The absorbance values at 406 nm and 430 nm increased in a time-dependent manner.

<p>Absorbance increase at 406(♦) and 430 nm (•) of 0.04% HGA solution in the presence of 1 M NaOH. Results are the mean ± S.E. of three experiments.</p

Effects of AA on the absorption spectra of HGA and alkaptonuric urine incubated with NaOH.

<p>1% HGA solutions or the urine samples from the patients with alkaptonuria (Case #1 and Case #2); then, 1 M NaOH was added to each sample, followed by incubation of the samples at room temperature for 1 min.</p

The absorbance conversion of HGA and alkaptonuric urine after addition of NaOH.

<p>The absorption spectra of 0.04% HGA solution (A) and the urine samples from Case #1 (B) and Case #2 (C) of alkaptonuria incubated with NaOH at room temperature for each of the indicated durations (1 min, 10 min, 30 min, and 60 min).</p

Absorption spectra of alkaptonuric urine showed characteristic peaks following the addition of NaOH.

<p>The absorption spectra of urine samples from the patients with alkaptonuria (Case #1 and Case #2) after treatment with 1 M NaOH for 1 min, B, The absorption spectra of urine samples from healthy individuals (#1–#5) after incubation with 1 M NaOH at room temperature for 1 min. C, The absorption spectra of urine samples from patients with phenylketonuria (Cases 1, 2 and 3), and solutions of 0.04% gentisic acid and 0.04% 2-hydroxyphenylacetic acid after treatment with 1 M NaOH for 1 min.</p