EQUIPMENT

1. Perkin-Elmer Model 3300 Atomic Absorption Spectrophotometer
2. Perkin-Elmer FIAS 400 flow injection unit.
3. Perkin-Elmer AS 90 Autosampler
4. Selenium electrodeless discharge lamp
5. Perkin-Elmer System 2 EDL power supply
6. Dry heating bath
7. 16 x 100 mm. disposable glass tubes

GAS

1. Argon 99.99%

REAGENTS

1. Sodium Borohydride: NaBH₄
2. Sodium Hydroxide: NaOH
3. Hydrochloric Acid: HCl

STANDARDS

1. Stock Solutions
   1. 1000 ppm Selenium - Use certified, NIST traceable standard.
   2. 10 ppm Selenium - Pipet 10 mL of 1000 ppm Selenium standard into a 1 liter volumetric flask. Dilute to volume with deionized water and mix well.
   3. 50 ng/mL Selenium - Pipet 5 mL of 10 ppm Selenium standard into a 1 liter volumetric flask. Dilute to volume with deionized water and mix well.
2. Instrument Calibration Standards
   1. Pipet the designated mL of 50 ng/mL Selenium standard into 50 mL volumetric flasks containing 20 mL of deionized water. Add 15 mL of hydrochloric acid. Dilute to volume with deionized water and mix well.

      Standard	mL 50 ng/mL Selenium	Final Selenium Concentration (ng/mL)
      blank	0	0
      1	1	1
      3	3	3
      5	5	5

3. Spiking solution
   1. 10 ng/mL Selenium - Pipet 20 mL of 50 ng/mL selenium standard into a 100 mL volumetric flask. Dilute to volume with deionized water and mix well.

SOLUTIONS

1. 0.2% sodium borohydride, 0.05% sodium hydroxide
   1. Weigh 0.50 g sodium hydroxide into a 1 liter volumetric flask containing 600 mL, deionized water. Dissolve and swirl to mix.
   2. Add 2 g sodium borohydride. Dissolve, dilute to volume with deionized water and mix well.
2. 10% HCl carrier solution.
   1. Add 100 mL hydrochloric acid to a 1 liter volumetric flask containing 600 mL of deionized water. Dilute to volume with deionized water and mix well.

SAMPLE PREPARATION

1. Liquid Samples
   1. Pipet 1 to 5 mL sample solution into a 16 x 100 mm glass tube.
   2. Add 3 mL of hydrochloric acid.
   3. Add enough deionized water to bring the final volume to 10 mL
   4. Place tube on a dry heating bath and heat for 45 minutes at 95 degrees C.
   5. Remove tube from the dry heating bath and allow to cool.
2. Solid Samples
   1. Digest 1 g of sample as in the arsenic solid digestion method, page 140.
   2. Proceed as in steps 1a through 1e for liquid samples.

ANALYSIS PROTOCOL

1. Analyze client samples in groups of 10 or less.
2. Analyze one quality control sample before and after each group of client samples.
3. For acid digested samples, prepare a reagent blank, a digest blank, and a digest blank spike to be analyzed with the first group of client samples analyzed during the day.
4. For liquid samples, prepare only a regent blank to be analyzed with the first group of client samples analyzed during the day.
5. Prepare a client sample spike for each group of client samples analyzed.
6. Print a copy of the ID/WT file before beginning analysis.

SPIKE PROCEDURE

1. Client sample spike
   1. Pipet the same amount of sample solution that was used in analysis for selenium into a 16 x 100 mm. glass tube.
   2. Add 1 mL of 10 ng/mL selenium solution.
   3. Add 3 mL hydrochloric acid.
   4. Add enough deionized water to bring the final volume to 10 mL
   5. Place the tube on a dry heating bath and heat for 45 minutes at 95 degrees C.
   6. Remove the tube from the dry heating bath and allow to cool.
2. Blank Digestion Spike
   1. Add 10 mL nitric acid to a 150 mL glass beaker.
   2. Add 5 mL perchloric acid.
   3. Add 5 mL of 50 ng/mL selenium solution and cover with a watch glass.
   4. Heat on a hot until dense white fumes are observed.
   5. Allow the sample to cool and add 10 mL of 25% hydrochloric acid.
   6. Transfer into a 100 mL volumetric flask.
   7. Dilute to volume with deionized water and mix well.
   8. Pipet 5 mL of the spiked blank digest into a 16 x 100 mm. glass tube.
   9. Add 3 mL of hydrochloric acid.
   10. Add 2 mL Deionized water.
   11. Place on a dry heating bath and heat for 45 minutes at 95 degrees C.
   12. Remove tube from the dry heating bath and allow to cool.

PROCEDURE

1. Follow the same procedure as given in the Arsenic, Gaseous Hydride Atomic Absorption Method, page 144-146, with the following changes.
   1. Step 1 - change to - Install selenium electrodeless lamp.
   2. Step 2 - change to - Turn on the System 2 EDL power supply. With the "MOD" button switched off (green light off), set the output level to 280 milliamps.
   3. Step 5 - change to - Click on "MHS-FIAS", double click on"ROUTINE", click on "ELEMENT FILE", click on "SE.MEL", then click on "OK".
   4. Step 6 - change to - Press the "MOD" button (green light on) on the System 2 EDL power supply. And set the output to 210 milliamps.
   5. Step 10 - change to - Click on 1 of the following:
      1. "SE_DIG"
      2. "SE_WATER"
   6. Step 18 - change to - Load the autosampler in the following manner:

      Position 1	blank
      Position 2	1 ng/mL selenium standard
      Position 3	3 ng/mL selenium standard
      Position 4	5 ng/mL seleniun standard
      Position 8	quality control sample
      Positions 9-40	client samples

QUALITY CONTROL

1. Values on the quality control sample must be within the limits established by the supplier.
2. Recovery of selenium from the spiked samples and spiked digest blank must be between 75% and 125%.
3. The r value for the calibration curve must be greater than 0.990.

REFERENCES

1. Perkin-Elmer Corp., Recommended Analytical Conditions and General Information for Flow Injection Mercury/Hydride Analyses Using the Perkin- Elmer FIAS 100/400, p 14, Order No. TSAA-10C.
2. Arsenic and Selenium by Hydride Generation Atomic Absorption Spectrometry, in Standard Methods for the Examination of Water and Wastewater, 19th Edition, 1995, chapter 3, p 28-31.