SU1709195A1 - Method of iron determination in the aqueous solution - Google Patents

Abstract

The invention relates to methods for the photometric determination of iron-water solutions and can be used in the analysis of solutions of complex composition. The purpose of the invention is to increase the sensitivity and selectivity of the analysis. The essence of the invention is in the processing of a sample with a macroporous cation exchange resin, modified with A-

Description

This invention relates to analytical chemistry, in 4actHocTM, to the determination of the total concentration of iron in aqueous solutions. salts and waters, and can be used to control water and salts.

Among photometric methods, the most sensitive and widely used method is Chromeisurol-S. The iron complex (ill) with this reagent is characterized by an absorption spectrum with an opt of 575 nm and a molar light absorption coefficient of b, 3–10, pH o & o.

The disadvantages of this method are low sensitivity (13 µg / l) and low selectivity. The definition is hampered by C ,. Co, Ni, Zn, Pb, Ti, Cr, Al, Ga, In and Ce.

A photometric method is known for determining iron in natural water with 4- (2-pyridylazo) -resorcin (PAR). At pH 8.0 - 3.3 a complex compound 530 is formed, nm and 6. 6.04 "10. The detection limit of iron is 9.3 µg / L.

But this method is characterized by low selectivity; Cu, Ag, Zn, Cd, Hg, Al, Ga, In, Tl, Sc, J, La, Ce (III), P3E, Sn (IV) interfere with the determination and to eliminate their influence Neither should one add kiruyuschie reagents to the test solution, which reduces the accuracy and sensitivity of the analysis. To increase the selectivity of the method, they used an extraction-photometric variant, which was used to determine iron in seawater: 100 ml of water was acidified to a pH of 2.5, incubated for 15 minutes and 1.5 ml of M ethanolic PAR solution were introduced and extracted with 20 cm dientipyrylmethane 8 solution of chloroform, the mass fraction of which is 10%. The measurement of the optical density of extract I was carried out on a photoelectric colorimeter, at 500, the detection limit of 10 µg / l. The elements of seawater A., Ga, and In do not interfere with the measurable quantities of the elements. The common drawbacks of all the methods described are low sensitivity and low selectivity. The closest to the invention is the method of determining iron j, which consists in introducing hydroxylamine in a test solution containing Fe (II) and Fe (III) to reduce iron, a solution of 1,10-phenanthroline, an acetate buffer (pH 5jOy The resulting solution is 30 min. In | dated with a Dowex 50W cation exchanger, after which the solid phase containing the complex is separated — the light absorption of the powder layer is measured in special cells with specular side walls with a 51 Hitachi spectrophotometer, model EPS-3T . -: The disadvantages of the known method S consists of the following .. The sensitivity of the determination of iron is 20 µg / l, low, which is related to the denitometric measurement in thin cuvettes (1 0.1 cm). The selectivity of the method is not high enough. Cr and Zn are interfered with; 10-fold excess ; Co and Cu-3 mg / l NX mg / l; Organic materials are also not defined. Measurement of the light absorption of a solid layer requires additional devices — special cuvettes. The reproducibility of the data obtained is 8 communications, with the difficulty of screening off the cation exchanger grains of exactly the same size and spill degree of their packing in a cuvette. In addition, the low selectivity of the method requires the use of masking agents — for the reduction of iron it is necessary to introduce hydroxyl ammonia into the solution, and a buffer solution for creating the necessary acidity. All this contributes to the contamination of the test solution with iron ions. There is a difficulty in acquiring a cation exchanger manufactured abroad. The purpose of the invention is to increase the sensitivity and selectivity of the analysis. To achieve this goal, a method was proposed for determining iron in water and salt solutions,. consisting in that a sorbent is inserted into the analyzed sample — a macroporous KU-23 cation exchanger previously modified (2-pyridylazo) -resorcin in an amount of 50-62.5 May. The painted complex of iron with PAR is eluted with an alkali solution at pH 11, 8-12,3 followed by photometric measurement of the eluate. A comparative analysis of the invention with the prototype shows that the proposed method differs from the well-known one in that the colored complex is obtained by concentrating iron ions on a cation exchanger previously modified by PAR (0.5-0.625 g of reagent per 1 g of sorbent) and the absorption intensity of the complex is recorded the eluate obtained by processing the sorbent containing the complex of iron with PAR, an alkali solution at pH 11 ,. In prototype 8, sorption is carried out by a Dayac-50W cationic metabolin. In this process, the complex previously obtained in solution is sorbed. It has been established that the use of such a technique for sorption by the domestic cation-exchanger does not ensure the complete extraction of iron from the analyzed solution, since this forms a neutral complex of iron with PAR not absorbed by the cation-exchanger. Therefore, the macroporous KU-23 cation exchanger was pre-modified by PAR and used for sorption of iron from solution. The use of a domestic sorbent of a different structure, e.g. gel KU-2, is impossible, since this sorbent is only modified with a reagent, but the sorption of iron on it is not carried out. The macroporous KU-23 cation exchanger was modified with 20 organic reagents widely used in the photometric analysis method. The resulting ion exchangers were used to concentrate metal ions from solutions of varying degrees of mineralization. KU-23 modified with PAR {KU-23-PAR) has the best sorption characteristics. The advantage of KU-23-PAR in comparison with other studied modified cation-exchangers is also the possibility of elution of complexes from its surface. metals with PAR in alkaline medium. This allows the use of a simple photometric method that does not require special cuvettes and has better reproducibility compared to solid-phase spectrophotometry. In addition, PARs form highly colored complexes with a high molar light absorption coefficient with many metal catalysts. It has been established that during elution in an alkaline medium, it is possible to photometrically determine the sum of heavy metal cations and selectively determine iron. For determining the amounts of heavy metals, it is necessary to photometric the solution at SlO nm, since at this wavelength the eluates of all metal complexes, including iron, have the same molar absorption coefficient l / 3 ". 10. The selective determination of iron is due to the possibility of photometric measurement of the eluate at (750 nm), since the absorption spectrum of an iron complex with PAR, unlike other metal cations, is characterized by two maxima: / {nm and D / g. 750 nm. When q complex compounds of copper, cobalt, cadmium, nickel,; Lead, zinc, chromium, manganese, and aluminum with PAR do not affect the quantitative and selective determination of micron amounts of iron in natural waters and salt solutions. Thus, the high sensitivity and selectivity of the determination of iron is achieved by quantitative sorption of iron ions by a modified sorbent and quantitative elution of iron, with PAR in the next photometric measurement of the eluate. At the same time, the amount of PAR on the sorbent and the pH of the elution of the complex were selected from the conditions providing high sensitivity of the determination of iron (Table 1, examples 1-9). . An extreme decrease in the PAR content on the sorbent leads to a decrease in the detection sensitivity. The lower limit of iron detection is increased due to the fact that with a lower PAR content, non-quantitative interaction of iron ions with the reagent occurs, resulting in a decrease in the optical density of the eluate (Table 1, Examples-1, 11.). The proposed upper limit amount of the modifier (PAR) is limited by the steric factor and the capacity of the cation exchanger, since the equivalent replacement of hydrogen ions in the cation exchanger by the reagent molecules takes place. An extreme decrease in the pH of the eluate does not provide a detection sensitivity of 0.5 µg / L. A slight change in pH leads to a sharp change in the sensitivity of the determination of iron (examples 12, 13). This is due to the fact that an incomplete extraction of the iron complex C from the surface of the sorbent occurs. The extreme increase in the pH of the eluate leads to a partial destruction of the complex being eluted, resulting in a decrease in the optical density of the eluate and, consequently, the sensitivity of the determination of iron decreases (Table 1, examples 14, 15). Based on the obtained dyne, a sorbcio-photometric method was developed for determining total iron and the sum of metal cations (Cu, Co, Cd, Cr, Mn, A1, Pb, Ki, Zn, and Fe) using a modified KU-23-PAR cation-exchanger in drinking water and salt qualification osch. Reagents and apparatus used. Nitric acid, concentrated. GOST 461-77 хч О - 10. Hydrochloric acid, concentrated, GOST ЗПЬ-77 хч 0-1t. Metal solutions: Fe; Co, C, Cd, Mn, Cr, Zn, Al; Ni; Pb is prepared by dissolving spectrally pure metals in nitric acid. The macroporous KU-23 cation exchanger is purified with 5N hydrochloric acid, washing in the column with colorless wash water (washed thoroughly with bidistillate) and saturated at pH 5.0-10.0 with a solution of PAR (M solution in water) per 1 g of KU-23 requires 0.5-0.625 g of reagent} .. The modified cation-exchanger is washed with bidistillate and dried in air. 71 Sodium hydroxide, GOST 432877 xch 0-26. PCT-29 photometry Optical density of solutions on FEK-56 M npH-Ji tfip nm, 1 2 cm and SF-5 at / j-pffj 750 nm, 1 5 cm. The proposed method is illustrated by The following examples: Pr and m 6 p t. Determination of iron in distilled water. 100 cm 3 of distilled water is acidified with 0.2 cm 5 of concentrated nitric acid (pH 3.0), iron B is introduced in an amount of 0.8 µg / l, add 0.3 g KU-23-PAR (50% modifier) and shake in a flask with a ground stopper in the crown for 30 minutes. The solution is decanted, cation-exchanger and added to the last 25 cm3 of 0.01 M. solution sodium hydroxides (pH 12.0). After boiling for 3 minutes, the solution was shaken for 15 minutes and the optical density was measured with respect to the comparison solution ( at reagent) at 750 nm at SF-3, 1 5 cm. Calibration graphs are drawn in a concentration range of 0.5-28.0 μg / l of iron. 5 parallel experiments were carried out (p 0 95) 0.82 µg / l of glands was found; the determination error was 5% (table 2 example). This table illustrates the high sensitivity of the proposed method. When determining iron, at concentrations close to the detection limit, the accuracy of the method is lower than in the determination of iron, concentrations greater than, h 1C μg / l. However, if we compare the accuracy of determination of large concentrations of iron of the proposed method with the prototype, we see a clear advantage of the proposed method (Table 2). Example 2. Determination of the concentration of iron ions and the sum of heavy metal cations in some salts. A weighed amount of about 0, .8 g, weighed with an error of no more than 0.0002 g, is dissolved in 100 cm of distilled water. The resulting solution was placed in a flask with a ground-in stopper, the pH of the solution was equal to 3.0 with nitric acid, 0.3 g of the modified sorbent was added. The flask was closed with a stopper and the mixture was stirred for 30 minutes, after which the solution was decanted from the cation-exchanger. The latter was washed with distilled water. Metal cations were eluted with 25 cm of NaOIi solution (pH 12.0) with heating for 3 minutes in a water bath and shaken for 15 minutes. After cooling the solution, its optical density on FEC-56 M, .9 nm, 1.5 cm was measured. In this way, it is possible to determine the sum of metal cations in salts. When determining the concentration of iron in salts, the optical density of the solution was measured on an SF-5 spectrophotometer at Φ 750 and 1.5 cm. To build a calibration graph, a solution of a mixture of metal cations of 2-30 µg / l was taken, where each element is including iron, 0, 2-0,3 mcg / l. The obtained data on the iron content and the sum of metal cations are presented in Table 3 (example 2). The determination of the sum of heavy metals and the selective determination of iron is possible in a number of other salts (Examples 1.3 in Table 3). The concentration of iron in all samples was controlled by the method of additives and photometrically with sulfesalicyclic acid, and the concentration of the sum of metal cations by extraction with diethyldithiocarbaminate, followed by displacement of metal cations with copper and photometry of the extract. For comparison, the data obtained are also given in Table 3. Froze Determination of the concentration of iron ions and the sum of metal cations in tap water. Drinking & ODE (100 cm3) is acidified with 0.2 cm3 of concentrated nitric acid and boiled for 3 minutes. 0.3 g of KU-23-PAR (60% modifier) is added to the cooled water and shaken in a flask with a glass stopper for 30 minutes. The solution is decanted from the cation exchanger and Kaun (pH 12.0) is added to the last 25 cm 3, the mixture is heated to boiling and gently boiled for 5 minutes. After cooling as it was, shake for 5 minutes and measure the absorbance with respect to the comparison solution (reagent eluate) on FEC-56 M ,. see. To determine the concentration of iron, the optical density is measured at 750 nm on an SF-5, 1.5 cm.

The calibration graph is constructed in the concentration range of 0.2-0.5 µg / l of both the sum of metal cations and iron (Table 3, example). The control of the completeness of the extraction was carried out by the same methods as in the determination of the separation of metals of salt and salt.

The proposed method for the determination of iron is highly selective. The presence of a 100-fold excess of Cu, Co, Cd, Mn, Zn, A1, Ni, Pb, Cr in the solution does not affect the selective determination of delech in waters and salts.

An increase in the content of heavy metal ions to 200 times excess with respect to iron causes an error in the determination of iron to 10 (Table 4).

The proposed method makes it possible to increase the sensitivity of the determination of iron compared with prototyping 50 times. The method is highly selective. A significant excess of heavy metal ions Ht affects the sensitivity and accuracy of the determination of iron by this method. Precise and selective

Claims (1)

the determination of iron is possible in waters of varying degrees of mineralization and salt. The developed method is distinguished by its simplicity, fast, good reproducibility, low detection limit and high (Selectivity of iron determination. Formula of the invention The method of determining iron in aqueous solutions, including its conversion into a complex compound with an organic reagent, concentrating the resulting complex on a sorbent, and photometric measurements, is distinguished by the fact that, in order to increase the sensitivity and selectivity of the analysis, the conversion into a complex compound and concentration are on the sorbent, in which use macroporous cation exchanger, pre-modified with an organic reagent to its content 0.5-0.625 g / g, as which is altered - (2-pyridylazo) -resorcinol, the resulting complex compound is eluted from the sorbent alkali solution at pH 11 and the eluate is subjected to photometry. Table Beyond Limit eleven 0.0 water, mg / l 12 1709195 Table 2 T a b l and c a 3 0.42 0.30 0.29 13 14 1709195 T a b l and 14 a k