Spectrophotometric determination of water in organic solvents with solvatochromic dyes

The correlation between the absorbance at a fixed wave-length of a betaine dye in an organic solvent and the water content of the same solvent has been investigated. The betaine dyes investigated are 2,4,6-triphenyl-N-(3,5-diphenyl-4-hydroxyphenyl)pyiidinium betaine (I), 1-methyl-8-hydroxyquinolinium betaine (II), 1-methyl-6-hydroxyquinolinium betaine (III) and 2-methyl-5-isoquinolinium betaine (IV), and the organic solvents are ethanol, isopropanol, acetone, dioxan, acetonitrile and pyridine. The possibility of determining a trace amount of water in an organic solvent is demonstrated. The sensitivity of the method depends on solvent and dye but for example, 0.06 mg of water in 1 ml of acetonitrile can be detected with III with an ordinary spectrophotometer. The limitations of practical applications are discussed.     

Spectrophotometric determination of water in organic solvents with solvatochromic dyes-II

The correlation between the absorbance of a merocyanine dye in an organic solvent and the water content of the solvent has been investigated. The merocyanine dyes investigated are 1-methyl-4-[(4-oxocyclohexa-2, 5-dienylidene)-ethylidene]-1,4-dihydropyridine (I), 1-methyl-4-[(2-oxocyclohexa-3,5-dienylidene)-ethylidene]-1, 4-dihydropyridine, 1-methyl-2-[(4-oxocyclohexa-2,5-dienylidene)-ethylidene]-1, 2-di-hydropyridine and 1-methyl-2-[(oxocyclohexa-3,5-dienylidene)-ethyl-idene]-1, 2-dihydropyridine, and the organic solvents are isopropanol, acetone, acetonitrile and pyridine. The possibility of determining a trace amount of water in an organic solvent is demonstrated, and a procedure is proposed for the determination of trace water in pyridine. The sensitivity of the method depends on the solvent, being more sensitive in an aprotic solvent than in a protic one ; for example, 0.05 or 0.27 mg of water in 1 ml of acetonitrile or of isopropanol respectively can be detected with I, by use of an ordinary spectrophotometer.     

Spectrophotometric determination of traces of oxygen in water

Winkler's method of determining oxygen in water by titration of the iodine can not be applied with concentrations below 0.03 mg O₂/litre. We studied the spectrophotometric determination of the iodine-starch complex described by bairstow, francis, and wyatt and succeeded in improving its stability by the addition of potassium sulphate. The intensity of the blue colour is very sensitive to variation of temperature. Below 10° C this influence can be neglected. Upwards from 30° C the intensity rapidly decreases. Instead of performing the determination at 10° C we plotted the extinction coefficient of dilute solutions as a function of the iodine concentration for temperatures ranging from 10 to 30° C. With “the aid of this graph the iodine concentration can be found when the extinction coefficient and the temperature of a solution are determined.With this method we can determine oxygen in water in concentrations ranging from 0.005 to 0.4 mg O₂/litre. Duplicates (for water with a low content of oxygen) differ not more than 0.002 mg O2/litre.     

Spectrophotometric determination of trace water in organic solvents with a near infrared absorbing dye

A spectrophotometric method for the determination of trace water in organic solvents using a near infrared absorbing dye has been developed. This method is based on the effect that a minor change in polarity of the solvent caused by trace water content determines the extent of aggregation of a near-infrared dye monomer. This change can be detected spectrophotometrically. The calibration curves for methanol, ethanol, and isopropanol were determined. This method has the highest sensitivity (em = 16.73 unit) for water in isopropanol and the lowest sensitivity (em = 2.806 unit) for water in methanol. The correlation coefficient (R)(2) values for the regression lines ranges from 0.990-0.998. The linear range of the method for ethanol is 0.001-0.5%, for isopropanol is 0.001-0.1%, and for methanol is 0.001-1.0%. The limit of detection for ethanol, isopropanol, and methanol are 0.0001, 0.0001, and 0.005% water, respectively. The developed method is sensitive, simple and easy to operate, and the cost of analysis is low.     

海水中有机污染物的光度法测定

海水中有机污染物在强碱性条件下被KMnO4所氧化。通过对生成物溶液中K2MnO4浓度的光度法测量（λ=430nm）,直接测定海水中有机物含量（以COD表示）。该方法的线性范围为0．40—4．50mg／L（以邻苯二甲酸氢钾＋甲酸钠体系为标准混合物溶液）,测定海水COD的相对标准偏差RSD为8．9％,回收率为90％～114％。     

Spectrophotometric determination of traces of arsenic

Arsenic(III) is extracted into carbon tetrachloride from 3.5M sulphuric acid that is 0.8M in potassium iodide. 8-Mercaptoquinoline and acetone are added to the organic extract and the absorbance of the arsenic(III)-8-mercaptoquinolinate formed is measured at 380 nm. Repeating the extraction procedure highly increases the selectivity of the method; only tin(II) interferes with the determination.     

Spectrophotometric determination of traces of antimony

Antimony(III) is extracted into carbon tetrachloride from 4M sulphuric acid that is 0.05M in potassium iodide. 8-Mercaptoquinoline and acetone are added to the organic extract and the absorbance of the complex formed is measured at 390 nm. Repeating the extraction procedure greatly increases the selectivity of the method.     

Spectrophotometric determination of traces of formaldehyde

Summary A comparative study of various colorimetric methods for determining and detecting traces of formaldehyde has been made. Chromotropic acid and 2,7-duiydroxynaphthalene were found to be the best reagents and were subjected to a thorough study. Precise and accurate methods for determining formaldehyde using either chromotropic acid or 2,7-dihydroxynaphthalene are described. The color system produced by following the standard procedure obeys Beer's law. Using chromotropic acid 0.05 g to 2.0 g of formaldehyde per ml can be determined quite accurately. Acrolein seems to be the only seriously interfering substance, and its interference can be much diminished by slightly modifying the standard procedure. The reagent solutions are perfectly stable.     

Spectrophotometric study of pseudopurpurin-Pd(II) dimer complex. Spectrophotometric determination of traces of Pd(II)

We have studied spectrophotometrically the Pseudopurpurin-Pd(II) complex in an ethanolic-water medium ¦Ethanolamine ¦_optimum = 4 × 10⁻¹M; λ = 670 nm; 20% H₂O; stable for at least 4 hr; ¦Reagent¦_optimum = 5 × 10⁻⁵M; stoichiometry 2:2; log K = 17.7. A new method for the spectrophotometric determination of Pd traces is proposed for concentrations between 0.30 and 2.40 ppm. The relative error and the interferences of the method have been investigated.     

Role of water traces in the liquid-phase catalytic hydrochlorination of olefins in organic solvents

The liquid-phase hydrochlorination of 4,5,6,7,8,8,-hexachloro-3′,4,7,7′-tetrahydro-4,7-methanoindene (Chlordene) catalyzed by gallium or aluminum halides occurs in the presence of water traces in an aprotic organic solvent. Complexes H₂O·M₂X₆, where M is metal and X is halogen, catalyze this reaction. The reaction proceeds under homogeneous conditions. Under heterogeneous catalytic conditions, the solid phase in the AlCl₃−CCl₄ system attains the required concentration of AlCl₃ in the solution. It was shown using quantum-chemical PM3 calculations that the water molecule facilitates the transfer of proton in the form of the hydroxonium ion from an HCl molecule to olefin. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 248–252, February, 1998.     

Spectrophotometric determination of traces of cobalt in water after preconcentration on reagent-loaded polyurethane foams

Open-cell Polyurethane foam loaded with 1-(2-pyridylazo)-2-naphthol (PAN) is used for the preconcentration of traces of cobalt from water at the ppb level with a preconcentration tration factor of 1000 or more. Cobalt is retained quantitatively from thiocyanate solution on the loaded foam placed in a column, at flow rates up to 100 ml min^-1, and then recovered completely from the foam by elution with acetone. Cobalt is determined spectrophotometrically with 4-(2-pyridylazo)-resorcinol at 510 nm, after the removal of interfering ions with a Dowex 1-X8 column. The amount of PAN leached by the water percolating through the column is too low to affect quantitative retention of traces of cobalt.     

Spectrophotometric determination of traces of selenium with diaminobenzidine

Diaminobenzidine is suitable for the spectrophotometric determination of traces of selenium. The reaction is very sensitive, the molecular extinction coefficient being as high as 10,200. The reaction is specific, the most common ions causing no perturbation. The procedure is especially valuable for the determination of traces selenium in tellurium and in sulfur, provided that the latter is present in the sulfate form.     

Determination of water traces in various organic solvents using Karl Fischer method under FIA conditions

Flow injection methods utilising the Karl Fischer (KF) reaction with spectrophotometric and potentiometric detection are described for the determination of the trace water content in various organic solvents. Optimisation of the methods resulted in an accessible (linear) working range of 0.01-0.2% water for many solvents studied with a typical precision of 1-2% R.S.D. Only 50 mul of organic solvent was injected and the sampling frequency was about 120 samples per h. Since the slopes of the calibration curves were different for different solvents appropriate calibration was required. Problems associated with spectrophotometric detection and caused by refractive index changes were pointed out and a nested-loop configuration was proposed to overcome this kind of interference. The potentiometric method with a novel flow-through detector cell was shown to surpass the performance of spectrophotometric detection in any respect. The characteristics of the procedures developed made them well applicable for on-line monitoring of technical solvent distillations in an industrial plant.     

Inorganic analysis in organic solvents: Spectrophotometric determination of chromium following a chromatographic separation

A new method is described for the determination of chromium. In a suitable solution, trivalent chromium is precipitated as its 8-hydroxyquinolate, or 8-hydroxyquinaldate, in the presence of trivalent iron. The dried precipitate is dissolved in chloroform, and the solution, diluted once with benzene, is passed through an activated alumina Chromatographic column. The optical density of the eluate, containing the chromium complex only, is measured at 410 or 425 mμ with respect to the solvent. Aluminium, vanadium and cobalt interfere when 8-hydroxyquinoline is used as reagent; but when 8-hydroxyquinaldine is used, the method is unequivocal.     

Spectrophotometric determination of traces of selenium(IV) in various environmental samples using the flow-injection technique (FIT)

A simple, sensitive, and rapid flow-injection spectrophotometric method was developed for the determination of trace amounts of selenium(IV). The method is based on the oxidation reaction of 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) by selenium(IV) followed by the coupling reaction with chromotropic acid (4.5-dihydroxy naphthalene-2.7-disulphonic acid) in a basic medium (phosphate buffer, pH 10.5) to give a pink derivative with λ_max 530 nm that is stable for more than 7 days at 35°C. The reaction and flow conditions of the full experimental design were optimized. A detection limit (2s) of 0.25 μg/L Se(IV) was obtained at a sampling rate of 10 samples per hour. Beer’s law is obeyed for a Se(IV) concentration range of 0.05–0.5 μg/mL at the wavelength of maximum absorption. The detailed study of various interference ions indicates that the method is highly selective. The method was successfully applied to the determination of traces of selenium(IV) in various water samples. The results obtained were in good agreement with those obtained by the reported methods at the 95% confidence level. The text was submitted by the authors in English.