SummaryUse of HMPA in Co(II) thiocyanate colour system gives a simple, sensitive and selective method for the determination of Co(II). Maximum colour intensity is attained in the acidity range of 0.15–0.75M HCl and thiocyanate concentration of 0.5–1.0M. The colour is completely extractable into chloroform, when 2 to 4 ml HMPA is used. The colour system shows maximum absorption at 610 nm. The Beer's law range is 2 to 52μg Co/ml with optimum concentration range of 6–48μg Co/ml. The molar absorptivity and sensitivity are 1.24 x 103 l·mole−1·cm−1 and 0.047μg Co/cm2 respectively. The method has been applied to the determination of cobalt in steel.ZusammenfassungAuf der Grundlage der Farbreaktion von Kobalt(II)thiocyanat mit HMPA wurde eine einfache, empfindliche und selektive Methode zur Bestimmung von Co(II) entwickelt. Das Farbmaximum erhält man in 0,15–0,75M salzsaurer Lösung bei 0,5–1,0M Thiocyanat-Konzentration. Die Färbung ist mit Chloroform vollständig extrahierbar, wenn 2—4 ml HMPA verwendet werden. Die maximale Absorption liegt bei 610 nm. Der optimale Konzentrationsbereich liegt zwischen 6 und 48μg Co/ml. Die molare Absorption beträgt 1,24 x l03l·mole−1·cm−1, die Empfindlichkeit 0,047μg Co/cm2. Die Methode wurde zur Bestimmung von Kobalt in Stahl verwendet.

Liquid-liquid extraction of cobalt(II) thiocyanate with hexamethyl phosphoramide: Direct spectrophotometric determination in the organic phase@@@Flssig-flssig-Extraktion von Kobalt(II)thiocyanat mit Hexamethylpbos-phoramid (HMPA) und spektrophotometrische Bestimmung in der organischen Phase

Ru(III)-thiocyanate has been extracted with hexamethylphosphoramide (HMPA) in methyl isobutyl ketone (MIBK). Thus the extractability, sensitivity and selectivity are improved over the simple binary Ru(III) thiocyanate system in spectrophotometric determination of ruthenium in the organic phase. The maximum colour develops on the steam bath, at the acidity range of 1.5–2.5M with HCl and ammonium thiocyanate concentration range of 0.25–0.5M. The colour is completely extractable in MIBK when 1.5–3.0 ml HMPA is used and show maximum absorbance at 570 nm. The colour system obeys Beer's law for 0.7–13 νg Ru/ml and the optimum concentration range is 2–13 νg/ml. The molar absorptivity and sensitivity are 69401-mole−1 cm−1 and 0.0145 νg/cm2 respectively. The percent relative error is 2.72%. The method is very simple and does not require oxidation and subsequent distillation. The method can be applied in the presence of osmium.

Liquid-liquid extraction of ruthenium(III) thiocyanate with hexamethylphosphoramide: Direct spectrophotometric determination in the organic phase

Chapter 18 – Cobalt

Thiothenoyltrifluoroacetone (1,1,1-trifluoro 4-(2-thienyl) 4-mer-captoput-en-3-2-one) is used for the simultaneous extraction and spectrophotometric determination ofμg amounts of cobalt(II). 10 ml of 0.001M STTA in carbon tetrachloride quantitatively extracts, at pH 6.5, 20μg of cobalt(II) as red orange colored complex which can be measured photometrically at 490 nm. The system conforms to Beer's law in the concentration range of 0.5–6.0μg/ml of Cobalt(II). Studies on the effect of varying volume and concentration of the reagent, stability of the complex, and the period of equilibration were also reported. It is possible to extract and determine cobalt(II) quantitatively in the presence of large number of cations and anions. The method can be made selective by making use of appropriate masking agents.

R. R. Mulye

Papers

Simultaneous extraction and spectrophotometric determination of cobalt(ii) with thiothenoyltrifluoroacetone