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
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