Primary amine supramolecular solvent microextraction for smartphone-based determination of calcium in milk and infant formula

Abstract

In this work, we proposed a primary amine supramolecular solvent microextraction approach for smartphone-based digital image colorimetry for the first time. We found that amphiphile (primary amine) acted as an alkaline agent for the calcium colored complex formation with 1-(2-pyridylazo)-2-naphthol in deproteinized food sample. After coacervation agent (electrolyte) addition, a spontaneous supramolecular solvent phase separation and calcium complex microextraction took place. We constructed a lab-made colorimetric box to capture the image of a vial containing two separated liquid phases by the smartphone without extract transfer into a cuvette. We used color component values in RGB (red, green, blue) color model as analytical signals for the calcium quantification. The developed microextraction approach provided effective calcium separation from food sample matrices (extraction recovery 97%) and satisfactory selectivity for its determination by the inexpensive, simply operated portable smartphone device. Under optimal conditions, the limit of detection was 40 mg L−1. The calibration plot was linear over the range of 120–5000 mg L−1, which enabled calcium determination in real milk and infant formula samples.