Fast and sensitive colorimetric detection of pigments from beverages by gradient zone electrophoresis on a paper based analytical device

This study proposed gradient zone electrophoresis on a paper-based analysis device (PAD) for sensitive and rapid colorimetric detection of multiple analytes with smartphone imaging. With experimental optimization, simultaneous stacking and separation of color pigments was successfully demonstrated in 60 s as visualized by real-time smartphone photography. Compared with isocratic zone electrophoresis, the separation was obviously improved. Meanwhile, due to the allowance of larger sample introduction volume in the proposed method, the band intensity was also largely enhanced. Practical application of this PAD method was demonstrated by detection of synthetic pigments in commercial beverages. With the enrichment capability of the proposed method, the signal intensity of brilliant blue and amaranth was enhanced by 60 and 180 times, respectively. The limits of detection (LOD) for the common food pigments brilliant blue and amaranth in beverages were 0.35 and 0.14 μg/mL, respectively. Thanks to the simultaneous separation and enrichment functions of this PAD method, not only a detection LOD close to that of a benchtop spectrophotometer can be simply achieved with a smartphone camera, but spectral interference could also be avoided in multi-component analysis.