RU2563984C1 - Method of separating and determining iron (iii) and iron (ii) - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method includes preparing a solution containing iron (III) and iron (II), creating the necessary pH, reacting the solution with a sorbent, measuring the diffuse reflection factor at 500 nm and determining iron content from a calibration curve, where in order to separate iron from the solution in different oxidation states, the sorbent used is silica which is successively modified with polyhexamethylene guanidine and pyrocatechol-3,5-disulphonic acid, wherein iron (III) is separated from the solution with pH=3, and then iron (II) from the solution with pH=6.

EFFECT: high information value and reliability of analysis.

1 ex

Description

The invention relates to the field of analytical chemistry of elements, namely to methods for the separate determination of iron (II) and iron (III), and can be used in their determination in natural and man-made waters.

To determine iron (III) and iron (II) in objects of various compositions, the photometric method is used, based on measuring the color intensity of complexes of iron (III) and iron (II) with organic and inorganic reagents.

Photometric methods for determining iron in solutions using various reagents, in particular N-heterocyclic bases, are based on determining the concentration of iron (II), reducing iron (III) present in solutions to iron (II), and determining the total iron content. The iron (III) content is found as the difference between the total iron content and the iron (II) content. The methods do not allow individual determination of iron (III) and iron (II) in one sample of the solution.

To determine iron (III) and iron (II) in one sample solution, a mixture of two reagents is used, one of which selectively interacts with iron (II) - in most cases these are N-heterocyclic bases, and the other with iron (III).

A known method for the determination of iron (III) and iron (II) in the flow-injection variant, based on the formation of complexes of iron (II) with thiocyanate ions, and iron (II) with 1,10-phenatrolin [Lineh TP, Kernogham NJ, Wilson JN Speciation of metals in solution by flow injection analysis. Part 2. Determination of iron (III) and iron (II) in mineral process liquors by simultaneous injection into parallel stream // Analyst. 1984. V. 109. No. 7. P. 843-846].

The method involves passing solutions with a volume of 20 μl with a frequency of 120 injections per hour through two parallel capillaries. A solution of thiocyanate ions is introduced into one capillary to determine iron (III), and into another, a solution of 1,10-phenanthroline to determine iron (II). The method allows to determine 0.5-180 μg / ml of iron (III) and 0.5-120 μg / ml of iron (II).

A known method for the determination of iron (III) and iron (II), based on the formation of complexes of iron (III) with salicylic acid, and iron (II) with 1,10-phenatrolin [Safavi Α., Abdollahi Η. Application of Η-point standard addition method to the speciation of Fe (II) and Fe (III) with chromogenic mixed reagents // Talanta. 2001. V. 54. P. 727-734].

The method is based on adding to a solution containing iron (III) and iron (II), a mixture of salicylic acid reagents and 1,10-phenatrolin. The optical density of the solution is recorded at 460 and 530 nm when iron (III) is added to the solution and at 535 and 540 nm when iron (II) is added to the solution. Using a mathematical algorithm and determined the content of iron (III) and iron (II). The range of determined iron (II) contents is 0.2-5.0 μg / ml, iron (II) is 0.5 m-25 μg / ml.

A known method for the determination of iron (III) and iron (II) in the flow-injection variant, based on the formation of complexes of iron (III) with sulfosalicylic acid, and iron (II) with 1,10-phenatrolin [Kozak J., Gutowski J., Kozak Μ., Wieczorek Μ., Kościelniak P. New method for simultaneous determination of Fe (II) and Fe (III) in water using flow injection technique // Analytica Chimica Acta. 2010. V. 668. P. 812].

The method is based on the formation in aqueous solutions at pH = 3 of colored complexes of iron (III) compounds with sulfosalicylic acid having a maximum in the absorption spectrum at 490 nm, and colored complexes of iron (II) with 1,10-phenatroline at 512 nm. Registration is carried out at 530 nm, at which both complexes are absorbed. While passing the solution, ethylenediaminetetraacetic acid (EDTA) is added to it as a titrant. When EDTA is added, the complex of iron (III) with sulfosalicylic acid is destroyed with the formation of a more stable complex with EDTA, which is not absorbing at 530 nm. The optical density corresponding to the iron (III) content with 1,10-phenatrolin is measured. The iron (II) content is determined by the peak width as the difference before and after the addition of EDTA. The method allows to determine 0.1-3 μg / ml of iron (II) and 0.9-3.5 μg / ml of iron (III).

A known method for the determination of iron (II) and iron (III) [Zolgharnein J., Abdollahi Η., Jaefarifar D., Azimi G.H. Simultaneous determination of Fe (II) and Fe (III) by kinetic spectrophotometric Η-point standard addition method // Talanta. V. 57. P. 1067-1073], based on the difference in the rates of interaction of iron (III) and iron (II) with gallic acid in aqueous solutions at pH = 5. The complex of iron (III) with gallic acid is formed much faster than the complex of iron (II). Registration of optical density at 560 nm after 30 and 200 s makes it possible to determine 0.02-4.5 μg / ml of iron (II) and 0.02-5 μg / ml of iron (III).

The disadvantages of these methods are the difficulty of determining using two reagents and using a complex mathematical apparatus for calculating the contents of iron (II) and iron (III).

Closest to the proposed method according to the technical nature and the achieved results is a method for determining iron (II, III) [O.V. Kuznetsova, V.M. Ivanov, N.V. Treasury. Sorption-spectroscopic determination of iron in the sorbent phase in the form of pyracatechin-3,5-disulfonate // Tomsk State University Journal. Mosk. University. Ser. 2. Chemistry. 1997.V. 38. No. 1. P. 53-56], based on the sorption of iron complexes with pyrocatechol-3,5-disulfonic acid on an anion exchanger AB-17x8-Cl. The method involves the following operations:

- in a solution containing iron (II) and iron (III), a solution of pyrocatechol-3,5-disulfonic acid, 2 ml of a 10% solution of hydroxylamine during complexation of iron (II) is introduced;

- create the necessary pH value: pH = 3.5 - to determine iron (III), pH = 6 - to determine the amount of iron (III) and iron (II);

- diluted with deionized water to a volume of 15 ml;

- contribute 0.3 g of sorbent - anion exchanger AB-17x8-Cl;

- intensively mixed for 15 minutes;

- the sorbent is transferred to a Schott funnel, the filtrate is collected in a collection tube and dried in air;

- measure the coefficient of diffuse reflection at 500 and 540 nm.

The total iron content is found according to the calibration graph built in similar conditions. The range of determined contents is 0.03-6.7 μg / ml. The detection limit of iron is 0.01 μg / ml with a solution volume of 15 ml and a sorbent mass of 0.3 g.

The disadvantage of this method is the impossibility of separation and determination of iron (III) and iron (II), as well as a narrow range of determined contents.

The technical result of the invention is the separation of iron in various degrees of oxidation, namely iron (III) and iron (II), their subsequent determination and expansion of the range of determined concentrations of iron (III) and iron (II).

The specified technical result is achieved by the fact that in the method of separation and determination of iron (III) and iron (II), including the preparation of a solution containing iron (III) and iron (II), the creation of the required pH value, the interaction of the solution with the sorbent, measurement of the diffuse coefficient reflection at 500 nm and determining the iron content according to the calibration graph, it is new that sorbent - silica, sequentially modified polyhexamethylene, is used to isolate iron in various degrees of oxidation aniline and pyrocatechol-3,5-disulfonic acid, while iron (III) is sequentially isolated from a solution with pH = 3, and then iron (II) from a solution with pH = 6.

Signs that distinguish the claimed technical solution from the prototype are not identified in other technical solutions when studying data and related areas of technology and, therefore, provide the claimed solution with the criteria of "novelty" and "inventive step".

The essence of the method is that the sorbent is silica sequentially modified with polyhexamethylene guanidine and pyrocatechol-3,5-disulfonic acid (tyrone) selectively extracts iron (III) from a solution with pH = 3 containing iron (III) and iron (II). At this pH, iron (II) is not removed and remains in solution. After the isolation of iron (III), the pH of the solution was adjusted to 6 and iron (II) was recovered. During the complexation of iron (II) with pyrocatechol-3,5-disulfonic acid, fixed on the surface of silica, it is oxidized by the reagent to iron (III). Thus, upon sorption of iron (III) and iron (II), a complex of iron (III) with pyrocatechol-3,5-disulfonic acid is formed on the surface of the sorbent, which has a maximum in the diffuse reflection spectrum at 500 nm. This allows you to use one calibration graph to determine iron (III) and iron (II).

The sorption of iron (III) and iron (II) at appropriate pH values in the static mode proceeds quickly - the time for establishing sorption equilibrium does not exceed 5 minutes. During the sorption of iron (III) and iron (II), a colored complex of iron (III) with pyrocatechol-3,5-disulfonic acid is formed on the surface of the sorbent, having a maximum in the diffuse reflection spectrum located at 500 nm. However, to prevent oxidation of iron (II) to iron (III) by atmospheric oxygen while mixing the solution with the sorbent in a static mode, sorption must be carried out in degassed solutions or in an atmosphere of an inert gas - argon.

A complicated procedure for degassing solutions or using an inert gas can be avoided by carrying out the sorption of iron (III) and iron (II) in a dynamic mode.

The implementation of the method is as follows.

To synthesize the sorbent, 10 ml of silica are added with 100 ml of a 5% solution of polyhexamethylene guanidine in water, stirred for 5 minutes, the silica is separated from the solution by decantation and washed with distilled water. Then, silica treated with polyhexamethylene guanidine is treated with 1.6 · 10 ^-3 Μ solution of tiron in water, stirred vigorously for 5 minutes, the sorbent is separated from the solution by decantation, washed with distilled water, and dried in air.

A solution with pH = 3 containing iron (III) and iron (II) is passed through the first chromatographic microcolumn (inner diameter 3 mm, height 5 cm) containing 0.1 g of sorbent. The solution passed through the microcolumn was adjusted to pH = 6 by the addition of NaOH, and passed through a second microcolumn containing 0.1 sorbent. Sorbents are removed from the microcolumns, placed in a fluoroplastic cell and diffuse reflection is measured at 500 nm. The content of iron (III) and iron (II) is determined by the calibration graph, built in similar conditions.

The detection limit of iron does not depend on its oxidation state and is 0.02 μg of iron per 0.1 g of sorbent. The linearity of the calibration graph is maintained up to 20 μg of iron per 0.1 g of sorbent.

Example

To determine the iron (III) content, 100 ml of an aqueous solution with pH = 3 containing 1 μg of iron (III) and 1 μg of iron (II) is passed through a chromatographic microcolumn containing 0.1 g of sorbent - silica sequentially modified with polyhexamethylene guanidine and pyrocatechol -3,5-disulfonic acid, at a rate of 1 ml / min.

The sorbent is removed, placed in a fluoroplastic cell and the diffuse reflectance is measured at 500 nm. Then, to determine the iron (II) content, NaOH was added to the solution passing through the first microcolumn to pH = 6 and passed through a second chromatographic microcolumn containing 0.1 g of sorbent.

After passing the solution, the sorbent is removed from the microcolumn, placed in a fluoroplastic cuvette, and the diffuse reflection coefficient is measured at 500 nm.

The amount of iron (III) and iron (II) is found according to the calibration graph, built in similar conditions.

Found 0.96 ± 0.05 μg of iron (III) and 1.0 ± 0.05 μg of iron (II).

The method is characterized by high sensitivity, ease of implementation and does not require the use of expensive equipment, harmful substances and inaccessible sorbents. The use of silica modified with polyhexamethylene guanidine and pyrocatechin-3,5-disulfonic acid, allows almost three times to expand the range of the determined contents in comparison with the prototype and reduce the analysis time. The dependence of the length of the red colored sorbent zone in the microcolumn on the iron content on its surface allows the use of this sorbent as a test tool in the test determination of iron in the indicator tube variant.

Claims (1)

The method of separation and determination of iron (III) and iron (II), including the preparation of a solution containing iron (III) and iron (II), the creation of the required pH value, the interaction of the solution with a sorbent, the measurement of diffuse reflection coefficient at 500 nm and the determination of iron content according to the calibration schedule, characterized in that sorbent - silica sequentially modified with polyhexamethylene guanidine and pyrocatechol-3,5-disulfonic acid is used to isolate iron in various oxidation states from the solution ovatelno recovered iron (III) from the solution to pH = 3, then iron (II) - from a solution with pH = 6.