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.     

Fluorescence quantification of tetracycline in the presence of quenching matrix effect by means of a four-way model

In this work, a four-way tensor is used to model the quenching effect in fluorescent measurements. By means of the analysis of excitation-emission matrices obtained in the determination of tetracycline in tea, which acts as quencher, it is shown as the impossibility to use a calibration, or an addition standard based on a three-way model. It is analysed the quencher multiplicative effect made on the tetracycline signal by means of an ANOVA. However, by arranging the experimental data in a four-way tensor, it is viable to perform a calibration based on the parallel factor analysis, PARAFAC, decomposition and a four-way partial least squares, 4-PLS, regression to quantify the tetracycline in the presence of the matrix quencher effect. 4-PLS calibration provides better results. In the range from 40 to 220 μg L⁻¹ gives an average of relative errors in absolute value equal to 8.02% in prediction (3.40% in calibration). The repeatability as standard deviation in this range is 5.08 μg L⁻¹ and the method is accurate, slope and intercept being statistically equal to 1 and 0, respectively when a regression calculated versus true concentration is performed. Moreover, it has a decision limit (CCα) of 13.87 μg L⁻¹ for a probability of false positive, α, equal to 0.05 and a capability of detection (CCβ) of 26.63 μg L⁻¹ (for probabilities of false positive, α, false negative, β, equals to 0.05).     

Separation of catechins and methylxanthines in tea samples by capillary electrochromatography

In this paper, the simultaneous separation of several polyphenols such as (+)‐catechin, (–)‐epicatechin, (–)‐epigallocatechin, theophylline, caffeine in green and black teas by capillary electrochromatography (CEC) was developed. Several experimental parameters such as stationary phase type, mobile phase composition, buffer and pH, inner diameter of the columns, sample injection, were evaluated to obtain the complete separation of the analysed compounds. Baseline resolution of the studied polyphenols was achieved within 30 min by using a capillary column (id 100 μm) packed with bidentate C₁₈ particles for 24.5 cm and a mobile phase composed of 5 mM ammonium acetate buffer pH 4 with H₂O/ACN (80:20, v/v). The applied voltage and the temperature were set at 30 kV and 20°C. Precision, detection and quantification limits, linearity, and accuracy were investigated. A good linearity (R² > 0.9992) was achieved over a concentration working range of 2–100 μg/mL for all the analytes. LOD and LOQ were 1 and 2 μg/mL, respectively, for all studied compounds. The CEC method was applied to the analysis of those polyphenols in green and black tea samples after an extraction procedure. Good recovery data from accuracy studies ranged between 90% and 112% for all analytes.     

Fast Multi‐residue Screening for 84 Pesticides in Tea by Gas Chromatography with Dual‐tower Auto‐sampler,Dual‐column and Dual Detectors

A fast multi‐residue screening method for determining pesticides in tea is described. Pesticides are extracted from tea with acetone and methylene chloride, then enriched and cleaned up with solid phase extraction (SPE) prior to gas chromatographic determination. The fast screening is achieved by a gas chromatograph system equipped with dual‐column, dual‐tower auto‐sampler and both electron capture detector (ECD) and flame photometric detector (FPD). Optimal conditions are investigated for the prospective pesticides including column selection, detection mode, the retention behaviors, quantitative calibration, as well as the recoveries and repeatability of pesticides from tea samples. Under the optimal conditions, with the FPD‐P detector accompanied CP‐SIL 13CB column, 48 pesticides can be separated well and detected within 38 min; and with a DB‐5 column, 35 ECD‐detectable pesticides can be separated and detected within 46 min. The recoveries of 84 pesticides in tea samples are 65–120% with 0.34–16% RSD for spiking 0.02–3.0 mg/kg standard species. Because of the thermal instability of most pesticides, direct cold extraction of pesticides from a tea sample is recommended. The proposed method provided a very fast and efficient procedure to screen 84 pesticides from a complicated tea sample matrix.     

树脂对茶多酚与咖啡因的吸附分离

从低档绿茶末的水提取液中，利用离子交换，吸附树脂成功地分离出茶多酚与咖啡因，并详细考察了其交换与吸附性能。与其它方法相比，该树脂法具有产品收率高，成本低廉等特点。     

痕量铁的光化学伏安分析法及其应用研究

在稀硫酸介质中及活化剂草酸存在下，痕量铁（Ⅲ）对结晶紫光化学褪色反应有强烈催化作用，结晶紫的光化学反应产物于－０．７０产生一灵敏的２．５次微分级谱波。     

原子吸收光度法间接测定茶叶中单宁

基于乙酸铜与单宁生成沉淀，原子吸收光度法测定剩余铜的原理，间接测定茶叶单宁，样品前处理简单，测定单宁的线性范围为１￣４０ｍｇ／Ｌ，重复测定７次１０ｍｇ／Ｌ的单宁溶液，相对标准偏差为３．１６％，已用于几种不同茶样中单宁含量的测定。     

Determination of four sulfonylurea herbicides in tea by matrix solid‐phase dispersion cleanup followed by dispersive liquid–liquid microextraction

Matrix solid‐phase dispersion combined with dispersive liquid–liquid microextraction has been developed as a new sample pretreatment method for the determination of four sulfonylurea herbicides (chlorsulfuron, bensulfuron‐methyl, chlorimuron‐ethyl, and pyrazosulfuron) in tea by high‐performance liquid chromatography with diode array detection. The extraction and cleanup by matrix solid‐phase dispersion was carried out by using CN‐silica as dispersant and carbon nanotubes as cleanup sorbent eluted with acidified dichloromethane. The eluent of matrix solid‐phase dispersion was evaporated and redissolved in 0.5 mL methanol, and used as the dispersive solvent of the following dispersive liquid–liquid microextraction procedure for further purification and enrichment of the target analytes before high‐performance liquid chromatography analysis. Under the optimum conditions, the method yielded a linear calibration curve in the concentration range from 5.0 to 10 000 ng/g for target analytes with a correlation coefficients (r²) ranging from 0.9959 to 0.9998. The limits of detection for the analytes were in the range of 1.31–2.81 ng/g. Recoveries of the four sulfonylurea herbicides at two fortification levels were between 72.8 and 110.6% with relative standard deviations lower than 6.95%. The method was successfully applied to the analysis of four sulfonylurea herbicides in several tea samples.     

超高效液相色谱-串联质谱法测定不同茶叶中草甘膦、氨甲基膦酸及草铵膦的残留

建立了超高效液相色谱-串联质谱同时快速测定不同茶叶中草甘膦、氨甲基膦酸及草铵膦的方法。样品用0.05 mol/L NaOH提取,并以HCl调节pH值,Oasis HLB小柱净化除杂,氯甲酸-9-芴基甲酯(FMOCCl)柱前衍生反应后,超高效液相色谱-串联质谱法测定。本方法在5~1000μg/L浓度范围内,不同茶叶基质中草甘膦、氨甲基膦酸、草铵膦线性关系良好(R2>0.99)。在0.1,0.4和4 mg/kg添加水平下,不同茶叶(绿茶、红茶、乌龙茶、普洱茶)中3种化合物回收率均介于72.1%~109.9%之间,相对标准偏差RSD在0.5%~9.8%之间(n=6),方法定量限(LOQ)在0.03~0.08 mg/kg之间(S/N=10)。本方法稳定,简便,灵敏,能够满足检测需求。     

番红花红O-Mn2+-H2O2光度法测定茶叶的抗氧化性

在硫酸介质中,Mn2 -H2O2体系产生的羟自由基可以迅速氧化番红花红O,使其颜色变浅。实验证明,茶叶提取液具有可清除溶液中的羟自由基的功能,从而使番红花红O溶液的褪色程度降低。根据溶液吸光度的这一变化,可建立一种测定茶叶对羟自由基清除率的新方法。将本法用于8种茶叶的抗氧化性的测定,结果满意。