Method of metronidazole determination

FIELD: medicine.

SUBSTANCE: described is method of quantitative determination of metronidazole by spectrophotometry of determined substance and standard sample of comparison, and as solvent for preparing determined solution applied is 0.1M solution of hydrochloric acid, spectrophotometry is carried out at wave length 276 nm, as sample for comparison applied is benzoic acid or phenolphthalein and calculation is carried out by formula.

EFFECT: method makes it possible to increase repeatability of determination results, reduce cost, labour consumption, analysis error, standardise analysis methods.

3 ex

 

The present invention relates to the field of medicine and can be used in analytical laboratories for standardization and quality control of drugs.

The current system of quality control of medicines requires pharmaceutical science continually improving the effectiveness of existing methods of analysis.

Among the modern methods of pharmaceutical analysis, an important place is occupied by the optical inspection methods, which are commonly used for the purposes of quantification, and control of purity and identification of drugs.

There are various ways to define metronidazole (1-(β-oxyethyl)-2-methyl-5-intorimidazole), used as an Antiprotozoal drugs.

The known method acidimetric determination of metronidazole, which consists in preparing a solution of metronidazole in glacial acetic acid followed by titration with 0.1 M solution of chloric acid to a greenish-yellow color with crystal violet indicator (FS 42-0257-07 "Metronidazole"). Also there is a method of spectrophotometric determination of metronidazole by preparing solutions of the test substance and the working standard sample (RNO) metronidazole using a solvent mixture consisting of ethyl alcohol is about 95%, 0.1 M solution of sodium hydroxide and phosphate buffer solution and the reference solution, followed by their spyektrofotomyetrirovaniya wavelength at 317 nm and calculation results on the RNO metronidazole (Fund 42-12994-03).

The most loved and accepted us for the prototype is the way of standardization of metronidazole in tablets of 0.25 g by preparing solutions of the test substance and the working standard sample (RNO) metronidazole using water as solvent and solution comparison with their subsequent spyektrofotomyetrirovaniya in at a wavelength of 318 nm and calculation results from the calibration graph RDF metronidazole (Avempace, Energetic, Wegelius. Differential spectrophotometric determination of metronidazole // pharmacy 1973, vol 22, No. 1. P.45-48). In this paper we propose a spectrophotometric method for the determination of metronidazole via a calibration curve, therefore the analysis and calibration in this way are held in different experiments, which leads to increased errors of analysis.

Recommended regulatory documentation titrimetric method for quantitative determination of metronidazole highly toxic, insensitive, time-consuming. The use of spectrophotometric method for the analysis of substance metronidazole is difficult due to the lack of state standard clicks scow on this drug. The release of such standard samples is costly, since they are used only in pharmaceutical analysis. Therefore, the detection method using the state standard samples will not be available for many laboratories.

The technical result of the proposed method is to improve the reproducibility of the determination, reducing the cost, complexity and error analysis.

The technical result is achieved by preparing a solution of analyte and standard reference sample with their subsequent spyektrofotomyetrirovaniya and calculation results.

New in the achievement of the technical result is that as the solvent for the preparation of defined solution using 0.1 M hydrochloric acid solution, and as a standard reference sample using benzoic acid or phenolphthalein, measure the optical density of the solutions at the wavelength of 276 nm and injected into the formula results in a conversion factor.

The studied substance changes the absorption spectrum depending on the pH of the environment. Based on experimental data and properties of metronidazole, the authors proved that the optimal solvent for the spectrophotometric determination is 0.1 M hydrochloric acid solution. About the optimum solvent provides stabilization of the test solution, that improves the reproducibility of the determination results and reduces the error of the analysis.

Absorption spectrum of metronidazole in 0.1 M solution of hydrochloric acid is characterized by a single absorption band with a maximum at 276±1 nm. Increasing the solution pH to 3.1 leads to a bathochromic shift of the maximum absorption to 313±1 nm with simultaneous hyperchromic effect. Further increase of pH to 12.5 leads to the shift of the maximum of 5 nm in delawarebuy region of the spectrum. The study of stability of solutions during the day showed that for all values of pH change of the optical properties of metronidazole does not occur. As the optimal solvent chosen 0.1 M hydrochloric acid solution, as this solvent is suppressed acidic properties of medicinal substances, and it is in the form of a salt according to ammonium.

The use of a 0.1 M solution of hydrochloric acid as solvent and 276 nm as the analytical wavelength allows to reduce the error analysis, which confirms the comparison of accuracy of definition F=0,12% for the proposed method and E=0.23 percent to close analogue, therefore, has been changed method can reduce the error analysis in comparison with the prototype. In addition, increases the reproducibility of the determination results, which confirms the comparison of the variances of two sample sets using the F-distribution with f 1=f2=10, p=99% for the proposed method and close analogue. Set (Fex.=13,5% when Ftable.=of 8.47, therefore, the proposed method has higher reproducibility.

Based on the established dependence, according to which the specimen can be applied substances for which the interval between the analytical wavelength and the maximum (or minimum absorption) of the reference sample does not exceed half of his half-width of the absorption band, as a standard reference sample in the proposed method, the authors use benzoic acid or phenolphthalein. Ideal absorption of benzoic acid in 0.1 M solution of hydrochloric acid, in which it can be used as a reference sample, are 266-280 nm and phenolphthalein 268-282 nm. Benzoic acid and phenolphthalein are mass-produced by industry categories of analytical grade, they are GOST: GOST 10521-78 for benzoic acid and GOST 5850-72 for phenolphthalein, regulating their quality.

Solutions of benzoic acid and of phenolphthalein in a 0.1 M solution of hydrochloric acid stable when stored for a long time. The use of benzoic acid and phenolphthalein, which is less expensive (10 times less) compared to a working standard sample metronidazole is, leads to the reduction of error and cost analysis.

Comparative analysis of the prototype shows that the claimed technical solution is characterized by the fact that for the preparation of the test solution using 0.1 M hydrochloric acid solution, and the sample comparison using benzoic acid or phenolphthalein, spectrofotometrically carried out at a wavelength of 276 nm and injected into the formula results in a conversion factor, which corresponds to the criteria of the invention of "novelty."

A new set of features provides improved reproducibility determination, reduction of error analysis, and also allows you to reduce the cost of analysis, to unify the methods of analysis that meets the criterion of "industrial applicability".

In the analysis of known solutions revealed that they lack information about the impact of the distinctive features on the achievement of technical solutions, therefore, the invention meets the criterion of "inventive step".

The method is as follows. Prepare a solution of a reference sample of benzoic acid or of phenolphthalein for the analysis of metronidazole. To do this, the exact mass of benzoic acid (0.2 g) or phenolphthalein (0.2 g) was placed in a volumetric flask with a capacity of 50 ml, dissolved in 20 ml of alcohol this is new, bring the volume of solution of the same solvent up to the mark and peremeshivayte ml of the resulting solution is placed in a volumetric flask with a capacity of 200 ml, the volume was adjusted solution of 0.1 M hydrochloric acid solution up to the mark and mix.

Then conduct a quantitative determination of metronidazole in substance. To do this, the exact mass of the product (0.05 g) was placed in a volumetric flask with a capacity of 50 ml, dissolved in 20 ml of ethyl alcohol, bring the volume of solution of the same solvent up to the mark and mix. 1 ml of the resulting solution is placed in a volumetric flask with a capacity of 200 ml, bring the volume of the solution up to the mark with 0.1 M hydrochloric acid and stirred. Measure the optical density of the test solution on the spectrophotometer at a wavelength of 276 nm in a cell with the length of the working layer 10 mm as the reference solution using 0.1 M hydrochloric acid solution. Simultaneously measure the optical density of the sample solution comparison of benzoic acid or of phenolphthalein on the spectrophotometer at a wavelength of 276 nm in a cell with the length of the working layer 10 mm relative to 0.1 M hydrochloric acid.

Calculation of results the quantitative determination of metronidazole is conducted according to the formula:

,

where Dxand Dsunoptical density of the analyte and is Azza comparison, respectively;

axand asun- accurate sample analyte and the reference sample, respectively;

V1and V2- the volume of the solution prepared analyte;

V3- volume aliquots of analyte;

and- the volume of the prepared sample solution is compared.

- the volume of the aliquot of sample comparisons;

100 - coefficient for conversion in percent;

W - moisture content, %;

Klane- the conversion factor.

The conversion factor is found from the expression:

,

where Esun- specific absorption of the reference sample of benzoic acid at the analytical wavelength;

EOS- specific absorption of the working of the reference sample determined (analyzed) substances at the analytical wavelength (determined during development of the methodology);

Klane- benzoic acid in 0.1 M hydrochloric acid equal to 0,1935; phenolphthalein - 0,3213.

The contents of metronidazole should be not less than 99.0% in terms of dry substances according to the normative document.

The proposed method is illustrated by the following examples.

Example 1. Prepare solutions of the analyte and the reference sample as described above. Metering the Ute on the spectrophotometer optical density of the solutions prepared. Next are the calculation results according to the formula, using the conversion factor.

When determining metronidazole for benzoic acid obtained the following results:

Dx=0,371; Dsun=0,301; andx=0,0486; andsun=0,2049; humidity = 0,01%; X=100,56%. The results of the experiments are statistically processed:

When n=7;S2=0,0601; S=0,2451;ΔX=0,227; E%=0,228; Sr=0,0025.

When determining metronidazole for phenolphthalein:

Dx=0,575; Dsun=0,471; ax=0,07495; andsun=0,19015; humidity = 0,01%; X=99,52%. The results of the experiments are statistically processed:

When n=7;; S2=0,4705; S=0,6856;; ΔX=0,635; E%=0,633; Sr=0,0068.

These examples confirm that the content of metronidazole meets the requirements of the normative document.

The proposed method using a reference sample of benzoic acid or phenolphthalein is optimal for the quantitative determination of metronidazole tablets metronidazole, and also allows with sufficient accuracy to conduct a control test "dissolution" tablets of metronidazole.

The method of quantitative determination of metronidazole in pharmaceutical form differs from the method of quantitative determination of metronidazole in substance only cooking ispycameltoe.

Example 2. For the quantitative determination of metronidazole tablets metronidazole 0.25 g take the exact weight of a powder of crushed tablets (0.08 g), placed in a volumetric flask with a capacity of 50 ml, dissolved in 20 ml of ethyl alcohol, bring the volume of solution of the same solvent up to the mark and mix. The solution is filtered, the first 10-15 ml of the filtrate is discarded and 1 ml of the resulting solution is placed in a volumetric flask with a capacity of 200 ml, the volume was adjusted solution of 0.1 M hydrochloric acid solution up to the mark and mix.

The contents of metronidazole tablets metronidazole 0.25 g must be 0,238-0,262 g, considering the average weight of one tablet.

In the analysis of tablets metronidazole 0.25 grams of benzoic acid results:

Dx=0,455; Dsun=0,442; andx=0,07535; andsun=0,3185; Pcf=0,2945; X=0,2479,

In the analysis of tablets metronidazole 0.25 g on phenolphthalein

Dx=0,473; Dsun=0,521; andx=0,07765; andsun=0,2016; Pcf=0,2945; X=0,2515,

Thus, the contents of metronidazole tablets meet the requirements of the normative document.

Example 3. For control test "dissolution" tablets metronidazole for a basis took a standardized methodology (GFH ed., S-160). As the environment dissolution used 0.1 M hydrochloric acid solution, the time of dissolution - 45 the minutes, volume environment dissolution of 1000 ml, the rotation speed is 100 rpm and temperature (37±1)°C.

In the analysis of tablets metronidazole 0.25 g in a basket placed one tablet, after 45 minutes of rotation of the selected sample. The solution was filtered and 10 ml of the filtrate is placed in a volumetric flask with a capacity of 100 ml, bring the volume of the solution up to the mark with 0.1 M hydrochloric acid and stirred.

According to (GF XI ed., S-160) on Wednesday dissolution must pass at least 75% active substance content in the dosage form.

In the analysis of tablets metronidazole 0.25 g external reference sample of benzoic acid release substance was: 83,59%, 83,45%, 83,40%. 82,25%, 84,12%, 80,28%, 82,07%, 79,65%, 81,95%, 81,43% for ten tablets, respectively.

In the analysis of tablets metronidazole 0.25 g external reference sample to the phenolphthalein release substance was: 81,61%, 83,42%, 81,40%, 82,29%, 82,18%, 80,28%, 83,09%, 79,35%, 81,75%, 76,95% for ten tablets, respectively.

Thus, the proposed method for the determination of metronidazole using a reference sample of benzoic acid or of phenolphthalein can improve the reproducibility of the analysis, to reduce the error analysis, to reduce its cost, to unify methods of analysis.

The method of quantitative determination of metronidazole by spectrometrybased analyte and the conventional sample comparison characterized in that the solvent for the preparation of defined solution using 0.1 M hydrochloric acid solution, spectrophotometrically carried out at a wavelength of 276 nm, as the comparison sample using benzoic acid or phenolphthalein and the calculation is conducted according to the following formula:
,
where Dxand Dsunoptical density of the analyte and the reference sample, respectively;
andxand asun- accurate sample analyte and the reference sample, respectively;
V1and V2- the volume of the solution prepared analyte;
V3- volume aliquots of analyte;
and- the volume of the prepared sample solution comparison;
- the volume of the aliquot of sample comparisons;
100 - coefficient for conversion in percent;
W - moisture content, %;
Tolane- the conversion factor
the conversion factor is found from the expression:
,
where Esun- specific absorption of the reference sample of benzoic acid or of phenolphthalein at the analytical wavelength;
EOS- specific absorption of the working of the reference sample determined (analyzed) substance in the analyte is achieved wavelength.



 

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