In situ imprinted polymers

In situ-imprinted polymers [39] To further simplify construction of such sensors we investigated the use of in situ or rod imprinted polymers using the technique pioneered by Matsui et al. (see Chapter 13). Solutions of template, either DEAEMA or AA as functional monomers, EDMA and initiator in the porogen (4 1 octanohdodecanol, w/w) were introduced into 100 x 4.6 mm (i.d.) HPLC columns and polymerised in situ at either 50 or 70°C. These rods were then flushed with MeCN until a stable absorbance and back pressure were obtained. The most selective polymers were those polymerised at 50°C using DEAEMA as the functional monomer, with a functional monomer/template ratio of either 2 1 or 4 1. The latter was chosen for use in the sensor so as to directly compare the results obtained using bulk and in situ imprinted polymers. 

McNiven S, Kato M, Yano K, Karube I (1998) Chloramphenicol sensor based on an in situ imprinted polymer. Anal Chim Act 365(6) 69-74... 

The in situ molecular imprinting protocol employing dispersion polymerisation has some advantageous features. The dispersion polymer can be removed from a column and re-packed when a column is damaged after repeated use. Back-pressure of agglomerated polymer particles is less problematic therefore, this in situ method can be applied to a wider range of analytical techniques. Here, two applications of in situ dispersion polymer, solid phase extraction (SPE) and CE are described. 

An early example of an MIP-QCM sensor was a glucose monitoring system by Malitesta et al. (1999). A glucose imprinted poly(o-phenylenediamine) polymer was electrosynthesized on the sensor surface. This QCM sensor showed selectivity for glucose over other compounds such as ascorbic acid, paracetamol, cysteine, and fructose at physiologically relevant millimolar concentrations. A unique QCM sensor for detection of yeast was reported by Dickert and coworkers (Dickert et al. 2001 Dickert and Hayden 2002). Yeast cells were imprinted in a sol-gel matrix on the surface of the transducer. The MIP-coated sensor was able to measure yeast cell concentrations in situ and in complex media. A QCM sensor coated with a thin permeable MIP film was developed for the determination of L-menthol in the liquid phase (Percival et al. 2001). The MIP-QCM sensor displayed good selectivity and good sensitivity with a detection limit of 200 ppb (Fig. 15.7). The sensor also displayed excellent enantioselectivity and was able to easily differentiate the l- and D-enantiomers of menthol. 

Impedance spectroscopy 807, 814 Imprinted polymers 57 In Situ Generation of Mercury 144 In-channel 837, 839-842, 844, 849-851, 854, 856... 

New in situ techniques with enhancements in sensitivity and selectivity (sensors based on molecular imprinted polymers)... 

Molecularly imprinted polymers with a variety of shapes have also been prepared by polymerizing monoliths in molds. This in situ preparation of MIPs was utilized for filling of capillaries [20], columns [21], and membranes [22, 23]. Each specific particle geometry however needs optimization of the respective polymerization conditions while maintaining the correct conditions for successful imprinting. It would be advantageous to separate these two processes, e.g., to prepare a molecularly imprinted material in one step, which then can be processed in a mold process in a separate step to result the desired shape. 

Unfortunately, to date, this technique has received little attention from the molecular imprinting community and only one report of a dispersion polymerisation method had appeared until very recently [26]. This is probably better classified as a precipitation polymerisation, since random aggregates were produced rather than beads. No colloidal stabilisers were included in this procedure. The aggregates were made in situ in chromatography columns, which avoided the need to grind and sieve the polymer and pack the columns. Due to the rather polar nature of the solvent mixtures used (cyclohexanol, dodecanol, isopropanol), good imprints were only achieved for compounds which interact strongly with functional monomer... 

In situ molecular imprinting can be defined as a technique for preparing imprinted polymers in a place where the polymers are subsequently utilised. Imprinted polymers prepared by an in situ technique, therefore, require no subse-... 

Fig. 13.3. In situ procedure for preparing molecularly imprinted polymer rods.

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