High sensitivity and wide range chlorophyll-a determination by simultaneous measurement of absorbance and fluorescence using a linear CCD

In the determination of chlorophyll with the fluorescence method in the natural water, the suspended particles and colloids will seriously interfere with the incident light and the fluorescence. Based on the analysis of the interaction between light and the measured substances, a high sensitivity, wide range of chlorophyll-a concentration measurement strategy, which combines optical information of fluorescence and absorbance with the CCD integration time transformation method, is proposed. Correspondingly, a novel algorithm, which can significantly correct the attenuation of incident light due to the absorption of suspended particles and the deviation of detected fluorescence caused by the scattered light and reflected light, is proposed to realize turbidity compensation. For verification, a self-designed compact optical experimental device consisting of a single LED and a linear CCD was set up to obtain the fluorescence spectrum and absorbance spectrum simultaneously. The experimental results demonstrate that the compensation strategy can commendably compensate for the impact of the suspended particles. The relative error of chlorophyll-a measurement is less than 5%, even in a high turbidity environment. Furthermore, the minimum detection limit is significantly reduced from conventional 0.01 μg/L to 0.0025 μg/L in the range of 0.0025-130 μg/L with the CCD integration time transformation method, which improves the measurement sensitivity. This device and method have the potential to be applied to the in situ online measurement of chlorophyll-a concentration in natural water.