Sensitive detection of alkali metal formates in formic acid

A simple and selective colour reaction based on reaction with acetic anhydride and citric acid is described. The identification limit is 10 μg of sodium formate.     

The colorimetric determination of dialkyl phosphites using cacotheline

The estimation of dialkyl phosphites by means of its colour reaction with cacotheline in sodium carbonate solution is described. The effect of dialkyl phosphite upon the spectrum and polarographic response of the reagent is discussed to reveal the stoichiomctry of the reaction and the group involved in colour production.     

Spectrophotometric determination of formaldehyde in air

A spectrophotometric method for the determination of formaldehyde in air is described, based on the colour reaction of formaldehyde, p-aminoazobenzene and sulphur dioxide in hydrochloric acid medium. Beer's law is obeyed at 505 nm in the range 2-12 mug of formaldehyde per 25ml of final solution (0.08-0.48 ppm). Optimum conditions for colour development, and possible interferences, have been studied.     

A new spectrophotometric method for the determination of formaldehyde in air

A new spectrophotometric method for the determination of formaldehyde is described, based on a colour reaction with oxalyidihydrazide and copper(II). The optimum reaction conditions, and other analytical parameters such as interferences, Beer's law, sensitivity, collection efficiency, etc. have been studied.     

A Highly Sensitive Colour Reaction of Titanium and its Analytical Application

A highly sensitive colour reaction between titanium and p-Bromocar-boxyazo-m was described. The suitable conditions forming the β-type complex and the influences of acid media、temperature、organic solvents, and surfactants on the complex formation reaction were examined.     

有机溶剂化效应对多元配合物显色反应作用的研究 Ⅰ.有机溶剂对 M-CAS-CTMAB 体系显色反应微环境影响之初探

本文研究了有机溶剂加入后,表面活性剂增敏型体系微环境的变化。用核磁共振方法确定了有机溶剂分子与CTMAB胶束分子的作用部位。通过CTMAB溶液电导率测定及c.m.c值的测定,发现有机溶剂加入确实形成了一种新胶束。还研究了有机溶剂对显色反应速度的影响。并考察了体系微环境变化与相应显色液吸光度值的关系。我们的实验初步表明,有机溶剂的存在,改变了原有的CTMAB胶束,是增敏作用的重要因素,因而改变了发生显色反应的微环境。     

Über die Bestimmung von hochmolekularen Flockungsmitteln in technischen Löselaugen

The method is based on the colour change of organic dyes which is measured by photometry. In some examples the procedure is transferred to other salt solutions and to water. Several experiments are described in order to elucidate the reaction.     

Use of ammonium molybdate in the colorimetric assay of cephalosporins

A colorimetric method for the determination of five cephalosporins (cefoxitin sodium, cefotaxime sodium, cephapirin sodium, cephalothin sodium and cephaloridine), based on the blue colour formed by reaction of the cephalosporins with ammonium molybdate, is described. The effects of reagent concentration and reaction conditions are discussed. The proposed method has been applied to the analysis of cephalosporin injections, the results of which are in good agreement with those obtained by the official method of the British Pharmacopoeia.     

Analytical properties of 5,5-dimetyl 1,3-cyclohexanedione dithiosemicarbazone monohydrochloride; spectrophotometric determination of chromium(VI) in alloy steels and industrial effluents

The analytical properties of 5,5-dimethyl 1,3-cyclohexanedione dithiosemicarbazone monohydrochloride (5,5-DiMe-1,3-CHDT.HCl) are described. The reagent gives pink coloured solutions with chromium(VI) in acetic medium. The maximum colour intensity is observed in 0.5-2.5 pH range. This colour reaction (molar absorptivity, 1.63 x 10(4) 1 mol(-1) cm(-1) at 360 nm) has been used for the spectrophotometric determination of total chromium in alloy steels and industrial effluents.     

Application of simplified complementary tristimulus colorimetry to chemical kinetics in solution-I: analysis of reaction mixtures and determination of first- or pseudo first-order rate constants

A graphical method is described which allows estimation of the number of reacting light-absorbing species from the plots of complementary colour points which are obtained with the use of simplified complementary tristimulus colorimetry (SCTS method) from absorption spectra of a series of kinetics solutions. It is shown that the mole function of the reactant or the product at any time can be calculated from the complementary colour points, so that the rate constant can also be determined. The present method has some advantages over the common approach to the determination or reaction rates in presence of a colour impurity.     

New qualitative colour reaction for the identification of copper(I) compounds and complexes

The colour reaction of copper(I) salts and complexes, in sulphuric acid medium, with ferricyanide and ammonia, has been used for the general identification of cuprous compounds. A sulphuric acid solution of Cu(I) compound, when treated with a dilute ferricyanide solution in the presence of ammonia, gives a salmon-pink, red-pink, pink-purple or purple colour or precipitate, characteristic of copper(I). Copper(II) compounds fail to give a positive response. The reaction also forms the basis of a test for ammonium ion and differentiation between ferrocyanide and ferricyanide. The preparation of the copper(I) complex of 1-allyl-2-tetrazoline-5-thione is described.     

New methods for the detection of carboxylic acid groups in organic compounds, with acriflavine

The dye acriflavine is used for the selective detection of the carboxylic acid group in organic compounds. Two simple, rapid, and reliable colour tests are reported; these are based on the development of a violet colour and a yellow to yellowish-brown precipitate when a carboxylic acid is treated with acriflavine/sodium nitrite and acriflavine/potassium chromate respectively. Other acidic compounds such as phenols, thiophenols, sulphinic acids, sulphonamides, and acid imides do not interfere. Sulphonic acids (with the exception of their amino derivatives) interfere with both the tests. Enols and salts of organic bases do not interfere in the former test, whereas they do interfere in the latter test. The probable nature of the reaction products in both the tests has been discussed. Based on the former reaction, a procedure is described for the selective detection of nitrite ion. The limit of detection is 25 mug of nitrite per ml. Only iodide interferes.     

Nachweis von Farbstoffen auf alten Textilien

A simple method of identifying the more important natural dyes that have found widespread use for dyeing textiles is described. This involves thin-layer chromatographic comparison on Mikropolyamid F 1700 (Schl. & Sch.). The reliability of dye recognition is increased by combining various methods of identification on the chromatogram by employing the following procedure: (1) The normal coloration, (2) the fluorescent colour in UV light, (3) the change in shade with ammoniacal steam, and (4) the colour reaction with aluminium salts or, where hydroxyflavones have already been identified by reaction (3), with iron(III) chloride. In addition, various specific reactions for identifying individual natural colours are given. Furthermore, methods are indicated whereby identification can be effected by comparing infra-red spectra after a simple preparation of the sample.     

A novel route to copper(II) detection using 'click' chemistry-induced aggregation of gold nanoparticles

A simple colorimetric method for the detection of copper ions in water is described. This method is based on the 'click' copper(I)-catalyzed azide-alkyne cycloaddition reaction and its use in promoting the aggregation of azide-tagged gold nanoparticles by a dialkyne cross-linker is described. Nanoparticle cross-linking, evidenced as a colour change, is used for the detection of copper ions. The lowest detected concentration by the naked eye was 1.8 μM, with the response linear with log(concentration) between 1.8-200 μM. The selectivity relative to other potentially interfering ions was evaluated.     

Spectrophotometric determination of hydroxylamine and its derivatives in pharmaceuticals

A sensitive spectrophotometric method for the determination of hydroxylamine is described. The method is based on the oxidation of hydroxylamine to nitrite using sodium arsenate under alkaline condition. The formed nitrite is determined based on the diazo coupling reaction between p-nitroaniline and N-(1-naphthyl)ethylenediamine dihydrochloride [NEDA]. The system obeys Beer's law over the concentration range 0-7 microg of hydroxylamine at 545 nm and the colour is stable for 3 h. The molar absorptivity of the colour system is found to be 6.7 x 10(4) l mol(-1) cm(-1). The relative standard deviation is 1.2% for ten determinations at 4 microg of hydroxylamine. Interferences due to various foreign ions have been studied and the method has been applied to the determination of hydroxylamine and its derivatives used in pharmaceutical formulations after hydrolysis.     

A new sensitive and specific test for vanadium with sulphosalicylic acid

A very sensitive and specific test for vanadium^V is described using sulphosalicylic acid as reagent. When this reagent is brought into contact with solid vanadium^V (a drop of the test solution evaporated to dryness on a watch glass) in the presence of concentrated sulphuric acid or 80% syrupy phosphoric acid, a blue colour is developed. Using this colour reaction, it is possible to detect 0.05 μg of vanadium^V in 0.05 ml of test solution. Aluminium^III, arsenic^V, beryllium^II, cadmium^II, chromium^III, chromium^VI, copper^II, iron^III, molybdenum^VI, nickel^VI, tungsten^VI, uranium^VI and vanadium^IV do not interfere with this colour test, although some of them are known to form coloured complexes with sulphosalicylic acid under different conditions. Reducing agents like iron^II, uranium^IV, molybdenum^V and hydroquinone discharge the colour. The colour of the vanadium^V-sulphosalicylic acid compound is also discharged if the temperature is raised to 60°, though it reappears on cooling.     

Kinetic spectrophotometric determination of low levels of nitrite by catalytic reaction between pyrogallol red and bromate

A kinetic spectrophotometric method for the determination of trace nitrite (0.003-1.000 microg/ml) based on its catalytic effect on the reaction between potassium bromate and pyrogallol red in acidic media is described. The reaction is monitored spectrophotometrically by measuring the decreasing colour of pyrogallol red at 467 nm by the fixed-time method. At a given time of 3.0 min at 30 degrees, the detection limit is 0.001 microg/ml and the relative standard deviation for 0.010 microg/ml nitrite is 1.8% (n = 8). The method is free from most interferences, especially from large amounts of nitrate and ammonium. The procedure was successfully applied to the determination of trace nitrite in natural water without preconcentration.     

Spectrophotometric determination of platinum in experimental catalysts

Conditions have been established and procedures are described for the colorimetric determination of platinum in experimental catalysts and miscellaneous materials. The methods are based on the measurement of the intensity of colour produced by the reaction of chloroplatinic acid with tin(II) chloride. Interference from metals such as chromium, molybdenum and nickel, which are often also present in catalysts, is overcome by selective extraction of the complex into isoamyl alcohol followed by measurement of the absorbance of the alcohol layer.     

Spectrophotometric determination of vanadium and its application to gas-turbine fuel-oils

A very sensitive spectrophotometric method for the determination of vanadium in furnace oils is described. The intense indigo-blue colour developed by the reaction of vanadium with tannin and thioglycollic acid is measured at a wavelength of 600 nm at pH 4 and obeys Beer's law between 0.5 and 5 ppm vanadium. The method is applicable to gas-turbine fuel-oil and special navy fuel-oils. The common mineral constituents usually present in such oils do not interfere.     

Determination of boron as boric acid in eye lotions using a sequential injection system

A simple and reliable sequential injection analysis (SIA) system is described for the determination of boron as boric acid in eye lotions. This method is based on the complexation reaction between d-sorbitol and boric acid followed by the acid-base reaction with methyl orange (MO). The colour change reaction is monitored at 520 nm. The system is able to monitor boron at a frequency of 30 samples per h with a relative standard deviation of less than 0.6%. The calibration graph is linear up to 12-mg l(-1). The system has a detection limit of 0.06-mg l(-1). No significant differences (at 95% probability level) were found between the proposed SIA method and the reference method.