Overview
ISO 13900:1997 specifies a standardized analytical procedure for the determination of boron in steel using the curcumin spectrophotometric method after distillation. The method is intended for low-level boron analysis in steel in the range 0.00005 % (m/m) to 0.0010 % (m/m). It describes sample preparation, chemical decomposition, distillation of methylborate, formation of the curcumin–boron complex, spectrophotometric measurement (≈550 nm) and calibration/blank correction procedures.
Key topics and technical requirements
- Scope and range: Applicable for boron between 0.00005 % and 0.0010 % (m/m) in steel.
- Sample size and blanks: Typical test portion ≈0.50 g; blank tests and determination of boron in pure iron are required to correct results.
- Chemical decomposition: Dissolve sample in HCl + HNO3, then decompose boron compounds with orthophosphoric and sulfuric acids at about 290 °C for 30 minutes.
- Distillation: Convert boron to methylborate by adding methanol and distilling; collect methylborate in receiver containing 8 g/L NaOH. Carrier gas flow ~50 mL/min and distillation rate ~30 mL per 20 min are specified.
- Colour development: Evaporate distillate, react residue with curcumin in acetic acid (1.25 g/L) in specified acid mixtures to form the yellow/orange curcumin–boron complex.
- Spectrophotometry: Measure absorbance at 550 nm in a 1 cm cell against methanol blank.
- Calibration: Prepare a calibration graph (straight line through origin) using a series of spiked pure-iron samples (seven levels) with the ISO 13900 standard boron solutions.
- Reagents & apparatus: Uses high-purity reagents (methanol ≥99.6%), low-boron orthophosphoric acid (