Internal Standard-Amplitude Modulated Multiplexed Flow Analysis

Abstract

A new concept of flow analysis, internal standard-amplitude modulated multiplexed flow analysis, is proposed. A proof of concept was verified by applying it to the determination of ferrous ion (Fe 2+ ) by 1,10-phenanthroline (o-Phen) spectrophotometry. The flow rates of sample solutions containing Methylene Blue (MB) as an internal standard substance were sinusoidally varied at different frequencies. The solutions were merged with a color reagent (o-Phen) solution, while the total flow rate was held constant. Downstream, analytical signals were monitored at the maximum absorption wavelengths of Fe 2+ -o-Phen complex and of MB (510 and 644 nm, respectively). The signals were respectively analyzed by fast Fourier transform. The concentrations of the analytes in respective samples were simultaneously determined from the amplitudes of the corresponding wave components. The precision, linearity of the calibration curve, limit of detection and robustness against deliberate fluctuation in flow rate were greatly improved by introducing the internal standard method. Good recoveries of around 100% were obtained for Fe 2+ spiked into real water samples.

Factors affecting the determination of iron species in the presence of ferric iron

“…The spectrophotometric methods have been commonly used for the analysis of iron content such as 2,2′-bipyridyl and 2,2′,2″-terpyridyl 4,7-diphenyl-1 method (Moss and Mellon 1942), 4,7-diphenyl-1,10-phenanthroline method (Clark 1962), ferrozine method (Herrera et al 1989) and 1,10-phenanthroline method (Tamura et al 1974). The 1,10-phenanthroline method is used widely due to its high sensitivity (Tong et al 2016;Amonette and Matyáš 2016;Sumitomo et al 2017). The high concentration Fe 3+ affects the analysis of Fe 2+ in the process of colorimetry by the 1,10-phenanthroline method such as AMD samples, so F − is added into the solution to eliminate interferences (Herrera et al 1989).…”

Flow-based Analytical Techniques

“…12 Sumitomo et al used an internal standard, the amplitude modulation of flow rates for sample solutions and fast Fouriertransformation signal processing, to determine two different samples simultaneously. 13 A validation of the method was demonstrated by using the determination of iron(II) with 1,10-phenanthroline. The stability of this unique system was improved by an internal standard solution (methylene blue).…”