In the aqueous solution above 60 ℃, potassium persulfate can decompose to produce potassium bisulfate and atomic oxygen. Potassium bisulfate dissociates in the solution to produce hydrogen ions. Therefore, the decomposition process can be promoted to be complete in the alkaline medium of sodium hydroxide.

分解出的原子态氧在120～124℃条件下，可使水样中含氯化合物的氮元素转化为硝酸盐。并且在此过程中有机物同时被氧化分解。可用紫外分光光度法于波长220和275nm处，分别测出吸光度A220及A275按式(1)求出校正吸光度A：

The decomposed atomic oxygen can convert the nitrogen element containing chloride compound into nitrate at 120 ~ 124 ℃. And in this process, the organic matter is oxidized and decomposed at the same time. The absorbance a220 and A275 can be measured by UV spectrophotometry at the wavelengths of 220 and 275 nm respectively, and the corrected absorbance a can be calculated according to formula (1):

A＝A220－2A275………………………………………………(1)

A＝A220－2A275………………………………………………(1)

按A的值查校准曲线并计算总氮(以NO3－N计)含量。

Check the calibration curve according to the value of a and calculate the content of total nitrogen (calculated by NO3-N).

4 试剂和材料

4 reagents and materials

除非(4.1)另有说明外，分析时均使用符合标准或标准的分析纯试剂。

Unless otherwise specified in (4.1), analytical pure reagents conforming to national standards or professional standards shall be used for analysis.

4.1 水，无氨。按下述方法之一制备；

4.1 water, no ammonia. Prepare according to one of the following methods;

4.1.1 离子交换法：将蒸馏水通过一个强酸型阳离子交换树脂(氢型)柱，流出液收集在带有密封玻璃盖的玻璃瓶中。

4.1. 1 ion exchange method: the distilled water is passed through a strong acid cation exchange resin (hydrogen type) column, and the effluent is collected in a glass bottle with a sealed glass cap.

4.1.2 蒸馏法：在1000mL蒸馏水中，加入0.10mL硫酸(p=1.84g／mL)。并在全玻璃蒸馏器中重蒸馏，弃去前50mL馏出液，然后将馏出液收集在带有玻璃塞的玻璃瓶中。

4.1. 2 distillation method: add 0.10ml sulfuric acid (P = 1.84g/ml) to 1000ml distilled water. And re distill in an all glass distiller, discard the first 50ml distillate, and then collect the distillate in a glass bottle with a glass stopper.

4.2 氢氧化钠溶液，200g／L：称取20m氢氧化钠(NaOH)，溶于水(3.1)中，稀释100mL。

4.2 sodium hydroxide solution, 200g / L: weigh 20m sodium hydroxide (NaOH), dissolve in water (3.1), and dilute to 100ml.

4.3 氢氧化钠溶液，20g／L：将(4.2)溶液稀释10倍而得。

4.3 sodium hydroxide solution, 20g / L: obtained by diluting (4.2) solution 10 times.

4.4 碱性过硫酸钾溶液：称取40g过硫酸钾(K2S2OB)，另称取15g氢氧化钠(NaOH)，溶于水(4.1)中，稀释1000mL，溶液存放在聚乙烯瓶内，更长可贮存一周。

4.4 alkaline potassium persulfate solution: weigh 40g potassium persulfate (k2s2ob) and 15g sodium hydroxide (NaOH), dissolve it in water (4.1), dilute it to 1000ml, and store the solution in a polyethylene bottle for up to one week.

4.5 盐酸溶液，1＋9。

4.5 hydrochloric acid solution, 1 + 9.

4.6 硝酸钾标准溶液。

4.6 potassium nitrate standard solution.

4.6.1 硝酸钾标准贮备液，CN＝100mg／L：硝酸钾(KNO3)在105～110℃烘箱中干燥3h，在干燥器中冷却后，称取0.7218g，溶于水(4.1)中，移1000mL容量瓶中，用水(4.1)稀释标线在0～10℃暗处保存，或加入1～2mL三氯甲烷保存，可稳定6个月。

4.6. 1 potassium nitrate standard stock solution, CN = 100mg / L: dry potassium nitrate (KNO3) in an oven at 105 ~ 110 ℃ for 3h. After cooling in a dryer, weigh 0.7218g, dissolve it in water (4.1), transfer it to a 1000ml volumetric flask, dilute it with water (4.1) to the mark, store it in the dark at 0 ~ 10 ℃, or add 1 ~ 2ml trichloromethane for 6 months.

4.6.2 硝酸钾标准使用液，CN＝10mg／L：将贮备液用水(4.1)稀释10倍而得。使用时配制。

4.6. 2 potassium nitrate standard solution, CN = 10mg / L: it is obtained by diluting the stock solution 10 times with water (4.1). Prepared when in use.

4.7 硫酸溶液，1＋35。

4.7 sulfuric acid solution, 1 + 35.

5 仪器和设备

5 instruments and equipment

5.1 常用实验室仪器和下列仪器。

5.1 common laboratory instruments and the following instruments.

5.2 紫外分光光度计及10mm石英比色皿。

5.2 ultraviolet spectrophotometer and 10mm quartz cuvette.

5.3 医用手提式蒸气器或家用压力锅(压力为1.1～1.4kg／cm2)，锅内温度相当于120～124℃。

5.3 medical portable steam sterilizer or domestic pressure cooker (pressure is 1.1 ~ 1.4kg / cm2), and the temperature in the cooker is equivalent to 120 ~ 124 ℃.

5.4 具玻璃磨口塞比色管，25mL。

5.4 colorimetric tube with glass ground plug, 25ml.

所用玻璃器皿可以用盐酸(1＋9)或硫酸(1＋35)浸泡，清洗后再用水(4.1)冲洗数次。

The glassware used can be soaked in hydrochloric acid (1 + 9) or sulfuric acid (1 + 35), washed with water (4.1) for several times.