SPECTROPHOTOMETRIC METHODS FOR THE DETERMINATION OF METHOTREXATE IN PHARMACEUTICAL FORMULATIONS

Three visible spectrophotometric methods (A-C) for the determination o f Methotrexate (MTX) in pharmaceutical formulations are described. Met hod A is based on the reduction of Fe(III) to Fe(II) by the drug which forms a coloured complex (lambda(max): 510 nm) with 1,10-phenanthroli ne (PHEN). Method B involves the reduction of Folin-Ciocalteu (F-C) re agent by the drug and the reduced species produced possesses a charact eristic intense blue colour (lambda(max): 770 mm). Method C is based o n the coupling reaction through the involvement of an aromatic seconda ry amino group in p-N-methylaminobenzoylglutamic acid (released throug h reduction of the drug with zinc and HCl) with 1,2-naphthaquinone-4-s ulfonic acid sodium salt (NQS) to form a coloured product (lambda(max) : 500 fim). Regression analysis of a Beer's plot showed good correlati on in the concentration ranges of 1.0-8.0, 2.0-14.0 and 25.0-300.0 mu g.ml(-1) for methods A,B and C, respectively. No interference was obse rved from the additives and the applicability of the methods was teste d bq analysing the pharmaceutical formulations containing methotrexate , Recoveries were 98.9-101.1%.