DPP Modes Research Articles

Stability-Indicating Polarographic Determination of Acyclovir Through Chelation with Nickel(II)

A simple and sensitive, stability-indicating polarographic method was developed for the determination of acyclovir (ACV) in raw materials and dosage forms. The proposed method relies on the chelation of ACV with nickel(II) in Britton Robinson buffer (pH 5) and measuring the resulting polarographic wave either in the direct current (DCt) or differential pulse (DPP) modes. The polarographic wave has been characterized as being catalytic reduction prewave. Different experimental parameters affecting the formation of the Ni-ACV chelate and its polarographic activity were studied and optimized. The current concentration relationship was found to be linear over the range of 0.8-8 and 1-8 microg/mL, with minimum detectabilities of 0.10 and 0.19 microg/mL using DPP and DCt modes, respectively. The method was used to investigate the kinetics of the acid-induced degradation of the drug. The apparent first-order rate constants and half-life times were calculated.

Polarographic Analysis of Quetiapine in Pharmaceuticals

The voltammetric behaviour of quetiapine (QTP) was studied using direct current (DC t), differential pulse (DPP) and alternating current (AC t) polarography. The drug manifests cathodic waves over the pH range of 6 – 11.8. The waves were characterized as being irreversible, diffusion-controlled with limited adsorption properties. At pH 8, the diffusion current-concentration relationship was rectilinear over the range of 8 – 44 µg/mL and 4 – 44 µg/mL using DC t and DPP modes, respectively, with minimum detection limits (LOD) of 0.06 µg/mL and 0.04 µg/mL using the DC t and DPP modes, respectively. The diffusion-current constant (I d) is 1.36 ± 0.04 (n = 10). The proposed method was successfully applied to the determination of the studied compound both in pure form and in formulations. The results obtained were favourably compared with those obtained using a reference method. A pathway for the electrode reaction was postulated.

Voltammetric Determination of Rosiglitazone in Pharmaceutical Preparations and Human Plasma

The voltammetric behavior of rosiglitazone was studied using direct current (DCt), differential pulse (DPP), and alternating current (ACt) polarography. The drug manifests cathodic waves over a pH range of 2–11.2. In Britton‐Robinson buffer (BRb; pH 4), the diffusion current–concentration relationship was found to be rectilinear over a range of 4–24 µg · mL−1 and 0.1–16 µg · mL−1 using DCt and DPP modes, respectively, with minimum limits of detection (LOD) of 0.15 µg · mL−1 and 0.07 µg · mL−1 using the DCt and DDP modes, respectively. The diffusion‐current constant (I d) was 6.63±0.03 (n=5). The proposed method was successfully applied to the determination of the studied compound both in pure form and in formulations. The mean percentage recoveries in tablets were 100.09±1.18 and 100.85±0.88 (n=5) using DCt and DPP modes, respectively. Furthermore, the proposed method, adopting the DPP mode, was applied to the determination of rosiglitazone in spiked human plasma and the obtained mean percentage recoveries were 99.14±3.29 (n=4).

Anodic Polaroqraphic Determination of lsradipine in Pharmaceutical Formulations

The anodic behaviour of isradipine was studied using cyclic voltammetry (CV), direct current (DCt) and differential-pulse (DPP) polarography. lsradipine exhibited well-defined anodic polarographic waves over the pH range of 4–8 in Britton-Robinson buffer (BRb). At pH 6, the analytical pH, the diffusion-current constant (Id) was 2.12 ± 0.42 (n = 4). The oxidation potential is −0.10 V vs AgIAgCl reference electrode with correlation coefficients of 0.9977 and 0.9948 in the DCt and DPP modes, respectively. The current-concentration plots were rectilinear over the ranges 5–14 µg/ml and 2.4–12 µg/ml using the DCt and DPP modes, respectively. The lower detection limit was 1.12 µg/ml (3.02 x 10−6 M) adopting the DPP mode. The proposed method was applied to commercial tablets and capsules, the % recoveries were 100.52 ± 1.267 and 99.4 ± 0.87 (n = 6) for the tablets and 101.3 ± 1.57 and 100.7 ± 2.10 (n = 6) for the capsules adopting both DCt and DPP modes, respectively. The number of electrons involved in the electrode process was accomplished and a proposal of the electrode reaction was presented.

Polarographic determination of flubendazole in spiked human urine and plasma

The voltammetric behavior of flubendazole was studied using direct current (DC t), differential pulse (DPP) and alternating current (AC t) polarography. The drug manifests a cathodic wave in 20% v/v formic acid solution. The wave was characterized as being irreversible, diffusion-controlled with limited adsorption properties. The diffusion current–concentration relationship was found to be rectilinear over the range 3.2–14.4 μg/ml and 0.1 to 12.8 μg/ml, using DC t and DPP modes, respectively, with minimum detectability of 0.161 μg/ml (5.14×10 −7 M) and 0.0.057 μg/ml (1.82×10 −8 M) using DC t and DPP modes, respectively. Furthermore, the proposed method was applied to the in-vitro determination of flubendazole in spiked human urine and plasma adopting the DPP technique. The percentage recoveries were 100.20±0.62 and 97.42±0.95, respectively.

Voltammetric determination of isradipine in dosage forms and spiked human plasma and urine

The voltammetric behavior of isradipine was studied using direct current (DC t), differential-pulse (DPP) and alternating current (AC t) polarography. Isradipine exhibited well-defined cathodic waves over the whole pH range in Britton–Robinson buffer (BRb). At pH 5, the analytical pH, the diffusion-current constant (Id) was 8.27±0.52. The current-concentration plots were rectilinear over the range 1–20 and 0.1–18 μg/ml using the DC t and DPP modes, respectively, with minimum detectability of 0.01 μg/ml (2.7×10 −8 M) using the latter technique. The current has been characterized as being diffusion-controlled, although adsorption phenomenon played a limited role in the electrode process. The proposed method was applied to commercial tablets and capsules. The percentage recoveries were in good agreement with those given by the manufacturer. The method was further extended to the in-vitro determination of the drug in spiked human urine and plasma, the percentage recoveries were ( n=4) 100.12±1.42 and 103.88±5.13, respectively. The number of electrons involved in the reduction process was accomplished and a proposal of the electrode reaction was presented.

Voltammetric analysis of trazodone HCl in pharmaceuticals and biological fluids

The voltammetric behavior of trazodone (TRZ) HCl was studied using direct current (DC t), differential pulse (DPP) and alternating current (AC t) polarography. The drug manifests cathodic waves over the pH range of 10–14. The waves were characterized as being irreversible, diffusion-controlled with limited adsorption properties. At pH 10, the diffusion current–concentration relationship was found to be rectilinear over the range 4–32 and 0.8–24 μg ml −1 using DC t and DPP modes, respectively, with minimum detectability ( S/ N=2) of 0.104 μg ml −1 (2.45×10 −6 M) and 0.314 μg ml −1 (7.397×10 −6 M) using the DPP and DC t modes, respectively. The diffusion-current constant ( I d) is 4.31±0.02 ( n=6). The proposed method was successfully applied to the determination of the studied compound either in pure form or in formulations. The results obtained were favorably compared with those given using a reference method. Furthermore, the proposed method was applied to the determination of TRZ in spiked human urine and plasma adopting the DPP technique. No prior extraction step is needed in case of urine. The percentage recoveries were 98.43±0.79 and 97.44±0.705 ( n=4) in spiked human urine and plasma, respectively. A pathway for the electrode reaction was postulated.

Voltammetric Determination of Benazepril and Ramipril in Dosage Forms and Biological Fluids through Nitrosation

A simple and highly sensitive voltammetric method was developed for the determination of benazepril (I) and ramipril (II). The compounds were treated with nitrous acid, and the cathodic current produced by the resulting nitroso derivatives was measured. The voltammetric behavior was studied by adopting direct current (DCt), differential pulse (DPP), and alternating current (ACt) polarography. Both compounds produced well-defined, diffusion-controlled cathodic waves over the whole pH range in Britton-Robinson buffers (BRb). At pH 3 and 5, the values of diffusion-current constants (Id), were 5.90 +/- 0.40 and 6.66 +/- 0.61 for I and II, respectively. The current concentration plots for I were rectilinear over the range of 1.5-40 and 0.1-30 microg/mL in the DCt and DPP modes, respectively; for II, the range was 2-30 and 0.1-20 microg/mL in the DCt and DPP modes, respectively. The minimum detectabilities (S/N = 2) were 0.015 microg/mL (about 3.25 x 10(-8)M) and 0.012 microg/mL (about 2.88 x 10(-8)M) for I and II, respectively, adopting the DPP mode. Results obtained for the proposed method when applied to the determination of both compounds in dosage forms were in good agreement with those obtained using reference methods. Hydrochlorthiazide, which is frequently co-formulated with these drugs, did not interfere with the assay. The method was also applied to the determination of benazepril in spiked human urine and plasma. The percentage recoveries adopting the DPP mode were 96.2 +/- 1.21 and 95.7 +/- 1.61, respectively.

Differential-Pulse Polarographic Determination of Some N-Substituted Phenothiazine Derivatives in Dosage Forms and Urine Through Treatment with Nitrous Acid

A highly sensitive differential-pulse (DPP) polarographic method is described for the determination of three N-substituted phenothiazine derivatives, chlorpromazine (CZ), promazine (PZ) and promethazine (PMZ). The method involves the use of nitrous acid as an oxidant. Polarographically-active sulphoxides with diffusion-current constants (Id) of 2.53, 3.05 and 3.37 were obtained for CZ, PZ and PMZ, respectively. The polarographic waves were characterized as being diffusion-controlled, irreversible and partly affected by adsorption phenomena. All parameters affecting the oxidation process and polarographic behaviour were optimized and incorporated into the procedure. The limiting current-concentration plots in the DPP mode were rectilinear over the range: 0.006–0.1 mM, 0.005–0.08 mM and 0.008–0.1 mM for CZ, PZ and PMZ, respectively, with minimum detectability (S/N=3) of 3 × 10−7 M for CZ and PZ, and 4 × 10−7 M for PMZ, respectively. The kinetic parameters of the electrode reaction, including rate constant, free energy of activation ΔG and effect of temperature on both parameters were studied. The proposed method was successfully applied to the determination of phenothiazines in dosage forms; the results obtained were in agreement with those given with the official methods. The method was further applied to the determination of promazine in spiked human urine. The percentage recovery was 96.86 ± 0.30. The advantages of the proposed method over other reported methods were discussed. A proposal of the electrode reaction was made.

Voltammetric determination of isoxsuprine and fenoterol in dosage forms and biological fluids through nitrosation.

A simple and highly sensitive voltammetric method was developed for the determination of isoxsuprine HCl (I) and fenoterol HBr (II) in dosage forms and biological fluids. The method is based on treatment of the two compounds with nitrous acid followed by measuring the cathodic current produced by the resulting nitroso derivatives. The voltammetric behavior was studied adopting Direct Current (DCt), Differential Pulse (DPP) and Alternating Current (ACt) polarography. Both compounds produced well-defined, diffusion-controlled cathodic waves over the whole pH range in Britton-Robinson buffers (BRb). At pH 11 and pH 9, the values of diffusion-current constants (Id), were 9.4 +/- 0.3 and 7.7 +/- 0.4 for I and II, respectively. The current-concentration plots for I were rectilinear over the range of 0.6-12 microg/ml and 0.1-12 microg/ml in the DCt and DPP modes, respectively. As for II, the range was 1-20 microg/ml and 0.1-20 microg/ml in the DCt and DPP modes, respectively. The minimum detectability (S/N = 2) were 0.02 microg/ml (approximately 6 x 10(-8) M) and 0.01 microg/ml (approximately 2.6 x 10(-8) M) for I and II, respectively, adopting the DPP mode. The proposed method was applied to the determination of both compounds in dosage forms and the results obtained were in good agreement with those obtained using reference methods. The proposed method was further applied to the determination of isoxsuprine in spiked human urine and plasma. The percentage recoveries adopting the DPP mode were 98.84 +/- 1.18 and 99.26 +/- 0.97, respectively.

Polarographic Determination of Some 4-Quinolone Antibacterials via Their Ni(II)-Complexes

The voltammetric behavior of Ni(II) complexes of three 4-quinolone antibacterials, namely: norfloxacin (NFX), ciprofloxacin (CFX) and sparfloxacin (SFX), was studied using direct current (DCt) differential pulse (DPP) and alternating current polarography (ACt). The different experimental parameters affecting the cathodic waves were carefully investigated, then a simple and sensitive method for the analysis of these compounds was developed. The proposed method depends upon the polarographic activity of Ni(II)-4-quinolone complexes in Britton-Robinson buffers (BRb) over the pH range (4.0–8.0). A well-defined, cathodic wave was created at pH 6.0, 5.5 and 6.5 for NFX, CFX and SFX, respectively. The waves were characterized as being irreversible, diffusion-controlled with limited adsorption properties. The current-concentration relationship was found to be linear over the range 2.0–6.4×10–5 M, 0.8–3.2×10–5 M, for NFX, 2.0–6.4×10–5 M, 0.8–5.6×10–5 M for CFX and 2.0–7.2×10–5 M, 0.8–4.8×10–5 M for SFX using DCt and DPP modes, respectively. with minimum detectability (S/N=2) of about 2×10–7 M for all the studied compounds. The method described was successfully applied to the determination of NFX, CFX and SFX in bulk and tablet formulations. The average % recoveries for the studied compounds were 99.58±0.72 to 100.50±0.79 and 99.50±0.71 to 100.17±0.29 using DCt and DPP, respectively. The results obtained were favorably compared to those given by a reference method.

Voltammertric Behaviour of Clonixin and its Differential Pulse Polarographic Determination in Tablets

ABSTRACT Clonixin, a non-steroid analgesic, can be both reduced at the mercury electrode and oxidised at the glassy carbon electrode. The anodic response shows well-defined waves in a pH range between pH 2-12. The polarographic response shows two irreversible waves or peaks in the range between pH 1-6 shifting cathodically when pH increases. Above pH 7.0 all the signals disappeared. The first signal in the dpp mode at pH 1.8 was selected for analytical use. The polarographic

Polarographic determination of EDTA in certain pharmaceutical dosage forms

A highly sensitive polarographic method was developed for the determination of EDTA added as a preservative in certain pharmaceutical preparations. The method involved chelation with Eu(III) followed by polarographic measurement of the chelate formed. A well-defined cathodic wave was developed in Britton–Robinson buffers over the pH range 2–12. The wave was characterized as being quasi-reversible and diffusion controlled. The current–concentration relationship was found to be rectilinear over the ranges 8–160 and 2–120 μg ml −1, using DCt and DPP modes, respectively, with limit of detection of 0.1 μg ml −1 using the DDP technique. The mechanism of the electrode reaction was verified. The proposed method was applied for the determination of EDTA in certain pharmaceutical dosage forms, and the results obtained were in agreement with those obtained by a reference method.

Differential pulse polarographic determination of ofloxacin in pharmaceuticals and biological fluids

A sensitive method is described for the determination of ofloxacin in its pure form, dosage forms and biological fluids. The proposed method depends upon the polarographic activity of ofloxacin in Britton Robinson buffers, whereby a well-defined cathodic wave is produced over the pH range 4.1–10.3. The wave was characterized as being irreversible, diffusion-controlled with limited adsorption properties. The current-concentration relationship was found to be rectilinear over the range 5×10 −5–5×10 −4 M and 1×10 −5–5×10 −4 M using the DC t and DPP modes respectively, with a minimum detectability (S/N=3) of 3×10 −7 M. The proposed method was successfully applied to the determination of ofloxacin in tablets and biological fluids. The results obtained were found to be in agreement with those obtained by a reference method.

Polarographic behaviour and determination of azintamide

Azintamide was found to be reduced at the dropping mercury electrode over the pH range 1.8–9.4 in Britton Robinson buffers containing 20% methanol. At pH 7.42 a well defined diffusion-controlled cathodic wave was produced. The limiting current versus concentration plot was linear over the range 0.025–1.0 mM and 0.005–1.0 mM in the DCt and DPP modes, respectively, with a lower detection limit of 1 × 10−7 M by the latter technique. A mechanism for the electrode reaction has been proposed. The method has been applied to the determination of azintamide in tablets, and the results obtained were in agreement with those obtained by a reference method.

Pulse voltammetry and polarography: Recent progress in microprocessor instrumentation

A new microprocessor-based voltammetric and polarographic analyzer has been developed. Its outstanding features include the use of a high-level language for programming operation sequences and an algorithm giving the derivatives of the peaks obtained in the DPV, DPP, DNPV, DNPP and SWV modes; it has been shown that the amplitude measured between the two derived peaks is proportional to the amplitude of the original peak, and inversely proportional to the potential difference between the peak extremes of the derivative curves; this potential difference is in turn proportional to RT/nF, for a reversible reaction. This calculation method allows the automatic compensation of the residual slope, due either base line current or to an overlapping peak. This new analyzer has been tested successfully, for example, in the determination of UO 2+ 2 ions by adsorbed chathodic stripping voltammetry (ACSV). Some results obtained for in vivo analysis of dopamine traces in the DNPV mode on a carbon fiber microelectrode are also given; the microfiber electrode had previously undergone a particular electrochemical treatment which improved both sensitivity and selectivity notably.