Automated quantitative analysis of isolated (nonconjugated) trans isomers using fourier transform infrared spectroscopy incorporating improvements in the procedure

The online version of the original article can be found at     

Upgrading the AOCS infrared trans method for analysis of neat fats and oils by fourier transform infrared spectroscopy

An automated protocol for the direct, rapid determination of isolated trans content of neat fats and oils by Fourier transform infrared (FTIR) spectroscopy was devised, based on a simple modification of the standard AOCS trans method, eliminating the use of CS₂ and methylation of low trans samples. Through the use of a commercially available, heated transmission flow cell, designed specifically for the analysis of neat fats and oils, a calibration (0–50%) was devised with trielaidin spiked into a certified, trans-free soybean oil. The single-beam spectra of the calibration standards were ratioed against the single-beam spectrum of the base oil, eliminating the spectral interference caused by underlying triglyceride absorptions, facilitating direct peak height measurements as per the AOCS IR trans method. The spectrometer was preprogrammed in Visual Basic to carry out all spectral manipulations, measurements, and calculations to produce trans results directly as well as to provide the operator with a simple interface to work from. The derived calibration was incorporated into the software package, obviating the need for further calibration because the program includes an automatic recalibration/standardization routine that automatically compensates for differences in optical characteristics between instruments, instrument drift over time, and cell wear. The modified AOCS FTIR analytical package was evaluated with Smalley check samples for repeatability, reproducibility, and accuracy, producing SD of ± 0.07, 0.13, and 0.70 trans, respectively, the FTIR predictions being linearly related to the Smalley means (r=0.999; SD=± 0.46), and well within one SD of the Smalley sample means. Calibration transfer was assessed by implementing the calibration on a second instrument and reanalyzing the Smalley check samples in cells of two different pathlengths (25- and 50-μm). There were no statistically significant differences between the FTIR trans predictions obtained for the Smalley samples from the two instruments and two cells, indicating that the software was able to adjust the calibrations to compensate for differences in instrument response and cell pathlength. The FTIR isolated trans analysis protocol developed by the McGill IR Group has the benefit of being based on the principles of an AOCS-approved method, matches its accuracy, and allows the analysis to be performed on both neat fats and oils, producing trans predictions in less than 2 min per sample. It is suggested that this integrated approach to trans analysis, which requires a minimum level of sample manipulation and operator skill, be considered as a modification of the proposed Recommended Practice CD14b-95.     

Quantitative analysis of palm carotene using fourier transform infrared and near infrared spectroscopy

β-Carotene content is usually determined by using ultraviolet (UV)-visible spectrophotometry at 446 nm. In this study, two spectroscopic techniques, namely, Fourier transform infrared (FTIR) and near infrared (NIR) spectroscopy, have been investigated and compared to UV-visible spectrophotometry to measure the β-carotene content of crude palm oil (CPO). Calibration curves ranging from 200 to 800 ppm were prepared by extracting β-carotene from original CPO using open-column chromatography. Separate partial least squares calibration models were developed for predicting β-carotene based on the spectral region from 976 to 926 cm⁻¹ for FTIR spectroscopy and 546 to 819 nm for NIR spectroscopy. The correlation coefficient (R ²) and standard error of calibration obtained were 0.972 and 25.2 for FTIR and 0.952 and 23.6 for NIR techniques, respectively. The validation set gave R ² of 0.951 with standard error of performance (SEP) of 25.78 for FTIR technique and R ² of 0.979 with SEP of 19.96 for NIR technique. The overall reproducibility and accuracy did not give comparable results to that of spectrophotometric method; however, the standard deviation of prediction was still within ±5% β-carotene content over the range tested. Because of their rapidness and simplicity, both FTIR and NIR techniques provide alternative means of measuring β-carotene content in CPO. In addition, these two spectroscopic techniques are environmentally friendly since no solvent is involved.     

Determination of low trans levels in refined oils by fourier transform infrared spectroscopy

A Nicolet 410 Fourier (FTIR) spectrophotometer, equipped with a DGTS detector and a sample cell with NaCl windows (nominal pathlength=50 μm), was used for the development of an FTIR method for routine analysis of low trans levels in physically refined oils. The approach of the study differed from those previously described in that a separate calibration curve was established for each type of oil. Quantitation was established by use of Basic Quant Software® and by measuring the peak height at 967 cm^?1 relative to a baseline drawn between 1002 and 932 cm^?1. The slope of the different calibration curves established in six vegetable oils (soybean, corn, sunflower, high-oleic sunflower, low-erucic rapeseed, and high-erucic rapeseed) was close to 1 (0.9942–1.0041), and correlation coefficients (r ²) were rather good (0.9990–0.9999). FTIR spectra of 20 soybean oil samples were collected and quantitated with the different calibrations. Compared to previous reported literature data, increased accuracy (mean difference=0.05%; standard deviation of difference=0.11%) and reproducibility (r ²=0.09–0.12%) were obtained when the FTIR spectra were quantitated with a calibration curve based on 10 physically refined soybean oil samples.     

The characterization of short chain branching in polyethylene using fourier transform infrared spectroscopy

The characterization of short chain branching in polyethylene using transmission FTIR spectroscopy is investigated. Traditional methodologies, using the methyl deformation band for qualitative and quantitative analyses, have recognized shortcomings. The methyl and methylene rocking bands, which are more characteristic of short chain branch type, were found to be more useful. Methyl, ethyl, butyl, isobutyl, and hexyl branches are qualitatively and quantitatively characterized in LLDPE copolymers by FTIR spectroscopy. Methyl branches were characterized by an absorbance at 935 cm^?1, ethyl branches at 770 cm^?1, butyl branches at 893 cm^?1, isobutyl branches at 920 cm^?1, and hexyl branches at 888 cm^?1. Fourier self-deconvolution was used to resolve overlapping bands for ethyl, butyl, and isobutyl branches. Using calibrations derived for LLDPE copolymers from ¹³C NMR data, FTIR spectroscopy was also used to characterize LLDPE terpolymers and LDPE resins. The FTIR and NMR data are in qualitative and quantitative agreement. In some cases correction were made to the FTIR results using data obtained from the methyl deformation band. The FTIR technique is less costly and faster than NMR spectroscopy. © 1994 John Wiley & Sons, Inc.     

Characterization of model anaerobic adhesive cure using real-time fourier transform infrared spectroscopy and dielectric spectroscopy

A technique has been developed based on Fourier transform infrared spectroscopy (FTIR) in the attenuated total reflectance (ATR) mode, which is suitable for the investigation of the heterogeneous cure of surface-initiated redox polymerizations in thin and thick bondline situations. The results of the investigations into the surface-catalyzed and anaerobically promoted cure of some model adhesives using this method are reported. The systems under investigation were designed to exhibit different levels of cure heterogeneity or “cure through volume” (CTV) so that the influence of the bondline thickness and the formulation variables may be assessed. The analysis of the data provides evidence that supports our concept of the heterogeneous cure distribution existing in the form of a cure gradient. This concept of a cure gradient is developed further using dielectric spectroscopy. Here the cure gradient is characterized in terms of the parameters obtained using an empirical equation to fit the dielectric relaxation data. The results obtained using the infrared and dielectric spectroscopic methods are in satisfactory agreement and are shown to be most informative in characterizing and quantifying the CTV performance of the model anaerobic adhesives. © 1994 John Wiley & Sons, Inc.     

Rapid quantitative determination of free fatty acids in fats and oils by fourier transform infrared spectroscopy

Rapid direct and indirect Fourier transform infrared (FTIR) spectroscopic methods were developed for the determination of free fatty acids (FFA) in fats and oils based on both transmission and attenuated total reflectance approaches, covering an analytical range of 0.2–8% FFA. Calibration curves were prepared by adding oleic acid to the oil chosen for analysis and measuring the C=O band @ 1711 cm^–1 after ratioing the sample spectrum against that of the same oil free of fatty acids. For fats and oils that may have undergone significant thermal stress or extensive oxidation, an indirect method was developed in which 1% KOH/methanol is used to extract the FFAs and convert them to their potassium salts. The carboxylate anion absorbs @ 1570 cm^–1, well away from interfering absorptions of carbonyl-containing oxidation end products that are commonly present in oxidized oils. Both approaches gave results comparable in precision and accuracy to that of the American Oil Chemists’ Society reference titration method. Through macroprogramming, the FFA analysis procedure was completely automated, making it suitable for routine quality control applications. As such, the method requires no knowledge of FTIR spectroscopy on the part of the operator, and an analysis takes less than 2 min.     

Milled rice surface lipid measurement by diffuse reflectance fourier transform infrared spectroscopy (DRIFTS)

Diffuse reflectance Fourier transform infrared spectroscopy was investigated as a method for rice surface lipid determination. Long- and medium-grain rice was milled at four degrees of milling to obtain samples with various levels of residual bran, and total lipids were determined by solvent extraction. Fourier transform infrared spectra were collected between 4000 and 400 cm⁻¹. Weighted regression analysis identified changes in surface chemical functional groups with bran removal. Groups typical of lipids increased with bran content whereas those typical of carbohydrates and protein decreased. Partial least squares (PLS) regression analysis showed a high degree of correlation between the spectra in the 4000–400 cm⁻¹ range and extracted lipids of long-grain rice (R ²=0.96) and medium-grain rice (R ²=0.96); a high degree of correlation was also observed when long- and medium-grain rice data were combined (R ²=0.96). There was a high positive correlation between the spectra and extracted lipids in the 1300–1000 cm⁻¹ range for the long-grain rice (R ²=0.98), medium-grain rice (R ²=0.98), and combined long-/medium-grain rice data (R ²=0.94). PLS selected spectral regions that correlated positively with functional groups of lipid/lipid oxidation products and negatively with functional groups of protein and carbohydrates.     

Determination of phospholipids in vegetable oil by fourier transform infrared spectroscopy

A method was developed to determine the total phospholipid content in vegetable oil by Fourier transform infrared spectroscopy (FTIR). Calibration curves of I-α-phosphatidylcholine (PC), I-α-phosphatidylethanolamine (PE), and I-α-phosphatidylinositol (PI) in hexane were generated at different concentrations. The optimal phospholipid absorption bands between 1200–970 cm⁻¹ were identified and used for quantitative determination. High R ²≥0.968 were observed between band areas and phospholipid standard concentrations. Phospholipids from crude soybean oil were obtained by water degumming, and purification was performed on a silicic acid column. The phospholipid contents of purified phospholipid extract, degummed and crude soybean oil determined from calibration equations were >90, 0.0113, and 1.77%, respectively. High correlations of determination (R ²≥0.933) were observed between the FTIR method and thin-layer chromatography-imaging densitometry method for the determination of phospholipid content. FTIR was found to be a useful analytical tool for simple and rapid quantitative determination of phospholipids in vegetable oil.     

Trans fatty acid determination in fats and margarine by fourier transform infrared spectroscopy using a disposable infrared card

The use of a disposable polyethylene infrared (IR) card as a sample carrier for the quantitative determination of trans content of fats and oils and margarine by Fourier transform IR spectroscopy was investigated. Standards prepared by dissolving trielaidin in a zero-trans oil were used to develop partial least squares (PLS) calibrations for both the IR card and a 100-μm transmission flow cell. These calibrations were then used to predict a series of gas chromatographically-preanalyzed unknowns, the trans predictions obtained using the card being comparable to those obtained with the transmission flow cell. Somewhat improved performance could be obtained when the spectral data from the card were normalized to compensate for inherent variations in path length and variability in sample loading. Both IR methods tracked the gas chromatographic reference trans values very well. A series of margarine samples was also analyzed by the card method, producing results similar to those obtained using a flow cell. For the analysis of margarines, the card method has the advantage that the trans analysis can be performed directly on microwave melted emulsions because moisture is not retained on the card. Overall, the disposable IR card was shown to work well and has the benefit of allowing trans analyses to be carried out without requiring investment in a heated flow cell or attenuated total reflectance accessory.     

Stoichiometric determination of hydroperoxides in fats and oils by fourier transform infrared spectroscopy

A primary Fourier transform infrared (FTIR) spectroscopic method for the determination of peroxide value (PV) in edible oils was developed based on the stoichiometric reaction of triphenylphosphine (TPP) with hydroperoxides to produce triphenylphosphine oxide (TPPO). Accurate quantitation of the TPPO formed in this reaction by measurement of its intense absorption band at 542 cm⁻¹ provides a simple means of determining PV. A calibration was developed with TPPO as the standard; its concentration, expressed in terms of PV, covered a range of 0–15 PV. The resulting calibration was linear over the analytical range and had a standard deviation of ±0.05 PV. A standardized analytical protocol was developed, consisting of adding ∼0.2 g of a 33% (w/w) stock solution of TPP in hexanol to ∼30 g of melted fat or oil, shaking the sample, and scanning it in a 100-μm KCI IR transmission cell maintained at 80°C. The FTIR spectrometer was programmed in Visual Basic to automate scanning and quantitation, with the reaction/FTIR analysis taking about 2 min per sample. The method was validated by comparing the analytical results of the AOCS PV method to those of the automated FTIR procedure by using both oxidized oils and oils spiked with tert-butyl hydroperoxide. The two methods correlated well. The reproducibility of the FTIR method was superior (±0.18) to that of the standard chemical method (±0.89 PV). The FTIR method is a significant improvement over the standard AOCS method in terms of analytical time and effort and avoids solvent and reagent disposal problems. Based on its simple stoichiometry, rapid and complete reaction, and the singular band that characterizes the end product, the TPP/TPPO reaction coupled with a programmable FTIR spectrometer provides a rapid and efficient means of determining PV that is especially suited for routine quality control applications in the fats and oils industry.     

Mechanism of degradation of poly(vinyl butyral) using thermogravimetry/fourier transform infrared spectrometry

A TG/FTIR system was used to identify the products of thermal oxidative degradation of PVB, and also to elucidate the mechanism of degradation. This technique is useful in the kinetic analysis of fast reactions such as polymer degradation, unlike the use of a TG/GC/FTIR system, in which long retention times are needed to separate the products. A computer resolution method based on a pattern recognition technique is proposed to resolve the dynamic mixture IR spectra of the degradation products. A four-component synthetic mixture was used to evaluate the performance of the resolution algorithm and was found to be accurate within ±5%. The method was then applied to PVB degradation. The dynamic information of PVB thermal oxidative degradation obtained by resolving the mixture IR spectra was used to elucidate the reaction mechanism and to determine the kinetic parameters. Results showed that PVB degradation in air took place at a temperature 50K lower and the overall activation energy dropped from 338 kJ/mole (in nitrogen) to 200 kJ/mole (in air) compared with the degradation in a nitrogen atmosphere.     

Influence of a photoinitiator on the photochemical stability of poly(methyl methacrylate) studied with fourier transform infrared spectroscopy

Fourier transform infrared (FTIR) spectroscopy was used to investigate the effect of a commercial photoinitiator [2,2‐dimethoxy‐2‐phenylacetophenone (DMPA); Irgacure 651, Ciba, Basel, Switzerland] incorporated into poly(methyl methacrylate) (PMMA). Pure PMMA and modified PMMA (containing 5% DMPA) films were exposed to a xenon lamp in air. Qualitative and quantitative analyses of the recorded FTIR absorption spectra were done. This allowed us to determine the differences in the course of polymer photooxidative degradation occurring in PMMA and PMMA doped with DMPA. We found that the initiator added to polymer film enhanced the efficiency of the formation of the photooxidized products containing functional groups of different types, which could be distinguished by mathematical treatment of the FTIR spectra. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Kinetic parameters of the thermoplastic/thermoset epoxy reaction by fourier transform infrared spectroscopy

The melt state reaction, or fusion process of bisphenol-A and the diglycidyl ether of bisphenol-A can produce both linear phenoxy backbone chains and crosslinked network structures. The linear chains can be thought of as thermoplastic polymer, while the crosslinked molecular matrix is a thermoset; therefore, this resin system can be termed a thermoplastic/thermoset epoxy. Fourier transform infrared spectroscopy has been employed to study the chemical kinetics of the urea catalyzed system. The reaction of bisphenol-A and the diepoxide follows first order kinetics with respect to epoxide concentration, through 95 percent consumption of the epoxide for reaction temperatures of 130°C and above while lower temperatures show deviation from first order behavior at 75 percent conversion. When the differential form of the kinetic equation is used for analysis, the system follows first order behavior through 60 percent conversion of the epoxide at which point the order increases to a value of 1.5. Rapid spectral collection techniques have been employed to study this behavior for the temperatures 110 to 160°C. Upon incorporation of 3,4′ bisphenol-A into the system first order behavior still adequately describes the kinetic behavior; however the rate of epoxide consumption and the activation energy are affected. Since the stoichiometric ratio of bisphenol-A to diepoxide was found to affect the rate constant, the reaction mechanisms of linear chain growth and crosslinking cannot be clearly distinguished by the sole use of this technique.     

Simultaneous determination of lodine value and trans content of fats and oils by single-bounce horizontal attenuated total reflectance fourier transform infrared spectroscopy

A method for the simultaneous determination of iodine value (IV) and trans content from the Fourier transform infrared (FTIR) spectra of neat fats and oils recorded with the use of a heated single-bounce horizontal attenuated total reflectance (SB-HATR) sampling accessory was developed. Partial least squares (PLS) regression was employed for the development of the calibration models, and a set of nine pure triacylglycerols served as the calibration standards. Regression of the FTIR/PLS-predicted IV and trans contents for ten partially hydrogenated oil samples against reference values obtained by gas chromatography yielded slopes close to unity and SD of <1. Good agreement (SD<0.35) also was obtained between the trans predictions from the PLS calibration model and trans determinations performed by the recently adopted AOCS FTIR/SBHART method for the determination of isolated trans isomers in fats and oils.     

A quantitative analysis of low density polyethylene and linear low density polyethylene blends by differential scanning calorimetery and fourier transform infrared spectroscopy methods

Blends of low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) are widely used for blown film applications. An accurate and rapid test scheme to identify the type and composition of α-olefin in LDPE/LLDPE blends has been developed that utilizes differential scanning calorimetery (DSC) and Fourier transform infrared (FTIR) spectroscopy techniques. The melting point of LDPE varies with density and usually is in the range of 106°C to 112°C for film grade resins. The DSC thermogram of LLDPE is characterized by a broad range of melting peaks with a lower melting peak around 106°C to 110°C and a higher one in the range of 120°C to 124°C. In a blend with LDPE, the ratio of the two endothermic peak heights changes. At a given weight percent of LDPE, this ratio depends on the type of LLDPE (i.e., the comonomer used). Separate calibrations for butene-1, hexene-1, and octene-1 LLDPEs have been developed to quantify the blend composition from DSC thermograms where the α-olefin type is successfully identified by FTIR over the entire blend composition range. The calibration curves are applicable to narrow melt index (MI) and density range conventional film grade LDPE and LLDPE resins and are not intended to be used for the metallocene type LLDPEs.     

Polymerization kinetics of polyurethane and vinyl ester resin interpenetrating polymer networks by using fourier transform infrared spectroscopy

Fourier transform infrared spectroscopy (FTIR) was applied to the study of polymerization kinetics of simultaneous interpenetrating polymer networks (SINs) composed of polyurethane (PU) and vinyl ester resin (VER), in which the pendent hydroxyl groups were capped with acetyl groups to minimize the possibility of chemical binding between the two networks. It was found that during the course of synthesis the two pairs of reactants interfere with each other in the SIN systems, giving rise to depressed reaction rates, although they follow different polymerization mechanisms. Increasing the reaction temperature could be more effective than increasing the free-radical initiator level with regard to the final conversions of both components. The reaction sequence could be varied through the amount of the step-growth polymerization catalyst and free-radical initiator as well as the reaction temperature adjustment. Using VER containing pendent hydroxyl groups could strongly affect the reaction kinetics of such SINs and lead to hybrid structures. The quick formation of one network would always depress the conversion of the other network in all SINs studied. © 1996 John Wiley & Sons, Inc.