Caffeine residues

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. ... 

Until the 1980s, synthetic organic solvents commonly were used in the United States to extract the caffeine, either by direct contact as above or by an indirect secondary water-based system (36). In each case, steaming or stripping was used to remove residual solvent from the beans and the beans were dried to their original moisture content (10—12%) prior to roasting. 

Decaffeination Regulations. Eor decaffeinated roasted coffee, EEC standards indicate the maximum content of caffeine as 0.1% db for decaffeinated instant coffee it is 0.3% db. In the United States, decaffeination usually signifies that 97% of the caffeine has been removed. Permissible solvents for decaffeination processes are defined by national legislation, eg, EDA or EEC directive. The maximum residual solvent content after decaffeination, roasting, or instant coffee processing is to be kept within good manufacturing practice, ie, very low ppm levels or below at point of sale (46). 

Several selective interactions by MIP membrane systems have been reported. For example, an L-phenylalanine imprinted membrane prepared by in-situ crosslinking polymerization showed different fluxes for various amino acids [44]. Yoshikawa et al. [51] have prepared molecular imprinted membranes from a membrane material which bears a tetrapeptide residue (DIDE resin (7)), using the dry phase inversion procedure. It was found that a membrane which contains an oligopeptide residue from an L-amino acid and is imprinted with an L-amino acid derivative, recognizes the L-isomer in preference to the corresponding D-isomer, and vice versa. Exceptional difference in sorption selectivity between theophylline and caffeine was observed for poly(acrylonitrile-co-acrylic acid) blend membranes prepared by the wet phase inversion technique [53]. 

In some cases, the solids themselves are subjected to extraction by a solvent. For example, in one process used to decaffeinate coffee, the coffee beans are mixed with activated charcoal and a high-pressure stream of supercritical carbon dioxide (carbon dioxide at high pressure and above its critical temperature) is passed over them at approximately 90°C. A supercritical solvent is a highly mobile fluid with a very low viscosity. The carbon dioxide removes the soluble caffeine preferentially without extracting the flavoring agents and evaporates without leaving a harmful residue. 

Another scheme for methylxanthine isolation involves the extraction of the dried ground plant with 10% ammonium hydroxide chloroform (1 10). A large proportion of the extraction mixture is used, relative to the sample, to ensure complete extraction of any theobromine. Caffeine and theophylline will be extracted easily under these conditions.20 After removing water from the organic layer, filtration, and solvent removal, any methylxanthines present will be in the residue together with some impurities. An approach to finally isolating these methylxanthines from this... 

HPLC with thermospray MS was reported by Hurst et al.40 where residues from an archeological site were analyzed for caffeine and theobromine using reversed phase HPLC coupled to a thermospray MS interface. Samples were extracted in water and separated on a reversed phase column. The presence of theobromine in this sample was confirmed by monitoring the MH+ ion at 181 for theobromine. 

Decaffeination of green coffee beans is most usually carried out with a water/solvent partition system. The green coffee beans are first steamed until they are hot, wet, and swollen, to make the caffeine available. Solvent is then used to extract the caffeine out of the aqueous phase of the beans. Finally, the beans are steamed to drive off residual solvent. The coffee beans lose their wax surface covering in the process, as well as some flavor components. For this reason, the Robusta and Brazilian Arabica coffees that are dry-processed and have the most powerful flavors are usually the types that are decaffeinated. They become milder in the process. Mechanical polishing is used to improve the appearance of decaffeinated green coffee beans if they are not to be roasted immediately. Extra care is required, however, to store these decaffeinated beans since the loss of wax covering as well as caffeine renders them much more susceptible to fungal attack. 

Beaumont, M., Batejat, D., Coste, O. et al. (2005). Recovery after prolonged sleep deprivation residual effects of slow-release caffeine on recovery sleep, sleepiness and cognitive functions. Neuropsychobiology 51 (1), 16-27. 

Water is a good choice of solvent in a standard kitchen percolator because it removes all the water-soluble components from the coffee - hence the flavour. Clearly, however, a different solvent is required if only the caffeine is to be removed. Such a solvent must be cheap, have a low boiling point to prevent charring of the coffee and, most importantly, should leave no toxic residues. The presence of any residue would be unsatisfactory to a customer, since it would almost certainly leave a taste and there are also health and safety implications when residues persist. 

The pale yellow chloroform solution is decolorised by shaking, first with a few cubic centimetres of sodium hydroxide solution, then with the same volume of water, and is evaporated to dryness. The residue of crude caffeine is recrystallised from a little hot water. Yield 2-0-2-5 g. Soft, flexible, silky needles containing one molecule of water of crystallisation. 

Caffeine and other purine derivatives can be detected by the Murexide test. In this test the alkaloids are mixed with a tiny amount of potassium chlorate and a drop of hydrochloric acid and evaporated to dryness, and the resulting residue is exposed to ammonia vapour. Purine alkaloids produce pink colour in this test. 

Food Applications, Carbon dioxide, a nontoxic material, can be used to extract thermally labile food components at near-ambient temperatures. The food product is thus not contaminated with residual solvent, as is potentially the case when using conventional liquid solvents such as methylene chloride or hexane. In the food industry, C02 is not recorded as a foreign substance or additive. Supercritical solvents not only can remove oils, caffeine, or cholesterol from food substrates, but can also be used to fractionate mixtures such as glycerides and vegetable oils into numerous components. 

In the case of the Group 3 compounds anthraquinone, caffeine, and quinoline, it seems likely that the low trap recoveries and high residual concentrations of quinoline and caffeine in the raffinate were due to the... 

Substances being measured—caffeine and theobromine in this case—arc called analytes. The next step in the sample preparation procedure was to make a quantitative transfer (a complete transfer) of the fat-free chocolate residue to an Erlenmeyer flask and to dissolve the analytes in water for the chemical analysis. If any residue were not transferred from the tube to the flask, then the final analysis would be in error because not all of the analyte would be present. To perform the quantitative transfer, Denby and Scott added a few milliliters of pure water to the centrifuge tube and used stirring and heating to dissolve or suspend as much of the chocolate as possible. Then they poured the slurry (a suspension of solid in a liquid) into a 50-mL flask. They repeated the procedure several times with fresh portions of water to ensure that every bit of chocolate was transferred from the centrifuge tube to the flask. 

To complete the dissolution of analytes, Denby and Scott added water to bring the volume up to about 30 mL. They heated the flask in a boiling water bath to extract all the caffeine and theobromine from the chocolate into the water. To compute the quantity of analyte later, the total mass of solvent (water) must be accurately known. Denby and Scott knew the mass of chocolate residue in the centrifuge tube and they knew the mass of the empty Erlenmeyer flask. So they put the flask on a balance and added water drop by drop until there were exactly 33.3 g of water in the flask. Later, they would compare known solutions of pure analyte in water with the unknown solution containing 33.3 g of water. 

Caffeine has been isolated from waste tea and from the decaffeiniza-tion of coffee by extraction at 70°C, using rotating countercurrent drums and an organic solvent, frequently trichloroethylene. The solvent is drained off, and the beans steamed to remove residual solvent. The extraction solvent is evaporated, and the caffeine is hot-water-extracted from the wax, decolorized with carbon, and recrystallized. 

To a mixture of 1-bromoadamantane (0.3 mmol), TPDS (0.45 mmol), and caffeine salt (1.5 mmol) with camphorsulfonic acid was added AIBN (0.45 mmol) over 8 h (5 times in 2 h intervals). After 4 h, TPDS (0.45 mmol) was added again. After a total of 22 h, sat. aq. NaHC03 solution was added and the mixture was extracted with ethyl acetate. The organic layer was dried over Na2S04. After removal of the solvent, the residue was chromatographed on silica gel to provide 2-(l-adamantyl)caffeine in 55% yield [30]. 

Remove the dichloromethane by evaporation in the hood. Be careful not to overheat the solvent, since it may foam over. The solid residue which remains after the solvent is gone is the crude caffeine. Reweigh the cooled flask (3). Calculate the weight of the crude caffeine by subtraction (4) and determine the percent yield (5). 

Methylene chloride (CH2C12) and chloroform (CHC13) are also good solvents for cleaning and degreasing work. Methylene chloride was once used to dissolve the caffeine from coffee beans to produce decaffeinated coffee. Concerns about the safety of coffee with residual traces of methylene chloride prompted coffee producers to use liquid carbon dioxide instead. Chloroform is more toxic and carcinogenic than methylene chloride it has been replaced by methylene chloride and other solvents in most industrial degreasers and paint removers. 

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