H. Sanke Gowda

Spectrophotometric method for the determination of phenothiazines and its application to phenothiazine drugs

A method for the spectrophotometric determination of four phenothiazines (promazine hydrochloride, mepazine hydrochloride, chlorpromazine hydrochloride and prochlorperazine maleate), based on the coloured compounds formed between the phenothiazines and molybdoarsenic acid, is described. The infrared and electron spin resonance spectra of these coloured compounds showed that the molybdoarsenic acid oxidises phenothiazines to a radical cation with which it subsequently forms the coloured compound. The method is simple and rapid. The influence of the substrates commonly employed as excipients with phenothiazine drugs was studied. The proposed method has been applied to the analysis of commercial phenothiazine-containing preparations, the results of which are in good agreement with those obtained by the official method of the British Pharmacopoeia.

Thioridazine hydrochloride as a new reagent for the spectrophotometric determination of chromium

Thioridazine hydrochloride is proposed as a new sensitive and selective reagent for the spectrophotometric determination of chromium. The reagent forms a blue coloured radical cation with chromium(VI) instantaneously at room temperature in 1–4 mol l–1 orthophosphoric acid medium. The blue species exhibits an absorption maximum at 640 nm with a molar absorption coefficient of 2.577 × 104 I mol–1 cm–1. A 27-fold molar excess of the reagent is necessary for the development of the maximum colour intensity. Beers law is obeyed over the concentration range 0.05–2 ppm of chromium(VI) with an optimum concentration range of 0.2–1.6 ppm. The effects of acidity, time, temperature, order of addition of reagents, reagent concentration and the tolerance limit of the method towards various cations and anions usually associated with chromium are reported. The method has been used successfully for the determination of chromium in chromium steels.

Simultaneous spectrophotometric determination of palladium(II) and gold(III) with methiomeprazine hydrochloride: analysis of alloys and minerals

Methiomeprazine hydrochloride (MMH) is proposed as a reagent for the simultaneous spectrophotometric determination of palladium(II) and gold(III). The reagent instantaneously forms an orange-red 1:1 complex with palladium(II) and a blue species with gold(III) in hydrochloric acid-sodium acetate buffer. The palladium-MMH complex has an absorption maximum at 480 nm with a molar absorptivity of 3.6 × 103 l mol–1 cm–1. The blue species has an absorption maximum at 630 nm with a molar absorptivity of 1.3 × 104 l mol–1 cm–1. Beers law is obeyed for the range 0.4–21 p.p.m. of palladium(II) and 0.2–10 p.p.m. of gold(III). Molar excesses of 4-fold and 35-fold of the reagent are required for palladium(II) and gold(III), respectively. The concentration of two metals in an unknown mixture can be simultaneously determined in the range of 0.5–15 p.p.m. of palladium(II) and 1–10 p.p.m. of gold(III) using the following equations: [Pd]× 104= 3.023A480– 0.840 3A630[Au]× 104= 0.8177A630– 0.195 9A480 The method has been used successfully for the determination of palladium and gold in alloys and minerals.

Vanadametric estimation of hypophosphite and phosphite

1. New methods have been developed for the estimation of hypophosphorous (A) and phosphorous acids (B). These methods consist in allowing a measured volume of (A) or (B) to react with excess of a standard solution of vanadate at the boiling water bath temperature for about fifteen minutes in the presence of silver sulphate as catalyst and the appropriate concentration of sulphuric acid. The mixture is cooled and then titrated with a standard solution of Mohrs salt to determine the unreacted vanadate. 2. A mechanism has been suggested for the catalysis by silver sulphate.Summary1.New methods have been developed for the estimation of hypophosphorous (A) and phosphorous acids (B). These methods consist in allowing a measured volume of (A) or (B) to react with excess of a standard solution of vanadate at the boiling water bath temperature for about fifteen minutes in the presence of silver sulphate as catalyst and the appropriate concentration of sulphuric acid. The mixture is cooled and then titrated with a standard solution of Mohrs salt to determine the unreacted vanadate.2.A mechanism has been suggested for the catalysis by silver sulphate.

Spectrophotometric method for the rapid determination of microgram amounts of platinum

10-[3-(4-Methyl-1-piperazinyl)propyl]phenothiazine dimalonate (perazine) forms a yellowish brown complex with platinum(IV) at room temperature (27 ± 1 °C) in orthophosphoric acid medium containing copper as catalyst. The complexation is complete within 1 min. The complex exhibits an absorption maximum at 512 nm with a molar absorptivity of 1.6 × 104 1 mol–1 cm–1. Beers law is valid over the concentration range 0.4–6.8 p.p.m. A 50-fold molar excess of the reagent is necessary for the full development of the colour intensity. Calculations by Jobs method of continuous variation, the molar-ratio method and the slope-ratio method indicate a 1 + 1 composition for the complex. The effects of acidity, time, temperature, reagent concentration, order of addition of reagents and the interferences of various ions are reported. The reagent has been used successfully for the determination of platinum in minerals and alloys.

Vanadametry Estimation of Thiosulphate

Abstract 1.(a) We have found that sodium thiosulphate is quantitatively oxidized to tetrathionate in five minutes at room temperature (28°) by excess sodium vanadate in a medium containing sulphuric acid at 0.06 N to 0.1 N concentration and a little copper sulphate as catalyst. (b) Quantitative emulation of sodium thiosulphate to tetrathionate has also been achieved by the action of excess sodium vanadate during five minutes at room temperature in a medium containing 2.0 N —8.0 N acetic acid and a little copper salt as catalyst. Further oxidation to sulphate does not occur, even if the mixture is heated to boiling. (c) The excess of unreacted vanadate in 1(a) and 1(b) can be titrated with a standard solution of ferrous ammonium sulphate using diphenylbenzidine as indicator, after adding the requisite quantity of syrupy phosphoric acid. 2. On the other hand, sodium thiosulphate is easily and quantitatively oxidized to sulphate at room temperature, when. acted upon by excess sodium vanadate in a medium containing hydrochloric acid at an overall concentration of 5-6 N and 1.0 ml of iodine monochloride as catalyst. The time required for reaction is ten minutes. The unreacted vanadate can be estimated by titration with a standard solution of ferrous ammonium sulphate, using N-phenylanthranilic acid as indicator or with diphenylbenzidine as indicator after suitably diluting and adding phosphoric acid.

N-substituted phenothiazines as redox indicators in titrations with N-bromosuccinimide

Butaperazine dimaleate, trifluoperazine dihydrochloride, diethazine hydrochloride, promethazine hydrochloride, prochlorperazine maleate and chlorpromazine hydrochloride are proposed as redox indicators in the macro- and micro-titration of hydroquinone, Metol (N-methyl-4-aminophenol sulphate) and ascorbic acid with N-bromosuccinimide in hydrochloric, sulphuric and acetic acids. They give very sharp and reversible colour changes at the equivalence point. A simple titrimetric method for the determination of hydroquinone, Metol and ascorbic acid and a potentiometric method for the determination of Metol are described.

Naphthidines and o-dianisidine as redox indicators in titrations with N-bromosuccinimide

The optimum conditions for the successful use of naphthidine, 3,3′-dimethyl-naphthidine, 3,3′-dimethylnaphthidinedisulphonic acid and o-dianisidine as indicators in macro- and micro-titrations of hexacyanoferrate(II), iron(II), hydroquinone, metol and ascorbic acid with N-bromosuccinimide have been established. The indicators give a very sharp reversible colour change at the equivalence point and have advantages over the existing redox indicators. Hydrazinium sulphate and hydroxylammonium chloride have been determined indirectly. Anhydrous hexacyanoferrate(II) and iron(II) are suggested for the standardisation of N-bromosuccinimide solutions.

Promethazine hydrochloride as indicator in cerimetry

Promethazine hydrochloride (I) was used as indicator in ceriometric titrns. of Fe(II), U(IV), and hydroquinone in dil. H2SO4-H3PO4. I undergoes a reversible 1-electron oxidn. to a red radical, which is oxidized irreversibly to a colorless sulfoxide with the loss of another electron. The redox potential is 842-83 mV in 0.25-1.5M H2SO4. The max. errors in the titrns. of Fe 5-113, U 24-247, and hydroquinone 5-112 mg were 0.03, 0.12, and 0.05 mg, resp. The sensitivity of I to oxidizing agents decreases in the order MnO4- > BrO3- > V5+ > Cr2O72- > Ce4+ > IO3- > [Fe(CN)6]3-. [on SciFinder(R)]

3,3′-Dimethylnaphthidinedisulphonic acid as a selective and sensitive reagent for the spectrophotometric determination of vanadium(V) and its application to vanadium-bearing minerals and alloys

3,3′-Dimethylnaphthidinedisulphonic acid is proposed as a selective and sensitive reagent for the spectrophotometric determination of vanadium(V). It forms a violet coloured species with vanadium(V) in 8–13 M orthophosphoric acid medium. A 2-fold molar excess of reagent is necessary for the full development of the colour. The violet species exhibits an absorption maximum at 555 nm with a molar absorptivity of 1.94 × 104 l mol–1 cm–1. Sandells sensitivity is 2.6 ng cm–2. Beers law is obeyed for the range 0.08–3.5 p.p.m. of vanadium(V) with an optimum concentration range of 0.1–3.1 p.p.m. The proposed method offers the advantages of simplicity, high sensitivity, good selectivity and the opportunity to carry out the determination at room temperature without the need for an extraction step. The method has been used successfully for the determination of vanadium in ilmenite and vanadium steels.