CS239710B1 - Method of analysis of active chlorine - Google Patents

Abstract

The method is solved in such a way that the analyzed sample containing active chlorine is reacted with dinitronaphthol in solution or on a carrier, for example paper, and the presence and concentration of active chlorine in the sample is determined based on the time taken for the color change to occur. The indicator system according to the invention enables quick and simple determination of the content of active chlorine. It can be used in the analysis of bleaching baths used in the processing of cellulose and paper and in the textile industry.

Description

The invention relates to a method for the analysis of active chlorine.

Determination of active chlorine is mainly solved by the iodometric titraoe method. Colorimetry was also used for detection, when chlorine reacts with the reagent in solution or on the carrier while changing color. 4-Dimethylazobenzene-2-carbo (xylic acid) was used as reagent.

It was dissolved in methanol and saturated with diatomaceous earth. The color of impregnated diatomaceous earth is changed by chlorine gas or even hydrogen chloride. The limit of detection is 100 µg of chlorine, see pat. PLR, No. 112 060.

In addition to color reactions, precipitation reactions are used where chlorine is reduced to chloride and this reacts with silver nitrate to silver chloride, which is photolyzed to metallic silver on paper under the ultraviolet radiation source and densitometrically evaluates the brown spots formed, see pat. GDR, No 124 554.

An instrument based on voltammetric indication with platinum electrodes has been developed for the determination of chlorine in air, see pat. Great Britain, No. 1,423,314.

Said methods of analysis are suitable for detecting or determining free and bound chlorine at various oxidation stages. This makes it possible to apply these methods in particular for air control. In the analysis of solutions, with the exception of iodometric titration, these procedures are less suitable, particularly in terms of selectivity.

The detection of chlorine by 4-dimethylazobenzene-2-carboxylic acid is impaired by the presence of mineral acids and bases. For the determination of active chlorine, that is, the chlorine which is released after acidification and which is capable of further oxidation, these methods of analysis are not always satisfactory.

The principle of the active chlorine analysis method is based on reacting the analyzed chlorine-containing sample with dinitronaphthol in solution or on a carrier, such as paper, and determining the presence and concentration of active chlorine in the sample according to the color change time.

The main advantages of the active chlorine analysis method according to the invention are that the control of hypochlorite solutions up to 3% active chlorine content can be easily ensured.

Compared to the iodometric titration performed so far by this control, the method of analysis according to the invention is faster.

He did

A stock methanol solution of 2,4-dinitro-1-naphthol at a concentration of 5 mg / ml, a stock solution of calcium hypochlorite at a concentration of 1.10 < -1 > mol.l " and hydrogen phthalate buffer solutions were prepared. 1.10 mol.1 with a pH of 1 to 5.

To a tempered cuvette with an edge length of 10 mm, 2 ml of pH 1.0 buffer was dosed at 20 ° C; 3.0 and 5.0, 0.2 dye solution and 2 ml calcium hypochlorite solution, prepared by diluting the stock solution to form a set of twenty solutions with concentrations of 1.10 "2 to 1.10 ^-4 mol.l" in one tenth of a mole . The change in staining as a function of the concentration used was graphically evaluated by changing the time at which the original solution decolorized.

Example 2

20 solutions of calcium hypochlorite were prepared with concentration from 1.10 "to 1.10" ^ mol.l "'in one tenth. Pipettes of 2 ml of 1.10 " mol.l " buffer and pH 1 were pipetted into the tubes; 3 and 5.

0.2 ml of a 5 mg / ml acetone solution of 2,4-dinitro-1-naphthol was added. After the addition of 2 ml of the hypochlorite solution, the time at which the visual change of color was not observed was read on the stopwatch. The test solution was found to contain less than 0.5% active chlorine over a period of time longer than 60 seconds. The content of 0.5 * chlorine corresponds to the interval at which the decolorization takes place in 40 + seconds.

If the test solution discolored after 20 ± 5 seconds, it contained 1% active chlorine.

For an active chlorine content greater than 2%, the time taken for the solution to decolorize is less than 20 seconds.

Example 3

Dissolving stock solution was prepared by dissolving 2.5 g 2,4-dinitro-1-naphthol in a 1: 1 v / v methanol / water mixture in a total volume of 250 ml. This allowed impregnating strips of 10 x 50 mm Whatman 1 chromatographic paper so that 1 g of paper contained 5 mg of dye.

Calcium hypochlorite solutions containing 0.2 to 5.0% active chlorine by 0.2% were prepared. These solutions were allowed to warm to 10, 25, 30, 40 and 60 ° C. 3 parallel measurements were used for each temperature.

After tempering to a given temperature, it was immersed on impregnated paper and the time taken for the paper to decolorize was subtracted. It was found that the decolorization rate of the indicator paper increased with temperature. Solutions with an active chlorine content above 5 * decoloured the paper in less than ± 5 seconds.

Example

Aqueous solutions of calcium hypochlorite, benzenchlorosulfonamide in 1,2-dichloroethane containing 0.5; 1.0 and 3.0% active chlorine. Subsequently, 10 x 50 mm strips of chromatographic paper were impregnated with a saturated aqueous solution of 2,4-dinitro-1-naphthol to give 5 mg of dye per 1 g of Whatman 1 paper.

After drying, the papers were immersed in individual solutions containing active chlorine. At 20 ° C, the time to decolour the papers was measured. For each concentration and each substance, the actual test and observation was repeated 3 times. Hypochlorite solutions containing 1% active chlorine bleached indicator paper within 25 seconds, benzene chlorosulfonamide bleached within 35 seconds.

The use of color solutions and impregnated papers 2,4-dinitro-1-naphtholene allows detection and determination of active chlorine in solution. Knowing the dilution and the time it takes to discolour the respective indicator solution or paper, the active chlorine content and hence its quality can be determined with an accuracy of 0.5%.

The indicator system of the present invention allows fast and simple pouring of active chlorine-containing solutions. This results in higher efficiency of the process while reducing material costs.

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Claims (1)

SUBJECT OF THE INVENTION Method for analyzing active chlorine, characterized in that the analyzed sample containing active chlorine is reacted with dinitronaphthol in solution or on a carrier, for example paper, and the presence and concentration of active chlorine in the sample is determined by the time of color change.