Three green, simple, precise, accurate and sensitive spectrophotometric methods were developed for the determination
of a binary mixture of lidocaine hydrochloride (LDC) and cetylpyridinium chloride (CPC) in the presence
of dimethylaniline (DMA). In the three methods, the interference of DMA spectrum is eliminated using
the ratio subtraction method. Method (A) depended on determining LDC and CPC by measuring the first derivative
of the ratio spectra (1DD) at 271.0 and 268.4 nm, respectively. Method (B) was the ratio difference (RD),
based on dividing the absorption spectrum of the binary mixture by a standard spectrum of CPC or LDC, then
measuring the amplitude difference of the ratio spectra (ΔP) between 231.2 and 240.0 nm for LDC and between
242.8 and 258.0 nm for CPC. Method (C) based on the application of dual wavelength coupled with the
isoabsorptive point method. This was achieved by measuring the absorbance difference (ΔA) between 243.0
and 268.6 nm for the determination of LDC, followed by application of isoabsorptive point method comprised
ofmeasurement the total content of the mixture of LDC and CPC at their isoabsorptive point at 240.0nm. The content
of CPCwas obtained by subtraction. The specificity of the developed methods was investigated by analyzing
laboratory prepared mixtures containing different ratios of LDC and CPC in presence of DMA. The proposed
methods displayed useful analytical characteristics for the determination of LDC and CPC in bulk powder and
their combined dosage form. The obtained results were statistically comparedwith those obtained by the official
methods, showing no significant difference with respect to accuracy and precision.

Kinetics studies are important in quality control to assure the safety and efficacy of the pharmaceutical compounds.
Recently, potentiometric ion-selective electrodes (ISEs) breakthrough kinetics study due to their ability
to provide real-time measurements which meet “green analytical chemistry” (GAC) principles. A polyvinyl
chloride (PVC) matrix membrane was fabricated to monitor bromhexine (BR) oxidative degradation kinetics
using tetraphenylborate as a cation exchanger. At-line monitoring of the oxidative degradation kinetics of BR was
performed; by continuous measuring the decrease in the sensor potential over time. So a real-time observation
and a continuous profile were obtained for the oxidation of BR under various H2O2 concentrations and temperature.
This kinetic study determines the oxidation activation energy that was 6.4 kcal mol−1. To expand the
application of this sensor, BR was determined in bulk powder and dosage form in the presence of both coformulated
drug (acefylline piperazine) and dosage form additives. The proposed sensor had been characterized
according to IUPAC recommendations and a linear dynamic range was 5×10−6 to 1×10−3M and other sensor
parameters had been calculated.