Vol 74, No 12 (2019)
- Year: 2019
- Articles: 12
- URL: https://journals.rcsi.science/1061-9348/issue/view/11459
Reviews
Microbial Biosensors for the Determination of Pesticides
Abstract
Along with traditional methods for the determination of environmental pollution, biosensors have become widely used in recent years. The review surveys modern microbial biosensors for determining pesticide residues in the environment. A microbial biosensor is a complex analytical device in which a microorganism is a sensitive element that responds to the presence of a pesticide in the test sample and the analytical signal depends on the concentration of the compound to be determined. The basic principles of the formation of these biosensors and their advantages and disadvantages are described. Methods of the immobilization of microorganisms as the constituents of a biosensor and various types of signal transducers are presented. The future prospects for this line of inquiry are considered.
Articles
Application of Ultrasound-assisted Cloud-point Extraction and Spectrophotometry for Preconcentration and Determination of Trace Amounts of Copper(II) in Beverages
Abstract
A new method for preconcentration of trace Cu(II) in beverages before determination by spectrophotometry is presented. The method is based on the ternary complex formation of Cu(II) with Safranin T in presence of pyrogallol at pH 5.5 followed by its extraction into the micellar phase of Triton X-114. The ternary complex was monitored by spectrophotometry at 532 nm. Variables affecting extraction efficiency were evaluated and optimized. Under the optimal conditions, the detection limit was 0.6 µg/L in the range of 2–300 µg/L with sensitivity enhancement of 55 after preconcentration from 15 mL of the sample, and precision was in the range of 2.5–3.9%. The accuracy was verified by the analysis of two certified samples and recovery studies of the spiked samples. The intra- and inter-day precision varied in the ranges of 3.7–4.6 and 3.9–5.2%, respectively. The method was successfully applied to determination of trace Cu(II) in beverages.
Determination of Mercury in Sediments by Slurry Sampling Electrothermal Atomic Absorption Spectrometry
Abstract
The concentration of mercury in suspensions of sediments is determined by electrothermal atomic absorption spectrometry (ET-AAS) using a novel chemical modifier (ChM) based on activated carbon treated by iron(II) formate. The efficiency of chemical modifiers based on activated carbon, also modified by Ag(I), Au(III), Pd(II), Co(II), and Ni(II) compounds is studied. The optimum conditions are found for the temperature and time program of the atomizer; they prevent mercury losses at the stage of drying sample suspensions and also exclude spectral interferences at the stage of atomization and measurement of the analytical signals. The minimum characteristic mass of mercury (52 pg) is reached using an iron-containing chemical modifier based on activated carbon. The conditions of ET-AAS analysis using this ChM are tested on certified reference materials of sediments and a sample selected near the sea port of Temryuk (Sea of Azov). The limit of detection found by the 3s-test was 0.05 mg/kg and the relative standard deviation was 5% at the concentration of mercury in the sample 149 mg/kg.
Development of a Method for Identifying Wood Species in Archaeological Materials by IR Spectroscopy
Abstract
We investigated 53 coniferous wood samples and 77 deciduous wood samples of trees in the central Russia by single-reflection attenuated total reflection IR spectroscopy. The characteristic absorption bands in the IR spectra of the samples are described, and the regions of absorption bands characteristic of coniferous and deciduous wood are identified. Characteristic differences in the spectra of coniferous and deciduous wood species suitable for their identification are found. Wood species of three archaeological materials were identified using these characteristic differences.
Chromatographic Separation and Determination of Functional Additives in Turbine Oil
Abstract
A procedure is proposed for the simultaneous determination of functional additives (ionol, V 15/41, D-157) in turbine oil, including two-stage solid-phase extraction and the analysis of the extract by reversed-phase HPLC. The procedure for the simultaneous determination of functional additives was tested in the analysis of an industrial sample of used TP-22 S turbine oil. Monitoring of additive concentrations in the operation of compressor stations enables the timely control of the dynamics of turbine oil degradation over the period of its use and proper recommendations on the intervals for its replacement in the system.
Determination of 1,2,4-Trithiolane in Oil and Petroleum Products by Gas Chromatography
Abstract
A procedure is developed for the quantitative determination of 1,2,4-trithiolane in oils and petroleum products by gas chromatography with flame photometric detection. The analytical range is 2‒100 mg/kg, relative standard deviations are 2‒5%. A possibility of using the developed procedure for establishing the fact of using formaldehyde-containing absorbers of hydrogen sulfide in the preparation of oil is shown.
Application of TiO2 Nanoparticles Modified Carbon Paste Electrode for the Determination of Vitamin B2
Abstract
In the present work, a modified carbon paste electrode was fabricated by grinding the mixture of graphite powder and paraffin oil (as a binder) with a sufficient amount of TiO2 nanoparticles. The electrochemical behavior of vitamin B2 (riboflavin) was investigated on the surface of the electrode using cyclic voltammetry and differential pulse voltammetry (DPV). The results showed that the electrochemical response of riboflavin was improved considerably at the modified electrode comparing to the unmodified electrode. Effects of TiO2 percentage, pH value, pulse time, and pulse amplitude were optimized using DPV technique. Under the optimized conditions, a linear dynamic range of 2.4 × 10–6 to 2.4 × 10–4 M with the detection limit of 1.6 × 10–6 M for vitamin B2 was obtained. The effects of some common interferences were examined, and the method was successfully employed to the detection of riboflavin in pharmaceutical formulations.
Gold Nanoparticles–Fe3O4 Beads/multiwalled Carbon Nanotubes Modified Glassy Carbon Electrode as a Sensing Platform for the Electrocatalytic Determination of Loratadine in Biological Fluids
Abstract
Abstarct
The glassy carbon electrode was modified by gold nanoparticles (AuNps)–Fe3O4 beads/multiwalled carbon nanotubes (MWCNTs). Surface morphology characterization of the bare and modified electrodes was characterized by scanning electron microscopy technique. This modified glassy carbon electrode was applied for electro-catalytic determination of loratadine. The modified electrode lowered the reduction overpotential of loratadine with the enhancement of its peak current; this behavior was attributed to the electro-catalytic activity of the modified electrode toward loratadine electro-reduction. Various parameters, such as pH of the working solution, amounts of MWCNTs, Fe3O4 beads and AuNps affecting the electrochemical performance of the modified electrode toward loratadine determination were optimized. The linear response of the modified electrode toward loratadine concentration using hydrodynamic amperometry method was between 0.05–5 μM with a detection limit of 0.04 μM (S/N = 3). The modified electrode figures of merit were high repeatability, reproducibility, long-term life time and low response time (<3 s). The practicability of this proposed method was examined by loratadine content quantification in commercial pharmaceutical samples, human blood serum and urine samples and satisfactory results were obtained.
Potentiometric Determination of Paracetamol in Pharmaceutical Formulations by the Analyte Pulse Perturbation Technique using Belousov–Zhabotinskii Oscillating chemical Reaction
Abstract
The present work proposes the development of an analytical procedure for paracetamol determination in pharmaceutical formulations using a system of continuous flow analysis associated with potentiometric detection allowing the study of the Belousov–Zhabotinskii (BZ) oscillating reaction. This method is based on paracetamol determination using the disturbance in the oscillation pattern of the BZ reaction promoted by this substance. The analytical curve showed the detection and quantification limits of 4 × 10–6 and 1.2 × 10–5 M, respectively. The relative standard deviation (n = 6) of the standard solution with paracetamol concentration of 6 mM was 2.3%. The analysis of real samples by the proposed and official methods (spectrophotometry/UV) showed similar results.
Determination of Methionine in Medicines by Stripping Voltammetry
Abstract
A method is proposed for the determination of methionine by stripping voltammetry on a carbon-containing electrode modified by vitamin B12. The procedure is based on the reaction of methionine reduction to homocysteine. The preparation of the electrode consists in the formation of a vitamin B12 film on the surface of a carbon-containing electrode modified with carbon nanotubes by cyclic voltammetry with a potential sweep from –1.4 to +1 V. The conditions of analysis are optimized: accumulation potential, accumulation time, and sweep rate. The limit of detection for methionine is 1 × 10–7 M.
An Enantioselective Voltammetric Sensor System Based on Glassy Carbon Electrodes Modified by Polyarylenephthalide Composites with α-, β-, and γ-Cyclodextrins for Recognizing D- and L-Tryptophans
Abstract
We developed an enantioselective voltammetric sensor system based on glassy carbon electrodes modified by polyarylenephthalide composites with α-, β-, and γ-cyclodextrins for the selective recognition and determination of tryptophan (Trp) enantiomers. The electrochemical characteristics of the electrodes and surface morphology were studied by cyclic voltammetry, electrochemical impedance spectroscopy, and atomic force microscopy. The proposed sensor system with recording voltammograms by three electrodes and the chemometric processing of the data using principal component analysis and projections to latent structures discriminant analysis was used to recognize tryptophan enantiomers in food additives and to determine their manufacturer.
Determination of Nitrogen Dioxide by Thin-Film Chemical Sensors Based on CdxPb1 –xS
Abstract
The results of a study of sensors based on thin semiconductor films of CdxPb1 – xS solid solutions intended for the determination of nitrogen dioxide in air are described. For a comparative assessment of the composition, morphology, and functional properties of the films, they were synthesized from reaction mixtures containing various cadmium salts. It was found that the maximum response is provided by layers obtained using cadmium acetate, in which the composition of the solid solution differs in the maximum supersaturation level in CdS. The films were formed of crystallites with average sizes of ~200 nm. When the concentration of nitrogen dioxide in air was 0.05‒200 mg/m3, the relative change in the ohmic resistance of sensors ranged from 8 to 80%. It was shown that the threshold concentration of NO2 in air was about 0.02 mg/m3. The reversible nature of the gas adsorption process opens a possibility for the creation of reusable chemical sensors based on CdxPb1 – xS films, differing in a relatively low threshold concentration of NO2 detection and selective response in the presence of significantly higher concentrations of O2, CO2, and H2.