Hydrazine, N₂H₄, is a powerful reducing agent which is used in various chemical processes as a raw material, and in boiler water as an oxygen scavenger.

To control corrosion, residual hydrazine typically is maintained in the range of 0.05 to 0.1 mg/L. Higher levels may be used to guard against corrosion when the boiler is out of service for an extended period.

The Colorimetric Method. CHEMetrics' method is based on PDMAB, paradimethylaminobenzaldehyde. PDMAB in acid solution reacts with hydrazine to form a yellow product. Results are expressed as ppm (mg/L) N₂H₄.