Caffeine-imprinted polymer

Fig. 6a-c. Scatchard plots for a caffeine binding to a caffeine imprinted polymer b theophylline binding to a theophylline imprinted polymer c caffeine to a theophylline imprinted polymer [29]... 

Similar kind of studies using MM method and Hyperchem 7.5 software package was performed on caffeine-imprinted polymers [Farrington et al., 2006]. The nature of interaction between template... 

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. 

In a further application of MI-SPE, theophylline could be separated from the structurally related caffeine by combining the specific extraction with pulsed elution, resulting in sharp baseline-separated peaks, which on the other hand was not possible when a theophylline imprinted polymer was used as stationary phase for HPLC. A detection limit of 120 ng mb1 was obtained, corresponding to a mass detection limit of only 2.4 ng [45]. This combination of techniques was also used for the determination of nicotine in tobacco. Nicotine is the main alkaloid in tobacco and is the focus of intensive HPLC or GC analyses due to its health risk to active and passive consumers. However, HPLC- and GC-techniques are time-consuming as well as expensive, due to the necessary pre-purification steps required because the sample matrices typically contain many other organic compounds besides nicotine. However, a simple pre-concentration step based on MI-SPE did allow faster determination of nicotine in tobacco samples. Mullett et al. obtained a detection limit of 1.8 jig ml 1 and a mass detection limit of 8.45 ng [95]. All these examples demonstrate the high potential of MI-SPE to become a broadly applicable sample pre-purification tool. 

However, the theophylline-imprinted polymer beads also bound more caffeine than theophylline, pointing out the fact that nonspecific hydrophobic interactions may play a role in the absorption phenomenon. 

Table 5 Comparison of performance of quartz crystal microbalance chemosensors using molecularly imprinted polymer for determination of caffeine... 

LAI E P C, FARFARA A, VANDERNOOT V A, KONO M and POLSKY B (1998), Surface plasmon resonance sensors using molecularly imprinted polymers for sorbent assay theophylline, caffeine and xanthan , Can J Chem, 76, 265. 

LIANG c, PENG H, bao x, nie L and yao s (1999), Study of a molecular imprinting polymer coated BAW bio-mimic sensor and its application to the determination of caffeine in human serum and urine , Analyst, 124, 1781-1785. 

Mosbach and co-workers developed a method to prepare molecularly imprinted polymers by precipitation polymerization [24]. They started from a dilute, homogenous solution of the monomer methacrylic acid (MAA) and the crosslinker trimethylolpropane trimethacrylate (TRIM) or ethylene glycol dimethacrylate (EGDMA). The polymer formed in the presence of the template molecule 17/1-estradiol, theophylline, or caffeine contained a high proportion of discrete spheres of diameter less than a micron. Because the effect of coalescence becomes predominant with higher solid content of the reaction mixture, this approach is limited to solid contents of typically <2 wt%. 

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... 

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]. 

Ethylene glycol dimethacrylate (EDMA)-methacrylic acid (MAA) copolymer-based imprinted polymer particles were mixed with poly(vinyl chloride) in THF, and the solution was then spread on the electrode of the QCM by spin coating. After evaporation of the THF, the polymer particles were immobilized on the surface. A phenobarbital-imprinted QCM sensor prepared in this way worked in ethanol [1], while epinephrine- and caffeine-imprinted QCMs worked in buffer solutions (pH 6.0 and pH 8.0, respectively) [2, 3],... 

This approach has been used to imprint theophylline [74], which was attached to the surface of silica gel particles and an imprinted polymer assembled around the inorganic particles. When polymerization was complete, the silica was dissolved away with hydrofluoric acid. This yielded imprinted polymer particles with a narrow pore size distribution with diameters between 254 and 257 A compared with conventionally prepared imprinted polymers which have pore diameters in the range 30-1000 A. The imprinted polymer showed a high selectivity for theophylline over the related compounds caffeine and theobromine. 

Thus, Mayes and Lowe showed that an MIA for morphine worked equally well when the MIP was synthesized using a morphine MAA ratio of 1 500 as 1 5 [21], while Yilmaz et al. showed an MIA for theophylline worked equally well with a theophylline MAA ratio of 1 1000 as 1 4 [22] Theophylline-imprinted polymers employing only 2.5 pmol template per gram of monomers (compared with 151 pmol g in Vlatakis et al. s MIA [16]) were employed, and the MIA functioned well, with caffeine cross-reacting less than 0.1%. These works demonstrate that the oft-quoted drawback of MIPs, the cost of the template required for their preparation, may be overcome MIA is applicable even to expensive templates. 

Liang, C. Peng, H. Bao, X. Nie, L. Yao, S. Study of Molecular Imprinting Polymer Coated Baw Bio-Mimetic Sensor and Its Application to the Determination of Caffeine in Human Serum and Urine. Analyst 1999, 124, 1781-1785. 

Alizadeh, T. Ganjali, MR. Zare, M Norouzi, P. (2010). Development of a voltammetric sensor based on a molecularly imprinted polymer (MIP) for caffeine measurement. Electrochimica Acta, 55,1568-1574. 

B.S. Ebarvia, C.A. Binag and F. Sevilla, Biomimetic piezoelectric quartz sensor for caffeine based on a molecularly imprinted polymer, Anal. Bioanal. Chem., 378 (5) 1331-1337, 2004. 

Fig. 15. Displacement of radio-labeled analyte analog binding to MI spheres under equilibrium condition. B/B0 is the ratio of the amount of radio-labeled ligand bound in the presence of the displacing ligand (analyte), B0. Displacement of [8-3H]theophylline binding to a polymer imprinted with theophylline. Displacing ligands theophylline ( ) theobromine (+) xanthine (o) caffeine (A). Reprinted with permission from Ye L, Cormack PAG, Mosbach K (1999) Anal Commun 36 35. Copyright 1999 The Royal Society of Chemistry...

Separation of theophylline and caffeine by column containing polymer imprinted with theophylline. Caffeine washed right through with CHCI3 solvent. Addition of 20 id. of CH3OH to the solvent breaks hydrogen bonds between theophylline and the polymer and elutes theophylline in a volume of t mL [From W. M. Mulleti and P C. Lai. Anal. Chem. 1998, 70.3636.]... 

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