Ammonia-Salicylate Test
Reagents & Equipment
Colorimeter
Cuvettes with caps (preferably macro cuvettes)
Sodium hydroxide, Carolina Biologicals # 889425
6% sodium hypochlorite (household bleach)
Sodium salicylate, Sigma # S2679-100G
Sodium nitroferricyanide, Sigma #228710-5G
1 mL pipette
2 x 100 mL volumetric flasks
Distilled water
Colorimeter set-up
Wavelength: 625 nm. Red led (colorimeter RGB board)
Ammonia standard data: Low-range (0 - 2.5 ppm NH3). Download a data file or prepare your own ammonia standard data
Before measuring blank the colorimeter against water or a distilled water sample developed with Salicylate reagents as described below
Method
Step 1: Prepare fresh reagents
Hypochlorite solution:
Fill a 100 mL volumetric flask with 70 mL of DI water.
Add 1 mL of bleach and 0.5 grams of NaOH and mix until dissolved.
Fill flask to the 100 mL mark.
Salicylate/catalyst solution:
Fill a 100 mL volumetric flask with 70 mL of DI water.
Add 10 g of sodium salicylate, 0.04 g sodium nitroferricyanide and mix until dissolved.
Add 0.5 g of NaOH to adjust pH to the ~12.0 range.
Fill flask to the 100 mL mark.
Transfer solution into a dark, airtight glass bottle for maximum longevity. Prepare fresh weekly due to limited storage life.
Step 2: Colorimetric assay
Transfer 1 mL of each sample to be tested into a cuvette
Add 0.25 mL of hypochlorite solution, cap cuvette and invert several times to mix
Add 0.25 mL of salicylate/catalyst solution, cap cuvette and invert several times to mix
Let tubes stand for 5-10 mins to develop color.
Place the cuvette in the colorimeter and click measure. The program will return the ammonia concentration in ppm.