Kinetic Spectrofluorometric Determination of Certain Calcium Channel Blockers via Oxidation with Cerium (IV) in Pharmaceutical Preparations

Abstract

A simple and sensitive kinetic spectrofluorometric method was developed for the determination of some calcium channel blockers namely, verapamil hydrochloride, diltiazem hydrochloride, nicardipine hydrochloride and flunarizine. The method is based upon oxidation of the studied drugs with cerium (IV) ammonium sulphate in acidic medium. The fluorescence of the produced Ce (III) was measured at 365 nm after excitation at 255 nm. The different experimental parameters affecting the development and stability of the reaction product were carefully studied and optimized. The fluorescence-concentration plots were rectilinear for all the studied compounds over the concentration range of 0.01 to 0.12 μg mL(-1). The limits of detections for the studied compounds ranged from 2.93 × 10(-3) to 0.012 μg mL(-1) and limits of quantification from 9.76 × 10(-3) to 0.04 μg mL(-1) were obtained. The method was successfully applied to the analysis of commercial tablets. The results obtained were in good agreement with those obtained with reference methods.

Keywords: Cerium (IV); diltiazem hydrochloride; nicardipine hydrochloride; verapamil hydrochloride.

Figure 1

Structural formulae of the studied drugs.

Figure 2

Excitation and emission spectra of induced Ce(III) by oxidation of 0.06 μg mL^-1 DLT with Ce (IV) where: (A), Excitation spectrum; (A`), Emission spectrum.

Figure 3

Effect of volume of 5 × 10^-4 M Ce (IV) on the relative fluorescence intensity. ●, 0.06 μg mL^-1 DLT; □, 0.1 μg mL^-1 VP; Δ, 0.1 μg mL^-1 FZ; ■, 0.1 μg mL^-1 NC.

Figure 4

Effect of molar concentration of H₂SO₄ on the relative fluorescence intensity. ●, 0.06 μg mL^-1 DLT; □, 0.1 μg mL^-1 VP; Δ, 0.1 μg mL^-1 FZ; ■, 0.1 μg mL^-1 NC.

Figure 5

Effect of the heating time on the relative fluorescence intensity. Δ, 0.06 μg mL^-1 DLT; ●, 0.1 μg mL^-1 VP; □, 0.1 μg mL^-1 FZ; ■, 0.1 μg mL^-1 NC.

Figure 6

Plot of Log reaction rate (Log ΔF/Δt) versus Log concentration of: A, VP; B, DLT; C, NC; D, FZ.

Figure 7

Stoichiometry of the reaction between VP and Ce (IV) adopting limiting logarithmic method. A, Log (VP] vs log ΔF; B, Log (Ce (IV)] vs log ΔF.

Figure 8

Proposal for the reaction between VP and Ce (IV).

Figure 9

Proposal for the reaction between DLT and Ce (IV).

Figure 10

Proposal for the reaction between NC and Ce (IV).

Figure 11

Proposal for the reaction between FZ and Ce (IV).