A portable and 3D printing microplasma-based device coupling with visual colorimetry for field speciation analysis of...

In this work, a portable and 3D printing sulfur speciation analysis device was constructed, which effectively integrated with a vapor generation system, a microplasma chamber and a colorimetric unit. Point discharge microplasma was used for highly efficient oxidation of gaseous H₂S to SO₂, thus the simple and time-saving nonchromatographic speciation analysis of S^2- and SO₃^2- was achieved by simply adjusting the plasma "on" or "off". In this process, S^2- were converted to volatile H₂S by acidification reaction and then oxidized to SO₂ by microplasma, prior to a specific discoloring reaction with yellow fluorescein derivative, which effectively alleviated the interference from sample matrix and further improved the analytical sensitivity. The absorbance value of fluorescein derivative at 482 nm was used for quantitative analysis of S^2- and SO₃^2-. Under optimal conditions, the detection limit was calculated to be 6.22 μmol L^-1 for both analytes in the concentration range of 30-210 μmol L^-1, while 60 μmol L^-1 analytes were recognizable by the naked eye. The whole 3D-printed device was miniaturized, portable and easy to operate, with fast response time (<1 min), which was only the size of an adult's palm and equipped with one 3.7 V lithium battery for power. This method has been successfully utilized to field analysis of toxic S^2- and SO₃^2- in real environmental water samples.