Attenuated Total Reflection Fourier Transform Infrared Measurements Research Articles

Detection of meloxicam residues in milk using ATR- FTIR spectroscopy coupled with chemometrics

Meloxicam (MELX), a non-steroidal anti-inflammatory drug (NSAID), is frequently administered to cattle, poses a risk to human health when it is found in milk. Regulatory bodies of EU, Canada, China and India have prescribed maximum residue limits for MELX in milk as 15, 35 and 15 and 10 μg/kg, respectively. This study explores the use of attenuated total reflectance- Fourier transform infrared (ATR-FTIR) spectroscopy in conjunction with chemometric techniques to detect MELX residues in milk. Samples of pure milk and milk samples spiked with MELX at different concentrations ranging from 1 to 50 μg/kg were analysed. ATR-FTIR measurements were taken in the wavenumber range of 4000–400 cm−1 for all the samples. Principal component analysis (PCA) was applied in the regions of 2940–2840 and 1765–1730 cm−1 to differentiate clusters of milk sample with those of MELX and milk spiked with MELX samples. The coefficient of determination (R2) values for calibration and validation sets in wavenumber regions of 2940–2840 and 1765–1730 cm−1 were >0.92 and > 0.94, respectively for the developed partial least squares regression (PLSR) models. All the samples showed 100% classification efficiency using the soft independent modeling of class analogy (SIMCA) technique. The study concluded that the presence of MELX residues can be detected in milk even at 1 μg/kg level using ATR-FTIR and chemometrics. Results obtained from developed FTIR based chemometric method were in agreement with those obtained from LC-MS/MS method and have the potential for application in screening milk samples for the presence of MELX.

Estimation of time since deposition of semen stain on different fabric types using ATR-FTIR spectroscopy and chemometrics

Various body fluids such as blood, semen, vaginal secretions, and saliva are frequently encountered at crime scene. In cases of sexual assault, semen stains are one of the most reliable evidence of biological origin. In this study, our objective was to develop a method for estimating the time since deposition of semen stains on five different fabric types using Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) Spectroscopy, with a focus on a time frame of up to 8 weeks. Semen samples from six different volunteers were dripped onto five distinct fabric materials, and ATR-FTIR measurements were obtained at 17 different time points. Principal component analysis (PCA) and partial least squares (PLS) methods were employed to differentiate semen stains on various fabric samples and estimate the age of semen stains. Models constructed using PCA and PLSR achieved high R2 values and low root-mean-square error (RMSE). While the performance varies depending on fabric types, it was observed that age estimation of semen stains can be made within following intervals: 0.39–0.76 days for 0–7 day range, 2.59–3.38 days for the 1–8 week range, and 3.98–8.1 days for the 0–56 day range. This study demonstrates the effectiveness of using ATR-FTIR spectroscopy in combination with chemometrics to estimate the age of human semen stains on various fabric types based on time-dependent spectral changes.

Real-Time Infrared Spectroscopic Measurement of Natural Moisturizing Factor

Real-Time Infrared Spectroscopic Measurement of Natural Moisturizing Factor

Arrangement of Hydrogen Bonds in Aqueous Solutions of Different Globular Proteins.

This work presents the first evidence that dissolved globular proteins change the arrangement of hydrogen bonds in water, with different proteins showing quantitatively different effects. Using ATR-FTIR (attenuated total reflection—Fourier transform infrared) spectroscopic analysis of OH-stretch bands, we obtain quantitative estimates of the relative amounts of the previously reported four subpopulations of water structures coexisting in a variety of aqueous solutions. Where solvatochromic dyes can measure the properties of solutions of non-ionic polymers, the results correlate well with ATR-FTIR measurements. In protein solutions to which solvatochromic dye probes cannot be applied, NMR (nuclear magnetic resonance) spectroscopy was used for the first time to estimate the hydrogen bond donor acidity of water. We found strong correlations between the solvent acidity and arrangement of hydrogen bonds in aqueous solutions for several globular proteins. Even quite similar proteins are found to change water properties in dramatically different ways.

New approaches with ATR-FTIR, SEM, and contact angle measurements in the adaptation to extreme conditions of some endemic Gypsophila L. taxa growing in gypsum habitats

Gypsophila L. taxa growing on gypsum soils have to withstand limiting and restrictive conditions for plant life. This study aims to identify functional mechanisms determine the main functional groups in the vegetative and reproductive organs of some endemic Gypsophila taxa growing in gypsum soils, as well as to understand the relationship between the hidrophobicities and their micromorphological structures of the leaves of these plants grown in arid conditions. In this context, a series of Attenuated Total Reflection-Fourier Transform Infrared (ATR-FTIR), water contact angle (CA) measurements, and scanning electron microscopy (SEM) analyses were performed that may help to understand the survival mechanisms of Gypsophila eriocalyx Boiss., Gypsophila germanicopolitana Hub.-Mor. and Gypsophila simonii Hub.-Mor. growing in gypsum habitats. Our results showed the presence of O-H and C-O stretching bands belong to gypsum and calcium oxalate in the roots, stems, leaves and flowers of Gypsophila taxa is thought to be a way of tolerating the excess Ca and sulphate in the extreme habitat where these species grow. Leaves of Gypsophila taxa showed CAs above 90°, which indicates that G. eriocalyx, G. germanicopolitana, and G. simonii were hydrophobic. This study offers new approaches to understanding the adaptation of Gypsophila taxa to the extreme conditions typical of gypsum soils. The characterization of gypsum plants such as Gypsophila taxa, whose mechanisms for competition and survival on gypsum are still not fully understood, is very important in terms of shedding light on the adaptation of endemic plants to gypsum habitats.

Thin Film Mixed Matrix Hollow Fiber Membrane Fabricated by Incorporation of Amine Functionalized Metal-Organic Framework for CO2/N2 Separation.

Membrane separation technology can used to capture carbon dioxide from flue gas. However, plenty of research has been focused on the flat sheet mixed matrix membrane rather than the mixed matrix thin film hollow fiber membranes. In this work, mixed matrix thin film hollow fiber membranes were fabricated by incorporating amine functionalized UiO-66 nanoparticles into the Pebax® 2533 thin selective layer on the polypropylene (PP) hollow fiber supports via dip-coating process. The attenuated total reflection-Fourier transform infrared (ATR-FTIR), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX) mapping analysis, and thermal analysis (TGA-DTA) were used to characterize the synthesized UiO-66-NH2 nanoparticles. The morphology, surface chemistry, and the gas separation performance of the fabricated Pebax® 2533-UiO-66-NH2/PP mixed matrix thin film hollow fiber membranes were characterized by using SEM, ATR-FTIR, and gas permeance measurements, respectively. It was found that the surface morphology of the prepared membranes was influenced by the incorporation of UiO-66 nanoparticles. The CO2 permeance increased along with an increase of UiO-66 nanoparticles content in the prepared membranes, while the CO2/N2 ideal gas selectively firstly increased then decreased due to the aggregation of UiO-66 nanoparticles. The Pebax® 2533-UiO-66-NH2/PP mixed matrix thin film hollow fiber membranes containing 10 wt% UiO-66 nanoparticles exhibited the CO2 permeance of 26 GPU and CO2/N2 selectivity of 37.

Reagent-free total protein quantification of intact extracellular vesicles by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy

Extracellular vesicles (EVs) are lipid bilayer–bounded particles that are actively synthesized and released by cells. The main components of EVs are lipids, proteins, and nucleic acids and their composition is characteristic to their type and origin, and it reveals the physiological and pathological conditions of the parent cells. The concentration and protein composition of EVs closely relate to their functions; therefore, total protein determination can assist in EV-based diagnostics and disease prognosis. Here, we present a simple, reagent-free method based on attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy to quantify the protein content of EV samples without any further sample preparation. After calibration with bovine serum albumin, the protein concentration of red blood cell–derived EVs (REVs) were investigated by ATR-FTIR spectroscopy. The integrated area of the amide I band was calculated from the IR spectra of REVs, which was proportional to the protein quantity in the sample‚ regardless of its secondary structure. A spike test and a dilution test were performed to determine the ability to use ATR-FTIR spectroscopy for protein quantification in EV samples, which resulted in linearity with R2 values as high as 0.992 over the concentration range of 0.08 to 1 mg/mL. Additionally, multivariate calibration with the partial least squares (PLS) regression method was carried out on the bovine serum albumin and EV spectra. R2 values were 0.94 for the calibration and 0.91 for the validation set. The results indicate that ATR-FTIR measurements provide a reliable method for reagent-free protein quantification of EVs.Graphical abstract

Exploring water and ion transport process at silicone/copper interfaces using in-situ electrochemical and Kelvin probe approaches

In general, packaging materials which encapsulate light emitting diodes (LEDs) and microelectronic devices offer barrier protection against several environmental hazards such as water and ionic contaminants. However, these encapsulants may provide pathways for water and ionic contaminants to reach the metal/polymer interfaces and provoke local corrosion of electronics, which is a major reliability concern for polymer encapsulated LEDs and microelectronics. As the water and corrosive constituents play a crucial role in their reliability, water uptake kinetics, interfacial ion transport and delamination behaviour of silicone coated copper model system, mimicking a typical microelectronics packaging system, is explored in the present work. Electrochemical impedance spectroscopy (EIS) integrated with attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy studies revealed that water diffusion inside the silicone network is Fickian in nature and the evolution of the observed time constants are related to the diffusion and interfacial reactions. A decrease of impedance magnitude with time was observed in EIS measurements concurrently with water absorption bands shifting towards lower wavenumber in ATR-FTIR measurements, implying the growth of strong hydrogen bonding between water molecules and the silicone network. The estimated diffusion constant of water using the capacitance method was in the order of 7 × 10-12 m2 s−1 and the water absorption volume fraction was in the range of 0% to 0.30%. Scanning Kelvin probe studies elucidated the ion transport process occurring at the silicone/copper interface in a humid atmosphere. The interfacial ion transport process is controlled by the interfacial electrochemical reactions at the cathodic delamination front and the estimated average delamination rate is 0.43 mm h-1/2. This work demonstrates that exploring ion and water transport in the silicone coating and along the silicone/copper interface is of pivotal importance as part of a detailed reliability assessment of the polymer encapsulated LEDs and microelectronics.

Determining surface chemical composition of silver nanoparticles during sulfidation by monitoring the ligand shell.

Evaluating the surface and core compositions of transforming nanoparticles (NP) represents a significant measurement challenge but is necessary for predicting performance in applied systems and their toxicity in natural environments. Here, we use X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy to characterize both the surface and core ofpolyvinyl pyrollidone-silver nanoparticles in the presence of two Suwannee River fulvic acid (FA) standards and humic acid (HA) during sulfidation, the predominant transformation pathway in environmental systems. Only by using data from both spectroscopic methods was a clear relationship established between AgNP core composition and FA affinity established, where concomitant loss of FA was observed with Ag2S formation. Using XPS to measure AgNP surface composition, overlapping trends from XPS on FA I desorption from the AgNP surface as function of surface sulfidation were observed with FA II in the ATR-FTIR measurements. The reproducibility of the changing heterogeneous coating as a function of AgNP sulfidation provided a transferable method to determine the extent of Ag sulfidation without further need for the high resolution, high cost measurement tools that underpinned validation of the method. The relationship was not observed for HA, where a lower affinity to the AgNP surface was observed, suggesting distinct binding to the NP.

Photophysics, TiO2 sensitization and photovoltaic performance of Zn-ProtoporphyrinIX

Chlorophylls are playing an important role in natural photosynthesis. Hence, in the present investigation, a chlorophyll analogue Zn-Protoporphyrin IX (ZnPPIX) was selected for dye sensitized solar cell applications. The properties of ZnPPIX were fully investigated by optical spectroscopy, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), density functional theory (DFT) calculations, electrochemical and photovoltaic measurements. The optical and electrochemical HOMO-LUMO gaps were consistent with those estimated by PBE functional. The nature of the binding of ZnPPIX onto the TiO2 surface was investigated using ATR-FTIR and XPS measurements. The amount of adsorbed ZnPPIX on TiO2 surface was reasonably fit using the Langmuir adsorption isotherm, with a binding constant value of 25,800 M−1. The power conversion efficiency of ZnPPIX is smaller than those of reference cell under the optimized conditions (η = 0.6% for ZnPPIX; η = 6.3% for N3).

Area-selective epoxy coatings by DBD-PECVD in 3D cavities for protein coupling

Biofunctional coatings containing epoxy groups coatings were deposited on selective areas on the inner surfaces of three-dimensional (3D) cavities using a chemical vapor deposition process activated by a dielectric barrier discharge. The binding capacity of plasma polymers to proteins was analyzed. The chemical functionalization was carried out using glycidyl methacrylate as a precursor. Thin coatings with a high density of epoxy groups were achieved which form the basis to bind proteins. Using a specially developed electrode, geometry coatings were deposited in the form of four parallel rectangular bands of identical dimensions along the inner surface of a polypropylene syringe. The chemical composition was analyzed by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. To prove the reactivity of the coatings, these were exposed to hydrochloric acid vapors which cause an opening of the ring of the epoxy group. Resulting OH groups were also determined by the ATR-FTIR measurements. For evaluation, samples were incubated in bovine serum albumin solution and afterward colored by Coomassie Brilliant Blue G-250. Proteins, immobilized on the coating, were detected by an immunoglobulin G antibody coupled with horseradish peroxidase. Visualization was performed by using 3,3′,5,5′-tetramethylbenzidine solution. The results show a great potential of atmospheric-pressure plasma processes for generating chemically reactive area-selective coatings on 3D substrates to achieve a coupling of biomolecules to polymer surfaces.

Interfacial nanobubbles are leaky: permeability of the gas/water interface.

Currently there is no widespread agreement on an explanation for the stability of surface nanobubbles. One means by which several explanations can be differentiated is through the predictions they make about the degree of permeability of the gas-solution interface. Here we test the hypothesis that the gas-solution interface of surface nanobubbles is permeable by experimental measurements of the exchange of carbon dioxide. We present measurements by attenuated total reflection Fourier transform infrared (ATR-FTIR) and atomic force microscopy (AFM), demonstrating that the gas inside surface nanobubbles is not sealed inside the bubbles, but rather exchanges with the dissolved gas in the liquid phase. Such gas transfer is measurable by using the infrared active gas CO2. We find that bubbles formed in air-saturated water that is then perfused with CO2-saturated water give rise to distinctive gaseous CO2 signals in ATR-FTIR measurements. Also the CO2 gas inside nanobubbles quickly dissolves into the surrounding air-saturated water. AFM images before and after fluid exchange show that CO2 bubbles shrink upon exposure to air-equilibrated liquid but remain stable for hours. Also air bubbles in contact with CO2-saturated water increase in size and Ostwald ripening occurs more rapidly due to the relatively high gas solubility of CO2 in water.

Removal of arsenate with hydrous ferric oxide coprecipitation: Effect of humic acid

Insights from the adverse effect of humic acid (HA) on arsenate removal with hydrous ferric oxide (HFO) coprecipitation can further our understanding of the fate of As(V) in water treatment process. The motivation of our study is to explore the competitive adsorption mechanisms of humic acid and As(V) on HFO on the molecular scale. Multiple complementary techniques were used including macroscopic adsorption experiments, surface enhanced Raman scattering (SERS), extended X-ray absorption fine structure (EXAFS) spectroscopy, flow-cell attenuated total reflectance Fourier transform infrared (ATR-FTIR) measurement, and charge distribution multisite complexation (CD-MUSIC) modeling. The As(V) removal efficiency was reduced from over 95% to about 10% with the increasing HA concentration to 25 times of As(V) mass concentration. The SERS analysis excluded the HA-As(V) complex formation. The EXAFS results indicate that As(V) formed bidentate binuclear surface complexes in the presence of HA as evidenced by an As-Fe distance of 3.26–3.31 Å. The in situ ATR-FTIR measurements show that As(V) replaces surface hydroxyl groups and forms inner-sphere complex. High concentrations of HA may physically block the surface sites and inhibit the As(V) access. The adsorption of As(V) and HA decreased the point of zero charge of HFO from 7.8 to 5.8 and 6.3, respectively. The CD-MUSIC model described the zeta potential curves and adsorption edges of As(V) and HA reasonably well.

Understanding the VOC sorption processes on fluoro alkyl substituted phthalocyanines using ATR FT-IR spectroscopy and QCM measurements

Abstract In this work the sorption of volatile organic compounds (VOCs) by phthalocyanines is studied and modelled using in situ attenuated total reflection (ATR) Fourier transform infrared (FT-IR) spectroscopy and gas sensor data. A series of fluoropropoxyphthalocyanines (Pcs) either in the metal free form or as nickel and cobalt complexes were synthesised and coated on quartz crystal microbalance and ZnSe ATR substrates as thin films with the jet spray technique. The VOCs for the gas exposure experiments were selected according to their physico-chemical properties such as acidity, basicity, polarity etc. The influence of the humidity on the interaction mechanism and the sensor signal was also investigated. The in detail analysis of the ATR FT-IR measurements revealed that the analytes interact mainly with the centre of the Pcs (a metal ion or N H group), the aromatic CH group of the Pc core, and the substituent group. The aromatic C H groups of the Pc core were identified as active centres for the first time and were found to play an active role in the sensing mechanism and determine the sensitivity of the sensors. They may interact with a π system of an analyte via H π bonding or with OH groups via hydrogen bonds.

Effect of annealing on self-organized gradient film obtained from poly(3-[tris(trimethylsilyloxy)silyl] propyl methacrylate-co-methyl methacrylate)/poly(methyl methacrylate-co-n-butyl acrylate) blend latexes

The effect of annealing on the self-organized morphology and component gradient distribution of films prepared from bimodal latexes blend containing 1:1 silicon-containing acrylate copolymer/silicon-free acrylate copolymer blend was studied using attenuated total reflectance–Fourier transform infrared (ATR-FTIR) spectroscopy, scanning electron microscopy with X-ray energy-dispersive (SEM-EDX) spectrometry, and atomic force microscopy (AFM). The distribution of silicon through the whole thickness of the film as a function of annealing was investigated using confocal Raman spectroscopy (CRS). AFM results show that poly(methyl methacrylate-co-n-butyl acrylate) latex fuses to form a continuous film at 25 °C. The wettability of the acrylate components and the heterogeneous composition of poly(3-[tris(trimethylsilyloxy)silyl] propyl methacrylate-co-methyl methacrylate) result in a graded block film. ATR-FTIR and SEM-EDX measurements reveal silicon-containing components segregate at the film–air interface upon annealing. CRS further shows that the nonlinear model gradient distribution of silicon is obtained, where the content of silicon component is enhanced and it gradually varies in the bulk. When the annealing temperature increases to 120 and 180 °C, blend latexes films demonstrate varying topography and phase images, indicating phase separation is induced by annealing. Furthermore, CRS implies that the destruction of the gradient structure is attributed to the phase separation of the two blend components.

Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy of a single endothelial cell

Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) with the use of a slide-on germanium accessory followed by chemometric analysis allowed for providing meaningful information about the biochemical composition of a single endothelial cell. In this work, the methodology of the ATR-FTIR measurements of dried cells and dried cells immersed in water solution is presented. The contact of the cell and Ge crystal was set up manually and monitored through the integration of the amide I band. Additionally, the cell imaging in transreflection mode was tested, but the spectral differences between sub-cellular structures were not prominent in the registered spectra. It has been shown that the ATR-FTIR method gives better results due to the increased spatial resolution and S/R ratio as well as small contribution of the optical artifacts.

Interfacial Orientation and Secondary Structure Change in Tachyplesin I: Molecular Dynamics and Sum Frequency Generation Spectroscopy Studies

Recent advances in the collection and interpretation of surface-sensitive vibrational spectroscopic measurements have made it possible to study the orientation of peptides and proteins in situ in a biologically relevant environment. However, interpretation of sum frequency generation (SFG) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) vibrational spectroscopy is hindered by the fact that orientation cannot be inferred without some prior knowledge of the protein structure. In this work, molecular dynamics simulations were used to study the interfacial orientation and structural deformation of the short β-sheet peptide tachyplesin I at the polystyrene/water interface. By combining these results with ATR-FTIR and SFG measurements, reasonable agreement was found with the simulation results, suggesting that tachyplesin I lies parallel to the surface, although the simulation results imply a broader distribution of peptide twist angles than could be characterized using available experimental measurements. The interfacial structure was found to be deformable even when disulfide bonds were preserved, and these local deviations from a purely extended β-sheet conformation may be of importance to future developments in the interpretation of SFG and ATR-FTIR spectra.

Aluminum Nanoparticles Capped by Polymerization of Alkyl-Substituted Epoxides: Ratio-Dependent Stability and Particle Size

We report here on the polymerization of epoxide monomers on incipient aluminum nanoparticle cores and the effects of changing the epoxide-capping precursor and the metallic monomer ratio on the resultant stability and particle size of passivated and capped aluminum nanoparticles. When altering the ratio of aluminum to cap monomer precursor, nanoparticles capped with epoxydodecane, epoxyhexane, and epoxyisobutane show a clear decreasing trend in stability with decreasing alkane substituent length. The nanoparticle core size was unaffected by cap ratio or composition. PXRD (powder X-ray diffraction) and DSC/TGA (differential scanning calorimetry/thermal gravimetric analysis) confirm the presence of successfully passivated face-centered cubic (fcc) aluminum nanoparticles. We also report preliminary results from ATR-FTIR (attenuated total reflectance-Fourier transform infrared), (13)C CPMAS (cross-polarization/magic-angle spinning), and (27)Al MAS solid-state NMR (nuclear magnetic resonance) measurements. The most stable aluminum nanoparticle-polyether core-shell nanoparticles are found at an Al:monomer mole ratio of 10:1 with an active Al(0) content of 94%.

Improving hydrophilicity and protein antifouling of electrospun poly(vinylidenefluoride-hexafluoropropylene) nanofiber membranes

Poly(vinylidenefluoride-hexafluoropropylene) (PVDF-HFP) nanofiber membranes with improved hydrophilicity and protein fouling resistance via surface graft copolymerization of hydrophilic monomers were prepared. The surface modification involves atmospheric pressure glow discharge plasma (APGDP) pretreatment followed by graft copolymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA). The success of the graft modification with PEGMA on the PVDF-HFP fibrous membrane is ascertained by X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance Fourier transform infrared measurements (ATR-FTIR). The hydrophilic property of the nanofiber membranes is assessed by water contact angle measurements. The results show that the PEGMA grafted PVDF-HFP nanofiber membrane has a water contact angle of 0° compared with the pristine value of 132°. The protein adsorption was effectively reduced after PEGMA grafting on the PVDF-HFP nanofiber membrane surface. The PEGMA polymer grafting density on the PVDF-HFP membrane surface is measured by the gravimetric method, and the filtration performance is characterized by the measurement of water flux. The results indicate that the water flux of the grafted PVDF-HFP fibrous membrane increases significantly with the increase of the PEGMA grafting density.

Increasing permittivity in HfZrO thin films by surface manipulation

We report on the electrical and physical characterization of nanoscale crystalline HfxZr1−xO2 films by x-ray diffraction (XRD) and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. Increasing the ZrO2 content generally led to an increase in tetragonal phase fraction and dielectric constant. This was reflected in both XRD and ATR-FTIR measurements. We demonstrate that not only the composition, but also the distribution of ZrO2 throughout the film determines phase formation. Concentrating ZrO2 at the top surface of the film allowed the dielectric constant to be optimized for a given composition. These observations are explained by a surface energy thermodynamic model.