Method of separately determining resorcinol and 2,4- dinitroresorcinol in presence of 4-nitrosoresorcinol

FIELD: analytical methods.

SUBSTANCE: invention is directed to controlling treated waste waters from varnish-and-paint industry enterprises and discloses a method of separately determining resorcinol and 2,4-dinitroresorcinol involving potentiometric titration in dimethylformamide medium, determination being carried out in aqueous sample preliminarily acidified to pH 2-3 and treated with acetone in presence of ammonium sulfate as salting-out agent in amount 36.5-40.0% of the weight of sample. Organic layer containing resorcinol and 2,4-dinitroresorcinol is then separated, diluted with dimethylformamide at volume ratio 1:5, and titrated with solution of potassium hydroxide in isopropyl alcohol. Content of each of resorcinols is calculated from differential titration curves in according to formula: C = Co100/R wherein C and Co are concentrations of resorcinols in initial aqueous sample and in extract, respectively, mg/dm3, and R degree of recovery of resorcinols in acetone/water-salt solution, %.

EFFECT: enabled selective determination of resorcinol and 2,4-dinitroresorcinol, reduced detection limits (extraction concentration operation), and expanded application area.

2 tbl, 12 ex

 

The invention relates to analytical chemistry of organic compounds and can be applied for monitoring of treated wastewater enterprises in the paint industry.

As a prototype of the selected method of potentiometric titration of phenols in nonaqueous medium (Denis I. Titration in nonaqueous media. - M.: Mir, 1971. - 257).

The disadvantages of the method - neselektivno determination of phenolic compounds, high detection limits, failure analysis in aqueous solutions.

The objective of the invention is to increase the selectivity of the determination of resorcinol and 2,4-dinitroresorcinol in the presence of 4-nitrosobenzene (elimination at the stage of preparation of the interfering influence of 4-nitrosobenzene), lower detection limits.

This object is achieved in that way separate determination of resorcinol and 2,4-dinitroresorcinol in the presence of 4-nitrosobenzene, including potentiometric titration in a medium of dimethylformamide, what is new is that the definition is carried out in an aqueous sample, which is pre-acidified to pH 2-3, treated with acetone in the presence of vicariates of ammonium sulfate in the amount of 36.5-40.0 wt.% with respect to the sample, separating the organic layer containing resorcinol and 2,4-dinitroresorcinol, dilute it with dimethylformamide in a volume ratio of 1:5 and titrate with the potassium hydroxide solution in isopropyl alcohol, and the content of each of resorcinol calculated from the differential titration curves according to the formula

where C and C0- concentration resorcinol in the original water sample and extract, mg/DM3;

R is the degree of extraction resorcinol in the system acetone - water-salt solution, %.

The technical result consists in the fact that the proposed method allows you to selectively determine resorcinol and 2,4-dinitroresorcinol in the presence of 4-nitrosobenzene, lower detection limits resorcinol (extraction concentration) and to widen the application.

How is that to 50 cm3water samples containing resorcinol, 2,4-dinitroresorcinol and 4-nitrocresols, acidified to pH 2-3 add to 36.5-40.0 wt.% in relation to the sample of ammonium sulfate and 8.5 cm3acetone (Korenman YA, Ermolaeva, T.N., Mishina AV and other Triple-chart water - ammonium sulphate - hydrophilic solvent. Lipetsk, 1995. - Depv VINITI No. 295-In-95. - 10 C.), is extracted on vibrometer. After separation of phases (15 min) to separate the organic layer, diluted with dimethylformamide (DMF) in a volume ratio of 1:5, is placed in the cell for potentiometric titration, equipped with a magnetic stirrer, and titrated with a solution of potassium hydroxide in isopropyl alcohol. Conditions titration: the indicator electrode - card is new; the reference electrode is a saturated chloresteral; temperature 20±2° C.

Resorcinol and 2,4-dinitroresorcinol almost completely extracted by acetone from acidified solutions of ammonium sulfate, with 4-nitrocresols practically does not pass into the organic phase and is separated in the extraction step.

The degree of extraction resorcinol (R, %) was calculated according to the formula (I):

where D is the distribution coefficient resorcinol in the system acetone - water-salt solution; r is the ratio of the equilibrium volumes of aqueous and organic phases.

Get a clear differential titration curves, which set the volumes of the solutions of KOH, followed by titration of resorcinol and 2,4-dinitroresorcinol, and expect their content in the extract With0taking into account the ratio of the equilibrium volumes of aqueous and organic phases and translation molar concentration equivalent (mol/DM3) concentration (mg/DM3the formula (2)

where C0- concentration resorcinol extract, mg/DM3;

(1/1 CON) - molar concentration equivalent titrant, mol/DM3;

V(KOH) is the volume of titrant, went to the titration resorcinol, cm3;

Mp- molar mass equivalent resorcinol, g/mol;

Ve- volume of extract, cm3;

r - the ratio of the equilibrium volumes of aqueous and organic phases (10).

Content resorcinol in the original water sample is calculated by the formula (3)

where C and C0- concentration resorcinol in the original water sample and extract, mg/DM3;

R is the degree of extraction resorcinol in the system acetone - water-salt solution, %.

Examples of the method

Example 1. Solutions resorcinol prepared from drugs qualification “h”, purified by sublimation. The degree of purity of drugs controlled by the melting temperature. The original aqueous solutions with accurately known concentration is prepared by the method of dilution of the standard solutions.

To 50 cm3water samples containing resorcinol, 2,4-dinitroresorcinol and 4-nitrocresols with equal concentrations of 5 mg/DM3was acidified to pH 2-3 add 38.5 wt.% in relation to the sample of ammonium sulfate and 8.5 cm3acetone, extracted with 15 minutes After separation of phases (15 min) to separate the organic layer, diluted with dimethylformamide (DMF) in a volume ratio of 1:5, is placed in the cell for potentiometric titration, equipped with a magnetic stirrer, and titrated with a solution of potassium hydroxide in isopropyl alcohol with a molar concentration equivalent To(1/1 CON)=0,011 mol/DM3. Conditions titration: the indicator electrode platinum; El is trod comparison - rich chloresteral; temperature 20±2° C.

The distribution coefficients resorcinol determined photometrically at fotoelektrokalorimetry CPK-2 by reaction with diazotized sulfanilic acid (L(resorcinol)=240) or on its own coloration (D(2,4-dinitroresorcinol)=590 & D(4-nitrosobenzene)=0,09). The degree of extraction of resorcinol, 2,4-dinitroresorcinol and 4-nitrosobenzene calculated by the formula 1 when r=10, respectively- 96; 98;0, 89 (%).

Resorcinol and 2,4-dinitroresorcinol almost completely extracted by acetone from acidified solutions of ammonium sulfate, with 4-nitrocresols practically does not pass into the organic phase and is separated in the extraction step.

Get a clear differential titration curve (the drawing), which establish the volumes of solutions of KOH, followed by titration of resorcinol and 2,4-dinitroresorcinol. The content of 2,4-dinitroresorcinol (C1) and resorcinol (C2in the analyzed water solution is:

for 2,4-dinitroresorcinol

C1=C0·100/R=4,89· 100/98=to 4.98 mg/DM3

for resorcinol

With2=C0·100/R=4,84· 100/96=5,04 mg/DM3

Way feasible.

Example 2. To 50 cm3water samples containing resorcinol, 2,4-dinitroresorcinol and 4-nitroso zorzin, acidified to pH 2-3, type of 36.5 wt.% in relation to the sample of ammonium sulfate and 8.5 cm3of acetone. Review analogously to example 1. Way feasible.

Example 3.

To 50 cm of water samples containing resorcinol, 2,4-dinitroresorcinol and 4-nitrocresols, acidified to pH 2-3 add 40.0 wt.% in relation to the sample of ammonium sulfate and 8.5 cm3acetone, extracted with 15 minutes Further analyze analogously to example 1. Way feasible.

Example 4. To 50 cm3water samples containing resorcinol, 2,4-dinitroresorcinol and 4-nitrocresols, acidified to pH 2-3, add 35 wt.% in relation to the sample of ammonium sulfate and 8.5 cm3of acetone. Review analogously to example 1. The method is not feasible, because the isolated extract contains significant amounts of water.

Example 5. To 50 cm3water samples containing resorcinol, 2,4-dinitroresorcinol and 4-nitrocresols, acidified to pH 2-3 add to 41.0 wt.% in relation to the sample of ammonium sulfate and 8.5 cm3of acetone. Review analogously to example 1. The method is not feasible, since the precipitated salt crystals adsorb resorcine.

Example 6. To 50 cm3water samples containing resorcinol, 2,4-dinitroresorcinol and 4-nitrocresols, acidified to pH 2-3 add to 36.5-40.0 wt.% in relation to the sample of ammonium sulfate and 8.5 cm3acetone, extracted with 15 m is N. After separation of phases separated organic layer, dilute with dimethylformamide to volume ratio of 1:4. Review analogously to example 1. Potentiometric curves fuzzy, get reproducible results. The method is not feasible.

Example 7. To 50 cm3water samples containing resorcinol, 2,4-dinitroresorcinol and 4-nitrocresols, acidified to pH 2-3 add to 36.5-40.0 wt.% in relation to the sample of ammonium sulfate and 8.5 cm3acetone extracted. After separation of phases separated organic layer, dilute with dimethylformamide to volume ratio of 1:6. Review analogously to example 1. The method is feasible, but the dilution of the extract DMF increases the detection limits resorcinol.

Example 8. To 50 cm3water samples containing resorcinol, 2,4-dinitroresorcinol and 4-nitrocresols, acidified to pH 2 add to 36.5-40.0 wt.% in relation to the sample of ammonium sulfate and 8.5 cm3of acetone. Review analogously to example 1. Way feasible.

Example 9. To 50 cm3water samples containing resorcinol, 2,4-dinitroresorcinol and 4-nitrocresols, acidified to pH 2.5 to add to 36.5-40.0 wt.% in relation to the sample of ammonium sulfate and 8.5 cm3of acetone. Review analogously to example 1. Way feasible.

Example 10. To 50 cm3water samples containing resorcinol, 2,4-dinitriles rcin and 4-nitrocresols, acidified to pH 3 add to 36.5-40.0 wt.% in relation to the sample of ammonium sulfate and 8.5 cm3of acetone. Review analogously to example 1. Way feasible.

Example 11. To 50 cm3water samples containing resorcinol, 2,4-dinitroresorcinol and 4-nitrocresols, acidified to pH 1 add to 36.5-40.0 wt.% in relation to the sample of ammonium sulfate and 8.5 cm3of acetone. Review analogously to example 1. The method is not feasible.

Example 12. To 50 cm3water samples containing resorcinol, 2,4-dinitroresorcinol and 4-nitrocresols, acidified to pH 4 add to 36.5-40.0 wt.% in relation to the sample of ammonium sulfate and 8.5 cm3of acetone. Review analogously to example 1. The method is feasible, but the degree of extraction resorcinol reduced.

The correctness of the method is tested by the method introduced-found (table 1. Determination of resorcinol, 2,4-dinitroresorcinol in the presence of 4-nitrosobenzene in aqueous solution). The relative error of determination does not exceed 10%.

Comparative characteristics of the proposed method and the prototype are given in table 2.

The proposed method allows the determination resorcinol in aqueous solutions, to increase the selectivity of detection and to reduce the detection limit in 10 times.

Table 1

The definition is of torsina, 2,4-dinitroresorcinol in the presence of 4-nitrosobenzene in aqueous solution; n=5; P=0,95
Entered, mg/DM32,4-DinitroresorcinolResorcinol
±δ , mg/DM3Sr±δ , mg/DM3Sr
5,00,150,030,240,05
0,50,0250,050,0530,12
Table 2

Comparative characteristics of the proposed method and prototype
OptionsThe known methodThe proposed method
Selectivity defineImpossibleMay
The objects of analysisNonaqueous solutionsNon-aqueous and aqueous solutions
The limit of detection, mg/DM350,5

The way the separate determination of resorcinol and 2,dinitroresorcinol in the presence of 4-nitrosobenzene, including potentiometric titration in a medium of dimethylformamide, characterized in that the determination is carried out in an aqueous sample, which is pre-acidified to pH 2-3, treated with acetone in the presence of vicariates of ammonium sulfate in the amount of 36.5-40.0 wt.% with respect to the sample, separating the organic layer containing resorcinol and 2,4-dinitroresorcinol, dilute it with dimethylformamide in a volume ratio of 1:5 and titrated with a solution of potassium hydroxide in isopropyl alcohol, and the content of each of resorcinol calculated from the differential titration curves according to the formula

,

where C and C0- concentration resorcinol in the original water sample and extract, mg/DM3;

R is the degree of extraction resorcinol in the system acetone - water-salt solution, %.



 

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3 ex

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7 dwg, 12 ex

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2 cl, 2 ex

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