Nitrate-Nitrogen by Cadmium Reduction using Flow Injection FIALab 2500

(See water procedures for instrument set-up)

Extraction reagent: 0.04 M (NH4)2SO4

To make 10 L: Add 6 L DI water to a 20 L carboy. Weigh 52.80 g (NH4)2SO4 and add to carboy. Dilute to 10 L mark and stir with a magnetic stirrer.

Standards and standard stock

Make 1000 NO3-N stock solution by weighing 0.7218 g dry KNO3 and transferring to 100 mL volumetric flask.  Add 1 mL Boric acid preservation solution (see water procedure) then dilute to 100 mL with dionized water.

Make 1, 2, 3, 4 ppm NO3-N solutions by diluting the stock 1:1000, 2:1000, 3:1000, and 4:1000 respectively with dionized water.


  1. Use 4 mL (approximate 5 g) mineral scoop and scoop soil into an extraction cup.
  2. Add 25 mL extraction reagent and shake for 5 minutes, then let stand for 30 minutes.
  3. Filter the extract through Whatman 42 filter paper into nitrate analyzer test tubes.
  4. Analyze according to flow injection FIALab 2500 instrument procedures.
  5. Set the 1, 2, 3, 4, standards to read 5, 10, 15, 20 to allow for the 1:5 dilution factor.

Reference: J. Benton Jones, Jr., Laboratory Guide for Conducting Soil Tests and Plant Analysis, p123, CRC 2001.