Method / Description Nitrite

Eppendorfpipettes (10-100 µl, 100-1000 µl und 1-5 cm3)
Various volumetric flasks
Various cylinders und beakers
Various bottles to store the reagents

Sulphanilamide:  Dissolve 1.0 g of sulphanilamide in 10 cm3 conc. HCl and 60 cm3 pure water. After cooling make up to 100 cm3. Store in brown glass bottle. Stable for several weeks.
NED: 100 mg N-(1-naphthyl)-ethylendiamine-dihydrochlorid (NED) are dissolved in 100 cm3
pure water and stored refrigerated in a glass bottle. Stable until a brown color develops.
NO2-standard: MERCK 1 g NO2 per liter (= 21.734 mmol/l)
Saltwater: 36 gNaCl per liter

Stock-Standard: NO2-Standard (MERCK) = 21.734 mmol/l
Work standard: Dilute the stock-standard with salt water in different relations to obtain standards with different concentrations for a calibration (5-6 calibration points).
Calibration area: 1.087 µmol/l - 5.435 µmol/l

To 5.0 cm3 of undiluted sample or standard 0.1 cm3 Sulphanilamide-solution and 0.1 cm3 NED-solution are added. Read the absorbance of the red azo dye after 30 minutes at 540 nm.

High concentrations of H2S (> 1mM) in the sample disturbe the measurements. Therefore these samples should be acified with 10 µl HCL (65%/suprapur) per cm3 sample and then be stored for 1-2 days, without lid, in a cool room.
(Don`t forget the dilution factor of the acid when you calculate the final result!)