Ultraviolet Absorption Spectroscopy Research Articles

Study on the interaction mechanism of virgin olive oil polyphenols with mucin and α-amylase

The interaction mechanism of mucin and α-amylase with virgin olive oil (VOO) polyphenols (oleuropein (OL), tyrosol (TY), hydroxytyrosol (HT)) was analyzed by fluorescence, ultraviolet (UV) absorption, attenuated total reflection Fourier transform infrared (ATR-FTIR), circular dichroic (CD) spectroscopy and molecular docking. A total of 17 polyphenols have been identified in the selected VOO, and the TY, HT and OL were the main compounds. The quenching mechanism between mucin/α-amylase and three VOO polyphenols was static, mainly through van der Waals forces and hydrogen bonds. The results of UV absorption, ATR-FTIR, and CD spectroscopy revealed that the conformation of mucin changed after combining with the three polyphenols, while that of the α-amylase changed little. Molecular docking predicted the interaction sites of the three polyphenols with human salivary mucin and α-amylase. The present study could provide the theoretical foundation for further research on the interaction between human salivary protein and phenolic compounds in VOO.

Potentials of N-(2, 4-dinitro-1-naphthyl)-p-toluenesulphonamide and 2, 4-dinitro-1-naphthol as novel charge transfer acceptors in pharmaceutical analysis of some quinolones and cephalosporins

BackgroundQuinolones and cephalosporins are antibiotic agents with activity against Gram-positive and Gram-negative bacteria. They contain chromophores and amine groups which are electron-rich centres capable of donating electrons to electron-deficient compounds. A survey of the literature revealed that 2, 4-dinitro-1-naphthol, a nitroaromatic useful in chemical synthesis, can accept electrons in charge transfer reactions. This work investigates N-(2, 4-dinitro-1-naphthyl)-p-toluenesulphonamide and 2, 4-dinitro-1-naphthol in the formation of charge transfer complexes by accepting electrons from selected quinolones and cephalosporins. Five other nitroaromatics (i.e. 4-nitro-1-naphthylamine, 2-nitro-1-naphthol, 2,4-dinitro-1-naphthylamine, 1-nitronaphthalene and 1,4-dinitronaphthalene) were screened in addition to the aforementioned and compared for charge transfer complexes formation. Spot test was used to establish charge transfer complex formation at room and elevated temperatures with determination done by visual inspection and thin layer chromatographic analysis of the reaction mixture. Ultraviolet visible absorption spectroscopy was used to estimate the extent of complexes.ResultsOnly solutions of adducts of N-(2, 4-dinitro-1-naphthyl)-p-toluenesulphonamide and 2, 4-dinitro-1-naphthol gave instant and distinct colour with each drug used at room and elevated temperature. While the former gave deep golden yellow, the latter gave golden yellow against their blank reagent solutions which were, lemon and greenish yellow respectively. Visual inspections of 2-nitro-1-naphthol adduct solutions showed no colour change from the yellow colour of the blank reagent solution, even though the Ultraviolet visible absorption spectra revealed the formation of charge transfer complexes. The adducts solutions of 4-nitro-1-naphthylamine, 2,4-dinitro-1-naphthylamine, 1-nitronaphthalene and 1,4-dinitronaphthalene showed no colour change from their blank reagent solutions and their Ultraviolet visible absorption spectra revealed no formation of charge transfer complexes.ConclusionUltraviolet visible absorption spectral analysis shows superiority of N-(2, 4-dinitro-1-naphthyl)-p-toluenesulphonamide and 2, 4-dinitro-1-naphthol in charge-transfer complex formation over other nitroaromatics screened. N-(2, 4-dinitro-1-naphthyl)-p-toluenesulphonamide and 2, 4-dinitro-1-naphthol are good acceptors of electrons from these drugs, hence could be useful as charge transfer reagents in ultraviolet visible spectrophotometric analysis of these drugs.

Synergistic effects of Piper longum mediated MgO nanoparticles for bacterial and fungal inhibition

A simple, cost-efficient green synthesis has been reported in the present study to synthesise and study the antimicrobial activity of the Piper longum assisted magnesium oxide nanoparticles (MgO-NPs). The MgO nanoparticles were prepared by co-precipitation method and characterised by x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and ultraviolet visible absorption spectroscopy (UV-vis), energy dispersive x-ray (EDX) and transmission electron microscopy (TEM) analysis. The XRD study represents the FCC lattice of MgO- NPs. The adsorption of polyphenols and proteins in the P.longum extract on the surface of the prepared MgO-NPs was identified by FTIR. HR-TEM shows spherical particles with average size 22.67 nm due to the sufficient amount of capping. The energy band gap for MgO-NPs was found to be 5.1 eV. The optical studies indicate the quantum confinement effect of magnesium oxide NPs prepared with increasing concentration of Piper longum. The results indicated that small particle sized MgO-NPs have improved antimicrobial activity towards Pseudomonas aeruginosa, Staphylococcus aureus and Aspergillus flavus. The functional activities of the Piper longum assisted magnesium oxide NPs were influenced largely by the particle size. The obtained results revealed that the green synthesised MgO-NPs demonstrated assuring biomedical potentials.

Effects of “nine steaming nine sun-drying” on proximate composition, protein structure and volatile compounds of black soybeans

Nine steaming nine sun-drying is a traditional processing technology for food or medicinal materials. The dynamic changes of the proximate composition, protein structure and volatile compounds during nine-time steaming and sun-drying of black soybeans (BS) were studied. The proximate composition results showed that the content of protein, carbohydrate and fat of BS decreased after processing, whereas the relative content of amino acids remained basically unchanged. Protein structure was evaluated using Fourier transform infrared spectroscopy (FT-IR), Ultraviolet absorption spectroscopy (UV) and Fluorescence spectroscopy. FT-IR result revealed that the relative contents of β-sheet and β-turn of the secondary structure of black soybean protein isolate (BSPI) decreased but the relative contents of α-helix and random coil increased after steaming and sun-drying. The results of UV and fluorescence spectroscopy confirmed changes in the protein conformation. In addition, SPME-GCMS analysis demonstrated that hydrocarbons, alcohols and aldehydes were the main volatile compounds. The relative contents of 1-octen-3-ol and hexanal, which are the main sources of beany flavor decreased significantly compared with raw BS. Principal component analysis (PCA) results showed that the volatile compounds of nine steamed and nine sun-dried BS could be well distinguished during the process. These findings may therefore provide a scientific basis for the application of nine-time steamed and sun-dried BS in food industry and contribute to the understanding of process-induced chemical transformations in this ancient processing technique.

Molecular interactions of esculin with bovine serum albumin and recognition of binding sites with spectroscopy and molecular docking

Esculin is structurally a hydroxycoumarin found in various medicinal plants. This study investigates the binding mode of esculin with bovine serum albumin by employing numerous spectroscopic studies and molecular docking approaches. Ultraviolet absorption spectroscopy revealed ground state complex formation between esculin and bovine serum albumin. At the same time, steady-state fluorescence studies showed quenching in the fluorescence emission spectra of BSA in the presence of esculin. To get insight into the location of the binding pocket of esculin on BSA, warfarin and ibuprofen site markers were used. Competitive site marker displacement assay revealed that esculin binds to Sudlow’s site I (subdomain IIA) in bovine serum albumin. Thermodynamic parameters suggested that hydrogen bonding and van der Waals interaction stabilizes the esculin-BSA complex. Förster's non-radiation energy transfer analysis described the high propensity of energy transfer between bovine serum albumin and esculin. The molecular docking approach facilitated locating the binding pocket, amino acid residues involved, types of interacting forces, and binding energy (ΔG) between esculin and BSA. Circular dichroism revealed the effect of the binding of esculin on the secondary structure and helped understand the thermal unfolding profile of BSA in the presence of esculin. Communicated by Ramaswamy H. Sarm

Exploring the underlying mechanisms on NaCl-induced reduction in digestibility of myoglobin

In this paper, the structural changes of myoglobin after salt treatment and the binding mode of substrate and pepsin/trypsin were studied by ultraviolet absorption spectroscopy, synchronous fluorescence spectroscopy, LC-MS/MS and molecular dynamics simulation. NaCl treatment changed the heme structure and hydrophobic cavity of myoglobin, which in turn decreased the digestibility of the protein. Trypsin was more effective for digestion of high molecular weight peptides. Molecular dynamics simulation showed that the binding of myoglobin and pepsin/trypsin was mainly maintained by hydrogen bond and hydrophobicity. In addition, the catalytic active center of pepsin is not suitable for long-time existence of low-molecular weight peptide under salt treatment. The findings provide a new insight into the low bioavailability of myoglobin.

Green synthesis of highly stable zero-valent iron nanoparticles for organic dye treatment using Cleistocalyx operculatus leaf extract

Zero-valent iron nanoparticles are considered promising nanomaterials for wastewater treatment. However, the use of highly toxic and expensive chemicals such as sodium borohydride during synthesis has significantly limited the broad application of zero-valent iron. In this study, zero-valent iron nanoparticles (nZVI) were facilely and friendly synthesized using Cleistocalyx operculatus leaf extract as a reducing agent. The morphology and structure of the as-prepared nanomaterials were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) analysis. The obtained product was spherical with an average diameter of approximately 100 nm. The prepared nZVI exhibited remarkably stable stability, which remained in the nZVI form for more than one month in open air. The removal efficiency of rhodamine B (RhB) by nZVI reached over 95% in 30 min, proving that the nZVI nanomaterials exhibited a high and quick degradation performance toward RhB. The RhB removal efficiency of nZVI, which was proportional to the amount of nZVI and influenced by pH conditions, was determined using the visible ultraviolet absorption spectroscopy.

Experimental study of nonlinear phenomenon of NO ultraviolet broadband absorption spectroscopy

Ultraviolet broadband absorption spectroscopy (UV-BAS) has been widely used to measure the concentration of gas pollutant, such as NO. However, the nonlinear dependence of the absorbance on the optical thickness (<i>XL</i>) caused by the broadening effect of instrument function is observed. In this paper, the nonlinear behavior of NO absorbance is investigated both theoretically and experimentally, and a database using a polynomial to describe the nonlinearity is established to present a simple method of measuring NO concentration. First, the nonlinear relationship between absorbance and <i>XL</i> is deduced. Second, the nonlinearity of an isolated spectral line is simulated, and the dependence of nonlinear behavior on instrument width is investigated. Third, the nonlinerities of peak absorbance in <i>γ</i> (0, 0) band with different instrumental widths are calculated, the nonlinear expression is given in a polynomial form, and the corresponding coefficient database is established. In addition, the nonlinearities in different vibration bands with the same instrumental width are compared with each other. Finally, two spectrometers are used to measure NO absorption spectra in different instrumental widths in order to validate the above-mentioned results of theoretical analysis. The relative error between the measured peak absorbance and theoretical calculation is less than 4%, and that between experimental results and the interpolation polynomial results is less than 8%. The experimental results demonstrate the accuracy of theoretical calculation and the reliability of database.

Quantification of C5-PFK Gas Mixture Based on Ultraviolet Differential Optical Absorption Spectroscopy (UV-DOAS)

C5 perfluoroketone (C5-PFK) has recently attracted attention as an ecofriendly gas insulating medium. Its concentration plays a key role in the dielectric strength of the gas mixture. Currently, there is no relevant detection method for C5-PFK concentration for engineering applications. Herein, we explore the spectral absorption curve of the C5-PFK molecule based on the density functional theory (DFT). A quantitative detection technology for C5-PFK concentration using ultraviolet differential optical absorption spectroscopy (UV-DOAS) is proposed for the first time. The calibration curve determined by the standard concentration of C5-PFK gas demonstrated high linearity with a linear determination coefficient (<inline-formula> <tex-math notation="LaTeX">${R}^{{2}}$ </tex-math></inline-formula>) above 0.9999. We also find that with this technique, the relative error of the concentration of C5-PFK in the gas mixture prepared by the Dalton partial pressure method, and that of the calibration curve, which can reach 8.1&#x0025;, can be determined. With the gas supplement and detection method proposed in this study, the accuracy of the partial pressure method is similar to that of the gravimetric method. The results of this article could guide the rapid preparation of the C5-PFK gas mixture and the online monitoring of C5-PFK concentration changes in engineering applications.

Synchronic measurements of temperatures and concentrations of OH, NH, and NO in flames based on broadband ultraviolet absorption spectroscopy

Temperature is an important parameter influencing the combustion reaction path and rate and determining the combustion and energy exchange efficiency. The OH, NH, NO and other species are involved in the key elementary reactions of combustion and determine the generation of NO&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt; pollutants. Therefore, temperature and concentration measurements of OH, NH, and NO are of great significance for combustion diagnostics and research on reaction or emission mechanisms. In this work, a measurement system with high spatial resolution based on broadband ultraviolet absorption spectroscopy is established to realize simultaneous measurements of the temperature and concentrations of OH, NH, and NO in flames. Low detection limits of these three species are achieved by using the established measurement method. The 1&lt;i&gt;σ&lt;/i&gt; detection limit of NH is 1.8 ppb·m (1560 K), which is realized for the first time in atmospheric-pressure flames using absorption spectroscopy. The 1&lt;i&gt;σ&lt;/i&gt; detection limits of OH and NO are 60 ppb·m (1590 K) and 1 ppm·m (1380 K), respectively, which are obviously better than the existing results obtained by using infrared laser absorption spectroscopy. Then, the distributions of temperatures and concentrations of OH, NO and NH are acquired at various heights in an atmospheric-pressure NH&lt;sub&gt;3&lt;/sub&gt;/CH&lt;sub&gt;4&lt;/sub&gt;/air premixed flat flame with a high spatial resolution of nearly 0.1 mm. The broadband absorption spectra of OH and NH are acquired simultaneously inside the flame front, and the spectra of OH and NO are acquired simultaneously above the flame front. Inside or near the flame front, the temperatures deduced from the spectra of OH, NH, and NO are consistent, verifying the ability of these three species to be used to measure temperature. In addition, OH, NH, and NO are found to be suitable for different regions in combustion. The OH absorption is suitable for the post-combustion region with temperatures higher than 1000 K, the NH absorption can be used to acquire the temperature inside the flame front in complex combustion, and the NO absorption was able to provide the temperature in the region before or outside combustion at lower temperatures. Additionally, the experimental temperature and concentration profiles are in good agreement with the computational fluid dynamics predictions based on the mechanism, exhibiting the accuracy of the simultaneous temperature and concentration measurements by using broadband ultraviolet absorption spectra. Moreover, the differences in temperature and OH concentration between experiments and simulations indicate that the carbon sub-mechanism in the mechanism given by Okafor et al. [Okafor E C, Naito Y, Colson S, Ichikawa A, Kudo T, Hayakawa A, Kobayashi H &lt;ext-link ext-link-type="uri" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://doi.org/10.1016/j.combustflame.2017.09.002"&gt;2018 &lt;i&gt;Combust. Flame&lt;/i&gt; &lt;b&gt;187&lt;/b&gt; 185&lt;/ext-link&gt;] should be further improved for more accurate predictions of NH&lt;sub&gt;3&lt;/sub&gt;/CH&lt;sub&gt;4&lt;/sub&gt; combustion.

Photothermal effect of nano-copper sulfide against tongue squamous cell carcinoma

To investigate the anti-tumor effect of BSA@CuS-PEG nanocomposites on tongue squamous cell carcinoma. Transmission electron microscopy, dynamic light scattering, Zeta potential and ultraviolet absorption spectroscopy were used to characterize the synthesized BSA@CuS-PEG nanocomposite, whose photothermal properties was assessed with near infrared Ⅱ region excitation light (1064 nm). The cytotoxicity of the nanocomposite in Cal27 and SCC9 cells was evaluated using CCK-8 assay, and its effect on cell cycle distribution was analyzed using flow cytometry. The in vivo antitumor effect of BSA@CuS-PEG was investigated in a Balb/c mouse model bearing subcutaneous Cal27 tumor xenograft. The synthesized BSA@CuS-PEG nanocomposite showed a temperature variation (ΔT) of about 30 ℃ under near-infrared (NIR) irradiation (0.5 W/cm2), suggesting its excellent photothermal sensitivity. CCK-8 assay showed that BSA@CuS-PEG had no significant toxicity to tumor cells, but upon NIR irradiation, the nanocomposite produced a significant stronger inhibitory effect on Cal27 and SCC9 cells than free nanocomposites (P < 0.001). Cell cycle analysis showed that compared with free nanocomposites, BSA@CuS-PEG plus NIR irradiation caused more obvious cell cycle arrest at G2/M phase in tongue cancer cells (P < 0.001). In the tumor-bearing mice, BSA@CuS-PEG combined with NIR irradiation produced a significant anti-tumor effect as compared with saline treatment plus NIR irradiation (P < 0.001). The BSA@CuS-PEG nanocomposite shows prominent photothermal properties and good anti-tumor effects both in vivo and in vitro, and thus provides a promising method for non-invasive early diagnosis and non-surgical treatment of primary tongue cancer.

Fischer–Tropsch synthetic wastewater treatment with Fe/Mn@CH: Catalytic ozonation and process evaluation

• Fe-Mn@CH with high catalytic activity was prepared. • The organic matter is transformed into protein-like and tryptophan-like substances. • Ozone catalytic oxidation process is closer to the secondary reaction kinetics. • A multi-level-gray relational evaluation model is established. In this study, the honeycomb ceramic catalyst Fe/Mn@CH with high catalytic activity was prepared. The effect of preparation conditions on the catalytic performance of Fe/Mn@CH was systematically studied. Scanning electron microscope; X-ray energy spectrum analysis; X-ray diffraction; specific surface area, pore distribution and adsorption performance analysis; X-ray fluorescence spectroscopy; and X-ray photoelectron spectroscopy were performed to analyze the structural characteristics of the catalyst. The optimal working conditions of the catalytic ozonation system for the degradation of Fischer–Tropsch synthesis wastewater were also studied. The metal elements Fe and Mn were successfully loaded on the surface of the honeycomb ceramic carrier in the form of α-MnO 2 and α-Fe 2 O 3 oxides. The optimal COD removal rate could reach 64.37% at pH of 9, ozone dosage of 6 g/h, Fe/Mn@CH dosage of 50 g/300 mL, and reaction time of 60 min. The specific mechanism of catalytic ozonation in the presence of tert -butanol was explored through ultraviolet absorption spectroscopy and three-dimensional fluorescence spectroscopy. The COD removal efficiency for Fischer–Tropsch synthesis wastewater was analyzed on the basis of catalytic oxidation reaction kinetics. Finally, a multilevel gray correlation evaluation model was established for the quantitative evaluation of the ozonation catalytic oxidation of Fischer–Tropsch wastewater.

Effect of Cu doping on the optical property of green synthesised l-cystein-capped CdSe quantum dots

Abstract In the present study, the synthesis of water-soluble copper-doped CdSe nanoparticles (NPs) via a low cost, facile, and environmentally benign method is reported. Simple reagents such as selenium powder, cadmium chloride, and copper sulphate were used as selenium, cadmium, and copper precursor, respectively, while l-cysteine was used as a capping ligand without the use of an additional stabiliser. The as-synthesised copper-doped CdSe NPs were characterised using ultraviolet (UV-Vis) absorption and photoluminescence (PL) spectroscopy, Fourier-transform infrared spectroscopy, and transmission electron microscopy. By varying the dopant concentration, the temporal evolution of the optical properties and the shape of the nanocrystals were investigated. The observation and the results showed that the colour of the solution changed rapidly from orange to black, and the PL shifted to a longer wavelength at the high dopant concentration. The micrographic images revealed that the as-synthesised materials are small and could be used for bio labelling.

Carrier-Specific Hot Phonon Bottleneck in CH3NH3PbI3 Revealed by Femtosecond XUV Absorption.

Femtosecond carrier cooling in the organohalide perovskite semiconductor CH3NH3PbI3 is measured using extreme ultraviolet (XUV) and optical transient absorption spectroscopy. XUV absorption between 44 and 58 eV measures transitions from the I 4d core to the valence and conduction bands and gives distinct signals for hole and electron dynamics. The core-to-valence-band signal directly maps the photoexcited hole distribution and provides a quantitative measurement of the hole temperature. The combination of XUV and optical probes reveals that upon excitation at 400 nm, the initial hole distribution is 3.5 times hotter than the electron distribution. At an initial carrier density of 1.4 × 1020 cm-3 both carriers are subject to a hot phonon bottleneck, but at 4.2 × 1019 cm-3 the holes cool to less than 1000 K within 400 fs. This result places significant constraints on the use of organohalide perovskites in hot-carrier photovoltaics.

Polymer thin films as universal substrates for extreme ultraviolet absorption spectroscopy of molecular transition metal complexes.

Polystyrene and polyvinyl chloride thin films are explored as sample supports for extreme ultraviolet (XUV) spectroscopy of molecular transition metal complexes. Thin polymer films prepared by slip-coating are flat and smooth, and transmit much more XUV light than silicon nitride windows. Analytes can be directly cast onto the polymer surface or co-deposited within it. The M-edge XANES spectra (40-90 eV) of eight archetypal transition metal complexes (M = Mn, Fe, Co, Ni) are presented to demonstrate the versatility of this method. The films are suitable for pump/probe transient absorption spectroscopy, as shown by the excited-state spectra of Fe(bpy)32+ in two different polymer supports.

Removal of correlated background in a high-order harmonic transient absorption spectra with principal component regression.

We demonstrate a 40x mean noise power reduction (NPR) in core-to-valence extreme ultraviolet (XUV) femtosecond transient absorption spectroscopy with a high harmonic generation (HHG) light source. An adaptive iteratively reweighted principal component regression (airPCR) is used to analyze and suppress spectrally correlated HHG intensity fluctuations. The technique requires significantly less user input and leads to a higher mean NPR than a previously introduced edge-pixel PCR method that relies on the manual identification of signal-free spectral regions. Both techniques are applied in a time-resolved XUV absorption study of the 2snp1Po (n ≥ 2) autoionizing Rydberg states of helium, demonstrating sub-10-3 optical density sensitivity.

Optical and upconversion properties of bismuth tellurite glasses Co-doped with Er3+-Yb3+ ions

Heavy glass system (HGS) with batch compositionsTeO2-Bi2O3-Na2O co-doped with rare earth ions Er2O3&Yb2O3 are synthesized by melt- quench and press method. The batch composition is taken (80-x-y)%TeO2-10%Bi2O3-10%Na2O-x%Er2O3-y%Yb2O3 where (x, y) are (0.1, 0) and (0.5, 0.5). Thermal study of the synthesized sample is done by Differential Scanning Calorimetry (DSC). Amorphous nature of samples is characterized by X-Ray diffractogram. Heaviness of the samples justifies by the calculated densities of the glass samples. For the study of optical properties, Refractive index (R.I.), Optical energy gap (Eg), Urbach’s energy (Eu) absorption spectroscopy in ultra violet –visible-Infrared (UV–VIS-IR) region is carried. For upconversion (UC) characteristics photoluminescence spectroscopy studied.

Quantitative imaging of KOH vapor in combustion environments using 266 nm laser-induced photofragmentation fluorescence

In biomass thermal conversion processes, the release of potassium in high temperature environments crucially influences the operating efficiency and safety. The dominant potassium species can be potassium hydroxide (KOH) and/or potassium chloride (KCl). We report a species-specified quantitative measurement of potassium hydroxide (KOH) in combustion environments using laser-induced photofragmentation fluorescence (LIPF). Ultraviolet (UV) light sources with different wavelengths (193, 213 and 266 nm) were investigated to select a proper source ensuring that the excited potassium atoms in the 42P state could be only generated from the KOH molecules, not another major potassium compound, potassium chloride (KCl), and emit fluorescence at 766/769 nm after the photodissociation. After direct comparison, the fourth-harmonic of Nd:YAG laser at 266 nm was found to be the most proper light source. The fluorescence signal was strongly influenced by temperature as KOH molecules at thermally populated excited vibrational levels were needed to produce excited potassium atoms after the 266 nm photolysis. After the calibration using broadband UV absorption spectroscopy, the detection limit of the LIPF planar imaging system was determined to be about 3 ppm at 1750 K under a harsh condition, where about 80% of the fluorescence was re-absorbed by the potassium atoms present in the background gas. The technique was applied to quantitatively measure KOH concentration in the hot flue gasses provided by potassium carbonate seeded flames with varying equivalence ratios, and it was also used to visualize the distribution of KOH vapor above a piece of burning wood char.

Determination of vacuum ultraviolet detector response factors by hyphenation with two-dimensional comprehensive gas chromatography with flame ionization detection.

Two-dimensional comprehensive gas chromatography is an established technique, employed for the characterization of complex samples. Broadband vacuum ultraviolet absorption spectroscopy detection has recently attracted a lot of attention as it is a universal detection technique characterized by good selectivity but also ease of use and amenability to coupling with two-dimensional comprehensive gas chromatography. Vacuum ultraviolet spectroscopy is particularly interesting due to the possibility of performing spectral decomposition for species that coelute in gas chromatography analysis. This detector has quantitative capabilities, however not all species absorb vacuum ultraviolet radiation the same. Unfortunately, vacuum ultraviolet relative response factors for compounds are not always available. Methods to rapidly measure vacuum ultraviolet relative response factors and generate a large database that would allow calibration free quantitative analysis of complex mixtures are therefore of great interest. In this work, a universal methodology that permits rapid measurement of vacuum ultraviolet relative response factors is reported. It involves flow modulated two-dimensional comprehensive gas chromatography with dual vacuum ultraviolet and flame ionization detection. In this set-up, flame ionization detection is employed as a quantitative reference allowing to scale vacuum ultraviolet responses of investigated compounds. This approach was validated by flow measurements and by comparing relative response factors obtained for model compounds with literature data.

Coupled valence carrier and core-exciton dynamics in WS2 probed by few-femtosecond extreme ultraviolet transient absorption spectroscopy

Few-femtosecond extreme ultraviolet (XUV) transient absorption spectroscopy, performed with optical 500-1000 nm supercontinuum and broadband XUV pulses (30-50 eV), simultaneously probes dynamics of photoexcited carriers in WS$_{2}$ at the W O$_3$ edge (37-45 eV) and carrier-induced modifications of core-exciton absorption at the W N$_{6,7}$ edge (32-37 eV). Access to continuous core-to-conduction band absorption features and discrete core-exciton transitions in the same XUV spectral region in a semiconductor provides a novel means to investigate the effect of carrier excitation on core-exciton dynamics. The core-level transient absorption spectra, measured with either pulse arriving first to explore both core-level and valence carrier dynamics, reveal that core-exciton transitions are strongly influenced by the photoexcited carriers. A $1.2\pm0.3$ ps hole-phonon relaxation time and a $3.1\pm0.4$ ps carrier recombination time are extracted from the XUV transient absorption spectra from the core-to-conduction band transitions at the W O$_{3}$ edge. Global fitting of the transient absorption signal at the W N$_{6,7}$ edge yields $\sim 10$ fs coherence lifetimes of core-exciton states and reveals that the photoexcited carriers, which alter the electronic screening and band filling, are the dominant contributor to the spectral modifications of core-excitons and direct field-induced changes play a minor role. This work provides a first look at the modulations of core-exciton states by photoexcited carriers and advances our understanding of carrier dynamics in metal dichalcogenides.