Sensitive extractive spectrophotometric methods for the determination of trazodone hydrochloride in pharmaceutical formulations

Bromocresol purple in the processes of cation-anionic interactions in aqueous solutions: UV-Vis spectroscopy and computer simulation of dissimilar association

The formation of associates between single- or double-charged anions of bromocresol purple (3,3'-dimethyl-5,5'-dibromophenolsulfonephthalein) and single-charged cations of cyanines (quinaldine blue, quinaldine red) has been investigated. The equilibrium constants of the association have been determined on the basis of UV-Vis spectroscopy data. The energy of the cation-anion interaction (the standard enthalpy of formation of ions and associates), as well as the probable structure of associates, were established using the PM7 semiempirical method. The presented results can be useful in the development of new spectroscopic methods for the detection of organic additives in water (e.g. acetone) due to the spectral properties of dissimilar associates.

Extractive spectrophotometric method for the determination of tropicamide

Two simple, rapid, and extractive spectrophotometric methods were developed for the determination of tropicamide (TPC). These methods are based on the formation of ionpair complexes between the basic nitrogen of the drug with bromocresol purple (BCP) and methyl orange (MO) in acidic buffer solution. The formed complexes were extracted with chloroform and measured at 408 and 427 nm using BCP and MO, respectively. Beer's law was obeyed in the range 1.0–16 μg ml^–1 with correlation coefficient (n=6) ≥0.9991. The molar absorpitivity, Sandell sensitivity, detection, and quantification limits were also calculated. The composition of the ion pairs was found 1:1 by Job's method. The proposed methods have been applied successfully for the analysis of TPC in pure and in its eye drops.

Application of a trazodone-selective electrode to pharmaceutical quality control and urine analyses

A trazodone-selective electrode for application in pharmaceutical quality control and urine analysis was developed. The electrode is based on incorporation of a trazodone-tetraphenylborate ion exchanger in a poly(vinyl chloride) membrane. The electrode showed a fast, stable and Nernstian response over a wide trazodone concentration range (5 x 10(-5)-1 x 10(-2) M) with a mean slope of 59.3 +/- 0.9 mV/dec of concentration, a mean detection limit of 1.8 x 10(-5) +/- 2.2 x 10(-6) M, a wide working pH range (5-7.5) and a fast response time (less than 20 s). The electrode also showed good accuracy, repeatability, reproducibility and selectivity with respect to some inorganic and organic compounds, including the main trazodone metabolite. The electrode provided good analytical results in the determination of trazodone in pharmaceuticals and spiked urine samples; no extraction steps were necessary. Dissolution testing of trazodone tablets, in different conditions of pH and particle size, based on a direct potentiometric determination with the new selective electrode is presented as well.