Predicting the redshift on the ultraviolet spectrum using the peak area method

Abstract

The ultraviolet (UV) absorption peaks of NaCl, NaOH, and β -phenylethylamine (PEA) in an aqueous solution move toward redshift. We proposed the peak area method for the quantitative analysis of PEA, NaCl, and NaOH. First, we obtained the predictable regularities of the redshift of the single component sample. Then, we obtained the regularities of the redshift of the UV spectrum for the mixture by the peak height and peak area methods. Finally, the BP-ANN algorithm was applied to determine the concentration of the mixture using the peak height and peak area method. The results of the testing set showed that correlation coefficients ( R 2 ) of 0.992, 0.993, and 0.992 were obtained by peak height method and 0.997, 0.998, and 0.998 were obtained by peak area method for NaCl, NaOH, and PEA, respectively. Meanwhile, the relative errors of the prediction of NaCl, NaOH, and PEA obtained by peak area method were less than 3%, whereas the REP of NaCl, NaOH, and PEA obtained by peak height method were more than 5%. Compared with the results of the peak height method, the results showed that the peak area was more accurate than the peak height in predicting the redshift of the UV spectrum.

Effect of (De-)protonation on the UV Spectra of Sodium Oleate: Experimental and Electronic Structure Investigation

“…The maximum concentration range from which λ max became unchanged for NaOH, Na 2 CO 3 , HCl, and H 2 SO 4 is in the range of 1–5, 10–50, 6.85–68.49, and 1000–1300 mM, respectively. The findings of this study agree with previous studies, which also observed this behavior and reported the same range of wavelengths, , attributing the stabilization of λ max to the solution saturation effect.…”

“…Deprotonation on the other hand is expected to have an opposite effect by contracting the spectra and enhancing the absorbances − at least at lower concentrations − as previously observed on other chromogens. 27,28 However, this may decrease the absorbance at higher concentrations of NaOL, since intramolecular charge transfer is increased, 56,57 which was also observed in this study (Figure 5). As explained above, the introduction of acids (H + ) in the system will displace the equilibrium of oleic acid dissociation toward the formation of the molecular form (since it is a weak acid), while the introduction of bases tends to deprotonate the solution and prevents the formation of molecular oleic acid.…”

“…In previous studies, some of these species were associated with the disruption of ultraviolet spectra of chromogens. 28,55 In this study, in the case of solution protonation, part of the protons is consumed in the formation of molecular oleic acid. This makes the solution richer in anions (auxochromes) from pH regulators, which increases the electronic density (increased likelihood for light absorption).…”

“…27 OH − and Cl − have been associated with the disruption of UV spectra when the species of interest peak below 200 nm, a region where both NaCl and NaOH UV spectra not only peak but also display redshifts. 28 Sodium oleate presents its main peak around or below 200 nm, 8 making its ultraviolet spectra susceptible to disruption by the species that make up the pH regulators. If unaccounted for, this may lead to an incorrect interpretation of UV NaOL adsorption data.…”

“…Some chemical species are known to promote UV red/blue shifts of organic molecules containing chromophore groups in their structures, which implies that such species can interfere with UV measurement of the species of interest . OH – and Cl – have been associated with the disruption of UV spectra when the species of interest peak below 200 nm, a region where both NaCl and NaOH UV spectra not only peak but also display redshifts . Sodium oleate presents its main peak around or below 200 nm, making its ultraviolet spectra susceptible to disruption by the species that make up the pH regulators.…”