INTRODUCTION
Donepezil Hydrochloride (DH) is a new antialzeimer drug. It is the potent acetylcholine esterase inhibitor (Barner and Grey, 1998; Martindale, 2002). Chemically it is 2,3-Dihydro-5, 6- dimethoxy- 2-{{1- (phenylmethyl)- 4 piperidinyl} methyl} -2, 3, dihydro- 1 H-indene- 1-one (Fig. 1). This drug is not official in any Pharmacopoeia. So far only HPLC methods have been reported for its estimation from plasma (Yasui-Furukori et al., 2002; Nakashima et al., 2006; Wada et al., 2007). No spectrophotometric method has been reported for the estimation of DH in bulk and its formulation. In the present paper, we are reporting two simple spectrophotometric methods that can be used for routine analysis of DH in bulk and tablet formulation.
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| Fig. 1: |
Chemical structure of donepezil hydrochloride |
MATERIALS AND METHODS
Apparatus
A Shimadzu model 1601 double beam UV-visible spectrophotometer with a pair
of 10 mm matched quartz cells was used to measure absorbance of the resulting
solutions. Shimadzu electronic one pan balance, ultrasonicator were also used
in the study. Drug was supplied by Wockhardt Research Centre, Aurangabad. DH
tablets were purchased from a local market. All analytical grade reagents were
used. Double distilled water was used throughout the study.
Solutions
Donepezil hydrochloride standard stock solution was prepared by dissolving
10 mg of drug in 100 mL methanol (100 μg mL-1). Solution of
2, 4-dinitrophenyl hydrazine (2% w/v) was prepared in 0.1 N sulphuric acid.
Construction of Calibration Curve
For method A, aliquots of the working standard solution of DH (0.5-4 mL)
were transferred in a series of 10 mL volumetric flask and suitably diluted
with methanol to get concentration of 5, 10, 15 upto 40 μg mL-1.
These solutions were scanned in spectrum mode between 400 to 200 nm to determine
λ max. The λ max of DH was found to be 231 nm. The absorbances of
resulting solutions were measured at 231 nm and calibration curve was plotted.
For method B, aliquots of the working standard solution of DH (1-6 mL) were transferred in a series of 10 mL volumetric flask so as to get concentration of 10, 20, 30 to 60 μg mL-1. Then 2 mL of 2, 4-dinitrophenyl hydrazine in 0.1 N sulphuric acid was added in each flask. The volume was adjusted with methanol. The flasks were kept aside for 30 minutes for development of colour. The keto group of DH was reacted with 2, 4-dinitrophenyl hydrazine to form orange coloured complex. The solution of 40 μg mL-1 was scanned between 800 to 400 nm to determine λ max. The λ max of DH was found to be 454 nm. The absorbance of resulting solutions was measured at 454 nm and the calibration curve was plotted.
Procedure for Assay of Donepezil Hydrochloride in Tablet Formulations
For analysis of drug in tablet dosage form, twenty tablets were weighed
accurately and triturated in the mortar to get fine powder. The amount of tablet
powder equivalent to 10 mg of DH was weighed and transferred to 100 mL volumetric
flask and dissolved in methanol for method A and B. The solution was kept in
ultrasonicator for 10 min and filtered through Whatman’s filter paper No.
41. The tablet solution was further diluted to get final concentration of 10,
15, 20, 25, 30, 35 and 40 μg mL-1 for method A and B. Appropriate
aliquots of drug solution were taken and the individual assay procedure was
followed for the estimation of drug content in tablets. The concentration of
drug present in tablets was calculated using calibration curve.
RESULTS AND DISCUSSION
Determination of λ Max
Donepezil hydrochloride when treated with 2,4, dinitrophenylhydrazine orange
color is formed. To determine λ max a solution of 40 μg mL-1
was scanned between 800 to 400 nm. The λ max of DH was found to be 454
nm. The effect of time on maximum absorbance was tested by measuring absorbance
of solution at regular interval and it was found that solution showed maximum
absorbance after 30 min and was stable for 2 h.
| Table 1: |
Optical characteristics of the proposed methods |
 |
| Where, A is simple UV spectrophotometric method and B is colorimetric
method |
| Table 2: |
Analysis of donepezil hydrochloride in tablet formulations |
 |
| Where, A is simple UV spectrophotometric method and B is colorimetric
method; D1 and D2 are two different brands of tablet
formulations; *: n = 6, average of six readings |
Optical Characteristics and Validation of Method
Optical characteristics for DH such as Beer’s law limit, molar absorptivity,
Sandell’s sensitivity are shown in Table 1. The recovery
was carried out by standard addition method (Table 2).The
percent recovery obtained indicates noninterference of drug with common excipients
used in formulations. The reproducibility, repeatability and accuracy of two
methods were found to be good, which is evidenced by low standard deviation.
Interference Studies
To study interference of commonly used excipients on absorbance a recovery
study was done. Under the experimental condition employed to a known amount
of drug different excipients were added. The excipients up to concentration
of 40 mg mL-1 do not interfere in studies. Recovery for all excipients
was close to 100%. The precision of method was confirmed by their low RSD.
CONCLUSION
All proposed spectrophotometric methods for determination of DH are simple, sensitive, accurate, precise and reproducible. In method B, colour reaction neither requires any stringent condition nor any specific reagent or buffers. These methods can be successfully applied for routine estimation of DH in bulk and pharmaceutical dosage forms.
ACKNOWLEDGMENTS
The authors are thankful to the Head, Department of Chemical Technology, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad-431004 (MS), India for providing the Laboratory facility.
