Monitoring of cyanobacteria using derivative spectrophotometry and improvement of the method detection limit by changing pathlength

Abstract

Effective monitoring tools and methods are needed for the early detection and management of cyanobacteria in water bodies to minimize their harmful impacts on the environment and public health. This research investigated changing the cuvette pathlength (10-, 50-, and 100-mm) to improve the detection of cyanobacteria using UV-Vis spectrophotometry with subsequent application of derivative spectrophotometry and Savitzky-Golay (S-G) transformation. A non-toxigenic strain of blue-green cyanobacteria, Microcystis aeruginosa (CPCC 632), and a green algae strain for comparison, Chlorella vulgaris (CPCC 90), were studied in a wide range of concentrations (955,000 to 1855 cells/mL). In each concentration range, method detection limits were established with absorbance measurements and S-G first derivative of absorbance using 10-, 50-, and 100-mm cuvette pathlengths. Increasing the cuvette pathlength from 10 to 100 mm resulted in a 15-fold improvement in sensitivity with absorbance and a 13-fold improvement with S-G first derivative of absorbance for M. aeruginosa. Overall, adoption of 100 mm pathlength and application of S-G derivative spectra improved the method detection limit for M. aeruginosa from 337,398 to 4916 cells/mL, which is below the WHO guideline for low probability of adverse health effects (,20,000 cells/mL). Similarly, the detection limit for C. vulgaris was improved from 650,414 to 11,661 cells/mL. The results also showed that spectrophotometry could differentiate M. aeruginosa from C. vulgaris based on the variations in their pigment absorbance peaks.