正丁醇萃取-原子荧光光谱法间接测定茶叶中的钼

建立了正丁醇萃取原子荧光光谱法间接测定茶叶中钼的方法。基于As?和钼酸铵在0.3 mol/LH2SO4介质中能形成砷钼杂多酸,且形成的杂多酸可以被有效地萃取到有机溶剂中,原子荧光光谱法直接测定有机相中的砷,间接得到钼的含量。在优化的实验条件下,钼含量在0.09～15.0-g/L范围内呈良好的线性关系,方法的检出限是0.09-g/L,相对标准偏差为2.3%,据此对不同茶叶样品进行分析,加标回收率为95.2%～96.9%。本方法对茶叶中Mo的检测结果与电感耦合等离子体原子发射光谱法相符合。     

Development of a candidate certified reference material of cypermethrin in green tea

This paper presents the preparation of a candidate certified reference material (CRM) of cypermethrin in green tea, GLHK-11-01a according to the requirements of ISO Guide 34 and 35. Certification of the material was performed using a newly developed isotope dilution mass spectrometry (IDMS) approach, with gas chromatography high resolution mass spectrometry (GC–HRMS) and gas chromatography–tandem mass spectrometry (GC–MS/MS). Statistical analysis (one-way ANOVA) showed excellent agreement of the analytical data sets generated from the two mass spectrometric detections. The characterization methods have also been satisfactorily applied in an Asia-Pacific Metrology Program (APMP) interlaboratory comparison study. Both the GC–HRIDMS and GC–IDMS/MS methods proved to be sufficiently reliable and accurate for certification purpose. The certified value of cypermethrin in dry mass fraction was 148 μg kg⁻¹ and the associated expanded uncertainty was 14 μg kg⁻¹. The uncertainty budget was evaluated from sample in homogeneity, long-term and short-term stability and variability in the characterization procedure. GLHK-11-01a is primarily developed to support the local and wider testing community on need basis in quality assurance work and in seeking accreditation.     

Determination of Total and Fluoride Bound Aluminium in Tea Infusions by Ion Selective Electrode and Flame Atomic Absorption Spectrometry

ABSTRACT

Speciation of metallic compunds is important especially for their bioavailability. In this present study fluoride bound aluminium species were determined in tea infusion. Total aluminium was measured using flame atomic absorption spectrometry (FAAS). Free fluoride and total fluoride were measured by fluoride selective ion electrode (FISE) with the assistance of TISAB buffer solution used for adjustment of pH and total ionic strength, and ALCOA buffer solution which decomposes all of the Al-fluoride complexes in solution.

During the studies, the effects of pH and time on the formation of Al-F complexes and interference of some metal ions found in tea infusion such as Al³⁺, Mg²⁺, Fe²⁺, Fe³⁺ and Mn²⁺ on the concentration of free fluoride were investigated. The concentration of each Al-fluoride complexes in tea fusion were determined indirectly by calculation using pF-Mole Fraction Diagram. It was found that 1.13±0.15 mg 1^? of 12.00±0.86 mg 1^? total aluminium is fluoride bound aluminium, which means that appoximately 10% of total aluminium in tea infusion is complexed with fluoride.     

Selective removal of caffeine from tea extracts using macroporous crosslinked polyvinyl alcohol adsorbents

The hydrolysis reaction of ester groups in vinyl acetate (VAc) was used to introduce hydroxyl groups into the matrix of a macroporous adsorbent, which was itself prepared by free radical suspension copolymerization of triallyl isocyanurate (TAIC) and VAc. Therefore, the copolymerization incompatibility between the hydrophilic and the hydrophobic monomer was overcome successfully and the hydrophobic matrix of the polymeric adsorbent containing a polyvinyl alcohol (PVA) segment was obtained. Introduction of the PVA segment decreased the hydrophobic adsorption affinity of the adsorbent while producing the hydrogen-bonding interaction. When isolating the two active components, polyphenols (TPh) and caffeine (CAF), from green tea extracts, this polymeric adsorbent, namely poly(TAIC-co-VA), exhibited good adsorption selectivity towards TPh over CAF. The adsorption mechanism leading to this selectivity involved a hydrophobic interaction mechanism for CAF and multiple weak hydrophobic and hydrogen-bonding interactions for TPh. The adsorption thermodynamics for TPh on poly(TAIC-co-VA) were studied. The effects of adsorbent structure and gradient desorption conditions on isolation were investigated. The result showed that adsorbent, with 20% TAIC content, was able to efficiently remove CAF from different tea extracts with different ratios of TPh and CAF. Finally, almost no CAF was detected in the TPh fraction and the recovery of TPh was greater than 95%.     

微波消解-氢化物发生-冷原子吸收光谱法测定茶叶中的镉

采用微波消解法对茶叶样品进行处理,使用改进的雾化装置,在室温下用原子吸收光谱法测定茶叶中的镉,对各种实验参数进行了优化,镉的检出限(K=3,n=11)为18ng.L-1,其相对标准偏差为3.5%,回收率在94.8%—104.2%之间。方法操作简单、实用、灵敏度高,适用于茶叶中镉的快速测定。     

基于共聚焦显微拉曼光谱揭示炭疽病侵染下茶叶细胞壁变化的研究

采用共聚焦显微拉曼技术研究了炭疽病感染所致茶叶细胞壁结构和化学成分的变化。对茶叶健康和染病组织细胞进行微米级空间分辨率的显微拉曼光谱扫描,并结合透射电镜观察炭疽病侵染所致的细胞超微结构变化,结果显示染病前后细胞壁的拉曼光谱位移和强度都有明显的差异,表明炭疽病侵染导致细胞壁中化学成分发生了较大的变化。其中由纤维素,果胶,酯类化合物产生的拉曼峰强度都有明显下降,说明细胞壁中这些物质的含量在染病后减少了;而木质素拉曼散射引起的拉曼峰强度有所上升,说明木质素的含量在染病后有所增加。随后基于纤维素的拉曼指纹波数和显微空间结构信息实现了茶叶健康组织和染病组织细胞壁中纤维素的化学成像分析,结果显示炭疽病侵染不仅导致细胞壁中纤维素的含量大大减少,而且纤维素的有序结构被破坏。由此得出结论：在无需对样本进行染色或复杂的化学处理的情况下,共聚焦显微拉曼可以揭示由炭疽病侵染引起的茶叶细胞壁化学成分和结构的变化,本研究是共聚焦显微拉曼技术首次用于植物病理学中寄主-病原物互作机制的研究,将为深入研究寄主-病原物在细胞层面上的互作机制开辟蹊径。     

氢化物发生-原子荧光光谱法测定茶叶中的铅

氢化物发生-原子荧光光谱法测定茶叶中铅,在优化的分析条件下,相对标准偏差0.68%,回收率104%,用于标准样品(GBW08505)测定,结果与标准值吻合。该方法用于实际样品测定,与石墨炉原子吸收法对比,结果令人满意。     

茶多酚中总儿茶素的近红外光谱分析

采用近红外光谱分析技术对茶多酚中儿茶素进行了光谱分析,结果表明该技术能够解析出儿茶素中各主要基团在近红外波段的吸收特性,并且结合定标过程定量快速检测总儿茶素在茶多酚中的含量,分析结果在很大的样品浓度范围内给出了很高的精度,SEC=2．15％,相关系数(r)为0．9947。     

共振瑞利散射法测定微量硒

在稀HCl中硒(Ⅳ)与抗坏血酸(Vc)反应生成单质硒Se(0),并在液相中以纳米粒子的形式存在。利用此纳米粒子在470nm处的共振瑞利散射峰可对硒进行测定。在0.028~5.640μg/mL范围内,共振瑞利散射强度与硒(Ⅳ)的质量浓度成线性关系,检出限为0.00789μg/mL,相对标准偏差为4.7%。应用此法测定了茶叶、螺旋藻、黄芪样品中的总硒量,通过与例行方法DAN荧光法对照、干扰实验、回收率实验及质量控制对本方法进行了评价。     

Centrifugal precipitation chromatography,a powerful technique for the isolation of active enzymes from tea leaves (Camellia sinensis)

Centrifugal precipitation chromatography was developed approximately 10 years ago. In contrast to other counter-current chromatographic techniques, the centrifugal precipitation chromatography system is operated with two mutually miscible solutions separated by a cut-off membrane. Centrifugal precipitation chromatography was firstly introduced for the separation of proteins using an ammonium sulfate gradient. In this study we describe a novel approach using solvent-based protein precipitation for the isolation of active plant enzymes from tea leaves (Camellia sinensis) by centrifugal precipitation chromatography. We developed a gradient based on acetone and Tris-buffer, because the biological activity of carotenases in tea leaves cannot be preserved in the presence of ammonium sulfate. Parameters such as the critical solvent concentration, flow rate, buffer concentration, and sample load were determined and/or optimized. Subsequently, the newly developed separation protocol was successfully used for the isolation of active carotenoid cleavage enzymes from tea leaves. The isolated enzymes showed high enzymatic activities and purities and could be directly used for enzymatic assays and structure elucidation.