离心萃取-紫外光谱法测定可乐饮料中咖啡因的含量

建立了一种快速、准确,溶剂消耗少的测定可乐饮料中咖啡因含量的紫外光谱分析方法,并将大相比离心萃取应用于仪器分析样品微制备过程。该方法将2mL三氯甲烷直接加入装有100μL可乐饮料的离心试管中,离心萃取3min后取清液在278nm处进行紫外光谱测定,操作简单、快速,重现性好,相对标准偏差小于3%;在3种可乐饮料中加入不同浓度的咖啡因标准溶液,回收率在96.6%～106.1%之间。线性范围为0.5～30mg/L,相关系数为0.9999;检出限为0.001mg/L。将本方法应用于市售可乐饮料中咖啡因含量分析,取得了满意的结果。     

气泡微萃取-气相色谱-质谱法测定尿中咖啡因

建立了气泡微萃取结合气相色谱/质谱技术(GC-MS)测定尿中咖啡因的方法.对影响萃取效率的实验条件进行了优化,确定了最佳萃取条件:三氯甲烷作为萃取溶剂,萃取溶剂暴露体积1 μL,气泡体积1.6 μL,搅拌速度300 r/min,萃取时间5 min,盐度15%(m/V),气泡与磁子间距离1 cm.在优化条件下,所建立方法在咖啡因浓度0.005~10 mg/L范围内有较好的线性关系,相关系数可达0.986,检出限为0.003 mg/L.在人尿液中添加不同浓度的咖啡因(0.050、0.500和5.000 mg/L),回收率为89.2%~107.5%,相对标准偏差小于8%(n=6).     

以马来松香丙烯酸乙二醇酯为交联剂的咖啡因分子印迹电化学传感器

以咖啡因为模板分子, 含菲环骨架的马来松香丙烯酸乙二醇酯为交联剂, 甲基丙烯酸为功能单体, 在玻碳电极表面以自由基热聚合的方式制备分子印迹聚合物敏感膜, 构建了测定咖啡因的新型分子印迹膜电化学传感器. 通过循环伏安法、 差分脉冲伏安法及电化学交流阻抗法研究了传感器对咖啡因的响应特性. 结果表明, 在最佳的实验条件下, 传感器的峰电流与咖啡因浓度在3.00×10^-3~2.73 mmol/L范围内呈现良好的线性关系, 检出限(S/N=3)为1.12×10^-4 mmol/L. 传感器具有良好的选择性和重现性. 将该传感器用于可口可乐饮料中咖啡因含量的测定, 平均回收率为98.7%.     

某些功能性饮料中咖啡因的快速检测方法研究

本文研究了测定咖啡因的拟反相色谱法。采用极性色谱柱配以高水量的流动相,所测饮料样品均能在4min内快速完成测定。系统考察了影响咖啡因保留的多种因素。其最佳测定条件为高纯硅胶柱为固定相,流动相为乙腈—水(甲酸钠溶液0.03 mol·L-1,pH 2.9)(5∶95)。由于分析时间短,同时流动相中乙腈的比例只占5%,极大降低了有机溶剂的消耗和排放,兼具经济和环保的优点。将其用于功能性饮料中咖啡因的测定,操作简便,分离效果好,检测时间短。应用线性范围宽,在浓度范围0.2～1000μg·mL-1内,r=0.9997(n=5),方法的检测下限(S/N=3)为0.05μg·mL-1,加标回收率95.6%～103.9%,相对标准偏差1.6%～2.3%,是检测咖啡因含量的理想方法。同时还对咖啡因的保留机理进行了探讨。     

拟反相液相色谱法快速测定饮料中咖啡因含量的研究

本文建立了饮料中咖啡因含量的快速检测方法。采用拟反相色谱法,以极性硅胶柱配以高水量的流动相,所测9种饮料样品均能在4min内快速完成分离测定。系统研究了影响咖啡因保留的多种因素,优化后的最佳测定条件为:采用Inertsil100-5SIL色谱柱(150×4.6mm i.d.,5μm),以乙腈-0.03mol·L-1甲酸钠溶液(pH=2.9)(体积比5∶95)为流动相,检测波长274nm。将其用于饮料中咖啡因的测定,线性范围为0.2~1 000μg·mL-1(r=0.9995),检出限(S/N=3)为0.05μg·mL-1。回收率为92.3%~105.7%,精密度(RSD)<3.5%。同时还对咖啡因的保留机理进行了探讨。     

咖啡因离子选择性电极的研制及其用于测定可乐饮料中咖啡因

研制了以咖啡因-磷钼酸缔合物为电活性物质的离子选择性电极。试验表明:该离子选择性电极对咖啡因具有良好的选择性和电位响应特性。在pH 2.54磷酸盐缓冲溶液中,电极电位呈现能斯特响应,线性范围为5.0×10~(-6)～1.0×10~(-2)mol·L~(-1),斜率为51.4mV·pc~(-1)。将该电极用于测定可乐饮料中咖啡因的含量,测得方法的回收率在98.4%～102.4%之间。     

超临界流体色谱法测定复方氨酚烷胺中咖啡因和对乙酰氨基酚含量

建立超临界流体色谱法分离测定复方氨酚烷胺中咖啡因和对乙酰氨基酚含量的方法,并研究其影响因素.Kromasil Slica填充柱(250×4.6mm,5μm),流动相为含18%甲醇的CO2,流速2.0mL/min,柱温50℃,背压200bar,检测波长275nm.在测定范围内,对照品浓度与峰面积呈良好的线性关系,以峰面积和保留时间计算精密度分别为咖啡因0.49%.1.88%和对乙酰氨基酚0.44%和1.09%.该方法在所用分析条件下,5 min即可完成测定,且具有较好的重现性和线性关系.     

以甲基橙为显色剂萃取光度法测定喜树中总生物碱

为测定喜树中总生物碱含量,取样品的提取液100μL,在pH 5的柠檬酸-磷酸盐缓冲介质中与甲基橙反应.反应混合液在25℃保持5 min后,用三氯甲烷10 mL进行萃取将生物碱转入有机相中,用光度法于366 mm波长处以三氯甲烷溶剂作参比测定其吸光度.用纯喜树碱作对照品,测得的吸光度与喜树碱质量浓度在6.5～104.0 mg·L-1范围内呈线性关系.取来自同一批的样品5份,按所提出的方法测定其总生物碱量,测定值的相对标准偏差为1.62%.在一已知样品的基础上,用标准加入法进行了回收试验,测得平均回收率为98.7%.     

胶束电动毛细管电泳同时测定饮料中的多种添加剂

建立了分析饮料中山梨酸,苯甲酸,１０－羟基基癸烯酸,咖啡因和糖精钠五种添加剂的胶束电动细管电泳法。讨论了电压,缓冲溶液浓度和ＰＨ值,胶束浓度对分析结果的影响。５种添加剂的迁移时间和测定回收率的变异系数分别小于１．５％和５％,检测限分别为１０,１０,５,１０,２０μｇ／ｋｇ。     

茶叶中咖啡因的纸基质室温燐光法体内药代动力学研究

以快速定量滤纸为基质 ,用KI NaAc为重原子微扰剂建立了测定痕量咖啡因的滤纸基质室温光(PS RTP)分析法。并用于茶叶中咖啡因的测定及其在人体内的药代动力学研究。实验表明 :PS RTP法用于茶叶中咖啡因的测定准确、灵敏。受试者饮茶后 1～ 2h尿样中咖啡因排泄达高峰 ,2 4h后基本排泄完毕。咖啡因的尿排泄量占总摄取量的 64 .2 5 %。     

Solventless determination of caffeine in beverages using solid-phase microextraction with fused-silica fibers.

Caffeine concentrations in beverages were determined using a simple and rapid method based on microextraction of caffeine onto the surface of a fused-silica fiber. The uncoated fiber was dipped into the beverage sample for 5 min after the addition of isotopically labeled (trimethyl 13C)caffeine. The adsorbed caffeine was then thermally desorbed in a conventional split/splitless injection port, and the concentration of caffeine was determined using gas chromatography with mass spectrometric detection. Quantitative reproducibilities were ca. 5% (relative standard deviation) and the entire scheme including sample preparation and gas chromatographic analysis was completed in ca. 15 min per sample. The potential of the microextraction technique for the analysis of flavor and fragrance compounds in non-caffeinated beverages is also demonstrated. Since no solvents or class-fractionation steps are required, the method has good potential for automation.     

Liquid chromatographic analysis of cinchona alkaloids in beverages

A method for the determination of Cinchona extract (whose main components are the alkaloids cinchonine, cinchonidine, quinidine, and quinine) in beverages by liquid chromatography was developed. A beverage with an alcohol content of more than 10% was loaded onto an OASIS HLB solid-phase extraction cartridge, after it was adjusted to pH 10 with 28% ammonium hydroxide. Other beverages were centrifuged at 4000 rpm for 5 min, and the supernatant was loaded onto the cartridge. The cartridge was washed with water followed by 15% methanol, and the Cinchona alkaloids were eluted with methanol. The Cinchona alkaloids in the eluate were chromatographed on an L-column ODS (4.6 mm id x 150 mm) with methanol and 20 mmol/L potassium dihydrogen phosphate (3 + 7) as the mobile phase. Cinchona alkaloids were monitored with an ultraviolet (UV) detector at 230 nm, and with a fluorescence detector at 405 nm for cinchonine and cinchonidine and 450 nm for quinidine and quinine (excitation at 235 nm). The calibration curves for Cinchona alkaloids with the UV detector showed good linearity in the range of 2-400 microg/mL. The detection limit of each Cinchona alkaloid, taken to be the concentration at which the absorption spectrum could be identified, was 2 microg/mL. The recovery of Cinchona alkaloids added at a level of 100 microg/g to various kinds of beverages was 87.6-96.5%, and the coefficients of variation were less than 3.3%. A number of beverage samples, some labeled to contain bitter substances, were analyzed by the proposed method. Quinine was detected in 2 samples of carbonated beverage.     

Determination of caffeine and associated compounds in food, beverages, natural products, pharmaceuticals, and cosmetics by micellar electrokinetic capillary chromatography

A method is described for quantitating caffeine, theobromine, theophylline, paracetamol, propyphenazone, acetylsalicylic acid, salicylic acid, and codeine phosphate in corresponding real samples of food, beverages, natural products, pharmaceuticals, and cosmetic preparations by micellar electrokinetic capillary chromatography. The separation is carried out at 25 degrees C and 25 kV, using a 20mM phosphate buffer (pH 9.0), 80mM sodium dodecyl sulfate, and 7.5% (v/v) acetonitrile. UV detection is at 210 nm. The method is shown to be specific, accurate (recoveries over the range 98.9-101.2%), linear over the tested range (correlation coefficients >/= 0.9993), and precise (relative standard deviation below 2.1%). The method is applied for the quantitative analysis of these compounds in different foods, beverages, natural products, pharmaceuticals, and cosmetic products.     

Determination of ethanol in fuel ethanol and beverages by Fourier transform (FT)-near infrared and FT-Raman spectrometries

Fourier transform-near infrared (FT-NIR) and FT-Raman spectrometries have been used to design partial least squares (PLS) calibration models for the determination of the ethanol content of ethanol fuel and alcoholic beverages. In the FT-NIR measurements the spectra were obtained using air as reference, and the spectral region for PLS modeling were selected based on the spectral distribution of the relative standard deviation in concentration. In the FT-Raman measurements hexachloro-1,3-butadiene (HCBD) has been used as an external standard. In the PLS/FT-NIR modeling for ethanol fuel analysis 50 ethanol fuel standards (84.9-100% (w/w)) were used (25 in the calibration, 25 in the validation). In the PLS/FT-Raman modeling 25 standards were used (13 in the calibration, 12 in the validation). The PLS/FT-NIR and FT-Raman models for beverage analysis made use of 24 standards (0-100% (v/v)). Twelve of them contained sugars (1-5% (w/w)), one-half was used in the calibration and the other half in the validation. Different spectral pre-processing were used in the PLS modeling, depending on the type of sample investigated. In the ethanol fuel analysis the FT-NIR pre-processing was a 17 points smoothed first derivative and for beverages no spectral pre-processing was used. The FT-Raman spectra were pre-processed by vector normalization in the ethanol fuel analysis and by a second derivative (17 points smoothing) in the beverage analysis. The PLS models were used in the analysis of real ethanol fuel and beverage samples. A t-test has shown that the FT-NIR model has an accuracy equivalent to that of the reference method (ASTM D4052) in the analysis of ethanol fuel, while in the analysis of beverages, the FT-Raman model presents an accuracy equivalent to the reference method. The limits of detection for NIR and Raman calibration models were 0.05 and 0.2% (w/w), respectively. It has also been shown that both techniques, present better results than gas chromatography (GC) in evaluating the ethanol content of beverages.     

Fast quantitative detection of cocaine in beverages using nanoextractive electrospray ionization tandem mass spectrometry

Without any sample pretreatment, effervescent beverage fluids were manually sprayed into the primary ion plume created by using a nanoelectrospray ionization source for direct ionization, and the analyte ions of interest were guided into an ion trap mass spectrometer for tandem mass analysis. Functional ingredients (e.g., vitamins, taurine, and caffeine, etc.) and spiked impurity (e.g., cocaine) in various beverages, such as Red Bull energy drink, Coco-cola, and Pepsi samples were rapidly identified within 1.5 s. The limit of detection was found to be 7 ∼ 15 fg (S/N = 3) for cocaine in different samples using the characteristic fragment (m/z 150) observed in the MS³ experiments. Typical relative standard deviation and recovery of this method were 6.9% ∼ 8.6% and 104% ∼ 108% for direct analysis of three actual samples, showing that nanoextractive electrospray ionization tandem mass spectrometry is a useful technique for fast screening cocaine presence in beverages.     

Simultaneous determination of caffeine, theobromine, and theophylline by high-performance liquid chromatography

This work relates the development of an analytical methodology to simultaneously determine three methylxanthines (caffeine, theobromine, and theophylline) in beverages and urine samples based on reversed-phase high-performance liquid chromatography. Separation is made with a Bondesil C18 column using methanol-water-acetic acid or ethanol-water-acetic acid (20:75:5, v/v/v) as the mobile phase at 0.7 mL/min. Identification is made by absorbance detection at 273 nm. Under optimized conditions, the detection limit of the HPLC method is 0.1 pg/mL for all three methylxanthines. This method is applied to urine and to 25 different beverage samples, which included coffee, tea, chocolate, and coconut water. The concentration ranges determined in the beverages and urine are: < 0.1 pg/mL to 350 microg/mL and 3.21 microg/mL to 71.2 microg/mL for caffeine; < 0.1 pg/mL to 32 microg mL and < 0.1 pg/mL to 13.2 microg/mL for theobromine; < 0.1 pg/mL to 47 microg/mL and < 0.1 pg/mL to 66.3 microg/mL for theophylline. The method proposed in this study is rapid and suitable for the simultaneous quantitation of methylxanthines in beverages and human urine samples and requires no extraction step or derivatization.     

Comparative study of robustness between micellar electrokinetic capillary chromatography and high-performance liquid chromatography using one-variable-at-a-time and a new multi-variable-at-a-time approach

Micellar electrokinetic capillary chromatography and reverse-phase liquid chromatography methods were developed in order to perform robustness testing to determine the caffeine content in beverages. Both methods were fully validated and two different robustness approaches were applied. One-variable-at-a-time (OVAT) approach at eleven levels (0; ±1; ±2; ±3; ±4; ±5 units) was carried out and compared with multi-variable-at-a-time (MVAT) approach at three levels (±1 unit per investigated parameter). Four analysts in two laboratories on two capillary electrophoresis and two RPLC equipments have tested the samples. Robustness was statistically analyzed using peak area, migration or retention time, symmetry, and resolution of caffeine and sulfacetamide as internal standard, and presented as R.S.D. values. The RPLC method was found to be more sensitive than the MEKC method. Both methods showed acceptable robustness level for OVAT approach, whilst MEKC method was more robust when the determination of real samples coming from different beverages was based on the MVAT approach.     

Simple method for the simultaneous quantification of medium-chain fatty acids and ethyl hexanoate in alcoholic beverages by gas chromatography-flame ionization detector: development of a direct injection method

Free medium-chain fatty acids (MCFAs) can negatively influence the fermentation process and taste quality in alcoholic beverages. Ethyl hexanoate is important in providing a fruit-like flavour to drinks, particularly in Japanese sake. In this study, we developed a direct injection method for a gas chromatography-flame ionization detector following the semi-purification of chemical components, such as esters, alcohols and MCFAs in alcoholic beverages. Evaluation of MCFAs by this method gave a limit of detection on the order of sub-ppm and relative standard deviations less than 10% in standard solution. Good repeatability and recovery rates against MCFAs and ethyl hexanoate were also obtained in non-distilled real alcoholic beverages. Because this method enabled us to simultaneously quantify the concentrations of MCFAs and ethyl hexanoate, the proportion of ester against MCFAs was proposed as a quality control index. This method could be suitable for routine analysis in the alcohol beverage industry.     

高效液相色谱法同时测定功能饮料中烟酰胺、咖啡因、维生素B_6、柠檬黄、胭脂红和苯甲酸的含量

建立了一种同时快速检测功能饮料中烟酰胺、咖啡因、维生素B_6、柠檬黄、胭脂红和苯甲酸6种食品添加剂的高效液相色谱方法。6种食品添加剂的检出限分别为烟酰胺0.1 mg/L,咖啡因0.1 mg/L,维生素B6 0.2 mg/L,柠檬黄0.2 mg/L,胭脂红0.1 mg/L,苯甲酸0.1 mg/L,测定结果的相对标准偏差不大于4.57%(n=6),加标回收率在95.80%~113.68%之间。该方法满足GB/T 5009.197–2003,GB/T 23495–2009和SN/T 2105–2008对于上述6种食品添加剂检出限的要求。     

Caffeine and theobromine in coffee, tea and cola-beverages

Summary A new method based on reversed-phase ion-interaction HPLC is described for the identification and quantitation of theobromine, theophylline and caffeine in beverages. The interaction reagent used is octylamine orto-phosphate which also constitutes the mobile phase. The stationary phase is a microparticulate reversed-phase C-18 packing. With spectrophotometric detection at 274 nm, detection levels of 0.15, 0.30 and 0.40 ppm were achieved for theobromine, theophylline and caffeine, respectively.Quantitative analysis was performed by the standard addition method for theobromine and caffeine contents in tea, espresso-coffee, decaffeinated coffee, decaffeinated tea and cola-beverages.