ISO 23497:2019

Overview

ISO 23497:2019 specifies requirements and measurement methods for technical buffer solutions used to calibrate and adjust technical pH measuring equipment and pH measuring installations. The standard defines how to determine pH values and buffer capacity of technical buffers by traceable comparison to reference buffer solutions in accordance with ISO 23496. Annex A provides practical examples of commonly used technical buffer solutions (e.g., glycine, acetate, citric/phosphate, boric acid/NaOH, HCl, NaOH).

Key topics and requirements

• Purpose: Provide higher ionic strength (higher buffer capacity) solutions suitable for industrial and technical pH calibration where reference buffers (low ionic strength) are impractical.
• Traceability: pH values of technical buffers are measured based on ISO 23496 reference buffers and in accordance with DIN 19268 to ensure traceability to primary standards.
• Measurement uncertainty:
  • pH < 10 at 25 °C: expanded uncertainty U ≤ 0.03 (k = 2).
  • pH ≥ 10 at 25 °C: expanded uncertainty U ≤ 0.05 (k = 2).
• Buffer capacity requirement: Technical buffers shall have β ≥ 0.05 mol·L⁻¹.
• Measurement method: Use combined electrodes with transference in the configuration: Reference electrode || buffer | pH measuring electrode. pH measurement procedures follow DIN 19268.
• Buffer capacity determination: Calculated from titration: β = (Δn / V) · (1 / ΔpH), where Δn is moles of added acid/base, V is volume, and ΔpH is the observed change. Measurements are typically done at (25 ± 1) °C.
• Practical considerations:
  • Minimize alkali error of glass electrode; follow manufacturer guidance.
  • Use combined electrodes with liquid reference electrolyte; KCl refill solution should be ≥ 3.0 mol·L⁻¹.
  • Use diaphragms with high electrolyte outflow (ground-joint, platinum, capillary).
  • Maintain isothermal conditions (±0.5 K) and allow temperature equilibration of electrode and solution.
  • Keep KCl level inside reference electrode at least 5 cm above test solution; keep refill opening open.
  • If measuring at multiple temperatures, perform separate measurements per temperature.

Applications and users

ISO 23497:2019 is directly applicable to:

• Calibration labs and metrology services performing pH calibrations for industrial installations.
• Process control and quality assurance teams in chemical, water treatment, food, pharmaceutical and paint & varnish industries.
• Manufacturers of pH electrodes and pH measuring systems.
• Calibration service providers and instrument validation teams requiring traceable pH standards with higher buffer capacity for rugged environments.

Keywords: ISO 23497:2019, technical buffer solutions, pH calibration, buffer capacity, pH measurement, ISO 23496, DIN 19268.

Related standards

• ISO 23496 - Reference buffer solutions for pH calibration
• DIN 19268 - pH measurement procedures and uncertainty evaluation
• ISO 80000-9 - Quantities and units (physical chemistry)
• ISO 1042 - Volumetric flasks (preparation)
• ISO 19396-1 - pH electrodes with glass membrane