Characterization of soils using photoacoustic mid-infrared spectroscopy

This study investigates the use of photoacoustic spectroscopy (PAS) for rapid soil analysis. Photoacoustic spectroscopy requires very minimal sample preparation (air-drying), which is a major advantage compared to the more traditional transmittance technique, which requires time-consuming preparation of pellets. The amount of information contained in the PAS spectra appears to be similar to that contained in transmittance spectra, and the PAS spectra exhibit a large number of bands that can be associated with various soil constituents such as quartz, calcium carbonate, and various types of clay. Comparison with attenuated total reflection (ATR) spectra of saturated soil pastes shows that the PAS spectra provide much more information than the ATR spectra due to the strong water bands present in the latter. PAS quantitative analysis of clay, calcium carbonate, and organic matter is presented, with respective determination errors of approximately 12% clay, approximately 5% CaCO(3), and approximately 0.2% organic matter.     

Cavity ringdown spectroscopy of thin films in the mid-infrared

To demonstrate the potential of the cavity ringdown technique in mid-infrared spectroscopy of thin film samples, we measured absorption losses in a C60 film on a BaF2 substrate using a tunable optical parametric amplifier source. With a Brewster angle sample geometry, we achieved a fractional loss sensitivity as small as 1.3 x 10(-7) with 1.5 cm(-1) resolution, an improvement in sensitivity of 2 orders of magnitude compared to standard Fourier transform infrared methods. At an absorption sensitivity of 5 x 10(-7), spectra of several C60 overtone lines were recorded.     

Determination of glucose in whole blood samples by mid-infrared spectroscopy

We have determined the glucose concentration of whole blood from mid-infrared spectra without sample preparation or use of chemical reagents. We selected 1119-1022 cm(-1) as the optimal wavelength range for our measurement by making a first-loading vector analysis based on partial least-squares regression. We examined the influence of hemoglobin on samples by using different calibration and prediction sets. The accuracy of glucose prediction depended on the hemoglobin level in the calibration model; the sample set should represent the entire range of hemoglobin concentration. We obtained an accuracy of 5.9% in glucose prediction, and this value is well within a clinically acceptable range.     

A method of measuring the concentrations of hydrogen sulfide and ethyl mercaptan in their mixture in air

A method of measuring the concentrations of hydrogen sulfide and ethyl mercaptan in their mixture in air using a modified gas-analyzer system based on an MOS-sensor, which operates on the basis of the difference in the temperatures at which these gases burn, is considered. The use of these gas analyzers to monitor the odor level and to detect leakages of domestic gas is proposed. __________ Translated from Izmeritel’naya Tekhnika, No. 5, pp. 61–62, May, 2007.     

Application of a mid-infrared fiber bundle in remote measurement of gas concentrations in a chemical vapor deposition chamber

A fiber bundle has been designed for measurement of gas concentrations in a chemical vapor deposition (CVD) chamber. The bundle is broadband, covering the spectrum range from 500 to 6000 cm(-1). Using this bundle, we have designed Fourier Transform infrared (FTIR) sampling configurations with reduced beam divergence (from 0.4 to 0.1 rad) and focal spot diameters (from 12 to 4 mm). The FTIR spectrum of tetraethoxysilane vapors in a CVD chamber was determined with the bundle and modified SAM connectors. An ellipsoid reflector was designed that yielded improved signal-to-noise ratios (SNR's) in the fiber-based spectra by a factor of 2. The incorporation of this reflector in spectrometers by use of the fiber bundle has the potential to reduce the sampling times for spectra while retaining acceptable SNR's.     

Direct determination of peracetic acid, hydrogen peroxide, and acetic acid in disinfectant solutions by far-ultraviolet absorption spectroscopy

In this paper we propose a rapid and highly selective far-ultraviolet (FUV) spectroscopic method for the simultaneous determination of peracetic acid (PAA), hydrogen peroxide, and acetic acid (AA). For this purpose we developed a novel FUV spectrometer that enables us to measure the spectra down to 180 nm. Direct determination of PAA, H(2)O(2), and AA, the three main species in disinfectant solutions, was carried out by using their absorption bands in the 180-220-nm region. The proposed method does not require any reagents or catalysts, a calibration standard, and a complicated procedure for the analysis. The only preparation procedure requested is a dilution of H(2)O(2) with pure water to a concentration range lower than 0.2 wt % in the sample solutions. Usually, the required concentration range can be obtained by the 10 times volume dilution of the actual disinfectant solutions. As the measured sample does not leave any impurity for the disinfection, it can be reused completely by using a circulation system. The detection limit for PAA of the new FUV spectrometer was evaluated to be 0.002 wt %, and the dynamic ranges of the measured concentrations were from 0 to 0.05 wt %, from 0 to 0.2 wt %, and from 0 to 0.2 wt % for PAA, H(2)O(2), and AA, respectively. The response time for the simultaneous determination of the three species is 30 s, and the analysis is applicable even to the flowing samples. This method may become a novel approach for the continuous monitoring of PAA in disinfectant solutions on the process of sterilization.     

Application of mid-infrared spectroscopy to the development and transfer of a manufacturing process for an active pharmaceutical ingredient

The use of in situ mid-infrared spectroscopy to support the development of a pharmaceutical manufacturing process is disclosed. Data on this two-stage telescoped reaction from several reaction scales (<50 mL to 1600 liters) and at multiple manufacturing locations is shown. In addition to providing data on both reactions in the telescope, the mid-IR data has been used to monitor an intermediate distillation operation and therefore it has been possible to profile the whole process. Data is also shown on aliquot addition during the first chemical transformation, which is used to check the instrumentation.     

Differentiation of selected Salmonella enterica serovars by Fourier transform mid-infrared spectroscopy

Salmonella enterica serovars include pathogens responsible for high numbers of foodborne salmonellosis. Fourier transform infrared (FT-IR) spectroscopy can be used to rapidly and accurately identify microorganisms based on unique spectra of bacterial cell components. The objectives of this study were to discriminate closely related Salmonella enterica serovars by using FT-IR spectroscopy and multivariate analysis and to compare the performance of three techniques for differentiating among Salmonella serovars. Selected serovars of S. enterica were streaked onto plate count agar and incubated (37 degrees C, 24 h). Isolated colonies were suspended in phosphate buffer or 50% ethanol (10 microL). Suspensions were placed on (1) ZnSe crystals for transmission, (2) disposable polyethylene membranes (DPM) for transmission, and (3) diamond crystal plate for attenuated total reflectance (ATR) analyses; all samples were dried under vacuum. Classification models, soft independent modeling of class analogy (SIMCA), from derivatized infrared spectra (1300-900 cm(-1)), discriminated among Salmonella serovars presumably attributed to cell's lipopolysaccharides (1000-980 cm(-1)). Samples on DPM required high cell density for reliable spectra. High-quality spectra were obtained when a single colony was suspended in ethanol or buffer and mounted on ZnSe crystals for transmission or diamond plate for ATR analysis. Prediction of unknowns, representative of serovars used to construct classification models, showed that all techniques were suitable for the rapid and accurate differentiation of Salmonella serovars.     

Fabrication of tunnelling barriers by oxidation in hydrogen peroxide

One of the major experimental difficulties in electron tunnelling work is the preparation of very thin insulating barriers. This paper describes a method based on oxidation of the substrate in hydrogen peroxide. Good results have been obtained with gallium and tin, and the technique may be useful for other metals as well.     

Glucose quantification in dried-down nanoliter samples using mid-infrared attenuated total reflection spectroscopy

The aim of this study was to determine the feasibility of minimally invasive glucose concentration measurement of a body fluid within the physiologically important range below 100 nL with a number of samples such as interstitial fluid, plasma, or whole blood using mid-infrared spectroscopy, but starting with preliminary measurements on samples of simple aqueous glucose solutions. The Fourier transform infrared spectrometer was equipped with a Golden Gate single reflection diamond attenuated total reflection (ATR) accessory and a room-temperature pyroelectric detector. As the necessary detection limits can be achieved only for dried samples within the spectrometric conditions realized by a commercial instrument, the work focused on the optimization of such ATR measurements. We achieved quantification of samples with volumes as low as 7 nL between 10 and 600 mg/dL. The standard error of prediction (SEP) for the concentration range 10-100 mg/dL is 3.2 mg/dL with full interval data between 1180 and 940 cm(-1). The performance of the prediction is given by a coefficient of variation of prediction (CV(pred) ) of 6.2%. When all samples within the whole concentration range are included, the SEP increases to 20.2 mg/dL, and hence the CV(pred) to 10.6% due to a nonlinear signal dependence on glucose concentration. A detection limit for glucose of 0.7 ng with a signal-to-noise ratio of 10 was obtained.     

Silver nanoclusters in BSA template: a selective sensor for hydrogen peroxide

Fluorescent silver nanoclusters (Ag NCs) have been bio-labeled to bovine serum albumin (BSA) protein by wet chemistry. The conformational changes of protein were studied using circular dichroism spectroscopy. The spectroscopic and chemical properties of these BSA-Ag NCs are explored to study their chemical sensing behavior. These NCs exhibit an intense fluorescence peak at 650 nm. Fluorescence behavior of Ag NCs has been explored for sensitive and selective detection of hydrogen peroxide.     

Fiber-optic fourier transform mid-infrared reflectance spectroscopy: a suitable technique for in situ studies of mural paintings

A prototypical in situ noninvasive study of ancient mural painting materials has been carried out using an easily manageable fiber-optic Fourier transform mid-infrared (mid-FT-IR) reflectance spectrophotometer. The reported object of the study is the Renaissance fresco by Pietro Vannucci, called il Perugino, located in the church of Santa Maria delle Lacrime (1521, Trevi, Perugia Italy). For the first classification and interpretation of infrared spectra, principal components analysis was used. Spectral artifacts due to lacunas, restoration materials, or alteration products have been identified, as well as two different secco refinements bound in a tempera medium. For the characterization of inorganic pigments, mid-FT-IR spectra have been integrated with other data obtained through in situ X-ray fluorescence (XRF) elemental analysis. This complementary noninvasive approach led to the characterization of Perugino's pigments, even in the presence of complex mixtures. The mid-FT-IR noninvasive technique, in combination with XRF, is thus recommended as a valuable first approach for the examination of mural paintings, permitting the assessment of the execution technique as well as contributing to the evaluation of the conservation state.     

Detection of hydrogen peroxide using photofragmentation laser-induced fluorescence

Photofragmentation laser-induced fluorescence (PF-LIF) is for the first time demonstrated to be a practical diagnostic tool for detection of hydrogen peroxide. Point measurements as well as two-dimensional (2D) measurements in free-flows, with nitrogen as bath gas, are reported. The present application of the PF-LIF technique involves one laser, emitting radiation of 266 nm wavelength, to dissociate hydrogen peroxide molecules into OH radicals, and another laser, emitting at 282.25 nm, to electronically excite OH, whose laser-induced fluorescence is detected. The measurement procedure is explained in detail and a suitable time separation between photolysis and excitation pulse is proposed to be on the order of a few hundred nanoseconds. With a separation time in that regime, recorded OH excitation scans were found to be thermal and the signal was close to maximum. The PF-LIF signal strength was shown to follow the same trend as the vapor pressure corresponding to the hydrogen peroxide liquid concentration. Thus, the PF-LIF signal appeared to increase linearly with hydrogen peroxide vapor-phase concentration. For 2D single shot measurements, a conservatively estimated value of the detection limit is 30 ppm. Experiments verified that for averaged point measurements the detection limit was well below 30 ppm.     

Concentration measurements in ionic liquid-water mixtures by mid-infrared spectroscopy and indirect hard modeling

An analytical method for the quantitative characterization of binary mixtures of water and ionic liquids (ILs) is presented. Mid-infrared (mid-IR) spectroscopy in combination with indirect hard modeling (IHM) is employed to quantify the water content in 1-butyl-3-methylimidazolium chloride (BMIMCl), 1,3-dimethylimidazolium dimethylphosphate (DMIMDMP), and 1-ethyl-3-methylimidazolium acetate (EMIMAc). Despite significant nonlinear shifts of the spectral bands, a good spectral fit with calibration errors of less than 2.3 wt % can be achieved almost over the whole concentration range. A profound analysis of the spectral models including peak assignment substantiates the physico-chemical foundation of the spectral models. Furthermore, the shift of peak functions in the spectral models is shown to provide a measure of molecular interaction in IL-water mixtures, which can also be utilized quantitatively. The vibrational bands of the water dipole reveal differences in the strength of hydrogen bonding with water in the IL studied. These properties of the spectral hard models demonstrate their quantitative analytical potential and set the stage for multiway calibration in comprehensive reaction monitoring in these highly interacting mixtures of IL and water.     

The depolymerization mechanism of chitosan by hydrogen peroxide

Water-soluble chitosan with low molecular weight was prepared by the depolymerization of chitosan with aqueous H₂O₂ solution. The IR and ¹H-NMR studies verify that depolymerization leads to the breakage of 1,4--D-glucoside bonds of chitosan. X-ray analysis shows the depolymerization takes place at the surface of the chitosan in crystal region by so called peeling-off process while the amorphous portion is depolymerized by penetrating pattern.     

Detection of hydrogen peroxide at mesoporous platinum microelectrodes

Mesoporous (H(I)-ePt) platinum microelectrodes electrodeposited from the hexagonal (H(I)) lyotropic liquid crystalline phase are shown to be excellent amperometric sensors for the detection of hydrogen peroxide over a wide range of concentrations. Good reproducibility, high precision, and accuracy of measurements are demonstrated. Mesoporous microelectrodes retain the high rates of mass transport typical of conventional microelectrodes, and their high real surface area greatly enhances their catalytic activity. This unique combination of properties overcomes the limitations of previous amperometric hydrogen peroxide sensors and yields outstanding qualitative and quantitative results.     

Simultaneous electroanalysis of peroxyacetic acid and hydrogen peroxide

The electrochemical behavior of peroxyacetic acid (PAA) in the presence of hydrogen peroxide (H2O2) has been investigated using cyclic voltammetry and hydrodynamic techniques [rotating disk electrode (RDE) voltammetry and rotating ring-disk electrode (RRDE) voltammetry]. The results have been analyzed aiming at simultaneous electroanalysis of both species. Glassy carbon and gold electrodes were used for this investigation. It was found that the reduction of PAA, as well as H2O2, is highly sensitive to the electrode material; for example, at 100 mV s-1, the reduction peak potentials of PAA were 0.2 and -1.1 V at gold and glassy carbon electrodes, respectively. The well-separated steady-state limiting currents were obtained using a gold electrode for the reduction of both PAA and H2O2 and also a well-defined one for the oxidation of H2O2. On the basis of the RDE experiments, good calibration curves were obtained for both species over a wide range of their concentrations, for PAA and H2O2 in the range of 0.36 to 110 and 0.11 to 34 mM, respectively. The simultaneous and selective electroanalysis of PAA and H2O2 in their coexistence is demonstrated for the first time.