The Method of Using 220nm and 275nm Ultraviolet Filters to Measure Total Nitrogen Content in Aqueous Solutions

Nitrogen in water includes nitrite nitrogen, nitrate nitrogen, inorganic ammonium salts, dissolved ammonia, and organic nitrogen-containing compounds, which can transform into each other through biochemical actions. Total nitrogen refers to the total nitrogen content in soluble and suspended particulate forms. When the content of nitrogen and phosphorus in surface water is too high, the water body becomes eutrophic. This leads to the proliferation of microorganisms, vigorous growth of plankton, and deterioration of water quality, such as red tides.

In aqueous solutions above 60°C, potassium persulfate can decompose to produce atomic oxygen as follows:

K2S2O3 + H2O2KHSO4 + [0]

The atomic oxygen produced can oxidize most organic nitrogen compounds, ammonia, and nitrite nitrogen into nitrate under high-pressure steam conditions between 120°C and 140°C. Using urea (CO(NH2)2) as a representative of soluble organic nitrogen compounds, the oxidation of various forms of nitrogen is represented as follows:

CO(NH2)2+2NaOH +8[0] 2NaNO3 +3H2O + CO₂

(NH4)2SO4 +4NaOH+8[0] 2NaNO3 + Na₂SO₄ +6H₂O

NaNO₂ +[0]-NaNO3

Nitrate ions have a characteristic strong absorption at 220nm under UV light, but virtually no absorption at 275nm; dissolved organic matter absorbs at both 220nm and 275nm. Therefore, absorbances at 220nm (A220) and 275nm (A275) can be measured. The corrected absorbance is calculated using the following formula:

A = A{220} - 2A{275}

After subtracting the absorbance of a blank experiment, the total nitrogen content (calculated as NO3-N) is determined through a calibration curve or regression equation.

Product Recommendation:

BP220nm - 15

BP275nm - 15