Method of detecting phenol in aqueous solution

FIELD: chemistry.

SUBSTANCE: in the method of detecting phenol in aqueous solution via reverse-phase micro-column high-performance liquid chromatography with a preliminary sample preparation step through liquid-liquid extraction with acetonitrile, extraction is carried out at temperature 263±2 K for 30 minutes with ratio of equilibrium volume of water to the organic phase equal to 1:1.

EFFECT: simple and cheap method, high degree of extracting phenol, low detection limit.

1 ex, 3 tbl

 

The invention relates to analytical chemistry of organic compounds and can be recommended for analytical control of the content of chemical compounds in the effluents of the industries of pharmaceuticals and chemical industries.

The closest in technical essence and the achieved effect is a method of determining dihydroxybenzenes in aqueous solutions (RU patent 2315994, BI No. 3 from 27.01.2008), which includes extraction concentration of dihydroxybenzenes from acidified aqueous acetonitrile in the presence of vicariates of ammonium sulfate in the amount of 36.5-40.0 wt.% with respect to the sample mass and definition in their separated organic phase by the method of reversed-phase microcolumn liquid chromatography

The disadvantages of the method: high consumption of expensive and scarce reagent (ammonium sulfate); the need for pH control; the duration of the analysis.

The technical result of the invention is to simplify and cheapen the way, increasing the degree of extraction of phenols, lower detection limits.

The task and the technical result is achieved in that in the method of determination of phenol in aqueous solution by the method of reversed-phase microcolumn high-performance liquid chromatography with pre-stage promophoto and method liquid-liquid extraction with acetonitrile, according to the invention the extraction is carried out at a temperature of 263±2 within 30 minutes when the ratio of the equilibrium volumes of aqueous and organic phases 1:1.

The simplification and cheapening of the method is due to the exclusion from the stage of preparation of vicariates (ammonium sulfate) and acidifier.

The method of determination of phenols (phenol, o-, m-, p-cresol and o-tert-butylphenol) in aqueous solutions as follows.

In a separating funnel to make 10 ml of an aqueous solution analyzed phenol (concentration 0.02-1.0 mg/l), add to it 10 ml of acetonitrile and placed the funnel in the freezer, maintaining temperature of 263 K (-10°C). Withstand test (30 min) prior to the formation of two liquid phases, the upper organic layer is separated from the water and analyze by method of reversed-phase HPLC on a Gilson instrument (odnonasosnaya version with pump 302 Piston Pump and detector NM Holochrome UV/Vis). To enter samples into the chromatograph used injector Rheodyne 7125 loop with a capacity of 20 µl. Chromatograph conditions were as follows: column Nucleosil 100-C18, particle size 5 μm, column size 4×250 mm; the volume of injected sample 5 µl; mobile phase of water - acetonitrile (1:4), flow rate of mobile phase, 1 ml/min; analytical wavelength of 274 nm. The retention times of: phenol 2.5 min, Cresols 2.7 min (isomers are not separated), o-tert-butylphenol 4.1 minutes

The concentration of phenols in the extract With ODA is really on the calibration curve S=S (linear ranges 0-1 .20 mg/l), and the content of phenols in the original water sample is determined by the formula:

Withabout=100/(R r),

where S is the analytic signal detector, mV·; K is the calibration coefficient; C is the concentration of phenol in the extract, mg/l;aboutthe concentration of phenol in the original water sample, mg/l; r is the ratio of the equilibrium volumes of aqueous and organic phases; R is the degree of extraction of phenol in the water - acetonitrile, %. The degree of extraction of phenols in calculated by the formula:

R=100D/(D+r),

where D is the distribution coefficient of phenols in the water - acetonitrile.

The duration of the analysis sample preparation for 40-45 minutes. The degree of extraction of phenols proposed method is of 97.8-99.2%, and the detection error does not exceed 10%.

Table 1 - table of distribution coefficients D and the degree of extraction of phenols R; n=5, P=0.95.

Table 2 shows the results of observation of the formation of heterogeneous phase when conditions change analysis. Table 3 shows the comparative characteristic of the proposed method and prototype.

The method is illustrated by the following example.

Solutions prepared from phenols drugs qualification "HC" (Merck, Germany). The original aqueous solutions with accurately known concentration is prepared by the method of dilution of the standard solutions.

In a separating funnel to make 10 ml of an aqueous solution analyzed phenols (to the centering of 0.02-1.0 mg/l), add to it 10 ml of acetonitrile and placed the funnel in the freezer, maintaining temperature of 263 K (-10°C). Withstand test (30 min) prior to the formation of two liquid phases, the upper organic layer is separated from the water and analyze by method of reversed-phase HPLC on a Gilson instrument (odnonasosnaya version with pump 302 Piston Pump and detector NM Holochrome UV/Vis). To enter samples into the chromatograph used injector Rheodyne 7125 loop with a capacity of 20 µl. Chromatograph conditions were as follows: column Nucleosil 100-C18, particle size 5 μm, column size x mm; the volume of injected sample 5 µl; mobile phase of water - acetonitrile (1:4), flow rate of mobile phase, 1 ml/min; analytical wavelength of 274 nm. The retention times of: phenol 2.5 min, Cresols 2.7 min (isomers are not separated), o-tert-butylphenol 4.1 minutes

The concentration of phenols in the extract is determined by calibration curve S=S (linear ranges 0-1 .20 mg/l), and the content of phenols in the original water sample is determined by the formula:

Co=100C/(R r),

where S is the analytic signal detector, mV·; K is the calibration coefficient; C is the concentration of phenol in the extract, mg/l;aboutthe concentration of phenol in the original water sample, mg/l; r is the ratio of the equilibrium volumes of aqueous and organic phases; R is the degree of extraction of phenol in the water - acetonitrile, %. The degree of extraction of phenols in calculated by the formula:

=100D/(D+r),

where D is the distribution coefficient of phenols in the water - acetonitrile.

The duration of the analysis sample preparation for 40-45 minutes. The degree of extraction of phenols proposed method is of 97.8-99.2 percent.

Table 2 shows the results of observation of the formation of heterogeneous phase from a mixture of acetonitrile with water at various ratios of their volumes (τ - aging time at a temperature of 263 K: 1 - homogeneous liquid system; 2 - two-phase heterogeneous system liquid - liquid; 3 - two-phase heterogeneous system ice - water and the organic liquid phase)

As can be seen from table 2, when the reduction of the time of low-temperature extraction does not result in formation of two-phase heterogeneous system liquid-liquid, the increase in time is not feasible; the change in the ratio of the equilibrium quantities in the direction of increasing the organic phase leads to the decrease in the concentration, the decrease in the volume of the organic phase does not lead to the formation of heterogeneous systems. With decreasing temperature is observed sorption of phenols on the surface of the formed ice crystals, which leads to loss of focus phenol and extractant in the form of the resulting liquid micro inclusions in the ice phase.

The correctness of the method is tested on the model solutions of phenols method "introduced - found". Relative oshi is ka determination of phenols does not exceed 10%.

Given in table 3 comparative characteristics of the proposed method and the prototype shows that the simplified method and reduced the run time analysis due to the exclusion from the stage of preparation of vicariates and acidifier. Decreased the detection limit of 5 times. Expanded scope to control the content of phenols (phenol, o-, m-, p-cresol and o-tert-butylphenol).

The method of determination of phenol in aqueous solution by the method of reversed-phase microcolumn high-performance liquid chromatography with pre-stage of the sample preparation method of liquid-liquid extraction with acetonitrile, characterized in that the extraction is carried out at a temperature of 263±2K for 30 min with a ratio of the equilibrium volumes of aqueous and organic phases 1:1.



 

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