Nitrite

Introduction

Nitrite is measured with the standard Greiss test. In this test, sulfanilamide reagent is converted to a diazonium salt by nitrite (NO2) in the water sample. The diazonium salt is then reacted with NED (N-1-napthylethylene diamine dihydrochloride) reagent to form an azo dye which has a purple/magenta color that is measured at 520-550 nm (suitable for the colorimeter 528 nm green LED).

Reagents

  • API nitrite test kit

  • 1,000 ppm N (3,280 ppm as NO2) standard, Labchem Cat # LC17930-7

  • Distilled water

Equipment

List of vendors and prices: https://sites.google.com/iorodeo.com/colorimeter/equipment

  • Colorimeter with RGB board (use green for measurement)

  • Cuvettes

  • 9 x 10 mL capped tubes

  • 2 x 100 mL volumetric flask

  • Pippete pump

  • 5 mL, 10 mL pipettes

Prepare Calibration Solutions

  • 100 ppm NO2 working stock #1: 3.05 mL of the 3,280 ppm (1,000 ppm as N) standard in 100 mL distilled water in volumetric flask. Fill to the line with distilled water.

  • 2.5 ppm NO2 working stock #2: 2.5 mL of the 100 ppm working stock in 100 mL distilled water in volumetric flask. Fill to the line with distilled water.

  • Dilute the 2.5 ppm working stock as outlined in the Table below

Standard Curves v1

Method

  • To each 5 mL sample, add 5 drops of API Nitrite Test Solution

  • Cap the tube and invert several times to mix.

  • Wait 5-10 mins for the color to fully develop.

  • Transfer approx. 1mL of each calibration solution to a cuvette.

  • In the colorimeter plotting program, select the Green (528 nm) LED on the standard RGB board and ppm as units. Calibrate the colorimeter with the 0 ppm nitrite solution and measure absorbance of all of the solutions in duplicate.

Sample calibration data

  • To view/use: Download the file and open in the colorimeter plotting software as described here.

In addition to the API test kit, there is a second Greiss test using off-the-shelf reagents described here: http://public.iorodeo.com/docs/nitrite/greiss.html