Determination Of Caffeine In Tea Research Articles

A surface-modified silicon carbide nanoparticles based electrochemical sensor for free interferences determination of caffeine in tea and coffee

In this work, the surface-modified silicon carbide nanoparticles (SiC-NPs) were used as a sensing material for the determination of caffeine. The [Cu(pydc) (apym)]2 loaded on the surface of functionalized SiC-NPs. The mixture of SiC-NPs/[Cu(pydc)(apym)]2 and graphene nanosheets used as a new electrode material. Cyclic Voltammetry technique used to study the electrochemical behavior of the GC/Gr/SiC-NPs/[Cu(pydc)(apym)]2 modified electrode. The GC/Gr/SiC-NPs/[Cu(pydc)(apym)]2 modified electrode shows excellent electrocatalytic activity toward caffeine oxidation and dramatically reduce the oxidation overpotential. The typical amperometry method is used to evaluate the performance of the sensing material for the determination of caffeine. Under optimum conditions, the detection limit and sensitivity were obtained, 0.313 µM and of 134.1 μA/nM−1, respectively. The performance of the designed sensor was evaluated by the successful determination of caffeine in commercial tea and coffee.

Langmuir-Blodgett films of Nafion-nitrogen Doped Carbon Nanotubes as New Sensing Materials for the Determination of Caffeine in Tea

Langmuir-Blodgett films of Nafion-nitrogen Doped Carbon Nanotubes as New Sensing Materials for the Determination of Caffeine in Tea

Preconcentration and GC–MS determination of caffeine in tea and coffee using homogeneous liquid–liquid microextraction based on solvents volume ratio alteration

A simple, fast and green homogeneous liquid–liquid microextraction (HLLME) method based on solvents volume ratio alteration (SVRA) combined with gas chromatography–mass spectrometry (GC–MS) was developed for the preconcentration and determination of caffeine in tea and coffee samples. In the proposed HLLME-SVRA method, the primary extraction from solid samples was achieved by a 2:1 ethanol-water mixture. A micro-volume of dichloromethane (DCM) formed a homogeneous solvent with this mixture after choosing an appropriate volume ratio between the three solvents. After vigorous shaking, an extra volume of water was added that resulted in phase separation due to the solvents volume ratio alteration. As a result, complete extraction of caffeine was achieved after centrifugation. The sedimented dichloromethane phase was then injected into GC–MS for the analysis. The influence of a number of parameters influencing the efficiency of the extraction was investigated and optimized. Under the optimal conditions, an enrichment factor of 11, a limit of detection of 0.05 μg mL−1 and a limit of quantification of 0.16 μg mL−1 were obtained for caffeine. A linear dynamic range of 0.16 to 50 μg mL−1 and a determination coefficient (R2) of 0.9980 were achieved. The precision of the method, expressed as relative standard deviation, was 4.8% for six replicated measurements. The method was successfully applied to the determination of caffeine in tea and coffee samples.

A simple, effective and highly sensitive analytical method used for the determination of caffeine in tea and energy drink samples, and method optimization using a central composite design

A rapid, simple and highly sensitive analytical method based on a microextraction method, followed by high-performance liquid chromatography was developed for the determination of caffeine in different tea and energy drink samples.

Nafion covered lead film electrode for the voltammetric determination of caffeine in beverage samples and pharmaceutical formulations

This paper presents a sensitive, selective and low-cost voltammetric method for the determination of caffeine using a Nafion covered lead film electrode. The sensor was prepared on a glassy carbon electrode modified with lead film recovered by a Nafion layer. Caffeine was accumulated and then oxidised at the modified electrode surface to produce two anodic peaks at 0.86 and 1.40V (vs. Ag/AgCl) in 0.1molL−1 H2SO4 medium. The obtained detection limits for caffeine following 120s of accumulation time were equal to 1.7×10−8molL−1 (for peak 1) and 2.2×10−7molL−1 (for peak 2). The method was successfully applied to determination of caffeine in tea, coffee, soft and energy drink samples as well as pharmaceutical formulation and the contents closely corresponded to those quoted by the manufacturer and those obtained by the reported spectrophotometric method.

Dynamic microwave-assisted extraction coupled on-line with clean-up for determination of caffeine in tea

A rapid method based on dynamic microwave-assisted extraction (DMAE) coupled on-line with clean-up was developed for the determination of caffeine in tea samples. A TM 010 microwave resonance cavity was applied to concentrate the microwave energy. An extraction vessel was placed in microwave irradiation zone of the TM 010 microwave resonance cavity. A silica gel column connected with the extraction vessel was used to remove chlorophyll in tea. The extraction and clean-up procedures were carried out simultaneously in a single step. The DMAE parameters were optimized by the Box–Behnken design. The maximum extraction efficiency was achieved using 70 W of microwave power, 3.5 mL of extraction solvent and 1.0 mL min −1 of extraction solvent flow rate. The limit of detection obtained is 0.012 mg g −1. The RSDs of intra- and inter-day of eight kinds of tea samples are 2.7%–5.4% and 5.1%–7.3%, respectively. The recovery of caffeine in the tea samples is in the range of 88.2%–99.3%.The proposed method has selectivity and sensitivity and considerably less labor and time for determination of caffeine in tea compared with conventional extraction methods, such assoxhlet extractionand liquid–liquid extraction.

Quasi-flow injection analysis for rapid determination of caffeine in tea using the sample pre-treatment method with a cartridge column filled with polyvinylpolypyrrolidone

The sample pre-treatment method using a polyvinylpolypyrrolidone (PVPP) cartridge column combined with a quasi-flow injection analysis (quasi-FIA) system realized the rapid determination of caffeine in three types of tea, green, oolong and black tea. The measurement time for each tea sample pre-treated using a PVPP cartridge column was shortened to 20 s. In the present system, the limits of detection and quantification were 0.3 μM (1.5 pmol injected) and 0.7 μM (3.5 pmol injected), respectively, and a linear calibration curve was afforded up to 800 μM (4 nmol injected). Within-run precision of analysis of standard solutions of 10 and 100 μM caffeine was 0.11 and 0.16% ( n = 6), respectively. Between-run precision of analysis of the same solutions over 6 days was 0.78 and 0.74% ( n = 6), respectively. Comparison with the conventional HPLC method indicated that the present quasi-FIA method using sample pre-treatment with a PVPP cartridge column was useful for the simple and precise determination of caffeine in green, oolong and black tea samples.

Improved Sample Pre-treatment for Determination of Caffeine in Tea Using a Cartridge Filled with Polyvinylpolypyrroridone (PVPP)

We have improved sample pre-treatment for the effective removal of polyphenols and simple analysis of caffeine in tea using a cartridge filled with polyvinylpolypyrroridone (PVPP). Nearly 100% of catechins were removed from the green tea sample and caffeine was completely recovered in the range of 98.2-101.3% by sample pre-treatment with a PVPP cartridge. Reproducibility of preparing PVPP pre-treatment cartridges was sufficient for quantitative analysis, because RSDs of analytical values for caffeine obtained by using three individual pre-treatment cartridges filled with 10-200 mg PVPP were 0.60-2.8%. The PVPP pre-treatment cartridge also removed polyphenols perfectly and recovered caffeine faultlessly from oolong and black tea samples. Comparison with the conventional method without sample pre-treatment indicated that the present pre-treatment method with a PVPP cartridge was useful for the simple and precise analysis of caffeine in green, oolong and black tea samples.

Rapid determination of caffeine in tea leaves

For the purpose of efficient screening of low-caffeine tea shoots, a method for the rapid determination of caffeine was developed using high-performance liquid chromatography. Polyvinylpolypyrrolidone was packed in a pre-column and used to remove polyphenols from tea extracts on-line. The concentrations of caffeine extracted from powdered tea leaves at 50°C during 1 day could be analyzed in 2–5 min intervals. The pre-column and the analytical column could be used for the analysis of more than 2000 samples.

HPLC determination of caffeine in tea, chocolate products and carbonated beverages

Different brands of mate and black tea, chocolate products and carbonated beverages available on the Brazilian market were analysed for caffeine by high-performance liquid chromatography with a UV-vis detector at 254 nm. The column was a reverse phase C18 and the mobile phase consisted of methanol–water (30:70, v/v), acetonitrile–water (10:90, v/v) and methanol–water (25:75, v/v) for tea, chocolate products and soft drinks respectively. Caffeine content ranged from 1.05 to 15.83 mg per cup in mate tea, from 32.21 to 36.23 mg per cup in black tea, from 0.14 to 0.95 mg g−1 in chocolate products from 2.73 to 7.49 mg per can in guarana-type soft drinks and from 19.81 to 45.89 mg per can in cola soft drinks. These data indicate that the levels of caffeine in Brazilian teas, chocolates and soft drinks are within the ranges reported for similar products in other countries. © 1999 Society of Chemical Industry

Determination of caffeine in tea by high-performance liquid chromatography and a modified digestion procedure

A more rapid and efficient method of sample preparation was needed for caffeine determination than the ones currently available. A variation of the existing AOAC method for coffee was developed using a Tecator digestion block normally used in determining nitrogen. Replicate samples were analyzed varying the digestion time and MgO content. The analysis parameters yielding the best results were chosen for the final method.

A study of caffeine in tea. I. A new spectrophotometric micro-method. II. Concentration of caffeine in various strengths, brands, blends, and types of teas2–3

A new spectrophotometric micro-method for the determination of caffeine in tea is described. This method is then used to evaluate the caffeine content of a variety of brands and blends of bagged and loose hot tea prepared in different strengths and by different brewing methods. In addition, the caffeine content of instant tea, ice tea, and Mr. Coffee automatic tea is evaluated.