SL/T 272-2001 Water quality — Determination of total selenium — Iron(II)-O-phenanthroline indirect spectrophotometry
1 Scope
This standard is applicable to determination of total selenium in surface water, underground water, domestic sewage and industrial wastewater.
50mL of water sample is taken, and the minimum detectable concentration of selenium is 0.003mg/L. Determination range: 0.01mg/L to 0.2mg/L.
2 Interference and elimination
The interference of copper, iron, molybdenum and other metal ions can be eliminated by EDTA. 10 times of arsenic and 20 times of sulfide did not interfere with the determination of selenium.
3 Principle
After the sample was digested by nitric acid-perchloric acid mixture (see 4.8), various forms of selenium were transformed into selenium (VI) ions. Selenium (VI) was quantitatively reduced to selenium (IV) by hydrochloric acid under the condition of heating. In an acidic medium, potassium borohydride reduces selenium (IV) to hydrogen selenide (H2Se), while the hydrogen stream produced by the decomposition of potassium borohydride carries it into the absorption solution. Hydrogen selenide reduces the iron (III) in the absorption solution to iron (II), and the light yellow iron (III)-O-phenanthroline complex is transformed into orange red iron (II)-O-phenanthroline complex. The amount of the latter is directly proportional to the concentration of selenium in the sample.
4 Reagents
4.1 Test water: deionized water.
4.2 Nitric acid (HNO3), ρ20 = 1.42g/mL, guaranteed reagent.
4.3 Hydrochloric acid (HCl): ρ20 = 1.19 g/mL, guaranteed reagent.
4.4 Perchloric acid (HClO4), ρ20 = 1.68g/mL, guaranteed reagent.
Foreword II
1 Scope
2 Interference and elimination
3 Principle
4 Reagents
5 Apparatus
6 Analytical procedures
7 Calculation of analysis results
8 Precision and accuracy
9 Cautions
