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carbodiimide hydrochloride and 2-nitrophenyl-hydrazine to form hydrazide, which is subject to heat
treatment to produce purple under alkaline conditions followed by detection at VIS 530 nm [108].
Simple pretreatment and specificity of this method was applied to the commercially available carbonic
acid analyser [109].

Fig. 1.2.5.
Chromatogram of a commercial sample of Italian wine (Asti
Spumante). Peaks: 1 = lactate (1.54 g/1); 2 = acetate (0.4 g/1); 3
= tartrate (2.83 g/1); 4 = malate (0.74 g/1); 5 = succinate (0.30
g/1); 6 = citrate (0.50 g/1). I.S. = Internal standard. (Reproduced
from ref. 105: J. Chromatogr., (1986) 362, p. 51, Fig. 1.).

The use of a devised post-column method is reported. After separation of organic acids on the HPLC
column, the method includes enzyme reaction in immobilized enzyme reactor and ECD detection of
produced hydrogen peroxide [110]. This method was applied to the analysis of lactic acid in yogurt and
concentrated tomatoes using reversed-phase HPLC and L-lactate oxidase as a immobilized enzyme
reactor.

1.2.2.5—
Vitamins

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