There are many methods for the detection of total selenium content in sewage, and atomic fluorescence spectrometry is generally used, and its range is 0.0005mg/L-0.1mg/L. It uses potassium borohydride as a reducing agent in a hydrochloric acid medium to generate hydrogen selenide from selenium, and uses argon gas as a carrier gas to introduce hydrogen selenide into a quartz furnace atomizer for atomization, and use selenium special hollow cathode lamp. As an excitation light source, selenium atoms are excited by light radiation to generate electronic transitions. When the electrons in the excited state return to the ground state, the fluorescence intensity is proportional to the content of selenium within a certain concentration range.
Instruments and reagents used for testing
1. Atomic fluorescence photometer.
2. Hydrochloric acid 1.19g/mL.
3. Nitric acid 1.40g/mL.
4. Perchloric acid 1.67g/mL.
5. Potassium borohydride alkaline solution.
Weigh 2 g of potassium hydroxide and dissolve it in 200 mL of laboratory first-grade pure water, add 20 g of potassium borohydride and dissolve it, and dilute to 1000 mL with water.
6. Selenium standard stock solution 100mg/L
Weigh 0.1000g (spectral or superior grade) metal selenium, add 2mL of nitric acid solution, then heat to dissolve, then add 2mL of perchloric acid, heat it on a water bath until white smoke is emitted to remove nitric acid, and after a little cooling, add 8.4mL of hydrochloric acid Continue to heat for 2min, cool to room temperature, and finally transfer it to a 1000mL volumetric flask to constant volume and store in a refrigerator. 1mL of this solution contains 100ug of selenium.
7. Selenium standard solution 0.1mg/L
Dilute the selenium standard stock solution to 1L step by step, this solution contains 0.1mg selenium.
8. Argon with a purity greater than 99.99%.
Water sample pretreatment method
Take 20 mL of experimental water sample, put it in a 100 mL beaker, add 5 mL of nitric acid and 5 mL of perchloric acid, and heat it on an electric hot plate until white smoke is emitted. (If it contains interfering elements, an appropriate amount of masking agent should be added), shake well and place for testing. Water samples should be stored in clean glass or plastic bottles after collection, and then measured. If it cannot be determined immediately, it should be stored in the refrigerator.
Check the specific steps
The working conditions of the instrument are set as: lamp current 60mA-80mA, negative high pressure 280V-320V, argon pressure 0.02MPa, carrier gas flow 800mL/min, shielding gas flow 1000mL/min, furnace temperature 800℃-1000℃, atomizer height 8mm, reading time 10s, delay time 2s, regeneration fluid flow rate 5mL/min, syringe 25uL (injection through quantitative tube). After setting the working conditions of the instrument, measure the sample according to the procedures specified by the instrument, and record the fluorescence signal value.
Note: Water quality testing personnel can modify the working conditions of the instrument according to different types of instruments
Working curve drawing
Pipette 0.50mL, 1.00mL, 2.50mL, 5.00mL, 10.00mL, and 15.00mL of selenium standard solution into six 100mL volumetric flasks, add 20mL of hydrochloric acid, dilute to the mark with laboratory first-grade pure water, and spread evenly. The corresponding concentrations are 0.50ug/L, 1.00ug/L, 2.50ug/L, 5.00ug/L, 10.00ug/L, and 15.00ug/L, respectively. Measure according to the detection steps, and draw the working curve of fluorescence intensity versus selenium concentration. .
The content of metallic selenium in the final water sample can be calculated by the formula.
