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Fig. 2.9.
Formation of DABTH-amino acids by reaction of DABITC
with amino acids.

absorptivity at 436 nm = 34 000. Quantitative coupling with DABITC requires a temperature of 75 °C.
Thus, the double coupling method is performed instead at 52 °C. The second coupling is with PITC to
drive the reaction to completion [54].

2.2.4—
1,2-Naphthoquinone-4-sulfonate (NQS)

NQS reacts with amino acids in an alkaline medium giving a derivative which is detected at 305 and
480 nm [55-57].

NQS reacts with primary and secondary amino groups under relatively mild conditions. The reaction of
amino acid with NQS is thought to be as in Fig. 2.10.

A new chromatographic method for the determination of amino acids has been developed

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