GB/T 609-2018Chemical reagent -- General method for the determination of total nitrogen (English PDF)

1 Scope

This Standard specifies a general method for the determination of total amount of trace inorganic nitrogen compounds by Nessler’s reagent colorimetric method and salicylic acid-hypochlorite colorimetric method.

This Standard is applicable to the determination of the total amount of trace inorganic nitrogen compounds (including nitrates, nitrites and ammonium salts) in the chemical reagents. The detection range of Nessler’s reagent visual colorimetric method and spectrophotometry is 0.05µg/mL~0.8µg/mL (in terms of N); while the detection range of salicylic acid=hypochlorite visual colorimetric method and spectrophotometry is 0.04µg/mL ~1µg/mL (in terms of N).

2 Normative References

The following documents are essential to the application of this document. For the dated documents, only the versions with the dates indicated are applicable to this document; for the undated documents, only the latest version (including all the amendments) are applicable to this document.

GB/T 601 Chemical Reagent - Preparations of Standard Volumetric Solutions

GB/T 602 Chemical Reagent - Preparations of Standard Solutions for Impurity

GB/T 603 Chemical Reagent - Preparations of Reagent Solution for Use in Test Method

GB/T 6682 Water for Analytical Laboratory Use - Specification and Test Methods

GB/T 9721 Chemical Reagent -General Rules for the Molecular Absorption Spectrophotometry (Ultraviolet and Visible)

3 Method Principle

Appendix A (Normative) Preparation Method of Sodium Hypochlorite Stock Solution and Determination of Effective Chlorine Concentration and Free Base Mass

Concentration A.1 Preparation method Titrate the hydrochloric acid to the potassium permanganate solid; introduce the evolved chlorine gas into the sodium hydroxide solution (2mol/L) for absorption; obtain the pale greenish sodium hypochlorite stock solution, which was stored in a plastic bottle and placed in the dark. This solution is unstable, and determine the effective chlorine concentration prior to use.

A.2 Determination of mass concentration of effective chlorine Take 10.00mL sodium hypochlorite stock solution; place into 100mL volumetric flask; add water to dilute to the mark; shake up. Pipette 10.00mL; place into 250mL iodine volumetric flask; add 40mL of water and 2g of potassium iodide; shake up. Add 10mL of sulfuric acid solution (20%); cover with water seal; shake up; stand in the dark place for 5min; titrate with the sodium thiosulfate standard titration solution [c(Na2S2O3) = 0.1mol/L] till the solution turns to light yellow; add 1mL of starch indicator solution (10g/L); continue to titrate till the blue color of the solution disappears. Meanwhile do the blank test.

Calculate the effective chlorine concentration as per the Formula (A.1).

Where.

rho - mass concentration of effective chlorine, in g/L;

V - volume of sodium thiosulfate standard titration solution, in mL;

V0 -volume of sodium thiosulfate standard titration solution consumed by blank test;

in mL;

c - concentration of sodium thiosulfate standard titration solution; in mol/L;