SU1737317A1 - Method of iron determination - Google Patents

Abstract

The invention relates to methods for photometric determination of trace amounts of iron and can be used to reduce the detection limit of iron in various objects. The invention consists in converting iron into a complex compound from 0.5-2 M rodanide / w in an environment of 0.005-1.0 M H2SO4, sorption on polyurethane foam, and measuring diffuse reflection. The detection limit of iron is reduced to 8 µg / ml. 1 hp f-ly, 2 tab.

Description

The invention relates to analytical chemistry and can be used to determine trace amounts of iron in natural and industrial objects.

There is a known method for determining iron, which involves translating it into a complex compound with potassium rhodanide in an acidic medium, sorption of the complex formed on polyurethane foam and subsequent quantitative registration on a sorbent.

The disadvantage of this method is the high lower limit of detectable iron contents,

The purpose of the invention is to reduce the detection limit.

The goal is achieved by treating the analyzed solution with potassium rhodium to an equilibrium concentration of 0.5-2 M, acid is added to an equilibrium concentration of 0.005-1 M, the colored rhodanide iron complex on polyurethane foam is separated and the subsequent measurement of its diffuse reflection is carried out.

It has been established that the separation of the colored rhodanide iron complex on polyurethane foam and the measurement of its diffuse reflection lead to a decrease in the lower limit of the determined iron content. During the sorption of the complex from solutions containing potassium rhodanide, the degree of iron extraction is maximum compared with solutions containing rhodanides of other cations (ammonium, tetramethylammonium, lithium, sodium, cesium), which leads to a decrease in the lower limit of the determined iron contents. At a potassium rhodanide concentration of 0.5-2 M, the degree of iron extraction is maximum. A further increase in the concentration of potassium rhodanide (2 M) does not increase the recovery rate. When the concentration of potassium rhodanide is less than 0.5 M, the degree of iron extraction decreases, which leads to an increase in the lower limit of the determined contents.

It is preferable to sorb the rhodanide iron complex with an acidity of 0.005-1 M.

Example 1: 5 µg of iron (III) was added to a shaking vessel, 5 ml of 5 M was added.

cl

WITH

vi with XI W

x |

potassium Rodanide, 5 ml of 2.5 M sulfuric acid, water to a total volume of 25 ml, polyurethane foam in the form of a tablet with a diameter of 8 mm and a height of 5 mm (10 mg mass of sorbent), shake the vessel on a mechanical vibrator for 30 minutes, polyurethane foam is removed from the vessel, washed with water, dried in air to an air-dry state, and diffuse reflection R is measured on a Spectroton color meter at I 490 nm.

Example 2. Under the conditions of Example 1, a calibration characteristic in the coordinates (1-R) 2 / 2R — iron content, µg / ml (in solution) or µg (on a sorbent) is constructed, the lower limit of the determined contents is found and the limit is calculated iron detection.

The lower limit of the detectable iron content is (, 95) (8 ± 2) µg / ml and (2.0 ± 0.4) 10 2-µg.

The relative detection limit of iron is 1 µg / ml, the absolute limit is 2.

The data on the lower boundaries of the determined iron contents at other concentrations of potassium rhodanide are given in the table, 1,

The calibration characteristic is linear to an iron content of 0.16 µg / ml (in solution) and 4 µg (on a sorbent).

Data on the lower boundaries of the determined iron contents at other concentrations of sulfuric acid are given in Table 2.

The given metrological characteristics of the proposed method do not change when replacing sulfuric acid with hydrochloric or nitric acid.

Iron does not interfere with the determination of n 10-fold amounts of magnesium, calcium, strontium, n 104-fold phosphate and citrate ions, n 10-fold acetate, tartrate, oxalate ions, and nickel, 25-fold zinc, 5-fold cobalt.

Example 3. A variable amount of iron (III) was introduced into the shaking vessel, 50 ml of 5 M potassium roganide, 50 ml of 2.5 M sulfuric acid and water were added to a total volume of 250 ml, then proceeded analogously to examples 1 and 2

The lower limit of the detectable iron content is (, Р-0.95) (8 ± 2) 10 5 μg / ml, (2.0 ± 0.4) 10 2 μg

The relative detection limit for iron is 1-10 µg / ml.

Example 4. A variable amount of iron (III) is introduced into shaking vessels. then proceed as described in example 1, the introduction of polyurethane foam in the form of tablets with a diameter of 6 mm and a height of 2.5 mm (mass of sorbent 3 mg). Visually measuring the color of polyurethane foam, it can detect up to 6 µg of iron (on a sorbent).

PRI me R 5. Determination of iron in a standard sample of water GCFM-2.

An aliquot part (0.4 ml) of a standard sample of HCORM-2 water, previously diluted 100 times, is introduced into a shaking vessel, then proceeds as described in Example 1. The iron content is determined by calibration which is described in example 2.

Found iron: (1.0 ± 0.1) mg / ml (, 95). Iron content on passport data: 1 mg / ml.

Thus, the proposed method for the determination of iron makes it possible to reduce the lower limit of the determined contents from 0.4 to (8 ± 2) µg / ml (with a sample volume of 25 ml), (8 ± 2) µg / ml (with a sample volume of 250 ml) The relative detection limits for iron are respectively 1 10 and 1 10 5 µg / ml, absolute - 2 µg. Moreover, the method allows a 20-fold increase in the linearity range of the calibration characteristic

Claims (2)

1. A method for determining iron, including its conversion into a complex compound with potassium rhodanide in an acidic medium, sorption of the complex formed on polyurethane foam and subsequent quantitative registration on a sorbent, characterized in that, in order to reduce the detection limit, the conversion into a complex compound is carried out when the concentration of potassium rhodanide in the analyzed solution is 0.5-2.0 M and the registration on the sorbent is carried out by the method of diffuse reflection. 2. Method pop. 1, characterized in that the conversion into the complex compound is carried out at a concentration of H 2 SO 4 (0.005-1) M. The lower boundaries of the abnormal contents (CH) of iron (10 mg absorbent, 73 percent of the solution is 25 ml; n 5, P 0.95) at potassium rhodanide concentrations table 2 The lower boundaries of the determined contents (CH) of iron (10 mg absorber, / solution analysis - 25 ml; p. 5, P 0.95) at sulfuric acid concentrations