It is established a precise DeLIF (Dual Emission Laser-Induced-Fluorescence) system for an instant measurement of pH field. This method is very important in studies of the biological impacts of CO2 sequestration, i.e., effects of pH on organisms. Quinine and sulforhodamine were used as fluorescence dyes. The molar absorption coefficient and emission intensity of quinine depend on pH of aqueous solutions, while those of sulforhodamine are not affected by pH. The ratio of fluorescence intensities represents pH at each point of the image. As a result, the pH field was successfully measured with uncertainty of approximately +/- 0.005, for 3.0 < pH. (c) 2005 Elsevier Ltd. All rights reserved.