A new method of histamine colorimetry using 2,3-naphthalenedicarboxaldehyde on a silica–gel column cartridge

In our work, we found, by chance, that 2,3-naphthalenedicarboxaldehyde (NDA) acts as a color development reagent to histamine (HA) in the absence of a reductant, e.g., cyanide anion, even in a weakly acidic environment. The NDA-induced color development reaction to HA shows the maximum absorption of 552 nm at pH 6 after a minimal interval of 10 min. By using this chemical property, a simple and convenient new method of visual colorimetry of HA on a short silica–gel column cartridge (called an “HA cartridge” in this study, which consisted of 50 mg of silica–gel packed into a 1.0 ml disposable syringe) was developed. The new visual method involves extraction of a 5 g sample with 5% trichloroacetic acid solution (TCA, 35 ml), followed by neutralizing with 1 M sodium hydroxide. After loading the TCA extract (500 μl) into the HA cartridge, the cartridge was then washed with a 0.1 M phosphate buffer, pH 6 (200 μl) and water (200 μl × 3 times). When a solution of 1 mM NDA in acetonitrile (200 μl) was passed through the HA cartridge, the color inside the cartridge was observed to changed at 3 min after the NDA loading from white to indigo-blue, for concentrations of HA ranging from 25 to 1000 mg kg−1. This sequence requires only 5 min to perform.