RU2464368C1 - Method of producing universal acid-base indicator paper - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: universal acid-base indicator paper for determining pH of a solution is obtained by saturating chromatographic paper with a solution of a mixture of acid-base indicators and a fixing agent. The fixing agent used is tetraalkylammonium halide with content thereof in the solution of 0.2-2.0 wt %, which is selected from: tetramethylammonium chloride, bromide or iodide, tetraethylammonium chloride, bromide or iodide, tetrapropylammonium chloride or bromide, trimethyloctylammonium bromide, wherein the solution of the mixture of acid-base indicators and fixing agent is turned yellow by 0.1 n sodium hydroxide solution.

EFFECT: invention enables to obtain a universal acid-base indicator paper, having contrast colour transitions on a wide pH scale, from 2 to 12, resistance to washing off of the resultant colour after contact with the analysed sample, which enables to determine pH in aqueous solutions, suspensions and emulsions with high accuracy.

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Description

The invention relates to the field of research or analysis of materials using chemical indicators, in particular to a method for producing acid-base indicator paper, and can be used in analytical chemistry, chemical technology to determine the pH of aqueous solutions, suspensions, emulsions and biological fluids.

A known method of obtaining an acid-base indicator strip by impregnation of filter chromatographic paper with solutions of acid-base indicators (SU 524534, 1976, class D21F 11/14).

The disadvantage of indicator paper obtained by these methods is the weak fixation of the indicator on a cellulose carrier, washing out the indicator from the paper into the analyzed solution, as well as the erosion of the color of the indicator paper in contact with the analyzed solution, which reduces the accuracy of pH determination due to zones arising due to the capillary effect various indicator colors.

There is also a method of producing acid-base indicator paper for determining pH in the range of 5-9 by treating filter paper with a mixture of reagents containing 0.0012 g of methyl red, 0.016 g of bromothymol blue, 2.40 g of polyvinyl alcohol, 0.04 g of polyoxyethylene sorbate monolaurate, in 40 ml 35 % ethanol [GB 922606, 1963].

The disadvantage of this method of obtaining acid-base indicator paper is the difficulty of obtaining polyoxyethylene sorbitan monolaurate, and the composition of the impregnating solution is complex and not reproducible, as it consists of a mixture of fixatives.

There is also a method of producing indicator paper for determining protein, glucose and urine pH by impregnating filter paper with a solution of a mixture of pH indicators containing nitrazine yellow, thymol blue, bromothymol blue, p-nitrophenol, and gelatin [CS 178708, 1979, cl. G01N 33/16].

The disadvantage of this method of obtaining indicator paper is that indicator paper in contact with the analyzed solutions takes a heterogeneous color due to the erosion of the indicator dye, because gelatin does not improve its stability in alkaline environments.

The closest in technical essence to the proposed method is a method of producing an acid-base indicator paper for determining the pH of a solution [SU 1127935] (prototype) by impregnating chromatographic paper with a solution of an acid-base indicator and fixative, which is used as a 0.3 ÷ 1.8% sodium sulfate solution in 40 ÷ 60% ethanol.

The disadvantage of the known prototype method for producing acid-base indicator paper is its limited scope, only for pH 5-9, in the range of color transitions from yellow at pH 5 to dark blue at pH 9 through yellow-green and green-blue tones.

The second disadvantage is that sodium sulfate is insoluble in alcohol, while a number of indicators, on the contrary, are insoluble in a water-alcohol solution, which limits the use of the prototype for universal paper.

The technical result of the invention is to increase the accuracy of measuring the pH of the medium in a wider range of acidity and alkalinity, while increasing the stability of the universal mixture of acid-base indicators to erosion during the use of universal acid-base indicator paper.

The specified technical result is achieved by the fact that in the known method for producing a universal acid-base indicator paper for determining the pH of a solution by impregnating chromatographic paper with a solution of a mixture of acid-base indicators and a fixing agent according to the invention, tetraalkylammonium halide with its content in solution of 0.2 ÷ 2.0 wt is used as a fixing agent .%, which is selected from the series: tetramethylammonium chloride, bromide or iodide, tetraethylammonium chloride, bromide or tetrapropylammonium chloride or bromide I trimetiloktilammoniya bromide, the mixture solution of acid-base indicators and fixer is adjusted to yellow 0.1N. sodium hydroxide solution.

As indicators, for example, methyl red, methyl orange, methyl yellow, bromothymol blue, thymol blue, xylenol blue, phenolphthalein, alizarin yellow P, tropeolin OO, etc. are used.

As fixers, the row given in the formula was selected, which allows to achieve a high technical result. However, this enumeration is not limited to the use of equivalent chemical analogs - tetraalkylammonium halides.

Of the number of fixatives, it is preferable to use cheaper and non-toxic tetraethylammonium chloride and bromide.

The content of tetraalkylammonium halide in the solution of 0.2 ÷ 2.0 wt.% Is due to the fact that at a concentration of less than 0.2 wt.%, The action of the fixing agent is significantly reduced, and at a concentration of more than 2.0 wt.%, Further achievement of the result is difficult due to the increase in drying time of the paper and increase in the cost of the product with the exclusion of further improvement in the contrast of color transitions.

In preparing a solution of a mixture of acid-base indicators and fixing agent, known solvents are used, preferably based on ethanol.

The proposed method of obtaining a universal acid-base indicator paper (UKOIB) is as follows.

Prepare a solution of a mixture of acid-base indicators and fixative. The resulting solution is fed into the impregnation bath of an impregnation-drying machine. A roll of base paper for express tests of brand III TU 13-730800-721-85 (160 g / m ² ) with a diameter of 260 mm and a width of 8.5 cm weighing 2150 g is inserted into the holders of the impregnation unit of the impregnation-drying machine and the tape is passed by turning on the broaching device paper through an impregnation bath equipped with a contact roller, into which the impregnation solution flows by gravity, then the impregnated paper is fed through the supply and exhaust drying zones at 60 ° C to the take-up reel with receiving rotation. A yellow UKOIB bobbin is obtained.

Obtained by this method, the universal acid-base indicator paper (UKOIB) has a uniform color and the accuracy of determination exceeds the quality of UKOIB obtained from the same indicators by other known methods.

A convenient analytical form is prepared from UKOIB. The tape with a width of 8.5 cm is duplicated with double-sided adhesive tape with a protective layer. The resulting preform is cut lengthwise into 1 cm wide tapes, the protective layer is removed from the tape and the tape is fixed along the edge of the polymer substrate (for example, polyvinyl or polypropylene). Then, the polymer substrate with the fixed indicator tape is cut across using a size cutting device into strips representing a polymer strip-substrate 1 cm wide with a square of 1 cm UKOIB at the end.

Using the proposed method allows to obtain a universal acid-base indicator paper in the form of indicator strips with a more uniform color and clear color transitions when determining pH, with better contrast color transitions in a wide pH range and resistance to erosion by liquid media.

The implementation of the proposed method is illustrated by specific examples of obtaining UKOIB pH 2-10 and UKOIB pH 2-12 with various color transitions. The examples illustrate but do not limit the proposed method.

Example 1. UKOIB pH 2-10 (color transition option 1)

A paper impregnation solution was prepared by dissolving methyl yellow 0.186 g, methyl red 0.124 g, bromothymol blue 0.280 g, thymol blue 0.324 g, phenolphthalein 0.068 g, tetraethylammonium bromide (TEAB) 9.0 g in 740 ml of ethanol (1.52 wt.% TEAB ) 0.1 N was added dropwise to the resulting solution. sodium hydroxide solution until a yellow color appears. They impregnated a roll of base paper for express tests of grade III on an impregnation-drying machine with this solution. Produced indicator strips, which were packaged in pencil cases with a color comparison scale in the pH range of 2-10. The obtained UKOIB pH 2-10 (color transition 1) gave the following color pH - color: 2 - red, 3 - orange-red, 4 - orange, 5 - orange-yellow, 6 - yellow, 7 - greenish-yellow, 8 green, 9 is greenish blue, 10 is dark blue. The error in determining the pH of the solution was 2%.

Example 2. UKOIB pH 2-12 (color transition 2)

A paper impregnation solution was prepared by dissolving the tropeolin OO 0.7 g, methyl orange 1 g, methyl red 0.8 g, bromothymol blue 4 g, phenolphthalein 5 g, alizarin yellow P (sodium p-nitrobenzene azosalicylate) 0.6 g, tetraethylammonium chloride (TEAC) 20 g in 1 l of 50% ethanol (2.0 wt.% TEAC). The resulting solution was impregnated with chromatographic paper grade "G" GOST 10395-75. Obtained UKOIB pH 2-12 (color transition 2) gave the following color pH - color: 2 - orange-red, 3 - red-orange, 4 - orange, 5 - yellow-orange, 6 - orange-yellow, 6.5 - yellow 7 - green-yellow, 8 - green, 9 - green-blue, 9.5 - blue-violet, 10 - violet, 12 - red-violet. The error in determining the pH of the solution was 4%.

Example 3. Determination of optimal ratios of indicators and tetraethylammonium chloride (TEAC)

Prepared a solution of a mixture of indicators in 50% aqueous ethanol according to example 2. Separately prepared a solution of 4 wt.% TEAC in ethanol. Various mixtures of impregnating solutions were prepared from indicator solutions, a TEAX solution, and ethanol, which were used to impregnate base paper sheets for rapid tests, fix them on a white polymer substrate, and compare their properties.

A comparison was made of samples No. 2-5 of the acid-base indicator paper UKOIB pH 2-12 (color transition 2) with sample No. 1 of the acid-base indicator paper obtained with the same indicators, but without the use of a fixing agent - tetraalkylammonium chloride.

The test was carried out according to the criterion of "1 pH" at pH levels: 2.0; 3.0; 4.0; 5.0; 6.0; 7.0; 8.0; 9.0; 10.0; 11.0 and 12.0, by testers who were previously familiarized with the method of working with indicator strips of UKIB. Each technologist made 22 pH determinations using indicator strips.

Comparative data on the quality of UKOIB pH 2-12 are summarized in Table 1.

Table 1 Sample No. UKOIB TEAC in an impregnating solution, wt.% Error in determining pH,% one - fourteen 2 0.2 5 3 0.4 four four 0.8 3 5 1.6 2 according to Example 2 2.0 3

As a result of these tests, it was found that in the case of UKOIB samples with a fixer, the determination error is much smaller than in a UKOIB sample without a fixer (see Table 1). This indicates a high accuracy of pH measurements using USOIB obtained by the proposed method.

Example 4. UKOIB with different content of fixative

Prepared seven solutions for impregnation of paper, as in the case of UKOIB Example 1 (color transition 1), for each solution, various tetraalkylammonium halides from the series indicated in the claims were used as fixative. The test results of UKOIB (color transition option 1) with different content of fixatives are presented in Table 2.

table 2 Fixing agent in impregnating solution The amount of fixative in solution, wt.% Error in determining pH,% Tetraethylammonium iodide 1.8 2 Tetrapropylammonium chloride 1.4 one Tetrapropylammonium bromide 1.0 2 Tetramethylammonium chloride 0.2 5 Tetramethylammonium bromide 0.3 5 Tetramethylammonium iodide 2.0 2 Trimethyloctylammonium bromide 1.8 3

The acid-base indicator paper obtained by the proposed method has a yellow color and has contrasting color transitions on a scale, the strength of indicator fastening, the lack of erosion and the greater resistance of the resulting color after contact with the analyzed samples, which allows high accuracy to determine the pH in aqueous solutions suspensions and emulsions.

Claims (1)

A method of obtaining a universal acid-base indicator paper for determining the pH of a solution by impregnating chromatographic paper with a solution of a mixture of acid-base indicators and a fixing agent, characterized in that tetraalkylammonium halide with its content in the solution of 0.2-2.0 wt.% Is used as fixing agent which is selected from the series: tetramethylammonium chloride, bromide or iodide, tetraethylammonium chloride, bromide or tetrapropylammonium chloride or tetrapropylammonium bromide, trimethyloctylammonium bromide, wherein the solution is a mixture of acid-os The new indicators and fixative are adjusted to yellow with a 0.1 N sodium hydroxide solution.