Indian Journal of Forensic Medicine & Toxicology, April-June 2020, Vol. 14, No. 2 1043 Spectrophotometric Determination of Isopropamide Iodide based on Ion-pair Complex Formation with Thymol Blue Wasan Ajam Hannoun 1 , Khalid Waleed S. Al-Janabi 2 1 M.Sc. Student, 2 Assist. Prof., Chemistry Department, College of Education for Pure Sciences/ Ibn Al-Haitham, University of Baghdad, Baghdad, Iraq; Email: khalid.janabi@gmail.com Abstract A simple, accurate, affordable, and rapid spectrophotometric approach has been established for the quantifcation of the medicinal compound of Isopropamide iodide (ISO) in pharmaceutical preparations. An ion-pair complex which absorbs at 404nm has formed the reaction of the drug and the coloring reagent of Thymol blue (TB) at an acidic medium of pH=4. The calibration curve showed excellent linearity over a quantifcation range of (1-40 μg/ml) with an excellent coeffcient of correlation (= 0.9993). The examined limit of detection (LOD) was (0.3 μg/ml) for repeatability of (n= 3). The approach witness no interference of the commonly used excipients in such pharmaceutical formulation that contains Isopropamide iodide. Validation of the method was accomplished by calculating the relative standard deviation (RSD %) and found to be in the range of (1.1938-0.5954). While recovery percentage for (n=3) was (97.4 – 101.4%). The analytical parameters of the method were optimized and were effcaciously applied to the Isopropamide iodide determination in pure form and in the mixture of a tablet form. The approach can be functional for determining other active pharmaceuticals. Keywords: Isopropamide iodide, spectrophotometry, ion-pair complex, Thymol blue, pharmaceuticals. Introduction Isopropamide iodide (ISO), in IUPAC “(4-amino- 4-oxo-3,3-diphenylbutyl)-methyl-di(propan-2-yl) azanium;iodide”, an off-white odorless bitter powder with a molar mass of 480.434 g/mol (1,2) as it shown in (Figure 1). Its an anticholinergic medication having long effect duration 3 . ISO is a wide spectrum pharmaceutic drug used in the treatment of several disease symptoms, not limited to; Assist in gastrointestinal (GI) spasm relief 4 , the remedy of peptic ulcer, thyroid disorder 5 , rhinitis redaction, some types of diarrhea, duodenitis spasm, chronic cholelithiasis, biliary dyskinesia, curing of gastritis, rest of spastic colon, disturbance of the urinary tract 6 those correlated to the spasm of smooth muscle, and some other disorders (7–10). The Iraqi “State Company For Drugs Industry And Medical Appliances (SDI – Samarra)” produces tablets for the treatment of “irretable bowel syndrome” called Salabid which composed of ISO and trifuperazine hydrochloride11. A literature survey revealed that ISO has been determined in the presence of other active drugs by derivative spectrometry (12,13) . Also, it has been extracted from physiological fuids via solid-phase extraction cartridges 14 (SPE) followed by the chromatographic analysis of HPLC at 220 nm (15,16) . Likewise, platforms of electrochemical sensing were used for a simultaneous determination of ISO in a bulk pharmaceutical mixture 17 . Fig. 1. The chemical structure of the pharmaceutical molecule of Isopropamide iodide 15