The use of trichloroacetic acid imprinted polymer coated quartz crystal microbalance as a screening method for determination of haloacetic acids in drinking water

An alternative screening method for haloacetic acids (HAAs) disinfection by-products in drinking water is described. The method is based on the use of piezoelectric quartz crystal microbalance (QCM) transducing system, where the electrode is coated with a trichloacetic acid-molecularly imprinted polymer (TCAA-MIP). This MIP comprises a crosslinked poly(ethyleneglycoldimethacrylate-co-4-vinylpyridine). The coated QCM is able to specifically detect the analytes in water samples in terms of the mass change in relation to acid-base interactions of the analytes with the MIP. The TCAA-MIP coated QCM showed high specificity for the determination of TCAA in aqueous solutions containing inorganic anions, but its sensitivity reduced in water samples containing hydrochloric acid due to a mass loss at the sensor surface. Cross-reactivity studies with HAA analogs (dichloro-, monochloro-, tribromo-, dibromo-, and monobromo-acetic acids) and non-structurally related TCAA molecules (acetic acid and malonic acid) indicated that recognition of the structurally related TCAA compounds by the TCAA-MIP-based QCM is due to a carboxylic acid functional group, and probably involves a combination of both size and shape selectivity. The total response time of sensor is in the order of 10 min. The achieved limits of detection for HAAs (20-50 μg l⁻¹) are at present higher than the actual concentrations found in real-life samples, but below the guidelines for the maximum permissible levels (60 μg l⁻¹ for mixed HAAs). Recovery studies with drinking water samples spiked with TCAA or spiked with mixtures of HAAs revealed the reproducibility and precision of the method. The present work has demonstrated that the proposed assay can be a fast, reliable and inexpensive screening method for HAA contaminants in water samples, but further refinement is required to improve the limits of detection.     

Thin-Layer Chromatographic Separation of Chiral drugs on Molecularly Imprinted Chiral Stationary Phases

JPC – Journal of Planar Chromatography – Modern TLC - This report describes the TLC separation of two classes of chiral drug, including β-blocking drugs and non-steroidal...     

A simplified liquid chromatography-mass spectrometry assay for artesunate and dihydroartemisinin, its metabolite, in human plasma

Artesunate (AS) is a potent antimalarial that is used worldwide for the treatment of malaria. A simple method with a total run time of 12 min was developed and validated for the quantification of AS and dihydroartemisinin (DHA), its active metabolite, in human (heparinized) plasma based on one-step protein precipitation in acetonitrile using artemisinin (ARN) as an internal standard, followed by liquid chromatography with a single quadrupole mass spectrometry system connected to a C18 column. Peak area ratio responses were fitted to the 2nd-order curve type, polynomial equation with weighting (1/concentration) over a quantification range between 3.20/5.33-3,000/5,000 nM (1.23/1.52-1153/1422 ng/mL) of AS/DHA showing linearity with very good correlation (r2>0.999). Single ion recordings of 5 μL injections of plasma extracts allowed for limits of detection of 1.02 nM (0.39 ng/mL) for AS and 0.44 nM (0.13 ng/mL) for DHA. The inter-assay and intra-assay accuracy and precision of the method was very good with an inaccuracy of ±12.4% and coefficients of variation of ≤10.7% at all tested concentrations. The recovery of the analytes from plasma was ≥95%. Other commonly used antimalarials including mefloquine, quinine, and chloroquine, did not interfere with the analysis. Post-preparative tests over 24 h in an autosampler (10 °C) showed that the DHA response was only 2.1% of AS from auto-hydrolysis, and β-DHA was the major, stable epimer that was used for quantification of DHA. In contrast, α-DHA increased steadily up to 600%. Artesunate and DHA in plasma were stable through three freeze/thaw cycles for up to 6 h at room temperature and up to one year at -80 °C.     

Temperature sensitive dopamine-imprinted (N,N-methylene-bis-acrylamide cross-linked) polymer and its potential application to the selective extraction of adrenergic drugs from urine

A temperature sensitive dopamine-imprinted polymer was prepared in 80% aqueous methanol solution by free-radical cross-linking co-polymerisation of methacrylic acid and acrylamide at 60 degrees C in the presence of N,N-methylene-bis-acrylamide as the cross-linker and dopamine hydrochloride as template molecule. The resulting molecularly imprinted polymer (MIP) formed temperature responsive materials, which could be used for the selective separation of appropriate dopamine and adrenergic compounds from a liquid matrix at ambient temperatures. The thermoresponsive MIP exhibited a swelling-deswelling transition in 80% aqueous methanol solution at about 35 degrees C. The capacity of the thermoresponsive MIP to recognise the template molecule when present in aqueous methanol solution changed with temperature, with the highest selectivity found at 35 degrees C. Additionally, binding parameters obtained from Scatchard analyses indicate that increasing temperature resulted in an increased affinity and binding capacity of specific binding sites, but had less effect on non-selective binding sites. Subsequently, the thermoresponsive MIP was tested for its application as a sorbent material, utilisable in the selective solid-phase extraction (SPE) of dopamine and other adrenergic compounds (epinephrine, isoproterenol, salbutamol and serotonin) from urine samples. It was shown that the compounds that were structurally related to dopamine could be removed by elution, while dopamine and serotonin, the analytes of interest, remained strongly adsorbed to the adsorbent during SPE applications. The thermoresponsive MIP displayed different efficiency in clean-up and enrichments using the SPE protocol at different temperatures.     

Development of a rubber elongation factor, surface-imprinted polymer-quartz crystal microbalance sensor, for quantitative determination of Hev b1 rubber latex allergens present in natural rubber latex products

Molecularly imprinted polymers (MIPs) for screening to detect rubber latex allergens (Hev b1) in natural rubber based products were designed as artificial recognition polymeric materials coated onto a quartz crystal microbalance (QCM). The polymers were prepared using a stamp imprinting procedure after mixing optimum amounts of methacrylic acid–vinylpyrrolidone–dihydroxyethylene bisacrylamide and Hev b1 latex allergen proteins, obtained from rubber gloves. QCM measurements showed that the resulting polymer layers after removal of the proteins used in their preparation could incorporate structures and features down to nanometer scale of protein templates into the imprinted polymer much better than a non-specific control polymer under controlled sensor conditions and an optimized polymerization process. This selective polymer but not the non-selective polymer clearly distinguished between the latex allergen Hev b1 and proteins such as lysozyme, ovalbumin and bovine serum albumin, with a selectivity factor of from 2 to 4, and the response of the rubber elongation factors by an astonishing factor of 12. The imprinted cavities recognized specific binding sites and could distinguish among related hevein latex allergenic proteins isolated from fresh natural rubber latex; Hev b1, Hev b2, and Hev b3 with a selectivity factor of from 4 to 6. The different QCM measurements obtained presumably reflected slightly different conformations and affinities to the MIP binding sites. The sensor layers selectively adsorbed Hev b1 within minutes in amounts ranging from 10 to 1500 μg L⁻¹ and with a detection limit of 1 μg L⁻¹. This work has demonstrated that this new sensor provides a fast and reliable response to natural rubber latex protein, even after being extracted from the matrix of rubber gloves.     

Chiral determination of various adrenergic drugs by thin-layer chromatography using molecularly imprinted chiral stationary phases prepared with alpha-agonists

Thin-layer chromatography (TLC) based on molecularly imprinted polymers (MIPs) of alpha-agonists as chiral stationary phases was applied to the determination of enantiomers of various adrenergic drugs including alpha- and beta-agonists and beta-antagonists (beta-blockers). In this study, three MIPs imprinted with (+)-ephedrine, (+)-pseudoephedrine and (+)-norephedrine plus a non-imprinted polymer (non-MIP) were prepared, processed and coated on a glass support as thin layers. then enantiomeric determination of adrenergic drugs was carried out by development of their racemates on the TLC plates, using established conditions. From the results, the racemates of the compounds used as print molecules were well separated into two isomers on the MIP-plates, except on the plate based on MIP of (+)-norephedrine. Most adrenergic drugs structurally related to print molecules were completely resolved into two spots with the MIP plates. In general the retention of (+)-isomers (or 1S-isomers) was greater than that of (-)-isomers (or 1R-isomers), indicating the stereoselectivity of the MIPs with the former isomers. Moreover, the role between the chemical structures of the analytes with chiral recognition of the MIPs has been investigated. The proposed method enables rapid determination of enantiomers and screening of large numbers for optical purity of adrenergic drugs.     

Novel adsorptive materials by adenosine 5ʹ‐triphosphate imprinted‐polymer over the surface of polystyrene nanospheres for selective separation of adenosine 5ʹ‐triphosphate biomarker from urine

In this study, we have developed a method to assess adenosine 5?‐triphosphate by adsorptive extraction using surface adenosine 5′‐triphosphate‐imprinted polymer over polystyrene nanoparticles (412 ± 16 nm) for selective recognition/separation from urine. Molecularly imprinted polymer was synthesized by emulsion copolymerization reaction using adenosine 5′‐triphosphate as a template, functional monomers (methacrylic acid, N‐isopropyl acrylamide, and dimethylamino ethylmethacrylate) and a crosslinker, methylenebisacrylamide. The binding capacities of imprinted and non‐imprinted polymers were measured using high‐performance liquid chromatography with UV detection with a detection limit of 1.6 ± 0.02 µM of adenosine 5′‐triphosphate in the urine. High binding affinity (Q_MIP, 42.65 µmol/g), and high selectivity and specificity to adenosine 5′‐triphosphate compared to other competitive nucleotides including adenosine 5?‐diphosphate, adenosine 5?‐monophosphate, and analogs such as adenosine, adenine, uridine, uric acid, and creatinine were observed. The imprinting efficiency of imprinted polymer is 2.11 for urine (Q_MIP, 100.3 µmol/g) and 2.51 for synthetic urine (Q_MIP, 48.5 µmol/g). The extraction protocol was successfully applied to the direct extraction of adenosine 5′‐triphosphate from spiked human urine indicating that this synthesized molecularly imprinted polymer allowed adenosine 5′‐triphosphate to be preconcentrated while simultaneously interfering compounds were removed from the matrix. These submicron imprinted polymers over nano polystyrene spheres have a potential in the pharmaceutical industries and clinical analysis applications.     

Development of trichloroacetic acid sensor based on molecularly imprinted polymer membrane for the screening of complex mixture of haloacetic acids in drinking water

This work shows developing conductometric sensor based on molecularly imprinted polymer (MIP) for the screening of complex mixture of haloacetic acids (HAAs) in drinking water. The recognition of the HAAs was achieved by trichloroacetic acid (TCAA)-imprinted polymers synthesised from the copolymerization of 4-vinylpyridine (4-VPD) and ethylene glycol dimethacrylate (EDMA) in the presence of the TCAA template in acetonitrile, either by bulk polymerization (BP) method or by a multi-step swelling polymerization (MSP) method. TCAA-imprinted polymer of both methods was tested for re-binding with the template and its analogs. It was found that these polymers could bind selectively to the template molecule and HAA derivatives. HAA measurements were carried out by the application of the polyvinyl chloride membrane fabricated with TCAA-imprinted polymer on conductometric sensors. The technological parameters (operating frequency, membrane composition, ionic strength and medium pH) for the sensors were identified and optimised in respect to the response to TCAA, using sensor fabricating with BP-based MIP as a model. The selectivity of the sensors constructed with MIPs made by either that of the two imprinting methods was also investigated, which the influence of the method of imprinting on the binding strength and selectivity of the recognition element embedded in sensor was observed. The sensors showed high sensitivity and selectivity for the response toward TCAA, the sensor modified with MSP-based MIP being better. In addition, the sensors, particularly when was constructed with MSP-based MIP exhibited good cross-reactivities with a wide range of HAAs, which is useful for the screening of the group of HAA usually present in chlorinated water in complex mixtures. Thus, the sensor modified with MSP-based MIP was chosen for analytical application. The calibration of this sensor was determined, showing the good linear graphs (R²>0.970) for HAAs over the concentration range of 25-1000 μg/l and the detection limit of each HAA in the range 0.2-5.0 μg/l. Moreover, the results in real analysis of the sensor indicate the simplicity and reliability of the method. The present work demonstrated that the sensor based on TCAA-imprinted polymer is a fast and sensitive screening method of HAAs in drinking water.