenyl groups. By the use of the suggested buffer, the running pH should be selected at 7.4-9.0 to compromise the resolution and elution speed.     

离子色谱法测定瓶(桶)装纯净水中痕量溴酸盐和亚硝酸盐的含量

采用离子色谱法同时测定瓶(桶)装纯净水中溴酸盐和亚硝酸盐的含量。水样经AG19-4mm保护柱及DIONEX AS19色谱柱分离,以不同浓度的氢氧化钾溶液为淋洗液,溴酸盐和亚硝酸盐得到很好的分离。BrO3-和NO2-分别在5.00～100.00μg.L-1和1.00～50.00μg.L-1范围内呈线性,检出限(3s/k)分别为0.08,0.14μg.L-1。方法用于瓶(桶)装水中溴酸盐和亚硝酸盐的测定,加标回收率在92.7%～98.4%之间,相对标准偏差(n=5)均小于5.0%。     

O2/CO2气氛下木醋调质石灰石再燃/先进再燃脱硝性能研究

在O₂/CO₂气氛下利用沉降炉脱硝实验台,对木醋调质石灰石和醋酸钙的再燃/先进再燃脱硝特性以及氨气的选择性非催化还原脱硝特性进行了研究。结果表明,木醋调质石灰石和醋酸钙的再燃脱硝效率随温度的升高先提高后降低,1 323 K时获得最高脱硝效率分别为82.70%和78.52%;再燃脱硝氧浓度不宜过高,合适的再燃比为14%~17%,停留时间为0.8 s。氨气选择性非催化还原脱硝在1 173 K时获得最高脱硝效率为95.41%,温度窗口为1 142~1 335 K;随着氧浓度的增大,脱硝效率不断降低,反应适宜的氨氮比为1.5,停留时间为1.2 s。按氨氮比0.75向再燃区喷入氨气可显著提高木醋调质石灰石和醋酸钙的再燃脱硝效率,同时脱硝反应适宜的温度区间也得到显著拓宽,1 323 K时两者获得的先进再燃脱硝效率分别为93.49%和92.79%。     

High-precision direct determination of the Sr/Sr isotope ratio of bottled Sr-rich natural mineral drinking water using multiple collector inductively coupled plasma mass spectrometry

We describe a precise and accurate method for the direct determination of the ⁸⁷Sr/⁸⁶Sr isotope ratio of bottled Sr-rich natural mineral drinking water using multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The method is validated by the comparative analysis of the same water with and without cation-exchange resin purification. The work indicates that isobarically interfering elements can be corrected for when ⁸⁷Rb/⁸⁶Sr < 0.05 (Rb/Sr < 0.015), and that the matrix elements (Ca, Mg, K and Na) have no significant effect on the accuracy of the Sr isotope data. The method is simple, rapid, eliminates sample preparation time, and avoids potential contamination during complicated sample-preparation procedures. Therefore, the high sample throughput inherent to the MC-ICP-MS can be fully exploited.     

The potentiality of NMR-based metabolomics in food science and food authentication assessment

In the last years, there was an increasing interest on nuclear magnetic resonance (NMR) spectroscopy, whose applications experienced an exponential growth in several research fields, particularly in food science. NMR was initially developed as the elective technique for structure elucidation of single molecules and nowadays is playing a dominant role in complex mixtures investigations. In the era of the “omics” techniques, NMR was rapidly enrolled as one of the most powerful methods to approach metabolomics studies. Its use in analytical routines, characterized by rapid and reproducible measurements, would provide the identification of a wide range of chemical compounds simultaneously, disclosing sophisticated frauds or addressing the geographical origin, as well as revealing potential markers for other authentication purposes. The great economic value of high-quality or guaranteed foods demands highly detailed characterization to protect both consumers and producers from frauds. The present scenario suggests metabolomics as the privileged approach of modern analytical studies for the next decades. The large potentiality of high-resolution NMR techniques is here presented through specific applications and using different approaches focused on the authentication process of some foods, like tomato paste, saffron, honey, roasted coffee, and balsamic and traditional balsamic vinegar of Modena, with a particular focus on geographical origin characterization, ageing determination, and fraud detection.     

“食醋中总酸含量测定”实验解析

对高职院校分析化学实验“食醋中总酸含量的测定”实验中NaOH标准溶液的配制、NaOH标准溶液的标定、食醋试样的制备以及总酸含量测定涉及的知识点进行解析,可以提高学生分析问题、解决问题的能力,也有利于提高教师的教学水平.     

黑曲霉酸性蛋白酶在食醋酿造中的催化效应

从麸醋母曲中分离出黑曲霉Asp 5609并以此为诱变出发菌株,采用紫外线照射结合亚硝基胍诱变剂处理,筛选出酸性蛋白酶高产变异株Asp 5609—7。用盐溶加温提取法从Asp 5609-7固体发酵物料中提取酸性蛋白酶粗酶液,经DE-30型中空纤维柱超滤浓缩,用于食醋酿造物料蛋白的酶解催化,可大幅度提高醋液中氨基酸含量。     

木醋液的成分分析

采用KarlFisher法测定了木醋液中的水分含量;在样品未经过处理的条件下和经乙醚萃取、浓缩后,分别采用气相色谱–质谱联机技术(GC/MS)分析,测得了其中的有机成分和它们的相对含量。实验结果表明,木醋液中除了主要成分乙酸外,另外还含有含量较少、种类繁多的酮类化合物、酚类化合物、酯类、醛类和醇类等化合物。     

应用近红外光谱技术快速检测果醋糖度

为了对果醋糖度值进行快速准确检测,应用近红外光谱技术并结合最小二乘支持向量机分析方法建立了果醋糖度检测模型.应用近红外透射光谱获取五种类型共计300份果醋样本的光谱透射曲线,利用主成分分析方法对原始光谱数据进行降维处理,根据主成分的累计贡献率选取6个主成分.选取的主成分即作为光谱优化特征子集以替代原来复杂的光谱数据.随后将300份果醋样本数据随机分为定标集和预测集,利用最小二乘支持向量机在225个定标集样本数据基础上建立起果醋糖度预测模型,应用此模型对75个预测集样本进行糖度预测.根据预测均方根误差(RMSEP)和预测结果的相关系数(r)对预测模型进行评价,利用此模型得到的样本糖度预测值r=0.993 9,RMSEP=0.363,均达到了较好的预测效果.     

Study of organic acids in Schisandrae Chinensis Fructus after vinegar processing

The ripened fruit of Schisandrae Chinensis Fructus has unique medical properties in Chinese medicine. It is commonly used after vinegar steaming. Vinegar steaming changes the color of Schisandrae Chinensis Fructus from red to black and enhances its acidic and astringent properties. Lignans are the well‐investigated components in this herb. However, Schisandrae Chinensis Fructus is acidic in the theory of Chinese medicine, and whether vinegar processing changes its organic acid components remains largely unknown. In this study, the organic acids in this herb were derived by the method of methyl esterification, and further analyzed by gas chromatography with mass spectrometry. A total of 39 organic acid compounds were identified. Interestingly, Schisandrae Chinensis Fructus after vinegar processing showed a significant increase in the content of levulinic acid as compared to the unprocessed ones. Pharmacological experiments demonstrated that levulinic acid inhibited the contractility of isolated intestine and had an inhibitory effect on the excessive hyperfunction of small intestinal propulsion. Moreover, the extracts of vinegar‐processed Schisandrae Chinensis Fructus had a stronger inhibitory on the excessive hyperfunction of small intestinal propulsion than that of unprocessed ones. Taken together, this study offers novel insight into the effect of Schisandrae Chinensis Fructus after vinegar processing.