Relationship between Individual and Competitive Adsorption Isotherms on Molecularly Imprinted Polymers

Zsanett Dorkó, Barbara Tamás, George Horvai
2016 Periodica Polytechnica: Chemical Engineering  
Molecularly imprinted polymers (MIP) are a new generation of selective adsorbents. In practical applications of MIPs simultaneous adsorption of at least two compounds occurs. Simultaneous (typically competitive) adsorption on MIPs has not yet been quantitatively analyzed. This paper shows that with a typical type of MIP the individual isotherms of two compounds coincide with their competitive isotherms in the logDlogq isotherm plot, where D is the distribution coefficient and q is the adsorbed
more » ... q is the adsorbed concentration. Based on this observation the usual competitive isotherm, i.e., the (c 1 ,c 2 ) to (q 1 ,q 2 ) mapping can be established from the two individual isotherms. (The c-s are the respective solution phase equilibrium concentrations.) Batch separation experiments can be easily designed and the selectivity of the MIPs is also easily determined without the tedious measurement of the full competitive isotherm. Keywords molecularly imprinted polymer, adsorption isotherm, competitive adsorption isotherm, propranolol, beta blocker 1 Introduction Molecularly imprinted polymers (MIP) are a new generation of selective adsorbents. They are the subject of vigorous research which produces hundreds of papers annually. After years of fundamental research the time appears to be ripe now for their practical applications. This is attested by the increasing number of patent applications (62 in the year 2015 [1]). MIPs may be used as chromatographic stationary phases (e.g., for chiral separations) [2-5], as solid phase extraction (SPE) materials in analytical sample preparation [6, 7], in different variants of capillary electrophoresis [8], as sensor materials [9-11], as artificial antibodies [12], as catalysts [13, 14], as slow release vehicles of pharmaceuticals [15, 16], as adsorbents for selective removal of contaminants [17, 18] and as membrane materials [19]. MIPs are typically made by polymerization of suitable monomers in the presence of a so-called template compound. After polymerization the template is removed from the polymer. This procedure leaves empty binding sites in the polymer, which are chemical and geometrical imprints of the template molecule. Due to these sites the MIP can rebind from solutions the template or other molecules which are chemically related to the template. The rebinding on a good MIP occurs selectively against compounds which are not very closely related to the template. The target compound of a practical application can be either the template or a closely related compound (e.g. if the template is expensive or toxic or its bleeding would disturb). Eventually a group of closely related compounds to the template may be targeted. For successful practical applications one needs to know if the MIP will show sufficient selectivity. Quantification of selectivity is a difficult problem in chemistry, and particularly in analytical chemistry [20] [21] [22] [23] [24] [25] . In the case of MIPs one may rely on a large body of experience in relation to chromatographic adsorbents. The selectivity of liquid chromatographic stationary phases is easily characterized (in a given eluent) if the adsorption isotherms of all adsorbed solutes are linear. In this case selectivity between two adsorbable compounds can be given by the ratio of the respective isotherm slopes, i.e., by the ratio of the respective,
doi:10.3311/ppch.9726 fatcat:s2ctbrduyzbr5fj3cmawkcrjjm