Department of Chemistry, C. M. P. Degree College, Allahabad-211 002, Uttar Pradesh, India Electrochemical Sensor Laboratory, Department of Chemistry, University of Allahabad, Allahabad-211 002, Uttar Pradesh, India E-mail : sunanda.das@gmail.com, mcc46@rediffmail.com Manuscript received 21 January 2002, revised 13 June 2006, accepted 13 June 2006 The 1 : 1 complex formed by lron(III) with salicylic acid and Its seven derivatives were studied by spectrophotometry and the effect of ph thalate-HCl and KCI-HCI buffers on the value of stability constants of 1 : 1 complex determined by spectrophotometry,was evaluated. The thermodynamic value of stability constant of each system was determined by obtaining the values at different ionic strength and extrapolating them to zero ionic strength. For extrapolation, a new approach was made which gives a straight line curve making It easier to extrapolate at zero ionic strength to get the thermodynamic value thus reducing the uncertainty in extrapolation.