Maximum Suppressor Research Articles

Effect of Maxima Suppressor and Supporting Electrolyte on Polarographic Wave of Dimethyl Sulfoxide and its Determination

The oxidation of the biologically very important dimethyl sulfoxide system has been the subject of investigations. In present study Dimethyl sulfoxide (DMSO) can be oxidized to dimethyl sulfone by anodic electrolysis at a rotating platinum electrode. The polarographic method has been used to study qualitatively the effect of maxima suppressor gelatin, fuchsin, methyl red, thymol blue and supporting electrolyte HCl, CH3COOH on oxidation wave of DMSO. Polarographic oxidation of DMSO in 0.1 M HCl, 0.1 M CH3COOH solution using optimum concentration of fuchsin, methyl red, thymol blue as surface active substances is followed to determine the DMSO present in synthetic sample by calibration method. Wave analysis indicate the irreversible nature of the oxidation process which involves oxidation of dimethyl sulfoxide to dimethyl sulfone thereby increasing the oxidation state of sulphur from +2 to +4 state.

Polarographic Study of Meta-Hydroxyacetanilide and its Determination

Present paper deals with polarographic study of effect of maxima suppressors and supporting electrolytes on anodic waves of meta-hydroxyacetanilide and polarographic determination of meta-hydroxyacetanilide under optimum concentration of maxima suppressors and supporting electrolytes. The polarographic method has been developed to study qualitatively the effect of maxima suppressor (fuchsin) and supporting electrolyte (nitric acid) on oxidation wave of meta-hydroxyacetanilide. Polarograms of system were recorded between 500 to 1300 mV by using Rotating Platinum micro Electrode as anode and Saturated Calomel Electrode as cathode on D.C. Recording Polarograph using Omniscribe recorder. It shows a similar behavior to that observed for paracetamol. It produces anodic wave at rotating platinum electrode. The oxidation yields the 3-N-acetylaminosemiquinone and represents a reversible reaction. Polarographically a value of 900 mV is found for decomposition potential of meta-hydroxyacetanilide. Wave analysis point to 1-electron step for each wave. Waves of meta-hydroxyacetanilide are only proportional to concentration at low concentrations.

Development of Calibration and Standard Addition Polarographic Determination of Ascorbic Acid

Aims: Effect of pH on polarographic waves of ascorbic acid were studied by recording polarograms of ascorbic acid solution, between 0 to 400 mV at different pH (0.065 to 9.6) using 0.008% solution of gelatin and 0.05 M potassium hydrogen phthalate buffer (containing 0.25% oxalic acid) as maxima suppressor and supporting electrolyte respectively. Methods: Ascorbic acid is strong reducing agent and produces an anodic wave which shifts with pH. There is no significant change in height of wave with change in pH from 2.25 to 4.85. For determination of ascorbic acid pH 4.0 is chosen. Ascorbic acid present in synthetic sample is determined by calibration, external standard addition and internal standard addition methods. The results obtained are in good agreement with the quoted values. Result: The number of electrons taking part in the reversible reaction is found to be 2. The half-wave potential is found to be independent of the ascorbic acid concentration. peak current is proportional to the concentration of ascorbic acid in the range 10-6-10-3M and the reproducibility is better than ±1 per cent. Chloride and sulphur compounds, such as sulphides and thiols, do not interfere, and sulphite can be determined at the same time as the ascorbic acid. Some substituted phenols interfere but can often be detected by reversing the direction of polarisation. Reductones interfere but tin(II) and manganese(II) do not. A method has also been developed to determine ascorbic acid in the presence of an excess of iron. Different extraction media are discussed in terms of their influence on the redox potential of iron. Comparative titrimetric determinations of ascorbic acid in some fruits, vegetables and beverages gave higher results than the voltammetric method (6). A polarographic study of the oxidation mechanism of L-ascorbic acid and of the reduction mechanism of dehydro-L-ascorbic acid was carried out in an acid medium. For L-ascorbic acid, the oxidation process involves a two electron transfer. The polarographic curve shows that the limiting current is governed by diffusion. On the rising portion of the wave, the two electron oxidation process consists of two consecutive one electron transfers, the second being the rate determining step. The reaction orders, together

Electrode kinetics of the O 2/O 2− redox couple at Hg electrode in the presence of PVC in aprotic media

The kinetic and thermodynamic parameters of the O 2/O 2 − redox couple at a mercury electrode in various aprotic solvents have been evaluated by normal pulse polarography and cyclic voltammetry in the presence of poly(vinyl chloride) (PVC) as a maximum suppressor. The polarographic maxima were observed on the rising portion of polarogram for O 2 reduction, but they are completely suppressed by the addition of a small amount of PVC. The adsorption behavior of PVC on a hanging mercury drop electrode is examined based on the measurement of the differential capacitance of the electrical double layer. The relevant kinetic and thermodynamic parameters, i.e., the standard rate constant, k°, the cathodic transfer coefficient, α c, and the formal potential, E°′ of the O 2/O 2 − redox couple were estimated together with the diffusion coefficients of O 2, D O 2 . An excellent linear relationship between the formal potential and solvent's acceptor number was found.

Study of complexes of cadmium(II) and lead(II) with mixed ligand (thioglycolate-oxalate/tartarate) systems in aqueous-methanol media at the droping mercury electrode

Complexes of Cd I I and Pb I I have been studied in mixed ligand (thioglycolate-oxalate/tartarate) systems in aqueous-methanol solvent mixture. Ionic strength was maintained with KNO 3 (μ = 0.1 M) and Triton X-100 was used as maxima suppressor. It was shown that only one mixed ligand entity MA i X j was formed, where i = 2 and j = 1 with both the metals. A and X are thioglycolate and oxalate or tartarate respectively. The composition and stability constants of the mixed ligand complexes formed have been evaluated.

Application of voltammetric methods for the analysis of lead and other trace metals in lepidolite rock sample

Convenient, simple, rapid and accurate voltammetric methods viz. DCP, DPP and DPASV have been used for the simultaneous determination of lead and other trace metals in lepidolite rock sample. The analysis has been performed using 0.1 M ammonium tartrate/0.1 M ammonium chloride/0.1 M lithium chloride as supporting electrolytes with 0.01% gelatin as maximum suppressor, respectively. The results show the presence of Pb I I (14.97), Zn I I (4.37), Fe I I I (4.73), Cr V I (3.36) and Co I I I (7.42) mg g - 1 of the sample. The quantitative analysis of metal ions was carried out by external spiking method. Statistical treatment of the observed voltammetric data revealed high accuracy and good precision of determination. The observed voltammetric results are comparable with those obtained using atomic absorption spectroscopic (AAS) method.

Application of voltammetric methods for the analysis of gold and other transition metals in quartzite rock.

Simple, rapid and accurate voltammetric methods viz. DCP, DPP and DPASV have been presented for the trace determination of gold and other transition metals in quartzite rock sample. The analysis has been performed using 0.1 M(NH4)2 tartrate, 0.1 M NaClO4 and 1 M NaOH as supporting electrolyte with 0.001% gelatin as maximum suppressor. The results show the presence of CuII(10.70), CoII(4.72), FeIII(66.96), AuIII(0.066), ZnII(1.68) and CdII(0.62) mg x g(-1) metal ions from the sample. Gold produced a well defined wave/peak with E1,2/Ep = -0.61 V/-0.64 V vs SCE, in 1 M NaOH supporting electrolyte. The quantitative analysis of metal inos was carried out by the method of standard addition. Statistical treatment of the observed voltammetric data reveals high accuracy and good precision of determination. The observed voltammetric results are comparable with those obtained using AAS method.

Current oscillation behavior of the O2/O2− redox couple at a HMDE in non-aqueous aprotic media

Abstract Electrochemical oscillatory phenomena have been observed in the redox reaction of the O 2 /O 2 − (superoxide ion) couple on a hanging mercury drop electrode (HMDE) in a limited aprotic medium. The current oscillation occurs during the reoxidation process of the electrogenerated O 2 − . It has been found that the observed oscillation is really irregular, complicated and affected by the addition of poly(vinyl chloride) as a maximum suppressor as well as many other experimental factors such as solvent, electrode substrate, concentration of O 2 − in the electrode vicinity and potential scan rate in cyclic voltammetry. The oscillation phenomena have been explained similarly to the maxima in classical polarography (i.e. by streaming phenomena) and in addition, based on the formation–destruction of a passive film on the electrode surface which results in the dissolution of the mercury electrode. The results obtained demonstrate that the electrogeneration and adsorption of O 2 − on HMDE are indispensable for the present oscillation.

Electrochemical trace analysis of gold in ore

Differential-pulse polarography (DPP) has been successfully used for the simultaneous determination of some trace metal ions in ore. Ammonium tartrate (0.1 mol l–1) was used as supporting electrolyte and 0.01% gelatin as maximum suppressor. The sample produced eight well defined polarographic peaks. The first signal with Ep=–0.08 V versus SCE in the polarogram may be due to AgI or AuIII. To confirm the presence of AgI and/or AuIII in the sample, EDTA was used as a complexing agent, which resulted in this single peak splitting into two, with Ep equal to –0.04 V and –0.2 V versus SCE, confirming the presence of both AgI and AuIII in the sample. The observed voltammetric results were compared with those obtained by using AAS.

Elicitors and Suppressors of Hydroxyproline-Rich Glycoprotein Accumulation are Solubilized from Plant Cell Walls by Endopolygalacturonase

Treatment of bean cell walls with a pure endopolygalacturonase of the bean pathogen Colletotrichum lindemuthianum race beta released oligogalacturonides and pectic fragments which were separated according to their charge and size. Among galacturonic-acid-containing components, elicitors and suppressors of the plant cell wall hydroxyproline-rich glycoprotein (HRGP) were recovered. Two active small oligogalacturonides with degrees of polymerization of 2 and 3 were characterized by high-performance anion-exchange-chromatography pulsed amperometric detection and fast-atom-bombardment mass spectrometry; they elicited 40-70% hydroxyproline increase within 48 hours at 450 nmol/bean cutting. In contrast, pectic fragments of higher molecular mass, predominantly composed of galacturonic acid and containing sugars typical of the rhamnogalacturonan II domain of pectic polysaccharides, had the ability to substantially suppress hydroxyproline deposition. Maximum suppressor activity, 30-40% below the activity of the control, occurred in 48 hours. In view of the low one-cycle turnover of these proteins in the cell wall and of their structural role, these changes might significantly affect cell wall properties. Elicitation and/or suppression of hydroxyproline were correlated to modifications of HRGP-extensin gene expression. Northern-blot analysis of RNA showed that changes in the transcript intensity became clearly visible within the first 12 hours after the start of either treatment. The results show that pectic components of the plant extracellular matrix have the potential to regulate wall matrix biogenesis. Implications of this finding in plant defense and development are discussed.

Elicitors and Suppressors of Hydroxyproline-Rich Glycoprotein Accumulation are Solubilized from Plant Cell Walls by Endopolygalacturonase

Treatment of bean cell walls with a pure endopolygalacturonase of the bean pathogen Colletotrichum lindemuthianum race beta released oligogalacturonides and pectic fragments which were separated according to their charge and size. Among galacturonic-acid-containing components, elicitors and suppressors of the plant cell wall hydroxyproline-rich glycoprotein (HRGP) were recovered. Two active small oligogalacturonides with degrees of polymerization of 2 and 3 were characterized by high-performance anion-exchange-chromatography pulsed amperometric detection and fast-atom-bombardment mass spectrometry; they elicited 40-70% hydroxyproline increase within 48 hours at 450 nmol/bean cutting. In contrast, pectic fragments of higher molecular mass, predominantly composed of galacturonic acid and containing sugars typical of the rhamnogalacturonan II domain of pectic polysaccharides, had the ability to substantially suppress hydroxyproline deposition. Maximum suppressor activity, 30-40% below the activity of the control, occurred in 48 hours. In view of the low one-cycle turnover of these proteins in the cell wall and of their structural role, these changes might significantly affect cell wall properties. Elicitation and/or suppression of hydroxyproline were correlated to modifications of HRGP-extensin gene expression. Northern-blot analysis of RNA showed that changes in the transcript intensity became clearly visible within the first 12 hours after the start of either treatment. The results show that pectic components of the plant extracellular matrix have the potential to regulate wall matrix biogenesis. Implications of this finding in plant defense and development are discussed.

Phenotype and suppressor activity of T-lymphocyte clones extracted from lesions of oral lichen planus.

Lymphocytes were extracted from six biopsy specimens of oral lichen planus. T-lymphocyte lines were expanded in culture with phytohaemagglutinin and interleukin 2, and cloned by limiting dilution. Fifteen T-cell clones were isolated with a probability of clonality of 96.3%. The majority of clones (n = 13) expressed the alpha beta T-cell receptor, and of these, 11 were CD8+ and two were CD4+. Two clones were CD4- and CD8-, and expressed the gamma delta T-cell receptor. The ability of these clones (effectors) to suppress concanavalin-A-stimulated proliferation of autologous lesional T-cell lines (responders) was assessed. Maximum suppressor activity ranged from 17 to 100%. The majority of clones (n = 12), including a CD3+ CD4+ CD8-alpha beta+ clone, displayed suppressor activity which was proportional to the effector to responder ratio. A CD3+CD4+CD8-alpha beta+ clone and a CD3+CD4-CD8-gamma delta+ clone displayed substantial helper activity at higher effector to responder ratios. These results demonstrate differential helper and suppressor activity of T-lymphocyte clones extracted from oral lichen planus lesions. The balance between help and suppression may be a fundamental determinant of immunological activity within the lymphocytic infiltrate of oral lichen planus, and hence may dictate the clinical behaviour of the disease.

Electrochemical reduction at mercury electrodes and differential-pulse polarographic determination of pentamidine isethionate

Reduction processes are observed for pentamidine isethionate at a dropping mercury electrode above pH 7: the reduction potential is independent of pH below about pH 10. Below pH 10, adsorption of the reduced species is observed, whereas above pH 10 there is a large contribution owing to adsorption of pentamidine isethionate. For the polarographic determination of pentamidine isethionate, a pH of 8–9 is recommended with the addition of Triton X-100 as a maximum suppressor. Pentamidine isethionate can be determined by differential-pulse polarography down to about 5 × 10–6 mol l–1.

Polarographic behaviour and determination of selenite and tellurite in simple solutions or in a binary mixture

The polarographic behaviour of simple solutions of selenite and tellurite in 1M ammonium salts of formate, acetate, tartrate, oxalate, and benzoate solutions in absence and in presence of Triton X-100 as a maximum suppressor and a temperature of 25°C has been investigated. Schemes for the mechanism of reductions occurring at the DME have been deduced. A method for analytical determination of selenite and tellurite in simple solutions as well as in a binary mixture in the presence of 4–14·10−3% Triton X-100 is reported.

The use of melamine as an electrocapillary-active substance and polarographic maximum suppressor

When melamine is added to a neutral de-aerated solution of potassium nitrate, it distorts the positive side as well as the negative side of the electrocapillary curves of mercury. It also causes a major shift in the electrocapillary maximum (ECM) towards negative potentials. Melamine is adsorbed in its planar orientation on the positively charged mercury surface. On the negatively charged mercury surface, melamine possibly acts as a depolarizer and hence catalyzes the hydrogen evolution reaction. Melamine also acts as a suppressor to positive (lead, copper) as well as negative (aluminum, nickel) maxima as it is adsorbed at the interface between the dropping mercury electrode (DME) and the electrolyte.

Determination of polyacrylamides by maximum suppression

The use of polarographic maximum suppression methods for determining polyacrylamides and polyacrylic acid-based polymers was investigated. Using the oxygen, Co2+, and Hg2+ maxima these polymers were determined at the low ppm level. The effectiveness of polymers as maximum suppressors was dependent on the charge of the polymer and that of the electrode at the potential at which the polarographic wave occurred. The maximum suppression of various binary mixtures of polyacrylamides indicated that in some mixtures suppression was additive while in other mixtures, particularly those containing both anionic and cationic polymers, the suppression was greatly reduced. Aqueous extracts of chosen coals contained various interfering substances which could be removed most efficiently using Sephadex G-75, although this resin was only compatible with anionic and neutral polymers.

A Polarographic Study of Some Aminoanthraquinones

Abstract Experimental data are given on the influence of the number and the position of the amino groups on the electrochemical reduction potentials of aminoanthraquinones. The polarographic conditions used for the reduction of some aminoanthraquinones on the dropping mercury electrode are described. The polarograms were obtained in partial aqueous media (the final ratio between dimethylformamide and water is of 20:5) using dimethylformamide as solvent, ammonum acetate as main electrolyte, and Triton X-100 as maxima suppressor. By this method concentrations as low as 0.1 – 0.5 mg/ml could be determined for each aminoanthraquinonic component. Some comparative data are also presented, from which a parallel variation of two features might be drawn: the redox potential and the wavelength of the visible absorption maximum of the investigated aminoanthraquinones. This variation was interpreted as being the result of a similar dependance of these two quantities on the degree of polarization of the carbonyl groups.

Mercurimetric and Polarographic Determination of Captopril

ABSTRACT Two different methods have been applied for the determination of captopril, namely,(i) a direct mercurimetric method using standard mercuric nitrate solution and diphenyl carbazone as an end-point indicator (ii) a differential pulse (DP50) polarographic method based on the measurement of the polarographic current at the peak potential of - 0.25V vs. Ag/AgCl (Kcl Sat.) reference electrode using acetate buffer of pH U.6 as a supporting electrolyte containing 0.01% w/v gelatin as a maximum suppressor. The accuracy obtained for the mercurimetric method is 99.8±0.7% and 100.2±1.3% for the authentic captopril and its tablets respectively. For the polarographic method, the linearity between current and concentration holds for the concentration range 2 to 45 ppm under the experimental conditions employed with an accuracy of 99. 4±0.8% and 99.9±1.9% for the authentic captopril and its tablets respectively.

Polarographic determination of gallium(III) with 3-hydroxypyridine-2-thiol

The polarographic behavior of europium(III) has been studied in 3-hydroxypyridine-2-thiol (HPT) as the supporting electrolyte. The polarographic wave in this electrolyte is diffusion controlled, quasi-reversible, and well defined, and there is no need of a maximum suppressor. The interference of various ions has been studied in detail, and this method has been utilized for the quantitative determination of europium in various synthetic samples

Spectrophotometric and Polarographic Studies of the Uranium in Acetate Medium in the Presence of Resorcinol

AbstractUranyl ion reduction was studied in acetate buffer‐resorcinol medium. Two waves were obtained for all pH. Resorcinol can be used as a maximum suppressor. Complexation of uranium with resorcinol was accompanied by a decrease in diffusion current and shift of half‐wave potential to more negative values. Mixed complexes of acetate and resorcinol were formed with uranium. Resorcinol stabilizes the pentavalent uranium by complexaion.