Highly sensitive determination of methotrexate at poly (l-lysine) modified electrode in the presence of sodium dodecyl benzene sulfonate

• This sensor exhibits excellent electrocatalytic activity toward methotrexate.
• Sodium dodecyl benzene sulfonate can keep the oxidation of methotrexate stable.
• The sensor was applied in real samples with satisfying results.

A simple and sensitive electrochemical sensor based on poly (l-lysine) modified glassy carbon electrode (PLL/GCE) was developed to sensitively detect methotrexate (MTX) in the presence of sodium dodecyl benzene sulfonate (SDBS). Fourier transform infrared spectroscopy, electrochemical impedance spectroscopy and cyclic voltammetry were carried out to characterize PLL film which exhibits excellent electrocatalytic activity toward the oxidation of MTX in 0.1 M phosphate buffer solution. In addition, the oxidation peak of MTX remained stable at PLL/GCE in the presence of SDBS and its current increased 8 times compared with that at bare GCE without SDBS. Experimental parameters were optimized with regard to pH, electro-polymerization segment, accumulation time and concentration of SDBS. Under optimum conditions, the square wave voltammograms exhibited that the oxidation peak current was linearly proportional to the concentration of MTX in the range of 5 nM – 0.2 μM with detection limit of 1.7 (± 0.06) nM (S/N = 3). Moreover, this method was applied to detect MTX in medicinal tablets with satisfying results.