RU2022256C1 - Method of extraction-spectrophotometric assay of inorganic phosphate (v) - Google Patents

Abstract

FIELD: analytical chemistry. SUBSTANCE: aqueous solution of ammonium molybdate (final concentration is 2·10^-4 M), solution of ammonium vanadate in 0.03M HCl (2·10^-3 М) and sulfuric acid solution (final concentration is 0.01 N) are added to examined sample. Triple heteropolyacid formed is reduced by adding of ascorbic acid up to concentration 0.5%. Prepared solution is heated on the boiled bath for 10 min, cooled and safranine-T solution is added up to concentration 1·10^-3 %. Reduced heteropolyacid forms associate with dye. A mixture of methylethylketone and butylacetate at the ratio 3:2 is added to analyzed solution, and the volume of aqueous solution must 2-fold exceeds that of volume of organic mixture. After extraction organic fraction is subjected for photometry at 530 nm. Phosphorus content is calculated by calibrating plot. EFFECT: improved method of assay. 2 tbl

Description

 The invention relates to analytical chemistry, in particular to extraction-spectrophotometric determination of trace amounts of inorganic phosphates (V) and can be used to analyze various environmental objects (drinking water, natural water, alloys, food products, etc.).

 Extraction-photometric methods for the determination of inorganic phosphates are very diverse and are divided into direct and indirect. Indirect methods for the determination of phosphorus are mainly based on the determination of molybdenum, since phosphorus and molybdenum enter the heteropoly acid in a ratio of 1:12 [1].

Direct methods for the determination of phosphorus, based on the formation of heteropoly acids, have an insufficient detection limit. The method proposed by GOST 2874-73 for the determination of phosphorus in drinking water by the blue phosphorus-molybdenum complex is not sensitive enough (1 ˙ 10 ^-3 -5 ˙ 10 ^-4 mg / cm ³ ) and requires preliminary concentration.

 The sensitivity of phosphorus determination increases with the interaction of the phosphorus-molybdenum complex (PMA) with the main dye (OK), and ionic associates (MPA-OK) are formed, which have been studied in detail [1].

 The disadvantage of the above analogues is the low resistance of MKF-OK associates, as a result of which a large excess of molybdate is necessary, which also forms complexes with OK. This complicates the analysis, leads to an increase in the error of the results.

A known method for the determination of phosphorus in drinking water, which is based on the reaction of the formation of an ionic associate of molybdovanadato-phosphoric acid with the main dye, crystalline violet (IMFC-CF [2,3]. The method allows to determine <2 · 10 ^-4 mg / cm ³ phosphorus ( V) Performing the analysis: an aliquot of the solution (0.1-0.6 μg of phosphorus) is placed in a separatory funnel, 1 ml of a solution of a mixture of ammonium molybdate and vanadate is added, diluted with water to 2.5 ml and incubated for 5 minutes, then 2 ml of 1.2 M HCl, 0.5 ml of 6.4˙ 10 ^-4 M KF solution and extracted with 5 ml of e of ethyl acetate 1 min, the Organic phase is washed twice (with 15 s) with 0.5 M HCl, poured 5 ml of acetone and measure the optical density of the resulting solution at λ = 590 nm in a cuvette with l = 1 cm relative to a solution of blank experiment (when using a light filter N 7) [4].

 The disadvantage of this analogue is the flotation separation of the ionic associate in the form of a film at the interface between the aqueous and organic phases. This analysis method is time consuming.

 The purpose of the invention is the simplification of the method.

 The goal is achieved by the fact that, according to the method, the test sample in the form of an aqueous solution is introduced into interaction with molybdate and vanadate, the triple heteropoly acid (MVPK) is restored with ascorbic acid, then it is involved in the reaction with safranin-T, and the resulting associate MVFC-saranin-T is extracted with a mixture 3: 2 methyl ethyl ketone and butyl acetate (volumetric), followed by photometric measurements of the organic extract on an SF-26 spectrophotometer at λ = 530 nm.

 The use of a mixture of methyl ethyl ketone-butyl acetate in a ratio of 3: 2 (volume) allows you to quickly separate the organic phase from the aqueous. This mixture practically does not extract the dye and the associate of molybdovanadate with safranin-T from the aqueous part.

The relative error of the method does not exceed + 5%. Beer's law is fulfilled in the concentration range 1˙ 10 ^-5 -3 ˙10 ^-4 mg / cm ³ .

The determination of phosphorus is not affected by the presence of 100-fold amounts of Fe ⁺³ , Ni, Co, Cr ⁺³ , 25-fold amounts of silicon. Arsenic, which must first be removed, interferes with the determination of phosphorus.

 PRI me R 1. Determination of inorganic phosphorus (V) in drinking and natural waters.

5 ml of a sample (pH = 5-7) containing 1˙ 10 ^-5 -3˙ 10 ^-4 mg / cm ^{3 of} phosphorus are placed in a conical flask with a capacity of 25 ml, 1.0 ml of 0.1 N solution is added to the sample before extraction H ₂ SO ₄ , 2 ml of a 0.001 M solution of ammonium molybdate, 1 ml of ammonium vanadate (preparation of ammonium vanadate: 0.234 g of NH ₄ VO _{3 is} dissolved in 50 ml of H ₂ O - 2.8 ml of concentrated HCl, and diluted with water to 100 ml) , 0.5 ml of a 10% solution of ascorbic acid and heated in a boiling water bath for 10 minutes

 The contents of the flask are cooled and 0.5 ml of a 0.02% safranin-T solution is added, the mixture is kept at room temperature for 2 minutes, poured into 20 ml tubes and shaken with a mixture of 3 ml of methyl ethyl ketone and 2 ml of butyl acetate.

 After the layers are separated into organic and aqueous phases (3 min), the first is transferred to a 10 mm cuvette and the solution is photographed on SF-26 at λ = 530 nm.

 The amount of phosphorus is found according to the calibration graph; in parallel, a blank experiment is conducted that does not contain phosphorus.

 Examples of the method in the analysis of drinking and natural water are given in table. 1 and 2.

 PRI me R 2. Determination of inorganic and organic phosphorus in water.

In a heat-resistant flask with a capacity of 50 ml is placed 5 ml of an aqueous solution with a certain content of organic phosphates (1 · 10 ^-5 -1 · 10 ^-4 mg / ml according to P).

The sample is evaporated almost to dryness, 2 ml of concentrated nitric and perchloric acids and 1 ml of concentrated H ₂ SO ₄ are added, mixed and heated on an electric stove until thick white vapors appear. Mineralization is continued for another 5-10 minutes until the solution becomes discolored. With stirring, a sodium hydroxide solution is added to the test solution to a neutral medium (pH = 6-7) according to a universal indicator. paper. Then 5 ml of the sample is placed in a conical flask with a capacity of 25 ml and treated according to example 1. The amount of phosphorus is found according to the calibration schedule.

 PRI me R 3. Determination of phosphorus in steels and alloys.

A portion of steel or alloy (0.25 g) is dissolved by heating the mixture with 15 ml of HCl (1: 1) and 5 ml of HNO ₃ (1: 1), the solution is evaporated to a syrupy state, 20 ml of 1: 1 HCl are added and evaporated again. This operation is repeated twice more, adding 20 ml of water each time. 5 ml of HCl (1: 1) was added to the residue and iron (III) was reduced to iron (II) 20 ml of 1 m Na ₂ SO ₃ by boiling. The solution was transferred to a 25 ml volumetric flask. It is neutralized with a 1 M sodium hydroxide solution to a pH of 6-7 and diluted with water to the mark. An aliquot (5 ml) of the solution was analyzed analogously to example 1.

Claims (1)

METHOD FOR EXTRACTION-SPECTROPHOTOMETRIC DETERMINATION OF INORGANIC PHOSPHORUS (V), which consists in preparing a sample solution, injecting an acid solution into it, a solution of ammonium molybdate, ammonium vanadate, a dye solution, adding an extractant, separating its organic phase, determining the phosphor, the phosphor is determined calibration curve, characterized in that, in order to simplify the method, a solution of sulfuric acid is introduced to a concentration of 0.01 N., a solution of ammonium molybdate to 2 · 10 ^-4 M, a solution of ammonium vanadate in 0.03 M HCl to 2 · 10 ^{- 3} M, then m add ascorbic acid to a concentration of 0.5%, the resulting solution is heated in a boiling water bath for 10 minutes, cooled, a solution of dye is injected with a solution of safranin-T to a concentration of 1 · 10 ^-3 %, a mixture of methyl ethyl ketone and butyl acetate is added as extractant to a ratio of 3: 2 to obtain the volume of the aqueous phase, twice the volume of the organic phase, and photometri at 530 nm.

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