Advanced Spectrophotometric Resolution Techniques for a Spectrally Overlapping Spasmolytic Binary Mixture along with Dichloroaniline as a Toxic Impurity: Application to Content Uniformity Testing.

Abstract

Irritable bowel syndrome (IBS) is a common disorder leading to undesirable pain. Phloroglucinol (PHG) and trimethylphloroglucinol (TMG) are co-formulated as spasmolytic medication that is considered to be effective in reducing smooth muscle spasm. 3,5-Dichloroaniline (DCL) is a specified PHG pharmacopoeial impurity which needs to be monitored to avoid its toxic effects. Different smart approaches are presented to provide simple, reliable, and economic spectrophotometric methods able to resolve the severe overlap in the spectra of PHG and TMG in their pure and pharmaceutical forms, in addition to their estimation in the presence of DCL as a toxic impurity of PHG without any need for initial separation. The presented work includes univariate methods, derivative ratio (DR), ratio difference (RD), mean centering (MCR) and deconvulated Fourier method (DF), which were able to determine PHG and TMG simultaneously in their binary mixture. Firstly, DCL was estimated in the zero order, where the two drugs have zero absorption at 247.0 nm, and then its contribution was eliminated by applying ratio subtraction method. Multivariate chemometric partial least squares (PLS) and principal component regression (PCR) models were also applied to determine PHG and TMG simultaneously in the presence of the impurity, DCL. Univariate methods were applied in the range 5.0-30.0, 2.5-25.0, and 1.0-12.0 µg/mL for PHG, TMG, and DCL, respectively. The proposed chemometric models were used in the range 6.0-14.0, 5.0-25.0 and 2.0-10.0 µg/mL for PHG, TMG, and DCL, respectively. These analytical approaches succeeded in estimating the cited drugs in their pharmaceutical formulation and assessing content uniformity of dosage units. The methods were statistically compared with a reported HPLC method, and the results revealed no significance statistical difference. This work provides for the first time successful univariate and multivariate PLS and PCR methods to assess PHG and TMG in the presence of DCL as a toxic impurity along with content uniformity testing of dosage units. Comparative univariate and multivariate spectrophotometric analytical approaches are presented, for the first time, for estimation of spasmolytic formulation of PHG and TMG in the presence of DCL as a PHG toxic impurity. Successful application to content uniformity testing of Stopspasm® dosage form is demonstrated. A statistical study, including t-tests and one-way analysis of variance (ANOVA), was conducted.