标准加入法数据处理的改进及用于测定宜昌茶叶的氟含量

利用氟离子选择电极,采用一种改进的标准加入法的数据处理方法测定湖北宜昌几种茶叶中的氟含量.与传统的标准加入法不同的是:以加入标准溶液后测得溶液中待测物质(如:氟离子)的总质量(样品及加入标准液后氟离子的质量之和)对加入标准液的中该物质的质量(标准液中氟离子的质量)作图.湖北宜昌某品牌茶叶中的氟含量为46.8±0.5 mg/kg,相对标准偏差(RSD)为0.79%,加标回收率在98.0%～102.5%之间.改进后的标准加入法的数据处理方法简单、快速,能够提供更多的信息(如:加标回收率).     

离子选择性电极法测定茶叶及茶水中的氟含量

将经典基础化学实验“离子选择性电极法测定水中微量的氟”实验改进为“离子选择性电极法测定茶叶及茶水中的氟含量”。实验内容由自来水中氟含量测定,拓展到茶叶及茶水氟含量、茶叶氟浸出率的测定;并增加了茶水比、冲泡温度、冲泡时间、冲泡次数、茶叶粒度对茶叶氟浸出率的影响等研究性内容;五大代表性茶样氟含量的测定结果表明,饮用黑茶有氟摄入过量的风险;此外,在离子选择性电极法测氟的应用领域及微量氟的其他检测方法等方面将该实验进一步拓展和延伸。研究性内容的引入及分组实验更有利于培养学生的科研思维和团结协作精神;探索性且具挑战力的实验内容,提高了学生的创新能力及解决实际问题的能力;茶与健康通识内容的渗透,贴近生活,增强了学生的健康意识。本实验内容丰富,趣味性强,易于操作及推广,适合在本科低年级学生中开设。     

改性5分子筛吸附剂从含氟水中除氟研究

研究了以5A分子筛为骨架吸附材料,经在含AI^3 或Fe^3 溶液中离子交换改性处理,获得了一种可吸附除氟的改性分子筛。实验表明,该种分子筛对水溶液中的低含量氟有良好的吸附性能。静态饱和吸附容量可达28．98和21．4mgF/g分子筛（分别对含AI^3 或Fe^3 分子筛）。含氟水经分子筛柱处理后,除氟率可达99％。吸附氟后的分子筛可用柠檬酸盐洗脱氟,洗脱率接近安全。洗脱后的分子筛可重复使用。得到一种新的效果显著的除氟方法。     

氟离子选择电极法测定药物中的氟喹诺酮

提出了测定氟喹诺酮类药物含量的一种新方法。先用氧瓶燃烧法进行有机物破坏,然后用氟离子选择电极定量。对该方法进行了研究,其回收率为98．5％—100．4％。测定了4个品种的氟喹诺酮类药物的含量,结果表明该方法简便、快速、准确,可以作为该类药物含量测定的通用方法。     

浅论绿茶与乌龙茶氟含量对人体健康的影响

分别用重蒸水和自来水，通过蒸煮法和浸泡法制出不同浓度的绿茶液和乌龙茶液，对比测定研究茶液中氟含量，结果表明，茶液中的氟含量随茶叶浓度增加而增加，且乌龙茶高于绿茶，当茶叶浓度超过１０．０ｇ／Ｌ时，茶液中的氟含量即超过国家饮水卫生标准，提示人们饮用水茶液浓度在５．０ｇ／Ｌ左右为宜。     

气相色谱-质谱联用仪测定茶叶中氟虫腈的不确定度评定

对气相色谱-质谱联用法测定茶叶中氟虫腈含量过程中可能引入的不确定度进行了分析和评定.当置信度水平为95％,包含因子k为2时,通过实验数据计算得到茶叶中氟虫腈含量的相对扩展不确定度为5.75％.对各分量在构成合成不确定度时的贡献率分析,得出质量控制的关键在于控制好样品的均匀性、代表性和测试方法的精密度.     

硝酸活化高灵敏度离子选择性电极法测定氟

先在0．5 mol·L-1硝酸介质中活化氟离子选择性电极,再在含硝酸的总离子强度调节混合液(TISAM)中测定氟,线性范围为1×10-7～1×10-2mol·L-1,检出限为1．9μg·L-1。该方法应用于绿茶饮料、水、牛奶中痕量氟的测定,结果的RSD小于4．8％,回收率在96．1％至100．2％之间,对氟离子选择性电极在硝酸介质中的活化机理作了阐述。     

离子选择电极法测定对氟聚苯乙烯聚合体中的氟含量

本文研究了分解对氟聚苯乙烯聚合体的条件,建立了用离子选择电极法测定对氟聚苯乙烯聚合体中氟含量的方法,对氟苯甲酸加标回收率为９９．９％,对氟聚苯乙烯分析结果的相对标准偏差为２．７％,方法简便,准确。     

人血清白蛋白共振RayIeigh光散射检测氟离子

通过研究F^-离子对人血清白蛋白(HSA)溶液共振Rayleigh光散射(RLS)的增强效应,建立一种基于生物蛋白RLS增强测定环境中氟离子的新型检测方法。实验条件为λex=λem=368nm,pH=5．80,t=32℃。结果表明,应用含氟离子溶液与空白溶液在368nm处RLS差值(△／),标准曲线法测定样品中的氟离子,方法线性范围为4．78～16．2μg／mL,r=0．992,检出限为1．43μg／mL。方法精密度(RSD为1．31％～5．72％)和准确度(回收率R为91％～109％)较好。     

二氧化钛光催化氧化-离子色谱法测定液晶材料中的氟含量

建立了TiO2光催化氧化-离子色谱法测定液晶材料中氟含量的方法。利用TiO2光催化氧化技术作为预处理手段对含氟液晶化合物进行有机破坏,使碳氟键断裂,生成的F-用离子色谱法测定。结果表明,TiO2催化剂用量为0.1g/L时,可达到最佳的光催化降解效果,最佳降解时间为50min。F-峰面积与其含量在0.005～1mg/g范围内呈良好的线性关系,检出限为2.1μg/g。测得3种液晶材料的氟含量分别为7.6,18.1及28.4mg/g,不同浓度的加标回收率为86.0%～118.0%,相对标准偏差RSD(n=5)在3.2%～5.7%之间。本方法不仅适用于有机氟体系,同时也为需经有机破坏后进行测定的有机化合物体系提供了新方法。     

Profiling of In Vitro Bioaccessibility and Intestinal Uptake of Flavonoids after Consumption of Commonly Available Green Tea Types

The aim of this study was to profile the bioaccessibility and intestinal absorption of epicatechins and flavonols in different forms of green tea and its formulation: loose leaf tea, powdered tea, 35% catechins containing GTE, and GTE formulated with green tea-derived polysaccharide and flavonols (CATEPLUS™). The bioaccessibillity and intestinal absorption of epicatechins and flavonols was investigated by using an in vitro digestion model system with Caco-2 cells. The bioaccessibility of total epicatechins in loose leaf tea, powdered tea, GTE, and CATEPLUS™ was 1.27%, 2.30%, 22.05%, and 18.72%, respectively, showing that GTE and CATEPLUS™ had significantly higher bioaccessibility than powdered tea and loose leaf tea. None of the flavonols were detected in powdered tea and loose leaf tea, but the bioaccessibility of the total flavonols in GTE and CATEPLUS™ was 85.74% and 66.98%, respectively. The highest intestinal absorption of epicatechins was found in CATEPLUS™ (171.39 ± 5.39 ng/mg protein) followed by GTE (57.38 ± 9.31), powdered tea (3.60 ± 0.67), and loose leaf tea (2.94 ± 1.03). The results from the study suggest that formulating green tea extracts rich in catechins with second components obtained from green tea processing could enhance the bioavailability of epicatechins.     

聚酰胺色谱法分离制备高纯度表没食子儿茶素没食子酸酯

表没食子儿茶素没食子酸酯;聚酰胺;液相色谱;提取工艺;正交实验;活性炭     

Removal of caffeine from green tea by microwave-enhanced vacuum ice water extraction

In order to selectively remove caffeine from green tea, a microwave-enhanced vacuum ice water extraction (MVIE) method was proposed. The effects of MVIE variables including extraction time, microwave power, and solvent to solid radio on the removal yield of caffeine and the loss of total phenolics (TP) from green tea were investigated. The optimized conditions were as follows: solvent (mL) to solid (g) ratio was 10:1, microwave extraction time was 6 min, microwave power was 350 W and 2.5 h of vacuum ice water extraction. The removal yield of caffeine by MVIE was 87.6%, which was significantly higher than that by hot water extraction, indicating a significant improvement of removal efficiency. Moreover, the loss of TP of green tea in the proposed method was much lower than that in the hot water extraction. After decaffeination by MVIE, the removal yield of TP tea was 36.2%, and the content of TP in green tea was still higher than 170 mg g⁻¹. Therefore, the proposed microwave-enhanced vacuum ice water extraction was selective, more efficient for the removal of caffeine. The main phenolic compounds of green tea were also determined, and the results indicated that the contents of several catechins were almost not changed in MVIE. This study suggests that MVIE is a new and good alternative for the removal of caffeine from green tea, with a great potential for industrial application.     

Simple and rapid UV spectrophotometry of caffeine in tea coupled with sample pre-treatment using a cartridge column filled with polyvinylpolypyrrolidone (PVPP)

We have applied a sample pre-treatment method with a cartridge column filled with polyvinylpolypyrrolidone (PVPP) to the effective removal of polyphenols and simple UV spectrophotometry of caffeine in tea. The absorption maximum length (lambda(max)) for caffeine was close to those for tea catechins in aqueous 1% acetic acid; therefore, the UV spectrum of a non-treated green tea sample had a large absorption wave. In contrast, the absorbance of the green tea sample was gradually reduced by PVPP cartridge treatment using PVPP from 0 to 50 mg, and was nearly constant using a pre-treatment cartridge with more than 100 mg PVPP, because tea catechins were effectively removed and caffeine was mostly recovered from a green tea sample by means of PVPP cartridge treatment. The PVPP pre-treatment cartridge also removed polyphenols successfully from oolong and black tea samples. Comparison with conventional HPLC analysis indicated that the present pre-treatment method with a PVPP cartridge was useful for the simple and selective UV spectrophotometric determination of caffeine in green, oolong and black tea samples.     

Constituents of the green tea seeds of Camellia sinensis

Green tea (Camellia sinensis) leaves are known to contain active ingredients such as catechins and caffeine, and are widely useful materials. Recently, green tea flowers also have been in the spotlight. However, little attention has been paid to the tea seeds. In this work, the constituents of green tea seeds and green tea leaves were compared. Caffeine was found in the seeds, whereas catechins (usually obtained from green tea leaves) were not observed. Next, we investigated the constituents of hexane extracts and methanol extracts of green tea seeds. We found that the hexane extracts contained high amounts of oleic glyceride (79.9%) in addition to linoleic glyceride (20%). We confirmed the structures of these glycerides by NMR spectroscopy and by synthesis from a fatty acid and glycerol. The methanol extract was found to contain naringenin glucosides by mass spectrometry and NMR spectroscopic analysis.     

Tea and fluorosis

Tea trees (Camellia sinensis), abundant in fluoride, selectively absorb F from the soil and air in the surrounding, and accumulate mainly in the tea leaves in the form of Al and F complex. Long-term consumption of high fluoride tea could result in chronic fluoride intoxication. This review summarized those data of the fluoride content in various tea commodities, and estimated the risk of fluorosis caused by high fluoride tea commodities. We also introduced fluorosis caused by tea from case reports, epidemiology observations and animal models. Fluorosis was easily misdiagnosed and over-looked and people made little acquaintance in the high fluoride in some tea commodities. So it is the time to pay more attentions on the over-looked safety problem of tea and tea products and some measures should be taken to the fluorosis caused by tea. Large-scale epidemiological investigations and further studies on tea-type fluorosis are in need for those tea-drinking areas. In addition, it is urgent that governmental and international agencies adopt safe standards of fluoride content in tea commodities.     

Green Synthesis of Fe and Fe/Pd Bimetallic Nanoparticles in Membranes for Reductive Degradation of Chlorinated Organics

Membranes containing reactive nanoparticles (Fe and Fe/Pd) immobilized in a polymer film (polyacrylic acid, PAA-coated polyvinylidene fluoride, PVDF membrane) are prepared by a new method. In the present work a biodegradable, non-toxic -"green" reducing agent, green tea extract was used for nanoparticle (NP) synthesis, instead of the well-known sodium borohydride. Green tea extract contains a number of polyphenols that can act as both chelating/reducing and capping agents for the nanoparticles. Therefore, the particles are protected from oxidation and aggregation, which increases their stability and longevity. The membrane supported NPs were successfully used for the degradation of a common and highly important pollutant, trichloroethylene (TCE). The rate of TCE degradation was found to increase linearly with the amount of Fe immobilized on the membrane, the surface normalized rate constant (k(SA)) being 0.005 L/m(2)h. The addition of a second catalytic metal, Pd, to form bimetallic Fe/Pd increased the k(SA) value to 0.008 L/m(2)h. For comparison purposes, Fe and Fe/Pd nanoparticles were synthesized in membranes using sodium borohydride as a reducing agent. Although the initial k(SA) values for this case (for Fe) are one order of magnitude higher than the tea extract synthesized NPs, the rapid oxidation reduced their reactivity to less than 20 % within 4 cycles. For the green tea extract NPs, the initial reactivity in the membrane domain was preserved even after 3 months of repeated use. The reactivity of TCE was verified with "real" water system.     

原子吸收光谱法测定比较5种不同品牌茶叶中微量元素含量

对市售茶叶崂山绿茶、茯茶、安溪铁观音、乌龙茶、茉莉茶王中微量元素Ca、Mg、Fe、Cu、Zn的含量进行考察.采用V(高氯酸)∶V(硝酸)=1∶4混酸消解的方法将样品在低温下消解,火焰原子吸收光谱法定量.实验测得5种茶叶中均含丰富的Ca、Mg,其中茯茶含Fe最多;崂山绿茶含Cu最多;安溪铁观音和崂山绿茶含Zn多.各元素工作曲线相关系数r0.9948,加标回收率94.38%～105.00%,相对标准偏差在2.26%以下.实验方法快速、定量准确,测得各品牌茶叶中微量元素含量可为消费者提供参考.     

Optimizing conditions for the extraction of catechins from green tea using hot water

Six different factors involved in the extraction of catechins from green tea using water were examined for their impact on the yield of catechins and on the efficiency of water use. The best temperature and time combination for catechin extraction was at 80°C for 30 min. The yield of catechins was also optimal with a tea particle size of 1 mm, a brewing solution pH <6 and a tea‐to‐water ratio at 50:1 (mL/g). In terms of efficient use of water in a single extraction, a water‐to‐tea ratio of 20:1 (mL/g) gave the best results; 2.5 times less water was used per gram of green tea. At the water‐to‐tea ratio of 20:1 mL/g, the highest yield of catechins per gram of green tea was achieved by extracting the same sample of green tea twice. However, for the most efficient use of water, the best extraction was found to be once at a water‐to‐tea ratio of 12:1 (mL/g) and once at a water‐to‐tea ratio of 8:1 (mL/g). Therefore, all six of the factors investigated had an impact on the yield of catechins extracted from green tea using water and two had an impact on the efficiency of water use.     

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.