Determination of fluvastatin sodium by differential pulse voltammetry
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《中华医药杂志》英文版
【Abstract】 Objective To establish method for the determination of fluvastatin sodium in Loscol capsule.Methods The electrochemical behavior of fluvastatin sodium on a glassy carbon electrode was investigated by cyclic voltammetry, linear sweep voltammetry and differential pulse voltammetry.Results It was found that fluvastatin sodium would give a sensitive oxidation peak at +0. 64V in the HAc-NaAc buffer solution(pH 5.10) under the differential pulse voltammetric (DPV) mode. The peak current was linear with the concentration of fluvastatin sodium in the range of 2.0~40mg/L. As a result, a DPV method for determination of fluvastatin sodium with the detection limit of 0.24mg/L has been developed. The proposed method has been used for determination of fluvastatin sodium in the Loscol capsule, the recovery was found to be in the range of 98.0%~101.2%. The mechanism for this electrochemical reaction at the glassy carbon electrode was also discussed in this paper.Conclusion The electrochemical analysis method described here enables simple and rapid determination of fluvastatin sodium in real samples.
【Key words】 fluvastatin sodium; electrochemistry; glassy carbon electrode
INTRODUCTION
Loscol (fluvastatin sodium) is a water-soluble cholesterol lowering agent which acts through the inhibition of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase. Fluvastatin sodium is [R*, S*-(E)]-(±)-7-[3-(4-fluorophenyl)-1-(1-methylethyl)-1H-indol-2-yl]-3,5-dihydroxy-6-heptenoic acid (Fig 1), monosodium salt. The empirical formula of fluvastatin sodium is C24H25FNO4Na and its molecular weight is 433.46. This molecular entity is the first entirely synthetic HMG-CoA reductase inhibitor, and is in part structurally distinct from the fungal derivatives of this therapeutic class. It is available by prescription only for the reduction of cholesterol levels. Specifically, Lescol is indicated for the use as an adjunct to diet to reduce elevated total cholesterol (TC), LDL-C, TG, and Apo B levels and to increase HDL-C in patients with primary hypercholesterolemia and mixed dyslipidemia (Frederickson Type Ⅱa and Ⅱb) whose response to dietary restriction of saturated fat and cholesterol and other nonpharmacological measures has not been adequate and to slow the progression of coronary atherosclerosis in patients with coronary heart disease as part of a treatment strategy to lower TC and LDL-C to target levels (from FDA Label).
Sporadic publications on the identification of fluvastatin sodium by spectrophotometric method[1], gas chromatography[2], HPLC[3] and electrochemical analysis method[4] have appeared in the literature. In this work reported here the utility of electrochemical analysis method using glass carbon electrode as working electrode for the determination of fluvastatin sodium in HAc-NaAc buffer solution (pH 5.10) for the first time. A sensitive differential pulse voltammetric peak of fluvastatin sodium at glass carbon electrode at about +0.64V (vs Ag/AgCl) is found.The electrochemical behavior and reaction mechanism of this system have been studied by cyclic voltammetry, linear sweep voltammetry and differential pulse voltammetry. There is a good linear relationship between the peak current and the concentration of fluvastatin sodium in the range of 2.0~40mg/L. The detection limit of the method is 0.24mg/L. The electrochemical analysis method described here enables simple and rapid determination of fluvastatin sodium in real samples. The concentration of fluvastatin sodium in Loscol capsules has been determined with recovery range of 98.0%~101.2% by this method.
MATERIALS AND METHODS
All measurements were carried out with a Model CHI832 multifunction voltammetric analyzer system (Shanghai Chenhua Electroanalysis Instruments Corporation, China). A glass carbon electrode with area 0.785mm2 was used as working electrode. An Ag/AgCl was used as a reference electrode together with a platinum wire as the counter-electrode. The pH measurements were carried out with a 25 pHS-2C model aidity meter (Leici Instrumental Factory, Shanghai, China), using a combination electrode. The electrolytic cell was a 50ml beaker. A SRD-1 Model magnetic stirrer and a stirring bar (2.5cm in length) provided the convective transport during the pre-concentration. All experiments were performed at room temperature, and dissolved oxygen was removed from the solutions by bubbling oxygen-free nitrogen through the cell for 10 minutes.
Fluvastatin sodium was obtained from Sigma and was used without further purification. Solution of 1×10-3mol/L fluvastatin sodium was prepared by dissolving fluvastatin sodium in twice-distilled water. All of the chemicals were of reagent grade (Merck, Darmstadt). Twice-distilled deionized water served as a solvent. Procedure: To evaluate the concentration of fluvastatin sodium, the standard curve method was used in the experiment. Transfer of the stock solution needed for assay into a 50ml standard flask, followed by the addition of 10.0ml 1.0mol/L HAc-NaAc buffer solution (pH 5.10), and made up to volume with distilled water. The solution was transferred into the electrolytic cell, then the pre-concentration step was performed in a stirred (ca. 500 rev/min) solution for 120s. During this period, the glass carbon electrode was held at 0.40V. The stirring was then stopped and after 10 seconds the voltamperogram was recorded by applying the differential pulse voltammetry (DPV) from 0.40V to 0.8V, and measured the peak height at about +0.64V.
RESULTS AND DISCUSSION
The concentration, pH value and the type of buffer were important parameters that greatly influence the voltammetric behaviors of fluvastatin sodium. In order to achieve the maximum sensitivity of the fluvastatin sodium, different supporting electrolytes such as hydrochloric acid, potassium chloride solution, sodium hydroxide solution, Britton-Robinson buffer solution, HAc-NaAc buffer solution and ammonia/ammonium chloride buffer solution, were compared and the results showed that there was a oxidation peak in neutral or acid solution and the 0.20mol/L HAc-NaAc solution was found to be best, the voltrammograms of fluvastatin sodium being well defined and the sensitivity reasonably high(Fig 2).
When the initial potential less than 0.40V, the peak height decreased with the decreasing potential. Within the chosen range of 0.30~0.50V, the peak height kept stable, so 0.40V was chosen as the initial potential. There was no effective affection on the peak height of the concentration of fluvastatin sodium when it was above 80mg/L.The peak height increased with the pre-concentration time firstly, but reached stable after pre-concentration at 0.40V for 120s if the concentration less than 80mg/L, so pre-concentration for 120s and quite for 10s were selected in all our experiments.
The effects of several types of interfering species on the determination of 5.0mg/L fluvastatin sodium were examined. The relative error range was below ±5% in the presence of 1000-fold sodium chloride, ammonium chloride, oxalic acid, citrate acid, tartaric acid, glucose, starch, or 100-fold histidine, glycine, glutamic acid, proline, and 50-fold methionine, tryptophan.
The typical repetitive cyclic voltammetric curves were shown in Fig 3. An oxidation peak was observed in ~+0.71V, and the oxidation peak in the first scan after an accumulation time of 120s which was much longer than in the second scan. No peak was observed in the catholic branch, indicating irreversibility of the oxidation.
The effect of the deposition time on the oxidation peak height of linear scan voltammetry was examined. The peak height increased with the adsorption time in the form of the adsorption isotherm. At relatively longer adsorption times, an equilibrium surface concentration was reached and the peak height became almost constant. Pre-concentration time of 120s the peak height, which varied linearly with concentration of the investigated compound showed the process, was diffusion controlled[5].
1 0.1mol/LHAc-NaAc (pH5.10) ；2 6.0mg/L fluvastatin sodium +0.1mol/L HAc-NaAc (pH5.10) ；3 10.0mg/L fluvastatin sodium +0.1mol/L HAc-NaAc (pH5.10) Figure 2 Differential pulse voltammograms of fluvastatin sodium 10.0mg/L fluvastatin sodium
+0.1mol/L HAc-NaAc (pH5.10) ；1 first scan; 2 second scan;3 third scanFigure 3 Cyclic voltammogram of fluvastatin sodium
Under the optimum conditions and over a concentration range of 2.0~40mg/L for fluvastatin sodium, the DPV peak height varied linearly with concentration of fluvastatin sodium, and the equation of the regression line obtained was expressed as ip(μA)=3.9232×c(mg/L)+3.4875(n=6, r2=0.992), the detection limit was 0.24mg/L(S/N=3).
Dissolved the sample fluvastatin sodium tablets, which was purchased from market and nominal 0.04g per tablet, in the water and diluted to the volume 20ml. Transferred of the solution needed for assayed into the electrolytic cell, the concentration of fluvastatin sodium was determined using the method of standard additions according to the voltammetric method described above, and the results were shown in Table 1.
CONCLUSIONS
The utility of electrochemical analysis method using glass carbon electrode as working electrode for the determination of fluvastatin sodium was reported for the first time. In the medium of HAc-NaAc buffer solution (pH 5.10), a sensitive differential pulse voltammetric peak of fluvastatin sodium at glass carbon electrode at about +0.64V (vs Ag/AgCl) was found. There is a good linear relationship between the peak current and the concentration of fluvastatin sodium in the range of 2.0~40mg/L. The detection limit of the method is 0.24mg/L. The electrochemical analysis method described here enables simple and rapid determination of fluvastatin sodium in real samples. The concentration of fluvastatin sodium in capsules has been determined with good results by this method.
REFERENCES
1. Erk N. Rapid spectrophotometric method for quantitative determination of simvastatin and fluvastatin in human serum and pharmaceutical formulations. Pharmazie Die,2002,57(12): 817-819.
2. Leis H.J, Windischhofer W. Quantitative determination of fluvastatin in human plasma by gas chromatography/negative ion chemical ionization mass spectrometry using [O-18(2)]-fluvastatin as aninternal standard.Rapid Communications in Mass Spectrometry,2005,19(2): 128-132.
3. Akinori Nakashima, Christoph Saxer, Miyuki Niina,et al. Determination of fluvastatin and its five metabolites in human plasma using simple gradient reversed-phase high-performance liquid chromatography with ultraviolet detection. Journal of Chromatography B: Biomedical Sciences and Applications,2001,760: 17-25.
4. Sibel A, Ozkan, Bengi Uslu. Electrochemical study of fluvastatin sodium-analytical application to pharmaceutical dosage forms, human serum, and simulated gastric juice.Analytical and Bioanalytical Chemistry,2002,372(4):582-586.
5. Zhen Yonghuai, Ma Hongyan. Electrochemical behavior of cephradine. Chin J Anal Chem,1997,9:1006-1009(in Chinese).
1 School of Chemical and Biological Engineering, Yancheng Institute of Technology, Yancheng,Jiangsu Province 224003, China
2 Women and Children Health Hospital of Yancheng, Yancheng,Jiangsu Province 224003, China
(Editor Guo Hui-ling)CLINICAL PRACTICE(YAN Jin-long， LU Xiu-ping)
【Key words】 fluvastatin sodium; electrochemistry; glassy carbon electrode
INTRODUCTION
Loscol (fluvastatin sodium) is a water-soluble cholesterol lowering agent which acts through the inhibition of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase. Fluvastatin sodium is [R*, S*-(E)]-(±)-7-[3-(4-fluorophenyl)-1-(1-methylethyl)-1H-indol-2-yl]-3,5-dihydroxy-6-heptenoic acid (Fig 1), monosodium salt. The empirical formula of fluvastatin sodium is C24H25FNO4Na and its molecular weight is 433.46. This molecular entity is the first entirely synthetic HMG-CoA reductase inhibitor, and is in part structurally distinct from the fungal derivatives of this therapeutic class. It is available by prescription only for the reduction of cholesterol levels. Specifically, Lescol is indicated for the use as an adjunct to diet to reduce elevated total cholesterol (TC), LDL-C, TG, and Apo B levels and to increase HDL-C in patients with primary hypercholesterolemia and mixed dyslipidemia (Frederickson Type Ⅱa and Ⅱb) whose response to dietary restriction of saturated fat and cholesterol and other nonpharmacological measures has not been adequate and to slow the progression of coronary atherosclerosis in patients with coronary heart disease as part of a treatment strategy to lower TC and LDL-C to target levels (from FDA Label).
Sporadic publications on the identification of fluvastatin sodium by spectrophotometric method[1], gas chromatography[2], HPLC[3] and electrochemical analysis method[4] have appeared in the literature. In this work reported here the utility of electrochemical analysis method using glass carbon electrode as working electrode for the determination of fluvastatin sodium in HAc-NaAc buffer solution (pH 5.10) for the first time. A sensitive differential pulse voltammetric peak of fluvastatin sodium at glass carbon electrode at about +0.64V (vs Ag/AgCl) is found.The electrochemical behavior and reaction mechanism of this system have been studied by cyclic voltammetry, linear sweep voltammetry and differential pulse voltammetry. There is a good linear relationship between the peak current and the concentration of fluvastatin sodium in the range of 2.0~40mg/L. The detection limit of the method is 0.24mg/L. The electrochemical analysis method described here enables simple and rapid determination of fluvastatin sodium in real samples. The concentration of fluvastatin sodium in Loscol capsules has been determined with recovery range of 98.0%~101.2% by this method.
MATERIALS AND METHODS
All measurements were carried out with a Model CHI832 multifunction voltammetric analyzer system (Shanghai Chenhua Electroanalysis Instruments Corporation, China). A glass carbon electrode with area 0.785mm2 was used as working electrode. An Ag/AgCl was used as a reference electrode together with a platinum wire as the counter-electrode. The pH measurements were carried out with a 25 pHS-2C model aidity meter (Leici Instrumental Factory, Shanghai, China), using a combination electrode. The electrolytic cell was a 50ml beaker. A SRD-1 Model magnetic stirrer and a stirring bar (2.5cm in length) provided the convective transport during the pre-concentration. All experiments were performed at room temperature, and dissolved oxygen was removed from the solutions by bubbling oxygen-free nitrogen through the cell for 10 minutes.
Fluvastatin sodium was obtained from Sigma and was used without further purification. Solution of 1×10-3mol/L fluvastatin sodium was prepared by dissolving fluvastatin sodium in twice-distilled water. All of the chemicals were of reagent grade (Merck, Darmstadt). Twice-distilled deionized water served as a solvent. Procedure: To evaluate the concentration of fluvastatin sodium, the standard curve method was used in the experiment. Transfer of the stock solution needed for assay into a 50ml standard flask, followed by the addition of 10.0ml 1.0mol/L HAc-NaAc buffer solution (pH 5.10), and made up to volume with distilled water. The solution was transferred into the electrolytic cell, then the pre-concentration step was performed in a stirred (ca. 500 rev/min) solution for 120s. During this period, the glass carbon electrode was held at 0.40V. The stirring was then stopped and after 10 seconds the voltamperogram was recorded by applying the differential pulse voltammetry (DPV) from 0.40V to 0.8V, and measured the peak height at about +0.64V.
RESULTS AND DISCUSSION
The concentration, pH value and the type of buffer were important parameters that greatly influence the voltammetric behaviors of fluvastatin sodium. In order to achieve the maximum sensitivity of the fluvastatin sodium, different supporting electrolytes such as hydrochloric acid, potassium chloride solution, sodium hydroxide solution, Britton-Robinson buffer solution, HAc-NaAc buffer solution and ammonia/ammonium chloride buffer solution, were compared and the results showed that there was a oxidation peak in neutral or acid solution and the 0.20mol/L HAc-NaAc solution was found to be best, the voltrammograms of fluvastatin sodium being well defined and the sensitivity reasonably high(Fig 2).
When the initial potential less than 0.40V, the peak height decreased with the decreasing potential. Within the chosen range of 0.30~0.50V, the peak height kept stable, so 0.40V was chosen as the initial potential. There was no effective affection on the peak height of the concentration of fluvastatin sodium when it was above 80mg/L.The peak height increased with the pre-concentration time firstly, but reached stable after pre-concentration at 0.40V for 120s if the concentration less than 80mg/L, so pre-concentration for 120s and quite for 10s were selected in all our experiments.
The effects of several types of interfering species on the determination of 5.0mg/L fluvastatin sodium were examined. The relative error range was below ±5% in the presence of 1000-fold sodium chloride, ammonium chloride, oxalic acid, citrate acid, tartaric acid, glucose, starch, or 100-fold histidine, glycine, glutamic acid, proline, and 50-fold methionine, tryptophan.
The typical repetitive cyclic voltammetric curves were shown in Fig 3. An oxidation peak was observed in ~+0.71V, and the oxidation peak in the first scan after an accumulation time of 120s which was much longer than in the second scan. No peak was observed in the catholic branch, indicating irreversibility of the oxidation.
The effect of the deposition time on the oxidation peak height of linear scan voltammetry was examined. The peak height increased with the adsorption time in the form of the adsorption isotherm. At relatively longer adsorption times, an equilibrium surface concentration was reached and the peak height became almost constant. Pre-concentration time of 120s the peak height, which varied linearly with concentration of the investigated compound showed the process, was diffusion controlled[5].
1 0.1mol/LHAc-NaAc (pH5.10) ；2 6.0mg/L fluvastatin sodium +0.1mol/L HAc-NaAc (pH5.10) ；3 10.0mg/L fluvastatin sodium +0.1mol/L HAc-NaAc (pH5.10) Figure 2 Differential pulse voltammograms of fluvastatin sodium 10.0mg/L fluvastatin sodium
+0.1mol/L HAc-NaAc (pH5.10) ；1 first scan; 2 second scan;3 third scanFigure 3 Cyclic voltammogram of fluvastatin sodium
Under the optimum conditions and over a concentration range of 2.0~40mg/L for fluvastatin sodium, the DPV peak height varied linearly with concentration of fluvastatin sodium, and the equation of the regression line obtained was expressed as ip(μA)=3.9232×c(mg/L)+3.4875(n=6, r2=0.992), the detection limit was 0.24mg/L(S/N=3).
Dissolved the sample fluvastatin sodium tablets, which was purchased from market and nominal 0.04g per tablet, in the water and diluted to the volume 20ml. Transferred of the solution needed for assayed into the electrolytic cell, the concentration of fluvastatin sodium was determined using the method of standard additions according to the voltammetric method described above, and the results were shown in Table 1.
CONCLUSIONS
The utility of electrochemical analysis method using glass carbon electrode as working electrode for the determination of fluvastatin sodium was reported for the first time. In the medium of HAc-NaAc buffer solution (pH 5.10), a sensitive differential pulse voltammetric peak of fluvastatin sodium at glass carbon electrode at about +0.64V (vs Ag/AgCl) was found. There is a good linear relationship between the peak current and the concentration of fluvastatin sodium in the range of 2.0~40mg/L. The detection limit of the method is 0.24mg/L. The electrochemical analysis method described here enables simple and rapid determination of fluvastatin sodium in real samples. The concentration of fluvastatin sodium in capsules has been determined with good results by this method.
REFERENCES
1. Erk N. Rapid spectrophotometric method for quantitative determination of simvastatin and fluvastatin in human serum and pharmaceutical formulations. Pharmazie Die,2002,57(12): 817-819.
2. Leis H.J, Windischhofer W. Quantitative determination of fluvastatin in human plasma by gas chromatography/negative ion chemical ionization mass spectrometry using [O-18(2)]-fluvastatin as aninternal standard.Rapid Communications in Mass Spectrometry,2005,19(2): 128-132.
3. Akinori Nakashima, Christoph Saxer, Miyuki Niina,et al. Determination of fluvastatin and its five metabolites in human plasma using simple gradient reversed-phase high-performance liquid chromatography with ultraviolet detection. Journal of Chromatography B: Biomedical Sciences and Applications,2001,760: 17-25.
4. Sibel A, Ozkan, Bengi Uslu. Electrochemical study of fluvastatin sodium-analytical application to pharmaceutical dosage forms, human serum, and simulated gastric juice.Analytical and Bioanalytical Chemistry,2002,372(4):582-586.
5. Zhen Yonghuai, Ma Hongyan. Electrochemical behavior of cephradine. Chin J Anal Chem,1997,9:1006-1009(in Chinese).
1 School of Chemical and Biological Engineering, Yancheng Institute of Technology, Yancheng,Jiangsu Province 224003, China
2 Women and Children Health Hospital of Yancheng, Yancheng,Jiangsu Province 224003, China
(Editor Guo Hui-ling)CLINICAL PRACTICE(YAN Jin-long， LU Xiu-ping)