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Measurement of tropospheric ozone by digital image analysis of indigotrisulfonate-impregnated passive sampling pads using a smartphone camera

2019; Elsevier BV; Volume: 154; Linguagem: Inglês

10.1016/j.microc.2019.104535

1095-9149

María Cerrato-Álvarez, Samuel Frutos-Puerto, Conrado Miró-Rodríguez, Eduardo Pinilla Gil,

Biosensors and Analytical Detection

In this work, we propose a low cost and portable method for the monitoring of daily tropospheric ozone levels, through the combination of passive sampling and digital analysis of images taken with the camera of a smartphone. The analytical signal used is the degradation of the blue color of indigotrisulfonate deposited on a passive sampling device, depending on its reaction with ozone to form colorless products. The discoloration was measured by tracking the RGB parameters obtained from images taken with the camera. The RGB signals were processed using different mathematical algorithms of digital image analysis, of which the effective absorbance from R channel (EAR) was selected as optimal. The detection limit was 3.3 μg m−3. The linear range obtained was between 11 and 109 μg m−3 for EAR, sufficient for the measurement of usual environmental levels of ozone in urban or rural environments. The practical application of the method was tested by measuring 24 h average levels of ozone in an suburban environment for three months, finding a good precision (RSD = 6.8%), accuracy (relative errors from −14.0 to 5.7%) and an adequate correlation (r = 0.77) against a spectrophotometric reference method. These results demonstrate the potential of the method as an auxiliary tool for the standard instruments, providing a rapid and decentralized measurement of ozone levels with adequate reliability.