Caffeine solid extraction

Caffeine is extracted from beverages by a solid-phase microextraction using an uncoated fused silica fiber. The fiber is suspended in the sample for 5 min and the sample stirred to assist the mass transfer of analyte to the fiber. Immediately after removing the fiber from the sample it is transferred to the gas chromatograph s injection port where the analyte is thermally desorbed. Quantitation is accomplished by using a C3 caffeine solution as an internal standard. 

Solid extracts of (1) alfalfa and (2) red clover (used in food flavorings) were examined by GC/MS. 389 of 450 detected components were identified in (1), vs. 210 of 309 components detected in (2). In both extracts, predominant compounds identified were esters (1) 105, (2) 55 acids (1) 42, (2) 31 alcohols (1) 34, (2) 31 and hydrocarbons (1) 28, (2) 14. Many other compounds were also found, including cannabinol, caffeine, scopolamine, isocoumarin, phenylpentadienal, phenylhexadiene, and nepetalactone.25... 

Caffeine is extracted at about the same rate as the remainder of the beverage solids as shown by the proportion of caffeine in the extracted solids. 

Because of its low cost, nonhazardous chemical nature, and low critical temperature, carbon dioxide has been used in many applications. A commercial process to remove caffeine from coffee, using supercritical C02 as the solvent, is shown in Fig. 17. While actually a liquid-solid extraction process, it demonstrates principles involved in SCFE. A commercial SCFE process has been reported for recovery of hydrocarbon liquid from heavy oil. As compared with conventional propane deasphalting, this SCFE process can reduce capital and energy costs. 

Extraction - making a cup of coffee involves extraction of the flavour chemicals and caffeine from the insoluble vegetable matter using hot water and is an example of liquid-solid extraction. 

In commercial solid extracts of alfalfa and red clover, traces of cannabinol, caffeine, scopolamine, isocoumarin, phenylpentadie-nal, phenylhexadiene, and nepetalactone have been reported. Whether or not these compounds were results of contamination or adulteration remains to be confirmed. 

Some commercial solid extracts of red clover have been reported to contain traces of cannabinol, caffeine, scopolamine, isocou-marin, phenylpentadienal, phenylhexadiene, and nepetalactone (see alfalfa) Contents of the major isoflavone constituents show wide variability. 

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). 

The dense fluid that exists above the critical temperature and pressure of a substance is called a supercritical fluid. It may be so dense that, although it is formally a gas, it is as dense as a liquid phase and can act as a solvent for liquids and solids. Supercritical carbon dioxide, for instance, can dissolve organic compounds. It is used to remove caffeine from coffee beans, to separate drugs from biological fluids for later analysis, and to extract perfumes from flowers and phytochemicals from herbs. The use of supercritical carbon dioxide avoids contamination with potentially harmful solvents and allows rapid extraction on account of the high mobility of the molecules through the fluid. Supercritical hydrocarbons are used to dissolve coal and separate it from ash, and they have been proposed for extracting oil from oil-rich tar sands. 

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. 

Instant tea produced as described above will dissolve completely in hot water but not in cold water, as the caffeine-polyphenol complexes are insoluble under those conditions. Since virtually all instant tea manufacture in the U.S. is for iced tea preparation, process modification is required. This initial extract may be cooled to 5 to 10°C and the cold water insoluble material or cream be allowed to precipitate. Under these conditions, 20 to 35% of the extract solids may be separated by centrifugation. The supernatant solids will reconstitute in cold water after concentration and drying.105 It is also possible to process the cream to make a portion of it compatible with the product and thereby retain the caffeine and some polyphenolic components that are present in this fraction.106 Commercial use of the enzyme Tannase, which removes gallic acid from gallated tea polyphenols107 and reduces cream formation108 can be used to reduce cream losses and manufacture instant teas retaining more of the natural polyphenol content. 

An XRPD system equipped with a heatable sample holder has been described, which permitted highly defined heating up to 250°C [55]. The system was used to study the phase transformation of phenan-threne, and the dehydration of caffeine hydrate. An analysis scheme was developed for the data that permitted one to extract activation parameters for these solid-state reactions from a single non-isothermal study run at a constant heating rate. 

Patsias, J. and E. Papadopoulou-Mourkidou. 2000. Development of an automated on-line solid-phase extraction-high-performance liquid chromatographic method for the analysis of aniline, phenol, caffeine and various selected substituted aniline and phenol compounds in aqueous matrices. J. Chromatogr. A 904 171-188. 

The potential of supercritical extraction, a separation process in which a gas above its critical temperature is used as a solvent, has been widely recognized in the recent years. The first proposed applications have involved mainly compounds of low volatility, and processes that utilize supercritical fluids for the separation of solids from natural matrices (such as caffeine from coffee beans) are already in industrial operation. The use of supercritical fluids for separation of liquid mixtures, although of wider applicability, has been less well studied as the minimum number of components for any such separation is three (the solvent, and a binary mixture of components to be separated). The experimental study of phase equilibrium in ternary mixtures at high pressures is complicated and theoretical methods to correlate the observed phase behavior are lacking. 

Solubilitiesattemperaturesand pressures above the critical values of the solvent liave important applications for supercritical separation processes. Examples are extraction of caffeine from coffee beans and separation of asplraltenes from heavy petroleum fractions. For a typical solid/vapor equilibrium (SVE) problem, tire solid/vapor saturation pressure P is very small, and the saturated vapor is for practical purposes an ideal gas. Hence 0 for pure solute vapor at this pressure is close to unity. Moreover, exceptfor very low values of the system pressure P, the solid solubility yj is small, and can be approximated by j, the vapor-phase fugacity coefficient of the solute at infinite dilution. Finally, since is very small, the pressure difference P — in the Poyntingfactor is nearly equal to P at any pressure where tins factor... 

Georga, K.A. Samanidou, V.F. Papadoyannis, l.N. The use of novel solid phase extraction sorbent materials for HPLC quantitation of caffeine metabolism products methyl-xanthines and methyluric acids in samples of biological origin. J. Chromatogr., B 2001, 759, 209 -218. 

Solid-liquid extraction is applied on an industrial scale to produce oils and fats from oil-bearing seeds. In the food and flavour industry, extracts and resins, such as hop, chamomile, peppermint, valerian, vanilla, red pepper and liquorice, are obtained from herbs, roots, seeds and drugs. The technology has also found application in the pharmaceutical industry for the extraction of antibiotics, alkaloids and caffeine. 

Tea drinks or iced teas are refreshing drinks containing soluble tea solids. Depending on tea extract quality, one can obtain turbid or clear products with a specific astringent tea flavour and red brownish colour. Flavours and colours alone are used for obtaining drinks with an authentic tea flavour and no caffeine to serve the children s market. In this area, fruit teas with bright red hibiscus extracts are also common. 

Farrington, K Magner, E. Regan, F., Predicting the performance of molecularly imprinted polymers, Selective extraction of caffeine by molecularly imprinted solid phase extraction, Anal. Chim. Acta. 2006, 566, 60-68... 

Rodrigues, C.I., Marta, L., Maia, R., Miranda, M., Ribeirinho, M., and Maguas, C. 2007. Application of solid-phase extraction to brewed coffee caffeine and organic acid determination by UV/HPLC. Journal of Food Composition and Analysis 20 440-448. 

Theodoridis, G. Manesiotis, P. Selective solid-phase extraction sorbent for caffeine made by molecular imprinting. J. Chromatogr. A. 2002, 948 (1-2), 163-169. 

The application of MIPs as the stationary phase in solid-phase extraction (SPE), often referred to as molecularly imprinted polymer solid-phase extraction (MIS P E), is a rapidly growing area [197-199]. With MISPE, highly specific enrichment of substances present at trace levels is possible. The technique has been applied to the analysis of drugs, for example, caffeine [200], scopolamine [201], naproxen [202], tetracycline [203], cholesterol [204] and local anesthetics [205], as well as environmental pollutants, exemplified by organophosphate flame retardants [206-208], triazines in soil and vegetable samples [71] and naphthalene sulfonates in river water [209]. 

---