红茶、绿茶和乌龙茶多糖及多酚对DNA的保护作用研究

用溴化乙锭(EB)作为荧光探针研究了各种茶叶多糖、多酚类化合物对DNA的保护作用.测定了龙井、普耳茶、乌龙茶等8种茶叶中多糖和多酚类提取物存在下DNA与EB混合液的荧光积分强度,并把不同茶叶与DNA相互作用的常数定义为结合常数D,根据D的大小讨论了多糖及多酚类化合物的存在DNA保护作用的影响.结果表明,8种茶叶与DNA...     

原子吸收光谱法测定茶叶中铅和镉时消解方法的优化

采用多种方法对同一种茶叶进行消解,用原子吸收光谱法测定不同方法消解的茶叶中有害微量元素铅和镉的含量并进行对比,探索了茶叶中微量元素铅和镉低损耗的最佳消解条件.实验结果表明,不同的消解方式对茶叶中微量元素的测定结果影响很大.测定茶叶中铅和镉元素时,采用硝酸-高氯酸加盖浸泡过夜方法较为理想.     

茶叶中铁、钙及蛋白质的定性检验

通过探究茶叶中的营养物质,使学生深刻理解化学与生活的密切联系.用水浸泡茶叶,取其浸泡液与浓硝酸反应,能明显检出茶叶中的蛋白质;取其浸泡液在碱性条件下与钙试剂反应,能检出茶叶中的钙;用3 mol/L左右的盐酸浸泡茶叶,取其浸泡液与饱和硫氰酸钾溶液反应,能检出茶叶中的铁.     

茶叶中微量硒的催化光度法测定

用催化光度法测定了23个茶叶样品中向量硒的含量,平均回收率97.2%.变异系数2.13%.     

茶叶中微量营养元素的原子吸收光谱分析

茶叶中的微量元素与茶叶的营养和药理作用有密切关系^[1],与茶树生长的生化活动也有密切关系^[2,3]。对茶叶中的微量营养元素的分析有助于了解茶叶的品质,研究茶叶的营养药理作用,促进茶叶生产的发展。为此,我们研究提出了用火焰原子吸收光谱法测定茶叶中铜、锰、铁、锌,方法简便、准确。     

共沉淀分离富集偏最小二乘法在茶叶重金属测定中的应用

以铜试剂为共沉淀剂,在pH值为10.0的条件下,共沉淀分离富集茶叶中痕量金属离子Ni^(2+)、Pb^(2+)、Cd^(2+)和Cu^(2+),并分析了铜试剂与金属离子形成配合物的最佳沉淀条件.用4-(2-吡啶偶氮)间苯二酚(PAR)作为这4种重金属离子的显色剂进行分光光度测定,采用偏最小二乘-紫外可见光度法同时测定了四组分金属离子的模拟混合试样,并在茶叶中进行上述金属离子含量的测定.方法操作简便、结果可靠,对茶叶中重金属测定有一定实用价值.     

加速溶剂萃取-气相色谱-负化学源质谱法测定茶叶中有机氯和拟除虫菊酯类农药残留量

建立了茶叶中13种有机氯和10种拟除虫菊酯农药残留量的气相色谱-负化学离子源.质谱(GC-NCl-MS)分析方法.茶叶样品用V(丙酮):V(CH2Cl2)=1:1混合液作提取剂经加速溶剂萃取,提取液经凝胶色谱净化除去大部分的色素、脂类和蜡质,再经活性炭-氨基(Carb-NH2)复合小柱和Florisil小柱净化后,用GC-NCl-MS的选择离子监测方式(SIM)进行定性和定量分析.添加50μg/kg 浓度水平时,农药回收率在45.6%～112.4%之间,相对标准偏差在0.57%～10.1%之间;方法的检出限(3倍信噪比)在0.05～10.0μg/kg之间.方法适用于出口茶叶农残检测实际工作.     

茶叶中氟虫腈残留量的测定

建立了快速测定茶叶中氟虫腈残留量的气相色谱方法.茶叶中的氟虫腈经丙酮与正己烷混合液提取,经中性氧化铝-石墨化碳混合柱净化,丙酮与正己烷混合液定容,用外标法定量,以气相色谱法（GC-μECD）测定.试验结果表明：样品中加入0.00080-0.00800 mg/kg浓度水平的氟虫腈,回收率在74.9%-116.8%,检测限为0.00080 mg/kg,相对标准偏差在0.94%-11.10%范围内,能满足我国茶叶对日出口检测的要求.     

GC-MS法快速测定茶叶中脂肪酸

建立了气相色谱-质谱联用技术(GC-MS)快速分析茶叶脂肪酸的新方法.对23批茶叶样品进行GC-MS分析,结合NIST 05谱库检索鉴定茶叶脂肪酸种类,并用峰面积归一化法测定其相对含量,比较不同加工方式的茶叶脂肪酸含量.结果表明,所有茶样中亚麻酸、亚油酸和棕榈酸含量最高,但绿茶和青茶脂肪酸含量高于发酵处理的红茶和黑茶.方法可以用于分析各种茶叶的脂肪酸,反映不同种类茶叶的性质差异.     

固相萃取-毛细管气相色谱法测定茶叶中11种残留有机磷农药

应用毛细管柱气相色谱法结合固相萃取分离测定了各种茶叶中11种残留农药.样品用乙腈进行超声萃取,萃取液中的农药经过ODS-C18固相萃取柱富集并净化,用甲醇作淋洗剂,洗脱液中各农药经HP-5石英毛细管色谱柱分离后用氮磷检测器进行检测.各农药在一定浓度范围内保持线性关系,分别对方法的回收率及精密度作了试验,回收率在85.3%～100.6%之间,相对标准偏差(n=7)在3.5%～8.4%之间,用此方法分析了9种茶叶样品并列表给出其农药残留量.     

Spectrophotometric determination of tannins in tea and beer samples with iron(III) and 1,10-phenanthroline as reagents

A simple and accurate spectrophotometric method is proposed for the determination of tannins in tea and beer samples based on the reduction of iron(III) to iron(II) by tannins at 80 degrees C for 20 min. The iron(II) was then reacted with 1,10-phenanthroline at pH 4.4 to form a coloured complex. Background correction could be effected by precipitating the tannins in the sample solution twice with gelatin and kaolin. Absorbance measurements were made at 540 nm and the calibration graph was linear from 0 to 5.5 micrograms ml-1 of tannic acid with a slope of 0.213 A p.p.m.-1. The precision for the determination of tannins in a tea sample containing 9.45% of tannins was 1.8%. Most of the ingredients commonly found in tea and beer samples do not interfere with the determination. Several tea and beer samples were analysed for their tannin content using the proposed method.     

双波长双指示剂催化动力学光度法测定痕量铁

铁是人体健康所必须的微量元素,它对人体的生理功能有一定影响.如果体内可利用的铁不能满足血红蛋白正常合成的需要,致使红细胞增殖能力下降,就会造成缺铁性贫血.相反,体内铁含量过高,又易产生癌症~([1]).     

光化学反应在流动注射分析中的应用研究 Ⅲ.甲基橙光化学反应体系测定亚硝酸根、硝酸根和铁(Ⅲ)

基于NO_2~-、NO_3~-和Fe(Ⅲ)对甲基橙光化学褪色反应的催化作用,利用自制流通式光化学反应器,建立了流动注射光化学反应同时测定NO_2~-和NO_3~-以及测定Fe(Ⅲ)的新方法。测定NO_2~-和NO_3~-的线性范围都是0.1～3.2mg/L,每小时可测30～40个样品,测定Fe(Ⅲ)的线性范围为0.06～1.2mg/L,进样频率为60～80次/h。应用于蔬菜中NO_2~-、NO_3~-的测定和茶叶中铁的测定,结果满意。     

Multi-element analysis of japanese tea leaves by neutron activation analysis and the single comparator method

The reliability of the single comparator method in neutron activation analysis has been studied by comparing the calculated and experimental k values and by determining the concentration of trace elements in iron. The method has been applied to the analysis of tea leaves for thirteen elements; their concentrations varied over five orders of magnitude.     

HPLC with electrochemical detection of metal-flavonoid-complexes isolated from food

Summary The electrochemical and chromatographic behaviour of flavonoid standards and of flavonoids extracted from food (green tea, black tea and onions) is investigated with respect to metalbinding properties. It is shown that metals such as iron, copper or aluminium are complexed by flavonoids, preferrably by those having an aromatic o-dihydroxy structure. This is confirmed by cyclic voltammetry on HPLC fractions (stopped flow) and by AAS measurement of metals. As the complexing sites of flavonoids are closely related to electrochemical properties, this is used for an indirect detection of metal species at low oxidation potentials. For iron species in particular a sensitive and selective detection is possible. For copper reductive detection can also be used.     

Simultaneous determination of trace iron and aluminum by catalytic spectrophotometry based on a novel oxidation reaction of xylene cyanol FF.

A new, simple, sensitive and selective method for the simultaneous determination of trace iron and aluminum by catalytic spectrophotometry was presented, based on the catalytic effects of iron and aluminum on the discoloring reaction of xylene cyanol FF proceeded by hydrogen peroxide and potassium periodate in weak nitric acid medium. No catalytic effect was obtained in the presence of hydrogen peroxide or potassium periodate only. With the conditional rate constants determined in reaction systems catalyzed by Al or Fe only, the concentrations of Fe and Al in the samples can be calculated. The method was applied to the simultaneous determination of trace Fe and Al in tap water, lake water, river water and tea leaves without separation and preconcentration.     

Heavy metal content of a medicinal moss tea for hypertension

The content of various heavy metals (arsenic, cadmium, chromium, copper, iron, lead, mercury, nickel, manganese and zinc) in the moss species Rhodobryum ontariense (Kindb.) Kindb. and its tea are presented in this study. Pursuant to the use of this tea in traditional Chinese medicine for hypertension, the aim of this study was to examine its safety in regard to the metals. All heavy metals were determined by adequate EPA methods. The concentrations of all metals for daily intake in its tea were below the safety levels for human consumption. These results indicate the importance of manganese in R. ontariense tea traditionally used for hypertension and other heart disorders.     

Flow field-flow fractionation-inductively coupled optical emission spectrometric investigation of the size-based distribution of iron complexed to phytic and tannic acids in a food suspension: implications for iron availability

Flow field–flow fractionation–inductively coupled plasma optical emission spectrometry (FlFFF–ICP–OES) was applied to achieve the size-based fractionation of iron in a food suspension in order to gain insights into iron availability. The binding of iron with phytic and tannic acids, employed as model inhibitors of iron availability in foods, was investigated at pH 2.0 (representing stomach fluid), pH 5.0 (the transition stage in the upper part of the duodenum), and pH 7.0 (the small intestine). In the presence of phytic acid, iron was found as a free ion or it was associated with molecules smaller than 1 kDa at pH 2.0. Iron associated with molecules larger than 1 kDa when the pH of the mixture was raised to 5.0 and 7.0. In the presence of tannic acid, iron was again mostly associated with molecules smaller than 1 kDa at pH 2.0. However, at pH 5.0, iron and tannic acid associated in large molecules (∼25 kDa), while at pH 7.0, most of the iron was associated with macromolecules larger than 500 kDa. Iron size-based distributions of kale extract and tea infusion containing phytic and tannic acids, respectively, were also examined at the three pH values, with and without enzymatic digestion. Without enzymatic digestion of the kale extract and the tea infusion at pH 2.0, most of the iron was released as free ions or associated with molecules smaller than 1 kDa. At other pH values, most of the iron in the kale extract and the tea infusion was found to bind with ~2 kDa and >500 kDa macromolecules, respectively. Upon enzymatic gastrointestinal digestion, the iron was not observed to bind to macromolecules >1 kDa but <500 kDa, due to the enzymatic breakdown of large molecules to smaller ones (<1 kDa). Figure Flow field–flow fractionation was exploited in order to achieve size-based iron fractionation and thus investigate iron-binding behavior under gastrointestinal conditions     

不同提取方法对红茶提取物抗氧化活性影响的研究

采取沸水浴法、回流法、微波法及超声波法探讨信阳红茶和印度红茶的抗氧化性,通过测定吸光度利用Fenton反应表征提取物对羟自由基的清除率.不同的提取方法对红茶抗氧化活性有一定的影响,羟自由基的清除率与红茶的抗氧化活性成正比.结果表明:信阳红茶沸水浴法提取率较高,印度红茶超声波法提取率较高.