Extractive Spectrophotometric Determination of Antiallergic Drugs in Pharmaceutical Formulations Using Bromopyrogallol Red and Bromothymol Blue
In view of the extensive applications of compounds viz., methdilazine hydrochloride (MDH), promethazine hydrochloride (PMH), and isothipendyl hydrochloride (IPH) as antiallergic drugs, it is necessary to develop new analytical methods for their determination in bulk samples and pharmaceutical preparations. A variety of spectrophotometric methods based on colored complex formation or oxidative reactions have been proposed. Some are lacking sensitivity, 1-6 require heating 7,8 or long standing 9
... or long standing 9 for color development. The reported methods 1-5 suffer from twin disadvantages of critical acid or oxidant concentration and instability of the colored species, the stability ranging from 10 -40 min. The literature on the extractive spectrophotometric methods for the assay of the above drugs is scanty, although these methods are wellsuited. The official methods 10-12 (MDH, 12 PMH, 10 and IPH 11 ) involve non-aqueous titrations or UV spectrophotometric methods, which are tedious and time consuming. In the present paper, we report two extractive spectrophotometric methods based on the formation of ionassociation complexes between the antiallergic drugs and Bromopyrogallol Red (BPR) or Bromothymol Blue (BTB), which are more sensitive (ε = 1.03 -2.55 × 10 4 l mol -1 cm -1 ) than the official 10-12 (ε = 1.0 -2.1 × 10 3 l mol -1 cm -1 ) and the reported extractive 6 (ε = 5.43 × 10 3 l mol -1 cm -1 ) or direct 1-5 spectrophotometric methods (ε = 3.1 -9.61 × 10 3 l mol -1 cm -1 ) for the assay of the selected drugs, the structures of which are shown in Fig. 1 . The proposed methods have been extended to the assay of these drugs in various pharmaceutical formulations.