F. Navarro-Villoslada

Application of multivariate analysis to the screening of molecularly imprinted polymers for bisphenol A

A key issue in the synthesis of molecularly imprinted polymers (MIPs) is the identification and optimisation of the main factors that affect the material structure and its molecular recognition properties. This paper describes the application of an experimental design and multivariate analysis method for the synthesis of bisphenol A (BPA)-selective MIPs. Six factors with a large impact on the MIP synthesis and its analytical performance have been optimised: the amount of template, the type and the percentage of functional and cross-linking monomers, the polymerisation method (i.e. thermal or UV initiation) and the porogenic solvent. The polymers have been prepared in small-scale (mini-MIPs) and, after careful removal of the template, their BPA rebinding capacity has been evaluated and related to the MIP composition. Among the two functional monomers tested, namely 4-vinylpyridine (4-vpy) and methacrylic acid (MAA), the former rendered the best selectivity for BPA analysis. The partial least squares (PLS) models revealed that the photoinitiated polymers with a 1:1 ratio of 4-vinylpyridine to cross-linker (EDMA or TRIM) yield the highest specific binding. Such procedure is time and cost effective and can be used as a general tool in the preparation of MIPs for different analytes.

Selection of calibration mixtures and wavelengths for different multivariate calibration methods

Abstract A comparative study to select calibration mixtures and wavelengths in multivariate calibration methods was made. The methods studied were classical least squares (CLS), inverse least squares (ILS), partial least squares (PLS), principal component regression (PCR) and Kaiman filter. For each method the calibration samples were selected from a total random population of 37 calibration standards, taking into account the standard error of prediction (SEP). The selection of analytical wavelengths for each method was carried out using different criteria: the condition number for CLS and Kalman filter methods, the signal-to-noise ( S N ) ratio and the condition number for ILS method, and all the previous criteria and the full spectrum for PCR and PLS methods. The best results were obtained using the condition number as criterion to select the analytical wavelengths. The study has been applied to the spectrophotometric determination of four priority pollutant chlorophenols.

Molecularly imprinted polymer diffraction grating as label-free optical bio(mimetic)sensor

Micropatterned molecularly imprinted polymer (MIP) transmissive 2D diffraction gratings (DGs) are fabricated and evaluated as label-free antibiotic bio(mimetic)sensors. Polymeric gratings are prepared by using microtransfer molding based on SiO(2)/Si molds. The morphology of the MIP gratings is studied by optical and atomic force microscopes. MIP 2D-DGs exhibit 2D optical diffraction patterns, and measurement of changes in diffraction efficiency is used as sensor response. The refractive index of the micropatterned MIP material was estimated, via solvent index matching experiments, to be 1.486. Immersion of a MIP 2D-DG in different solutions of target-antibiotic enrofloxacin leads to significant variations in diffraction efficiency, demonstrating target-molecule detection. On the other hand, no significant response is observed for both control experiments: MIP grating exposed to a non-retained analyte and an equivalent non-imprinted polymer grating exposed to the target analyte, showing highly specific antibiotic label-free optical recognition.

Preconcentration and flow-injection multivariate determination of priority pollutant chlorophenols

Abstract A combined flow-injection analysis and multivariate calibration method is developed for the simultaneous determination of priority pollutant chlorophenols (2-chlorophenol, 4-chloro-3-methylphenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol) in water. Chlorophenols were preconcentrated in an XAD-4 adsorbent resin. The ion pairs formed with tetrabutylammonium at pH 9.1 were extracted in chloroform and detected in a diode-array spectrophotometer in the wavelength range 200–430 nm. Three multivariate calibration methods, classical least squares (CLS), Kalman filter and partial least squares were used for comparative purposes. Comparison of the standard error of prediction shows significant differences for the determination of 2,4,6-trichlorophenol only, the best results being obtained by the CLS method.

DETERMINATION OF CHLOROPHENOXY ACID AND DICAMBA HERBICIDE RESIDUES BY CAPILLARY REVERSED-PHASE LIQUID CHROMATOGRAPHY

Capillary liquid chromatography combined with solid phase extraction in a column packed with an anion exchanger based on MFE-Polymer (hydroxyethylmethacrylate, HEMA) containing quaternary ammonium functional groups, has been studied for multiresidual analysis of seven chlorophenoxy acid herbicides; 2,4-D, MCPA, 2,4-DP, 2,4-DB, MCPB, 2,4,5-TP, and the benzoic acid derivative Dicamba in green bean samples. The chromatographic analysis was carried out on a C18 packed capillary column with gradient elution at 20°C. The chlorophenoxy acid and Dicamba have been assayed in green bean samples spiked with amounts between 0.30 and 0.08 mg.kg−1 for 2,4-D and MCPA, and between 0.15 and 0.04 mg.kg−1 for all the other herbicides. The recoveries obtained were between 41 and 119% (n=4 for each spiked level).

Preconcentration of triazine herbicides from water by an ion chromatography column and determination by gas chromatography-mass spectrometry

Abstract The efficiency of ion chromatography columns packed with styrene-divinylbenzene copolymer containing quaternary ammonium groups to preconcentrate triazine herbicides and their degradation products below μg/l levels has been established. Retention is studied for different types of water. Pure methanol was used in a one-step elution. Enrichment factors of at least 4000 are achieved. Determination was carried out by using gas chromatography-single-ion monitoring mass spectrometry. Recoveries for run-off agricultural water were between 67–100% and close to 100% for ground water. The maximum admissible concentration ion drinking water (0.1 μg/l) and the alert and alarm threshold values in surface water (1 and 3 μg/l, respectively) dictated by the European Union can be measured.

Cross-linkable linear copolymer with double functionality: resist for electron beam nanolithography and molecular imprinting

The first demonstration of a molecularly imprinted polymer patterned by electron beam lithography (EBL) direct writing is reported. The polymeric mixture is based on a linear co-polymer that behaves simultaneously as a positive-tone EBL resist and, after polymerization in the presence of rhodamine 123 (R123) as a model analyte, as a selective and sensitive synthetic receptor for the template. Analyte binding was evaluated by fluorescence confocal microscopy and the imprinting effect was confirmed in the presence of compounds structurally related to R123.

PRECONCENTRATION OF PHENOXY ACID HERBICIDE RESIDUES BY USING AN ION EXCHANGER BASED ON MFE-POLYMER

An anion exchanger based on MFE-Polymer (hydroxy-ethylmethacrylate, HEMA) containing quaternary ammonium functional groups has been used to pack a 150 × 4.6 mm id steel column, and the efficiency of this ion exchanger to preconcentrate phenoxy acid herbicides residues has been studied. The phenoxy acid herbicides studied were 2,4-dichlorophenoxy acetic acid (2,4-D), 4-(2,4-dichlorophenoxy)-butanoic acid (2,4-DB), 2,4,5-trichlorophenoxy acetic acid (2,4,5-T), 2-(2,4,5-trichlorophenoxy)-propanoic acid (2,4,5-TP), and 4-chloro-2-methylphenoxy acetic acid (MCPA). Dicamba (3,6-dichloro-2-methoxybenzoic acid), a benzoic acid herbicide usually used in technical products in mixtures with some of the related phenoxy acids, has also been included in the study. Retention of these herbicides on the referred ion exchanger is possible in aqueous acidic medium, probably because of the high polarizing power of the quaternary ammonium groups over the studied herbicides. Subsequent elution from the column was made with met...

Molecularly imprinted polymers as selective recognition elements for optical sensors based on fluorescent measurements

Molecularly imprinted polymers have been applied to the development of piezoelectric and electrochemical sensors and in radioactive competitive assays. However, its application to optical sensors is still limited due to the lack of appropriate fluorescent molecules able to compete with the template by the specific binding sites in the polymer. Optimisation of the polymer composition to get the maximum specific binding in the least time is another aim of research in this area. In this paper we present several approaches to address these issues namely the application of a experimental design for MIP optimization and the design and synthesis of novel fluorophores for the analysis of beta-lactam antibiotics using competitive assays or labeled MIPs.