Micropaper-based analytical device (μPAD) for the simultaneous determination of nitrite and fluoride using a smartphone

The design, optimization and evaluation of a micro paper-based analytical device (mu PAD) for the simultaneous determination of fluoride and nitrite in real water samples was developed. In order to create hydrophilic and hydrophobic zones on the laboratory filter paper device, a wax ink printer was used. The PAD has four reaction zones for each analyte where the respective colorimetric reactions took place using the SPADNS method and Griess method for fluoride and nitrite respectively. A Smartphone was used to capture the corresponding images which were then converted to the RGB colour space by the software ImageJ using a personal computer. Under the optimal conditions, the linear range was 0.23-2.26 mg L-1 for fluoride with limit of detection (LOD) and limit of quantification (LOQ) of 0.13 mg L-1 and 0.25 mg L-1. The working range for nitrite was 0.05-10.0 mg L-1 with LOD of 0.03 mg L-1 and LOQ 0.13 mg L-1. The PAD was used to determine the analytes in water samples obtaining satisfactory results in both cases. The validation of fluoride determination was performed comparing the PAD with the reference method and for nitrite determination, a recovery study was carried out. In both cases, the obtained results demonstrated a good agreement.