The use of vanadium-sulphosalicylic acid complex as a redox indicator

In a previous communication it was reported that vanadium^V gives an intense turquoise-blue colour with sulphosalicylic acid in concentrated sulphuric acid and that the colour reaction is specific and very sensitive for the detection of vanadium^V. During our studies on the nature of the complex, it was found that vanadium^IV gives a negative colour test and that the blue colour developed by the reagent with vanadium^V is discharged on the addition of a reducing agent like iron^II, uranium^IV or hydroquinone. It was also observed that the blue colour is restored by the addition cerium^IV solution. This reversible property of the complex has been further investigated to see if the complex can be used as a redox indicator.     

Correction of iron interface in the spectrophotometric flow injection catalytic determination of molybdenum in plants

Iron interference in the spectrophotometric catalytic determination of molybdenum based on the iodide-hydrogen peroxide reaction can be corrected by using sulphosalicylic acid as masking and color-forming reagent. The catalytic influence of iron ions is circumvented to the extent of about 90% and correction of any remaining iron ions is possible by monitoring the colored iron(III)-salicylate complex at 490 nm. In this way, iron is also determined. With the proposed system, molybdenum can be determined in plant and food digests within the 0–100 μg Mo 1⁻¹ range in the presence of up to 25 mg Fe 1⁻¹, at a sampling rate of about 50 determinations h⁻¹. The relative standard deviation of 10 consecutive measurements was estimated as < 2%. Results for samples were comparable with those obtained by graphite furnace atomic absorption spectrometry. In addition, recoveries within the range 94–100% were calculated.     

5-(6-Nitro-2-Benzothiazoleazo)-8-Aminoquinoline as a Sensitive Reagent for the Spectrophotometric Determination of Cobalt and Nickel

Since 8-aminoquinoline has (N,N) as its chelating atom,it is more selective than 8-hydroxyquinoline and 8-mercaptoquinoline. So recently, derivative of 8-aminoquinoline has attracted much attention as analytical reagent. In this work, a new type of 8-aminoquinoline derivative 5-(6-nitro-2-benzothiazoleazo)-8-aminoquinoline (NBTAQ) has been synthesized and tested as a possible chromogenic reagent for the spectrophotometric determination of cobalt and nickel. The result shows that in the presence of the cationic surfactant cetyltrimethylammonium bromide (CTAB) and borax buffer solution, cobalt and nickel react with the reagent to form 1:2 blue complexes, respectively. The absorption peaks of Co-NBTAQ and Ni-NBTAQ complexes were located at 650 and 615 nm, respectively, and the apparent molar absorbtivities are 9.21×l0⁴(Co) and 1.13×l0⁵ (Ni) I.mol^-1.cm^-1. The methods adhere to Beer's law for 0-0.32 μg. Ml^-1 of cobalt and 0-0.24 μg. Ml^-1 of nickel and the colour system is stable for no less than 24 h. The experimental variables affecting colour formation and the possible interference of co-existing ions were thoroughly studied. The optimum conditions established were incorporated in the recommended procedures.     

A sensitive flow-injection method for determination of trace amounts of nitrite

A new sensitive colour reaction for nitrite determination is presented. In acidic medium, nitrite was reacted with safranine to form a diazonium salt which caused the reddish-orange dye colour of the solution to change to blue. The carrier stream, into which the sample solution was injected, was doubly distilled water. The reagent solution stream, which contained safranine dye, hydrochloric acid and potassium chloride, was mixed with the carrier in a 3-m length of silicon tubing (bore 0.5 mm) maintained at 30°C in a thermostatic bath. The absorbance intensity was measured at 520 nm. The detection limit was 20 ng ml⁻¹ and the RSD% of 20 injections of 1 μg ml⁻¹ of nitrite was 0.65%. Analysis can be done at a rate of up to 30 h⁻¹. Under the optimum conditions in the concentration range of 30–4000 ng ml⁻¹ of nitrite ion, a linear calibration graph was obtained (r=0.9999). The method was applied successfully to the determination of nitrite in sausages.     

Determination of ultramicro amounts of sulphate as methylene blue—II The reduction

Sulphate may be determined spectrophotometrically as methylene blue after reduction to sulphide, which is allowed to react with p-aminodimethylaniline and ferric iron to form the dye. A previous paper¹ dealt with the colour reaction; this paper deals with the reduction.

A method for the reduction of sulphate to sulphide by hydriodic and hypophosphorous acids in acetic acid solution is proposed. It is founded on an investigation of the following variables: composition of the reducing reagent, composition of the carrier gas and gas-washing liquid, temperature at reduction, and time. The yield of the reduction is found to be 100% within the experimental errors. The standard deviation of a single determination of 100 μg S or 2 μg S is found to be 0.14 μg S or 0.05 μg S, respectively. Some interferences in connection with the application of the method for certain purposes are discussed.     

氧化的苏木色精与抗坏血酸分光光度法测定纳克量级的钼

本文报导了氧化的苏木色精与抗坏血酸在沸水里加热,高度灵敏的测定钼的分光光度法,这种方法已用于测定地面水和尿中的钼,并获得了满意的结果。     

Spectrophotometry Determination of Molybdenum with N-Cyanoacylacetaldehyde Hydrazone

N-cyanoacylacetaldehyde hydrazone (CAAH), which is a laboratory synthetic reagent, is proposed as a new reagent for spectrophotometry determination of microamounts of molybdenum at λ_max 790 nm. The reagent forms 1:1 blue coloured complex with molybdenum (VI) in phosphoric acid solution. The stable blue colour is obtained finally after changing from yellow to green. The colour development depends on temperature, time and concentration of phosphoric acid. This reagent is applied for the determination of molybdenum in steel alloys and the results are satisfactory.     

A new approach for obtaining total tryptophan recovery in plasma samples deproteinized with sulphosalicylic acid.

The treatment of plasma with a sodium dodecy sulphate solution before deproteinization with sulphosalicylic acid is described. With this treatment, the liberation of tryptophan from plasma albumin is complete and its determination can be made directly, together with that of other amino acids and related compounds, by automatic ion-exchange chromatography, eliminating the need for an extra analysis for the accurate determination of this amino acid. Results of tryptophan recovery tests, carried out both on plasma samples simply deproteinized with sulphosalicylic acid and on other samples pre-treated with sodium dodecylsulphate solution are reported. These results are also compared with those obtained when trichloroacetic acid was used as deproteinizing agent. A recovery study on a human albumin (fraction V) solution containing a known amount of tryptophan is also described.     

The effect of platinum oxide films on reaction kinetics at platinum electrodes

It has been known for some time that the pre-treatment of platinum electrodes often effects subsequent electrochemical reactions. Part of the effect of pre-treatment is due to the fact that anodized or chemically oxidized platinum electrodes become coated to some degree with a film of platinum oxide. This work was concerned with quantitative measurement of kinetic parameters as a function of the extent of oxide film formation. Whenever possible, variations in reaction mechanisms are proposed.

Most of the experimental evidence has been taken from current-potential curves but the techniques of chronopotentiometry and microscopy were also used.

The reduction of vanadium^V chromium^VI, arsenic^V, iodate and oxygen were investigated as well as the oxidation of vanadium^IV, arsenic^III, oxalic acid, and formic acid. The presence of the platinum oxide film effected the reactions studied in a variety of ways but in every case some variation in the kinetic parameters of the reactions studied was recorded. For a number of cases, a modified oxygen bridge theory was found useful.     

Perbenzoic acid as volumetric reagent

Summary Perbenzoic acid (0.05 M) chloroform solution is used as volumetric reagent for the determination of potassium ferrocyanide, arsenious oxide, tartar emetic, sodium sulphite, stannous chloride, hydrazine sulphate and sodium thiosulphate atph 4.0 to 4.5 in sodium acetate and acetic acid buffer solutions, using iodine as catalyst and preoxidiser. Appearance of faint violet colour in chloroform layer indicates the end point in visual titrations. In potentiometric titrations bright platinum foil is used as an oxidation-reduction electrode and it is coupled with saturated calomel electrode. At the equivalence point there is a sharp jump in potential in each titration.     

A fluorescence test for vanadium(V) with resorcinol

Summary In continuation of our previous work in which salicylic acid was reported to give a very sensitive and an almost specific colour reaction with vanadium(V), we have now found that vanadium(V) reacts with resorcinol in 20 N sulphuric or phosphoric acid solution to give a blue coloured product, which gives a vivid red fluorescence under filtered ultraviolet light. A sensitive test for vanadium(V) has now been developed making use of this red fluorescence or of the bright blue colour. Dichromate gives a somewhat less sensitive violet colour with the resorcinol reagent under the same conditions, but the product does not fluoresce. Manganese(VII), cerium(IV), iron(III), titanium(IV), uranium(VI), molybdenum(VI) and tungsten(VI) do not interfere with the colour reaction or the fluorescence test for vanadium(V).     

A new selective metallochromic reagent for the detection and chelatometric determination of calcium

A new reagent, Calcichrome, which gives a highly sensitive colour reaction with calcium ions in alkaline solution, has been synthesised. Neither barium, strontium nor magnesium react with the reagent, which is therefore proposed as a selective spot-test reagent for calcium. In addition, Calcichrome may be used as a metallochromic indicator for the accurate complexometric titration of calcium in the presence of at least twelve-fold amounts of barium. Trans-1:2-diaminocyclohexane-N:N:N':N'-tetra-acetic acid is used as titrant since it is the only complexan available which is sufficiently selective in its reactivity towards calcium and barium.     

A new oxidimetric reagent: potassium dichromate in a strong phosphoric acid medium—I Titrimetr1c determination of manganese

A new method has been developed for the direct titrimetric determination of manganese^II, depending on its oxidation to manganese^III with potassium dichromate at room temperature in a strong phosphoric acid medium using a potentiometric or photometric endpoint. Oxygen of the air does not interfere. The potentiometric method gives results to an accuracy within ± 0.3% for 20–150 mg of manganese/50 ml of titration solution; with the photometric method 5–17 mg of manganese/40 ml of titration solution can be determined with an error of 0.3–1.0% depending on the amount present. Potassium dichromate in 12.0M phosphoric acid has a formal redox potential of about 1.5 V and this reagent appears to have great possibilities in titrimetric analysis.     

The precipitation of hydrated cobalt 1-nitroso-2-naphtholate from homogeneous solution

A method has been developed for determining cobalt by precipitating cobalt^III 1-nitroso-2-naphtholate from homogeneous solution. The reagent is synthesised within the reaction mixture by treating 2-naphthol with nitrous acid in the presence of cobalt^II ion. Thus nitrous acid serves the dual role as oxidant for the cobalt^II ion and also as a reactant in the synthesis of the reagent. Excess reagent precipitates after the cobalt nitroso-naphtholate has settled. A washing procedure has been developed to eliminate the excess reagent without affecting the cobalt nitroso-naphtholate. After washing to remove excess reagent and filtration, the precipitate is dried at 115° and weighed as Co(C₁₀H₆O₂N)₃·H₂O.

The presence offluoride prevents the interference of iron, tungsten and other elements which form strong fluoride complexes.

The precision and accuracy is within 0-1 mg of cobalt at a 10-mg level and within 0-2 mg of cobalt at a 50-mg level.     

Determination of iron(III) with salicylic acid by the fluorescence quenching method

The spectrofluorimetric determination of Fe³⁺ using salicylic acid as an emission reagent has been investigated by measuring the decrease of fluorescence intensity of salicylic acid due to the complexation of Fe³⁺–salicylic acid. An emission peak of salicylic acid, which is decreased linearly by addition of Fe³⁺, occurs at 409 nm in aqueous solution with excitation at 299 nm. The determination of the ferric ion is in the range 1×10⁻⁶–10×10⁻⁶ M Fe³⁺ (0.0558–0.558 μg/ml) and the detection limit is 5×10⁻⁸ M. The quenching effect of Fe³⁺ on the fluorescence intensity of salicylic acid may be considered on the basis of complexation between salicylic acid and Fe³⁺. The effects of foreign ions were investigated.     

Interference from arsenate when determining phosphate by the malachite green spectrophotometric method

The effect of arsenate on phosphate determination by the malachite green spectrophotometric method was investigated. The molar absorptivities of the molybdophosphate and malachite green–molybdoarsenate species at 625 nm and a final acidity of 0.38 M were calculated as 10.4±0.13×10⁴ and 7.2±0.17×10⁴ l mol⁻¹ cm⁻¹ respectively, indicating that arsenate could interfere in phosphate measurement. Arsenate concentrations as low as 23 μg l⁻¹ caused increase in colour development in phosphate solutions. However, the extent of colour development for both anions depended on the final acid concentration of the solution. An acidified sodium sulphite solution (0.83 M NaSO₃, 0.83 M H₂SO₄) quantitatively prevented arsenate colour development up to 300 μg l⁻¹ As(V). It was also demonstrated that the method removed As(V) interferences in mixed As/P solutions and therefore can be used to treat natural water samples with elevated arsenate concentrations before phosphate measurement.     

Spectrophotometric method for the determination of the relative strengths of organic acids with sensitized schiff's reagent

1. Ammonium salts of the weak acids, oxalic, citric, taitaric, formic, lactic, succinic. acetic, n-butyric and propionic bring colour to sensitized Schiffs reagent. The intensity of the colour thus produced stands in inverse relationship with the dissociation constants of these acids and hence of their strengths. The intensity of colour is dependent on the concentration of the ammonium salts and hence the concent ration of the latter was adjusted to a suitable value, keeping in mind the range of the sensitivity of the reagent itself. 2. The colour produced by the different salts is the same as that of the solution. The probable mechanism appears to be that the ammonium salts react with SO₂ which displaces the acids from the salts. The greater the displacement the greater the intensity of colour and the weaker the acid.     

Repetitive determination of ascorbic acid using iron(III)-1.10-phenanthroline-peroxodisulfate system in a circulatory flow injection method

Ascorbic acid (AA) could be determined in large quantities of a co-existing oxidant. The incorporation of an on-line reagent regeneration step based on redox reaction eliminates the baseline drift in the procedure. This makes it possible to adopt a circulatory flow injection method (cyclic FIA) and to determine AA repetitively. The method is based on the reduction of iron(III) to iron(II) by the analyte, the reaction of the produced iron(II) with 1,10-phenanthroline (phen) in a weak acidic medium to form a colored complex, and the subsequent oxidation reaction of iron(II) to iron(III) by the co-existing peroxodisulfate. A solution (50 ml) of 3.0×10⁻⁴ mol l⁻¹ ferric chloride, 9.0×10⁻⁴ mol l⁻¹ phen and 5.0×10⁻² mol l⁻¹ ammonium peroxodisulfate in acetate buffer (0.2 mol l⁻¹, pH 4.5) is continuously circulated at a constant flow rate of 1.0 ml min⁻¹. Into this stream, an aliquot (20 μl) of the sample solution containing AA is quickly injected by means of a six-way valve. The complex formed is monitored spectrophotometrically (at 510 nm) in the flow system. The stream then returns to the reservoir after passing through a time-delay coil (50 m). The iron(II)–(phen)₃ complex is oxidized to iron(III)–(phen)₃ complex by peroxodisulfate which exists excessively in the circulating reagent solution. The proposed method allows as many as 300 repetitive determinations of 15 mg l⁻¹ AA with only 50 ml reservoir solution. The contents of AA in commercial pharmaceutical products were analyzed to demonstrate the capability of the developed system.     

Spectrophotometric determination of indoles using a modification of the ehrlich colour reaction

A sensitive spectrophotometric method for the determination of indole (1 μg/ml) in aqueous solution is described. It is also applicable to certain 3-substituted indoles. The method employs p-dimethylaminobenzaldehyde in aqueous trifluoracetic acid. With indoles this reagent gives stable colours which are more intense than those obtained in the conventional Ehrlich reaction. Factors affecting fading of the indole colour are discussed.     

碲(Ⅳ)-碘化钾-罗丹明-B-聚乙烯醇体系高灵敏显色反应的研究

基于在聚乙烯醇存在下[Tel₈]^4-络阴离子与罗丹明B形成离子缔合络合物,发展了1个高灵敏分光光度测定碲的方法。显色反应的适宜介质是0.64～1.28mol/L的磷酸溶液。用平衡移动法和连续变化法确定离子缔合物的组成是(RhB)₄·[TeI₈]。此反应具有非常高的灵敏度,摩尔吸光系数ε₆₀₀=1.65×10⁶L·mol^-1·cm^-1。方法有较好的选择性,可用于钢铁、硫磺及某些其它样品中痕量碲的分光光度测定。