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Carbohydrazide Test Kit

Visual Kit

Range MDL Method Type Kit Refill
0 - 0.50 ppm 0.05 ppm PDTS CHEMets K-1805 R-3902

A recent addition to the CHEMetrics range is a visual colourimetric test kit for the determination of Carbohydrazide in aqueous solutions. This CHEMets test kit is a portable self-contained, single range kit and is based on the patented Self-Filling Reagent Ampoule technology, employing the PDTS Method, delivering sensitivity and accuracy within two minutes or less. Premixed. Premeasured. Precise. Each kit contains 30 tests. Suitable for boiler feedwater testing.

The PDTS Method

Carbohydrazide reduces ferric iron to ferrous iron, which then reacts with the PDTS (3-(2-pyridyl)-5,6-bis(4-phenylsulphonic acid)-1,2,4-triazine disodium salt) to form a peach-pink coloured complex directly proportional to the carbohydrazide concentration. Test results are expressed as ppm (mg/l) carbohydrazide.

G. Frederick Smith Chemical Co., The Iron Reagents, 3rd ed., p. 47 (1980).


Carbohydrazide is used as a corrosion inhibitor (or oxygen scavanger) within a closed loop and closed circuit systems, and plays a critical role as an additive in boiler systems. Carbohydrazide also passivates metallic surfaces by encouraging the formation of magnetite, an iron oxide mineral, to minimise further corrosion. Carbohydrazide is often preferred over hydrazine for this purpose because it is significantly safer and less toxic a compound, and hydrazine is hazardous and potentially carcinogenic. Testing for carbohydrazide ensures the dosing of systems with sufficient chemical to protect metal from corrosion through O2 scavenging and metal passivation, but not so much that treatment chemicals are wasted. Regular testing therefore ensures maximum efficiency of the boiler system.

What is Carbohydrazide?

Carbohydrazide (CH6N4O) is an organic chemical compound and a white, water-soluble solid at room temperature. It is often manufactured from hydrazine (N2H4 and urea (CO(NH2)2). It reacts readily with oxygen at low temperatures and pressures, hence it's classification as an ‘oxygen scavenger’. The reaction products are CO2, N2 and water. CO2 dissolves in water as carbonic acid. So oxygen scavenging does not contribute to dissolved solids in the system. At high temperatures, carbohydrazide in solution breaks down in hydrazine and CO2 so is still able to function as a corrosion inhibitor, and is thus suitable for all types of boiler system.