SU67226A1 - Method for quantitative determination of vitamin C - Google Patents

Description

METHOD OF QUANTITATIVE DETERMINATION OF VITAMIN C

It was announced on September 29, 1945 to the Narkomzdrav No. 5144 (34127). Published 31 October 1946.

There are many methods for quantifying ascorbic acid (vitamin C) in a purely chemical, physicochemical, biological and other way. However, even the best of these methods, which give satisfactory and consistent determination results, have in each case their own significant drawbacks. For example;

1) Tilmais indophenolic method and its modifications are based on the use of 2,6-dichlorophenolindophenol, a very unstable reagent in solutions, the titer of which must be checked every day.

In addition, the reagent decomposes at low pH values of the titration medium and is far from being specific;

2) by the method. and Bonsignore is used as the oxidant methylene blue, which becomes so only in special lighting conditions, which requires special equipment and complicates the analysis. Method also

is far from being specific for vitamin C;

3) the physicochemical method - potentiometric - is rather complicated in execution and does not give distinct results;

4) the spectral method requires special equipment, which is not always available in clinics, and is also complex in its implementation;

5) the biological method - the test on guinea pigs - is very long (35-100 days) and is also far from specific, due to the individual sensitivity of animals and the specificity of the organism of each individual.

The author has developed and proposes an easy-to-perform and yielding consistent and accurate result method for the determination of ascorbic acid using reagents available and persistent in storage.

The method is based on the well-known ability of iron oxide salts at elevated temperatures to quickly and quantitatively reduce ascorbic acid to iron oxide salts according to the following equation:

with -one

O + 2 Fe- he

I SHELTER

SNGON

Multiple titrations confirmed this ratio of equivalents and correspondence of 1 ml of 0.0IN solution of ferric iron salt to 0.00088 mg of ascorbic acid (molecular weight of ascorbic acid 176).

As a working solution, a 0.01 N solution of ferric chloride PBS in 0.2N hydrochloric acid is taken. Its titer is set iodometrically using the Mohr or Koltgof method or ascorbic acid, which gives a more accurate correction factor. Optimal conditions for determination: solution temperature is 90 °, its pH is 4-4.5 .;

Titration is carried out in the presence of an ammonium rhodanide indicator with a 0.01 N solution of MicroCluret ReCl3 to a pink color of the extract discolored from pigments according to the Dev Tkin-Doroshenko method (with lead) or Bukin (with acetic acid mercury). The author suggests that the removal of reducing and pigmenting substances is carried out as follows: mercury nitric oxide (oxide) is added to the extract of vitamin C and, after 30 seconds, ammonium rodanide. The latter translates Hg into a weakly dissociated (almost undissociated) compound, which will no longer interact with ascorbic acid. After adding rhodanide, the mixture is quickly filtered into water saturated with hydrogen sulfide.

with about

O + 2 Fe- + 2Hc o

NA

nose

CH, HE

lindr) hydrogen sulphide is also passed into this mixture for 10 minutes, after which the HgS precipitate is filtered off and the resulting colorless filtrate after heating without removal of the HaS is titrated with a 0.0 III solution of FeCl3. Hydrogen sulfide under these conditions does not interfere with titration with ferric chloride, which does not interact with it. In addition, during the filtration and heating of the liquid, the concentration of hydrogen sulfide becomes insignificant and, therefore, the oxidized ascorbic acid does not have time to be restored at the time of titration.

The proposed method was tested by comparative titration of aqueous solutions of ascorbic acid: 2 - 6-dichlorophenolindophenol (Tillman's reagent), iodine and ferric chloride, and well-defined results were obtained within the range of experimental errors. The greatest discrepancies in the results did not exceed + 1.32%.

In order to create an acidic environment, the analysis should use non-ferrous hydrochloric acid; Also, all other reagents used should be free of iron. This condition is, however, necessary for any chemical method of determining vitamin C, since each ferric salt will react with ascorbic acid. up to a certain volume of liquid (in precisely graded qi //

The proposed method for the determination of vitamin C by ferrometric titration has the following advantages over other known methods:

1) storage stability of titrated solution of FeCl3 in 0.2N hydrochloric acid;

2) simplicity and speed of determination;

3) availability of reagents - ferric chloride and ammonium; ,,

4) indicator sensitivity is high;

5) relative specificity of the reagent, since FeCU does not interact with hydrolyzed sugars, hydrogen sulfide and other reducing agents that react with dichlorophenolindophenol.

Subject invention

A method for quantitative determination of vitamin C by oxidizing it with iron oxide salts, characterized in that a portion of the product under investigation is titrated with a solution of ferric chloride at a temperature of about 90 ° and a pH of about 4-4.5 in the presence of ammonium rhodium as an indicator to pink coloration and consumption solution of ferric chloride establish the content of vitamin C - in the test product.