Molar Range Detection Based on Sideband Differential Absorption Spectroscopy with a Concentrated Reference

Abstract

Conventional absorption spectroscopy (CAS) with a blank reference has only a slight capacity to detect high concentrations at characteristic wavelengths owing to the corresponding large molar absorption coefficient (ε) on the scale of 10 or 10 cm M. To monitor concentrated analytes as high as the molar range in a plating bath and on a chemical production line, we propose a new approach using sideband differential absorption spectroscopy (SDAS). SDAS is obtained by subtracting the absorption spectra of the samples, A(λ,C), from that of a reference containing a concentrated standard analyte, A(λ,C>C), resulting in concave spectra with peaks at the sideband of conventional spectra with generally low ε values on the scale of 100 cm M or less. The negative absorbance changes linearly with the sample concentration at a certain peak wavelength, obeying Lambert-Beer's law. In this work, SDAS was obtained and verified using inorganic and organic substances, such as chromate potassium, rhodamine B, and paracetamol.

Beer's Law – Why Absorbance Depends (Almost) Linearly on Concentration

“…These findings are of particular importance since recently a method has been introduced by Zhao et al, which allows molar range detection. [17] Interestingly, the authors took for each presented example the so-called sideband (actually, it is not really a band. Instead, an inverted peak develops based on changes in the flank of the band and the remaining detector saturation around the peak maximum) at the high-wavenumber side of the peak maximum.…”

Nanoceria dissolution at acidic pH by breaking off the catalytic loop

“…However, the optical signal saturates approximately at relatively low concentrations for similar reasons, which restricts kinetic studies (time evolution as a function of enzyme vs dye ratio) to minimal concentration ranges. Because of that, we choose to employ transparent ferrocyanide and its redox pair, yellowcoloured ferricyanide (absorbance peak at ∼420 nm), as a redox mediator 16 . As ferricyanide presents a much lower ε than most organic dyes used in the field (See table 1 SI), it allows for directly measuring a broader range of nanoceria/ferrocyanide concentration ratios before spectral saturation, allowing for easy reaction kinetics follow-up.…”

Rapid and green detection of manganese in electrolytes by ultraviolet-visible spectrometry to control pollutant discharge

“…Many aqueous solutions of transition metal salts are colored. Therefore, these metal ions absorb light in the UV-vis region, and their concentration can be directly determined by UV-vis absorbance with fast speed, simple procedure and no polluting reagents [16][17][18]. It is reasonable to deduce that the ideal method for measuring Mn 2+ concentration in industrial electrolyte can also be developed based on measuring its UV-vis absorbance.…”