SU1735759A1 - Method for determination of methanol in water - Google Patents

Abstract

This invention relates to analytical chemistry, in particular to the determination of methyl alcohol in water. The goal is to increase sensitivity and reduce analysis time. For this, the sample is treated with acid or alkali, 10% of the sample volume is distilled off (preferably 50 cm from 5QO cm3), followed by processing of an aliquot of the distillate with chromotropic acid. The minimum concentration of methanol in water is 0.1 mg / dm3, the time for determination is 1, 5 hours "1 or 3" 3

Description

This invention relates to analytical chemistry, in particular to a method for the quantitative determination of methyl alcohol (methanol) in water.

A known method for the quantitative determination of methanol, comprising treating the sample under investigation with sodium nitrite solution, concentrated sulfuric acid, followed by capturing the released methyl nitrite with a solution of urea in hypochlorous acid in the presence of a platinum catalyst, oxidizing the methanol to formaldehyde with a solution of potassium permanganate in phosphoric acid and potassium in a phosphoric acid with a solution of potassium in the presence of a platinum catalyst, phosphoric acid with potassium permanganate in a phosphoric acid and a solution of phosphoric acid in a phosphoric acid; the resulting solution o

The disadvantage of this method is its multi-stage, long duration and low sensitivity.

The known method for the chromatographic determination of methanol in water

The disadvantage of this method is low sensitivity.

A known method for the quantitative photocolorimetric determination of methanol in wastewater is by precursors. the distillation of the test sample with the addition of acid or alkali in order to separate the methanol from the interfering impurities under conditions that ensure the complete transfer of methanol to the distillate (200 cm of the original or diluted distilled water of the test sample is added depending on the impurities contained and 2 are distilled off (3 volumes of liquid), then another 100 cm of distilled water is poured into the distillation flask and again distilled, collecting 100 cm3 of distillate, which is added to the first portion of the distillate and then successively abotki 2.5 cm3 permanganate. potassium in an acidic environment, sodium bisulfite; hro

Wj

ate sj

in

: 0

with tropic acid and photometry of a colored product of the interaction of formaldehyde formed during methanol oxidation with chromotropic acid

The calibration graph is constructed by sampling 2.5 cm standard solutions each with a concentration of methanol in water of 0 mg / dm and processing them under the conditions of the analysis, while excluding the process of distillation

The disadvantages of the method are low sensitivity of the method.

to

The purpose of the invention is to increase the sensitivity and reduce the duration of the method for determining methanol in water.

The goal is achieved by distilling the test sample with the addition of acid or alkali, depending on the content of impurities to. achieving a distillate volume of 10% of the initial sample volume (preferably overtaking 50 cm from 500 cm of sample), determining methanol in the obtained distillate, treating 5 cm of distillate with potassium permanganate in acid

(0.5 mg / dm), which does not allow the control medium, then, after recovery from

The purpose of the invention is to increase the sensitivity and reduce the duration of the method for determining methanol in water.

The goal is achieved by distilling the test sample with the addition of acid or alkali, depending on the content of impurities to. achieving a distillate volume of 10% of the initial sample volume (preferably overtaking 50 cm from 500 cm of sample), determining methanol in the obtained distillate, treating 5 cm of distillate with potassium permanganate in acid

5 environment, then, after recovering from

the methanol content in the treated wastewater discharged into reservoirs, for which the norm in methanol content is 0.1-0 mg / dm (depending on the presence of other toxic substances in the sample and their concentrations), the error in the analysis of water samples is high, containing about 0.5 mg / dme of methanol (in the sensitivity range of the method), the duration of the analysis (2.5 hours), which does not allow timely detection of methanol content in the waste water in excess of the norm.

The closest in technical essence and the achieved result to the proposed is a method of quantitative photocolorimetric determination of methanol in water by reaction with chromotropic acid by preliminary distillation of the sample under conditions ensuring complete transition of methanol to distillation and subsequent processing of 5.0 cm of distillation of potassium permanganate, then sodium bisulfite and chromotropic acid. At the same time, to build a calibration graph, a series of standard solutions with a content of methyl alcohol of 0.25 to 10 mg / dm is analyzed in accordance with the course of the analysis, including the distillation process.

The disadvantages of the method are low sensitivity of the method L0.20 mg / dm5), which does not allow detecting the methanol content below 0.2 mg / dme and with sufficient accuracy to control the methanol content in the concentration range of 0.2 + 0.1 mg / dm ( in the field of sensitivity of the method), the duration of the analysis (2S5 h), which leads to untimely information about the content of methanol in water

five

0

potassium permanganate by-product sodium bisulfite and chromotropic acid, the product of interaction with which is photometrized and the methanol content is calculated according to a calibration graph constructed with a series of standard solutions with a methanol concentration of 0.05 1.0 mg / dm in full accordance with the conditions of the analysis , including stripping 10% „

The drawing shows calibration graphs for the determination of small amounts of methanol in water, constructed

a) under the conditions of the proposed method

b) under the conditions of a known method.

In the distilled fraction of the water being analyzed (and in the construction of the calibration graph — standard solutions), f is 10 o of the initial volume

5 of the sample, the proportion of methanol contained in the sample is transferred, which is about ku wt.% Of its initial amount in the recovered volume. This amount is taken into account when calculating the result

0 analysis due to the fact that the preliminary construction of the calibration curve is carried out by distilling and analyzing a series of standard solutions under the same conditions as when performing

$ analysis about

Assemble a sample distillation unit consisting of a round-bottom flask with a capacity of 1000 cm, a Kjeldahl droplet separator, a refrigerator, an alcohol bottle and a receiver. A measuring cylinder with a capacity of 50 cm is used as a receiver.

500 cm of the initial or previously diluted to a methanol concentration of 0.05 - is introduced into the distillation flask. 1.0 mg / dmz sample of water; 5.0 cm5 of 30% sodium hydroxide solution are added to the contents of the flask and distilled

517

exactly 50 cm of liquid. The distilled fraction is mixed. To a tube with a capacity of 20 cm with a ground stopper, 5.0 strips are added, 1.0 cm of diluted 1: 3 sulfuric acid, 0.5 cm of a solution of manganese-sour potassium with a concentration of 2 wt. % 0 The contents of the tube are mixed gently, turning three times (always the same number of times) and left to stand for 10 minutes.

At the same time, a blank experiment is done, for this, 5.0 cm of distilled water is poured into the tube, the same reagents as were introduced into the tube with the working solution are poured, and allowed to stand for 10 minutes after the indicated time, drop by drop in the tube, while stirring the solution, a saturated solution of sodium sulfite is poured until the manganese-sour potassium is decolorized. Then, the same amount of sodium sulfite solution is injected into a test tube with a working solution of 0 i. To the colorless solutions obtained in test tubes, 0.5 cm of an alkaline solution of chromotropic acid (1, 8-dioxynaphthalene –3 rb-disulfonic acids) and 5 cm are added. concentrated sulfuric acid. Close the tubes and mix gently, periodically opening the stopper. The tubes are closed with stoppers for 30 minutes in a boiling water bath. The contents of the tubes are then cooled and transferred to colorimetric cells with an absorbing layer thickness of 20 mm. The optical densities of the solutions are measured with a green light filter at a wavelength of nm with respect to distilled water I

Building a calibration graph. Preparing a series of standard solutions of methanol in distilled water with a volume of 500 cmu with a concentration of methanol of 0.05; 0.1; 0, 2; 0.3,., L0 kg / dm3. 50 cm3 of the solution are distilled out of 500 cm of each standard solution and then analyzed under the conditions described. According to the obtained data, a calibration graph is plotted, plotting the difference of optical densities of the working and blank experiments along the ordinate axis, and the corresponding methanol content on the abscissa axis. mg / dme) in standard solutions,

The methanol content in the test sample is calculated by the formula:

5759

at

500 V

five

Where X.- methanol content in the sample, mg / dm; Y is the sample volume taken for analysis,

cm ;

С is the methanol content corresponding to the difference in optical densities of the working and blank experiments, found from the graduation schedule, mg / dm-4; 500 is the volume to which it is diluted.

sample, see „

Analysis duration 80 - 110, min. The minimum detectable concentration is 0.05 mg / dm o.

The statistically processed results of the determinations with n 6, P 0.95 are given in table „1„

Table 1

25

thirty

Example 1. Build calibration curves with standard methanol solutions with a concentration of 0.05; 0.1; 0.25; 0.5; 0.75; 1.0 cm3 known and proposed methods „

The measurement results obtained in the construction of calibration graphs are given in gab0 2,

table 2

55

The data table. 2 and graphs show: the optical density value of 0.02 corresponds to the methanol content in water of 0.25 mg / dm5 by the known method and 0.05 mg / dm - according to the proposed method, which indicates a 5-fold increase in the sensitivity of the method while reducing the duration of one analysis for 60-80 minutes „

PRI me R 2, Standard growth - HOD. containing mg / dm5 of methanol, analyzed by the proposed and known methods.

17357598

Bones, 5.0 cm 3 vaadel of mixed distillate are selected for oxidation followed by reaction with chromo, tropic acid. The values of the measured optical density of the working and blank tests are: Dp 0.085; and 0, up to 0.04. The graph (graph a) determines the methanol content JJ corresponding to AD 0.0 t,, mg / dm5. The determination error is 16.6 rel,%; Duration of determination is 90 min

PRI me R 3. Standard solution

By a known method: to 200 cm containing 0.25 mg / dm5 of methanol., 20 cm are poured into the ana-test solution and lysed as indicated in Example 2,

Example

alkaline solution with a concentration of 30, 140 cm is distilled off, 100 cm3 of distilled water are poured into the flask e residue and another LOP cm is distilled off. Both distillates are discharged into a 250 cm volumetric flask, made up to the mark with water and stirred, 5.0 cm e the distillate is taken for oxidation followed by reaction with chromotropic acid.

Optical density of photometric solutions; Dp 0, Dx 0.045 ,. The result of the determination is the absence of methanol; analysis time 2.5 hours

According to the proposed method, 50 cm of an alkali solution with a concentration of 30 masts is poured into 500 cm of the test sample and exactly 50 cm of a standard solution is distilled.

containing 0.5 mg / dm3 of methanol, analyzed as indicated in example 2–20 Example 5U A standard solution containing 1.0 mg / dm of methanol, analyzed as indicated in example 2,

Example 6 A standard solution containing 0.025 mg / dm of methanol is analyzed as indicated in Example 2.

PRI me R 7. Biologically purified industrial water with a content standard. Methanol not more than 0.1 mg / dm is analyzed as indicated in Example 2, "Example 8, Standard solution with a concentration of methanol 3.0 mg / dm is analyzed by the known m proposed ways

The results of the procedure are given in Table. 3 Note C — the result of the determination of methanol; W - error

definitions; Ј duration of determination; - the analysis was performed with preliminary dilution of 150 cm samples to 500 cm-e with distilled water.

Example

Standard solution

containing 0.5 mg / dm3 of methanol, analyzed as indicated in example 2b Example 5U A standard solution containing 1.0 mg / dm of methanol, analyzed as indicated in example 2,

Example 6 A standard solution containing 0.025 mg / dm of methanol is analyzed as indicated in Example 2.

PRI me R 7. Biologically purified industrial water with a content standard. Methanol is not more than 0.1 mg / dm analyzed as indicated in Example 2, Example 8, Standard solution with a concentration of methanol 3.0 mg / dm is analyzed by the known m proposed in ways

The results of the study are given in Table. 3Table 3

From example 2 it follows that the content of methanol in water is 0, T2 mg / dm by a known method is not detected, and the method proposed is determined with; with an error of 16.6 rel.

The data of Tables 1 and 3 show that the relative determination error both by known and proposed methods depends on the concentration of the methane-JQ color intensity of which was measured and has a maximum value photoelectrocolorimetric, about t is the sensitivity range of the method. It is painful because, with high sensitivity, the proposed increase in sensitivity and low method makes it possible to increase the precision of the duration of the method, determine the methanol in the jj region, and preliminarily distill the sample from the known method to a distillation volume of 10%. from the sample (example 3) of the distilled sample.

Editor I. Yatsola

04 06 Off

Compiled by T. Akhmetova Tehred M. Didyk

Claims (1)

Claims. The method of determining methyl alcohol in water by pre-distilling the test sample with the addition of alkali or acid, oxidizing methanol to formaldehyde, reacting the latter with chromotropic acid to form a colored compound, 7 O C, mg / dm3 i Proofreader M. Samborska