A smartphone-based dual-channel flame photometric platform and its application in ratiometric determination of potassium ions

Abstract

Herein, a smartphone-based dual-channel flame photometric platform was developed for the ratiometric determination of potassium ions, which can potentially be operated in an on-site mode. The test solution was introduced into an air–butane flame from a windproof lighter using a combination of a cosmetic ultrasonic nebulizer and a T-glass tube assembly. With the help of a reflection mirror and two bandpass filters at central wavelengths of 760 and 850 nm, the images of flame atomic emission spectra of K (at 766 and 771 nm) and Cs (at 852 nm) were recorded by an external infrared camera controlled by a smartphone. The brightness of the K and Cs channels was measured for the simultaneous determination of K⁺ and Cs⁺. In a ratiometric detection mode, 100 µM of Cs⁺ was added to the Cs-free samples and standard solutions. The brightness ratios between the K and Cs channels were used as analytic signals, effectively eliminating errors caused by variations in aerosol amount, combustion conditions of the flame and the image detection area. Under optimal experimental conditions, the ratiometric brightness was in a linear relation with the K⁺ concentration in the range from 2 to 200 µM, with a detection limit of 0.61 µM. The portable flame photometric device was used in the determination of K⁺ in water, juice, urine, and compound fertilizer samples, offering the advantages of good portability, low cost and high reliability.