Caffeine determination

Typical Thin-Layer Chromatography (TLC) Systems for Theobromine and Caffeine Determinations... 

Caffeine The stimulant effect of coffee is due to caffeine, C8H10N4O2. Calculate the molar mass of caffeine. Determine its percent composition. 

Dependence of stacking affinity upon the replacement of purine nitrogens by CH groups. Complexes with caffeine determined at 7°. 

Allen used NIR for the quantitative determination of carisopro-dol, phenacetin, and caffeine [116]. Twenty tablets were pulverized and an aliquot dissolved in chloroform was measured. Standard solutions of carisoprodol, phenacetin, and caffeine were scanned between 2750 and 3000 nm. Caffeine and phenacetin were determined at 2820 nm (carisoprodol) and 2910 nm (phenacetin), with caffeine determined at 3390 nm. The coefficient of variation (CV) was 1.4% or less. 

Comparison of Gas-Liquid Chromatography with Nitrogen-Phosphorus Selective Detection and High-Performance Liquid Chromatography Methods for Caffeine Determination in Plasma and Tissues... 

Based upon these results, a simple, rapid, reproducible and accurate voltammetric method was proposed for the determination of xanthine, theophylline, theobromine and caffeine in the micromolar concentration range [26], The analytical performance characteristics of the method are comparable to those reported for the determination of xanthines by the use of chemically modified electrodes, biosensing techniques and differential pulse voltammetry. The excellent results obtained for caffeine determination in commercially available products, with very simple sample preparation, involving only dilution in electrolyte, demonstrates the practical analytical utility of the method. 

This publication provides several examples of the use of solid-phase extractions for separating analytes from their matrices. Some of the examples included are caffeine from coffee, polyaromatic hydrocarbons from water, parabens from cosmetics, chlorinated pesticides from water, and steroids from hydrocortisone creams. Extracted analytes maybe determined quantitatively by gas (GC) or liquid chromatography (LG). 

Yang, M. J. Orton, M. L. Pawliszyn, J. Quantitative Determination of Caffeine in Beverages Using a Combined SPME-GC/MS Method, /. Chem. Educ. 1997, 74,... 

Many pharmaceutical compounds are weak acids or bases that can be analyzed by an aqueous or nonaqueous acid-base titration examples include salicylic acid, phenobarbital, caffeine, and sulfanilamide. Amino acids and proteins can be analyzed in glacial acetic acid, using HCIO4 as the titrant. For example, a procedure for determining the amount of nutritionally available protein has been developed that is based on an acid-base titration of lysine residues. ... 

Procedures for determining the concentrations of caffeine, benzoic acid and aspartame in soda by these three methods are provided. In the example provided in this paper, the concentrations of caffeine and benzoic acid in Mello Yellow are determined spectrophotometrically. 

Caffeine in coffee, tea, and soda is determined by a solid-phase microextraction using an uncoated silica fiber, followed by a GC analysis using a capillary SPB-5 column with an MS detector. Standard solutions are spiked with G3 caffeine as an internal standard. 

The concentrations of benzoic acid, aspartame, caffeine, and saccharin in a variety of beverages are determined in this experiment. A Gig column and a mobile phase of 80% v/v acetic acid (pH = 4.2) and 20% v/v methanol are used to effect the separation. A UV detector set to 254 nm is used to measure the eluent s absorbance. The ability to adjust retention times by changing the mobile phase s pH is also explored. 

The concentration of caffeine in a typical serving of coffee and soda is determined in this experiment. Separations are achieved using a Gjg column with a mobile phase of 30% v/v methanol in water, with UV detection at a wavelength of 254 nm. 

Conte, E. D. Barry, E. E. Rubinstein, H. Determination of Caffeine in Beverages by Capillary Zone Electrophoresis, ... 

Caffeine in tea and coffee is determined by CZE using nicotine as an internal standard. The buffer solution is 50 mM sodium borate adjusted to pH 8.5 with H3PO4. A UV detector set to 214 nm is used to record the electropherograms. 

Students determine the concentrations of caffeine, acetaminophen, acetylsalicylic acid, and salicylic acid in several analgesic preparations using both CZE (70 mM borate buffer solution, UV detection at 210 nm) and HPLC (C18 column with 3% v/v acetic acid mixed with methanol as a mobile phase, UV detection at 254 nm). 

The amount of caffeine in an analgesic tablet was determined by HPLC using a normal calibration curve. Standard solutions of caffeine were prepared and analyzed using a lO-pL fixed-volume injection loop. Results for the standards are summarized in the following table. 

The theobromine and caffeine contents of several finished chocolate products as determined by hplc at Hershey s laboratories are presented in... 

High performance liquid chromatography is used for the separation and quantitative analysis of a wide variety of mixtures, especially those in which the components are insufficiently volatile and/or thermally stable to be separated by gas chromatography. This is illustrated by the following method which may be used for the quantitative determination of aspirin and caffeine in the common analgesic tablets, using phenacetin as internal standard where APC tablets are available the phenacetin can also be determined by this procedure. 

M.9 The stimulant in coffee and tea is caffeine, a substance of molar mass 194 g-mol When 0.376 g of caffeine was burned, 0.682 g of carbon dioxide, 0.174 g of water, and 0.1 10 g of nitrogen were formed. Determine the empirical and molecular formulas of caffeine, and write the equation for its combustion. 

Determine the amount of heat released and the molar energy of combustion of caffeine. 

NAIK J P and NAGALAKSHMi s (1997) Determination of caffeine in tea products by an unproved high-performance liquid chromatography method , JAgric Food Chem, 45, 3973-5. 

WANG H, HELLiwELL K and YOU X (2000a) Isocratic elution system for the determination of catechins, caffeine and gallic acid in green tea using HPLC ,Pood Chem, 68 (1), 115-21. 

FERNANDEZ P L, MARTIN M J, GONZALEZ A G, PABLOS F (2000) HPLC determination of catechins and caffeine in tea. Differentiation of green, black and instant teas, Analyst, 125,421-5. 

Zougagh, M., Valcarcel, M., and Rios, A., Automatic selective determination of caffeine in coffee and tea samples by using a supported liquid membrane-modified piezoelectric flow sensor with molecularly imprinted polymer. Trends Anal. Chem., 23, 399, 2004. 

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