Application of UV-Vis and resonance Raman spectroscopy to study bleaching and photoyellowing of thermomechanical pulps

Holzforschung ◽  
2006 ◽  
Vol 60 (3) ◽  
pp. 231-238 ◽  
Author(s):  
Anna-Stiina Jääskeläinen ◽  
Anna-Maija Saariaho ◽  
Jouko Vyörykkä ◽  
Tapani Vuorinen ◽  
Pavel Matousek ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Light Exposure ◽  
Resonance Raman Spectroscopy ◽  
Resonance Raman ◽  
Excitation Wavelength ◽  
Thermomechanical Pulp ◽  
Pulp Bleaching ◽  
Absorption Bands ◽  
Peroxide Bleaching ◽  
Brightness Reversion

Abstract The chemistry of thermomechanical pulp bleaching and brightness reversion was studied. First, UV-Vis reflectance spectroscopy was used to obtain information on the reactive structures in pulp. Based on these data, a Raman excitation wavelength was chosen close to the absorption bands of the chromophores formed to take advantage of the resonance enhancement (resonance Raman spectroscopy). Fluorescence was rejected with a picosecond Kerr gate. The results revealed that coniferyl aldehyde structures were partly removed by alkaline peroxide bleaching and these structures were further degraded during light exposure. However, this reaction was obviously not responsible for chromophore formation in the pulp. On the other hand, based on the resonance Raman spectra, formation of quinonoid structures, possibly para-quinones, was a more prominent explanation for the brightness reversion.

Fluorescence spectroscopy for chromophore studies on bleached kraft pulps

Holzforschung ◽  
2007 ◽  
Vol 61 (5) ◽  
pp. 509-515 ◽  
Author(s):  
Sirje Liukko ◽  
Ville Tasapuro ◽  
Tiina Liitiä
Keyword(s):  
Fluorescence Spectroscopy ◽  
Fluorescence Spectra ◽  
Lignin Content ◽  
Excitation Wavelength ◽  
Kraft Pulps ◽  
Carbonyl Groups ◽  
Residual Lignin ◽  
Pulp Bleaching ◽  
Peroxide Bleaching ◽  
Brightness Reversion

Abstract Fluorescence techniques are highly sensitive and, since aromatic lignin is the most likely source of natural pulp fluorescence, they are suitable for detailed investigation of residual lignin in bleached pulps. Such investigations are important to our understanding of the bleachability and brightness reversion of pulps. In this study, the effect of bleaching on pulps was evaluated using fluorescence spectra of two softwood kraft pulps bleached in six elemental chlorine-free and totally chlorine-free sequences. Fluorescence spectra were recorded in each bleaching stage using four different instrument settings. In general, pulp fluorescence at excitation wavelengths of 270 and 350 nm increased as bleaching proceeded. Below a certain lignin content, however, pulp fluorescence measured at an excitation wavelength of 430 nm decreased with the residual lignin content. Carbonyl groups have a quenching effect on fluorescence, and the formation of carbonyl groups after oxygen and ozone delignification induced a decrease in pulp fluorescence. The increase in pulp fluorescence after peroxide bleaching stages was due to the removal of carbonyl groups. Reactions of chromophores during brightness reversion also had an effect on pulp fluorescence. These findings demonstrate that fluorescence spectroscopy provides an interesting tool for pulp bleaching studies.

scholarly journals Rapid Raman Spectroscopic Analysis of Stress Induced Degradation of the Pharmaceutical Drug Tetracycline

Molecules ◽  
2020 ◽  
Vol 25 (8) ◽  
pp. 1866 ◽  
Author(s):  
Christian Domes ◽  
Timea Frosch ◽  
Juergen Popp ◽  
Torsten Frosch
Keyword(s):  
Raman Spectroscopy ◽  
Resonance Raman Spectroscopy ◽  
Resonance Raman ◽  
Pharmaceutical Products ◽  
Small Sample ◽  
Small Concentration ◽  
Stress Factors ◽  
Excitation Wavelength ◽  
Raman Spectroscopic ◽  
Concentration Changes

Stress factors caused by inadequate storage can induce the unwanted degradation of active compounds in pharmaceutical formulations. Resonance Raman spectroscopy is presented as an analytical tool for rapid monitoring of small concentration changes of tetracycline and the metabolite 4˗epianhydrotetracycline. These degradation processes were experimentally induced by changes in temperature, humidity, and irradiation with visible light over a time period of up to 23 days. The excitation wavelength λexc = 413 nm was proven to provide short acquisition times for the simultaneous Raman spectroscopic detection of the degradation of tetracycline and production of its impurity in small sample volumes. Small concentration changes could be detected (down to 1.4% for tetracycline and 0.3% for 4-epianhydrotetracycline), which shows the potential of resonance Raman spectroscopy for analyzing the decomposition of pharmaceutical products.

Sensitive algorithm for multiple-excitation-wavelength resonance Raman spectroscopy

2014 ◽  
Author(s):  
Balakishore Yellampalle ◽  
Hai-Shan Wu ◽  
William McCormick ◽  
Mikhail Sluch ◽  
Robert Martin ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Resonance Raman Spectroscopy ◽  
Resonance Raman ◽  
Excitation Wavelength

scholarly journals Resonance Raman Spectro-Electrochemistry to Illuminate Photo-Induced Molecular Reaction Pathways

Molecules ◽  
2019 ◽  
Vol 24 (2) ◽  
pp. 245 ◽  
Author(s):  
Linda Zedler ◽  
Sven Krieck ◽  
Stephan Kupfer ◽  
Benjamin Dietzek
Keyword(s):  
Structural Changes ◽  
Raman Band ◽  
Resonance Raman Spectroscopy ◽  
Spectroscopic Method ◽  
Resonance Raman ◽  
Reaction Pathways ◽  
Excitation Wavelength ◽  
Absorption Bands ◽  
The Individual ◽  
Sequential Reduction

Electron transfer reactions play a key role for artificial solar energy conversion, however, the underlying reaction mechanisms and the interplay with the molecular structure are still poorly understood due to the complexity of the reaction pathways and ultrafast timescales. In order to investigate such light-induced reaction pathways, a new spectroscopic tool has been applied, which combines UV-vis and resonance Raman spectroscopy at multiple excitation wavelengths with electrochemistry in a thin-layer electrochemical cell to study [RuII(tbtpy)2]2+ (tbtpy = tri-tert-butyl-2,2′:6′,2′′-terpyridine) as a model compound for the photo-activated electron donor in structurally related molecular and supramolecular assemblies. The new spectroscopic method substantiates previous suggestions regarding the reduction mechanism of this complex by localizing photo-electrons and identifying structural changes of metastable intermediates along the reaction cascade. This has been realized by monitoring selective enhancement of Raman-active vibrations associated with structural changes upon electronic absorption when tuning the excitation wavelength into new UV-vis absorption bands of intermediate structures. Additional interpretation of shifts in Raman band positions upon reduction with the help of quantum chemical calculations provides a consistent picture of the sequential reduction of the individual terpyridine ligands, i.e., the first reduction results in the monocation [(tbtpy)Ru(tbtpy•)]+, while the second reduction generates [(tbtpy•)Ru(tbtpy•)]0 of triplet multiplicity. Therefore, the combination of this versatile spectro-electrochemical tool allows us to deepen the fundamental understanding of light-induced charge transfer processes in more relevant and complex systems.

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