Method of determining iron (ii)

FIELD: chemistry.

SUBSTANCE: method includes the preparation of a sorbent, solution of iron (III, II), addition of a hydroxylamine solution to reduce iron (III) to iron (II), extraction of iron (II) from the solution by the sorbent, transfer of iron (II) in a complex compound on the sorbent surface, separation of the sorbent from the solution, measurement of the coefficient of diffusion reflection of the surface iron (II) complex and determination of the iron content by a calibration graph, with the application as the sorbent of aluminium oxide, successively modified by polyhexamethyleneguanidine and 3-(2-pyridyl)-5,6-diphenyl-1.2,4-triazine-4',4''-disulphoacid (ferrozine), with carrying out the measurement of a diffusion reflection coefficient at 560 nm.

EFFECT: increased sensitivity and self-descriptiveness of the analysis.

4 ex

 

The invention relates to the field of analytical chemistry, namely to methods of iron determination, and can be used in its definition in technological solutions, natural and industrial waters.

For the determination of iron (II) objects of different material composition is widely used sorption-photometric method based on the sorption selection of iron (II) sorbents, with functional groups which iron (II) forms an intensely colored complexes, and subsequent determination of the photometric method directly in the phase sorbent. Sorption-photometric method with a lower limit of detection elements and higher selectivity compared to the photometric determination of iron (II) in solutions.

For sorption-photometric determination of iron (II) is the most widely as the organic reagents used Ν-heterocyclic bases (1,10-phenanthroline, 2,2'-dipyridyl and their derivatives) fixed on the surface of solid matrices of different nature. These reagents form with iron (II) intensely colored complex compounds, which allows to achieve high sensitivity for determination of iron (II).

The known method of determination of iron in the form of a complex of iron (II) with 1,10-phenanthroline on kationoobmena�Kah KU-2 and CB-4, used as sorbents [Ulyukaev A. F. Testing and chromaticity determination of iron (II, III) in the form of sorbate phenantroline iron (II) / A. F. Ulyukaev, V. M. Ivanov, A. G. Cycerin / Journal of analytical chemistry, 2002. - Vol. 57, No. 11. P. 1197-1201].

The method involves the following operations:

- to a solution of iron (II, III) was added 10% solution of ascorbic acid for reduction of iron (III) to iron (II);

- administered acetate sodium buffer solution;

- add 2 ml of 4.26·10-3Μ solution of 1,10-phenanthroline;

- administered 0.3 g of sorbent Latinoamerica KU-2 or CB-4;

- intensively stirred;

- sorbate was filtered on a glass filter;

- measure the coefficient of diffuse reflection or chromaticity function.

The iron content found on the calibration schedule is constructed in a similar situation. The detection limit of iron is 2.5 µg/l in the solution volume of 20 ml and the mass of the sorbent 0.3 g.

The disadvantage of this method is preventing the influence of non-ferrous metals (Cu, Ni, Zn, Co) on the interaction of iron (II) with 1,10-phenanthroline.

The known method of determination of iron with the use of composite films on the basis of silicon oxide [Najafova O. Y. Optimization and application of composite coatings based on silicon oxide and polyvinylacetate for sorption-spectrophotomet�algebraic definition of phenantroline iron (II) and zinc (II) / O. Yu. Najafov, M. V. Drozdova, E. V. Heaven, Ishchenko, V. B. //Journal of analytical chemistry, 2007. - Vol. 62, No. 12. P. 1259-1266], which provides for the following operations:

- obtaining composite coatings: the Sol solution, the synthesis was carried out using acid hydrolysis of triethoxysilane (TEOS) in the presence of nonionic surfactant Tween 20 adding an aqueous solution of polyvinylacetate (PVA) in a volume ratio of Sol: PVA=1:1, applied on glass, which are air dried during the day, then glass with applied films soaked in 10 ml of a mixture (7:3) ethanol-water;

- to a solution containing iron, add a 0.01 M solution of 1,10-phenanthroline, acetate buffer solution with pH=5,0-5,5 and water to a total volume of 5 ml;

- in the resulting solution for 10 min down the glass, film-coated;

- glass removed, rinsed with bidistilled water;

- measure the optical density of the glasses at 490 nm.

The iron content found on the calibration schedule is constructed in a similar situation. The range of linearity of calibration curve for iron (II) from 0.2 to 5.6 mg/l solution of 5 ml. detection Limit for the preconcentration of iron from 5 ml of the solution is 0.18 mg/L.

The disadvantages of the method include the high detection limit and narrow the range of the designated contents, the complexity and length�alnost preparation of modified glasses the inability to use the films in the dynamic variant sorption concentration.

Closest to the proposed method to the technical essence and achieved result is a method for the determination of iron (II) [RU No. 2374639, G01N 31/22, publ. 27.11.09], which provides the following operations:

- preparation of the sorbent based on sequential processing of silica with aqueous solutions of polyhexamethylenguanidine and 4,7-dimethyl-1,10-financialincentives;

- entering into a graduated test tube of solution of iron (II), a 0.01 M solution of hydroxylamine, add NaOH to pH=4-7 and water to a total volume of 10 ml;

- the introduction of 0.1 g of sorbent and intensive agitation;

- separation of the sorbent from the solution by decantation, drying in air;

- measurement of diffuse reflection coefficient at 530 nm ;

- determination of iron content on the calibration schedule.

The technical result is to reduce the detection limit and the extension of the range of the designated contents.

Said technical result is achieved in that in the method of determination of iron (II), comprising preparing a sorbent, a solution of iron (III, II) adding a solution of hydroxylamine for reduction of iron (III) to iron (II), extraction of iron (II) from solution by the sorbent, the conversion of iron (II) in Ko�complex compound on the surface of the sorbent, the separation of the sorbent from the solution, the measurement of the coefficient of diffuse reflection of the surface complex of iron (II) and determination of iron content on the calibration chart, what is new is that as the sorbent used is aluminum oxide, consistently modified polyhexamethylenguanidines and 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine-4',4"-disulphonate (is ferrozine), and the measurement of the coefficient of diffuse reflection is carried out at 560 nm.

The features distinguishing the claimed technical solution from the prototype, not identified in other technical solutions in the study data and related areas of technology and, therefore, provide the claimed solution according to the criteria of "novelty" and "inventive step".

The essence of the method lies in the fact that in the solution with pH=2.5 to 6.5 iron (II) quantitatively (the degree of extraction is 99%) is extracted by the sorbent, which is used as the aluminum oxide, successively modified polyhexamethylenguanidines and 3-(2-pyridyl)-5,6-diphenyl-1,2,4-thiazin-4',4"-disulphonate (is ferrozine).

Sorption of iron (II) in the static mode is fast - the time of the establishment of sorption equilibrium does not exceed 10 min. In the process of sorption on the surface of the sorbent is formed is colored purple, the complex of iron (II) with ferrozine, they�describing the maximum in the spectrum of diffuse reflection, situated at 560 nm.

The method is as follows.

For the synthesis of the sorbent to 10 g of alumina was added 100 ml of 2% solution of polyhexamethylenguanidine and stirred for 5 min, the alumina was separated from the solution by decantation and washed with distilled water. Then treated polyhexamethylenguanidines alumina treated with 2·10-4Μ's solution ferrozine and intensively stirred for 5 min, the Sorbent is separated from the solution by decantation, washed with distilled water and dried on the air.

In the test solution with pH=2.5 to 6.5, containing iron (III, II), add 1 ml of a 0.1 M solution of hydroxylamine for reduction of iron (III) to iron (II) introduce 0.1 g of sorbent is alumina, consistently modified polyhexamethylenguanidines and ferrozine, stirred for 10 min.

The sorbent was separated from the solution by decantation, placed in a Teflon cuvette and measure the diffuse reflection coefficient at 560 nm.

The iron content found on the calibration schedule is constructed in a similar situation. The limit of detection of 0.007 μg of iron of 0.1 g of sorbent, which is 3 times less than the detection limit achieved by the known method (prototype).

This amount of iron is the minimum concentration that can be displayed�to on a given sorbent suspension on existing devices relative to the background signal regardless of the method of concentrating iron (static or dynamic mode). The use of dynamic mode sorption allows concentration of iron (II) used on the mass of the sorbent from large volumes of solutions. Thus, the sorption of iron from 10 ml of a solution relative detection limit of iron is 7·10-4μg/ml, while the sorption of 100 ml of solution - 7·10-5μg/ml (7·10-5mg/l). Thus, the iron content determined by the inventive method, in an arbitrary volume of the solution should not be less than 0.007 μg. Calibration curve linearity is maintained up to 8 µg of iron of 0.1 g of sorbent.

Example 1 (prior art). In solution containing 1.0 μg of iron (II), pour 1 ml of 0.1 M hydrochloric acid hydroxylamine, NaOH to pH=4-7, introduce 0.1 g of silica, consistently modified polyhexamethylenguanidines and 4,7-dimethyl-1,10-financialincentives, intensively stirred for 5 min, the sorbent is separated from the solution by decantation, placed in a Teflon cuvette and measure the diffuse reflection coefficient at 530 nm.

The iron content found on the calibration schedule is constructed in a similar situation. Was found to be 0.97±0.05 mg.

Example 2 (the proposed method). To 10 ml of solution with a pH=2.5 to 6.5, containing 0.25 μg of iron, administered 1 ml of 0.1 M hydrochloric acid hydroxylamine, contribute sorbent alumina, consistently modified polyhexamethylenguanidines and Ferros�nom, intensively stirred for 10 min, the sorbent is separated from the solution by decantation, placed in a Teflon cuvette and measure the diffuse reflection coefficient at 560 nm.

The amount of iron found by calibration schedule is constructed in a similar situation. Found 0,26±0,02 g.

Example 3 (the proposed method). To 10 ml of solution with a pH=2.5 to 6.5, containing 2.5 mg of iron, administered 1 ml of 0.1 M hydrochloric acid hydroxylamine, contribute sorbent alumina, consistently modified polyhexamethylenguanidines and ferrozine, intensively stirred for 10 min, the sorbent is separated from the solution by decantation, placed in a Teflon cuvette and measure the diffuse reflection coefficient at 560 nm.

The amount of iron found by calibration schedule is constructed in a similar situation. Found 2,48±0,04 µg.

Example 4 (the proposed method). To 500 ml of an aqueous solution with pH=2.5 to 6.5, containing 0.1 µg of iron, administered 1 ml of 0.1 M hydrochloric acid hydroxylamine, and pass this solution through a chromatographic column containing 0.1 g of sorbent, at a speed of 5 ml/min, the Sorbent is removed, placed in a Teflon cuvette and measure the diffuse reflection coefficient at 560 nm.

The amount of iron found by calibration schedule is constructed in a similar situation. Found 0,11±0,03 µg.

Character way�ized high sensitivity and ease of implementation. The use of aluminum oxide-modified polyhexamethylenguanidines and ferrozine, reduces the relative limit of detection of iron (II) in 3 times, to extend the range of detectable concentrations in comparison with the prototype.

The increase in intensity of colouring of the sorbent by increasing the concentration of iron on its surface allows the use of the sorbent as a test tool for Express determination of iron.

Method for determination of iron (II), comprising preparing a sorbent, a solution of iron (III, II) adding a solution of hydroxylamine for reduction of iron (III) to iron (II), extraction of iron (II) from solution by the sorbent, the conversion of iron (II) complex compound on the surface of the sorbent, separation of the sorbent from the solution, the measurement of the coefficient of diffuse reflection of the surface complex of iron (II) and determination of iron content on the calibration schedule, characterized in that as a sorbent use aluminum oxide, consistently modified polyhexamethylenguanidines and 3-(2-pyridyl)-5,6-diphenyl-1.2,4-triazine-4',4"-disulphonate (is ferrozine), and the measurement of the coefficient of diffuse reflection is carried out at 560 nm.



 

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