Acetonitrile and methanol of HPLC grade were obtained from Winlab laboratory, UK, whereas orthophasphoric acid and potassium dihydrogen phosphate were obtained from BDH and Avonchem Laboratory England.
All reagents were of analytical grade unless stated otherwise.
All aqueous solutions and buffers were prepared using water that was purified using Milli-QR Gradient A10R (Millipore, Moscheim Cedex, France) having pore size 0.22 µm