Mid-infrared Attenuated Total Reflectance Research Articles

Multimodal fiber probe for simultaneous mid-infrared and Raman spectroscopy

A fiber probe has been developed that enables simultaneous acquisition of mid-infrared (MIR) and Raman spectra in the region of 3100–2600 cm−1. Multimodal measurement is based on a proposed ZrO2 crystal design at the tip of an attenuated total reflection (ATR) probe. Mid-infrared ATR spectra are obtained through a pair of chalcogenide infrared (CIR) fibers mounted at the base of the crystal. The probe enables both excitation and acquisition of a weak Raman signal from a portion of the sample in front of the crystal using an additional pair of silica fibers located in a plane perpendicular to the CIR fibers. The advantages of combining MIR and Raman spectra in a single probe have been discussed.

Detection of bacterial spoilage during wine alcoholic fermentation using ATR-MIR and MCR-ALS

A new methodology is proposed to describe the evolution of the main chemical compounds of grape must during wine alcoholic fermentation using Attenuated Total Reflectance Mid Infrared (ATR-MIR) spectra in combination with Multivariate Curve Resolution Alternating Least-Squares (MCR-ALS). In addition, we have developed a process control strategy to detect differences between fermentations running under Normal Operation Conditions (NOC) and fermentations intentionally spoiled with lactic acid bacteria at the beginning of alcoholic fermentation (MLF) to promote deviations from NOC. MCR-ALS models on these data showed a good data fit (R 2 = 99.95% and lack of fit = 2.31%). It was possible to resolve the spectral profiles of relevant molecules involved in the alcoholic fermentation process, including the one related to bacterial spoilage (lactic acid). MSPC charts were built based on the concentration profiles obtained from the MCR-ALS models and using T 2 and Q statistics. Spoiled wines showed off-limit values for T 2 after 96 hours, making it possible to detect lactic acid bacteria spoilage in early stages of alcoholic fermentation. Thus, the use of ATR-MIR spectra and MCR-ALS analysis shows a great potential for a rapid control of the state of the alcoholic fermentation process, making it possible to early detect the appearance of undesired molecules during the process, which allows the winemaker to apply corrective measures and obtain a good final product. • ATR-MIR and MCR-ALS allow resolving main compounds involved in wine fermentation. • T 2 and Q MSPC charts are built using MCR-ALS concentration profiles. • The concept of ‘Inverse’ MSPC charts' is introduced. • Early detection of undesired molecules related to bacterial spoilage is achieved.

Form quantitation in desmotropic mixtures of albendazole bulk drug by chemometrics-assisted analysis of vibrational spectra

Albendazole is a benzimidazole-type active pharmaceutical ingredient, and one of the most effective broad-spectrum anthelminthic agents. The drug has two solid-state forms (ALB I and ALB II) which are desmotropes; both of them seem to be currently marketed. However, using the wrong crystalline solid form for formulation may have an undesired impact on the physicochemical and/or bioavailability properties of the drug product.In order to develop new, simple, and less expensive alternatives toward the determination of the level of albendazole ALB I in its mixtures with ALB II, both desmotropes were prepared, and properly characterized by spectroscopic [solid-state nuclear magnetic resonance and near infrared (NIR)] and diffractometric (powder X-ray diffraction) methods.Then, the NIR and attenuated total reflectance-mid infrared (ATR-MIR) spectra of both forms were conveniently pre-treated and employed for the development and optimization of partial least squares (PLS)-potentiated quantification models (NIR/PLS and ATR-MIR/PLS). The latter were also subjected to validation (accuracy, precision, limits of detection and quantification, etc.) and further used to assess the level of the unwanted ALB II form in the bulk drug. The NIR/PLS method displayed the most satisfactory characteristics, including a limit of quantitation interval of 3.6 ± 1 %w/w; it outperformed both, the ATR-MIR/PLS counterpart (limit of quantitation interval of 14.0 ± 3.4 %w/w) and a previously published and more demanding Raman/PLS alternative.

Development of Attenuated Total Reflectance Mid-Infrared (ATR-MIR) and Near-Infrared (NIR) Spectroscopy for the Determination of Resistant Starch Content in Wheat Grains.

The chemical method for the determination of the resistant starch (RS) content in grains is time-consuming and labor intensive. Near-infrared (NIR) and attenuated total reflectance mid-infrared (ATR-MIR) spectroscopy are rapid and nondestructive analytical techniques for determining grain quality. This study was the first report to establish and compare these two spectroscopic techniques for determining the RS content in wheat grains. Calibration models with four preprocessing techniques based on the partial least squares (PLS) algorithm were built. In the NIR technique, the mean normalization + Savitzky–Golay smoothing (MN + SGS) preprocessing technique had a higher coefficient of determination (Rc2 = 0.672; Rp2 = 0.552) and a relative lower root mean square error value (RMSEC = 0.385; RMSEP = 0.459). In the ATR-MIR technique, the baseline preprocessing method exhibited a better performance regarding to the values of coefficient of determination (Rc2 = 0.927; Rp2 = 0.828) and mean square error value (RMSEC = 0.153; RMSEP = 0.284). The validation of the developed best NIR and ATR-MIR calibration models showed that the ATR-MIR best calibration model has a better RS prediction ability than the NIR best calibration model. Two high grain RS content wheat mutants were screened out by the ATR-MIR best calibration model from the wheat mutant library. There was no significant difference between the predicted values and chemical measured values in the two high RS content mutants. It proved that the ATR-MIR model can be a perfect substitute in RS measuring. All the results indicated that the ATR-MIR spectroscopy with improved screening efficiency can be used as a fast, rapid, and nondestructive method in high grain RS content wheat breeding.

Detection of glibenclamide adulterated in antidiabetic Chinese patent medicine by attenuated total reflectance -infrared spectroscopy and chemometrics

There have been many reports of adulterated Chinese patent medicine with synthetic prescription that are claimed to be “pure natural”. The present work investigates the feasibility of combining attenuated total reflectance-Mid-infrared (ATR-MIR) spectroscopy and several interval-based PLS algorithms for detecting the glibenclamide illegally adulterated in antidiabetic Chinese patent medicine (Jiangtangning). The full-spectrum PLS, four kinds of traditional interval PLS algorithms (iPLS, biPLS, siPLS and mwPLS) and a modified algorithm, i.e., a combination of mwPLS and window size optimization, named cmwPLS, were used for building calibration models. A total of 21 samples adulterated with 0–3.5% glibenclamide were prepared. The dataset was equally split into a training set and a test set for building and testing the prediction models, respectively. For those interval-based PLS, the whole wavenumber axis was divided into 20 sub-intervals. In terms of the prediction on the test set, the new cmwPLS produce the best model, followed by mwPLS. The modified algorithm can optimize automatically the window width (i.e., the number of adjacent variables used for modeling) and position. It can be concluded that cmwPLS coupled with ATR-MIR technique is a good alternative to other traditional chemical analysis for detecting the adulteration of Chinese patent medicine.

Nutritional Quality and Bioactive Constituents of Six Australian Plum Varieties

ABSTRACT While plums are widely touted for their health benefits, there is little data available on the levels of beneficial anthocyanins and other antioxidative compounds found in commercial Australian plums. As such, this study aims to provide context data on the typical levels and variation in plums available to consumers. Six commercial plum varieties were sourced from Central Queensland grocery stores, including two varieties developed and grown exclusively in Australia – Croc Egg and “King Midas” yellow plums – as well as four varieties grown both in Australia and internationally: black, Dapple Dandy, red and sugar plums. These were analyzed for antioxidants, phenolics, anthocyanins and mineral contents. Significant differences between varieties were observed in the levels of total phenolics (65–160 mg gallic acid equivalents 100 g−1 on a fresh weight basis), antioxidants (cupric reducing antioxidant potential of 174–542 mg Trolox equivalents 100 g−1) and anthocyanins (0.3–21.5 mg cyanidin-3-glucoside equivalents 100 g−1), as well as in the flavonols quercetin (0.02–0.15 mg 100 g−1) and quercetin-3-glucoside (0.21–2.87 mg 100 g−1). Mid-infrared attenuated total reflectance (MIR-ATR) spectroscopy combined with principal component analysis could separate varieties based on their phytochemical composition. The findings suggest that commercially available Australian plums contain similar levels of health-benefitting compounds to those found internationally, although the levels of these compounds depend strongly on the considered variety.

Near- and mid-infrared determination of some quality parameters of cheese manufactured from the mixture of different milk species.

This study aimed to evaluate the performance of both near-infrared (NIR) diffuse reflectance and mid-infrared-attenuated total reflectance (MIR-ATR) in determining some quality parameters of a commercial white cheese made of unknown ratios of various milk species. For this purpose, 81 commercial Ezine cheese samples, a special ripened cheese produced in Turkey, containing unknown ratios of bovine, caprine, and ovine milk, were used. Reference analyses, including textural properties, protein content, nitrogen fractions, ripening index coefficients, fat, salt, dry matter-moisture, and ash contents as well as pH and titratable acidity levels, were conducted in the samples following the traditional gold standards. For NIR applications, the spectra of both intact cubes and hand-crushed cheese samples were collected, whereas the spectra of only hand-crushed cheese samples were collected for MIR-ATR. PLSR (Partial Least Squares Regression) calibration models were developed for each parameter (n = 61) and then validated using both cross-validation (leave-one-out approach) and an external validation set (n = 20). Overall, PLSR models developed for total protein, fat, salt, dry matter, moisture, and ash content, as well as pH and titratable acidity, yielded satisfactory performance statistics in the complementary use of NIR and MIR spectroscopy. However, PLSR models of the other parameters, including textural properties, nitrogen fractions, and the ripening index, could only separate high and low values and were not able to make accurate quantitative predictions. NIR spectroscopy was found to be more accurate than that of MIR-ATR spectroscopy for almost all the parameters except for pH and titratable acidity, for which MIR-ATR spectroscopy was superior.

Design and Performance of Diamond‐Based Mid‐Infrared Sensor

Herein, finite‐element analysis is used to optimize the performance of mid‐infrared (MIR) (7.7–13.7 μm) waveguides by selecting optimal waveguide and substrate materials, waveguide size, and boundary field. The results show that a diamond waveguide has a substantially higher sensitivity than Si‐ or Ge‐based waveguides owing to its higher boundary evanescent field at the same depth. Furthermore, it is found that AlN substrates have better optical stabilities than SiO2 and Si3N4 substrates, because AlN substrates do not have apparent absorption characteristics in the MIR range (7.7–13.7 μm). Geometry of diamond waveguide on AlN substrate is optimized, and a section length of 45 μm is chosen for optimal signal transmission quality. The calculations of the infrared attenuated total reflection (ATR) of the diamond waveguide applied to water, alcohol, and diisopropyl methyl phosphate are highly consistent with the actual infrared absorption spectrum. This proves the feasibility of applying AlN/diamond waveguides in MIR ATR detection, which is of great significance for the preparation of high‐sensitivity MIR detectors.

ATR-MIR spectroscopy as a tool to assist ‘Tempranillo’ clonal selection process: Geographical origin and year of harvest discrimination and oenological parameters prediction

The present study evaluated the ability of Attenuated Total Reflectance – Mid-Infrared (ATR-MIR) spectroscopy combined with Partial Least Squares Discriminant Analysis (PLS-DA) to discriminate the origin and harvest year of 'Tempranillo' grape clones and with Partial Least Squares (PLS) regressions to predict its contents in soluble solids (SS), pH and titratable acidity (TA). Normalized spectra of grape homogenates and normalized plus 1st Derivative spectra of grape skins allowed an overall percentage of correct classifications of 99.6% and 96.7% in validation, according to origin, and 98.3% and 90.0% in validation, according to harvest year, respectively. The normalized spectra of grape homogenates allowed a calibration and validation determination coefficients (R2) of 0.92 and 0.90 for SS, 0.90 and 0.84 for pH, 0.88 and 0.84 for TA, respectively.The ATR-MIR combined with multivariate analysis showed to be an appropriate tool to assist the clonal selection process of 'Tempranillo'.

ATR-MIR Spectroscopy Predicts Total Phenolics and Colour for Extracts Produced by Microwave-Assisted or Conventional Thermal Extraction Methods Applied Separately to Mixtures of Grape Skins from White or Red Commercial Cultivars

Attenuated total reflectance mid-infrared (ATR-MIR) spectra were collected from 480 grape skin extracts produced in a wide range of conditions. The conditions were created at different phases in parallel response surface RS-optimisation experiments aiming to maximise the total phenolics in red and white grape skin extractions by microwave-assisted (MAE) or conventional thermal (CTE) methods. Skins mixtures for six white and six red Australian commercial cultivars were prepared from grapes collected at veraison and harvest. The total phenolics were measured for individual extracts with the Folin-Ciocalteu method. Partial least squares (PLS1) regression was employed on the spectra to predict the total phenolics (TP) and colour (CIELAB chroma C*) of individual extracts. Models based on the raw spectra and their second derivative (Savitzky-Golay, 20 points) were examined using the full range of spectra 4000–400 cm−1, and sub-ranges: 4000–1100 cm−1, 1500–400 cm−1, 1500–1100 cm−1 and 1457–1168 cm−1. The PLS1 models based on the second derivative of the range of 4000–1100 cm−1 provided the best results for both TP and C*, for each skin colour. Overall, the residual predictive deviation (RPD) exceeded 3.0, indicating the PLS1 models’ ability for fair classification, suitable for screening. A comparative analysis was performed for the range of 4000–1100 cm−1 between the spectra of white and red skin mixture extracts: the peaks at 3840 cm−1, 2940 cm−1, 2358 cm−1, 2197 cm−1, 2136 cm−1, 1725 cm−1, 1100 cm−1 and 1148 cm−1 are flagged to be investigated in further research. ATR-MIR spectroscopy can reduce the time and costs of TP and C* analyses in grape skin extracts.

Assessment of ATR-NIR and ATR-MIR spectroscopy as an analytical tool for the quantification of the total polyphenols in Dendrobium huoshanense.

In this study, the potentiality of applying attenuated total reflectance near-infrared (ATR-NIR) and attenuated total reflectance mid-infrared (ATR-MIR) techniques combined with a partial least squares (PLS) regression technology to quantify the total polyphenols (TPs) in Dendrobium huoshanense (DHS) was investigated and compared. The real TP contents in the DHS samples were analysed using methods of reference. The capability of the two IR spectroscopic techniques to quantify the TPs in DHS was assessed by the root-mean-square error of calibration (RMSEC) and determination coefficients (R2 ). The results showed that both NIR and MIR might be used as a fast and simple tool to replace traditional chemical assays for the determination of the TP contents in DHS, and the best NIR model showed slightly better prediction performance [root-mean-square error of prediction (RMSEP): 0.307, R2 : 0.9122, ratio performance deviation (RPD): 4.43] than the best MIR model (RMSEP: 0.440, R2 : 0.9069, RPD: 3.09). Results from this study indicated that both the NIR and MIR models could be used to quantify the TP in DHS, and ATR-NIR appeared to be the more predominant and more robust technique for the quantification of the TP in DHS.

Screening Malaysian edible bird’s nests for structural adulterants and geographical origin using Mid-Infrared – Attenuated Total Reflectance (MIR-ATR) spectroscopy combined with chemometric analysis by Data-Driven – Soft Independent Modelling of Class Analogy (DD-SIMCA)

Edible bird’s nest (EBN) is widely consumed in South-East Asia as a health food product. In recent years, the adulteration of EBN is quite common due to its high economic value and limited supplies of the natural authentic product. Authentication and traceability of EBN demands time-consuming sequential analytical measurements to confirm that the product quality meets technical and regulatory requirements. Mid Infrared spectroscopy combined with chemometric analysis by Data-Driven Soft Independent Modelling of Class Analogy (DD-SIMCA) was used in this study to screen Malaysian EBNs for structural adulterants and for confirmation of geographical origin. The samples used were authentic processed EBNs of different grades (2A, 3A, 4A and 5A) from the swiftlet species Aerodramus fuciphagus supplied by Ministry of Health, Malaysia. Similarly, adulterants commonly used in EBN namely agar, Karaya gum, bovine gelatin, fish skin, melamine and porcine gelatine were also characterized. Adulterant mixtures were prepared gravimetrically at concentrations of 1, 5 and 10%w/w by combining appropriate quantities of adulterants with individual authentic EBN samples. Samples were then analyzed by Mid-Infrared – Attenuated Total Reflectance (MIR-ATR) spectroscopy. All test samples are properly categorized as members of the target class. However, 61% of the tested adulterated EBNs were correctly classified as ‘alien’ or non-authentic samples. The sensitivity and specifity values for DD-SIMCA models applied to origin determination ranged from 90 to 100% for production regions from Kelantan, Perak and Malacca. MIR-ATR spectroscopy in combination with DD-SIMCA modelling has shown potential as a rapid screening technique to detect the presence adulterants and confirm the provenance of EBN produced in Malaysia. Further work is required to validate the approach with a larger set of authentic samples and for a wider range of adulterants including flavour enhancers and preservatives.

Prediction of the total acid number (TAN) of colombian crude oils via ATR–FTIR spectroscopy and chemometric methods

Reactions as the attack by naphthenic and hydrogen sulfide have caused corrosion problems in the petroleum industry due to they affect the crude oil heating furnaces and distillation towers at temperatures between 220 and 400 °C. The total acid number (TAN) measurement has been used as a test to quantify the acid compounds in crude oils and has shown to be a reliable indicator of their corrosion degree. However, the standard method for the TAN measurement, ASTM D-644, involves long times, environment unfriendly wastes and high costs for each analysis. A more appropriate method for the TAN determination is implemented in this paper, by correlating Fourier transform infrared spectroscopy (FTIR) spectral data of the samples with the standard method measurements using multivariate regression models. In particular, the intensities and frequencies of their mid-infrared attenuated total reflectance (MIR-ATR) spectra (4000 - 400 cm−1) are used as independent variables of several principal component regression (PCR) and partial least squares regression (PLSR) models. The latter are employed to correlate the spectra with their respective TAN values so as to obtain a suitable prediction model. Twenty-six (26) samples of Colombian crude oils are used for the study with a TAN ranging from 0.1 to 6.8 mg KOH/g crude oil (ASTM D-664). The models are evaluated according to the coefficient of determination (R2), the root mean square error of calibration (RMSEC) and of prediction (RMSEP). The best model is obtained via PLSR using as few as four components (i.e. factors), which attains a calibration R2 of 0.981 and an RMSEC of 0.317 mg KOH/g crude oil, while for prediction it attains an R2 of 0.996 and an RMSEP of 0.160 mg KOH/g crude oil. It is observed that the functional groups COOH, CH3 and CH2 contribute the most to the prediction models. The designed methodology is faster and environmentally friendly since it does not require sample pretreatment and the use of toxic reagents, and of low-cost compared with the standard procedure since FTIR measurements can be easily taken anywhere using a hand-held or portable spectrometer and a laptop.

Potato hierarchical clustering and doneness degree determination by near-infrared (NIR) and attenuated total reflectance mid-infrared (ATR-MIR) spectroscopy

Near-infrared (NIR) and attenuated total reflectance mid-infrared (ATR-MIR) spectroscopy were used to identify potato varieties and detect potato doneness degree. The varieties of potato tubers can be successfully classified by hierarchical cluster analysis (HCA). The partial least squares regression (PLSR) model exhibited good prediction result for the doneness degree evaluation. Principal component and first-derivative iteration algorithm (PCFIA) was introduced to select feature variables instead of using the full wavelength spectra for modelling. Based on two sets of feature variables selected from NIR and MIR regions, both NIR–PCFIA–HCA and MIR–PCFIA–HCA showed higher performances of hierarchical clustering. Moreover, NIR–PCFIA–PLSR and MIR–PCFIA–PLSR models were effectively used to predict tuber doneness degree, yielding the RP as high as 0.935 and the RMSEP as low as of 0.503. It is concluded that the PCFIA is an effective approach for feature variable selection, and both NIR and MIR spectroscopic techniques are capable of classifying potato varieties and determining potato doneness degree.

Chemometric compositional analysis of phenolic compounds in fermenting samples and wines using different infrared spectroscopy techniques

The wine industry requires reliable methods for the quantification of phenolic compounds during the winemaking process. Infrared spectroscopy appears as a suitable technique for process control and monitoring. The ability of Fourier transform near infrared (FT-NIR), attenuated total reflectance mid infrared (ATR-MIR) and Fourier transform infrared (FT-IR) spectroscopies to predict compositional phenolic levels during red wine fermentation and aging was investigated. Prediction models containing a large number of samples collected over two vintages from several industrial fermenting tanks as well as wine samples covering a varying number of vintages were validated. FT-NIR appeared as the most accurate technique to predict the phenolic content. Although slightly less accurate models were observed, ATR-MIR and FT-IR can also be used for the prediction of the majority of phenolic measurements. Additionally, the slope and intercept test indicated a systematic error for the three spectroscopies which seems to be slightly more pronounced for HPLC generated phenolics data than for the spectrophotometric parameters. However, the results also showed that the predictions made with the three instruments are statistically comparable. The robustness of the prediction models was also investigated and discussed.

Does sample drying temperature affect the molecular characteristics of organic matter in soil and litter? A statistical proof using ATR infrared spectra

At each step of sample handling and pretreatment it is important to consider potential effects on the result of the analysis. Sample drying is a basic procedure in sample preparation for many analyses. In practice, different sample drying procedures (e.g. freeze drying, air drying, or drying at different temperatures up to 105°C) may be used prior to perform attenuated total reflection (ATR) spectroscopy, but the effect of sample drying temperature is rarely assessed. The latter technique was used to test the influence of sample drying treatment on the molecular characteristics of six contrasting substrates which are common in soil science (two mineral soils, two organic soils and two foliar litter samples). We compared the mid-infrared ATR spectra of the samples after freeze-drying, as well as oven-drying at 60 and 105°C, respectively. Our results demonstrate a significant absence of any detectable influence of sample drying on the spectra of the six substrates under study, and hence on parameters which are reflected in the spectra. Accepting null hypothesis of no effect is linked to a risk of the second kind (β). Calculation of β needs a proper design of the experiment (DoE). By means of this DoE, the result is significant on a 5% level. In previous studies where drying temperature had influenced organic matter composition, either (1) labile compounds in fresh organic materials were under investigation, or (2) parameters were investigated which cannot be detected by using the ATR technique. Our results indicate that in the context of soil organic matter – where fresh materials containing labile compounds are of minor interest − the drying conditions do not affect the determination of parameters, which can be studied by means of the ATR technique.

Comparison of near-infrared diffuse reflectance (NIR) and attenuated-total-reflectance mid-infrared (ATR-IR) spectroscopic determination of the antioxidant capacity of Sambuci flos with classic wet chemical methods (assays)

An analytical strategy for the fast and easy determination of the antioxidant potential ofSambucus nigra.

Mid-Infrared Spectroscopic Method for the Identification and Quantification of Dissolved Oil Components in Marine Environments.

The use of mid-infrared sensors based on conventional spectroscopic equipment for oil spill monitoring and fingerprinting in aqueous systems has to date been mainly confined to laboratory environments. This paper presents a portable-based mid-infrared attenuated total reflectance (MIR-ATR) sensor system that was used to quantify a number of environmentally relevant hydrocarbon contaminants in marine water. The sensor comprises a polymer-coated diamond waveguide in combination with a room-temperature operated pyroelectric detector, and the analytical performance was optimized by evaluating the influence of polymer composition, polymer film thickness, and solution flow rate on the sensor response. Uncertainties regarding the analytical performance and instrument specifications for dissolved oil detection were investigated using real-world seawater matrices. The reliability of the sensor was tested by exposition to known volumes of different oils; crude oil and diesel samples were equilibrated with seawater and then analyzed using the developed MIR-ATR sensor system. For validation, gas chromatographic measurements were performed revealing that the MIR-ATR sensor is a promising on-site monitoring tool for determining the concentration of a range of dissolved oil components in seawater at ppb to ppm levels.

Seed set, pollen morphology and pollen surface composition response to heat stress in field pea.

Pea (Pisum sativum L.) is a major legume crop grown in a semi-arid climate in Western Canada, where heat stress affects pollination, seed set and yield. Seed set and pod growth characteristics, along with in vitro percentage pollen germination, pollen tube growth and pollen surface composition, were measured in two pea cultivars (CDC Golden and CDC Sage) subjected to five maximum temperature regimes ranging from 24 to 36 °C. Heat stress reduced percentage pollen germination, pollen tube length, pod length, seed number per pod, and the seed-ovule ratio. Percentage pollen germination of CDC Sage was greater than CDC Golden at 36 °C. No visible morphological differences in pollen grains or the pollen surface were observed between the heat and control-treated pea. However, pollen wall (intine) thickness increased due to heat stress. Mid-infrared attenuated total reflectance (MIR-ATR) spectra revealed that the chemical composition (lipid, proteins and carbohydrates) of each cultivar's pollen grains responded differently to heat stress. The lipid region of the pollen coat and exine of CDC Sage was more stable compared with CDC Golden at 36 °C. Secondary derivatives of ATR spectra indicated the presence of two lipid types, with different amounts present in pollen grains from each cultivar.

MIR-ATR sensor for process monitoring

A mid-infrared attenuated total reflectance (MIR-ATR) sensor has been developed for chemical reaction monitoring. The optical setup of the compact and low-priced sensor consists of an IR emitter as light source, a zinc selenide (ZnSe) ATR prism as boundary to the process, and four thermopile detectors, each equipped with an optical bandpass filter. The practical applicability was tested during esterification of ethanol and formic acid to ethyl formate and water as a model reaction with subsequent distillation. For reference analysis, a Fourier transform mid-infrared (FT-MIR) spectrometer with diamond ATR module was applied. On-line measurements using the MIR-ATR sensor and the FT-MIR spectrometer were performed in a bypass loop. The sensor was calibrated by multiple linear regression in order to link the measured absorbance in the four optical channels to the analyte concentrations. The analytical potential of the MIR-ATR sensor was demonstrated by simultaneous real-time monitoring of all four chemical substances involved in the esterification and distillation process. The temporal courses of the sensor signals are in accordance with the concentration values achieved by the commercial FT-MIR spectrometer. The standard error of prediction for ethanol, formic acid, ethyl formate, and water were 0.38 mol L − 1, 0.48 mol L − 1, 0.38 mol L − 1, and 1.12 mol L − 1, respectively. A procedure based on MIR spectra is presented to simulate the response characteristics of the sensor if the transmission ranges of the filters are varied. Using this tool analyte specific bandpass filters for a particular chemical reaction can be identified. By exchanging the optical filters, the sensor can be adapted to a wide range of processes in the chemical, pharmaceutical, and beverage industries.