Method of determining degree of deacetylation of chitosan

FIELD: chemistry.

SUBSTANCE: method involves taking a certain weighed amount of chitosanium chromate which is first purified from extraneous impurities and reduced to constant weight. The weighed amount is then turned into a stable weighted form through thermal treatment on air at temperature 800-900C to form chromium oxide Cr2O3. The weight of the formed chromium oxide is then determined. Content of chromic acid in the initial weighed amount of chitosanium chromate is then calculated from the weight of chromium oxide. The degree of deacetylation of chitosan is calculated using defined formulae.

EFFECT: invention enables to increase accuracy of determining degree of deacetylation of chitosan.

2 ex

 

The invention relates to methods of analysis of biopolymers, in particular, to a method of determining the degree of dezazetilirovanie chitosan chemical (weight) method, involving the use of as a weight of the form poorly soluble compounds chitosan.

The degree of dezazetilirovanie (ASD) is one of the most important chemical parameters characterizing chitosan, obtained in the process dezazetilirovanie and characterize the structure of the macromolecular chain biopolymer is chitosan. Values SDA affect such properties of chitosan as solubility in water and acidic environments, swelling in water, the ability to biodegradation, and determine the nature of the biological activity of chitosan. These properties of chitosan determine its potential application in various spheres of human activity (Rashidov N, Milusheva RYU, D., Voropaeva, Ruban I.N. Chitosan varying degrees of dezazetilirovanie. All-Russian conference "New developments in chemistry and chemical technology of vegetable raw materials". Proceedings of the II all-Russian conference. April 21-22, 2005 / edited Ngusaru, Wearking. Barnaul: Publishing house of Alt. University, 2005. Book I. - 372).

It is known that chitosan C6O4H9NH2as the base, due to the presence in its composition of amino groups capable of protonemata the ri interaction with acids with the formation of singly charged cation chitosane C 6O4H9NH3+forming soluble and water-insoluble salts (Chitin and chitosan: synthesis, properties and application. Ed. Kgosana, Gasiorowski, Wepfeemia. - M.: Nauka, 2002. 366 C.).

Soluble salts of chitosan is produced by interaction of chitosan with the appropriate acid taken in a stoichiometric ratio according to the following reaction equation:

where a is CH3Soo-, Cl-, NO3-and others.

Formed as a result of interaction of initial substances, the solution is evaporated to dryness and the solid residue salt of chitosan.

Insoluble salts, such as sulfate, chitosan, obtained by interaction of a solution containing a soluble salt of chitosan, with a solution containing sulfate anion, taken in a stoichiometric ratio according to the following reaction equation:

where a is the anion.

The precipitation of chitosan sulfate is filtered off, washed with water and dried.

Known salt of chitosan unsuitable for chemical (weight) of the method of determining the degree of dezazetilirovanie chitosan, because to some extent they are still water soluble. At wash them with water from an excess of the precipitant and by-products of metabolic reactions (2) there is a partial dissolution in what mylenium salts of chitosan and accordingly, the distortion of the results determine the extent of dezazetilirovanie (ASD) of chitosan. This necessitates the development of a weight determination method of the SDA chitosan, based on the use of less soluble salts of chitosan, translated in sustainable weight form.

Determination of the degree of dezazetilirovanie chitosan can be carried out by various methods.

Thus, known methods of determining the degree of dezazetilirovanie chitosan, which calculate the ratio of amino - and Aceto-groups of chitosan on the IR spectrum of the solid sample chitosan (Goryainov A.G., Goryainov GI TO the question about the use as a rapid method for determination of DM chitin infrared Fourier-transform spectroscopy. // Proc. Dokl. ninth international conference "Modern perspectives in the study of chitin and chitosan". Stavropol 2008. M: VNIRO. 2008. S-122).

The disadvantage of this method is its low accuracy (error of about 25-30%).

Described methods conductometric and potentiometric titration processes dezazetilirovanie chitin (U.S. Pat. No. 2043995, publ. 20.09.1995).

It is also known the use to determine the extent of dezazetilirovanie chitosan temperature-programmed desorption mass spectrometry (Wart T., Kulik, T., loaf of bread B.B. Application temperature-ol is grammirovanie desorption mass spectrometry to determine the extent of dezazetilirovanie chitosan. W-l Mass spectrometry. 2009 V.6. No. 3, s-237).

The advantages of instrumental methods of analysis lies in the speed and a high accuracy of definition SDA chitosan.

The disadvantages of these methods include the need for the use of the instrument base, not always available for small and medium-sized research-and-production enterprises.

The closest in technical essence to the claimed method is chemical (weight) method of determining the degree of dezazetilirovanie chitosan using as the weight of the form of the sulfate chitosane (Chitin and chitosan: synthesis, properties and application. Ed. Kgosana, Gasiorowski, Wepfeemia. - M.: Nauka, 2002. 366 C.).

The method is as follows. An accurately weighed sample of chitosan dissolved in the acid (acetic, hydrochloric, nitric), in which it forms soluble salts. To the obtained solution of chitosan salt containing chitosan with a defined degree of dezazetilirovanie, add a solution containing an excess of sulfate anion with respect to the cation chitosane compared with the stoichiometry of reaction (2). The formed precipitate the sulfate chitosane filtered on pre-weighed glass Frit, washed and dried to constant weight. The gain calculated given the molecular weight of managermagazin chitosan, and from it the degree of dezazetilirovanie by the formulas:

where

And is the mass of the original sample of chitosan,

In the mass of sediment sulfate chitosane,

Mm (H2SO4)- molecular weight of sulfuric acid,

PMM - the molecular mass of the Monomeric level of chitosan, the degree of dezazetilirovanie which is defined

XT - chitin,

XS - chitosan.

The disadvantage of this method is the difficulty of achieving the accuracy of determination of the degree of dezazetilirovanie chitosan, due to the following.

In the process of determining the ASD chitosan using as the weight of the form of the sulfate chitosane requires a very thorough washing of the precipitate soluble salts of chitosan from an excess of the precipitant (sulfate anions) and the resulting by-products of metabolic reactions. Insufficient washing is the overestimation of the molecular weight of the monomer of chitosan and, consequently, the underestimation of the extent of dezazetilirovanie. When using unlimited large volume of wash water, because of the residual solubility of the sulfate chitosane part of the sediment is lost. This leads to an underestimation of the molecular weight of the monomer of chitosan and to overstate the degree of dezazetilirovanie. Especially this disadvantage inherent in the chitosan with a low degree of p is liberizatsii, because it increases the solubility of chitosan sulfate.

The objective of the invention is to develop a method for determining the degree of dezazetilirovanie chitosan, which eliminates these drawbacks is the closest analogue, due to the use as a weight of the form less soluble salts of chitosan - chromate chitosane composition (C6O4H9NH3)2CrO4.

This compound, its properties and use in the method of determining the degree of dezazetilirovanie chitosan available to the applicant the information sources described previously were not.

Chromate chitosane produced by interaction of soluble salts chitosane with metal chromates, taken in the ratio of 2 moles of the cation chitosane on 1 mol of the chromate anion or bichromate metals in relation to 4 mol of the cation chitosane on 1 mol of the bichromate-anion, followed by the separation of the formed target product by filtration or centrifugation, solid, shaded from excess reagents and side products of the reaction and drying at a temperature not higher than 150C.

As a result of investigations of the interaction of chitosan with anions CrO42-and Cr2O72-it is established that in both cases, high yield is the formation of water-insoluble chromate chitosane according to the following level is the third reaction:

The property of the chromate chitosane combustion to give a solid residue of the oxide of chromium, and also confirmed by atomic absorption spectrometry analysis solution Cr2O3in sulfuric acid (AA spectrophotometer-780) fact quantitative transition chromate anions in the chromium oxide, allow the use of the chromate chitosane in the method of determining the degree of dezazetilirovanie chitosan chemical (weight) method.

The inventive method of determining the degree of dezazetilirovanie chitosan is as follows. As the weight of the form poorly soluble compounds chitosan use the chromate chitosane, when I take some sample pre-cleaned from impurities and brought to a constant weight of the chromate chitosane, which then quantitatively transferred to a sustainable weight form by heat treatment in air at a temperature of 800-900C with the formation of chromium oxide Cr2O3then determine the mass of the formed chromium oxide, the value of which calculate the contents of chromic acid in the original sample of the chromate chitosane, and the degree of dezazetilirovanie chitosan calculated by the following formulas:

where

And is the mass of the original sample combusted chromate chitosane,

In the mass of the formed chromium oxide,

With the content of chromic acid in the original sample of the chromate chitosane,

D - content of chitosan in the hinge of the chromate chitosane,

Mm is the molecular mass of the corresponding compounds (shown in brackets),

PMM - the molecular mass of the Monomeric level of chitosan, the degree of dezazetilirovanie which is defined

XT - chitin,

XS - chitosan.

The proposed method of determining the degree of dezazetilirovanie chitosan using as the weight of the form new chemical compounds, chromate chitosane, provides a more accurate definition of ASD and simultaneously extends the range of the chemical methods specified destination, which is the technical result of the claimed invention.

The possibility of carrying out the invention the following examples.

Example 1. As a source of chitosan use the product manufacture co., LTD "Biopolymers" (garritano Primorsky Krai) TU 9283-174-200472012-03 with a degree of dezazetilirovanie 75,0%, having the following elemental composition, mass. %AND 45.5; H - 6,8; N - 8,1; 39,6. This corresponds to the gross formula C6,5O4,25H9,5NH2and given the molecular mass of Monomeric link chitosan 171,71 UAE

0,1535 g (0,89 mg-mol) of chitosan was dissolved in 100 ml of 0.2%aqueous solution of acetic acid, containing 0.2 g of 3.33 mg-mol) CH3COOH, which corresponds to a marked excess of acid, resulting in a gain 0,20625 g (0,89 mg-mol) acetate chitosane6,5O4,25H9,5NH3CH3COO. A solution of the acetate chitosane filtered from the solids and add to it with stirring 50 ml of a solution of sodium chromate containing 0,08505 g (0,52 mg-mol) Na2CrO4that corresponds to a small excess of chromate compared with the stoichiometry of reaction (3). The sediment of the chromate chitosane (C6,5O4,25H9,5NH3)2CrO4separated from the solution by filtration, washed with water until the disappearance in the lavage of Na+and dried at 105C to constant weight. Part of the thus prepared (C6,5O4,25H9,5NH3)2CrO4the number 0,24600 g is burned in a pre-weighed porcelain crucible in air at a temperature of 800C. Receive 0,04055 g of chromium oxide Cr2O3. The degree of dezazetilirovanie calculated by equations 7-10, makes 75.5%. Absolute accuracy is 0.5%, the relative - 0.7%, which is within the accuracy of the methods of gravimetric analysis.

Example 2. 0,16535 g (0,96 mg-mol) of chitosan dissolved in 100 ml of 0.2%aqueous solution of acetic acid and get 0,22250 g (0,96 mg-mol)6,5O4,25sub> 9,5NH3CH3COO, as described in example 1. To the resulting solution was added 50 ml of a solution of bichromate of potash, containing 0,08875 g (0.30 mg-mol) (K2Cr2O7that corresponds to its slight excess compared with the stoichiometry of reaction (4) and carry out the allocation of the resulting (C6,5O4,25H9,5NH3)2CrO4as described in example 1. Part of the thus prepared (C6,5O4,25H9,5NH3)2CrO4the number 0,28115 g is burned in a pre-weighed porcelain crucible in air at a temperature of 900C. Receive 0,04625 g of chromium oxide Cr2O3. The degree of dezazetilirovanie calculated by equations 7-10, 74.3%. The absolute measurement error is 0.7%, relative to 0.9%, which is within the accuracy of the methods of gravimetric analysis.

The method of determining the degree of dezazetilirovanie chitosan using as weight form poorly soluble compounds chitosan, characterized in that as a poorly soluble compound of chitosan use the chromate chitosane, when I take some sample pre-cleaned from impurities and brought to a constant weight of the chromate chitosane, which quantitatively transferred to a sustainable weight form by heat treatment in air at which the temperature of 800-900C with the formation of chromium oxide Cr 2O3then determine the mass of the formed chromium oxide, the value of which calculate the contents of chromic acid in the original sample of the chromate chitosane, and the degree of dezazetilirovanie chitosan calculated by the following formulas:
C=BMm(H2CrO4):[0,5M.M.(Cr2O3)]=B118,02:[0,5152,00]=1,55B;
D=A-C=A-1,55B;
PMM=[MM(H2CrO4)D]:[2C];
SDA=100[Mm(HT)-PMM]:[Mm(HT)-Mm(XS)]=100[203,22-(PMM)]:(203,22-161,18)=[203,22-(PMM)]:0,4204,
where a is the mass of the original sample combusted chromate chitosane,
In the mass of the formed chromium oxide,
With the content of chromic acid in the original sample of the chromate chitosane,
D - content of chitosan in the hinge of the chromate chitosane,
Mm is the molecular mass of the corresponding compounds (shown in brackets),
PMM - the molecular mass of the Monomeric level of chitosan, the degree of dezazetilirovanie which is defined,
XT - chitin,
XS - chitosan.



 

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