[Spectrophotometric determination of nystatin based on Ashton and Tootill's method]

Estimation of the calculation formula coefficient for quantitative spectrophotometric determination of substances in the presence of a nonlinear absorbing admixture with the method of Ashton and Tutyl is illustrated with reference to nistatin. The procedure is based on representation of the admixture absorption spectrum by the ortogonal polynome of L power. The calculation formulas for the assay of nystatin containing admixtures, the absorption spectra of which may be depicted by the polynomes of the 2nd, 3rd and 4th powers of the wave length were developed with the use of the EI%Icm value of the International standard. The formulas were used for the assay of model mixtures of nistatin with nonidentified admixtures isolated from production samples and having different characters of the absorption spectra. The error of the assay ranged within 0.1-0.5% and increased to 5% only when the admixture had a pronounced absorption maximum in the used spectral region and 1-2. The standard error of an assay performed according to the described procedure with the nystatin content of 1 . 10(-3)% was about 2 . 10(-5)%. This correlated well with preliminary estimation of the assay reproducibility performed with the use of the previously suggested criterion.