Fluorescent derivatization of nitrite ions with 2,3-diaminonaphthalene utilizing a pH gradient in a Y-shaped microchannel

The on-chip derivatization of nitrite ions with 2,3-diaminonaphthalene (DAN ) utilizing a pH gradient formed in a Y-shaped microchannel was investigate d. Nitrite ions react with DAN at low pH, and strongly fluoresced at high p H. Therefore, a reaction at low pH followed by the addition of a strong alk aline solution is the usual procedure in a batch scheme. However, a strong alkaline solution, like an NaOH aqueous solution, erodes the wall of the mi crochannels in substrates made of glass or polymers, and has not been consi dered suitable for use in microchannels. We first investigated the derivati zation reaction and fluorescent properties of nitrite ions with DAN. We fou nd that the on-chip fluorescent derivatization reaction and detection witho ut the addition of an alkaline solution is possible by controlling the pH v alues of the nitrite solution and the DAN solution to form a suitable pH gr adient by utilizing a buffering effect of triethanolamine solution, which i s used as an NO2 gas-absorption medium. These results have suggested the fe asibility of novel reaction schemes which can provide the desired products due to a controlled pH gradient in the microchannels, as well as the possib ility of an on-site monitoring microchip device for ambient NO2.