Isolation and Determination of Volatile Organic Compounds from Water by Dynamic Purge-and-Trap Technique Coupled with Capillary Gas Chromatography

The preconcentration technique of purge-and-trap has been investigated in the present work for quantitative adsorption of volatile organic pollutants purged from water samples. A dynamic purging device with variable volume size has been constructed and tested to purge different concentrations of organic compounds. With Tenax GR as the adsorbent, a dynamic purge-and-trap technique was developed combining on-column preconcentration procedures using ambient trapping/thermal desorption/cryogenic focusing/back-flash injection prior to separation and determination using capillary gas chromatography. Various aromatic compounds in water were determined, giving linear working ranges over five orders of magnitude from 0.02 to 5000 µg/L. The analytical procedures were optimized under the assistance of ultrasonication with results validated for the determination of organic contaminants in underground water and tap water, giving over 93% recoveries and a detection limit of 0.01 µg/L, two orders of magnitude lower than those obtained using commercial available instruments with on-line configuration to minimize cross-contamination. The technique provides a potential automated method for in situ monitoring of volatile organic compounds in water.     

Determination of Nitrite via Reaction with Pyridine-4-Carboxylic Acid Hydrazide

Abstract

Nitrite is determined by its reaction with a measured but excessive amount of pyridine-4-carboxylic acid hydrazide in acid medium (when the two substances react in a 1:1 molar ratio) and evaluation of the surplus hydrazide by titration with chloramine-T in the presence of acidified potassium bromide, the end-point being shown by the decolorization of the methyl red indicator. Nitrate, copper(II), mercury(II), etc. are found not to interfere, and the determination of nitrite in the presence of diazotized aromatic amines is demonstrated.     

Investigation on Thioguanine by Solid Surface Fluorimetry

ABSTRACT

The solid surface fluorimetry (SSF) for the determination of 6-thioguanine (6-TG) has been presented. Several experimental conditions such as the type of solid substrate, pH of the medium, rigidity state of substrate, drying condition etc. were optimized. The new and highly sensitive procedure has a linear range of 3.3～668.6ng/spot with the correlation coefficient 0.999, the relative standard deviation (RSD) 3.16% and the limit of detection 0.47 ng/spot corresponding to three times the standard deviation of the blank (n=11). The recovery of standard 6-TG added to urine was over the range of 97.4-107.4%. The method is simple, rapid and sensitive and can be applied to analysis of urine without interference.     

Fluorimetric Analysis of Aluminum in Diluted Hemodialysis Solutions by Using a Novel Schiff Base

A spectrofluorimetric method has been developed for trace amount of aluminum(III) by using a novel Schiff base, N,N′-bis(salicylidene)-1,4-diaminobuthane (BUTAS), and 4-methyl-2-aminophenol (OAP). Since the aluminum complexes are generally fluorescent, aluminum(III) increases the fluorescence intensity of BUTAS-OAP by formation of Al-BUTAS-OAP complex. The fluorescence of the complex is measured at an excitation wavelength of 410 nm with an emission at 526 nm. Aluminum(III) can be detected within a concentration limit of 0.11–1.62 ppb and the lowest detection limit being 0.07 ppb. The proposed method was applied to diluted hemodialysis solution and spectrofluorimetric data was compared with data of standard pharmacopoeia method.     

Kinetic Study on Models of the Noncatalyzed Reaction Between α, ω -Dicarboxypolyamide-11 and α, ω -Dihydroxypolyoxyalkylenes

The kinetics of the noncatalyzed reaction between α, ω -dicarboxypoly-amide-11 and α, ω -dihydroxypolyoxyalkylenes is investigated by using the reactions of 11-dodecylamidoundecanoic acid with 1-dodecanol, 2-tridecanol, α-dodecyl-ω-hydroxypolyoxyethylene or α-dodecyl-ω;-hydroxypolyoxypropylene as models. Kinetic data fit a 3rd overall order (2 in acid and 1 in alcohol). Rate constants and activation parameters are determined and compared.     

Graphene grafted silica‐coated Fe3O4 nanocomposite as absorbent for enrichment of carbamates from cucumbers and pears prior to HPLC

In this paper, a novel graphene (G) grafted silica‐coated Fe₃O₄ nanocomposite was fabricated by the chemical bonding of G onto the surface of silica‐coated Fe₃O₄ nanoparticles. Some carbamates (metolcarb, carbaryl, pirimicarb, and diethofencarb) in cucumber and pear samples were enriched by this nanocomposite prior to their determination by HPLC with UV detection. Experimental parameters that may affect the extraction efficiency were investigated. Under the optimum conditions, a linear response was achieved in the concentration range of 0.5–100.0 ng/g for metolcarb, carbaryl, and diethofencarb, and 1.0–100 ng/g for pirimicarb with the correlation coefficients (r) ranging from 0.9956 to 0.9984. The LOD (S/N = 3) of the method were found to be in the range from 0.08 to 0.2 ng/g. The RSDs were in the range from 2.4 to 5.8%. The results indicated that the G grafted silica‐coated Fe₃O₄ nanocomposite was stable and efficient for magnetic SPE and has a great application potential for the preconcentration of other organic pollutants from real samples.     

Simultaneous Determination of Hydrogen Peroxide and Organic Hydroperoxides in Water

The kinetics of the reactions of H 2 O 2 and of methyl, ethyl, tert -butyl, and cumene hydroperoxides with I m were investigated in the presence and absence of molybdate as catalyst. These results were utilized to develop an analytical method for the simultaneous determination of H 2 O 2 and organic hydroperoxides in aqueous solutions. The total amount of H 2 O 2 and organic hydroperoxides can be determined by the spectrophotometric measurement of $ {\rm I}_3^ - $ formed quantitatively during 30 min of heating at 60°C. Catalase selectively decomposes H 2 O 2 in solutions containing organic hydroperoxides. The total amount of the latter can therefore be determined iodometrically after H 2 O 2 decomposition. In the oxidation of leuco crystal violet to crystal violet by H 2 O 2 and organic hydroperoxides, horseradish peroxidase exerts similar activities in the reactions involving methyl and ethyl hydroperoxides and H 2 O 2 , but its activity is much lower with tert -butyl and cumene hydroperoxide. It was observed that acetate buffer is unsuitable for pH adjustment in this type of hydroperoxide determination in consequence of the slow oxidation of the dye in the blank solution.     

Two organophosphorus pesticides: methyl parathion and dicapthon

Structural studies performed in this laboratory of organophosphorus pesticides continue with these related compounds. The –NO₂ groups of methyl parathion (systematic name: dimethyl 4‐nitrophenyl phosphorothioate, C₈H₁₀NO₅PS) and dicapthon (systematic name: 2‐chloro‐4‐nitrophenyl dimethyl phosphorothioate, C₈H₉ClNO₅PS) make dihedral angles of 10.67 (8) and 5.8 (1)°, respectively, with the planes of their attached rings, which accompanies angular distortion at the ring C atoms to which the –NO₂ groups are attached. Similar distortions are observed at the C atom to which the thiophosphate groups are attached. Significant differences in distances and angles around the phenolic O, versus the –OMe groups, explain why it is the site of hydrolysis for these compounds. A comparison of a torsion angle involving the thiophosphate group and phenolic O atom with similar pesticide structures is given and indicates steric influences on that angle.     

Synthesis and characterization of CuO nanoparticles utilizing waste fish scale and exploitation of XRD peak profile analysis for approximating the structural parameters

In this research, we strived to utilize waste fish scale (labeo rohita) for synthesizing CuO nano-particles (CuO NPs), which gained much attention due to its distinctive properties and versatile applications. Upon the heat treatment, the collagen content of the fish scale got transformed into gelatin which in turn converted the precursor material into CuO NPs. The X-Ray diffraction (XRD) analysis confirmed the formation of CuO NPs and revealed the structure to be of monoclinic lattice. The structural parameters i.e. crystallite size, lattice parameters, microstrain, dislocation density was evaluated for the synthesized CuO NPs using the XRD data. Scherrer’s Method (SM), Scherrer Equation Average Method (SEAM), Linear Straight Line Method (LSLM), Straight Line Passing the Origin Method (SLPOM), Monshi Scherrer Method (MSM), Williamson-Hall Method (WHM), Size-Strain Plot Method (SSPM), Halder-Wagner Method (HWM) was exploited for the estimation of crystallite size. According to the calculations, the crystallite size was found to be 87 nm, 41 nm, 1980 nm, 62 nm, 66 nm, 28 nm, 13 nm, 13 nm respectively and the dislocation density was found to be 1.32 × 10^-4, 5.95 × 10^-4, 0.002 × 10^-4, 2.60 × 10^-4, 2.29 × 10^-4, 12.75 × 10^-4, 59.17 × 10^-4 and 59.17 × 10^-4 respectively. UV–Vis absorption analysis also confirmed the formation of CuO NPs based on the absorption peak at 262 nm (λ_max) and Tauc Plot method was used to calculate the optical band gap which was 3.84 eV. Functional group, especially the Cu-O bonding was confirmed by the Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) data. Field Emission Scanning Electron Microscopy (FESEM) showed three different shapes of CuO NPs which was also confirmed by Transmission Electron Microscopy (TEM). Particle size was determined based on FESEM and TEM image using imageJ software and also by the Dynamic Light Scattering (DLS) technique. Thermal analysis showed a four stage weight loss in case of Thermogravimetric (TGA) analysis and three conversion steps was observed in Differential Scanning Calorimetric (DSC) analysis. Such synthesis pathway is evidently green and facile for synthesizing CuO NPs with potentiality of various applications and also utilization of waste fish scale is a perquisite.     

Determination of Bismuth by Adsorptive Stripping Voltammetry Using Aluminum Oxide for Elimination of Environmental Sample Matrix Interferences

The aim of this work was to find a fast new and simple method for efficient elimination of negative influence of humic substances and synthetic surfactants in the voltammetric determination of bismuth. The negative influence of the organic matrix present in environmental water samples due to their adsorption on aluminum oxide was successfully evaluated. The organic compounds such as humic substances and surface active compounds were removed by adsorption on the surface of aluminum oxide from the water samples. The application of this method was the recovery of Bi(III) from spiked water samples.