Determination of methotrexate in biological fluids and a parenteral injection using terbium-sensitized method

A new sensitive, simple and rapid method for determination of methotrexate (MTX) was developed based on quenching effects of MTX on the fluorescence intensity of Tb(3+)-1,10-phenanthroline complex. The fluorescence intensity was measured with excitation wavelength of 300 nm and emission wavelength of 545 nm and the quenched fluorescence intensity is proportional to the concentration of MTX in Tris-HCl buffer solution with a pH of 7.0. The effects of pH, time, order of addition of the reagents, temperature and the concentrations of Tb(3+), buffer and 1,10-phenanthroline were investigated and optimized. The obtained linear range for the determination of MTX was 0.02-10 μg/mL. The detection limits (signal: noise = 3) was 0.015 μg/mL and the relative standard deviation for replicated determinations of 1 μg/mL of MTX was 1.9%. The proposed method is a simple, practical and relatively free from interference effects and was successfully applied to assess MTX in urine, serum and samples of an injection solution.