Spectrophotometric determination of total polysaccharides in Viola herb

Introduction. Harmonization of pharmacopoeial requirements within the Eurasian Economic Union (EAEU) stimulates the unification of analytical procedures for medicinal plant raw materials. Violet herb (Viola herb), harvested from Viola arvensis Murr. and Viola tricolor L., contains a complex of biologically active compounds, including polysaccharides. Current pharmacopoeial documentation (FS.2.5.0044.15 of the State Pharmacopoeia of the Russian Federation, XIV edition) specifies gravimetric analysis for polysaccharides, which is associated with considerable analytical limitations. A spectrophotometric method utilizing picric acid, currently official for Tussilago farfara leaves, represents a promising alternative.

Aim. To evaluate the applicability of a spectrophotometric procedure with picric acid for quantifying total polysaccharides in Viola herb and to compare its analytical performance with the gravimetric method.

Materials and methods. The study evaluated three Viola herb batches: one wild-harvested sample (Leningrad region) and two commercial samples. The pharmacopoeial monograph for coltsfoot leaves (FS.2.5.0027.15) was utilized as the methodological basis. Extraction and acid hydrolysis parameters were optimized, followed by method verification in terms of specificity, linearity, and repeatability precision. Gravimetric determination was conducted according to monograph FS.2.5.0044.15.

Results and discussion. Optimal sample preparation parameters for Viola herb were identified: raw material particle size passing through a 2 mm sieve; raw material-to-extractant ratio of 1 : 40; and acid hydrolysis time of 2 hours. Analytical specificity was confirmed by identical absorption maxima at 470 nm for the glucose reference standard and the hydrolyzed plant extract. The method exhibited excellent linearity (r ≥ 0.995) across the analytical range and high repeatability precision (RSD = 1.2 %). Gravimetric analysis yielded systematically higher polysaccharide concentrations accompanied by increased variance, attributable to co-precipitation of non-carbohydrate polymers.

Conclusion. The spectrophotometric picric acid method is fully applicable for standardizing Viola herb following parameter optimization. The findings support unifying carbohydrate assay methodologies across diverse medicinal plant matrices within current pharmacopoeial harmonization frameworks.

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