Promoting effect of iodide on the hexacyanomanganate(IV)-arsenic(III) redox reaction, for kinetic determination of iodide

The rate of the reaction between hexacyanomanganate(IV) and arsenic(III) in an acid medium is strongly accelerated by iodide. The reaction kinetics indicates that the iodide activity decreases throughout the reaction, probably because manganese(IV) oxidizes iodide to iodate (an inactive form). This behaviour is defined as promotion, rather than catalysis, and this rate-modifying effect has been used to determine iodide by a kinetic method. A linear calibration plot was obtained by a two-point fixed-time procedure. A detection limit of 0.2 ng/ml, a quantification limit of 0.6 ng/ml and relative standard deviations of 5.5 and 13% for the 6.7 and 0.6 ng/ml levels respectively have been found. Positive kinetic interferences from osmium(VIII) and iodate have been observed, and copper(II), silver(I) and mercury(II) inhibit the iodide activity by precipitaton. The method has been applied to determination of iodide in sodium arsenite (reagent grade) and table salt. The method has been validated by recovery experiments.     

Liquid chromatographic determination of less polar ginsenosides in processed ginseng

A novel method for the determination of iodide by size exclusion chromatography was established. The method was simple and highly sensitive with good precision. Iodide was converted to iodine, then sequestered with starch, and separated from the matrix using a Shim-pack DIOL-150 (250 x 7.9 mm) size exclusion column with methanol-0.01 mol l(-1) aqueous phosphoric acid (10:90, v/v) as mobile phase at 1.2 ml min(-1) and UV detection at 224 nm. The calibration graph was linear from 1.0 ng ml(-1) to 100.0 ng ml(-1) for iodide with a correlation coefficient of 0.9992 (n=6). The detection limit was 0.2 ng ml(-1). The method was successfully applied to the determination of iodide in seawater and urine. The recovery was from 92% to 103% and the relative standard deviation was in the range of 1.5% to 3.7%.     

Flow injection determination of chromium(III) by pyrogallol chemiluminescence

A flow injection method is proposed for the determination of nanogram amounts of chromium(III) using a pyrogallol chemiluminescence system. It is based on its catalytic effect on the oxidation of pyrogallol with periodate at a neutral medium. The addition of 3-(N-morpholino)propanesulphonic acid to the reaction system increased the chemiluminescence signal for chromium(III). The present method allows the determination of 5-100ng/ml of chromium(III). The relative standard deviation of 2.2% (n = 10) was obtained at 20 ng/ml of chromium(III) and the detection limit (signal-to-noise ratio = 2) was 1 ng/ml with the sampling frequency of 25/hr.     

超痕量铑的催化动力学分析研究

在氯化钠存在的磷酸介质中，铑（Ⅲ）对高碘酸钾氧化罗丹明Ｂ裉色的反应具有强烈的催化作用，该催化反应对罗丹明Ｂ和铑（Ⅲ）均为一级反应，反应的表观活化能为６８．３８ｋＪ／ｍｏｌ。以该反应为指示反应建立的动力学光度法可测定０．０３－２．５ｎｇ／２５ｍｌ的铑，考察了３０多种离子的干扰情况，本法选择性好。     

A simple thermometric technique for reaction-rate determination of inorganic species, based on the iodide-catalysed cerium(IV)-arsenic(III) reaction

A very simple reaction-rate thermometric technique is used for determination of iodide (5-20 ng ml ), based on its catalytic action on the cerium(IV)-arsenic(III) reaction, and for determination of mercury(II) (1.5-10 ng ml ) and silver(I) (2-10 ng ml ), based on their inhibitory effect on this reaction. The reaction is followed by measuring the rate of temperature increase. The method suffers from very few interferences and is applied to determination of iodide in biological and inorganic samples, and Hg(II) and Ag(I) in pharmaceutical products.     

钴(Ⅱ)催化偶氮胭脂红B的褪色反应特性及应用

基于氢氧内介质中痕量钴对过氧化氢氧化偶氮胭脂红Ｂ的褪色反应的强烈催化作用,建立了催化光度法测定痕量钴的新方法。方法灵敏度为５．２４×１０＾－１２ｇ／ｍＬ,测定范围为０￣３５ｎｇ／１０ｍＬ,对质量浓度为３μｇ／Ｌ的Ｃｏ（Ⅱ）重复测定１１次的相对标准偏差为２．１６％。方法应用于维生素Ｂ１２和矿泉水中痕量钴的测定,结果满意。     

Use of the triiodide-hexadecylpyridinium chloride micellar system for the kinetic determination of tungsten (VI)

The associate formed by triiodide ion and hexadecylpyridinium chloride (cetylpyridinium chloride (CPC)) micelles was used to enhance the kinetic spectrophotometric determination of W(VI) by its catalytic action on the oxidation of iodide with hydrogen peroxide in an acidic medium. The reaction was monitored spectrophotometrically by measuring the increase in absorbance of I(3)(-)-CPC associate at 525 nm by the fixed-time method of 3 min from initiation of the reaction. The micellar medium allowed the determination of W(VI) at concentrations between 4 and 90 ng ml(-1) with a detection limit of 2.4 ng ml(-1) (i.e. about 12-13 times lower than those of methods implemented in aqueous media). The relative standard deviation for nine replicate analyses was 0.03% for 76.6 ng ml(-1) of W(VI). The proposed method was applied to the determination of W(VI) in aqueous extracts of soil sample with no prior separation.     

Flow-injection photometric determination of sub-nanogram amounts of cobalt by its catalysis of the oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone with N,N-dimethylaniline in a micellar medium

A catalytic flow-injection photometric method was developed for the determination of levels of cobalt as low as 10(-10) mol 1(-1). The method is based on the catalytic action of cobalt(II) on the oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone with N,N-dimethylaniline to form a colored dye (lambda(max) = 590 nm) in the presence of hydrogen peroxide. The extremely activating effect was obtained in the presence of 1,2-dihydroxybenzene-3,5-disulfonate (Tiron) and sodium hydrogencarbonate as activators. Furthermore, the sensitivity of the method was enhanced by adding sodium dodecylsulfate as a surfactant. Linear calibration graphs were obtained over the range 0.04-0.2 ng ml(-1) and 0.1-0.5 ng ml(-1) cobalt(II). respectively, at a sampling rate of 30 per hour. The detection limit (signal/noise = 3) was 5 pg ml(-1) and the relative standard deviations for 0.1 and 0.04 ng ml(-1) cobalt (n = 10) were 1.0 and 2.3%, respectively. The method was applied to the determination of cobalt in pepperbush.     

2,6-Bis[(o-hydroxy)phenyliminomethyl]-1-hydroxybenzene as a reagent for the selective spectrofluorimetric determination of aluminium

A spectrofluorimetric method for the determination of aluminium at ng/ml level has been developed. The method is based on the formation of a fluorescent 11 complex between Al(III) and 2,6-bis[(o-hydroxy)phenyliminomethyl]-1-hydroxybenzene at an apparent pH of 5.0 in an aqueous-ethanol medium (70% v/v ethanol). The influence of reaction variables is discussed. The range of concentration of the method is 1.0–10.0 ng/ml aluminium, the relative standard deviation 1.5% and the limit of detection 0.1 ng/ml. The advantages of the proposed method include high sensitivity and selectivity. The method has been applied to the determination of aluminium in natural waters.     

Determination of 0.1 to 1000 μ g/ml cadmium in a hydrometallurgical zinc refining process stream by a flow injection technique with computer controlled injection method

A computer-controlled flow injection system was developed for the determination of cadmium in a hydrometallurgical zinc refining process stream. An anion-exchange method in acidic potassium iodide medium was used for the on-line separation of cadmium from the matrix zinc. 1-(4-Nitrophenyl)-3-(4-phenylazophenyl)triazene (Cadion) was used as the chromogenic reagent for the spectrophotometric detection of cadmium. In order to expand the dynamic range of the flow injection - spectrophotometry, a computer-aided time-based variable-volume injection method has been employed for the introduction of the sample into the flow injection system. Samples ranging from 0.56 to 350 microl can be delivered by controlling the time period of the sample introduction valve and the flow rate of the carrier solution. The system permits a throughput of 5 samples per hour. The reproducibility has been proven to be satisfactory with a relative standard deviation of less than 6.2% (sample injected: 0.56 microl of 850 microg Cd/ml; n=100) and 5.0% (350 microl of 0.14 microg Cd/ml; n=5). The determination limit was 20 microg Cd/ml with 0.56 microl sample injection and 0.05 microg Cd/ml with 350 microl sample injection (the absolute amount of cadmium injected into the system was 11 ng and 17.5 ng, respectively).     

Flow Injection Determination of Trace Amounts of Iodide with Spectrophotometric Detection by its Catalytic Effect on the 4, 4' – Bis (Dimethylamino) Diphenylmethane-Chloramine T Reaction

ABSTRACT

A simple and accurate flow injection spectrophotometric procedure was developed for the determination of iodide based on its catalytic effect on the oxidation of 4, 4'-bis (dimethylamino) diphenylmethane (tetrabase) by Chloramine T in a weakly acidic solution. The optimum analytical conditions have been established. The linear range of the detection is 4-110 ng/mL, with a limit of detection 3 ng/mL. The method has been used to determine iodide traces in water.     

Sensitive flow-injection amperometric detection of iodide using Mn3+ and As3+.

A rapid, selective, and sensitive kinetic flow-injection method for iodide content determination with amperometric detection on a platinum electrode was developed. The method is based on the catalytic effect of iodide on the Mn3+ reaction with As3+ in the presence of sulfuric acid. The calibration curve was linear in the concentration range from 5.0 x 10(-7) to 1.0 x 10(-4) mol/L iodide. The limit of detection (LOD) was found to be 5.0 x 10(-9) mol/L iodide. The relative standard deviations (RSD) were 1.68% and 3.03% for 1.0 x 10(-3) mol/L standard and 1.0 x 10(-6) mol/L iodide solution (n = 6), respectively. The method has been successfully applied for determination of iodide in waters, table salts, fodder, organic substances and human blood sera. The results were compared with those obtained by a standard AOAC (Association of Official Analytical Chemists) method, as well as with those obtained by a kinetic spectrophotometric procedure for determination of iodide.     

Spectrofluorimetric kinetic determination of selenium (IV) by flow injection analysis in cationic micellar medium

A sensitive catalytic kinetic spectrofluorimetric method for determining ng ml(-1) of selenium by flow injection analysis has been developed. The method, based on the catalytic effect of Se (IV) on the reduction of resorufin by sulphide, in the presence of cetylpyridinium chloride, is monitored spectrofluorimetrically (lambda(ex)=480 nm; lambda(em)=583 nm). The linearity range of the calibration graph is dependent on the concentration of sulphide. The variables affecting the rate of the reaction were investigated. The method is simple, rapid, precise, sensitive, and widely applicable. The limit of detection is 1 ng ml(-1) Se (IV), and the calibration range is 5-1000 ng ml(-1). Sampling rate is 60 samples h(-1), and the relative standard deviation of 12 determinations of 100 ng ml(-1) Se was 0.76%. The determination of Se (IV) in the presence of Se (VI) and total selenium is described. The method was applied to the determination of Se in selenium tablets, and several synthetic samples.     

Catalytic kinetic determination of ultratrace amounts of ruthenium(III) based on the oxidation of benzylamine by alkaline hexacyanoferrate(III)

A kinetic method is proposed for the determination of ruthenium(III) by means of its catalytic effect on the oxidation of benzylamine by hexacyanoferrate(III) in alkaline medium. The reaction is followed spectrophotometrically by measuring the decrease in the absorbance of hexacyanoferrate(III) at 420 nm. Under the optimum experimental conditions ruthenium(III) can be determined in the range 10-121 ng/ml with an average error of 1.7% and maximum relative standard deviation of 1.3%. The influence of many potential interferents has been examined and the method has been tested for determination of ruthenium(III) in synthetic mixtures. The method is convenient, reliable and rapid.     

Selective kinetic spectrophotometric determination of copper at nanograms per milliliter level

A sensitive and selective kinetic method is proposed for the determination of nanogram amounts of copper. The method is based on the catalytic effect of copper on the reduction of Ponceau S by sodium sulfide in an alkaline media. The rate of the reaction is monitored spectrophotometrically at 560 nm. The method allows determination of copper concentrations in the range 2-400 ng ml(-1) with a relative standard deviation of approximately 2%. The proposed method, which is highly selective to copper, has been applied satisfactory to its determination in real samples.     

Spectrofluorimetric determination of thiabendazole in a micellar medium

A sensitive, selective Spectrofluorimetric method has been developed for the determination of thiabendazole in a sodium dodecylsulphate micellar medium. The method features a linear determination range of 0.020-15 g and a detection limit of 0.2 ng/ml, with a relative standard deviation of less than 3%. By using a straightforward extraction procedure with ethyl acetate and hydrochloric acid, the method provided average thiabendazole recoveries above 96% from apple, pear and potato samples.     

Continuous flow system for the determination of trace vanadium in natural waters utilizing in-line preconcentration/separation coupled with catalytic photometric detection

A sensitive and rapid method is presented for the determination of vanadium at ng to sub-ng ml(-1) levels in natural waters, in which in-line preconcentration/separation is directly coupled with catalytic detection of vanadium in a flow-injection system. Vanadium was adsorbed on a small column packed with Sephadex G-25 gel and desorbed with a small volume of 0.010 M HCl. The catalytic action of vanadium on the oxidation of chromotropic acid (1,8-dihydroxy-3,6-naphthalenedisulphonic acid) by bromate in pH 3.8 buffered media was used in the sensitive determination of vanadium. Effective preconcentration/separation of trace vanadium can be achieved from Fe(III), Cu(II) and a large excess of sodium chloride in seawater sample. A linear calibration using a 5 m sample loop was obtained for vanadium in the range 0-2.5 ng ml(-1). The limit of detection was 0.02 ng ml(-1) and the relative standard deviation was 1.2% for 1.0 ng ml(-1) vanadium (n=5). The present FIA system is rapid and sensitive and can be readily applied to river water and coastal seawater samples.     

Kinetic determination of ultramicro amounts of copper

A new catalytic reaction is proposed and a kinetic method developed for the determination of ultramicro amounts of Cu(II) on the basis of its catalytic activity in oxidation of the 2-thiosemicarbazone of sodium 1,2-naphthoquinone-4-sulphonate by hydrogen peroxide in the presence of ascorbic acid. Under optimal conditions the sensitivity of the method is 0.25 ng/ml. The relative error is 4.8-18.2% for the concentration range 5-0.8 ng/ml. Most foreign ions do not change the rate of the catalysed reaction. Co(2+) and I(-) catalyse the reaction, Ni(2+) extensively inhibits it, and in the presence of EDTA only the uncatalysed reaction takes place.     

Direct spectrophotometric determination of Nd in mixed rare earths with semi-xylenol orange and cetylpyridinium chloride

The derivative absorption spectra of the neodymium complex with Semi-Xylenol Orange and cetylpyridinium chloride has been investigated. The characteristic absorption of the complex is approximately 350 times that of neodymium chloride. The fourth-order derivative spectrum has been used to eliminate the interference of the other lanthanides, and to increase the sensitivity by a further factor of 6. Beer's law is obeyed for 0-7.5 microg of Nd in 25 ml of solution. The relative standard deviation for 7 determinations of 1.8 microg/25 ml neodymium was 1.3%. The detection limits were 5.8 ng/ml in the absence of lanthanum and 11.2 ng/ml in the presence of 44 ng/ml lanthanum (or 36 ng/ml yttrium). The method has been used for the determination of neodymium in mixed rare earths, with satisfactory results.