Acid-base potentiometric titration using a stainless steel electrode without oxidative treatment

An AISI 304 stainless steel laminar electrode without oxidative treatment was investigated for the potentiometric titration of hydrochloric acid with sodium hydroxide. The proposed electrode was obtained from metalworking cuttings. Scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray fluorescence spectroscopy and X-ray diffraction were used to study the surface morphology and chemical composition of the electrode. The electrode showed a sensitivity of 59.18 ± 0.37 mV/pH, which was reproducible under intermediate conditions. Potentiometric titration showed a curve with deviations from pH 9.5 with respect to the glass electrode. However, this did not affect the quantification as the jumps of the curves coincided. The endpoint was 9.25 mL for both electrodes and the hydrochloric acid concentration was 0.0845 mol/L, with a deviation of 0.0004 mol/L from the standard concentration of 0.0841 mol/L. The nonartificially oxidised electrode did not show any crystalline oxide phases, whereas after oxidation it showed semicrystalline phases of iron and chromium oxides and increased the crystallinity of the steel. Despite the low content of surface oxides, stainless steel electrodes can give a Nernstian response to pH, depending on the surface characteristics of the material. This leads to the need to calibrate any electrode prior to oxidative treatment to rule out a Nernstian response without surface modification.