Determination Of Caffeine In Beverages Research Articles

Development of an electrochemical device based on aptasensors for the determination of caffeine in beverages

Herein, we constructed a miniature electrochemical device for highly sensitive and selective detection of caffeine in beverages. A disposable gold-film plastic electrode was modified with the caffeine-specific aptamer to serve on the working electrode. It was then equipped in a detachable three-electrode test system to perform the electrochemical measurements. The whole device is robust, cost-effective, easy to fabricate, and convenient to maintenance. The preparation of the proposed device was carefully characterized and optimized. Under optimal analytical conditions, the concentration of caffeine in the range of 0.1 − 50 nM showed a good linear relationship, and the detection limit was as low as 0.079 nM. The developed method also exhibited good stability and selectivity. The practicality of this device was certified by testing the caffeine concentration in beverages on the market and comparing the results with the method based on UPLC-HRMS.

Extraction-Free, Direct Determination of Caffeine in Microliter Volumes of Beverages by Thermal Desorption-Gas Chromatography Mass Spectrometry.

An extraction-free method requiring microliter (μL) volumes has been developed for the determination of caffeine in beverages. Using a pyrolysis-gas chromatography mass spectrometry system, the conditions required for the direct thermal desorption-gas chromatography mass spectrometry (TD-GC/MS) determination of caffeine were optimised. A 5 μL aliquot was introduced to the thermal desorption unit, dried, and thermally desorbed to the GC/MS. The response was linear over the range 10 to 500 μg/mL (R2 = 0.996). The theoretical limit of detection (3 σ) was 0.456 μg/mL. No interferences were recorded from endogenous beverage components or from commonly occurring drugs, such as nicotine, ibuprofen, and paracetamol. Replicate caffeine determinations on fortified latte style white coffee and Pepsi Max® gave mean recoveries of 93.4% (%CV = 4.1%) and 95.0% (%CV = 0.98%), respectively. Good agreement was also obtained with the stated values of caffeine for an energy drink and for Coca-Cola®. These data suggest that the method holds promise for the determination of caffeine in such samples.

Caffeine determination in beverages by voltammetry with the carbon-containing electrodes modified with aryldiazonium salts

The method of carbon containing electrode ( CCE ) modification with tosylated arendiazonium salts ( ADT ) was proposed for the voltammetric ( VA ) determination of caffeine in beverages. The comparison of chemical spontaneous and electrochemical modification approaches was carried out for ADT modified CCE for VA caffeine determination for the first time. A new class of ADT is characterized by high solubility and stability for one month that plays significant role in the process of electrode surface modification. Salts with nitro and carboxy substituents were tested. The optimal conditions for the spontaneous chemical modification of the CCE were selected: ADT modifier with NO 2 substituent, electrode immersion time in the modifier solution for 10 seconds, modifier concentration of 5 mg / dm 3 . ADT deposition on the electrode surface was confirmed by the IR spectroscopy and scanning electron microscopy with the formation of covalent bonds between the carbon atoms of electrode surface and the benzene rings of the modifier. It was shown that the electroactive surface area increases by two times after the modification. Consequently, the technique sensitivity increasing the detection limit of 51 mg / dm 3 and linear range extension from 154 up to 500 mg / dm 3 was observed. While applying the modified electrode, the analysis time was reduced to 15 minutes. Furthermore, the suitability of CCE modified with NO 2 substituent was tested for the analytical purposes. As a result, the caffeine was determined in some tonic and carbonated drinks. The comparison of the results obtained by the proposed method with ADT modified CCE and the level declared by the manufacturer was carried out. The high compliance was established. In addition, the obtained data was consistent with the results by the independent spectrophotometric method. Keywords : caffeine, diazonium aromatic salts, modifier, carbon-containing electrode, voltammetry, spontaneous modification, SEM, IR spectroscopy, cyclic voltammetry DOI: http://dx.doi.org/10.15826/analitika.2020.24.1.007 E.V. Dorozhko, A.O. Gusar, E.A. Bedareva, G.B. Slepchenko, M.E. Trusova, E.I. Korotkova National Research Tomsk Polytechnic University, Lenina prosp., 30, Tomsk, 634050, Russian Federation

An automated homogeneous liquid-liquid microextraction based on deep eutectic solvent for the HPLC-UV determination of caffeine in beverages

This work presents an automated homogeneous liquid-liquid microextraction procedure for separation of caffeine from beverages. The microextraction procedure involved mixing sample and water-miscible deep eutectic solvent (DES, choline chloride with phenol at a 1:3 molar ratio) into a mixing chamber of a flow system resulting formation of homogeneous solution. Injection of aprotic solvent (tetrahydrofuran) into homogeneous sample solution promoted the fine DES droplets formation and caffeine extraction into DES phase separated. The automated homogeneous liquid-liquid microextraction procedure was coupled with a HPLC-UV system. The conditions of caffeine microextraction and its HPLC-UV determination in DES phase were studied and optimized. Under optimal experimental conditions the linear detection range and limit of detection, calculated from a blank test, based on 3σ were found to be 0.1–200 mg L−1 and 0.03 mg L−1, respectively. The application of the developed procedure was demonstrated in the determination of caffeine in commercial soft drinks samples.

Voltammetric determination of caffeine by using gold nanoparticle-glassy carbon paste composite electrode

In the present study, simple and sensitive voltammetric determination of caffeine was carried out by using a gold nanoparticle-glassy carbon paste composite electrode (AuNP-GCPE) in 3.2mM H2SO4 (pH 2.5). The effects of supporting electrolyte, pH and AuNP amount on caffeine peak current were investigated. After the optimization of experimental parameters, analytical characteristics of AuNP-GCPE were examined and two linear ranges were obtained between 25–150μM and 200–1000μM with limit of detection values of 0.96μM and 4.90μM, respectively. Relative standard deviation for 50μM caffeine was also calculated as 7.52% (n=3). In order to evaluate the analytical performance of AuNP-GCPE, caffeine contents of various brands of cola samples were measured and compared with the results obtained by UV–Vis spectrometer. The obtained results by using the proposed composite electrode are in accordance with the caffeine contents that manufacturers claimed compared to UV–Vis. This composite electrode which utilizes the catalytic effect of AuNP with the simple preparation of GCPE, offers a fast and sensitive determination of caffeine in beverages as a practical application.

Fluorescence Polarization Immunoassays for the Quantification of Caffeine in Beverages

Homogeneous fluorescence polarization immunoassays (FPIAs) were developed and compared for the determination of caffeine in beverages and cosmetics. FPIAs were performed in cuvettes in a spectrometer for kinetic FP measurements as well as in microtiter plates (MTPs) on a multimode reader. Both FPIAs showed measurement ranges in the μg/L range and were performed within 2 and 20 min, respectively. For the application on real samples, high coefficients of variations (CVs) were observed for the performance in MTPs; the CVs for FPIAs in cuvettes were below 4%. The correlations between this method and reference methods were satisfying. The sensitivity was sufficient for all tested samples including decaffeinated coffee without preconcentration steps. The FPIA in cuvettes allows a fast, precise, and automated quantitative analysis of caffeine in consumer products, whereas FPIAs in MTPs are suitable for semiquantitative high-throughput screenings. Moreover, specific quality criteria for heterogeneous assays were applied to homogeneous immunoassays.

Voltammetric sensor for caffeine based on a glassy carbon electrode modified with Nafion and graphene oxide

We report on a voltammetric sensor for caffeine that is based on a glassy carbon electrode modified with Nafion and graphene oxide (GO). It exhibits a good affinity for caffeine (resulting from the presence of Nafion), and excellent electrochemical response (resulting from the pressence of GO) for the oxidation of caffeine. The electrode enables the determination of caffeine in the range from 4.0 × 10−7 to 8.0 × 10−5 mol L−1, with a detection limit of 2.0 × 10−7 mol L−1. The sensor displays good stability, reproducibility, and high sensitivity. It was successfully applied to the quantitative determination of caffeine in beverages.

Large Phase Ratio Spontaneous Extraction Followed by GC–MS for the Determination of Caffeine in Beverages

A single-step large phase ratio spontaneous extraction procedure followed by gas chromatography–mass spectrometry (GC–MS) was successfully applied for the determination of caffeine in beverages. Before the GC–MS analysis, as little as 25 μL sample was spontaneously extracted with 1 mL chloroform in a 2 mL autosampler vial for 15 min. The methodology exhibited excellent linearity in the range of 0.001–20 mg L−1 with correlation coefficient of determination, r2 > 0.9999 and a detection limit of 0.004 mg L−1. Good repeatability of extraction performance was obtained with relative standard deviation lower than 2% and the recovery of the caffeine when spiked to three different brand beverages was in the range of 98.8–102.3%. The new application-oriented single-step spontaneous extraction method was fast, efficient, and is a good alternative to routine methods for caffeine analysis in beverages.

Simple and environmental friendly procedure for the gas chromatographic–mass spectrometric determination of caffeine in beverages

A simple, quick and organic solvent saving procedure has been developed for the GC/MS determination of caffeine in beverages. The procedure involves the mixing of 25 μL sample with 1 mL ethyl acetate, and a following simple desiccation procedure in a 1.5 mL autosampler vial. A linear calibration curve was generated with caffeine concentration ranging from 0.005 mg/L to 30.0 mg/L. The procedure developed provides a 0.001 mg/L detection limit of caffeine in the final solution by injection of 1 μL solution and the relative standard deviation (RSD) was less than 2% for independent measurement. The total amount of organic solvent used for individual detection is 1 mL of nontoxic ethyl acetate. The developed method was repeatable and could be applied to determine trace amounts of caffeine in popular commercial beverages.

Voltammetric determination of caffeine in beverages using a chemically modified electrode.

A Nafion-ruthenium oxide pyrochlore chemically modified electrode is used for the determination of caffeine in beverages by square-wave voltammetry. Compared to a bare glassy carbon electrode, the chemically modified electrode exhibits a marked enhancement of the current response. A linear calibration curve is obtained over the 5-200 microns range in 0.05 M HCIO4 solution with a detection limit (3 delta) of 2 micron. The results of 15 successive repetitive measurement-regeneration cycles showed a relative standard deviation of 2.7% for 10 micron caffeine. Thus, the electrode renewal gives a good reproducible surface. Quantitative analysis was performed by the standard addition method for caffeine content in tea, coffee, decaffeinated coffee, and cola beverages.

Quantitative Determination of Caffeine in Beverages Using a Combined SPME-GC/MS Method

Solid-phase microextraction (SPME) combined with gas chromatography/mass spectrometry (GC/MS) has been applied to the analysis of various caffeinated beverages. Unlike the current methods, this technique is solvent free and requires no pH adjustments. The simplicity of the SPME-GC/MS method lends itself to a good undergraduate laboratory practice. This publication describes the analytical conditions and presents the data for determination of caffeine in coffee, tea, and coke. Quantitation by isotopic dilution is also illustrated.

Determination of Caffeine in Beverages by Capillary Zone Electrophoresis: An Experiment for the Undergraduate Analytical Laboratory

Certain individuals may be sensitive to specific compounds in comsumer products. It is important to quantify these analytes in food products in order to monitor their intake. Caffeine is one such compound. Determination of caffeine in beverages by spectrophotometric procedures requires an extraction procedure, which can prove time-consuming. Although the corresponding determination by HPLC allows for a direct injection, capillary zone electrophoresis provides several advantages such as extremely low solvent consumption, smaller sample volume requirements, and improved sensitivity.

Gas Chromatographic Determination of Caffeine in Beverages by Alkali Aerosol Flame Ionization Detection

The quantitative ability of the presented alkali flame ionization detector to determine the amount of caffeine in selected beverages is examined. A sample cleanup and concentration procedure is employed followed by gas chromatographic separation with alkali flame ionization detection. The amount of caffeine in 12-ounce containers of the beverages ranged from 35 mg to 60 mg. The linear response range of caffeine was observed to be 3.7 orders of magnitude.

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.

Background-correction methods for the determination of caffeine in beverages, coffee and tea by using second-derivative ultraviolet spectrophotometry

Background-correction methods have been developed for the determination of caffeine in beverages, coffee and tea by second-derivative ultraviolet spectrophotometry. The second derivatives of caffeine were measured at 298.6 nm. Interference from tannins in beverages and tea was minimized by treating the sample with 0.1 mol dm–3 sodium hydroxide and by precipitating tannins with copper(II) acetate, respectively. Coffee samples were treated with sodium hydroxide (0.25–0.75 mmol dm–3). The calibration graphs for the three types of sample had slightly different slopes (0.00146–0.00152 A nm–2 ppm–1) and linear ranges. The precision for the determination ranged from 0.3 to 0.9%, at the 10 µg ml–1 level of caffeine. A number of cola drinks, energy drinks, lemon tea drinks, coffee samples and tea samples were analysed.

Determination of caffeine in beverages by high performance liquid chromatography

Determination of caffeine in beverages by high performance liquid chromatography

Separation of oxypurines by ligand-exchange chromatography and determination of caffeine in beverages and pharmaceuticals

Separation of oxypurines by ligand-exchange chromatography and determination of caffeine in beverages and pharmaceuticals