Test Method Technical Information


Tests For: Urea in Swimming Pool and Spa Water
Test Range: 0 – 3.5 mg/L
Reagent Chemistry Used: Diacetyl (Fearon) Reaction
Basis of Test Method: Chinese standard GB/T 18204.29-2000

Expected Performance

Level mg/L Urea Typical Tolerance mg/L
0.00 < 0.25
1.00 0.89 – 1.11
2.00 1.81 – 2.21
3.50 3.08 -3.73

Reagent Chemistry

In the diacetyl or Fearon reaction, diacetyl reacts with urea, in acidic conditions at elevated temperature, to produce yellow diazine. Additional reagents are included to stabilise the colour which is otherwise light sensitive.

The sample is added to a digestion tube along with sulfuric acid. Two further reagents are added in the form of a powder and tablet and the tube heated in a water bath where the yellow colour will develop.

Turbidity can be a problem, but the Palintest version of the method measures the result photometrically immediately after removing the tube from the bath to avoid the formation of turbidity at lower temperatures.

Testing for Urea

Urea, CO(NH₂)₂ is the main substance via which mammals excrete nitrogen. As such, it is routinely introduced into swimming pool and spa water by bathers and this leads on to the formation of various chloramines when chlorine is used as a disinfectant. These chloramines can cause irritation and harm to eyes and the respiratory system.

Mostly these chloramines are controlled by periodically oxidising them with high levels of chlorine or other oxidising agents when bathers are not present (known as shock dosing). The chlorine or oxidant levels are then returned to safe levels and the facility reopened to bathers. In some countries however, there is an obligation to measure and monitor Urea levels in bathing water directly.