Nawal A. Alarfaj

Flow-injection chemiluminometric analysis of some benzamides by their sensitizing effect on the cerium-sulphite reaction

A simple, highly sensitive chemiluminescent method using flow injection is described for the determination of three substituted benzamides, namely: sulpiride, sultopride and tiapride. The method is based on the sensitizing effect of these drugs on the chemiluminometric oxidation of sulphite by cerium(IV). The different experimental parameters affecting the chemiluminescence intensity were carefully studied and incorporated into the procedure. The method permits the determination of 0.05-2.5 mug ml(-1) sulpiride, 0.01-2.5 mug ml(-1) sultopride hydrochloride and 0.01-1.5 mug ml(-1) tiapride hydrochloride with minimum detectability of 0.01 mug ml(-1). The method was applied to the determination of these benzamides in pharmaceutical preparations and biological fluids.

Complexometric-spectrophotometric assay of tetracyclines in drug formulations.

An accurate, rapid and very simple spectrophotometric method for the assay of tetracyclines (tetracycline.HCl, chlorotetracycline.HCl, demeclocycline, oxytetracycline.HCl and doxycycline) has been developed. The method is based on the complexation of iron(III) with tetracyclines in 0.001M sulphuric acid. It has been successfully applied to the assay of tetracyclines in drug formulations, and the interferences of excipients have been examined. The results have been statistically compared with those obtained by two standard methods and found to be very satisfactory.

Determination of the anti‐viral drug Ribavirin in dosage forms via micelle‐enhanced spectrofluorimetric method

A simple and sensitive spectrofluorimetric method was developed for the determination of Ribavirin in pharmaceutical formulations. The proposed method was based on the fluorescence spectral behaviour of Ribavirin in a sodium dodecyl sulfate (SDS) micellar system. In an aqueous acetate buffer solution of pH 4.0, the fluorescence intensity of Ribavirin was significantly enhanced by about 217% in the presence of SDS. Fluorescence intensity was measured at 396 nm after excitation at 270 nm for Ribavirin. The fluorescence-concentration plot was rectilinear over the range of 0.01-3.0 µg/mL for Ribavirin with a lower detection limit of 5.02 x 10(-3) µg/mL. The method was successfully applied to the analysis of the drug in its commercial capsules. Results were in good agreement with those obtained with the official method. The application of the proposed method was extended to stability studies of Ribavirin after exposure to different forced degradation conditions such as acidic, alkaline, photo and oxidative conditions according to ICH guidelines.

Fluorimetric determination of isoxsuprine hydrochloride in pharmaceuticals and biological fluids

Two simple and highly sensitive fluorimetric methods have been developed for the determination of isoxsuprine hydrochloride in bulk, in dosage forms and in biological fluids. The first method involves the direct measurement of the native fluorescence of the drug in the concentration range 0.4-4.0 microg ml(-1), the second method is based on the oxidation of isoxsuprine HCl with cerium(IV) followed by fluorimetric measurement in the concentration range 0.02-0.2 microg ml(-1). The average % found were 99.9 +/- 0.78 and 100.0 +/- 0.62 for the two methods, respectively. The minimum detectability (3 S(B)) were 0.11 and 0.007 microg ml(-1) for the two methods, respectively. The methods results showed insignificant difference with those of the official method.

Sensitive assay for clavulanic acid and sulbactam in pharmaceuticals and blood serum using a flow-injection chemiluminometric method

A sensitive, simple and inexpensive chemiluminescence (CL) method using flow injection is described for the determination of two beta-lactamase inhibitors sulbactam sodium and clavulanic acid (potassium salt) in their pure form, in pharmaceutical preparations and added to blood serum. The method is based on the enhancing effect of these compounds on the CL generated by the oxidation of luminol with hydrogen peroxide in alkaline medium. The CL intensity is a linear function of sulbactam sodium concentration over the range 0.1‐150m gm l 1 with a detection limit (2noise) of 0.05m gm l 1 , and for clavulanic acid over the range 0.01‐12m gm l 1 with a detection limit of 0.01m gm l 1 . The method is applied successfully to the determination of the drugs in their dosage forms without interference from co-formulated drugs. The method is specific for the intact drugs in the presence of their degradation products.

Disposable screen-printed sensors for determination of duloxetine hydrochloride

A screen-printed disposable electrode system for the determination of duloxetine hydrochloride (DL) was developed using screen-printing technology. Homemade printing has been characterized and optimized on the basis of effects of the modifier and plasticizers. The fabricated bi-electrode potentiometric strip containing both working and reference electrodes was used as duloxetine hydrochloride sensor. The proposed sensors worked satisfactorily in the concentration range from 1.0 × 10-6-1.0 × 10-2 mol L-1 with detection limit reaching 5.0 × 10-7 mol L-1 and adequate shelf life of 6 months. The method is accurate, precise and economical. The proposed method has been applied successfully for the analysis of the drug in pure and in its dosage forms. In this method, there is no interference from any common pharmaceutical additives and diluents. Results of the analysis were validated statistically by recovery studies.

Square-wave adsorptive stripping voltammetric determination of antihypertensive agent telmisartan in tablets and its application to human plasma

The adsorptive stripping voltammetry of telmisartan was investigated with a hanging mercury drop electrode. This compound produced a catalytic hydrogen wave at −1.5 V in Britton Robinson buffer of pH 10.38, and the peak current increased with adsorptive accumulation at the electrode. Adsorptive stripping voltammetry with the catalytic hydrogen wave could provide a sensitive novel method for the determination of telmisartan. Various chemical and instrumental parameters affecting the monitored electroanalytical response were investigated and optimized for telmisartan determination. Under these optimized conditions the square-wave adsorptive stripping voltammetric (SW-AdSV) peak current showed a linear dependence on drug concentration over the range 0.05–3.00 μg/mL (1 × 10−7−6 × 10−6 M) (r = 0.999) with accumulation for 120 s at −1.0 V vs. Ag/AgCl. The proposed electrochemical procedure was successfully applied for the determination of telmisartan in pharmaceutical tablets and human plasma. The results of the developed SW-AdSV method were comparable with those obtained by reported analytical procedures.

Determination of enalapril maleate and atenolol in their pharmaceutical products and in biological fluids by flow-injection chemiluminescence

A chemiluminescent method using flow injection (FI) was investigated for rapid and sensitive determination of enalapril maleate and atenolol, which are used in the treatment of hypertension. The method is based on the sensitizing effect of these drugs on the Ce(IV)-sulfite reaction. The different experimental parameters affecting the chemiluminescence (CL) intensity were carefully studied and incorporated into the procedure. The method permitted the determination of 0.01-3.0 microg mL(-1) of enalapril maleate in bulk form with correlation coefficient r = 0.99993, lower limit of detection (LOD) 0.0025 microg mL(-1) (S/N = 2) and lower limit of quantitation (LOQ) 0.01 microg mL(-1). The linearity range of atenolol in bulk form was 0.01-2.0 microg mL(-1) (r = 0.99989) with LOD of 0.0003 microg mL(-1) (S/N = 2) and LOQ of 0.01 microg mL(-1). In biological fluids the linearity range of enalapril maleate was 0.1-2.0 microg mL(-1) in both urine and serum, and for atenolol the linearity range was 0.1-1.0 microg mL(-1) in both urine and serum. The method was also applied to the determination of the drugs in their pharmaceutical preparations.

Application of silver nanoparticles to the chemiluminescence determination of cefditoren pivoxil using the luminol–ferricyanide system

A new simple, accurate and sensitive sequential injection analysis chemiluminescence (CL) detection method for the determination of cefditoren pivoxil (CTP) has been developed. The developed method was based on the enhancement effect of silver nanoparticles on the CL signal arising from a luminol-potassium ferricyanide reaction in the presence of CTP. The optimum conditions relevant to the effect of luminol, potassium ferricyanide and silver nanoparticle concentrations were investigated. The proposed method showed linear relationships between relative CL intensity and the investigated drug concentration at the range 0.001-5000 ng/mL, (r = 0.9998, n = 12) with a detection limit of 0.5 pg/mL and quantification limit of 0.001 ng/mL. The relative standard deviation was 1.6%. The proposed method was employed for the determination of CTP in bulk drug, in its pharmaceutical dosage forms and biological fluids such as human serum and urine. The interference of some common additive compounds such as glucose, lactose, starch, talc and magnesium stearate was investigated. In addition, the interference of some related cephalosporins was tested. No interference was recorded. The obtained sequential injection analysis-CL results were statistically compared with those from a reported method and did not show any significant differences.

Spectrofluorimetric analysis of gemifloxacin mesylate in pharmaceutical formulations.

A simple, rapid and highly sensitive spectrofluorimetric method was developed for determination of gemifloxacin mesylate (GFX) in tablets. The method is based on measuring the native fluorescence of GFX in isopropanol at 400 nm after excitation at 272 nm. The fluorescence-concentration plot was rectilinear over the range of 0.01-0.50 µg/mL with a lower detection limit of 1.19 ng/mL and quantification limit of 3.6 ng/mL. The method was fully validated and successfully applied to the determination of GFX tablets with an average percentage recovery of 99.65 ± 0.532. The method was extended to the stability study of GFX. The drug was exposed to acidic, alkaline, oxidative and photolytic degradation according to International Conference on Harmonization guidelines. The rate of GFX degradation was found at its highest in acidic conditions, and in its lowest in the neutral one. However, it was stable under dry heat and photolytic degradation conditions.