Extraction-spectrophotometric determination of tungsten with thiocyanate and some amidines

The procedure is based on reduction of W(VI) to W(V) by tin(II) chloride in 6 M hydrochloric acid, and extraction of the resultant thiocyanate complexes with a benzene solution of amidine. The complex coagulates and is dissolved in the benzene by addition of 1-pentanol. The maximum molar absorptivities of the complexes with 8 amidines in benzene/1-pentanol (9:1, v/v) are in the range 12 100–18 400 mol^?1 cm^?1. The simplest compound, N,N-diphenylbenzamidine gives the best sensitivity; the linear range covers 5–90 μg W in 10 ml of final solution; the detection limit is 2 ng W ml^?1. The method is applied to alloy steels.     

Extractive separation and spectrophotometric determination of tungsten as phosphotungsten blue

Phosphotungsten blue is produced by tin(II) reduction of tungstate solution complexed with phosphate at a w/w ratio of W/P = 5, in 4M hydrochloric acid medium, and extracted with isoamyl alcohol; thus tungsten is separated from Fe(III), Ni, Co, Cr(III), V(V), As(V), Sb(III), Bi, Si, U(VI), Ca and Cu(II). In presence of bismuth (0.5 mg/ml), 99.7% W is separated in a single extraction. After alkaline back-extraction, tungsten is determined spectrophotometrically as phosphotungsten blue; it is measured at 930 nm in aqueous solution or at 900-960 nm after isoamyl alcohol extraction, the Beer's law ranges being 0.08-0.6 and 0.16-0.72 mg/ml respectively. The methods are shown to give satisfactory results in the analysis of practical samples containing some milligrams of tungsten.     

Extraction-spectrophotometric determination of amprolium hydrochloride using bromocresol green, bromophenol blue and bromothymol blue

A new procedure for the determination of amprolium hydrochloride by reaction with bromocresol green (BCG), bromophenol blue (BPB) and bromothymol blue (BTB) has been developed. The method consists of extracting the yellow ion-pair formed into chloroform from aqueous medium. The ion-pairs have absorption maxima at 420, 410 and 415 nm with molar absorptivities of 3.64 × 10⁴, 3.12 × 10⁴ and 2.31 × 10⁴1 mol^–1 cm^–1 for BCG, BPB and BTB, respectively. The method obeys Beer's law over the concentration ranges 0.6–12.0, 0.12–8.8 and 1.2–11.3 ag/ml amprolium hydrochloride for BCG, BPB and BTB, respectively. The method is simple, precise (relative standard deviation 0.665–2.210%), accurate (recovery 97.8–100.8%) and easily applied for pharmaceutical quality assurance for amprolium hydrochloride in raw materials and in formulated veterinary soluble powder.     

Extraction-spectrophotometric determination of hydrogen sulphide

A sensitive spectrophotometric method for the determination of trace amounts of hydrogen sulphide (H2S) after fixing in a modified zinc acetate-disodium ethylenediaminetetraacetate-sodium hydroxide solution is described. The fixed H2S is stable for 3 d. The reaction of iodate with H2S in the presence of acid and an excess of chloride leads to the formation of ICI which is stabilised as ICI2-. The species formed reacts with 2',7'-dichlorofluorescein to form 2',7'-dichloro-4',5'-diiodofluorescein which is extracted into a mixture of 15% isoamyl acetate in isoamyl alcohol. The colour system obeys Beer's law in the range 0-2.5 micrograms of H2S. The coefficient of variation is 4.5% for ten determinations of 2.0 micrograms of H2S. The effect of interfering gases on the determination is discussed. The method was applied to the determination of residual amounts of H2S present in a laboratory fume cupboard and the results obtained were compared with those given by the widely used Methylene Blue method. The method can be used to determine down to 0.3 micrograms of H2S.     

Extraction-spectrophotometric determination of small amounts of boron in copper metal and copper-base alloys with methylene blue

A sensitive and rapid spectrophotometric method for the determination of small amounts of boron in copper metal and some copper alloys is described. The method is based on the extraction of a BF(4)(-)-Methylene Blue complex into dichloroethane after decomposition of the sample with hydrogen peroxide and sulphuric acid. The optimum reaction conditions and the influence of alloying elements have been investigated. Boron contents in the range 0.00-0.1% can be determined with a relative error ranging from about 9 to 2%.     

Variamine blue as a gravimetric reagent Determination of tungsten

Tungsten can be precipitated by a solution of Variamine Blue at pH 5. The precipitate is ignited to constant weight at a temperature above 600 degrees and weighed as tungsten trioxide. The method can be used for the determination of tungsten in alloy steels.     

Extraction-spectrophotometric determination of chromium with Nitrotetrazolium Blue

The interaction of Cr(VI) and Nitrotetrazolium Blue has been examined. A 12 NTB (CrO₃Cl)₂ ion-associate is formed and is extractable into 1,2-dichloroethane. The optimum conditions have been established. The molar absorptivity at 260 nm was (8.2 ± 0.06) × 10⁴L mol^–1cm^–1. Beer's law was obeyed in the range 0.01–0.4 g ml^–1 Cr(VI). A sensitive and selective method for determination of micro-quantities of Cr(VI) in soils and steels is suggested.     

Extraction-spectrophotometric determination of thallium in high-purity indium

Trace amounts of thallium in high-purity indium are separated from the matrix by extraction from 6M hydrochloric acid by di-isopropyl ether. On shaking the extract with Brilliant Green in 0.15M hydrochloric acid, an ion-association complex is formed in the organic phase. Interference of other elements is removed by their reduction with metallic copper and scrubbing. The proposed method permits determination of 10(-5)-10(-6)% thallium in high-purity indium with good precision and accuracy.     

Extraction-spectrophotometric determination of mefenamic acid in pharmaceutical preparations

The optimal conditions of the formation and extraction of mefenamic acid ion associates with the astrafloxin polymethine dye are studied. The extraction of ion associates with isooctane-dichloroethane mixtures attains a maximum at pH 9–11 and dye concentration of (5–7) × 10^?5 M. The Beer law is fulfilled in the range 2.0–21.0 μg/mL; the detection limit for mefenamic acid is 0.72 μg/mL. A method is developed for the extraction-spectrophotometric determination of mefenamic acid in pharmaceutical preparations.     

Extraction-spectrophotometric determination of mercury with 1,2,4,6-tetraphenylpyridinium perchlorate

The characteristics of 1,2,4,6-tetraphenylpyridinium perchlorate (TPPP) as a reagent for the formation of ion-pair complexes with metal-bromide anions, and its application to the spectrophotometric determination of mercury are described. This reagent forms a 1:1 complex with bromomercurate(II) ions that is slightly soluble in water and can be extracted with isopentyl acetate. The optimum conditions are about 0.5 M sulphuric acid and 0.03 M potassium bromide. Mercury can be determined at 310 nm in the range 0.04–0.5 μg ml^?1; the apparent molar absorptivity is 2.63 × 10⁴ l mol^?1 cm^?1, and the conditional stability constant is log K - 4.7 ± 0.1 at 20°C. The main interferences are easily removed. Mercury can be determined in sphalerites and zinc amalgams.     

Extraction-spectrophotometric determination of iron with 1,2,4,6-tetraphenylpyridinium perchlorate

Summary In 7M hydrochloric acid medium, iron(III) forms an ion-association compound with 1,2,4,6-tetraphenylpyridinium perchlorate (TPPP) which is extractable into isoamyl acetate. The extracted ionpair, which has an Fe: TPPP mole ratio of 11, is used for the spectrophotometric determination of iron (=3.10×10⁴l·mole^–1· cm^–1) in the concentration range 0.1–1.5g/ml in the organic phase. The interference of a number of foreign ions has been investigated. The method is applicable to the determination of iron in various materials.     

Extraction-spectrophotometric determination of uranium/VI/ with tropolone

Tropolone reacts with uranium/VI/ and forms orange yellow precipitate extractable in chloroform. The maximum absorption occurs at 405 nm and the absorbance is found to remain constant in the pH range of 5.5 to 7.0. Beer's law is obeyed upto 37.6 ppm of U/VI/. The sensitivity of the colour reaction is 0.034 g cm^–2. Most of the common ions do not interfere. The method becomes more selective by masking some of the interfering cations with EDTA. The method was applied to determine uranium in monazite sand.This work is a part of the Ph.D. Thesis.     

Extraction-spectrophotometric determination of anionic surfactants with a flow-injection system

Anionic surfactants are preconcentrated from 5-ml samples by extraction as the ion-pair with ethyl violet into toluene. The absorbance of aliquots of the toluene phase is measured at 610 nm in a flow-injection system. A phase converter is located prior to the injection valve to convert a water stream to, pumped with ordinary pump tubing, to a toluene stream. The working range was 0.01–1.0 mg l^?1 and the reproductibility (r.s.d, n = 10) was 2% for 0.4 mg l^?1 sodium dodecyl sulphate. The non-aqueous flow-injection system serves to miniaturize the extraction from separatory funnel (200 ml) to test tube (10 ml) scale without loss of precision or validity.     

Extraction-spectrophotometric determination of palladium with triphenylphosphine (TPP)

Palladium is extracted with triphenylphosphine (TPP) solution in benzene from hydrochloric acid medium as the PdCl₂ · 2TPP complex showing maximum absorption at 346 nm and a molar absorptivity of ? = 2.26 × 10⁴.The conditions of palladium extraction have been examined and the composition of the extracted species has been found to be PdCl₂ · 2TPP.A 20-fold excess of other platinum and transition metals has no effect on the palladium extraction. Palladium can be determined at platinum concentrations up to 5 mg/ml provided that the result is corrected for the blank. The elaborated method has been applied to the analysis of platinum samples containing not less than 10^?3% of palladium.     

Extraction-spectrophotometric determination of selenium in organoselenium compounds using aromatic o-diamines

Procedures for the extraction-spectrophotometric determination of selenium in organoselenium compounds using a new reagent, 1,2-diamino-3,4,5,6-tetrafluorobenzene (DAFB), and a known reagent, 2,3-diaminonaphthalene (DAN), are developed. Complexes of DAFB or DAN with selenium(IV) are extracted with toluene, and the absorbance of the extracts is measured. The optimal conditions for the determination were found, and the spectrophotometric characteristics were determined. The calibration curves are linear in the range of selenium concentrations of 1–10.6 mg/L (DAFB) and 1–9.1 mg/L (DAN). Nitrogen, chlorine, bromine, fluorine, and sulfur present in organoselenium compounds do not interfere with the determination of selenium. The relative error of determination does not exceed ±2%.     

Extractive separation and spectrophotometric determination of tungsten as ferrocyanide

Tungsten, in amounts ranging from micrograms to milligrams, can be extracted into isoamyl alcohol, as the tungsten(V) ferrocyanide complex obtained by reduction of tungsten(VI) with tin(II) in 4M hydrochloric acid containing ferrocyanide. It can thus be separated from iron, cobalt, chromium, manganese, arsenic, antimony, bismuth, silicon, calcium and copper, their precipitation being prevented by addition of glycerol and, in the case of iron, sulphosalicyclic acid. Molybdenum, vanadium and nickel are not separated from tungsten, however. Tungsten can also be determined spectrophotometrically as tungsten(V) ferrocyanide. The absorbance of the brown complex is measured in aqueous solution or preferably after extraction into isoamyl alcohol. As many alloying elements interfere, they should be separated by the ferrocyanide extraction or other suitable method. Both the separation and the determination methods give satisfactory results with an overall error of not more than 0.5% in the analysis of practical samples containing low or high percentages of tungsten.