Andrey Bulatov

Stepwise injection spectrophotometric determination of epinephrine

Simple, rapid and fully automated methods for the manual and automated spectrophotometric determination of epinephrine have been developed by using schemes of stepwise injection (SWIA) and sequential injection analysis (SIA) implemented in the same manifold. The determination is based on the formation of reduced form of 18-molybdodiphosphate heteropoly anion by its reaction with epinephrine. Using of the reaction vessel in the general SWIA configuration instead of a holding and reaction coil in the SIA manifold provides several essential advantages, including higher sensitivity and lower reagent consumption. The linear dependence of the analytical signal on the epinephrine concentration was preserved over the range of 1.5-30, 3.0-30, and 1.5-25μmolL(-1) by using of SWIA, SIA and spectrophotometric analysis, respectively. The relative standard deviation for the SWIA determination of 10μmolL(-1) epinephrine was 1.8% (n=10).

Automated procedure for determination of ammonia in concrete with headspace single-drop micro-extraction by stepwise injection spectrophotometric analysis

A novel automatic stepwise injection headspace single-drop micro-extraction system is proposed as a versatile approach for automated determination of volatile compounds. The system application is demonstrated for ammonia determination in concrete samples. An ammonia gas was produced from ammonium ions and extracted on-line into 5 μL 0.1M H3PO4 to eliminate the interference effect of concrete species on the ammonia stepwise injection spectrophotometric determination. The linear range was 0.1-1 mg kg(-1) with LOD 30 µg kg(-1). The sample throughput was 4 h(-1). This system has been successfully applied for the determination of ammonia in concretes.

Determination of antipyrine in saliva using the dispersive liquid-liquid microextraction based on a stepwise injection system.

A fully automated stepwise injection spectrophotometric method for determination of antipyrine in saliva (agent for non-invasive assessment of the activity of the drug metabolizing system in hepatocytes) has been developed. The method is based on the antipyrine derivatization by nitrite-ion dispersive liquid-liquid microextraction (DLLME) of formed 4-nitrosoantipyrine with subsequent UV-vis spectrophotometric detection. Under optimal experimental conditions (0.5 М sulfuric acid, 6×10(-3) М sodium nitrite, time 6 min) the absorbance of the colored extract at the 345 nm obeys Beer׳s law in the range of 3-200 μM of antipyrine in saliva. The LOD, calculated from a blank test, based on 3σ, found to be 1 μM. The relative standard deviation for the determination of 50 μM antipyrine was 4.5% (n=10). The proposed method was successfully applied to the determination of antipyrine in saliva and the analytical results agreed fairly well with the results obtained by reference HPLC method.

Stepwise injection potentiometric determination of caffeine in saliva using single-drop microextraction combined with solvent exchange

A flow potentiometric method for determination of caffeine in saliva is suggested. This task is important for non-invasive assessment of drug metabolizing system activity in hepatocytes. In the current study, stepwise injection analysis (SWIA) was successfully combined with single-drop liquid microextraction (SDLME) and solvent exchange procedure. The method is based on the caffeine SDLME with subsequent solvent evaporation and dissolution of analyte in sulfuric acid followed by potentiometric detection using poly(vinyl chloride) membrane electrode containing potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate as electroactive component. SDLME was employed for elimination of interfering matrix effects of saliva and caffeine metabolites such as theophylline, theobromine and paraxanthine. A linear range of 10(-5)-10(-2)M was established for caffeine with detection limit at 6 × 10(-6)M. The sample throughput was 6 samples h(-1). The proposed method was successfully applied to the determination of caffeine in saliva and the analytical results agreed well with the results obtained with reference HPLC method.

Stepwise Injection Spectrophotometric Determination of Flavonoids in Medicinal Plants

A simple, rapid, and automated method for the spectrophotometric determination of flavonoids in medicinal plants was developed using a stepwise injection manifold. The determination was based on formation of colored complexes of flavonoids with Al(III) in micellar media. Analytical characteristics of the determination were significantly improved when cetylpyridinium chloride was used as a micellar catalyst. It was found that the rate of colored complex formation of rutin with Al(III) increased (k = (1.8 ± 0.1) · 104 min−1mol−2 L2) in the presence of cetylpyridinium chloride. Under the optimum conditions, a linear response was found from 0.004 to 0.2% (volume of weight %). The detection limit (3s) was determined as 0.001% rutin versus the weight of the sample. The developed method was used for the analysis of different medicinal plants for flavonoids.

Flow Analysis: A Novel Approach For Classification

ABSTRACT We suggest a novel approach for classification of flow analysis methods according to the conditions under which the mass transfer processes and chemical reactions take place in the flow mode: dispersion-convection flow methods and forced-convection flow methods. The first group includes continuous flow analysis, flow injection analysis, all injection analysis, sequential injection analysis, sequential injection chromatography, cross injection analysis, multi-commutated flow analysis, multi-syringe flow injection analysis, multi-pumping flow systems, loop flow analysis, and simultaneous injection effective mixing flow analysis. The second group includes segmented flow analysis, zone fluidics, flow batch analysis, sequential injection analysis with a mixing chamber, stepwise injection analysis, and multi-commutated stepwise injection analysis. The offered classification allows systematizing a large number of flow analysis methods. Recent developments and applications of dispersion-convection flow methods and forced-convection flow methods are presented.

Multicommutated stepwise injection determination of ascorbic acid in medicinal plants and food samples by capillary zone electrophoresis ultraviolet detection

An automation of the extraction of analytes from solid samples into the aqueous phase based on multicommutated stepwise injection analysis concept has been suggested. The feasibility of the approach has been demonstrated by determination of ascorbic acid as model analyte. The method includes automated extraction of ascorbic acid from solid sample into borate buffer solution pH 8 in mixing chamber during vigorous mixing by nitrogen stream, and subsequent detection by capillary zone electrophoresis at 254 nm. The method has a linear range of 0.1-5.0 mg g(-1) for ascorbic acid with the LOD of 0.03 mg g(-1). The sample throughput was 7 h(-1). This method was applied for determination of ascorbic acid in various medicinal plants and food samples.

Photometric cyclic-injection determination of phosphate and silicate ions simultaneously present in aqueous solutions

A unified procedure was developed for the cyclic-injection determination of phosphate and silicate ions simultaneously present in aqueous solutions. The analytical ranges were 1–90 and 0.5–25 mg/L, respectively; the procedure enabled 10 determinations per hour.

A fully automated effervescence assisted dispersive liquid-liquid microextraction based on a stepwise injection system. Determination of antipyrine in saliva samples

A first attempt to automate the effervescence assisted dispersive liquid-liquid microextraction (EA-DLLME) has been reported. The method is based on the aspiration of a sample and all required aqueous reagents into the stepwise injection analysis (SWIA) manifold, followed by simultaneous counterflow injection of the extraction solvent (dichloromethane), the mixture of the effervescence agent (0.5 mol L(-1) Na2CO3) and the proton donor solution (1 mol L(-1) CH3COOH). Formation of carbon dioxide microbubbles generated in situ leads to the dispersion of the extraction solvent in the whole aqueous sample and extraction of the analyte into organic phase. Unlike the conventional DLLME, in the case of EA-DLLME, the addition of dispersive solvent, as well as, time consuming centrifugation step for disruption of the cloudy state is avoided. The phase separation was achieved by gentle bubbling of nitrogen stream (2 mL min(-1) during 2 min). The performance of the suggested approach is demonstrated by determination of antipyrine in saliva samples. The procedure is based on the derivatization of antipyrine by nitrite-ion followed by EA-DLLME of 4-nitrosoantipyrine and subsequent UV-Vis detection using SWIA manifold. The absorbance of the yellow-colored extract at the wavelength of 345 nm obeys Beers law in the range of 1.5-100 µmol L(-1) of antipyrine in saliva. The LOD, calculated from a blank test based on 3σ, was 0.5 µmol L(-1).

An automatic chemiluminescence method based on the multi-pumping flow system coupled with the fluidized reactor and direct-injection detector: Determination of uric acid in saliva samples

A novel approach for the automatic chemiluminescence (CL) analysis of the complex samples is proposed. A multi-pumping flow system was successfully combined with fluidized reactor and direct-injection CL detector. The possibility of the approach was demonstrated on the determination of uric acid in saliva samples. Uric acid is clinically important analyte and its determination in biological fluids is related to human organism dysfunctions, such as gout. For the first time, the fast luminol - N-bromosuccinimide (NBS) reaction in an alkaline medium was used for the CL determination of uric acid in saliva samples. The CL intensity is greatly quenched in the presence of the analyte. The method includes on-line separation of uric acid from the saliva samples based on fluidized beds strategy using anion-exchange resin Dowex® 2×8 followed by the elution and CL determination using a direct-injection CL detector. The stroke pulsations of the solenoid micro-pumps provided the floating of the anion exchange resin in a sample phase and uric acid separation from the sample matrix into a sample pre-treatment block of flow system. To obtain efficient elution of analyte an eluent circulation was applied. Under the optimal conditions, the detector response for uric acid was linear in the logarithmic concentration ranges from 6·10-6 to 1·10-3molL-1. The limit of detection, calculated from a blank test based on 3σ, was 2·10-6molL-1. Fluidized bed strategy allows us to exclude saliva matrices influence on the luminol-NBS CL reaction, which results in improved selectivity. The applicability of the method developed is demonstrated with the help of real sample analysis. The obtained results are confirmed by reference HPLC-UV method.