Determination of olive oil free fatty acid by fourier transform infrared spectroscopy

A new procedure for determining free fatty acids (FFA) in olive oil based on spectroscopic Fourier transform infrared-attenuated total reflectance spectroscopy measurements is proposed. The range of FFA contents of samples was extended by adding oleic acid to several virgin and pure olive oils, from 0.1 to 2.1%. Calibration models were constructed using partial least-squares regression (PLSR). Two wavenumber ranges (1775–1689 cm⁻¹ and 1480–1050 cm⁻¹) and several pretreatments [first and second derivative; standard normal variate (SNV)] were tested. To obtain good results, splitting of the calibration range into two concentration intervals (0.1 to 0.5% and 0.5 to 2.1%) was needed. The use of SNV as a pretreatment allows one to analyze samples of different origins. The best results were those obtained in the 1775–1689 cm⁻¹ range, using 3 PLSR components. In both concentration ranges, at a confidence interval of α = 0.05, no significant differences between the reference values and the calculated values were observed. Reliability of the calibration vs. stressed oil samples was tested, obtaining satisfactory results. The developed method was rapid, with a total analysis time of 5 min; it is environment-friendly, and it is applicable to samples of different categories (extra virgin, virgin, pure, and pomace oil).     

红外光谱法鉴定爆炸物

依据爆炸物的种类,介绍了烟火药剂、硝酸钾类爆炸物、硝酸铵类炸药的分离方法。根据化学分离方法进行分离定量,利用红外光谱技术对各爆炸物分离组分进行定性,鉴定爆炸物的种类。     

Estimating the average carbon chain length of saturated fatty acid esters by infrared spectroscopy

The average carbon chain length of saturated fatty acid esters can be determined by comparing absorption intensities in the 3.3 and 5.75 μ infrared regions. Data are presented for triglycerides, monoglycerides, and methyl esters. The method was used to follow the fractionation of hydrogenated milk fat from acetone, and the average values for fatty acid chain length were in good agreement with those obtained by gas chromatographic methyl ester analysis. The I.R. method is particularly applicable when only a few mg of sample is available and the material being fractionated contains both long and short chain saturated fatty acids. Authorized for publication August 9, 1961, as Paper No. 2590 in the Journal Series of the Pennsylvania Agricultural Experiment Station. Supported in part by the U. S. Public Health Service (H3632).     

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.     

Analysis of fatty acid compositions of human tissues using Fourier‐transform infrared spectroscopy

We have developed an infrared spectroscopic technique (Fourier transform infrared spectroscopy with attenuated total reflectance system) for the non‐invasive measurement of saturated and unsaturated fatty acid compositions in human oral mucosa, and applied it to tissue from three nationalities: Iranian, Vietnamese, and Indonesian. The second derivative infrared spectra of the mucosal tissues were additionally analyzed with the partial least squares multivariate regression analysis method. Almost all fatty acid compositions of oral mucosa could be well predicted with differences between predicted (FTIR‐ATR) and measured values (GC‐MS). Consequently this technique may provide a great advancement to fatty acid analysis in the fields of food science, preventive medicine and epidemiology.     

Prediction of the goat milk fatty acids by near infrared reflectance spectroscopy

Near infrared reflectance spectroscopy (NIRS) was used to predict the goat milk fatty acid (FA) profile. The ability of cow milk broad‐based calibration equations to predict the goat milk FA profile was assessed. Three hundred twenty‐eight samples in the calibration set and 108 in the validation set were analyzed. We showed that the bias and unexplained error were significant for most of the FA despite an adequate standardized Mahalanobis distance (index to establish the boundaries of a population of samples) which allowed us to test the ability of bovine models to predict goat milk FA profiles. To better predict the goat milk FA composition, a specific goat model was investigated. The cross‐validation coefficient of determination (R²CV; proportion of variance explained by the model in cross‐validation) and residual predictive deviation (RPD; index which allows to standardize the standard error of prediction (SEP)) were >0.90 and 3, for saturated, monounsaturated, and unsaturated FA, total trans FA, isomer cis9trans11 of CLA, cis9‐, trans10‐, and trans11‐C18:1, respectively. Monitoring of the equation performance of milk FA included the calculation of the bias and unexplained error. Practical applications: In this work, we evaluated the ability of NIRS to predict FA composition of goat milk and tested the ability of using broad‐based cow milk calibration equations to monitor an independent set of goat milk samples. We tested the hypothesis that the calibration equations obtained for FA from cow milk could be applied on goat milk. As the spectra of goat milk are similar to those of cow milk when they are measured by the standardized Mahalanobis distance (index to establish the boundaries of a population of samples), we can accept the hypothesis. It will be possible to use the existing calibration equations for predicting FA profile on spectra of milk of a different specie. However, the rejection of the hypothesis would put in doubt the use of Mahalanobis distance as the unique index for testing the performance of calibration equations on different milk populations for predicting FA.     

Comparison of attenuated total reflection infrared spectroscopy to capillary gas chromatography for trans fatty acid determination

Gas chromatography (GC) has been a standard analytical tool in lipid chemistry. The rapid attenuated total reflection (ATR) infrared (IR) American Oil Chemists’ Society (AOCS) Recommended Practice (Cd 14d-97) was compared to the capillary GC AOCS Recommended Practice (Ce 1f-97) that was optimized to accurately determine total trans fatty acids on highly polar stationary phases. This comparative evaluation was validated in an independent laboratory. These procedures were used to quantitate the total trans fatty acid levels in partially hydrogenated vegetable oils, measured as neat (without solvent) triacylglycerols (TAG) by ATR and as fatty acid methyl ester (FAME) derivatives by capillary GC. Unlike FAME, TAG determination by ATR required no derivatization, but samples had to be melted prior to measurement. Five blind replicates for each of three accuracy standards and three test samples were analyzed by each technique. The GC and ATR determinations were in good agreement. Accuracy was generally high. The ratios of ATR mean trans values (reported as percentage of total TAG) to the true values (based on the amount of trielaidin added gravimetrically) were 0.89, 0.98, and 1.02 for accuracy standards having about 1, 10, and 40% trans levels. The corresponding GC values, determined as percentage of total FAME, were 0.98, 0.99 and 1.04. The ratios of mean trans values determined by these techniques were ATR/GC 0.85, 1.04, and 1.01 for test samples having trans levels of about 0.7, 8, and 38%, respectively. The optimized GC procedure also minimzed the expected low bias in trans values due to GC peak overlap found with the GC Official Method Ce 1c-89. Satisfactory repeatability and reproducibility were obtained by both ATR and GC.     

Near‐infrared spectroscopy for analysis of oil content and fatty acid profile in almond flour

Almond kernels show large variability for oil content and fatty acid profile. The objective of this research was to evaluate the potential of near infrared (NIR) reflectance spectroscopy (NIRS) for the analysis of these traits in almond flour. Ground kernels of 181 accessions collected in 2009 were used for developing calibration equations for oil content and concentrations of individual fatty acids. Calibration equations were developed using second derivative transformation and modified partial least squares regression. They were validated with samples from 179 accessions collected in 2010. The accuracy of calibration equations was measured through the coefficient of determination (r²) in external validation and the ratio of the SD in the validation set to the standard error of prediction (RPD). Both r² and RPD were high for oil content (r² = 0.99; RPD = 9.24) and concentrations of oleic (r² = 0.97; RPD = 5.37) and linoleic acids (r² = 0.98; RPD = 7.35), revealing that calibration equations for these traits are highly accurate. Conversely, the accuracy of the calibration equations for palmitic (r² = 0.54; RPD = 1.41) and stearic acids (r² = 0.52; RPD = 1.44) was too low for allowing their application in practice. NIRS discrimination of oil content and concentrations of oleic and linoleic acids was mainly based on the spectral region from 2240 to 2380 nm. Practical applications : NIRS is a high‐throughput analytical technique that allows fast measurement of several traits in a single analysis without using chemical reagents. We evaluated the feasibility of analyzing oil content and concentrations of palmitic, stearic, oleic, and linoleic acids in almond flour using fruits collected during 2 years from a world germplasm collection. The fruits collected in 2009 were used for NIRS calibration, whereas the fruits collected in 2010 were used for validation. NIRS equations were highly accurate for measuring oil content and concentrations of oleic and linoleic acids, which are important traits defining the quality of almond flour for specific uses in the food industry. These results have applications both in the research laboratory and the food industry, where NIRS is becoming a widely used technique for quality control.     

Measurement of fatty acids in whole soybeans with near infrared spectroscopy

Improvement of nutritional and/or functional properties of soybean oil by modification of soy fatty acid composition is one of the objectives of plant breeders. A major element of breeding is rapid identification and tracking of traits in seed samples. This discussion summarizes the progression of whole‐soybean fatty acid calibration developments at Iowa State University. Emphasis was placed on linolenic acid (18:3) and total saturates (16:0 + 18:0). Normal soybeans have 12–20% (of the oil) saturated fats; modified low saturate soybeans have 6–8% saturated fats. Normal soybeans have 6–12% linolenic acid; modified low linolenic soybeans have 1–3% linolenic acid. Infratec 122x/1241 and Bruins OmegaG NIRS units were calibrated to measure fatty acid levels as a percentage of total oil content, in whole soybeans. The first Infratec calibrations (in 1998) did not remain accurate as soybean genetics changed. Iterations of the calibration process yielded calibrations for total saturates and linolenic acid with standard errors of prediction (on 2005 crop samples not included in the calibration pool) of 1.0% percentage points and 0.8% points, respectively. These were sufficient to classify modified versus normal concentrations of the two fatty acids. The NIRS units could not determine the specific percentages within the classes of modified and normal soybeans.     

Determination of unsaturated fatty acid composition by high-resolution nuclear magnetic resonance spectroscopy

High-resolution nuclear magnetic resonance (NMR) spectroscopy provides useful data for analyzing fatty acid compositions of edible vegetable oils. Quantitation of each fatty acid was carried out by evaluation of particular peaks. According to the ¹H NMR method, terminal methyl protons, divinyl protons, and allyl protons are useful to calculate linolenic acid, linoleic acid, and oleic acid, respectively. The ω-2 carbon, divinyl carbon, and allylic carbons were used for calculation of these acids by the ¹³C NMR method. Compositional results obtained by NMR coincided well with those of the conventional gas chromatography (GC) method. Results from ¹³C NMR were in better agreement with those from GC than were the results obtained by the ¹H NMR method.     

Determination of unsaturated fatty acid composition by high-resolution nuclear magnetic resonance spectroscopy

High-resolution nuclear magnetic resonance (NMR) spectroscopy provides useful data for analyzing fatty acid compositions of edible vegetable oils. Quantitation of each fatty acid was carried out by evaluation of particular peaks. According to the ¹H NMR method, terminal methyl protons, divinyl protons, and allyl protons are useful to calculate linolenic acid, linoleic acid, and oleic acid, respectively. The ω-2 carbon, divinyl carbon, and allylic carbons were used for calculation of these acids by the ¹³C NMR method. Compositional results obtained by NMR coincided well with those of the conventional gas chromatography (GC) method. Results from ¹³C NMR were in better agreement with those from GC than were the results obtained by the ¹H NMR method.     

Identification of some boron-based curing agents in cured epoxy systems by computer-assisted infrared spectroscopy

The use of computer-assisted infrared spectroscopy has allowed identification of three different boroxines and a boron trifluoride complex used as curing agents in cured epoxy resins. Boroxines were distinguished from a boron trifluoride complex by the B? O stretch absorption near 1400 cm^?1 in the solid state. Detection of this absorption was enhanced by spectral subtraction methods in which the reference spectrum was that of the parent resin, or a suitably cured system of similar structure. Distinction between different boroxines was achieved by analysis of the gases evolved from samples heated at 300°C in nitrogen. Identification of the alcohol fraction of the original boroxine was improved by subtraction of the spectrum of water vapor. Boron trifluoride was detected in the gases evolved at 450–500°C from BF₃-cured systems, and also in the liquid pyrolyzates. Further simplification of the 300°C gas spectra by subtraction of alcohol and carbon dioxide revealed the presence of acrolein in the gases from boroxine-cured systems while BF₃-cured systems yielded acetaldehyde. These differences may be associated with different end groups in the cured resins.     

Application of infrared spectroscopy to the analysis of primary fatty amide mixtures

The composition of fatty amide mixtures, containing mostly simple primary amides, has been studied by means of an infrared method utilizing the Amide I carbonyl absorption band. In dilute chloroform solution the amides, CH₃(CH₂)nCONH₂, absorb consistently at about 5.95 μ and do not display apparent association or enolization. The concentration of unsubstituted amides has been quantitatively related to the intensity of the Amide I band throughout the range from 1 to 100%. With the scale expansion the sensitivity of the method may be extended to 0.03% without difficulty. The influence of certain impurities on the intensity of the Amide I band is discussed. Carbonyl absorption from fatty acids, ketones, and esters constitutes an interference.N-monosubstituted amides also contribute to the absorption observed at 5.95 μ, but their presence is indicated by additional absorption at about 6.60 μ. The determination of small amounts of amides in amines may be accomplished by measuring the total Amide I absorption of a sample dissolved in tetrachloroethylene and relating this absorption to that of known mixtures run under identical conditions.     

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.     

Ricinelaidic acid and methyl ricinelaidate. Their preparation and determination by infrared spectroscopy

Summary Improved methods for the preparation of ricinelaidic acid and methyl ricinelaidate are described. The methods depend upon the elaidinization of methyl ricinoleate with a relatively small quantity of a nitrite-nitric acid solution, fractional crystallization of the methyl ricinelaidate, and its subsequent hydrolysis to ricinelaidic acid. The infrared spectra of these two compounds are presented, and bands arising from a deformation of the C−H about thetrans C=C group are discussed. Absorptivity values for this band in chlorform and in carbon disulfide solutions are given as additional criteria of purity of ricinelaidic acid and its methyl ester. The infrared absorption procedure for the quantitative determination of isolatedtrans ethylenic bond was applied to the determination of both ricinelaidic acid and methyl ricinelaidate. Details of specific procedures for the determination of each compound are given with the equations necessary for their calculation. Use of these methods is illustrated with the analysis of elaidinization mixtures. The repeatability and accuracy obtaineble are given. A value is reported for the methyl ricinoleate—methyl ricinelaidate equilibrium and the mechanism of the reaction is discussed briefly. One of the laboratories of the Southern Utilization Research and Development Division, Agricultural Research Service, U. S. Department of Agriculture.     

红外光谱与热重分析法研究腐植酸改性脲醛树脂

将腐植酸(HA)进行羟甲基化改性,然后按照m(HA羟甲基化溶液)∶m[脲醛树脂(UF)]=1∶4比例将两者混合均匀,制得腐植酸-脲醛树脂(HUF)。采用红外光谱(FT-IR)、热重分析(TGA)及差示扫描量热(DSC)法等对UF和HUF的结构、热稳定性及玻璃化转变温度(Tg)等进行表征。结果表明:HUF与UF的FT-IR曲线基本相同,前者的FT-IR特征峰均有不同程度增强,热失重峰向高温区移动,说明HUF既保留了UF的原有结构,又具有较强的耐热性;当w(改性HA)=5%～30%时,HUF胶粘剂的胶接强度相对较大;与未改性UF相比,HUF价格更低(节约350元/t)、更环保(甲醛释放量达到GB 18 580-2001标准中E1级指标要求),故HUF具有较强的市场竞争力和良好的应用前景。     

基于热重-红外联用技术分析油酸的热解特性及动力学分析

利用热重红外联动技术（TG-DTG-FTIR）研究了橡胶籽油中的单不饱和游离脂肪酸油酸组分在不同升温速率（5℃/min、10℃/min、20℃/min、30℃/min）下的热解特性。然后,用多元线性回归法对油酸非等温热解所得到的特性参数进行研究并计算,求得不同升温速率下对应的反应级数、活化能和指前因子,并对不同升温速率下油酸热解反应活化能和指数前因子作线性拟合。结果表明：油酸热解过程主要可分为0～268℃和268～300℃两个阶段,由红外谱图特征峰的分析可知,不同升温速率下,在油酸热解的阶段内均出现了水蒸气、CH₄、CO₂和CO这4种主要气体挥发分。随着升温速率的增大,油酸热解的最大失重速率随之增大,热解区间也向着高温段移动,同时计算在升温速率从5～30℃/min的过程中,反应级数n=1时,热解反应活化能由105.57kJ/mol降低至93.99kJ/mol,指数前因子由6.99×10⁶降低至6.7×10⁵;n≠1时,热解反应活化能由102.45kJ/mol降低至93.38kJ/mol,指数前因子由3.13×10⁶降低至2.97×10⁴,反应活化能和指数前因子随升温速率的增大出现明显减小。通过对不同升温速率下油酸热解反应的活化能和指数前因子进行线性拟合后发现,两者间具有较好的补偿效应。     

Determination of the fatty acid profile by 1H‐NMR spectroscopy

The common unsaturated fatty acids present in many vegetable oils (oleic, linoleic and linolenic acids) can be quantitated by ¹H‐nuclear magnetic resonance spectroscopy (¹H‐NMR). A key feature is that the signals of the terminal methyl group of linolenic acid are shifted downfield from the corresponding signals in the other fatty acids, permitting their separate integration and quantitation of linolenic acid. Then, using the integration values of the signals of the allylic and bis‐allylic protons, oleic and linoleic acids can be quantitated. The procedure was verified for mixtures of triacylglycerols (vegetable oils) and methyl esters of oleic, linoleic and linolenic acids as well as palmitic and stearic acids. Generally, the NMR (400 MHz) results were in good agreement with gas chromatographic (GC) analyses. As the present ¹H‐NMR‐based procedure can be applied to neat vegetable oils, the preparation of derivatives for GC would be unnecessary. The present method is extended to quantitating saturated (palmitic and stearic) acids, although in this case the results deviate more strongly from actual values and GC analyses. Alternatives to the iodine value (allylic position equivalents and bis‐allylic position equivalents) can be derived directly from the integration values of the allylic and bis‐allylic protons.