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Abstract. The purpose of the present research was to design a method for the colorimetric determination of L-cysteine. We have employed PVA capped gold nanoparticles (GNPs) as a probe. The as-synthesized GNPs were further characterized by UV-vis absorption spectroscopy, transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS) and Zeta potential analyser. The results show that the presence of L-cysteine caused the quenching of the surface plasmon resonance band of the GNPs at 524 nm. It was accompanied by the appearance of a new absorbance of a new absorbance band at 670 nm. The color of the colloidal GNPs changed from wine red to blue. The change in color of the GNPs was due to their aggregation induced by the presence of L-cysteine. Based on these observations, the as-synthesized GNPs were utilized to develop a novel colorimetric sensor for L-cysteine detection in food samples. Significantly, other biomolecules such as alanine, proline, phenylalanine, tryptophane, valine, arginine, glutamic acid, lysine and histidine did not cause any change in the color of the GNPs solutions. This colorimetric probe showed excellent selectivity and high sensitivity for L-cysteine with a detection limit of 2.0 μg mL-1.

Ion exchange resins (IERs) are solid poly-electrolytes which have both sorption and exchange capacity of several organic compounds. They have the power to separate ionic and non-ionic substances with the surrounding medium. The drug materials or substances are adsorbed on resin, which is commonly known as resinate, these features of IERs have useful applications in pharmaceutical formation (i.e., taste masking, stability and solubility enhancement, etc.) and major applications in drug delivery (i.e., oral, nasal, ophthalmic, transdarmal drug delivery). IE principles have been exploited in the investigation of numerous drug industry problems for many years. Synthetic IERs have been extensively employed in pharmacy and medicine, especially for taste masking or controlled release of drugs and have been expansively studied in the development of novel drug delivery systems and other biomedical applications. In this review, the fascinating IERs involving ion exchange processes in pharmaceutical and clinical applications and also their recent advanced uses have been discussed.

The proposed method is based on flotation–dissolution an easy, impressible, extractive spectrophotometric determination, explained for easy investigation of the organophosphate pesticide phorate (O,O-diethyl S-[ethylthiomethyl] phosphorodithioate) on trace levels. A molybdophospho complex is generated when prorate is treated with ammonium molybdate in acidic medium. As an ion associate complex with methylene blue the complex is present in between of the water and organic layers which is extracted and then dissolved with acetone. The greenish blue complex produced show absorption maxima at 660 nm. Beer’s law range is found to be 0.5 to 16 µg per 10 ml for phorate. The molar absorptivity is 0.989×103 L mol-1 cm-1 and sandell’s sensitivity is 1.00×10-5 µg cm-2. Also calculated the standard deviation and relative standard deviation for the above method were ±0.006 and 1.95% respectively. The method has been applied and checked for the determination of phorate in water, soil and vegetables.

Surface active agents (SAAs) are a class of compounds, which find various applications in different fields of human activities. Surfactants are generally amphiphilic molecules, which are strongly adsorbed at interfaces between the phases. Surfactants windily used as detergency, emulsion, stabilizing and dispersing agents have led to the discharge of highly contaminated wastewaters in aquatic environment. Once reached in the various compartments of the environment such as rivers, lakes, soils, and sediments, surfactants can undergo aerobic or anaerobic degradation. Concentrations of surfactants in wastewaters, river waters, and sewage waters can range milligrams in maximum cases, while it reaches several grams in sludge, soil and sediments in environments. The environmental facts of SAAs and concentration in surface waters, soils or sediments are reviewed in details. This review provides information on levels of surface-active agents in various environmental samples including soil, sediments, sewage wastewater, river wastewater and aerosols.