E DETERMINATION OF NITRITE BY SFA

1 In a segmented-flow analysis (SFA) system, the sample is first subjected to dialysis. Nitrite ions from the extract pass the membrane and are taken in an understream of ammonium chloride. By addition of a-naphtylamine and sulphanilamide in acid medium, the nitrite forms a red-coloured diazo compound, of which the absorbance is measured at a wavelength of 540 nm. 

The dialysis serves to separate ions from interfering substances like colloids and coloured organic compounds. 

The colour reagent is known as the Griess-llosvay reagent. 

2 This determination may be carried out on extract 3.1 (extraction with water). 

1 This procedure yields a standard curve that is linear up to approximately 3 mg/L N-NO.  

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