Determination of aldehydes in rainwater using micro-solid-phase extraction and high-performance liquid chromatography

A simple and rapid extraction procedure was developed for determining aldehydes in rainwater samples. This extraction technique involved the use of micro-solid-phase extraction in which the sorbent was held within a polypropylene membrane envelope, followed by high-performance liquid chromatographic analysis. Aldehydes such as formaldehyde, acetaldehyde, propionaldehyde and valeraldehyde were used as model compounds. Extraction conditions were optimized. The method linearity ranged between 0.5 and 50 μg l⁻¹ with the correlation coefficient of 0.987–0.999. The relative standard deviations (RSDs) of the method ranged from 7 to 12%. Method detection limits were in the range of 0.07–0.15 μg l⁻¹, which is lower than those previously reported for solid-phase microextraction combined with gas chromatography–mass spectrometric techniques. The proposed extraction technique was used for determination of aldehydes in rainwater samples to demonstrate the applicability of the method.     

Synthesis,characterization, AC conductivity,and diode properties of polyaniline–CaTiO3 composites

Polyaniline–CaTiO₃ composites of different weight percentages were prepared by in situ polymerization. The prepared composites were characterized by Fourier transform infrared spectroscopy for structural studies, and a morphology analysis was carried out by scanning electron microscopy studies. Real and imaginary parts of the complex impedance were determined for given samples as a function of frequency. Current–voltage and capacitance–voltage measurements were also carried out. The carrier mobility μ values of neat polyaniline and polyaniline–CaTiO₃ composites were found to be 5.37 × 10^?3 and 2.73 × 10^?2, respectively, and a significant enhancement, as compared with the reported data, was observed. Therefore, this study may provide a better route for technological applications in all fields in the near future and can also be represented by a pure electronic model. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis of gold nanorods using concentrated aerosol OT in hexane and its application as catalyst for the reduction of eosin

The microemulsion method for the preparation of nanoparticles is well known. We have used the aqueous core of highly concentrated aerosol OT in hexane solution to synthesize gold nanorod by utilizing the aqueous core of surfactant aggregates as host nanoreactor. The shape and size of the aqueous core as well as the particles formed inside the core can be controlled by changing the parameter W₀ (water to surfactant ratio), concentration of gold salt and the concentration of surfactant. When the concentration of the surfactant is very high the shape of the aqueous droplet does not remain spherical but take the shape of prolate. In our study we have made gold nanorods by the reduction of gold chloride with sodium borohydride in the aqueous core of 1 M AOT hexane at a W₀ of 10. The rods are highly monodispersed with a diameter of about 20 nm and a length of 200 nm with an aspect ratio of 10. The absorption spectra of the gold nanorods show two different peaks one at 535 nm and the other at 965 nm. The particles were used as a catalyst for the reduction of eosin with sodium borohydride. The rate constant comes out be very large in comparison with that of uncatalysed reaction. The reaction was carried out at various temperatures between 20 and 60 °C and the activation energy of the reaction was calculated using Arrhenius plot between–ln k and 1/T. The activation energy of the gold nanorods catalysed reaction comes out to be more than two times as compared to uncatalysed reaction.     

Simple, sensitive, selective and validated spectrophotometric methods for the estimation of a biomarker trigonelline from polyherbal gels

Simple, accurate, reproducible, selective, sensitive and cost effective UV-spectrophotometric methods were developed and validated for the estimation of trigonelline in bulk and pharmaceutical formulations. Trigonelline was estimated at 265 nm in deionised water and at 264 nm in phosphate buffer (pH 4.5). Beer's law was obeyed in the concentration ranges of 1-20microg mL(-1) (r2=0.9999) in deionised water and 1-24 microg mL(-1) (r2=0.9999) in the phosphate buffer medium. The apparent molar absorptivity and Sandell's sensitivity coefficient were found to be 4.04 x 10(3)L mol(-1)cm(-1) and 0.0422 microg cm(-2)/0.001A in deionised water; and 3.05 x 10(3)L mol(-1)cm(-1) and 0.0567 microg cm(-2)/0.001A in phosphate buffer media, respectively. These methods were tested and validated for various parameters according to ICH guidelines. The detection and quantitation limits were found to be 0.12 and 0.37 microg mL(-1) in deionised water and 0.13 and 0.40 microg mL(-1) in phosphate buffer medium, respectively. The proposed methods were successfully applied for the determination of trigonelline in pharmaceutical formulations (vaginal tablets and bioadhesive vaginal gels). The results demonstrated that the procedure is accurate, precise, specific and reproducible (percent relative standard deviation <2%), while being simple and less time consuming and hence can be suitably applied for the estimation of trigonelline in different dosage forms and dissolution studies.     

Dielectric and electrical properties of a tungsten bronze tantalate ceramic

Using high temperature solid state reaction the polycrystalline sample of K₂Pb₂Dy₂W₂Ti₄Ta₄O₃₀ was prepared. Single-phase compound formation was confirmed by preliminary X-ray structural analysis. The surface morphology recorded by scanning electron microscope at room temperature exhibits a dense uniform grain distribution on the surface of the sample. Ferroelectricity in the material is confirmed by the variation of polarization with temperature. The temperature and frequency dependence of electrical parameters (impedance, modulus, conductivity, etc.) of the material exhibits a strong correlation with its microstructure (i.e., bulk, grain boundary, etc.) and electrical properties. A typical Arrhenius behavior was observed in the temperature dependence of dc conductivity. The nature of frequency dependence of ac conductivity obeys Jonscher's universal power law. The variation of current with temperature shows that the material has high pyroelectric coefficient and figure of merit, thus making it useful for pyroelectric sensors with working temperature upto 500 °C.     

Development of a liposome-based immunochromatographic strip assay for the detection of Salmonella

Salmonella species are ubiquitous human pathogens which pose a dangerous threat to the elderly and children worldwide. In this study, to develop a more efficient assay procedure for the rapid detection of Salmonella Typhimurium, an immunochromatographic strip assay was developed using immunoliposome (anti-Salmonella IgG-tagged) encapsulated with sulforhodamine B (SRB). The detection sensitivity of the developed immunochromatographic assay was compared with a commercial immunochromatographic test strip using colloidal gold nanoparticles. The liposomes were prepared through a reverse-phase evaporation method by using a lipid and phospholipid mixture and SRB, a fluorescence dye, which was encapsulated in the phospholipid bilayer. Furthermore, the outer surface of the SRB-encapsulated liposome was conjugated with antibody (affinity-purified polyclonal goat anti-Salmonella IgG) to form an immunoliposome (size, 223 nm), used as the analytical reagent in the developed immunoassay. For this strip assay, a plastic-backed nitrocellulose strip was immobilized with two antibody zones. The lower zone of the strip referred to Salmonella antigen capture zone (test line), while the other zone served as a positive control (control line). The lower zone was coated with affinity-purified polyclonal goat anti-Salmonella IgG, while the upper zone was coated with rabbit anti-goat IgG. During capillary migration of the wicking solution (diluted liposome and Salmonella culture, each 50 μl), Salmonella was captured with surface-bound immunoliposomes at the antigen capture zone, while the unbound liposomes migrated upward and bound to another zone. The color density of the antigen capture zone was directly proportional to the amount of S. Typhimurium in the test sample. As a result, the detection limit of the immunochromatographic strip assay developed in this study against S. Typhimurium was found to be 10² CFU/ml, which was significantly higher than the detection limit (10⁷ CFU/ml) of the commercial immunochromatographic test strip assay.     

Identification of impurities in polymyxin B and colistin bulk sample using liquid chromatography coupled to mass spectrometry

The European Pharmacopoeia (Ph. Eur.) describes liquid chromatography-ultraviolet (LC-UV) methods using C₁₈ stationary phases for the analysis of polymyxin B and colistin.Several unknown impurities were detected in commercial samples of those polypeptide complexes. However, the Ph. Eur. does not specify any related substances for polymyxin B and colistin. Since both methods use non-volatile buffers, the mobile phases were incompatible with mass spectrometry (MS). For the identification of related substances in bulk samples by LC/MS, volatile mobile phase systems were developed. However, the LC/MS methods (with volatile additives) showed inferior chromatographic separation compared to the LC-UV method (with non-volatile additives). Moreover, previously identified impurities by LC/MS could not be assigned in LC-UV methods as the separation in both systems was different.In this study, known impurities were traced in the LC-UV methods and new impurities present in polymyxin B and colistin bulk samples were characterized. To achieve this, each peak from the non-volatile system was collected separately and reinjected into an LC system with a volatile mobile phase coupled to MS. This way, collected impurity peaks were rechromatographed on a reversed phase column in order to separate the analyte from the buffer salts. Using this method, out of 39 peaks, five novel related substances were characterized in a polymyxin B bulk sample. Fourteen impurities, which were already reported in the literature were traced as good as possible in the LC-UV method. In the case of colistin, a total of 36 peaks were investigated, among which four new compounds. Additionally, 30 known impurities were traced in the LC-UV method.     

Synthesis of Phosphatidyl Glycerol Containing Unsymmetric Acyl Chains Using H-Phosphonate Methodology

Naturally occurring phospholipids, such as phosphatidyl glycerol (PG), are gaining interest due to the roles they play in disease mechanisms. To elucidate the metabolism of PG, an optically pure material is required, but this is unfortunately not commercially available. Our previous PG synthesis route utilized phosphoramidite methodology that addressed issues surrounding fatty acid substrate scope and glycerol backbone modifications prior to headgroup phosphorylation, but faltered in the reproducibility of the overall pathway due to purification challenges. Herein, we present a robust pathway to optically pure PG in fewer steps, utilizing H-phosphonates that features a chromatographically friendly and stable triethyl ammonium H-phosphonate salt. Our route is also amendable to the simultaneous installation of different acyl chains, either saturated or unsaturated, on the glycerol backbone.     

Confined Water in Amyloid‐Competent Oligomers of the Prion Protein

Conformational switching of the prion protein into the abnormal form involves the formation of (obligatory) molten‐oligomers that mature into ordered amyloid fibrils. The role of water in directing the course of amyloid formation remains poorly understood. Here, we show that the mobility of the water molecules within the on‐pathway oligomers is highly retarded. The water relaxation time within the oligomers was estimated to be ≈1 ns which is about three orders of magnitude slower than the bulk water and resembles the characteristics of (trapped) nano‐confined water. We propose that the coalescence of these obligatory oligomers containing trapped water is entropically favored because of the release of ordered water molecules in the bulk milieu and results in the sequestration of favorable inter‐chain amyloid contacts via nucleated conformational conversion. The dynamic role of water in protein aggregation will have much broader implications in a variety of protein misfolding diseases.