Lamotrigine [6-(2,3-dichlorophenyl)-1,2,4-triazine-3,5-diamine], is a broad-spectrum antiepileptic, used as monotherapy and as an adjunct with other antiepileptics for treatment of partial and generalized tonic-clonic seizures. Its use to treat neurological lesions and as a tranquilizer also has been studied.
1,2)Lamotrigine is not official in any pharmacopoeia, two stability indicating HPLC methods with UV detection at 210 nm have been reported with either longer analysis time 3) or at definite temperature 40°C.4) The present HPLC method differs from those reported previously 3,4) in terms of mobile phase, pH and temperature, so the main advantage is that the analysis was proceeded at ambient temperature (25Ϯ5°C) not at definite temperature 40°C. Moreover, an UV spectrophotometric method using 0.1 M sodium hydroxide was reported for its determination in tablets.5) But no work seems to have been done on colorimetric assay.Most methods for lamotrigine analysis utilized HPLC technique in biological fluids. [6][7][8][9][10][11][12] Few methods have been published for its determination including thin layer chromatography which needs 2 h for tank saturation and can not determine lamotrigine in presence of its impurity, 5) gas chromatography, 13) capillary electrophoresis 14,15) and immunoassay. 16,17) In the present study we suggest a simple selective and validated spectrophotometric method using p-chloranilic acid which is used as chromogenic agent for different drugs, it gives an immediate purple chromogen at room temperature.18) Also TLC and HPLC methods that can identify and quantitate lamotrigine in presence of its impurity 2,3-dichlorobenzoic acid, in bulk and dosage form.
ExperimentalInstrumentation Shimadzu UV/VIS spectrophotometer 1601. Shimadzu dual wave length flying spot densitomerter, Model CS-9301, photomodeϭreflection, scan modeϭzigzag and swing widthϭ10. TLC plates (10ϫ10 cm) aluminium plates precoated with 0.25 mm silica gel F254, were purchased from E. Merck. UV lamp-short wave length 254 nm. The HPLC system (Waters Co.) consisted of a Model 600 LC series pump and 600 controller unit, 486 tunable absorbance detector, an injector valve with a 20 ml constant loop, and 745 data module. A 250ϫ4.6 mm Alltech Adsorbosphere C 18 , 10 mm column was used for separation and quantification.Materials and Reagents Lamotrigine working standard, was supplied by Delta Pharma Co. (India), the purity of the sample was found to be 99.68Ϯ0.97% according to the reported specifications.3) 2,3-Dichlorobenzoic acid (99.90%), was purchased from Riedel-de Haem Pestanal. Lamictal tablets were purchased from Welcome Co. Egypt, labeled to contain 25 mg lamotrigine per tablet. p-Chloranilic acid (E. Merck ), 42 mg ml Ϫ1 in acetone. Methanol, acetonitrile and ethylacetate (Lab-scan, Ireland). Potassium orthophosphate (El-Nasr Co., Egypt). All chemicals are of spectroscopic and chromatographic grade.Standard Solutions Lamotrigine (1 mg ml
Ϫ1) was prepared in acetone for spectrophotometric method, and in methanol for TLC and HPLC m...
