Volume 30, Issue 3-4

The global pesticide market has grown steadily since the 1940s, with the agricultural sector being the largest user of pesticides. The effect of pesticides on human health is manifested either through direct exposure to the material or indirect exposure to contaminated resources. Farmers and those dwelling near areas where pesticides are used may suffer from direct exposure, while the general population might be exposed indirectly, for example, by drinking contaminated water. Exposure to pesticides may cause a variety of symptoms, including headaches, dizziness, and vomiting, damage the nervous system, and even cause death. The risks involved in pesticide use include air pollution and soil and water contamination. The environmental implications of pesticide use include development of resistance among pests, a decline in biodiversity, interruption of the food chain, and disruption of the ecological balance. Pesticide use may also cause changes in physical parameters of the ecosystem. Effective activity of pesticides requires reaching proper leaf coverage. To prevent pest attacks due to insufficient leaf coverage, farmers tend to apply pesticides in excess. In view of the environmental and health implications of pesticide use, there is a clear need to limit pesticide application. Yet farmers lack the means to perform real-time in situ assessment of leaf coverage. Existing pesticide detection methods are complex, time-consuming, and unsuited to field application. Optical methods have the potential to provide quick assessments and can be used in situ . Several optical methods for detection of pesticides in general and on leaves in particular were developed. The findings indicated that the main problems in pesticide detection using fluorescence are the low autofluorescence of the pesticides and the nonreproducible spectral response of the leaves. These obstacles were solved by employing labeling agents. For example, rhodamine was suggested, mainly due to its excellent surface adhesion and its extremely high fluorescence quantum yield. The labeling agents were sprayed on leaves in the form of aerosols, thus creating a uniform layer of nanocrystals and microcrystals on the surface of the leaves. The effects of pesticides on the spectral characteristics of the labeling agents were examined using laser-induced fluorescence (LIF) spectroscopy. When pesticide droplets were applied to a pretreated leaf, two phenomena were observed. The first was a substantial fluorescence increase. The second was material-specific spectral shifting as a result of interaction between the labeling molecules and organic components in the pesticide droplet. It was possible to utilize these spectral shifts for quantification of the pesticide concentration in the droplet. These spectral shifts enabled detection of pesticides on plants, although they were not sufficient for providing quantitative information on the extent of pesticide coverage. To detect pesticide coverage, several imaging data techniques were applied, such as LIF scanning of the examined plant surface. This method revealed the droplet shape by scanning and recording the fluorescence intensity at many points on a grid. Since application of this method is expensive and time-consuming, a second technique was also developed: it requires only a UV source and a CCD camera and it enables direct imaging of the pesticides on plants. The data obtained included the droplet shape and its location on the plant. When pesticide identification was required, application of a special hyperspectral fluorescence imaging method was introduced. Fourier transform hyperspectral imaging analysis provided simultaneous full spectral resolution at each pixel, enabling identification of the pesticide and its mapping on the plant. In practice, test plants have to be pretreated with labeling material before pesticide application. The changes in the labeling compound fluorescence can then be used for detection of the pesticide on the plant and quantification of the overall coverage. Low-cost mapping of the pesticide microdroplets could be obtained using a CCD camera, while accurate information could be based on Fourier transform hyperspectral imaging. Since these methods provide immediate results, they may allow the farmer to estimate leaf coverage during pesticide application and adjust spraying accordingly.

Lead and cadmium were determined in the presence of matrix modifiers. Under the optimal measure conditions, lead and cadmium in tea showed excellent linearities with correlation coefficients of 0.9996 and 0.9993 after digestion of tea with HNO 3 /HCl (3:1, v/v). The recoveries were 94–102% and 91–103% and RSD values were 8.86% and 13.1%, respectively.

Simple and accurate reversed phase liquid chromatographic and first derivative spectrophotometric methods have been developed for simultaneous determination of desloratadine and pseudoephedrine in combined dosage forms. The first method is based on the separation of both drugs by high performance liquid chromatography using a C18 column and 10 m m ortho-phosphoric acid: acetonitrile (77:23). The drugs are eluted at 1.0 ml/min flow rate and detected at 262 nm. Ondansetron was used as internal standard. The calibration graphs of desloratadine and pseudoephedrine were linear in the range of 1.0–10.0 μg/ml and 48–480 μg/ml, respectively. The detection limits of the method were found to be 0.14 μg/ml and 3.80 μg/ml for desloratadine and pseudoephedrine, respectively. The derivative spectrophotometric method depends on measuring the first derivative amplitudes at 280 and 244 nm for desloratadine and pseudoephedrine, respectively. The calibration graphs were linear in the range of 2.5–15.0 μg/ml for desloratadine and 120–720 μg/ml for pseudoephedrine. The detection limits were found at 0.38 μg/ml and 21.45 μg/ml for desloratadine and pseudoephedrine, respectively. The proposed methods were successfully applied to the determination of these drugs in commercially available tablets.

High performance liquid chromatography coupled with diode array detection (HPLC-DAD) was utilised for the identification of dyestuffs in different plants such as dyers weld, gallnut, walloon oak, woad, indigo shrub and cochineal. The most important dyestuffs detected were natural yellow, green, beige, black and blue dyes which are found in historical textiles. In addition, reversed-phase HPLC with DAD was employed in the identification of natural dyes in extracts of historical silk art objects, from historical textiles and newly dyed silk fibres. The objects examined were from the 15th to 17th century Ottoman period and belong to the collection of the Topkapi Palace Museum in Istanbul. Fibres with yellow, blue, black, beige and green colours were selected for the analysis. Dye components were identified in the extracts of 11 art objects analysed; both insect and plant dyes were detected.

A high-performance liquid chromatographic (HPLC) method for the determination of antidepressant drug desipramine as active metabolite of imipramine in plasma is reported. The method is based on the purple chromogen formed by displacement reaction of desipramine with 7,7,8,8-tetracyanoquinodimethane in acetonitrile at 80°C for 20 min. The assay is based on liquid-liquid extraction with chloroform and reversed-phase chromatography with UV-visible detection. Liquid chromatography was performed on a Luna C 18 column (250 mm×4.6 mm, 5 μm) with a mobile phase acetonitrile/water (70:30) at a flow rate of 1.0 ml/min. Paroxetine was used as internal standard. The retention time was 15.5 and 13.1 min for desipramine and paroxetine. The detector was operated at 567 nm. The method was linear in the range of 15–400 ng/ml with a correlation coefficient (r) of 0.9973. The limit of detection was 1 ng/ml at a signal-to-noise ratio of 3:1. Recoveries determined for three concentrations range between 86.14% and 88.98.1%. Intra-day and inter-day relative standard deviation values were found to be within 6.43–11.35% and 9.82–13.05%, respectively. Using the developed method, a pharmacokinetic study was performed for desipramine (as active metabolite of imipramine).

A simple and sensitive solid-phase spectrophotometric method was developed for the determination of rhodium(III) trace amounts. The proposed procedure is based on the reaction product of disodium-1-nitroso-2-hydroxynaphthalene-3,6-disulfonate(Nitroso R salt) previously loaded on Dowex 1×1 anion exchanger. To find the best analytical conditions for the determination, the experimental variables (wavelength, pH, amount of resin, sample solution volume) were optimized. Under the selected conditions, rhodium(III) can be accurately determined in the range of 0.5–2 μg/ml with an RSD of 1.18% and a degree of sensitivity, expressed by the molar absorptivity, of 3.0356×10 4  l/mol cm. The results obtained on synthetic solutions clearly indicate the feasibility of the proposed method for real sample analysis.

Electrochemical oxidation of quercetin (QR), 3-hydroxy­flavone (3HF), and baicalein (BN) and their grafting onto the glassy carbon (GC) electrode have been studied using the cyclic voltammetric (CV) technique. Electrochemical studies were performed within a one-compartment three-electrode cell at room temperature. The modification was carried out only in nonaqueous media, while the electrochemical characterization was done in both aqueous and nonaqueous media. In the nonaqueous experiments, 0.1  m tetrabutylammonium tetrafluoroborate in acetonitrile was used, whereas in the aqueous experiments, Britton-Robinson buffer solutions (pH=2) and 0.1  m KCl solutions were. Surface modifications were performed by CV for all compounds. The presence of QR, 3HF, and BN at the GC electrode surface was characterized by CV, electrochemical impedance spectroscopy, contact angle measurement, ellipsometry, and atomic force microscopy.

In this study, a simple and reliable cyclic voltammetry and linear sweep voltammetry method were developed and validated for determination of carvedilol in pharmaceutical preparations. The proposed method was based on electrochemical oxidation of carvedilol at platinum electrode in acetonitrile solution containing 0.1 m TBAClO 4 . The well defined three oxidation peaks were observed at 1.02, 1.17 and 1.42 V, respectively. Calibration curve that obtained by using current values measured for second peak was linear over the concentration range of 5–40 μg/ml. Intra- and inter-day precision values for carvedilol were <3.64 and accuracy (relative error) was better than 2.49%. The mean recovery of carvedilol was 99.8% for pharmaceutical preparations. The limits of detection and quantification were 1.32 and 4.00 μg/ml, respectively. No interference was found from three tablet excipients at the selected assay conditions. The method developed in this study is accurate, precise and can be easily applied to Dilatrend, Carvexal and Coronis tablets as pharmaceutical preparation.