This standard is applicable to the determination of nitrate-nitrogen in surface water and groundwater. The lowest mass concentration of detection of the method is 0.08 mg/L, the lower limit of determination is 0.32 mg/L and the upper limit of determination is 4 mg/L.
2 Principle
The quantitative determination of nitrate-nitrogen is carried out by virtue of the absorption of nitrate ion at 220 nm wavelength. The dissolved organics are also absorbed at 220 nm while nitrate ion is not absorbed at 275 nm. Therefore, another measurement shall be made at 275 nm so as to calibrate the nitrate-nitrogen value.
3 Reagents
Unless otherwise specified, the reagents adopted in this standard shall all be analytically pure chemical agents complying with the national standard, and the water for experiment shall be deionized water newly prepared.
3.1 Aluminium hydroxide suspension: dissolve 125g of aluminium potassium sulfate [KAI(SO4)2?12H2O] or aluminium ammonium sulfate [NH4Al(SO4)2?12H2O] in 1,000mL of water and heat to 60℃; add into 55 ml of stronger ammonia water during stirring, shift it into 1,000mL measuring cylinder after about 1 h and repeatedly wash it with water and precipitate it till there has no nitrate-nitrogen in the detergent; Pour off the entire supernatant after clarification, with dense suspension remained only; and add into 100mL of water at last; it shall be uniformly oscillated prior to use.
3.2 Zinc sulfate solution: 10% zinc sulfate water solution.
