Photoacoustic Infrared Spectroscopy Research Articles

Cesium adsorption ability of charcoal made from Japanese cedar and Japanese oak wood: effect of Fe3+-addition to starting materials

To investigate the effect of Fe-addition on the Cs+-adsorption ability (Cs+-AA) of woody charcoal, charcoal samples were prepared from Japanese cedar (JC) and Japanese oak (JO) wood impregnated with Fe3+ at 600 and 800 °C. The residual functional groups of the charcoal samples were examined using infrared-photoacoustic spectroscopy. OH groups were observed in the charcoal made at 600 °C, and no vibrational bands were detectable in the charcoal synthesized at 800 °C. The observation of Raman D-, G-, and G´-bands revealed that all charcoal samples contained sp2-carbon atoms but graphitization occurred only in the iron-loaded charcoal made at 800 °C. The Cs+-AA of the JC and JO charcoal samples were evaluated based on the adsorption isotherms of an aqueous CsCl (Cs+: 33 mg/L) solution. The addition of Fe3+ to wood had a negative effect on the Cs+-AA of the JO charcoal made at 600 °C, but a positive effect on the Cs+-AA of the JC charcoal prepared at 800 °C.

Infrared-Photoacoustic Spectroscopy and Multiproduct Multivariate Calibration to Estimate the Proportion of Coffee Defects in Roasted Samples

Infrared-photoacoustic spectroscopy (IR-PAS) and partial least squares (PLS) were tested as a rapid alternative to conventional methods to evaluate the proportion of coffee defects in roasted and ground coffees. Multiproduct multivariate calibration models were obtained from spectra of healthy beans of Coffea canephora and C. arabica (Arabica) and blends composed of defective and healthy beans of Arabica in different proportions. The blends, named selections, contained sour, black, broken, whole beans, skin, and coffee woods. Six models were built using roasted and ground coffee samples. The model was optimized through outlier evaluation, and the parameters of merit such as accuracy, sensitivity, limits of detection and quantification, the inverse of analytical sensitivity, linearity, and adjustment were computed. The models presented predictive capacity and high sensitivity in determining defects, all being predicted with suitable correlation coefficients (ranging from 0.7176 to 0.8080) and presenting adequate performance. The parameters of merit displayed promising results, and the prediction models developed for %defects can be safely used as an alternative to the reference method. Furthermore, the new method is fast, efficient, and suitable for in-line application in quality control industrial coffee processing.

Characterization of iron-loaded charcoal using infrared-photoacoustic spectroscopy: factors governing graphitization

Characterization of iron-loaded charcoal using infrared-photoacoustic spectroscopy: factors governing graphitization

Highly sensitive broadband differential infrared photoacoustic spectroscopy with wavelet denoising algorithm for trace gas detection

Enhancement of trace gas detectability using photoacoustic spectroscopy requires the effective suppression of strong background noise for practical applications. An upgraded infrared broadband trace gas detection configuration was investigated based on a Fourier transform infrared (FTIR) spectrometer equipped with specially designed T-resonators and simultaneous differential optical and photoacoustic measurement capabilities. By using acetylene and local air as appropriate samples, the detectivity of the differential photoacoustic mode was demonstrated to be far better than the pure optical approach both theoretically and experimentally, due to the effectiveness of light-correlated coherent noise suppression of non-intrinsic optical baseline signals. The wavelet domain denoising algorithm with the optimized parameters was introduced in detail to greatly improve the signal-to-noise ratio by denoising the incoherent ambient interference with respect to the differential photoacoustic measurement. The results showed enhancement of sensitivity to acetylene from 5 ppmv (original differential mode) to 806 ppbv, a fivefold improvement. With the suppression of background noise accomplished by the optimized wavelet domain denoising algorithm, the broadband differential photoacoustic trace gas detection was shown to be an effective approach for trace gas detection.

Durability Study of Automotive Additive Manufactured Specimens

<div class="section abstract"><div class="htmlview paragraph">The long-term weathering behavior of three different 3D printable, non-stabilized, UV cure resin formulations (A and B with thiol-ene base, and C with acrylate chemistry) was studied using tensile testing, nano-indentation, and photoacoustic infrared (FTIR-PAS) spectroscopy. To this end, type I tensile bars were printed from each resin system using a 3D printer, and were post UV-cured under a broad spectrum source. Systems A and C showed a similar trend after weathering. They first experienced an increase in modulus and tensile strength, due to additional crosslinking of the residual unreacted species. This increase in mechanical properties was followed by a drop in modulus, tensile strength, and percent elongation, due to the over-crosslinking and consequent embrittlement. System B, however, showed remarkable retention of the mechanical properties before/after weathering. Nano-indentation results were in good agreement with the tensile properties, showing a similar trend in hardness variations. Although Systems A and C outperformed System B in photooxidation performance, all three systems demonstrated promising results considering no hindered amine light stabilizers (HALS) were used in the formulations. Both photooxidation and mechanical properties of the specimens are expected to improve after addition of HALS.</div></div>

Intraspecific Cuticular Chemical Profile Variation in the Social Wasp Mischocyttarus consimilis (Hymenoptera, Vespidae).

Chemical compounds present on the cuticle of social insects are important in communication, as they are used in recognition of nestmates and sexual partners as well as in caste distinction, varying according to several factors, such as genetic and environmental. In this context, some studies have explored the cuticular chemical profile as a tool for assessing intra- and interspecific differences in social insects, although few studies have investigated this in social wasps. This study aimed to assess the differences in cuticular chemical profiles among different geographic samples of the wasp Mischocyttarus consimilis Zikán. Our hypothesis was that environmental factors are decisive to compose the cuticular chemical profiles of colonies of these social wasps and that there are differences regarding the geographic distribution among colonies. We used Fourier Transform Infrared-Photoacoustic Spectroscopy (FTIR-PAS) to assess the chemical profiles of samples. Our results show that despite there are differences between the cuticular chemical composition of the wasps' samples from different populations, there is no significant correlation compared to the spatial distribution of the colonies nor with the environment. Thus, our hypothesis was refuted, and we can infer that in this species neither exogenous nor genetic factors stand out to differentiate the chemical signature of their colonies, but a combination of both.

Assessing atmospheric nitrogen losses with photoacoustic infrared spectroscopy: Polymer coated urea.

Although N is beneficial and essential for life, it is also a common atmospheric pollutant as nitrous oxide (N2O) and ammonia (NH3)—contributed largely from N fertilization. Polymer-coated urea (PCU) fertilizer is a promising controlled release fertilizer that provides improved N-release timing. Glasshouse studies were conducted to compare N2O and NH3 emissions from PCU and uncoated urea to an untreated control utilizing a non-static, non-flow-through chamber in conjunction with photoacoustic infrared spectroscopy (PAIRS) for gas collection and analysis. Three short-term 20-Day Studies with sand, sandy loam, and loam soils and a full-term 45-Day Study with loam soil were completed. Volatilization of NH3 was reduced by 72% and 22% in the sandy loam and loam soils, respectively, in two of the short-term studies and by 14% in the loam in the full-term study. Evolution of N2O was reduced by 42% and 63% in the sandy loam and loam soils of the short-term studies and by 99% in the loam soil of the full-term study. No differences were observed in the sand soil. Overall, PCU decreased gaseous losses of N following fertilization while providing a steady supply of N to the plant. Higher temporal resolution was observed with the PAIRS instrumentation as compared to what is typically reported and, as such, we recommend PAIRS analysis as a viable method for studying N gas emissions.

Quantitative assessment of specific defects in roasted ground coffee via infrared-photoacoustic spectroscopy

Chemical analyses and sensory evaluation are the most applied methods for quality control of roasted and ground coffee (RG). However, faster alternatives would be highly valuable. Here, we applied infrared-photoacoustic spectroscopy (FTIR-PAS) on RG powder. Mixtures of specific defective beans were blended with healthy (defect-free) Coffea arabica and Coffea canephora bases in specific ratios, forming different classes of blends. Principal Component Analysis allowed predicting the amount/fraction and nature of the defects in blends while partial Least Squares Discriminant Analysis revealed similarities between blends (=samples). A successful predictive model was obtained using six classes of blends. The model could classify 100% of the samples into four classes. The specificities were higher than 0.9. Application of FTIR-PAS on RG coffee to characterize and classify blends has shown to be an accurate, easy, quick and “green” alternative to current methods.

Chemical Interaction Analysis of an Adhesive Containing 10-Methacryloyloxydecyl Dihydrogen Phosphate (10-MDP) With the Dentin in Noncarious Cervical Lesions

The purpose of this study was to evaluate the chemical bonds of a self-etch 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) adhesive to natural noncarious cervical lesions (NCCLs) and compare them with those occurring in sclerotic dentin in artificially prepared defects (APDs). Four human teeth with natural NCCLs on the buccal surface were selected. Artificial defects matching the natural lesions were prepared on the lingual surface of the same teeth serving as control. Micro-Raman (MR) spectroscopy was used to quantify mineral content in natural NCCLs and in APDs. Fourier transform infrared-photoacoustic spectroscopy (FTIR-PAS) readouts were taken before and after adhesive application to analyze the protein matrix/mineral (M:M) ratio and chemical interactions between 10-MDP adhesive and dentin. The MR and FTIR-PAS spectra collected from natural NCCLs demonstrated a larger area of the band (961 cm-1, PO4) and lower M:M ratio, respectively, characterizing a hypermineralized dentin, compared with APDs. FTIR-PAS demonstrated emergence of a peak (1179 cm-1, P=O) in spectra after adhesive treatment, demonstrating a more intense chemical interaction in natural NCCLs. The results demonstrated that chemical bonding of 10-MDP adhesive to natural NCCLs is more intense, due to the hypermineralized surface, and suggest that it is unnecessary to remove the hypermineralized layer with burs, as this may decrease the chemical bonding potential of 10-MDP.

Using FTIR-photoacoustic spectroscopy for phosphorus speciation analysis of biochars

In the last decade, numerous studies have evaluated the benefits of biochar for improving soil quality. The purposes of the current study were to use Fourier transform infrared-photoacoustic spectroscopy (FTIR-PAS) to analyse P species in biochar and to determine the effect of pyrolysis temperature on P speciation. The photoacoustic detector has a range of advantages for the very dark biochar samples in comparison to more traditional reflectance or transmission FTIR detectors. The spectra turned out to be more informative in the regions with P vibrations for biochar produced at temperatures above 400°C, where most of the remaining organic compounds were aromatic and therefore not overlapping with the P vibrations. For biochars produced from the solid fraction of digestate from biogas production, an increase in the pyrolysis temperature led to the formation of a large variety of P species. Hydroxylapatite and tricalcium phosphate were the most dominant P species in the mid to high temperature range (600–900°C), while at 1050°C apatite, iron phosphates, variscite and calcium phosphates were identified. However, the changes in P speciation in biochars produced from bone meal at different temperatures were smaller than in the biochars from digestate. Hydroxylapatite and calcium phosphates were identified in biochar produced at all temperatures, while there was some indication of struvite formation.

Calibrations for the determination of water species in bulk and hydrated obsidian by infrared photoacoustic spectroscopy

The obsidian hydration dating method requires a measurement of the amount of diffused water (%H2OD) within the surface hydration layer and an assessment of the structural water (%OH) contained within the underlying glass matrix. Infrared photoacoustic spectroscopy (IR-PAS) has the ability to sample deeply within the glass and capture both regions simultaneously. The calibrated infrared water band at 3570cm−1 may be used to measure total water (%H2Ot=H2Om+OH) content and the concentration of diffused molecular water (%H2OD) is assessed with the band at 1630cm−1. Subtraction of the band specific concentrations provides an estimate of the obsidian structural hydroxyl (%OH) content. Calibrations of the IR-PAS water bands, to permit inferring water concentrations from IR-PAS measurements, were developed using obsidians of known water content established by standard infrared transmission. Three calibration equations are presented, for H2Ot, H2Om, and OH, along with computed estimates of accuracy.

Technical Note: Characterisation of Loess Soils Using near Infrared Photoacoustic Spectroscopy

The photoacoustic spectroscopy (PAS) technique has emerged as a valuable tool for the study of soil materials. The present work developed the experimental set-up for near infrared (800–2400 nm) photoacoustic spectroscopy (NIR-PAS), which consists of photoacoustic (PA) accessory, tungsten bromine lamp, monochromator, chopper and lock-in-amplifier, and this spectrometer was first applied to record the spectra of soils ( n = 50) collected from the Loess Plateau of China; partial least-squares regression (PLSR) models and leave-one-out cross-validation were used to predict soil organic matter (SOM), clay, carbonate and available phosphorus content. The spectra varied among different soil samples; SOM played an important role in the spectral appearance, and the intensity and position of five typical absorption bands significantly shifted owing to the variances in the components and structure of SOM. The PLSR model demonstrated a good performance in the prediction of SOM with a root mean square error of 2.5 g kg−1 and a ratio of standard deviation to prediction error of 2.3. This pilot study demonstrates that NIR-PAS exhibits typical infrared absorptions and may be suitable for analysing soil samples.

NIR photoacoustic spectroscopy for non-invasive glucose measurement.

The use of near infra red (NIR) photoacoustic spectroscopy (PAS) for continuous non-invasive glucose measurement is outlined in the paper. A photoacoustic (PA) measurement apparatus was constructed and PA measurements were made on glucose solutions at multiple NIR excitation wavelengths. A variety of time and frequency domain features, including amplitude and area based features, were extracted from the PA measurements. These features were observed to be proportional to the glucose concentration of the sample. PA measurements from samples of whole blood at different glucose concentrations showed similar results. Subsequently, in vivo PA measurements made on a cohort of 30 volunteers were calibrated using a quadratic fit, and the results were compared to reference glucose concentrations made using a regular blood glucose meter. A comparison of 196 measurement pairs of predicted and reference glucose concentrations using a Clarke Error Grid gave a point distribution of 87.24% and 12.76% over zones A and B of the grid, with no measurement pairs falling in unacceptable zones C-E of the error grid. The predicted measurements had a mean absolute difference (MAD) of 12.57 ± 13.90 mg/dl and a mean absolute relative difference (MARD) of 9.61% ± 10.55%. This is an improvement over previous results obtained using PAS and other non-invasive techniques, validating the potential of PAS for continuous noninvasive glucose monitoring.

Short-term carbon dioxide emission under contrasting soil disturbance levels and organic amendments

Agriculture can be either a source or sink of atmospheric CO2 depending on soil management. The application of swine slurry in conventional tilled soils could enhance soil CO2 emission depleting soil organic C stocks. However, the use of recalcitrant C-rich organic fertilizers in no-till soils can offset soil CO2 emission promoting soil C sequestration. This hypothesis was tested by evaluating short-term CO2-C emissions from a Rhodic Nitisol under contrasting soil disturbance levels (disturbed (DS) and undisturbed soil (US)) top-dressed with mineral or organic fertilizers (urea (UR), raw swine slurry (RS), anaerobically digested swine slurry (ADS), and composted swine slurry (CS)). Soil CO2 emission was evaluated for 64 days using static chambers where gas samples were collected and analysed by photoacoustic infrared spectroscopy. Soil water-filled pore space (WFPS), temperature and meteorological data were concomitantly registered and a first-order exponential decay model was used to assess the decomposition of organic fertilizers and CO2 emissions induced by soil disturbance. Soil CO2-C emission was correlated with soil temperature, while limiting soil aeration impaired CO2-C efflux when WFPS >0.6cm3cm−3. Disturbance increased soil CO2-C efflux (36.3±2.2kg CO2-Cha−1 day−1) in relation to US (33.3±1.6kg CO2-Cha−1 day−1). Extra labile C input through RS amendment induced an increased soil CO2-C efflux for a longer period (t1/2=16.9 and 9.6 days in DS and US treatments, respectively), resulting in higher CO2-C emissions than soil amended with other fertilizers. The recalcitrant C input by ADS and CS had limited effect on soil CO2-C emissions. CS presented a genuine potential for substantial soil organic C accumulation while offsetting increased CO2-C emissions in comparison to RS amended soils.

Broadly tunable quantum cascade laser in cantilever-enhanced photoacoustic infrared spectroscopy of solids

An external cavity quantum cascade laser (EC-QCL) is applied in the photoacoustic detection of solid samples. The EC-QCL used has a broad tuning range of 676 cm−1 (970–1,646 cm−1) in the mid-infrared region, which enables accurate broadband spectroscopy of large molecules. The high spectral power density of the EC-QCL is combined with an extremely sensitive optical cantilever microphone of the photoacoustic detector to achieve an ultimate sensitivity. The carbon black, polyethylene, and hair fiber samples were measured with the EC-QCL photoacoustic detection using electrical amplitude modulation to demonstrate the possibilities of the setup. The same measurements were repeated with a Fourier transform infrared (FTIR) spectrometer combined with a photoacoustic detector for a comparison. The EC-QCL photoacoustic setup yielded roughly a decade better signal-to-noise ratios than the FTIR setup with the same measurement time.

Prehistoric settlement chronology on Rapa Nui, Chile: obsidian hydration dating using infrared photoacoustic spectroscopy

The prehistoric Polynesian inhabitants of Rapa Nui (Easter Island) utilized obsidian for nearly 700 years in many activities connected with daily life. The near ubiquitous occurrence of the natural glass in both domestic residences and religious structures makes the application of obsidian hydration dating highly suitable for the investigation of cultural change. We have applied previously developed calibrations that estimate hydration rates for obsidian based upon the structural water content of the glass as determined by infrared spectroscopy. The archaeological ages estimated by this method were compared with accelerator mass spectrometry (AMS) dates using short-lived woody species endemic to the island. The convergence between the two dating methods is strong and we suggest that obsidian hydration dating may be used on Rapa Nui to reliably date contexts where suitable material for AMS dating may not be available.

Social Parasitism and Dynamics of Cuticular Hydrocarbons in Paper Wasps of the GenusMischocyttarus

Facultative social parasitism has been recorded in several taxa of social insects. Most recently, this phenomenon has been recorded in colonies of the neotropical social wasp Mischocyttarus cerberus (parasitized by Mischocyttarus consimilis). This is the first case of interspecific parasitism described for the genus Mischocyttarus. How social parasites are able to remain in the host colony has been one of the central subjects of studies on this theme. Chemical signals are used by social insects to recognize their nestmates, which suggests that female parasites use a chemical strategy to hide their identity and become accepted as a member in host colonies. This study investigated the dynamics of cuticular hydrocarbons (CHs) of workers of M. consimilis and M. cerberus in both control and host colonies. Fourier Transform Infrared-Photoacoustic Spectroscopy (FTIR-PAS) was used to read the CHs; this technique is somewhat unusual but is quite reliable for this type of study. A stepwise canonical discrimination analysis detected significant differences between the mid-infrared spectra of the two species. This analysis provided a dispersion diagram of the results in order to differentiate the species, in which the first axis explained 61% of the results. These results demonstrated a clear difference in the CHs profile between non-conspecific workers from the control colonies. However, non-conspecific workers from the host colonies underwent a significant modification of CHs in comparison to the workers from the control colonies, and this modification was similar in all the host colonies non-conspecific workers. These data suggest that females of parasitic-specie modify the chemical profile of the host-specie females, and also alter their own profiles in order to be recognized as “nestmates” and to achieve success in parasitism.

Evaluation of photoacoustic infrared spectroscopy for simultaneous measurement of N2O and CO2 gas concentrations and fluxes at the soil surface

Simultaneous measurement of N2 O and CO2 flux at the soil surface with photoacoustic infrared spectroscopy (PAS) is gaining popularity due to portability, low maintenance, and ease-of-operation. However, the ability of PAS to measure N2 O with accuracy and precision similar to gas chromatography (GC) is uncertain due to overlap in N2 O, CO2 , and H2 O absorbance spectra combined with the large range in analyte concentrations. We tested the ability of six PAS units to simultaneously measure N2 O and CO2 gas concentrations and fluxes with accuracy and precision similar to two GC units. We also evaluated H2 O vapor and CO2 interferences with N2 O measurement. The accuracy and precision of standard gas concentration measurements with PAS and GC were similar. High water vapor (~26600ppm) and CO2 concentrations (~4500ppm) did not interfere with N2 O measurement across the concentration range typically observed in static flux chambers at the soil surface (~0.5-3.0ppm N2 O). On average, N2 O fluxes measured with the six PAS were 4.7% higher than one GC and 9.9% lower than the second GC.

Genetic tools to mitigate the environmental impact of milk production systems: Experience with a multi-point individual cow methane measurement system

Methane is one of the most potent greenhouse gases with about 21 times the Global Warming Potential (GWP) of carbon dioxide. Methane emission by dairy cows is not only a significant concern for the environment but also represent a loss of energy for milk production. Dairy cows lose 6 to 12% of feed energy and 95% of which is released through mouth as eructated methane. The most important avenue for reducing methane emissions from dairy systems is by improving the productivity and efficiency of dairy cows, through better nutrition and genetics. Attempts to reduce the ecological foot print of milk production require a sound understanding of the genetic basis of methane emissions. This requires reliable techniques for the measurement of methane output from individual cows. Enteric methane from ruminants is an important but often difficult source to quantify on an individual basis. So far, many of the available measurement techniques are either slow, expensive, labor intensive and are unsuitable for large scale measurements which is a prerequisite for genetic studies. This study evaluated a non-invasive Photoacoustic Infrared Spectroscopy (PAS) technique for quantifying enteric methane output from the breath of individual dairy cows. The study was conducted at MTT experimental dairy herd in Minkiö. A total of about 40 first-lactation Finnish Ayrshire cows were included. Individual cow methane, carbon dioxide (CO2), acetone, ammonia outputs were measured continuously over 3 weeks period using a multi-point PAS gas analyzer fitted to two feeding kiosks (sampling points). Whenever a cow visits a feeding kiosk, her breath was sampled and analyzed for the contents of the different gases. Measurements were made alternatively between the two sampling points and every other minute a gas was sampled and analyzed from each. Records from continuous three days measurements were analyzed. There were about 6-14 repeated measurements on each of the different gasses per cow and a total of 1690 and 1908 measurements from sampling point 1 and 2, respectively. Ratio of CH4:CO2 is concentration independent and can be used to quantify methane output in dairy cows. Thus for each cow, CH4:CO2 ratios were calculated using measurements of these gasses. Basic statistical measures were calculated. Between and within individual variability were quantified and the repeatability of CH4:CO2 were estimated using the General Linear Models (GLM) procedure. The overall mean(sd) of CH4:CO2 from kiosk1 and 2 were 0.071(0.049) and 0.073(0.042) and the repeatability of CH4:CO2 were 0.56 and 0.57 for kiosk1 and 2, respectively. Repeatability sets the upper limit to heritability. Compared to other studies, repeatabilities from this study are on the higher side and suggest the suitability of the PAS for individual cow CH4 measurements that is a requisite in genetic studies.

An in situ FTIR step-scan photoacoustic investigation of kerogen and minerals in oil shale

Step-scan photoacoustic infrared spectroscopy experiments were performed on Green River oil shale samples obtained from the Piceance Basin located in Colorado, USA. We have investigated the molecular nature of light and dark colored areas of the oil shale core using FTIR photoacoustic step-scan spectroscopy. This technique provided us with the means to analyze the oil shale in its original in situ form with the kerogen–mineral interactions intact. All vibrational bands characteristic of kerogen were found in the dark and light colored oil shale samples confirming that kerogen is present throughout the depth of the core. Depth profiling experiments indicated that there are changes between layers in the oil shale molecular structure at a length scale of micron. Comparisons of spectra from the light and dark colored oil shale core samples suggest that the light colored regions have high kerogen content, with spectra similar to that from isolated kerogen, whereas, the dark colored areas contain more mineral components which include clay minerals, dolomite, calcite, and pyrite. The mineral components of the oil shale are important in understanding how the kerogen is “trapped” in the oil shale. Comparing in situ kerogen spectra with spectra from isolated kerogen indicate significant band shifts suggesting important nonbonded molecular interactions between the kerogen and minerals.