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

Area of Science:

• Electrochemistry
• Materials Science
• Analytical Chemistry

Background:

• Standard electrodes for potentiometric titrations often involve precious metals or complex preparation.
• Investigating alternative, cost-effective materials like stainless steel is crucial for broader accessibility in analytical chemistry.
• The surface properties of electrodes significantly influence their electrochemical response and Nernstian behavior.

Purpose of the Study:

• To evaluate the suitability of AISI 304 stainless steel electrodes, derived from metalworking cuttings and without oxidative treatment, for potentiometric titration.
• To characterize the surface morphology and chemical composition of the stainless steel electrode.
• To compare the performance of the stainless steel electrode against a standard glass electrode in hydrochloric acid titrations.

Main Methods:

• Surface characterization using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), X-ray Fluorescence Spectroscopy (XRF), and X-ray Diffraction (XRD).
• Potentiometric titration of hydrochloric acid (HCl) with sodium hydroxide (NaOH).
• Determination of electrode sensitivity and comparison of titration curve endpoints with a glass electrode.

Main Results:

• The AISI 304 stainless steel electrode exhibited a reproducible sensitivity of 59.18 ± 0.37 mV/pH.
• Titration curves showed minor deviations above pH 9.5 but yielded accurate endpoint determination, coinciding with the glass electrode.
• The determined hydrochloric acid concentration (0.0845 mol/L) closely matched the standard concentration (0.0841 mol/L).
• The non-oxidized electrode lacked crystalline oxide phases, while oxidation introduced iron and chromium oxides, increasing steel crystallinity.

Conclusions:

• AISI 304 stainless steel electrodes, even without artificial oxidation, can achieve a Nernstian response for pH measurements, contingent on surface characteristics.
• The material's surface properties, rather than extensive oxidation, are critical for reliable potentiometric performance.
• Calibration of stainless steel electrodes before any oxidative treatment is essential to confirm their inherent Nernstian response.