Determination of Nitrate Nitrogen (N03-N) by Specific Ion Electrode
- EXTRACTION SOLUTION - In a 4 L beaker, add 173.2 g Al2(S04)3, 12.8 g H 3B0 3, and 0.7218 g KNO3 and 25.2 g sulfamicacid (NH2S03H) to 3 L deionized water. Stir to dissolve. Pour solution in carboy and dilute to 10 L with deionized water. Adjust to pH 3.0 adding at least 15 mL conc. NaOH (may need more).
- N03-N STANDARDS - To make 1000 ppm N stock solution, dissolve 0.7218 g KNO3 (dry and stored in desiccator) in deionized water in a 100 mL volumetric flask. Add 1 mL preservation solution then dilute to 100 mL. (Make up blank, 10 ppm, and 100 ppm N03-N standards using stock solution and diluting with extracting solution.)
- OUTER FILLING SOLUTION - 0.04 M ammonium sulfate - Add 0.52 g (NH4)2S04 to 100 mL vol. flask. Dilute with H20.
- INNER FILLING SOLUTION - Orion cat. 900002
- PRESERVATION SOLUTION - Dissolve 6.2 g Boric Acid in 100 mL hot deionized water. Allow to cool.
- ORION ION ANALYZER
- NITRATE ION ELECTRODE (ORION 93-07)
- REFERENCE ELECTRODE (ORION 90-02)
- MAGNETIC STIRRER
- Weigh 2 g plant or feed sample into 100 mL beaker. (When testing cotton petioles, weigh 0.25 g sample, follow steps 2-11, then multiply final answer by 8).
- Add 50 mL extraction solution.
- Let stand for 30 minutes.
- Check levels of inner and outer filling solutions in reference electrode (see reference electrode manual for specifications).
- To set up instrument, press 2nd function - 2 to select appropriate electrode.
- Press speed-0 to calibrate N03-N.
- Follow prompts - select 2 standards - Do blank correction. (Rinse electrodes and blot dry before switching solutions.)
- Set 10 ppm standard to read 25.
- Set 100 ppm standard to read 250.
- Measure N03-N in sample and multiply reading by 10. Record as ppm with no decimal.
- When finished place meter in standby mode by pressing speed-8. Submerge electrodes in proper solutions.
- Baker, A. S., and R. Smith. 1969. Extracting Solution for Potentiometric Determination of Nitrate in Plant Tissue. J. Agr. Food Chem. 17:1284-1287.
- Barker, A. V. 1974. Nitrate Determination in Soil, Water, and Plants. Massachusetts Agricultural Experiment Station Bulletin 611, p.35.
- Cantliffe, D. J., G. E. MacDonald, and N. H. Peck, 1970. The Potentiometric Determinations of Nitrate and Chloride in Plant Tissue. New York's Food and Life Sciences Bulletin 3, p.7.