Andrey Shishov

Vapor permeation-stepwise injection simultaneous determination of methanol and ethanol in biodiesel with voltammetric detection.

A novel vapor permeation-stepwise injection (VP-SWI) method for the determination of methanol and ethanol in biodiesel samples is discussed. In the current study, stepwise injection analysis was successfully combined with voltammetric detection and vapor permeation. This method is based on the separation of methanol and ethanol from a sample using a vapor permeation module (VPM) with a selective polymer membrane based on poly(phenylene isophtalamide) (PA) containing high amounts of a residual solvent. After the evaporation into the headspace of the VPM, methanol and ethanol were transported, by gas bubbling, through a PA membrane to a mixing chamber equipped with a voltammetric detector. Ethanol was selectively detected at +0.19 V, and both compounds were detected at +1.20 V. Current subtractions (using a correction factor) were used for the selective determination of methanol. A linear range between 0.05 and 0.5% (m/m) was established for each analyte. The limits of detection were estimated at 0.02% (m/m) for ethanol and methanol. The sample throughput was 5 samples h(-1). The method was successfully applied to the analysis of biodiesel samples.

Interfacial reaction using particle-immobilized reagents in a fluidized reactor. Determination of glycerol in biodiesel

A novel fluidized beads strategy for utilization of particle-immobilized reagents in flow analysis was developed in this study. The performance of the suggested strategy was demonstrated by the determination of glycerol in biodiesel. This analytical task was used as a proof-of-concept example. The method is based on on-line extraction of glycerol from biodiesel into aqueous stationary phase of extraction-chromatographic column, followed by elution and spectrophotometric determination in the form of copper glycerate formed in a fluidized reactor of stepwise injection system. The floating of cation exchange resin Dowex(®) 50WX4, saturated with Cu(II) ions in liquid phase, was accomplished by air-bubbling. The linear range was from 100 to 1000 mg kg(-1), and the limit of detection, calculated as 3s of a blank test (n = 5), was found to be 30 mg kg(-1). The method was successfully applied to the analysis of biodiesel and biodiesel-blend (B 20) samples.

Fully automated spectrophotometric procedure for simultaneous determination of calcium and magnesium in biodiesel.

An easily performed stepwise injection (SWIA) procedure based on on-line dilution of biodiesel samples and the formation of color-forming calcium (II) and magnesium (II) complexes with Eriochrome Black T (EBT) in an organic medium followed by spectrophotometric determination is presented. A sample of biodiesel was placed at the bottom of a mixing chamber connected to an automatic SWIA manifold. Isopropyl alcohol was used as the diluent under bubbling. The solution was submitted for on-line spectrophotometric simultaneous determination of calcium and magnesium based on the classic least-square method. The linear ranges were from 2 to 20 μg g(-1) and from 1.2 to 12 μg g(-1), and the detection limits, calculated as 3 s for a blank test (n=5), were found to be 0.6 μg g(-1) for calcium and 0.4 μg g(-1) for magnesium. The sample throughput was 30 h(-1). The method was successfully applied to the analysis of biodiesel samples.

Automated IR determination of petroleum products in water based on sequential injection analysis

The simple and easy performed automated method for the IR determination of petroleum products (PP) in water using extraction-chromatographic cartridges has been developed. The method assumes two stages: on-site extraction of PP during a sampling by using extraction-chromatographic cartridges and subsequent determination of the extracted PP using sequential injection analysis (SIA) with IR detection. The appropriate experimental conditions for extraction of the dissolved in water PP and for automated SIA procedure were investigated. The calibration plot constructed using the developed procedure was linear in the range of 3-200 μg L(-1). The limit of detection (LOD), calculated from a blank test based on 3σ was 1 µg L(-1). The sample volume was 1L. The system throughput was found to be 12 h(-1).

An automated continuous homogeneous microextraction for the determination of selenium and arsenic by hydride generation atomic fluorescence spectrometry

An automated continuous homogeneous microextraction approach based on a flow system has been developed and coupled with a hydride generation atomic fluorescence spectrometry system (HG-AFS). The developed approach was applied for the determination of trace arsenic and selenium in environmental water and liver samples. The nonanoic acid was investigated as a switchable hydrophilicity solvent (SHS) for homogeneous microextraction of As(III) and Se(IV) complexes with pyrrolidinedithiocarbamate (PDC). The procedure involved on-line mixing ammonium PDC (aqueous phase), sodium nonanoate (aqueous phase) and acid sample solution resulting in the formation of SHS (nonanoic acid) dispersed into the acid aqueous phase. By this continuous process, analytes complexes with PDC were formed and extracted into the fine SHS droplets followed by retention into a monolithic column packed with block of porous PTFE. Finally, the retained complexes were eluted with NaOH solution and delivered to the HG-AFS system. The limits of detection, calculated from a blank test based on 3σ, were 0.01μgL-1 for both analytes.

A paper-based analytical device for the determination of hydrogen sulfide in fuel oils based on headspace liquid-phase microextraction and cyclic voltammetry

An easily performed miniaturized, cheap, selective and sensitive procedure for the determination of H2S in fuel oil samples based on a headspace liquid-phase microextraction followed by a cyclic voltammetry detection using a paper-based analytical device (PAD) was developed. A modified wax dipping method was applied to fabricate the PAD. The PAD included hydrophobic zones of sample and supporting electrolyte connecting by hydrophilic channel. The zones of sample and supporting electrolyte were connected with nickel working, platinum auxiliary and Ag/AgCl reference electrodes. The analytical procedure included separation of H2S from fuel oil sample based on the headspace liquid-phase microextraction in alkaline solution. Then, sulfide ions solution obtained and supporting electrolyte were dropped on the zones followed by analyte detection at + 0.45 V. Under the optimized conditions, H2S concentration in the range from 2 to 20 mg kg-1 had a good linear relation with the peak current. The limit of detection (3σ) was 0.6 mg kg-1. The procedure was successfully applied to the analysis of fuel oil samples.