12 Automatic Analysers in Oenology 663
Characteristics of the Method
Intra-laboratory reproducibility: 4.5
Inter-laboratory reproducibility: 8.512.3.4.8 Determination of Iron in Wines and Musts
Principle
Chemical Method
The method is based on the Aquaquant©Rkit for iron commercialised by Merck. Fer-
rous ions react with the reagent, Ferrospectral (the sodium salt off (pyridyl-2)-3 bis
(phenyl-4-sulfonique)-5,6 triazine-1,2,4,acid) forming a violet complex. Only the
ferrous form of iron reacts with this reagent, so the inclusion of an additional reagent
containing ammonium thioglycolate digests weak iron complexes and reduces triva-
lent iron to the bivalent form.
Characteristics of the Method
Intra-laboratory reproducibility: 0.5mg/L
12.3.4.9 Determination ofα-Amino Nitrogen in Wines and Musts
Principle
Chemical Method
To t a lα-amino nitrogen is determined by its reaction witho-phthaldialdehyde. The
intensity of the absorbance 340 nm is compared to that obtained for standards of
known concentrations of isoleucine.
12.3.4.10 Determination of Ammoniacal Nitrogen in Wines and Musts
Principle
Enzymatic Method
In the presence of reduced nicotinamide-adenosine-dinucleotide (NADH), NH
- 4
ions are reacted with 2-oxoglutarate resulting in the formation ofL-glutamate, in
a reaction catalysed by glutamate deshydrogenase (GLDH):
NH
+
4 +2-oxoglutarate+NADH−> L-glutamate+NAD++H
2 O
( in the presence of GLDH)The quantity of NADH oxidised into NAD+is proportional to the quantity of
ammoniacal nitrogen present in the sample.