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Cation exchange properties of a terpolymer: synthesis and characterization

April 2012, Volume 3, No.2 International Journal of Chemical and Environmental Engineering Spectrophotometric Determination of Isoptin
(Verapamil Hydrochloride) in Pharmaceutical
Preparations using Bromothymol Blue Reagent

D. M. Salh
Chemistry Department, College of Science, Sulaimaniyah University, Kurdistan Region, Iraq
* Corresponding Author
Verapamil Hydrochloride (VH) has been determined spectrophotometrically Using Bromothymol Blue (BTB). The method based on
complexation between (BTB and VH). After shaking and diluting the complex solution with D.W, the pH was adjusted with NaOH
and HCl to pH 4. The colored complex formed between VH and the reagent was transferred into separating funnels and extracted
using 4.5 ml CCl4 and were shaken for (5 minutes). The extracted organic layer was used for preparation of the calibration curves for
spectrophotometric measurements of VH at 420nm. The blanks were carried out in exactly the same way throughout the whole
procedure. Molar absorptivity (ε, detection limit, limit of linearity (µ and r2 were, 1.74*105, 0.009253, 0.08 and
0.9951 for (VH-BTB) respectively. The method was used with reasonable accuracy and precision for the determination of (VH) in
synthetic samples of tablets, capsules and ampoules
Keywords: spectrophotometric determination, Verapamil hydrochloride, Bromothymol Blue, Ion Pair, Pharmaceutical.
1. Introduction
The oldest chromatography method in this review was Phosphorous Detection applied for determination of isopropylvaleronitrile hydrochloride, or (Isoptin) [1], have Verapamil in Human Plasma [3], which was appeared in the chemical structure as shown in (Fig.1): (1984). Later, many chromatographic methods for the determinations of this drug and its metabolites have been reported [4-7] attempting different modifications in the method to increase sensitivity, reducing steps of analysis, or other improvements, with the limit of linearity ranged between [2 ng L-1 – 1000 ng L-1]. Extensive search in the literature has showed many spectrophotometric methods for the determination of VH [8-12]. Among them, how use Spectrofluorometric and visible spectrophotometry, with different type of (Fig.1): Verapamil Hydrochloride Chemical Structure
optimizations to obey beers law, and limit of linearity ranged between [0–340 μg ml-1]. Verapamil was introduced in 1962 as a coronary Preliminary practical tests on many reagents revealed that vasodilator & is the prototype of the Ca2+ antagonists Bromothymol which the chemical structure as shown in used in cardiovascular diseases. Verapamil major effect the (Fig.2), was suitable reagents which have the is on the slow Ca channel. The inhibition of the action following chemical structure [13] to form colored potential inhibits one limb of the reentry circuit believed complexes with the drug VH and were exploited for its Superaventricular quantitative determination in capsules, ampoules and tachycardia that uses the AV node as a reentry point. It is categorized as a class IV antiarrhythmic drug .Hemodynamically; verapamil causes a change in the preload. After load contractility, heart rate, & coronary blood flow .The drug reduces systemic vascular resistance & mean blood pressure, with minor effect on cardiac Spectrophotometric Determination of Isoptin (Verapamil Hydrochloride) in Pharmaceutical Preparations using Bromothymol Blue Reagent
show some background of the reagent in the region of the complex which will have a negative effect on the sensitivity of the method. The complex; or an ion-pair formation between the two, has show an increasing intensity of the spectrum. This is certainly a negative analytical phenomenon; since no high sensitivity could be expected with this system. However, the reagent was expected to show promising results therefore, studies were continued for optimization of the (Fig.2): Bromothymol Blue Chemical Structure
2. Materials and Methods
2.1 Apparatus All measurements were taken with TU-1800S UV-Vis. spectrophotometer, with (1cm) path length quartz cells. The pH of the solutions was adjusted by using Hanna pH- meter with combined glass electrode (910600) Orion Comb pH, Water bath Thermostat Shaker (GFL 1083) was used during the extraction steps and Micro pipettes (variable and fixed). Wave length λ (nm)
2.2 Material Both analar and general purpose reagents were used from [Fluka, Rohm and Haas, GCC (Gainland Chemical Company), and Merck] without further purification. Ordinary distilled water prepared in all glass still and stored in polyethylene container was used. Verapamil hydrochloride ampoule [Knoll] which was (5mg/2ml), was taken as a stock solution, other concentrations were prepared by usual dilution. Methyl orange 0.05% aqueous Wave length λ (nm)
MO. Phthalate buffer (pH=4) was prepared by mixing Fig. (3): The spectrum of the (VH+BTB) complex, and blank
50ml of 0.1M (potassium hydrogen phthalate), with 49.9 spectru3.2 pH Optimization
ml of D.W and 0.1 ml of 0.1M HCl [14-15], and pH was A volume of 500 µL of 1% BTB was added to 1 ml of adjusted with a pH meter. VH, shaking for 3 min., then diluted to 25ml 2.3 Method in volumetric flasks. The pH was then adjusted between 2 to 6, by using 0.1M NaOH or 0.1M HCl. The rest of A volume of 500 µL 1% (BTB) reagent was added to a the test was then followed according to the procedure. certain amount of VH standard or samples containing The results reveal that the optimum pH for (VH-BTB) between (0.08-0.8 μgml-1) VH. The mixture was shaking complex is 4, shown in (Fig.4). for (3 min.) and diluted to 23.5ml in volumetric flasks using D.W. The pH was adjusted by adding 1.5 ml phthalate buffer (pH 4) to the BTB mixture and finally completed to 25ml. The resulting complex formed between VH and the reagent were transferred into separating funnels (100ml capacity) and extracted with Optimum pH=4
4.5 ml CCl4 in two portions to wash out the volumetric flasks for quantitative transfer of the solution and was shaken for 5 minutes. After separation, the organic layer was used for preparation of the calibration curves using spectrophotometric measurements of VH at 420nm. The blanks were carried out in exactly the same way Fig. (4): The pH optimization for (VH+BTB) complex
throughout the whole procedure. 3. Results and Discussion
3.1 Preliminary work The absorption spectra of the complex (VH-BTB) against blank, is shown in Figure (3) showing λ- max 420nm. A 3.2.2 Type of buffer used (pH-adjustment) clear spectrum of the VH-BTB with no observed shoulder For the pH adjustment of (VH-BTB) system different and blank spectrum are seen in (Fig.3). The spectra also buffers were tried, such as; acetic acid-sodium acetate and citric acid-sodium hydroxide, but Phthalate buffer pH = 4, Spectrophotometric Determination of Isoptin (Verapamil Hydrochloride) in Pharmaceutical Preparations using Bromothymol Blue Reagent
was found suitable to adjust pH of the complex (VH- BTB) complex as shown on (Fig.6) shows the ranges BTB). Different volumes of this buffer were added in between 4 – 5 mls the complex. A volume of 4.5 ml CCl4 two ways; either before completing the volumetric flask was found suitable and also sufficient to complete the by D.W to the mark, or until a small volume about 2ml was remaining then the buffer was added and completed to the mark. The results indicated that optimum volume were equal to 1.5 ml phthalate buffer with no difference in the time of addition before or after completing the volumetric flask by D.W (after mixing), and the result is shown in table (1). Table 1: Result of adding different volume phthalate buffer before
and after adding D.W to the mixture of VH and BTB.
Adding the buffer after mixing Adding the buffer before and after adding D.W until about completing the volumetric flask 2ml were remaining to complete by D.W (after mixing). Fig. (6): Optimization of CCl4 volume to be added for extraction the
(VH-BTB) complex.
1.5 ml Abs.= 1.193 3.2.6 Stability of the complexes: The stability of the complex formed between (VH—BTB) was followed by measuring absorbance against time. As shown in (Fig.7). It was found that the complex (VH— 3.2.3 Choosing a Suitable Solvent for Extraction: BTB) was stable for a period of 30 minutes, after Many solvents were tested for extracting the complex separation and only 5 minutes were needed to reach the formed between the BTB reagents with VH and the best true absorbance, and through this time there was time for shaking and for complete complexation that shown in the [dichloromethane, Benzene, Ethyl acetate, Dioxane, (Fig.8). Absorbance has, then increased after that due to Acetone, chloroform] was found is Carbon tetrachloride. the vaporization of the solvent. 3.2.4 Optimum amounts of the Reagents: Preliminary test shows that 500 µL of 1% BTB was suitable. Experiments were then performed with different volumes of the different concentrations to a constant volume 1 ml 0.1 mgml-1 VH. The results shown in (Fig.5) indicate that optimum volumes were 1.2ml for Fig.(7): Stability of the (VH –BTB) complex after separation
----Optimum amount ------
(Vol. BTB) ml
Fig. (5): Optimization of volume of 0.5% BTB
Fig.(8): Suitable time for shaking the (VH –BTB) complex after
3.2.5 Volume optimization of Carbon tetrachloride 3.2.7 Stoichiometry of the [VH-BTB] complex: The stoichiometry of the drug and BTB complexing Different volumes of the solvent dichloromethane reagent was examined by the mole ratio method at wave between 4 to 10 mls was used for extraction of the (VH- length of 420nm: Otimum Volume = 4.5ml
Spectrophotometric Determination of Isoptin (Verapamil Hydrochloride) in Pharmaceutical Preparations using Bromothymol Blue Reagent
The result of mole ratio method was obtained in two ways first by adding constant amount of VH to a series of different amounts of BTB solutions, and second by adding constant amount of BTB to a series of different amounts of VH solutions. Fig. (9a and 9b) show the results of mole ratio method. It was found that the ratio of Fig.(10): Calibration curve for (VH-BTB) complex.
(VH-to-BTB) was about (2 to 1). Determination of Verapamil hydrochloride [Isoptin] in synthetic sample solutions: The recovery test was performed for different concentration of VH with BTB reagent, results shown in Table 2: The accuracy of VH determination in synthetic samples
using BTB
[VH-BTB] complex. Determination of Verapamil hydrochloride in Two tablets were powdered and mixed thoroughly. An amount equivalent to 160 mg of verapamil hydrochloride was weighed accurately and extracted with chloroform to eliminate any interference from excipients. It was filtered through Whatmann No. 42 filter paper and the residue Fig.(9a and b):Determination of the Stoichiometry of the (VH to
BTB) by Mole Ratio
was washed well with chloroform for complete recovery of the drug. The chloroform was evaporated to dryness and the drug was dissolved in doubly distilled water and It was not possible to put forward a reasonable structure diluted to 1000mL with distilled water, It was further for the stoichiometry of VH: BTB of 2:1. According to diluted (1 to 10) [12]. their chemical structure, it was thought that a 1:1 or 1:2 In preparation of tablets, VH has been removed from the ratios would be reasonable. This will make a salt-like additives to make a solution. Therefore VH could be formation between the VH and BTB thus:- determined by calibration curve. Three different volumes (0.2, 0.5 and 1) mls of the sample of VH were determined 2 VH + BTB ---------►BTB (VH) by BTB according to the recommended procedure. The results are shown in tables 3. 3.2.8 Calibration curves: Table 3: Results of different volumes of VH sample (tablets)
The calibration curves obtained according to the determined by BTB reagent
recommended procedure were drawn for both (VH + Conc. Of VH ppm found in Tablets by BTB Using the Eqn. BTB) complex. The linear range was 0.08 – 0.8 µ y = 0.3548x + 0.0073 of VH with (r2 = 0.9951) for (VH + BTB) complex as shown in (Fig. 10). Of the sample taken To test for the existence of a systematic error in the y = 0.3548x + 0.0073
R2 = 0.9951
results shown in tables 3, the actual difference between (X) and (μ) was compared by t-test with the term [t.S / √N] at 95% confidence limit DOF = 2. Spectrophotometric Determination of Isoptin (Verapamil Hydrochloride) in Pharmaceutical Preparations using Bromothymol Blue Reagent
4. Conclusion
The direction of the errors (+) suggest the existence of a systematic error. This may be due to the extraction steps. Nearly non dependence of these errors on sample size between (0.2, 0.5 and 1) mls suggests the existence of both constant and proportional systematic errors. The difference between (X - μ) and [t.s / √N] was not significant at 95% C.L. in all cases (0.2 to 1) mls of VH sample, indicating the non existence, or present of a very small systematic error, which is mainly due to the extraction steps. If the recovery tests were considered only as it is the case with research workers, the value of (R %) in tables are quite reasonable. Precision and Accuracy: The precision of VH determination by BTB complexing reagent was performed on three synthetic samples containing VH in the range of the calibration curve, and their absorbance were measured 10 times for the same unknown, showing the precision of measurements. The precision was also found on 10 times repeating of the whole operation on the same sample. This will show the precision of the operation. The relative standard deviation for the (VH-BTB) complex ranged between 0.75 – 1.75% showing reasonable precision even at lower concentrations of VH. The accuracy shown in the previous sections also revealed reasonable accuracy giving sufficient validity for the application of BTB reagent to be used for the determination of VH in the Sensitivity of the methods: The results of the proposed method were statistically a. Molar absorptivity ε (, b. Limits of linearity, c.
compared with those obtained by the spectrophotometric (Recovery % and R.S.D) of different volumes of AH sample (tablets)
using proposed method, d D.L with correlation coefficient
method for determination of VH using two methods [12] and are summarized in (Table 4), the table show the results concerning sensitivity of the methods (Values of molar absorptivity (ε), slopes of the calibration curves (m), limits of linearity and detection limit (D.L= 3 S.D)). The results indicate reasonable sensitivity of the methods Thanks due to the head of chemistry department of with no significant deference between the methods Sulaimani Univ. and I whish to express my appreciation and extend my thanks to Dr.Bakhtyar K. Aziz. Table 4: Sensitivity of the proposed method
Spectrophotometric Determination of Isoptin (Verapamil Hydrochloride) in Pharmaceutical Preparations using Bromothymol Blue Reagent
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