B DETERMINATION OF TOTAL NITROGEN BY SFA

1 The determination is based on the Bertheiot reaction, in which a phenoi derivative (here saiicyiate) forms an azo dye in the presence of ammonia and hypochiorite. In alkaline medium, the indophenol thus formed has a green-blue colour, of which the absorbance is measured at a wavelength of 660 nm. This is a measure for the concentration of ammonium, formed by the nitrogen compounds in the sample. The determination is carried out as a so-called segmented-flow analysis (SFA). 

2 This determination may be carried out on digest 2.1 (digestion with H SO, - salicylic acid - HPj - Se) and digest 2.2 (digestion with HpO, - salicylic acid - HPj). 

1 This procedure yields a standard curve that is linear up to approximately 300 mg/L 

2 The detection limit is approximately 0.1 mg/L in the digest. The determination limit is approximately 0.3 mg/L (1.2 respectively 3.5 mmol/kg in the dried plant material). 

1 The reproducibility of determinations by this procedure should give, at reasonable control and thorough sample preparation, a coefficient of variation within 5 % + 5 mmol/kg. 

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