Effect of Polymer Concentration on Partitioning and Molecular Recognition in Plasticized Poly(vinyl chloride)

Abstract

Mixtures of poly(vinyl chloride) (PVC) with plasticizers have been used in ion-selective electrodes for many years. The same material has proven useful in solid-phase microextraction (SPME), both with and without artificial receptors. We hypothesized that by changing the polymer concentration in plasticized PVC membranes containing artificial receptor from the standard 33 wt %, the selectivity of the extraction of barbiturates over similar molecules could be improved. Partition coefficients and receptor-substrate formation constants of a target species, phenobarbital, in membranes with various polymer concentrations were determined. Diffusion coefficients of the solute phenobarbital in receptor-free membranes were also determined. Kamlet-Taft solvatochromic properties beta and pi* were measured for the PVC/dioctyl sebacate materials. Cohesive energy densities were calculated for the same materials. Partition coefficients for phenobarbital (from aqueous solution to membrane) decrease as [PVC] increases, while the formation constants for the complex of the solute with its receptor increase. Diffusion coefficients decrease as the polymer concentration increases as well. The increase in polymer concentration brings about a decrease in hydrogen-bonding basicity and an increase in dipolarity and cohesive energy density. The values of the solvatochromic parameters determined at various compositions are highly correlated; thus, it is impossible to calculate how much each factor contributes to the changes associated with partition and complex formation. The solvatochromic "polarizability correction factor" has been determined to be 0 for PVC. In SPME experiments at 30%, 40%, and 50% (w/w) PVC, as polymer concentration increases, selectivity for barbiturate extraction over other cyclic imides becomes better in the presence of barbiturate receptor and worse without receptor.

Barbituric Acid Sensor Based on Molecularly Imprinted Polymer‐ Modified Hanging Mercury Drop Electrode

“…This was evident from the fact that since MIP in DMF solvent is instantly soluble, it was recovered intact after solvent evaporation showing, through a chromatographic column, no alteration in the imprinting efficiency prior and after re-dissolution in DMF. As the polymer loading on the electrode increased, the voltammetric peak current went through a maximum at 25 ppm of P(BA) which apparently formed a thin film monolayer coat around the mercury drop in an optimum t acc of 120 s. Despite the fact that the increase in polymer concentration brings an increase in polarity and thereby cohesive energy density at mercury/polymer interface, the hydrogen bonding basicity of the polymer and diffusion coefficient of analyte across the thicker film might be decreased at the modified electrode/solution boundary [32]. This could be the reason that a drastic fall in the current response with peak splitting was observed in the present study at polymer concentration greater than 200 ppm.…”

“…The mercury thin film electrode, whether bare or modified, has equal possibility of contamination in complex matrices and requires a critical regeneration step for reuse. It should be born in mind that MIP-interfacing with transducers usually requires MIP-particle entrapments either in gel or in membrane and sometimes in MIP suspension with the help of an inert and soluble plasticizer [32] and as such critical problems of longer response time, nonspecific analyte binding, and diminishing binding capacities are likely to emerge. As a distinct measure, in the present investigation, the recognition property of the imprinted polymer was directly exploited over the surface of modified-HMDE in order to translate the binding event of BA into corresponding voltammetric signal.…”

Porous alumina-based fluorous liquid membranes: Dependence of transport on fluorous solvent

“…The membrane was dipped in a perfluorinated solvent and then mounted between two quartz cuvettes with holes in them [42]. Viton gaskets were required to prevent leaking.…”

A Screening Method for Chiral Selectors that Does Not Require Covalent Attachment

“…Since ordinary organic solvents are difficult to work with, especially at low volume, we prefer thin polymer films as the organic phase. Plasticized poly(vinyl chloride) (PVC) films have been used to study molecular recognition, so it is naturally a good choice for chiral recognition. Figure gives the sequence of operations for the screening procedure.…”

“…The value of selectivity is significant and similar to the value found in chromatography cited above. It is likely that, in normal organic solvents, the formation constants would be larger. 8a, In order for the solute distribution process to reveal binding, the solute partition coefficient (distribution without selector) must be in a certain range (which depends on phase ratio). For accurate calculation of K f , the selector should not be soluble in water and should have no self-association in film.…”