Determination Of Caffeine In Coffee Research Articles

Use of an Online Extraction Technique Coupled to Liquid Chromatography for Determination of Caffeine in Coffee, Tea, and Cocoa

Caffeine is the most widely studied psychoactive molecule in history due to its many pharmacological activities and a high number of biological and physiological effects. In literature, there is a great number of applications that describe extraction, identification, and quantification of caffeine in foods and beverages. For this purpose, an extraction step is followed by an analytical technique for the identification and quantification of caffeine. This work proposes an innovative method in which sample preparation, separation, and detection steps are unified in a single step. To the best of our knowledge, this is the first report on the determination of caffeine in coffee, tea, and cocoa by means of an online extraction coupled to a liquid chromatographic system equipped with a photodiode array detector. The developed methodology was validated in terms of sensitivity, detection limits, accuracy, and precision. The advantages of this technique are (i) a significant reduction of analysis time (more than 70%) and of solvents used (the extraction step is integrated in the chromatographic analysis), (ii) the whole procedure is thus completely automated drastically reducing possible operator errors to occur, and (iii) easily realized by using a conventional monodimensional liquid chromatography system.

Quantitative determination of caffeine in coffee by chemiluminescent method

Quantitative determination of caffeine in coffee by chemiluminescent method

Polymer modified glassy carbon electrode for the electrochemical determination of caffeine in coffee

4-Amino-3-hydroxynaphthalene sulfonic acid (AHNSA) was electropolymerized on a glassy carbon electrode. The deposited film showed electrocatalytic activity towards the oxidation of caffeine. The polymer-modified electrode showed high sensitivity, selectivity and stability in the determination of caffeine in coffee. The peak current increased linearly with the concentration of caffeine in the range of 6×10−8 to 4×10−5molL−1, with a detection limit of 1.37×10−7molL−1 (LoD=3δ/slope). Analysis of caffeine in coffee was affected neither by sample matrices nor by structurally similar compounds. Recoveries ranging between 93.75±2.32 and 100.75±3.32 were achieved from coffee extracts indicating the applicability of the developed method for real sample analyses.

Uncertainty in chemical analysis for the example of determination of caffeine in coffee

The comprehensive quantifying of uncertainty for the determination of caffeine in coffee is given according to the EURACHEM/CITAC Guide. The cause–effect diagram is very useful for the identification of the sources of uncertainty and the relationship between them. In this case the uncertainty caused by the pipette, the stock solution and the calibration curve are the three main sources. Concerning the concentration of the stock solution the purity of the caffeine was most important. The combined uncertainty showed that none of the three parts (stock solution, pipette, calibration curve) can be neglected. The expanded uncertainty (coverage factor k=2) is about 5.4%.

Automatic selective determination of caffeine in coffee and tea samples by using a supported liquid membrane-modified piezoelectric flow sensor with molecularly imprinted polymer

An on-line supported liquid membrane-piezoelectric detection based on molecularly imprinted polymer (SLM-PZ-MIP) manifold was developed and applied to the quantitative determination of caffeine in coffee and tea samples. The proposed assembly provides all the advantages of an on-line system as regards automation, in addition to good selectivity, acceptable sensitivity and precision. The slurry sample was directly placed in SLM unit located in the loop of an injection valve, and the caffeine released from the sample passed through the membrane ( n-undecane/hexyl ether) into an acidic acceptor stream. The caffeine is quantified by using a quartz crystal modified with a molecularly imprinted polymer (MIP). The method shows a linear range between 10 and 1000 ng ml −1, with a relative standard deviation of ±5% (at 50 ng ml −1). Satisfactory results were found by analysing real coffee and tea samples.

The Determination of Caffeine in Coffee: Sense or Nonsense?

If students in undergraduate analytical chemistry education analyze samples of known composition, their results can be verified. If the students get a "real" sample with an unknown composition in the frame of a problem-posing approach to teaching, it is difficult to check whether the students work accurately or not. Thus it is advisable to apply at least two different analytical methods. In this way the students gain a better insight into the differences and similarities of the diverse analytical methods and, by comparing the analytical results obtained with these methods, they get a better idea of the possibilities and accuracies. An important advantage in this approach is that students stimulate themselves to repeat experiments if different values are obtained from different analytical methods. This approach is demonstrated by the determination of caffeine in coffee applying a UV spectrophotometer, HPLC equipment, and CE apparatus. Some representative results are given showing the accuracy of the methods and showing the differences between the separation methods HPLC and CE versus UV spectrophotometry.

Flow injection Fourier transform infrared determination of caffeine in coffee

A fully automatized procedure has been developed for the Fourier transform infrared (FT-IR) spectroscopic determination of caffeine in coffee samples. The method involves the on-line extraction of caffeine with CHCl 3. Samples, weighed inside empty PTFE cartridges of 0.5 cm internal diameter (i.d.) and 1.5 ml volume, were humidified with four drops of 0.25 M NH 3. The cartridge was installed in a flow manifold, in which samples were extracted in a closed-flow system with 1 ml CHCl 3 during 6 min. Four hundred microliters of the extract were introduced in a microflow cell and absorbance measured as a function of time at 1659 cm −1, with a baseline established between 1900 and 830 cm −1, thus providing a fiagram. Peak height values of the FI recordings, obtained for samples, were interpolated in an external calibration line established from standard solutions of caffeine in CHCl 3. The method provided a limit of detection (LOD) of 9 mg l −1 caffeine, a relative standard deviation of 0.6% for five independent measurements of a solution containing 1 mg ml −1 and a sampling frequency of the whole procedure of 6 h −1. Results obtained for market samples agree well with those found by the official chromatographic–spectrometric method, but involving a drastic reduction of solvents, from the 200 ml ether and 50 ml CHCl 3 required for each sample preparation by the reference procedure to less than 30 ml CHCl 3 necessaries for the whole determination of caffeine in a sample, also including standards and carrier solution.

Spectrophotometric flow injection determination of caffeine in solid and slurry coffee and tea samples using supported liquid membranes

A method for the determination of caffeine in coffee and tea samples based on the use of supported liquid membranes coupled to a flow system has been developed. The sample may be analysed both as solid and slurry. In the case of solid sample, this is directly placed in the membrane unit, and when the sample is slurry, this is continuously pumped to the membrane unit. In both cases, the caffeine released from the sample passes through the membrane (PTFE/ n -undecane:hexyl ether) into an acidic acceptor stream. This stream flows through a spectrophotometric detector allowing the measurement of the absorbance of caffeine at 274 nm. The method shows a linear range between 0.5 and 15 g l −1 , with a relative standard deviation of ±3.7% and a sample throughput of 7–8 samples h −1 .

The Benefits of near Infrared Analysis for Food Product Quality

This is a poster presentation. Raw materials have a decisive influence on the quality of a product. Therefore it is important to check raw materials not only for quality and composition but also for identity. It is also essential to check material during the production process to prevent defective products and to save costs resulting from any out of specification batch. Such in-process measurements are also used for process control. The power of NIR spectroscopy includes both qualitative and quantitative analysis. Results can be obtained within a few seconds. Since no chemicals or time consuming sample preparation is necessary NIR spectroscopy is an ideal analytical method for at-line and in-line measurements. NIR spectroscopy is well established to measure moisture, protein, and fat – the three major constituents in food processing. For these three and a few other constituents a selection of 19 specific wavelengh filters can give all necessary information. But NIR spectroscopy is not only an appropriate tool to analyze these “standard parameters” it can also be very helpful when determining less conventional or minor parameters. Therefore often a higher flexibility regarding the wavelength selection is required which makes the collection of a full spectrum necessary. Some of these less common applications are the determination of caffeine in coffee, theobromine in chocolate or trans fatty acids in margarine. Other product specific parameters which have a strong influence on processing behaviour like the tenderness of peas or the degree of substitution in modified starch can also be measured by NIR.

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.

Reproducibility of the determination of caffeine in coffee by micellar electrokinetic capillary chromatography

AbstractSamples of regular and decaffeinated varieties of green coffee beans, instant coffee, and “roast & grind” coffee have been examined by micellar electrokinetic capillary chromatography (MECC). The separation conditions affecting the reproducibility of the determination of caffeine in these samples are presented. Sodium dodecyl sulfate (SDS) and cetyltrimethylammonium chloride (CTAC) Were employed to demonstrate the role of the surfactant system in reproducibility. The use of NaOH and HCl was explored for column rinsing to enhance the stability of the electroosmotic flow. The levels of caffeine ranged from 3.95% (by weight) for regular coffee to 0.07% for decaffeinated coffee. The relative standard deviation (RSD) for the migration time of the peak corresponding to caffeine in coffee samples was 0.74%. The RSDs for the peak areas and heights were 1.04 and 2.07%, respectively. The results of the quantitation of caffeine by MECC are compared to levels determined by high‐performance liquid chromatography (HPLC).

Determination of Caffeine in Coffee, Black Tea and Green Tea by High Performance Liquid Chromatography

A simple and practical method for the determination of caffeine in coffee, black tea and green tea is described. It is based on the extraction and clean-up of caffeine using an Extrelut column and analysis by means of high performance liquid chromatography with an ultraviolet detector (275nm). A column of Lichrosorb Si60 (silica gel) and H2O-saturated dichloromethane-ethanol (97:3) as a mobile phase are used.In this method, the average recoveries of caffeine from several samples were 98-102%, the relative standard deviations for the whole procedure were 0.61-7.8%, and the limit of determination for caffeine in sample solution was about 1μg per ml. The proposed method was applied to the determination of caffeine in coffee, canned coffee, black tea and green tea.

High-Pressure Liquid Chromatography of Caffeine in Coffee

A new method is described for the determination of caffeine in coffee, based on high-pressure liquid chromatography. The caffeine is extracted from the sample with water and/or methylene chloride, and then separated from interfering materials by passing an aliquot of the extract through a high-pressure column containing sulfonated cation exchange resin, using 0.01M nitric acid as the mobile phase. An ultraviolet detector measures the absorption of the solution directly. The method is rapid and eliminates the lengthy separations common to other methods. The procedure was applied successfully to decaffeinated and non-decaffeinated green, roasted, and instant coffees. This method gives a more accurate measure of the caffeine content in decaffeinated coffee samples than the micro Bailey-Andrew and modified Levine methods, with equal or better precision. This method gives results equal to those obtained by the official methods for non-decaffeinated samples.

Métodos de análise orgânica do café. II. Comparação entre métodos de determinação da cafeína em café verde

O método micro Bailey-Andrew, oficial da A. O. A, C. (1970) e o proposto por NAVELLIER et al. (1969) para determinação de cafeína em café, foram comparados. Para extração e purificação seguiu-se os dois métodos citados e para a determinação propriamente dita utilizou-se o peso, nitrogênio total, espectrofotometria com correção da linha de base e o pico à 273 nm. As seguintes conclusões foram tiradas: a) A determinação por pesagem não deve ser utilizada para nenhum dos dois métodos de extração e purificação, pois além dos valores encontrados serem bem acima dos reais, os coeficientes de variação também foram altos. b) O método de extração e purificação de NAVELLIER et al. (1969) não consegue remover interferentes nitrogenados, mas talvez possa ser utilizado quando a cafeína é determinada por espectrofotometria com correção da linha de base. c) Não houve diferença significativa entre a determinação da cafeína pelo nitrogênio e espectrofotometria com correlação da linha de base quando se seguiu a extração e purificação da A, O. A. C. (1970).

Note on the Determination of Caffeine in Coffee

Abstract A chromatographic-spectral method can be vised for the determination of caffeine in coffee products as well as in beverages and caffeine-containing drugs. Four methods (the official micro Bailey-Andrew and three chromatographic procedures) have been compared on six different types of coffees. A modified version of the Levine procedure appears to have value as a general purpose caffeine method.

The spectrophotometric determination of caffeine in coffee and tea products, with special reference to coffee and chicory mixtures

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