Maximum Analytical Signal Research Articles

STUDY OF REACTION OF NICKEL (II) WITH 2.4-TYAZOLIDINDYON COMPLEX AND ITS DERIVATIVES

Spectrophotometric methods are used to study the reaction of the nickel complex with 2.4- tyazolidindico (L) and its derivatives {5- (gasilysiliden) -2,4-tyazolidindio (L1), 5- (2-chlorbenzyliden) -2,4- tyazolidindion (L2), 5-(2-hydroxybenzylide) -2,4-tiazoleader (L3), 5- (4-hydroxybenzylide)-2,4- tyazolidindion(L4),5-(2-Brom-5-methoxybenzyiliden)-2,4-tiazolyidinedion (L5). With a single extraction, the chloroform is extracted by 97.8-98.4 % of the nickel. The study of the dependence of complexation on pH showed that the optimal range of acidity, at which the optical density is maximum and constant, is at pH 2.3- 8.0. The optimal condition for the formation and extraction of the nickel complex of these compounds is (2.0- 2.5) × 10-4 M concentration L. Nickel complexes with L are stable in water and organic solvents and do not decompose for three days, and after extraction for more than a month. The maximum optical density is achieved within 5 minutes. The maximum analytical signal during the complex of nickel L is observed at 470-482 nm/ molar absorption coefficients (1.37-1.61)×104 . The comprehensive form of nickel is Ni2+while the number of protons supplanted by it from one molecule L turned out to be equal to 1. Nickel and its complexes in the organic phase are not polymerized and are in a monomeric form (γ = 1.01-1.07). The proposed method under already established optimal conditions is used to determine Ni (II) in wastewater, bottom deposits, as well as in oil and oil products.

Development of the Spectrophotometric Method for the Determination of Atorvastatin Calcium in Tablets by using Bromophenol Blue

A simple, rapid, and inexpensive spectrophotometric method for the determination of atorvastatin calcium in tablets has been developed. It requires only one reagent (BPB) and suitable for routine pharmaceutical analysis with less sophisticated equipment. The procedure for atorvastatin determination is based on its interaction with bromophenol blue (BPB) in medium of organic solvent. As a result of the reaction, the intensity of the band of the doubly ionized form of the BPB with a maximum at 595 nm increases. The maximum analytical signal is observed in a solution of methanol, chloroform, or acetonitrile, while ethanol and ethyl acetate turned out to be unsuitable. The optimal concentration of BPB is 4.12·10-4 M. To study the stability, the absorbance of the obtained solution was measured under optimal conditions for 45 min. The stoichiometric ratio of components in the resulting associate, determined by the method of continuous variations, is 1:1. The calibration graph is linear in the range from 4.1 to 33 μmol/L. The calculated LOD and LOQ values were 1.36 μmol/L and 4.13 μmol/L, respectively. The systematic error of the method is statistically insignificant in the whole range of calibration graph. The developed method was successfully applied for the determination of atorvastatin in tablets.

Quantification of tributyltin in seawater using triple isotope dilution gas chromatography–inductively coupled plasma mass spectrometry achieving high accuracy and complying with European Water Framework Directive limits

A triple isotope dilution GC-ICPMS method for the determination of tributyltin (TBT) was developed and validated to meet the European Water Framework Directive (WFD) requirements. The validation procedure involved the evaluation of trueness, precision (repeatability, intermediate precision), limit of detection (LOD) and limit of quantification (LOQ), stability, measurement uncertainty and traceability studies. The method is one of the most sensitive methods published to date with good accuracy, 103% average recovery in the range with %RSDs of 2.8-6.7%. A LOD value of 0.015 ng L−1 for the TBT cation was achieved with a sample volume of 12 mL seawater. TBT was derivatized using 20 µL sodium tetraethylborate solution (0.05% NaBEt4) to make volatile for GC-ICPMS. Measurement uncertainty was in the range of 4.8-13% which was achieved through dissolution of tributyltinchloride (TBTCl) in 1-propanol, a low-volatility solvent combined with the use of a triple isotope dilution (ID) calibration technique. Isotope dilution calibration was performed by adding 117Sn isotopically enriched TBT to the seawater samples. The stability test results showed that TBT concentration was stable for three months in seawater samples after passing through a 0.2 µm filter and stored in amber glass bottles at 4°C. The response surface methodology (RSM) approach was successfully implemented to provide optimal conditions for large volume injection (LVI) to obtain the maximum analytical signal. The key variables selected in the experimental design were evaporation time, evaporation temperature, carrier flow, and injection speed. This method was applied to seawater samples collected from the Bay of Izmit, Kocaeli, Turkey, where TBT pollution has not been measured yet.

SPECTROPHOTOMETRIC DETERMINATION OF ANTIOXIDANT SODIUM METABISULPHITE CONTENT IN PREPARED MEDICINAL FORMS OF VETERINARY MEDICINAL PRODUCTS

An analytical method for the quantitative determination of antioxidant sodium metabisulphite in veterinary drugs has been proposed by spectrophotometric method. Based on the literature data, the optimal conditions of the analytical reaction were selected experimentally. The dependence of the value of the analytical signal on the temperature of the reaction medium, concentration of p-rosaniline and duration of the reaction was investigated to establish the optimal conditions of the analytical reaction and obtain a stable analytical signal. The stability of the colored analytical form in time was also checked and the linear dependence of the value of the analytical signal on the concentration of sodium metabisulphite was investigated. The analytical reaction at room temperature is optimal. The maximum analaytical signal is achieved by carrying out the analytical reaction for 10 minutes and then practically does not change for an hour. To achieve the maximum analytical signal, it is necessary to use a 20-fold excess of dye relative to sodium metabisulphite. The analytical signal remains stable only for the first hour, then gradually begins to decrease. Metrological characteristics of the method of determination of metabisulphite in veterinary drugs are calculated, the limits of spectrophotometric determination are 0.33 – 2.50 μg/ml. The correctness of the developed method was checked on model solutions by the method of "introduced-found" method of comparison in the presence of various biologically active substances that are part of drugs together with sodium metabisulphite. The content of sodium metabisulphite in veterinary drugs of domestic and foreign production at different intervals of their storage time was established. It is shown that the content of sodium metabisulphite in drugs decreases during their storage time, until complete disappearance, which directly affects the content of the active substance, because in the absence of antioxidant oxidative processes with biologically active substances begin to take place.

Formation of ionic associates with pyrogallol complexes of antimony (III) and their application for spectrophotometric determination of antimony

The possibility of using water soluble pyrogallol red (PRWS) as a photometric reagent for the quantitative determination of antimony (III) in real objects has been studied. Formation of a colored product is observed in acidic solutions (pH 3.8 - 4.5) with a weak oxidizing agent (iodine) present for preliminary oxidation of SbHg to salts of Sb (III). The excess iodine is eliminated through introduction of sodium thiosulfate solution after obtaining the photometric form. The maximum analytical signal of the colored form is observed at 378 nm (e = 5.936 x 103). A decrease in the acidity of the solution (pH > 7) is accompanied by the formation of sodium salts of the reagent which prevents further complexation, whereas the only one maximum in the absorbance within the recommended pH range directly indicates to the formation of the the only one ionic associate (AI). The ionic associate thus formed appeared low stability in time. Unfortunately, change in the dielectric constant of the solution failed to give a positive effect and measurements of the absorbance of the colored compound were limited to 3 minutes. Determination of the composition and possible mechanism of the ionic associate formation was carried out on using the methods of molar ratios and isomolar series. After stripping of stibine into the absorption system, an ionic associate of the composition M:R = 1:1 is formed with a calculated stability constant of 4.01 x 105. The obtained results are used to develop a spectrophotometric (SP) method for antimony determination with the limits of detection and quantitative determination of the element 1.30 and 4.32 pg/ml, respectively. The developed method is valid in terms of the specificity, linearity, precision and accuracy, and, therefore, can be recommended for determination of the antimony content in any control and analytical laboratory.

SPECTROPHOTOMETRIC DETERMINATION OF HEAVY METALS IN SOILS

Simple, selective and highly sensitive extraction-photometric methods for determination of Cu, Hg, У Mn, Fe, Co, and Ni are developed using dimercaptophenols (DF) and hydrophobic amines (Am) (2,6-dimercaptophenol(DMP), 2,6-dimercapto-4-methylphenol(DMMP), 2,6-dimercapto-4-ethylphenol(DMEP), 2,6-dimercapto-4-propylphenol(DMPP), and 2,6-dimercapto-4-tertbutylphenol(DMBP)) as complexing reagents. Optimal conditions for formation and extraction of heteroligand compounds (HLC) are specified and the ratios of the components in the complexes are determined. The optimum pH value providing maximum and constant optical density ranges within 3.0-8.1, chloroform (extraction ratio: 98.4-99.6%) being used as an extractant. Optimal concentrations of DP and Am are (0.6 - 0.8) x 10-3and (0.8 - 1.2) x 10-3mol/liter, respectively. HLC are stable and do not decompose for three days in aqueous and organic solvents, and after extraction for more than a month. The maximum analytical signal for M(II) complexing with DP and Am is observed at 464 - 630 nm (εk= 1.82 - 4.40 x 104). The structure of the HLC was studied using thermogravimetry and IR-spectroscopy Comparison of the analytical capabilities of the studied reagents showed that the contrast and sensitivity of the reaction decreases in the series DMBP — DMPP — DMEP — DMMP — DME The interfering impact of ions can be eliminated through changing pH of the medium, masking substances and extraction. The limits of photometric detection and quantitative determination of M (II) in the form of HLC were calculated using calibration graphs. The developed procedures have been successfully used in determination of the trace amounts of Cu, Hg, У Mn, Fe, Co, Ni in different soils: sod-podzolic sandy and sandy-loamy sod-podzolic loamy and clayey, gray forest, black soils, chestnut and river (soil of river floodplains) soils. The determination limits range within 27 - 43 ng/cm3.

Analytical Application of Ion Associates of Molybdenum with Dithiolphenols and Aminophenols

The mixed-ligand complexes of molybdenum(VI) with dithiolphenols (DP) {2,6-dithiol-4-methylphenol (DTMP), 2,6-dithiol-4-ethylphenol (DTEP) and 2,6-dithiol-4-tert-butylphenol (DTBP)} in the presence of hydrophobic amines have been investigated by spectrophotometric method. The condition of complexing and extraction, physical-chemical and analytical characteristics of this complex have been found. As hydrophobic amine 2(N, N-dimethylaminomethyl)-4-methylrphenol (АP1) and 2(N, N-dimethylaminomethyl)-4-xlor-phenol (AP2), 2 (N, N-dimethylamino-methyl)-4-brom-phenol (AP3) were used. It has been found that mixed-ligand complex was formed in weakly acidic medium (pH 4.1 - 5.9). The maximum analytical signal when complexing Mo(V) is observed at 516 - 534 nm. The calculated molar absorption (εmax) belongs to the range (4.16 - 5.35) × 104. The Beer’s law was applicable in the range of 0.3 - 22 μg/ml. The extraction photometric methods of the molybdenum determination were processed. The influence of diverse ions on determination of molybdenum has been studied. The proposed method was applied successfully to determine amount of molybdenum in steel and in soil.

Amperometric determination of uric acid, creatinine and cholesterol on planar electrodes modified by gold particles in the flow-injection system

A method of amperometric determination of uric acid ( UA ), creatinine ( Cr ) and cholesterol ( CHO ) on planar carbon electrodes ( PE ) modified by gold particles in a flow-injection system has been developed. PE with immobilized gold particles ( Au-PE ) is catalytically active with respect to UA, Cr and CHO. A multiple current increase at modifier oxidation potentials and an oxidation potential decrease of the organic compound as compared to the unmodified electrode during their electrooxidation on Au-PE was observed. The effect of the electrochemical and hydrodynamic parameters of the flow-injection system on the analytical signal was estimated for each compound. The working conditions (applied potential and flow rate) for the maximum analytical signal registration at the modified electrode for the studied biologically active compounds ( BAC ) were selected. With the joint presence of the considered BAC, the dependence graphs of the current on the analyte concentration in logarithmic units were linear in the range from 5x10 -9 to 5x10 -3 mol/l for UA, from 5x10 -7 to 5x 0 -3 mol/l for Cr and from 5x10 -8 to 5x10 -3 mol/l for CHO. Using the two-detector flow system and double planar electrodes ( DPE ) modified with gold particles ( Au-DPE ) allowed the simultaneous determination of the considered BAC. The proposed method was used to determine UA, Cr and CHO in the urine. Keywords: electrooxidation of uric acid, creatinine and cholesterol, modified planar electrode, gold particles, amperometric determination, flow-injection analysis DOI: http://dx.doi.org/10.15826/analitika.2019.23.3.005 (Russian) L. G. Shaidarova, I.A. Chelnokova, I.A. Abzalova, A.V. Gedmina, G.K. Budnikov Kazan (Volga region) Federal University (KFU), ul. Kremlyovskaya, 18, Kazan, 420008, Russia Federation

Ti/TiO2 indicator electrodes formed by plasma electrolytic oxidation for potentiometric analysis

ABSTRACTTi/TiO2 indicator electrodes were prepared by plasma electrolytic oxidation (PEO) method in the tetraborate electrolyte and were used for potentiometric indication of chemical reactions of different types and for analysis of surface and industrial wastewaters on the example of potentiometric determination of alkalinity and chloride. The electrodes formed at current densities of 0.05, 0.1, 0.15 and 0.2 A/cm2 are different in composition, surface morphology and electroanalytical properties. The electrodes formed at a current density of 0.05 A/cm2 exhibit the highest pH-sensitivity and generate the highest analytical signal at the equivalence point in the acid–base and precipitation titrations. The maximum analytical signal at the equivalence point, exceeding in magnitude the analytical signal, obtained by classical Pt electrode in oxidation–reduction and complexometric titrations generates PEO layers formed at a current density of 0.05 A/cm2 and a platinum-modified nanoparticles. The results of the potentiometric titration of the surface and technogenic waters using as indicator Ti/TiO2 electrodes are comparable with the conventionally used glass electrode (to determine alkalinity) and Ag electrode (to the determine chloride) and the results of visual titration. The advantage of the obtained metal oxide systems is the ability to determine two hydrochemical parameters due to their multifunctionality and opportunity to work with a single electrode. In addition, these sensors offer some analytical characteristics such as sensitivity, good reproducibility, high mechanical stability and a simple preparation procedure.

Ultratrace determination of arsenic in water samples by electrothermal atomic absorption spectrometry after pre-concentration with Mg–Al–Fe ternary layered double hydroxide nano-sorbent

A selective solid phase extraction method, based on nano-structured Mg–Al–Fe(NO3−) ternary layered double hydroxide as a sorbent, is developed for the pre-concentration of ultra-trace levels of arsenic (As) prior to determination by electrothermal atomic absorption spectrometry. It is found that both As(III) and As(V) could be quantitatively retained on the sorbent within a wide pH range of 4–12. Accordingly, the presented method is applied to determination of total inorganic As in aqueous solutions. Maximum analytical signal of As is achieved when the pyrolysis and atomization temperatures are close to 900°C and 2300°C, respectively. Several variables affecting the extraction efficiency including pH, sample flow rate, amount of nano-sorbent, elution conditions and sample volume are optimized. Under the optimized conditions, the limit of detection (3Sb/m) and the relative standard deviation are 4.6pgmL−1 and 3.9%, respectively. The calibration graph is linear in the range of 15.0–650pgmL−1 with a correlation coefficient of 0.9979, sorption capacity and pre-concentration factor are 8.68mgg−1 and 300, respectively. The developed method is validated by the analysis of a standard reference material (SRM 1643e) and is successfully applied to the determination of ultra-trace amounts of As in different water samples.

Determination of Rosuvastatin in Urine by Spectrofluorimetry After Liquid–Liquid Extraction and Derivatization in Acidic Medium

Statins are a class of drugs mostly used for treating hyperlipidemia, and rosuvastatin is the newest drug in the market belonging to this class. In this present work, a method was developed based on the molecular fluorescence technique, with the objective to quantify rosuvastatin in urine samples. For this purpose, the study of several parameters was made to achieve the maximum analytical signal (under reaction with sulfuric acid during 40 min). Also, a previous step to avoid matrix interference was carried out (liquid-liquid extraction). The limit of detection (LOD) and the limit of quantification (LOQ) were 0.38 and 1.28 mg L(-1), respectively. Linear relationship between rosuvastatin concentration and it's fluorescence intensity was found until 5.0 mg L(-1). The proposed method was tested in several samples spiked with rosuvastatin and recovery was found in the range of 90 ± 10%.

Mass-sensitive immunosensors for determining chloroacetanilide herbicides

Highly sensitive piezoelectric quartz immunosensors are proposed for the rapid selective determination of chloroacetanilide herbicides. Receptor coatings are hapten-protein conjugates immobilized on the presilanized surface of sensor silver or gold electrodes. Complementary pairs of immunoreagents ensuring the maximum analytical signal are selected on the basis of affinity constants found by the Sketchard method. The detection limits for acetochlor and alachlor are 0.02 ng/mL and that for butachlor is 0.002 ng/mL. Sensors were used to determine residual amounts of herbicides in foodstuffs and environmental objects.

Static and Hydrodynamic Monitoring of Citalopram Based on its Electro-oxidation Behavior at a Glassy-Carbon Surface

The electrooxidative behavior of citalopram (CTL) in aqueous media was studied by cyclic voltammetry (CV) and square-wave voltammetry (SWV) at a glassy-carbon electrode. The electrochemical behaviour of CTL involves two electrons and two protons in the irreversible and diffusion controlled oxidation of the tertiary amine group. The maximum analytical signal was obtained in a phosphate buffer (pH = 8.2). For analytical purposes, an SWV method and a flow-injection analysis (FIA) system with amperometric detection were developed. The optimised SWV method showed a linear range between 1.10 × 10−5–1.20 × 10−4 mol L−1, with a limit of detection (LOD) of 9.5 × 10−6 mol L−1. Using the FIA method, a linear range between 2.00 × 10−6–9.00 × 10−5 mol L−1 and an LOD of 1.9 × 10−6 mol L−1 were obtained. The validation of both methods revealed good performance characteristics confirming applicability for the quantification of CTL in several pharmaceutical products.

Catalytic Detection of Thiourea and Its Derivatives in HPLC Postcolumn Derivatization

A sensitive method for chromatographic determination of thiourea and its N‐derivatives has been developed. Thiourea, methyl‐, ethyl‐, dimethyl‐, diethyl‐, phenyl‐, allyl‐, acethylthiourea were eluted from high‐performance liquid chromatography C18‐bonded silica column by mobile phase containing 0.02 mol L−1 phosphate buffer solution (pH 5.0) and acetonitrile 20% (v/v). These compounds in the effluent were monitored by using photometric measurement of decreasing absorbance in postcolumn bromopyrogallol redhydrogen peroxide reaction catalyzed by each of thioureas. The optimum conditions for the catalytic reaction in static and flow modes were chosen. The conditions for the catalytic postcolumn reaction in the presence of thioureas were established by varying pH value, concentrations of bromopyrogallol red and hydrogen peroxide in the postcolumn‐reaction mixture and the reaction coil length. Careful choice of the reactor length and optimization of parameters for flow conditions was demonstrated to be very important for maximum analytical signal. It was shown, that the use of chromatographic separation with the catalytic detection allows increasing selectivity and sensitivity of determination of thiourea and its derivatives.

Determination of Food Dyes by Thin-Layer Chromatography with Cyclodextrin Mobile Phases

metrically by the decrease in the absorbance ofthe solution. In the flow-injection mode, we studiedthe effect of the length of the capillary on peakbroadening and found the optimal concentrations ofthe reagents that provide the maximum analyticalsignal. The interfering effect of some anions andcations was examined. Optimal conditions ofchromatographic separation were selected. The detec-tion limit of nitrite in water was one-fifth of the max-imum permissible concentration ( 1.5 × 10

High-performance liquid chromatography of selected organic peroxides with oxidative amperometric detection.

Reversed-phase high-performance liquid chromatography with oxidative amperometric detection was optimized for the determination of several organic peroxides in drinking water under ideal conditions. The determinations were performed under isocratic conditions using acetonitrile and methanol as the organic modifiers with 0.05 M potassium phosphate buffer solution. The oxidative amperometric response of the organic peroxides was dependent on the concentration of organic modifier and the electrode potential. The optimum electrode potential (EOxAPP), for the simultaneous determination of the organic peroxides was approximately +1.150 +/- 0.05 V versus the Ag/AgCl reference electrode. The maximum analytical signal for butan-2-one peroxide and tert-butyl hydroperoxide, when using acetonitrile, was obtained with 20% v/v organic modifier. For cumene hydroperoxide, the maximum analytical signal was achieved with approximately 35% v/v acetonitrile. The retention time of cumene hydroperoxide, on an octyldecylsilane column (250 x 4 mm id), decreased sharply from > 100 to < 10 min when the organic modifier concentration was varied from 5 to 50% v/v. The retention time of butan-2-one and tert-butyl hydroperoxide, under the same conditions, varied by < 10 min. The calibration curves for the aliphatic peroxides and aromatic peroxide were linear from 2 to 200 ng and from 0.2 to 200 ng injected, respectively.

Direct determination of metals in oils by inductively coupled plasma atomic emission spectrometry using high temperature nebulization

A method is described wherein a Babington V-groove nebulizer and heated spray chamber is utilized to nebulize edible oil and lubricating oil directly into an inductively coupled plasma (ICP) to determine the metal concentrations in the oils by ICP atomic emission spectrometry. Factors influencing the attainment of a maximum analytical signal are discussed. Both the methods of standard additions and normal calibration were used and calibration curves were linear in the range 0–10 µg g–1 for Fe, Cu, Cr, Ti, Al, Ni, Mg, Ag and Na. The following detection limits are reported: Fe, 0.032; Cu, 0.069; Cr, 0.051; Ti, 0.045; Al, 0.328; Ni, 0.131; Mg, 0.003; and Ag, 0.077 µg g–1.

Determination of metals in waxes by inductively coupled plasma atomic emission spectrometry using high-temperature nebulization of the molten wax

A method is described wherein a Babington V-groove nebulizer and a heated spray chamber are utilized to nebulize molten waxes directly into an inductively coupled plasma (ICP) to determine the concentrations of metal in the waxes by ICP atomic emission spectrometry. Factors influencing the attainment of a maximum analytical signal are discussed. The method of standard additions is used for calibration and calibration graphs are linear for additions of the analytes in the range 0–10 µg g–1. The following detection limits are reported: Fe, 0.47; Cu, 0.56; Cd, 0.31; and V, 0.87 µg g–1. Problems are still experienced with nebulizer instability, leading to poor repeatability and possible courses of action are suggested.

Improved Probe Coupling To a Microwave-Induced Plasma

Correlation of an analytical signal to a particular analyte is critically tied to impedance matching in the microwaveinducedplasma (MIP). Thefollowing research uses improved matching techniques to extend the optimum power and flow rate ranges of the MIP and increase the maximum analytical signal by 250%.

The determination of Cu, Ni, and Co using 2-(2-pyridylazo)-1-naphtol-4-sulfonic acid by multicomponent flow injection analysis (MC-FIA)

2-(2-Pyridylazo)-1-naphthol-4-sulfonic acid (1PAN4S) was used to develop a method for the simultaneous spectrophotometric determination of Cu(II), Ni(II), and Co(III) by reverse flow injection analysis (FIA) using a multichannel UV-VIS detector with a diode array. The method can be used to determine the individual ions in the range 5-50 μmol dm-3 Ni(II) or Cu(II) and 5-60 μmol dm-3 Co(III) in binary and ternary mixtures at ratios of 1 : 1 to 1 : 10 with a maximal relative deviation of units of per cent for the major components and tens of per cent for the minor components. The precision and accuracy of the determination are the same or slightly worse than for stationary measurements with half to one fifth the sensitivity. Measurement of the absorption spectra for the maximum analytical signal in digital form for c(1PAN4S) = 0·12 mmol dm-3, c(NaIO4) = 1·2 mmol dm-3 in 0·2M acetate buffer medium at pH 5·00 permits rapid determination (15 s per sample) of all the components using a simple program for multicomponent analysis in "overdetermined" systems.