RU2093817C1 - Method of photometrically determining urea and its derivatives - Google Patents

Abstract

FIELD: analytical methods. SUBSTANCE: determining compounds with general formula R_IHNCONHR₂ where

consists in adding sulfuric acid to test sample to achieve sulfuric acid concentration 25-30 wt % in solution obtained, whereupon solution is supplemented with dimethylglyoxime and thiosemicarbazide. Colored solution is then photometered at 525-530 nm. When R₁R₂=CnH_2n+1, solution is heated for 10 min. EFFECT: increased stability of colored reaction product. 2 cl, 1 tbl

Description

R₂
H, C_nH_2n+1.The invention relates to the field of analytical chemistry, and in particular to methods for the quantitative determination of urea and its derivatives of the general formula R ₁ NHCONHR ₂ , where R ₁ H, C _n H _{2n + 1} , - (CH ₂ ) ₃ CHNH ₂ COOH -COCHBrCH (CH ₃ ) ₂ ,

R ₂
H, C _n H _{2n + 1} .

 These compounds are used in medicine, agriculture and are products (or intermediates) of the chemical and pharmaceutical industries. The invention can be used in factory, sanitary and pharmaceutical control and analytical laboratories.

 Known photometric methods for determination based on the urea-diacetyl reaction (Firon reaction) [1] and its modifications [2] These methods have the disadvantages of low sensitivity, duration of procedures and laboriousness.

 The closest to the described invention in technical essence and the achieved result is a known method of quantitative determination, which consists in heating the analyzed sample with a reagent in the presence of sulfuric acid, followed by photometry of the colored solution [3] However, the known method is not sensitive enough, it is proposed to determine only urea and citrulline .

 The objective of the proposed method is to increase sensitivity.

The problem is achieved in that in the known method, which consists in sampling, heating it with a reagent in the presence of sulfuric acid, a concentration of about 12 wt. in a boiling water bath for 20 minutes, followed by photometry at 490 nm:
1) heat the analyzed sample of urea and all its derivatives in the presence of 25 to 35 wt. sulfuric acid, followed by photometry at 525-530 nm;
2) the analyzed samples of dialkylureas are heated for 10 minutes, and bromized for 30 minutes.

 It is heating in the presence of 25 -35 wt. sulfuric acid and photometry at 525 530 nm, and the heating time in the analysis of dialkylurea for 10 minutes, and in the analysis for 30 minutes, leads to an increase in the sensitivity of the method, which, in particular, is due to an increase in the stability of the colored product in the presence of 25 35 wt. sulfuric acid. The above allows us to talk about new properties of the set of essential features and the compliance of the claimed technical solution with the criterion of "inventive step".

Example 1. The definition of urea (M) (R ₁ , R ₂ H).

 About 0.1 g (accurately weighed) M is dissolved in water in a volumetric flask with a capacity of 200 ml and adjusted to the mark with water (solution A). 1.0 ml of solution A is transferred to a volumetric flask with a capacity of 100 ml and adjusted to the mark with water (solution B).

 2 ml of solution B is placed in a graduated tube with a capacity of 15 ml, 0.5 ml of a 1% solution of dimethylglyoxime in 96% ethanol and 2.5 ml of a 0.025% solution of thiosemicarbazide in 45 wt. sulfuric acid, mix thoroughly. The mixture is heated in a boiling water bath for 20 minutes. After cooling to room temperature, the optical density of the colored solution was measured at 525 nm. The contents of M are found according to the calibration schedule.

Example 2. Determination of methylurea (MM) (R CH ₃ , R ₂ H).

 Do as in example 1. The content of MM is found on the calibration curve.

Example 3. Determination of citrulline (CL) (R ₁ - (CH ₂ ) ₃ CHNH ₂ COOH, R ₂ H).

 About 0.1 g (accurately weighed) of CL is dissolved in water in a flask with a capacity of 100 ml and adjusted to the mark with water (solution A). 1 ml of solution A is transferred to a flask with a capacity of 100 ml and adjusted to the mark with water (solution B). Then proceed, as in example 1. The content of the CL is found according to the calibration schedule.

R₂ H).Example 4. Determination of phenylurea (FM) (

R ₂ H).

 About 0.1 g (accurately weighed) M was dissolved in 96% ethanol in a 100 ml volumetric flask and adjusted to the mark with ethanol (solution A). 1.0 ml of solution A is transferred to a volumetric flask with a capacity of 100 ml and adjusted to the mark with water (solution B).

 2 ml of solution B is placed in a graduated tube with a capacity of 15 ml, 0.5 ml of a 1% solution of dimethylglyoxime in 96% ethanol and 2.5 ml of a 0.025% solution of thiosemicarbazide in 62 wt. sulfuric acid. Then proceed as in example 1, but the determination of optical density is carried out at 530 nm. The content of the FM is found on a graded schedule.

Example 5. Determination of dimethylurea (DMM) (R ₁ , R ₂ CH ₃ ).

 Do as in example 1, but the mixture is heated for 10 minutes The content of DMM is found by the calibration graph.

Example 6. The definition of brominated (BI) (R ₁ -COCHBrCH (CH ₃ ) ₂ , R ₂ H).

 About 0.1 g (accurately weighed) BI was dissolved in 96% ethanol in a 50 ml volumetric flask and adjusted to the mark with ethanol (solution A). 1 ml of solution A is transferred to a 100 ml flask and adjusted to the mark with water (solution B). Then proceed as in example 4, but the mixture is heated for 30 minutes and the measurement of optical density is carried out at 525 nm. The content of the BI is found by the calibration graph.

 Construction of a calibration graph.

 0.1 g (accurately weighed) is dissolved in a volumetric flask with a capacity in the case of M, MM, DMM 200 ml, CL, FM 100 ml, BI 50 ml and the solvent is adjusted to the mark, the solvent in the case of M, MM, CL water, in the case FM, BI 96% ethanol (solution A).

 0.2; 0.4; 0.6; 0.8; 1.0; 1,2; 1.4; 1.6 ml of solution A was transferred to a 100 ml volumetric flask and adjusted to the mark with water (solution B).

 2 ml of solution B is placed in a graduated tube with a capacity of 15 ml, 0.5 ml of a 1% solution of dimethylglyoxime in 96% ethanol and 2.5 ml of a 0.025% solution of thiosemicarbazide in 45 wt. sulfuric acid (in the case of FM and BI use a 0.025% solution of thiosemicarbazide in 62 wt. sulfuric acid), mix thoroughly. The mixture is heated in a boiling water bath for: M, MM, CL, FM 20 min, DMM 10 min, BI 30 min. After cooling the contents of the test tube to room temperature, the optical density of the colored solution is measured on a spectrophotometer in the region of maximum absorption: M, MM, DMM, CL and BI at a wavelength of 525 nm; FM at a wavelength of 530 nm.

 Comparative characteristics of the proposed and known methods are shown in the table. As can be seen from the table, the sensitivity of the proposed method exceeds the sensitivity of the prototype 1.8 9 times. The relatively high sensitivity of the proposed method allows to expand the scope of its application in the analysis of urea derivatives, the quantification of which is difficult or impossible in a known manner due to its insufficient sensitivity.

Claims (2)

 1. The method of photometric determination of urea and its derivatives, which consists in the fact that the analyzed sample is taken, sulfuric acid, dimethylglyoxime and thiosemicarbazide are added to it, the resulting solution is heated, and then the colored solution is photographed in the absorption band of 490 560 nm, characterized in that the concentration sulfuric acid in a photometric solution is 25 35 wt. and photometric solution at 525 530 nm. 2. The method according to claim 1, characterized in that the determination of dialkylurea of the general formula R ₁ NHCONHR ₂ , where R ₁ , R ₂ C _n H _{2 n + 1} , is carried out under heating for 10 minutes, and the determination of bromized is carried out under heating in within 30 minutes

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