RU2021595C1 - Method of phenol determination in aqueous solution - Google Patents

Abstract

FIELD: analytical chemistry. SUBSTANCE: method involves concentration of phenol and nitro-derivatives from aqueous solution with methylethylketone in the presence of ammonium sulfate which is taken at concentration 40-43 wt. - % relation to analyzing aqueous sample. Phenol is determined by potentiometric titration in the medium of acetonitrile with isopropanol solution of potassium hydroxide. Method is used for determination of organic compounds. EFFECT: improved method of assay. 1 tbl

Description

 The invention relates to analytical chemistry and can be used in the analysis of natural and treated wastewater.

 A known method of potentiometric indirect determination of phenol in a non-aqueous solvent (1). However, this technique does not allow the determination of phenol in the presence of nitrophenols in wastewater.

 The closest in technical essence and the achieved result is a method for the photometric determination of phenol and nitrophenols in an aqueous medium by reaction with diazotized sulfanilic acid (2). The disadvantage of this method is that it is impossible to determine phenol and nitro derivatives separately, since the light absorption maxima of the reaction products of diazotized sulfanilic acid with phenol and mononitro derivatives are respectively 440 and 470 nm.

 The aim of the invention is to increase the selectivity and lower the detection limit of phenol in the presence of nitrophenols in aqueous media.

 This goal is achieved by the fact that in the method for determining phenol in an aqueous solution to increase the sensitivity and selectivity of determination in the presence of nitrophenols, methyl ethyl ketone, ammonium sulfate in an amount of 40-43 wt.% Relative to the sample are added to the analyzed sample, followed by titration of the resulting mixture in acetonitrile isopropanol solution of potassium hydroxide.

 The positive effect of the proposed method is achieved due to the fact that the combination of the determined extractant (methyl ethyl ketone), salting out agent (ammonium sulfate), as well as acetonitrile, as a medium for titration, can significantly reduce the phenol detection limit, as well as quantitatively selectively determine phenol in the presence of nitro derivatives. The achievement of this goal is also facilitated by the use of an isopropanol solution of KOH as a titrant and the presence in the aqueous solution of 40-43 wt.% Salting out agent.

 The method consists in the fact that to 100 ml of an aqueous sample containing phenol and nitrophenols, a salting out agent is added at room temperature (40-43 wt.%) And 1.5 ml of methyl ethyl ketone, extracted with a vibrating mixer for 10 minutes. After delamination of the system (5 min), the extractant is separated (without capturing the aqueous layer), placed in a titration beaker with 12-15 ml of acetonitrile and titrated potentiometrically with an isopropanol solution of potassium hydroxide.

 PRI me R (prototype). To 10 ml of an analyzed aqueous solution containing phenol and nitrophenols, 2 ml of diazotized sulfanilic acid are added, and after 5 minutes, 2 ml of a 5 M sodium carbonate solution are made alkaline. After 40 minutes, the optical density of the yellow or orange-yellow solution was measured at 420-470 nm. Separate determination of phenol and nitrophenols is impossible, due to the significant overlap of the absorption spectra of their reaction products with diazotized sulfanilic acid.

EXAMPLE 1. To 100 ml of an analyzed aqueous sample saturated with ammonium sulfate at room temperature (40 wt.% Salt) containing 0.6 mg / ml phenol (ratio of phenol concentration to total nitrophenol C ⁱⁿ _f / C ⁱⁿ _nf is 1: 1), 1.5 ml of methyl ethyl ketone are added. It is extracted for 10 minutes, after phase separation (5 minutes), the extract is taken off (without capturing the aqueous phase) and placed in a beaker containing 12-15 ml of acetonitrile dehydrated with calcined sodium sulfate. The extract is titrated with an isopropanol 0.05 M KOH solution in the presence of platinum and saturated silver chloride electrodes. The differential form of the titration curve determines the amount of alkali that went into the phenol titration. Under experimental conditions, phenol is titrated last in the potential range of 280-400 mV, separately with mononitrophenols.

, где C^в _ф - содержание фенола в анализируемом водном растворе, мг/мл;
C_КОН - концентрация титранта, моль/л;
V_КОН - объем титранта, пошедший на титрование фенола, мл;
V_э - объем экстракта, отобранного после расслаивания фаз, мл;
М_ф - эквивалентная масса титруемого вещества (фенола);
D - коэффициент распределения фенола между метилэтилкетоном и водным раствором, насыщенным сульфатом аммония;
τ- равновесное соотношение объемов водной и органической фаз.The phenol content in the aqueous solution is calculated by the equation:
C $\genfrac{}{}{0ex}{}{\text{at}}{\text{f}}$ =

where C ⁱⁿ _f is the phenol content in the analyzed aqueous solution, mg / ml;
C _KOH — titrant concentration, mol / L;
V _KOH - titrant volume, which went to the phenol titration, ml;
V _e - the volume of the extract selected after phase separation, ml;
M _f - equivalent mass titratable substance (phenol);
D is the distribution coefficient of phenol between methyl ethyl ketone and an aqueous solution saturated with ammonium sulfate;
τ is the equilibrium ratio of the volumes of the aqueous and organic phases.

= 0,56 мг/мл
П р и м е р 2. К 100 мл анализируемой водной пробы, насыщенной сульфатом аммония (41,5 мас.%), содержащей 0,6 мг/мл фенола (C^в _ф/C^в _нф=1:1), прибавляют 1,5 мл метилэтилкетона. Далее анализ выполняют, как указано в примере 1. Определение фенола возможно, C^в _ф=0,58 мг/мл.Calculation according to example 1
For titration of 1 ml of the extract in acetonitrile medium, 11.0 ml of titrant was consumed, concentration 0.05 mol / L, D = 1260, τ = 100. Then the phenol content in the analyzed aqueous solution is equal to:
C $\genfrac{}{}{0ex}{}{\text{at}}{\text{f}}$ =

= 0.56 mg / ml
PRI me R 2. To 100 ml of the analyzed water samples saturated with ammonium sulfate (41.5 wt.%) Containing 0.6 mg / ml phenol (C ⁱⁿ _f / C ⁱⁿ _nf = 1: 1), add 1.5 ml of methyl ethyl ketone. Further, the analysis is performed as described in example 1. The determination of phenol is possible, C ⁱⁿ _f = 0.58 mg / ml.

PRI me R 3. To 100 ml of the analyzed water samples saturated with ammonium sulfate (43 wt.% Salt) containing 0.6 mg / ml phenol (C ⁱⁿ _f / C ⁱⁿ _nf = 1: 1), add 1 , 5 ml of methyl ethyl ketone, then the analysis is carried out as described in example 1. Determination of phenol is possible C ⁱⁿ _f = 0.63 mg / ml.

PRI me R 4. To 100 ml of the analyzed water samples saturated with ammonium sulfate at room temperature (38 wt.%) Containing 0.6 mg / ml phenol (C ⁱⁿ _f / C ⁱⁿ _nf = 1: 1), 1.5 ml of methyl ethyl ketone are added. The method is not feasible, since the volume of extract released after phase separation is insufficient for further detection of phenol, moreover, it contains a significant amount of water, which negatively affects the determination.

PRI me R 5. To 100 ml of analyzed water saturated with a salting out agent at room temperature (45 wt.%) Containing 0.6 mg / ml phenol (C ⁱⁿ _f / C ⁱⁿ _nf = 1: 1), add 1 5 ml of methyl ethyl ketone. The method is not feasible, since precipitated salt crystals significantly adsorb phenol and nitrophenols.

PRI me R 6. To 100 ml of the analyzed water samples saturated with ammonium sulfate (40 wt.% Salt) containing 0.3 mg / ml phenol (C ⁱⁿ _f / C ⁱⁿ _nf = 1: 2), add 1 5 ml of methyl ethyl ketone. Further analysis is carried out as described in example 1. The definition of phenol is possible, C ⁱⁿ _f = 0.34 mg / ml.

PRI me R 7. To 100 ml of the analyzed water samples saturated with ammonium sulfate (41.5 wt.% Salt) containing 0.6 mg / ml phenol (C ⁱⁿ _f / C ⁱⁿ _nf = 1: 0.5 ), add 1.5 ml of methyl ethyl ketone. Further analysis is carried out as described in example 1. The definition of phenol is possible, C ⁱⁿ _f = 0.61 mg / ml.

PRI me R 8. To 100 ml of the analyzed aqueous samples saturated with ammonium sulfate (43 wt.% Salt) containing 0.03 mg / ml phenol (C ⁱⁿ _f / C ⁱⁿ _nf = 1: 1), add 1 5 ml of methyl ethyl ketone. Further, the method is carried out as described in example 1. The concentration of titrant of 0.005 mol / L. The determination of phenol is possible, C ⁱⁿ _f = 0.0052 mg / ml.

PRI me R 9 To 100 ml of an analyzed water sample saturated with ammonium sulfate (41.5 wt.% Salt) containing 0.03 mg / ml phenol C ⁱⁿ _f / C ⁱⁿ _nf = 1: 1), add 1 , 0 ml of methyl ethyl ketone. The method is not feasible, since the equilibrium volume of the organic phase and the phenol content in it are small and further determination is impossible.

PRI me R 10. To 100 ml of the analyzed aqueous samples saturated with a salting out agent at room temperature (40 wt.% Salt) containing 0.03 mg / ml (C ⁱⁿ _f / C ⁱⁿ _nf = 1: 1), add 2.0 ml of methyl ethyl ketone. Further, the analysis is carried out as described in example 1. The method is not feasible, since the initial ratio of the volumes of the aqueous and organic phases does not allow to achieve the required degree of extraction and concentration coefficient for further quantitative determination of phenol.

 From examples 1-10 and the table shows that the positive effect of the proposed method is achieved when using methyl ethyl ketone (1.5 ml per 100 ml of the original analyzed sample) as an extractant, and ammonium sulfate (40-43 wt.% In relation to to the analyzed water sample), as the medium for titration - acetonitrile, titrant - isopropanol solution of KOH, the concentration of which is determined by the content of the analyte in the sample (examples 1-7,8-10). When reducing the amount of salt (example 4) and the volume of extractant (example 9), the implementation of the method is impossible due to the partial dissolution of methyl ethyl ketone in water and insufficient for further determination of the volume of the equilibrium phase of the extract. At the same time, under these conditions, the extract contains a significant amount of water, which interferes with the determination of phenol. The increase in the volume of extractant (example 10) at the indicated content of phenol and nitrophenols in the aqueous sample does not allow them to be concentrated to the extent necessary for further determination. An increase in the amount of added salting out agent (Example 5) leads to the precipitation of salt crystals and their adsorption of the analyte.

 Compared with the prototype, the proposed technical solution has the following advantages: it is possible to quantify phenol in an aqueous sample in the presence of nitrophenols in a wide range of concentration ratios; the phenol detection limit is reduced under conditions when the determination of the prototype is impossible.

Claims (1)

 METHOD FOR DETERMINING PHENOL IN AQUEOUS SOLUTION, including treatment with a chemical reagent, characterized in that, in order to increase the sensitivity and selectivity of determination in the presence of nitrophenols, methyl ethyl ketone, ammonium sulfate in an amount of 40 - 43 wt. % with respect to the sample, followed by titration of the resulting mixture in acetonitrile medium with isopropanol solution of potassium hydroxide.

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