ЖУРНАЛ НЕОРГАНИЧЕСКОЙ ХИМИИ, 2013, том 58, № 3, с. 341-347
КООРДИНАЦИОННЫЕ ^^^^^^^^^^^^ СОЕДИНЕНИЯ
УДК 547
DETERMINATION OF MANGANESE(VII) AS 3,3'-DIANISOLE-4,4'-BIS(3,5-DIPHENYLTETRAZOLIUM CHLORIDE) COMPLEX AND ITS APPLICATION © 2013 г. D. Kostova*, D. Mehandjiev**
*Agricultural University, Plovdiv, Bulgaria E-mail: deny_kostova@yahoo.com **Bulgarian Academy of Sciences, Institute of Catalysis, Sofia Поступила в редакцию 02.12.2011 г.
A simple, rapid, selective and sensitive spectrophotometry method is described for the determination of trace amounts of manganese using Blue tetrazolium chloride as a chromogenic reagent. The method is based on the formation of ion-associate complex between manganese(VII) and the cation of ditetrazolium salt, having an absorption maximum at 255 nm. Beer's law is obeyed in the range of 0.1—1.6 ^g ml-1. The molar absorptivity and Sandell's sensitivity were found to be 4.97 x 104 l mol-1 cm-1 and 1.11 x 10-3 p.g cm-2, respectively. Limit of deterction is 6.86 ng ml-1 Mn(VII) and limit of quantitation is 22.8 ng ml-1 Mn(VII). Optimum reaction conditions were evaluated. The effect of interfering ions on the determination is described. The extraction, distribution and association constants, and the recovery factor have been calculated.
Keywords: manganese, blue tetrazolium chloride, soils, steels
DOI: 10.7868/S0044457X13030082
INTRODUCTION
Manganese plays a complex role in our ecosystems. The element has multiple roles metallurgical^, it is a cofactor of enzymes which are essential in plants and animals, and in recent years manganese has been recognized as important in human health.
Manganese is an essential element, which plays an important role in activation of many enzymes involved in metabolic processes. Manganese is involved in many physiological processes particularly in metabolism of proteins, carbohydrates, lipids. It is the cofac-tor of enzymes such as glutamine synthetase and de-carboxylase [1—4]. Manganese is most abundant in soils developed from rocks rich in iron owing to its association with this element [5]. Organic chelates derived from microbial activity, degradation of soil organic matter, plant residues, and root exudates can form metal complexes with micronutrient cations, and thereby increase manganese cation solubility and mobility [6]. Manganese toxicity is a major problem worldwide and occurs mainly in poorly drained acid soils [7].
A number of spectrophotometric methods based on complex formation are used for the determination of manganese. Owing to their low sensitivity and selectivity, preconcentration and/or separation steps are
usually necessary. The reagents suggested for spectro-photometric determination of manganese include: [a,P,y,S-tetrakis(4-carboxyphenyl)porphine (T(4-CP)] [8]; tris(2,2'-bipyridine)osmium(II) [9]; 2',4'-di-hidroxi-azo-benzene-4-sulphonic acid [10]; 3,4,5,6-tetrafluoro-2-carboxyphenyl-fluorone [11]; 1-(2-py-ridylazo)-2-naphthol [12]; triphenylphosphonium [13]; isophtaldihydroxamic acid [14]; 1,10-phenant-roline [15, 16]; 8-hydroxyquinoline [17]; 4-(2-pyridyl-azo) resorcinol [18]; 1-(2-pyridylazo)-2-naphthol [19, 20]; N-diphe-nylbenzamidine [21]; 2,3-dihy-droxinaphthalene [22]; triphenyltetrazolium chloride [23]; thiazolylblue tetrazolium bromide [24]; crystal violet [25]; toluidine blue [26]; methyl violet [27]. Some of the above mentioned extraction methods are characterized by a long procedure, are not very selective [15—20], low stability of the complexes obtained [13, 14], low sensitivity [14, 22-27].
This paper describes a sensitive and extremely simple spectrophotometric method for the determination of microquantities of manganese(VII) as 3,3'-Diani-sole-4,4'-bis (3,5-diphenyltetrazolium chloride) complex. The goal is to develop an extraction method using BTC for determination of manganese in soils and steels, superior, in some respects, to the existing methods.
EXPERIMENTAL
Reagents and apparatus
Analytical grade reagents and de-ionized distilled water were used throughout.
Blue tetrazolium chloride. 3,3'-Dianisole-4,4'-bis(3,5-diphenyltetrazolium chloride) (Blue tetrazolium chloride, BTC, Fluka). A 1 x 10-3 mol l-1 aqueous solution was prepared by dissolving 0.0364 g of BTC in 50 mL of distilled water. Other BTC concentrations were prepared by appropriate dilution. The solutions were stable for months.
Stock manganese(VII) solution. A 1 x 10-2 mol l-1 aqueous solution was prepared by dissolving 0.395 g of KMnO4 in 250 ml of distilled water. After 10 days the exact concentration of manganese(VII) was checked titrimetrically using oxalate titration. Working solutions containing 1.98 x 10-4 mol l-1 Mn(VII) were prepared by dilution.
Buffer solutions. Buffer compositions were as follows: buffers of pH 1, 2, 3 were of glycocoll plus HCl; buffers of pH 4, 5 were of acetic acid glacial plus NaOH; buffers of pH 6, 7 were of KH2PO4 plus Na2HPO4.
Foreign ion solutions. Solutions of diverse ions for interference studies were prepared by dissolving the amount of each compound needed to give 10 mg ml-1 concentration of the ion of interest.
1,2-Dichloroethane, p.a.; Hydrochloric, nitric, phosphoric, perchloric and sulphuric acids at concentrations of1.2, 1.55, 2, 0.9, 2 mol l-1, respectively, were used.
Absorbance measurements were made a spectrophotometer UV-VIS (Carl Zeiss, Germany) with 1 cm quarts cuvette.
The infrared spectra in the interval 4000-500 cm-1 are measured by means of Fourie spectrophotometer Bruker IF S 25 with a dividing ability <2 cm-1. The spectra are taken in tablets with a matrix of KBr.
Procedures
General procedure for the determination of manga-nese(VII). An aliquot of a sample solution containing 1-16 ^g of manganese(VII) was transferred into 100 ml separatory funnel. Add 2 ml of BTC 1 x x 10~4 mol l-1, 0.5 ml of sulphuric acid 2 mol l-1. The resulting solution was diluted with distilled water to a total volume of 10 ml. Then 3 ml of 1,2-dichloroet-hane was added, and the funnels were shaken for 15 s. Transfer the organic layer through a dry filter paper into a 1 cm cuvette and measure the absorbance at 255 nm against a reagent blank similarly prepared.
Procedure for determination of the distribution constant. The following solutions are introduced into 100 ml separating funnels: 0.4 ml of 1 x 10-3 mol l-1 BTC, 0.5 ml of sulphuric acid 2 mol l-1, and the cor-
responding amounts of manganese(VII). The volume of the aqueous phase is brought to 10 ml with distilled water. It is extracted with 3 ml of 1,2-dichloroethane for 15 s. After the separation of the two phases the organic phase is transferred through filter paper into a standard flask of 25 ml and is diluted to the mark with 1,2-dichloroethane. The light absorption ofthe organic phase is measured at X = 255 nm with a 1-cm light path cuvette. The absorbance (A) was measured, against a reagent blank prepared in the same way (without manganese present).
The distribution constant KD was found from the ratio KD = A/(Amax - A) where A is the light absorption for a single time extraction (at the optimum conditions) and Amax is the light absorption for three times extractions under the same conditions.
Procedure for a synthesis of oxo-complex of Mn(VII) with BTC used for IR spectrum. 100 ml
0.1 mol l-1 solution of potassium permanganate should be prepared, and 15 ml 2 mol l-1 solution of sulphuric acid should be added to it. It should be stirred with a magnetic stirrer and to this solution should be added 50 ml 1 x 10-2 mol l-1 solution of BTC. Thus the obtained mixture should be stirred with a magnetic stirrer for 1 h and 30 min so that some grounds could be obtained. After that the obtained grounds should be filtered through a filter G4, and dried in a room temperature.
Determination of manganese in steels. Dissolve a 0.1 g sample of the steel in 30 ml of a 1 : 3 v/v mixture of 1 : 1 v/v nitric acid and 1 : 1 v/v hydrochloric acid. Cool, add 10 ml of concentrated sulfuric acid and evaporate until SO3 fumes appear. Cool, take up the salts in water, and dilute to volume in a 100 ml standard flask. Oxidize a suitable aliquot as described above for soil samples. To a suitable aliquot of the resultant solution add 2 ml of BTC 1 x 10-4 mol l-1, 0.5 ml of sulphuric acid 2 mol l-1, 2 ml of saturated tar-trate solution (to mask any interfering ions) and dilute to10 ml with distilled water. Extract the ion associate and complete the determination as for soil analysis.
Determination of manganese in soils. 4 g of the air-dried soil sample is weighed and introduced into a platinum crucible, then heated for 3 hrs in a muffle furnace at 500-550°C to digest the organic matter. After cooling, the sample is transferred into a platinum bowl and 5 ml of concentrated H2SO4, 5 ml of concentrated HNO3 and 2 ml H2O2 are added. The sample was heated until the white fumes of SO3 appeared. Next, 1 ml of H2SO4 and 3 ml of HNO3 was added and evaporated to dryness. 5 ml of concentrated HCl and 2 ml of concentrated HClO4 were added to the dry residue, then heated to dryness evaporating chromium as chromylchloride with distraction of the organic compounds [28]. The dry residue is then dissolved in distilled water and acidified with hydrochloric acid. The solution obtained is then neutralized with concentrat-
1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1
0
100 200 300 Wavelengtn, nm
400
Fig. 1. Absorption spectra in 1,2-dichloroethane of ion-associ-
ation complex (1) and BTC (2); CMn(VII) = 2 x 10-5 mol l
-H2SO4
0.1 mol l-1, C
BTC =
1 x 10-5 mol l-1.
4000 3500 3000 2500 2000 1500 1000 500 Wavenumber, cm-1
ed ammonia solution to precipitate the iron(III) as the hydroside. The precipitate is filtered through filter paper and the filtrate is evaporated until the volume is about 30 ml. 3 ml of concentrated H2SO4, 2 ml of concentrated H3PO4 and 0.1 g of potassium periodate are added, the solution is heated to the boiling point and the temperature maintained for
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