Selenium
Selenium
Selenium_None_Other_DAB_Eng_Ody.fm Page 5 of 8
14. Fill a 250-mL beaker to the 75-mL mark with deionized water. Place it under
the drip tube. Elevate the beaker with a laboratory jack so the tube extends
below the level of the water.
15. Add 1.0 mL of 30% hydrogen peroxide solution to the flask. Turn the stir
control to 5 and the heat control to 10. Cap the distillation flask.
16. Heat the distillation flask until the yellow color is gone from the complete
distillation apparatus, including the J-tube and condenser. Remove the beaker
from under the drip tube.
17. Turn off the heater switch. When the J-tube and condenser have cooled, rinse
them with deionized water. Add the washings to the 250-mL beaker. Total
volume in the beaker should be approximately 100 mL.
18. Add the Phenol Solution drop-wise to the distilled sample to discharge the
bromine color (a white precipitate of tribromophenol will form).
19. Allow the precipitate to settle. Using a dropper, collect about 5 mL of the clear,
colorless distillate and transfer to a test tube.
20. Test the solution for completeness of precipitation by adding 2 drops of
Phenol Solution. If the solution becomes cloudy or white precipitate forms,
residual bromine is still present (proceed to next step). If no cloudiness occurs,
the sample is ready for analysis.
21. Transfer the 5-mL aliquot back to the beaker and continue to add Phenol
Solution until no turbidity is formed in subsequent 5-mL aliquots.
22. Transfer the entire sample into a 500-mL volumetric flask. Rinse the beaker
with deionized water and add to the flask.
23. Dilute to volume with deionized water, stopper and mix well. The distillate is
now ready for analysis.
Accuracy Check
Standard Additions Method (Sample Spike)
1. After reading test results, leave the sample cell (unspiked sample) in the
instrument.
2. Touch
Options. Touch Standard Additions. A summary of the standard
additions procedure will appear.
3. Touch
OK to accept the default values for standard concentration, sample
volume, and spike volumes. Touch
Edit to change these values. After values
are accepted, the unspiked sample reading will appear in the top row. See
3.2.2 Standard Additions for more information.
4. Snap the neck off a Selenium 2-mL Ampule Standard, 100-mg/L Se.
5. Prepare three sample spikes. Fill three mixing cylinders with 100 mL of
sample. Use the TenSette Pipet to add 0.1 mL, 0.2 mL, and 0.3 mL of standard,
respectively, to each sample and mix thoroughly.
6. Analyze each sample spike as described in the procedure above, starting with
the 0.1 mL sample spike. Accept each standard additions reading by touching
Read. Each addition should reflect approximately 100% recovery.
7. After completing the sequence, touch
Graph to view the best-fit line through
the standard additions data points, accounting for matrix interferences. Touch
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