UV-vis Imaging of Piroxicam Supersaturation, Precipitation, and Dissolution in a Flow-Through Setup.

Evaluation of drug precipitation is important in order to address challenges regarding low and variable bioavailability of poorly water-soluble drugs, to assess potential risk of patient safety with infusion therapy, and to explore injectable in situ suspension-forming drug delivery systems. Generally, drug precipitation is assessed in vitro through solution concentration analysis methods. Dual-wavelength UV-vis imaging is a novel imaging technique that may provide an opportunity for simultaneously monitoring changes in both solution and solid phases during precipitation. In the present study, a multimodal approach integrating UV-vis imaging, light microscopy, and Raman spectroscopy was developed for characterization of piroxicam supersaturation, precipitation, and dissolution in a flow-through setup. A solution of piroxicam dissolved in 1-methyl-2-pyrrolidinone was injected into a flowing aqueous environment (pH 7.4), causing piroxicam to precipitate. Imaging at 405 and 280 nm monitored piroxicam concentration distributions during precipitation and revealed different supersaturation levels dependent on the initial concentration of the piroxicam solution. The combination with imaging at 525 nm, light microscopy, and Raman spectroscopy measurements demonstrated concentration-dependent precipitation and the formation, growth, and dissolution of individual particles. Results emphasize the importance of the specific hydrodynamic conditions on the piroxicam precipitation. The approach used may facilitate comprehensive understanding of drug precipitation and dissolution processes and may be developed further into a basic tool for formulation screening and development.

Characterisation of aggregates of cyclodextrin-drug complexes using Taylor Dispersion Analysis.

There is a need to understand the nature of aggregation of cyclodextrins (CDs) with guest molecules in increasingly complex formulation systems. To this end an innovative application of Taylor dispersion analysis (TDA) and comparison with dynamic light scattering (DLS) have been carried out to probe the nature of ICT01-2588 (ICT-2588), a novel tumor-targeted vascular disrupting agent, in solvents including a potential buffered formulation containing 10% hydroxypropyl-ß-cyclodextrin. The two hydrodynamic sizing techniques give measurement responses are that fundamentally different for aggregated solutions containing the target molecule, and the benefits of using TDA in conjunction with DLS are that systems are characterised through measurement of both mass- and z-average hydrodynamic radii. Whereas DLS measurements primarily resolve the large aggregates of ICT01-2588 in its formulation medium, methodology for TDA is described to determine the size and notably to quantify the proportion of monomers in the presence of large aggregates, and at the same time measure the formulation viscosity. Interestingly TDA and DLS have also distinguished between aggregate profiles formed using HP-ß-CD samples from different suppliers. The approach is expected to be widely applicable to this important class of drug formulations where drug solubility is enhanced by cyclodextrin and other excipients.

Performance characteristics of UV imaging instrumentation for diffusion, dissolution and release testing studies.

UV imaging is capable of providing spatially and temporally resolved absorbance measurements, which is highly beneficial in drug diffusion, dissolution and release testing studies. For optimal planning and design of experiments, knowledge about the capabilities and limitations of the imaging system is required. The aim of this study was to characterize the performance of two commercially available UV imaging systems, the D100 and SDI. Lidocaine crystals, lidocaine containing solutions, and gels were applied in the practical assessment of the UV imaging systems. Dissolution of lidocaine from single crystals into phosphate buffer and 0.5% (w/v) agarose hydrogel at pH 7.4 was investigated to shed light on the importance of density gradients under dissolution conditions in the absence of convective flow. In addition, the resolution of the UV imaging systems was assessed by the use of grids. Resolution was found to be better in the vertical direction than the horizontal direction, consistent with the illumination geometry. The collimating lens in the SDI imaging system was shown to provide more uniform light intensity across the UV imaging area and resulted in better resolution as compared to the D100 imaging system (a system without a lens). Under optimal conditions, the resolution was determined to be 12.5 and 16.7 line pairs per mm (lp/mm) corresponding to line widths of 40µm and 30µm in the horizontal and vertical direction, respectively. Overall, the performance of the UV imaging systems was shown mainly to depend on collimation of light, the light path, the positioning of the object relative to the line of 100µm fibres which forms the light source, and the distance of the object from the sensor surface.

Study of antibacterial activity by capillary electrophoresis using multiple UV detection points.

A new methodology for an antibacterial assay based on capillary electrophoresis with multiple UV detection points has been proposed. The possible antibacterial activity of cationic molecules on bacteria (Gram-positive and Gram-negative) is studied by detecting the bacteria before, during, and after their meeting with the cationic antibacterial compound. For that, a UV area imaging detector having two loops and three detection windows was used with a 95 cm ×100 µm i.d. capillary. In the antibacterial assay, the bacteria (negatively charged) and the cationic molecules were injected separately from each end of the capillary. The bacteria were mobilized by anionic ITP mode while cationic molecules migrate in the opposite direction under conditions close to CZE. The cationic molecules were injected into the capillary as a broad band (injected volume about 16% of the volume of the capillary) to prevent dilution of the sample during the electrophoretic process. Bacteriolytic activity, as well as strong interactions between the small antibacterial molecules and the bacteria, can be investigated within a few minutes. The assay was used to study the antibacterial activity of dendrigraft poly-L-lysines on Micrococcus luteus and Erwinia carotovora. Because dendrigraft poly-L-lysines are nonimmunogenic and have low toxicity, this new class of dendritic biomacromolecules is very promising for antibacterial applications.

Focusing and mobilization of bacteria in capillary electrophoresis.

An isotachophoretic method has been developed for mobilizing and focusing bacteria. This allows quantification and detection of bacteria in a narrow zone. Very good linearity was obtained for Micrococcus lysodeikticus (also called Micrococcus luteus, studied as a model of Gram+ bacteria) in the range of 0.4 × 10(8) cells/mL to 2.9 × 10(8) cells/mL, with correlation coefficients for peak height and peak area as a function of cell concentration of 0.999 and 0.998, respectively. This method is usable on both bare and hydroxypropyl cellulose-coated fused silica capillaries. The best results were obtained using 13.6 mM Tris, 150 mM boric acid as terminating electrolyte, and 4.5 mM Tris, 50 mM boric acid, and 3.31 mM HCl as leading electrolyte. With a 33.5 cm ×100 µm i.d. capillary, short migration times were obtained while maintaining very low electrical current in order to minimize any Joule heating and lysis of the bacteria. A UV area imaging detector (ActiPix D100, Paraytec) was used with a 109 cm × 100 µm i.d. capillary having three loops and four detection windows to monitor the migration behavior of M. luteus and to show the stability of the zone of the focused bacteria along the capillary. Similar results were obtained for Erwinia carotovora (a model of Gram- bacteria), and for Enterobacter cloacae and Vibrio splendidus.

Electrically assisted capillary liquid chromatography using a silica monolithic column.

A silica monolithic capillary column was linked to an open capillary of the same internal diameter via a Teflon sleeve to form a duplex column to investigate the combination of chromatography and electrophoresis in the mode of electrically assisted capillary liquid chromatography (eCLC). Using a commercial CE instrument with an 8.5 cm long, 100 microm i.d. reversed phase silica monolithic section and a window 1.5 cm beyond the end of this in a 21.5 cm open section, a minimum plate height of 9 microm was obtained in capillary liquid chromatography (CLC) mode at a low driving pressure of 50 psi. In eCLC mode, high speed and high resolution separations of acidic and basic compounds were achieved with selectivity tuning based on the flexible combination of pressure (0-100 psi) and voltage. Taking advantage of the excellent permeability of silica monolithic columns, use of a step flow gradient enabled elution of compounds with different charge state.

Capillary action liquid chromatography.

Capillary action LC (caLC) is introduced as a technique using capillary action as the driving force to perform LC in capillary columns packed with HPLC type microparticulate materials. A dry packing method with centrifugal force was developed to prepare capillary columns in parallel (10 columns per 3 min) to support their disposable use in caLC. Using a digital microscope for real-time imaging and recording separations of components in a dye mixture, caLC was found to have flow characteristics similar to TLC. Based on the investigation of microparticulate HPLC silica gels of different size (1.5-10 microm) and a typical TLC grade irregular medium, Merck 60G silica, the van Deemter curves suggested molecular diffusion as the major contribution to band broadening in caLC. With Waters Xbridge 2.6 microm silica, plate heights down to 8.8 microm were obtained, comparable to those achievable in HPLC. Assisted by an image-processing method, the visual caLC separation was converted to a classical chromatogram for further data analysis and such a facility confirmed the observation of highly efficient bands.

Multi-compound electrophoretic assays for tyramine oxidase with a UV area detector imaging multiple windows on a looped capillary.

Active pixel sensor UV area imaging and capacitively coupled contactless conductivity detection have been applied in an electrophoretically mediated microanalysis (EMMA) assay for substrate specificity of tyramine oxidase (Arthrobacter sp.). Use of the UV area imaging detector to monitor four windows in a capillary with three loops provided intrinsic self-referencing for all species and identified tyramine and 2-phenethylamine as the only reactive components in a multi-compound mixture. Continuous engagement EMMA experiments showed significant benefits by comparison with plug-plug EMMA, improving sensitivity by extending enzyme-substrate interaction times and allowing measurement of time-dependent reaction in the substrate zones passing the four windows.

Quantitative ultraviolet measurements on wetted thin-layer chromatography plates using a charge-coupled device camera.

This paper presents the first study of the UV imaging of spots on thin-layer chromatographic plates whilst still wet with solvent. Imaging of spots of benzophenone during and after development was carried out using a charge-coupled device camera. Limits of detection were found to be 5ng on a wetted plate and 3ng for a dry plate and the relationship between peak area and sample loading was found to be linear in the low nanogram range over an order of magnitude for both wet and dry modes with r(2) values>0.99. It was found that UV measurements on wet glass-backed plates suffer from low sensitivity; however, the use of aluminium-backed plates gave increased sensitivity. The apparent absorption coefficient epsilon(app) of 10AUm(2)g(-1) at 254nm is consistent with reflection of the light from the aluminium surface with a double pass through the sorbent layer, and suggests that use of aluminium-backed plates should enable monitoring of separations by UV absorbance during TLC development.

Single-particle fritting technology for capillary electrochromatography.

Large perfusive silica beads (particle size 110 microm, through pore approximately 2 microm) held in place by the keystone effect were used as single-particle frits for the manufacture of particulate packed capillary columns. High-quality capillary electrochromatographic separations of a standard test mixture of alkylbenzenes were obtained over the full voltage range of 5-30 kV, with no requirement for pressurization. Excellent robustness was demonstrated by the reproducibility of migration times, peak efficiencies, and resolution during 100 consecutive runs at the highest voltage (30 kV) without thermostating and pressurization. Superior performance relative to traditional sinter-fritted columns is ascribed to the heat-free fritting process and short frit length of approximately 110 microm.

Electrophoretic method for assessment of substrate promiscuity of a heterogeneous biocatalyst using an area imaging ultraviolet detector.

We report a new electrophoretic set-up and method for rapid specificity screening of an immobilised enzyme against a range of substrates present in a mixture. The penicillinase-catalysed reaction is carried out on-the-fly, following separation of putative substrates and preceding separation of the reaction products. The new active pixel sensor detector gives an option of using multiple detection windows on a single flow line and enables efficient on-line monitoring of this heterogeneous biocatalytic process with multiple putative substrates injected simultaneously.

Electrophoretically mediated microanalysis of a nicotinamide adenine dinucleotide-dependent enzyme and its facile multiplexing using an active pixel sensor UV detector.

An electrophoretically mediated microanalysis (EMMA) method has been developed for yeast alcohol dehydrogenase and quantification of reactant and product cofactors, NAD and NADH. The enzyme substrate ethanol (1% (v/v)) was added to the buffer (50 mM borate, pH 8.8). Results are presented for parallel capillary electrophoresis with a novel miniature UV area detector, with an active pixel sensor imaging an array of two or six parallel capillaries connected via a manifold to a single output capillary in a commercial CE instrument, allowing conversions with five different yeast alcohol dehydrogenase concentrations to be quantified in a single experiment.

Electrophoretic assay for penicillinase: substrate specificity screening by parallel CE with an active pixel sensor.

We report application of a new UV imaging detector incorporating an active pixel sensor in an electrophoretic enzyme assay for penicillinase (beta-lactamase) with multiple substrates. The method based on electrophoretically mediated microanalysis was developed on a standard CE system with a single-point diode array detector and 200 nm UV wavelength, then transferred to a parallel capillary setup with the UV imaging detector for screening of penicillinase substrate specificity. One capillary is used for the assay and the other for reference, with an enzyme solution plug introduced into the first at the same time as a water plug into the second capillary. A mixture of antibiotics and markers is subsequently introduced as a sample plug to both capillaries, and driven through the enzyme (or water) plug by application of voltage. Most individual reactant and product peaks were separated and compounds amenable to beta-lactam hydrolysis could readily be identified and the extent of the reaction quantified within a single electrophoretic run.

Data processing in metabolic fingerprinting by CE-UV: application to urine samples from autistic children.

Metabolic fingerprinting of biofluids such as urine can be used to detect and analyse differences between individuals. However, before pattern recognition methods can be utilised for classification, preprocessing techniques for the denoising, baseline removal, normalisation and alignment of electropherograms must be applied. Here a MEKC method using diode array detection has been used for high-resolution separation of both charged and neutral metabolites. Novel and generic algorithms have been developed for use prior to multivariate data analysis. Alignment is achieved by combining the use of reference peaks with a method that uses information from multiple wavelengths to align electropherograms to a reference signal. This metabolic fingerprinting approach by MEKC has been applied for the first time to urine samples from autistic and control children in a nontargeted and unbiased search for markers for autism. Although no biomarkers for autism could be determined using MEKC data here, the general approach presented could also be applied to the processing of other data collected by CE with UV-Vis detection.

1,4-Benzoquinone-based electrophoretic assay for glucose oxidase.

The communication demonstrates feasibility of an enzyme microassay for glucose oxidase with 1,4-benzoquinone as an acceptor of electrons. The protocol uses the plug-plug mode of electrophoretically mediated microanalysis, with nanolitre injected volumes of enzyme and reactant solutions. The reactant and product, 1,4-benzoquinone and hydroquinone, are separated during the assay by differential binding to sulfated-beta-cyclodextrin used as additive to the phosphate buffer (pH 7) and monitored at selected wavelengths in their UV spectra. The assay covers glucose oxidase concentration from 0.01 to 0.1mgml(-1). Due to the strong UV absorbance of the both reactant and product, there is no need for use of a second enzyme (peroxidase) in the present assay.

Capillary electrophoresis-mass spectrometry characterisation of secondary metabolites from the antihyperglycaemic plant Genista tenera.

Genista tenera is endemic to the Portuguese island of Madeira, where an infusion of the aerial parts of the plant is used in folk medicine as an antidiabetic agent. Consequently the medicinal properties of the secondary metabolites of this plant have been the subject of an ongoing study. A recently reported LC-MS method using a 100 min separation allowed identification of five flavonoid components in an extract of the aerial parts of this plant. In order to obtain additional information on the range and complexity of the plant's secondary metabolite components a CE-MS method has been developed and applied for the analysis of an extract of G. tenera. Twenty-six different components are distinguished in an analysis time of only 10 min. Results demonstrate that CE-MS/MS rapidly generates data complementary to those obtainable by LC-MS/MS and is particularly suited to the analysis of plant metabolites where concentration is not limiting.

On-line low-volume transesterification-based assay for immobilized lipases.

A method has been developed for fast evaluation of transesterification activity of immobilized lipases using microlitre and submicrolitre volumes of substrate solutions. The model reaction (acylation of isopropanol with vinyl acetate) is catalyzed by microbial lipases immobilized on ceramic particles, diatoms or acrylic resin, packed into a Teflon tube connected to fused-silica capillary tubing. The substrate solution is pumped through the microreactor and the product of transesterification, acetaldehyde, quantified on capillary by UV absorbance at 280 nm. Using this system in the continuous-flow mode, comparisons were made of transesterification catalysed by PS-C II lipase in two different solvent mixtures. Acetonitrile was found to be a compatible solvent that can be used as a solubilizer without suppressing enzymatic activity. The method has been used to compare conversions at a fixed flow rate using a single pass of substrate through packed beds containing approximately 0.2 mg of supported enzyme. Spatial distributions of the product have been visualized using a complementary metal oxide semiconductor (CMOS) imaging detector in conjunction with the microreactor system operated in the stopped-flow mode.

Real-time image acquisition for absorbance detection and quantification in thin-layer chromatography.

This paper presents the first quantitative study of real-time acquisition of images of spots on thin-layer chromatographic plates during development. Procedures are described for imaging using a CCD camera and for image processing, incorporating corrections for fixed pattern effects and compensation for the moving solvent front, to measure the absorbance of the analyte. Imaging of Sudan II was carried out in transmission mode, and peak areas were found to be time-independent. Quantification of the relationship between peak area and sample loading was established over the range 1-50 ng. After averaging 55 images obtained during a single chromatographic run, which attenuates noise contributions from local nonuniformities in the sorbent layer, precision and detection limits were found to be comparable with values obtained in previous work using offline measurements.

Application of programmable temperature vaporisation injection with resistive heating-gas chromatography flame photometric detection for the determination of organophosphorus pesticides.

The combination of a programmable temperature vaporisation (PTV) injector with resistive heating GC (RH-GC), a form of fast GC, has been applied to the analysis of organophosphorus (OP) pesticides. The PTV injector was optimised in the 'at-once' solvent vent mode for the injection of ethyl acetate (10-40 microL) or ACN (10 microL). The short RH-GC column (5 m x 0.25 mm ID) with fast temperature ramps (up to 153 degrees C/ min) allowed the separation of a total of 20 OP pesticides in less than 6 min. Average recoveries between 67 and 119% were obtained for pesticides spiked at 0.01 mg/kg into apple and pear matrix. Extraction of orange juice with ACN provided higher recoveries (92-104%) for methamidophos, acephate and omethoate compared to ethyl acetate (62-73%). Results for analysis of OP pesticides in samples containing incurred residues were in good agreement with those obtained using GC-MS. The overall method was rapid, allowing 20 samples to be analysed in 4 h.

Enzymatic microreactors in chemical analysis and kinetic studies.

The fields of application of microreactors are becoming wider every year. A considerable number of papers have been published recently reporting successful application of enzymatic microreactors in chemistry and biochemistry. Most are devices with enzymes immobilized on beads or walls of microfluidic channels, whilst some use dissolved enzymes to run a reaction in the microfluidic system. Apart from model systems, mostly with glucose oxidase, horseradish peroxidase and alkaline phosphatase, the principal fields of application of microreactors are tryptic digestion of proteins and polymerase chain reaction in automated analyses of proteomic and genetic material, respectively. Enzymatic microreactors also facilitate characterization of enzyme activity as a function of substrate concentration, and enable fast screening of new biocatalysts and their substrates. They may constitute key parts of lab-on-a-chip and muTAS, assisting the analysis of biomolecules. This review provides systematic coverage of examples of reports on enzymatic microreactors published recently, as well as relevant older papers.