Method of aqueous medium analysis for phenol content

FIELD: chemistry.

SUBSTANCE: invention refers to drinking, natural and waste water, precipitation sanitary-hygienic control and analysis for phenol content. Method includes chemical phenol modification in 2,4,6-tribromphenol, extraction concentration of 2,4,6- tribromphenol and gas chromatography testing. Herewith chemical modification is preceded with humic acid removal on aluminium oxide from aqueous medium sample with copper sulphate in amount 0.05-0.25% of aqueous medium sample weight.

EFFECT: higher analysis reliability.

7 ex, 2 tbl, 7 dwg

 

The invention relates to analytical chemistry of organic compounds (concentration and definition) and can be used for sanitary and epidemiological control of the concentration of phenol in drinking water, wastewater, and precipitation.

The closest to the technical nature of the claimed solution is a gas chromatographic method for the determination of phenol in drinking water [Korenman YA, Gruzdev IV, contratenor BM, V. Fokin. Conditions of synthesized and gas chromatographic determination of phenols in drinking water // Journal of analytical chemistry. - 1999. - T. No. 12. - S-1138]. The disadvantage of the prototype is getting unreliable results determination of phenol in aqueous media containing humic acid. According to modern concepts [Orlov D.S. Chemistry of soils. - M.: Moscow state University press, 1992. - 400 C.] humic acid is irregular copolymers of aromatic oksipiridilovykh acids with inclusion of the nitrogen and carbohydrate fragments. Figure 1 shows a hypothetical structural formula of a fragment of humic acid. Used for chemical modification of phenol molecular bromine causes degradation of humic acids, one of the products is phenol. Figure 2 presents the processes that occur in water containing humic acid, in the presence of molecular bromine 1 - bromination of native phenol, 2 - destruction of humic acid, 3 - bromination of phenol formed during the degradation. This phenol is also subject to chemical modification in 2,4,6-tribromophenol, and the result of the analysis overestimated, as is the sum of the concentrations of native phenol and phenol formed during the degradation of humic acid.

The objective of the invention is to eliminate the interfering influence of humic acids in the determination of phenol in aqueous media. This is a technical result.

The solution of this problem is achieved in that in the method of determination of phenol in aqueous media, including its chemical modification of 2,4,6-tribromophenol, extraction concentration of 2,4,6-tribromophenol and subsequent gas chromatographic detection, new is the fact that before the chemical modification of a water sample to remove humic acid on aluminum oxide in the presence of copper sulfate in the amount of 0.05-0.25% by weight of a water sample.

Removal of humic acids on aluminum oxide based on the fact that the surface of hydrated aluminum oxide is charged positively, and the aggregates of humic acids carry a negative charge [S.Goldberg, J.A.Davis, J.D.Hem. The surface chemistry of aluminum oxides and hydroxides // The environmental chemistry of aluminum / edited by G.Sposito. NY: Lewis Publishers, 1996. - P.272-333].

Quantitative removal of Gumus what's acids in the absence of copper sulfate to achieve the impossible, because as you increase the amount of treated water layer of aluminum oxide overcome low molecular weight fragments of humic acids.

When introduced into an aqueous sample of copper sulfate formed copper cations interact with aluminum oxide, forming a narrow chromatographic zone, which by passing water is gradually progressing. Figure 3 shows a photograph of a glass chromatographic column filled with alumina: delete (right) and after removal (left) humic acids from water sample. In addition, the copper cations, being a good complexing agents interact with each other and with low molecular weight fragments of humic acids, binding and holding them in the layer chromatographic zone. Figure 4 presents a diagram of the formation of chemical bonds with the cation of copper in the oxide layer of aluminum (Al2O3- the surface of the aluminum oxide, GK - low molecular weight fragments of humic acids). Thus, humic acid will not get in the eluate as long as the copper cations will not overcome the aluminium oxide layer.

At the same time, the sorption of phenol on the surface of the aluminum oxide is practically absent and 2-3% for 2 grams of Al2About3and the concentration of phenol in water 0.1-10 ág/DM3. Figure 5 shows the dependence of the sorption of phenol on the aluminum oxide by weight A 2O3(volume of water sample - 25 cm3the concentration of phenol in water is 1 ág/DM3).

The method of determination of phenol in aqueous media includes four stages.

1) Removal of humic substances from aqueous samples on a column of aluminum oxide. Quantitative removal of humic acids is necessary because their presence in the water at the stage of chemical modification, even in trace quantities, leads to distortion of the results of the quantitative analysis of phenol.

2) Chemical modification of phenol - processing of humic substances-free water sample with molecular bromine. When bromirovanii bromine atoms replace hydrogen atoms in the aromatic nucleus of the phenol in positions 2, 4 and 6. At room temperature (20±5° (C) reaction of the synthesized phenol completed within 40-60 seconds with the quantitative formation of 2,4,6-tribromophenol.

3) Extraction concentration of 2,4,6-tribromophenol by the method of solvent extraction. This stage is designed for conversion of 2,4,6-tribromophenol in more convenient for subsequent gas chromatographic analysis of the organic phase, increasing its concentration in the extract and separation of interfering components.

4) Analysis of the extract by gas chromatography. The extract obtained 2,4,6-tribromophenol analyzed by capillary gas chromatography detector e C the grip (ECD). Halogenoalkanes DEATH provides maximum sensitivity gas chromatography determination of 2,4,6-tribromophenol.

Determination of phenol performed by the following method. To analyze the water sample volume of 30 cm3poured 0.3-1.5 cm3solution of copper sulphate (C(CuSO4·5H2O)=0.2 mol/DM3), which is 0.05-0.25% by weight of the sample, and pour the mixture into a pre-prepared glass chromatographic column filled with 2 g of aluminum oxide. The eluate is taken in a glass test tube with a capacity of 25.0 cm3, acidified with sulfuric acid to pH 2-3, add 1.0 cm3bromine water (Br2)=0.01 mol/DM3and bromilow within 1 minute. After completion of the reaction, the synthesized excess bromine is removed by the addition of 1.0 cm3solution of sodium thiosulfate (Na2Sa2O3)=0.01 mol/DM3). Next, enter the internal standard is 0.2 cm3alcohol solution of 2,4,6-trichlorophenol (ρ(2,4,6-trichlorophenol)=0.25 µ g/cm3), 1.0 cm3toluene and extracted for 5 minutes with continuous stirring. After separation of phases 3 mm3the organic extract was analyzed by gas chromatograph with ECD.

Conditions for gas chromatographic determination: temperature detector 320°C evaporator 320°C, thermostat columns 200°C; quartz Kapil is popular column 30 m× 0.25 mm×0.25 μm with slightly polar stationary liquid phase (SE-30, SE-52, SE-54), the flow rate of carrier gas (nitrogen, OSC) through a column of 0.8 cm3/min, positive pressure detector 20 cm3/min, the division of the flow of 1:50. Figure 6 shows a chromatogram of a standard solution of phenol concentration of 1 µg/DM3(SU - 2,4,6-trichlorophenol, internal standard, 2,4,6-TBP and 2,4,6-tribromophenol).

Identification of 2,4,6-tribromophenol in the analyzed sample of water is performed by relative retention time tx*:

tx*=tx/tarticle,

where txand tarticle- fixed the retention times of components of the sample and internal standard, respectively.

The relative retention times of components of the sample was compared with the relative retention time of 2,4,6-tribromophenol, obtained for a standard solution: tx*(2,4,6-tribromophenol)=2.752.

The mass concentration of phenol in the analyzed water sample was calculated by the equation derived from the calibration curve for standard aqueous solutions of phenol (table 1):

ρ(µg/DM3)=2.372 S/Sst-0,006(R2=0.9988),

where S/Sst- the ratio of the peak area of 2,4,6-tribromophenol to peak area of internal standard (2,4,6-trichlorophenol).

Table

The results of gas chromatographic analysis of standard solutions of phenol
ρ (phenol), µg/DM3S/Sst
10.432
52.146
104.152
156.325
208.458

Figure 7 shows the calibration dependence of the mass concentration of phenol (standard solutions) from the ratio of the area of the chromatographic peaks with S/Sst.

Examples of the method

Example 1.

A sample of natural water containing humic acid, ρ(phenol)=2 ág/DM3. To analyze the water sample volume of 30 cm3poured 0,03 cm3solution of copper sulphate (C(CuSO4·5H2O)=0.2 mol/DM3), which ranges from 0.005% by weight of the sample, and pour the mixture into a pre-prepared glass chromatographic column filled with 2 g of aluminum oxide. The eluate is taken in a glass test tube with a capacity of 25.0 cm3, acidified with sulfuric acid to pH 2-3, add 1.0 cm3bromine water (C(Br2)=0.01 mol/DM3and bromilow within 1 minute. After completion of the reaction, the synthesized excess bromine is removed by the addition of 1.0 cm3of sodium thiosulfate solution (C(Na2S2O3)=0.01 mol/DM3). Next, input the Yat internal standard 0.2 cm3alcohol solution of 2,4,6-trichlorophenol (ρ(2,4,6-trichlorophenol)=0.25 µ g/cm3), 1.0 cm3toluene and extracted for 5 minutes with continuous stirring. After separation of phases 3 mm3the organic extract was analyzed by gas chromatograph with ECD.

Detectable concentration of phenol in water is equal to 5.4 ág/DM3. The method is not feasible, because the interfering influence of humic acids with the concentration of copper sulfate in the sample 0.005% persists.

Example 2.

The content of copper sulfate in the sample - 0.015%. Analyze as described in example 1. Detectable concentration of phenol - 3.3 µg/DM3. The method is not feasible, because the interfering influence of humic acids persists.

Example 3.

The content of copper sulfate in the sample - 0.05%. Analyze as described in example 1. Detectable concentration of phenol - 1.9 µg/DM3. Way feasible.

Example 4.

The content of copper sulfate in the sample - 0.15%. Analyze as described in example 1. Detectable concentration of phenol - 2.1 µg/DM3. Way feasible.

Example 5.

The content of copper sulfate in the sample - 0.25%. Analyze as described in example 1. Detectable concentration of phenol - 2.1 µg/DM3. Way feasible.

Example 6.

The content of copper sulfate in the sample - 0.5%. Analyze as described in example 1. Defined conc the tion of phenol - 3.7 µg/DM3. The method is not feasible, because the interfering influence of humic acids persists.

Example 7.

The content of copper sulfate in the sample - 1.0%. Analyze as described in example 1. Detectable concentration of phenol - 4.5 µg/DM3. The method is not feasible, because the interfering influence of humic acids persists.

The results of determination of phenol in water by the proposed method are given in table 2.

Table 2

Examples of the method
# exampleThe content of copper sulfate to the sample mass, %The concentration of phenol in water, mg/DM3Detectable concentration of phenol in water, mg/DM3The ability of the proposed method
Prototype-27.3-
10.00525.4impossible
20.01523.3impossible
30.0521.9feasible
40.1522.1feasible
50.25 22.1feasible
60.523.7impossible
71.024.5impossible

From examples 1-7 and table 2 it follows that the proposed method for the determination of phenol in aqueous environments is feasible in the concentration range of copper sulfate 0.05-0.25% with respect to the sample mass. At lower concentrations of copper cations is insufficient to bind all of low molecular weight fragments of humic acids, some of them overcomes a column of aluminum oxide and into the eluate. At concentrations >0.25% of copper cations formed more than they can absorb on the aluminum oxide, and the excess falls into the eluate with attached particles of humic acids.

Compared with the prototype of the proposed solution has the following advantages.

1) Obtain reliable test results, regardless of the qualitative and quantitative composition of the analyzed water sample.

2) Complete removal of interfering components (coarse, fine and colloidal particles).

3) No formation of stable emulsions after extraction concentration, complicating subsequent gas chromatography is the distribution.

The method of determination of phenol in aqueous media, including its chemical modification of 2,4,6-tribromophenol, extraction concentration of 2,4,6-tribromophenol and subsequent gas chromatographic detection, characterized in that before the chemical modification of a water sample to remove humic acid on aluminum oxide in the presence of copper sulfate in a quantity of 0.05 to 0.25% by weight of a water sample.



 

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