Wayne M. Mullett

Determination of theophylline in serum by molecularly imprinted solid-phase extraction with pulsed elution.

The technique of molecular imprinting is used to produce an extensively cross-linked poly(methacrylic acid-co-ethylene dimethacrylate) material that contains theophylline as a print molecule. After Soxhlet extraction of the theophylline, binding sites are formed in the polymer with complementary size, shape, and positioning of chemical functionalities. The molecularly imprinted polymers (MIP) high theophylline selectivity, chemical stability, and physically robust nature make it an ideal stationary-phase material in columns for HPLC separation of theophylline from other structurally related drug compounds. Mobile-phase tests confirm that a retention mechanism typical of normal-phase chromatography governs the separation, and selectivity of the MIP column can be controlled by a combination of the mobile phase and the sample solvent. Under optimal conditions, the MIP column functions like a solid-phase sorbent for theophylline extraction. Rapid elution of the bound theophylline can be accomplished in a pulsed format through injection of 20 μL of a solvent that has the proper polarity and protic nature to disrupt the electrostatic interactions and hydrogen bonding between theophylline and binding sites. A concentration detection limit of 120 ng/mL is obtained using direct UV absorption detection at 270 nm, which corresponds to a mass detection limit of 2.4 ng. This new technique, molecularly imprinted solid-phase extraction with pulsed elution (MISPE-PE), permits on-line preconcentration of theophylline from a large volume of dilute sample solution. Using a sample volume of 300 μL, a 40 ng/mL standard solution produces a detectable peak signal. Application of MISPE-PE in serum analysis further demonstrates the high capability of the MIP column to selectively isolate theophylline from other matrix components for fast, accurate determination.

Is biosensor a viable method for food allergen detection

Abstract The emerging health issue of food-induced allergic reactions presents an important challenge to the food industry. Unfortunately, methods for food allergen detection are still mostly unavailable. Surface plasmon resonance (SPR) immunoassays are based on the biological input of antibody–allergen binding, while the measurable output is either a resonance angle or refractive index value. The feasibility of applying the experimental SPREETA™ evaluation kit as a commercially available biosensor to detect peanut allergens was examined. Preliminary results achieved a detection limit 0.7xa0μg/ml. This miniature biosensor technology may offer the food industry with a tool to allow for immediate, on-line detection and quantification of inadvertent allergens in food — during the food’s production — not after. Such a tool will be of great benefit to the food processor — enabling management decisions to be made early in the production cycle.

Determination of nicotine in tobacco by molecularly imprinted solid phase extraction with differential pulsed elution

A molecularly imprinted solid phase extraction-differential pulsed elution (MISPE-DPE) method has been developed for the determination of nicotine in tobacco. Nicotine and a trace alkaloid myosmine were able to bind to the molecularly imprinted polymer (MIP) packed in a micro-column when acetonitrile was used as the mobile phase. However, over 95% of the bound myosmine could be desorbed and washed away by a 20 µl pulse of methanol, compared to only 43% of the bound nicotine. The remaining quantity of bound nicotine was desorbed by a 20 µl pulse of 1% trifluoroacetic acid in water, for direct UV detection at 254 nm. This MISPE-DPE method provided inherent selectivity for nicotine that allowed both a shorter analysis time (3 min) and a lower analysis cost than liquid chromatographic methods. A detection limit of 1.8 µg ml–1 and a linear dynamic range up to 1000 µg ml–1 were obtained. Preconcentration of 845 µl of a 10 ng ml–1 nicotine standard solution produced a detectable peak signal. These analytical figures of merit are superior to those reported previously for several nicotine–MIP-based methods.

A 2-aminopyridine molecularly imprinted polymer surrogate micro-column for selective solid phase extraction and determination of 4-aminopyridine

Abstract Poly(methacrylic acid–ethylene glycol dimethacrylate) was prepared using 2-aminopyridine as the imprinting molecule. This molecularly imprinted polymer (MIP) was ground and packed into a micro-column for selective solid phase extraction (SPE) of 2-aminopyridine from 20xa0μl of sample solution. Non-specific adsorption was also confirmed for a structural analogue. Interestingly one of the isomers, 4-aminopyridine, bound most strongly to the MIP. The implication of resonance and basicity of this isomer molecule can be used to explain its strong binding with the self-assembled functional methacrylic acid (MAA) monomer. The monomer template complexion process was evaluated by Scatchard plots to determine a binding constant. The binding constant value is important for predicting the selectivity of a new MIP. After optimization of the molecular recognition process, a molecularly imprinted solid phase extraction–differential pulsed elution (MISPE–DPE) method was developed for the selective determination of 4-aminopyridine in serum with an analysis time of less than 3xa0min using a 2-aminopyridine micro-column for surrogate binding. The concentration detection limit was 0.5xa0μg/ml, which corresponded to an absolute detection limit of 10xa0ng. A larger sample volume of 845xa0μl afforded a better concentration detection limit of 52xa0ng/ml.

Rapid determination of theophylline in serum by selective extraction using a heated molecularly imprinted polymer micro-column with differential pulsed elution

Molecular imprinting of theophylline in poly(methacrylic acid ethylene dimethacrylate) form binding sites with complementary size, shape and chemical functionalities to theophylline. This molecularly imprinted polymer (MIP) can be packed into a micro-column for selective solid phase extraction (SPE) of theophylline from 20 microl of sample solution. Its chemical inertness and thermal stability allow the use of various organic solvents and elevated column temperatures for effective binding of theophylline. Non-specific adsorption of interfering drugs on the MIP surface is eliminated by an intermediate wash with 20 microl of acetonitrile, prior to quantitative desorption of the bound theophylline by 20 microl of methanol for in-line UV spectrophotometric determination. In this differential pulsed elution (DPE) technique, both the column temperature and solvent flow rate can be optimized to enhance selectivity. Application of this micro-analytical method, molecularly imprinted solid phase extraction DPE (MISPE-DPE), is demonstrated for accurate determination of theophylline in human blood serum. The method is validated over a linear range from 2 microg/ml to at least 20 microg/ml.

High-throughput polymer monolith in-tip SPME fiber preparation and application in drug analysis

BACKGROUNDnA simple, low-cost and reproducible automated procedure has been developed to prepare in-tip solid-phase microextraction (SPME) fibers coated with polymer monoliths using a photopolymerization technique. Up to 96 fibers were prepared at one time using a polymerization mixture consisting of ethylene glycol dimethacrylate, dimethoxy-α-phenylacetophenone and 1-decanol.nnnRESULTSnThe optimization procedures that affected polymer morphology, such as compositions of the crosslinkers and porogens, polymerization time and fiber thickness as well as extraction efficiency of the immobilized Oasis hydrophilic-lipophilic-balanced extraction sorbent were investigated. Also, the reproducibility of automated in-tip SPME fiber preparation, as well as sample process parameters, such as sample extraction and desorption volumes, are discussed.nnnCONCLUSIONnThe performance of the polymer monoliths in-tip SPME assessed with a model drug compound from clinical studies and a head-to-head comparison using in-tip SPME and conventional SPE clearly demonstrated that the SPME is a feasible approach for routine drug analysis in the pharmaceutical industry.

Silicate-entrapped porous coatings for preparing high-efficiency solid-phase microextraction sorbents

We present a novel way to prepare SPME fibers using a silicate entrapment of porous particles, followed by derivatization using classical organosilane chemistry. The fibers provide a good platform for on-fiber derivatization of desired extraction phases while providing porosity necessary for high extractions capacities. The porous network was created using potassium silicate and porous silica particles. Fibers derivatized using n-butyl, n-octyl, n-octadecyl and n-triacontyl groups were shown to extract benzodiazepines successfully. The coatings were determined to have an average thickness of ca. 8 microm, as determined by a scanning electron microscope, permitting equilibrium times as fast as 2 min. The fibers also showed very good ruggedness towards a vast range of solvents and prolonged use. It was determined that greater extraction efficiencies could be obtained using triacontyl as an extraction phase. The C18 and C30 fibers were also found to provide good linearity (>0.99) for the model analytes over two orders of magnitude, with limits of detection in the sub ng mL(-1) levels. C30 fibers were used to establish a correlation between structurally diverse beta-blockers and their literature reported Log P values. The C30 fibers provided a good correlation (R(2)=0.9255) between beta-blockers ranging in hydrophobicity from Log P(literature) 0.16-4.15 and their respective experimentally determined Log K(spme) values.

Stimulated Raman scattering activity of organic compounds

Abstract The stimulated Raman scattering (SRS) activity of over one hundred organic compounds was investigated at room temperature. Spectra were obtained successfully for the colourless neat liquids but not for the solid chemicals in solution, and their SRS shifts were measured systematically. The results confirmed that SRS Stokes shifts are usually the same as those observed in spontaneous Raman scattering, with occasional differences in frequency from the strongest spontaneous Raman bands. Empirical trends have been observed in functional group recognition, compound classification, degenerate vibrational modes, substituent group effects, hydrogen bonding and concentration threshold. Other new observations such as multiple peaks, exceptional SRS activity and distributed spectra are also reported. SRS offers several advantages over normal Raman spectroscopy in industrial process monitoring, and a potentially interesting scope of analytical utility is discussed.