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1.
A. A. Ismail F. R. van de Voort G. Emo J. Sedman 《Journal of the American Oil Chemists' Society》1993,70(4):335-341
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. 相似文献
2.
Rice bran with FFA levels above 0.1% cannot be used as a food ingredient due to oxidative off-flavor formation. However, extracting
high FFA oil from bran by in situ methanolic esterification of rice bran oil to produce methyl ester biodiesel produces greater yields relative to low-FFA
rice bran oil. Therefore, high-FFA bran could be exploited for biodiesel production. This study describes an FTIR spectroscopic
method to measure rice bran FFA rapidly. Commercial rice bran was incubated at 37°C and 70% humidity for a 13-d incubation
period. Diffuse reflectance IR Fourier transform spectra of the bran were obtained and the percentage of FFA was determined
by extraction and acid/base titration throughout this period. Partial least squares (PLS) regression and a calibration/validation
analysis were done using the IR spectral regions 4000-400 cm−1 and 1731-1631 cm−1. The diffuse reflectance IR Fourier transform spectra indicated an increasing FFA carbonyl response at the expense of the
ester peak during incubation, and the regression coefficients obtained by PLS analysis also demonstrated that these functional
groups and the carboxyl ion were important in predicting FFA levels. FFA rice bran changes also could be observed qualitatively
by visual examination of the spectra. Calibration models obtained using the spectral regions 4000-400 cm−1 and 1731-1631 cm−1 produced correlation coefficients R and root mean square error (RMSE) of cross-validation of R=0.99, RMSE=1.78, and R=0.92, RMSE=4.67, respectively. Validation model statistics using the 4000-400 cm−1 and 1731-1631 cm−1 ranges were R=0.96, RMSE=3.64, and R=0.88, RMSE=5.80, respectively. 相似文献
3.
Yaakob B. Che Man A. Rohman T. S. T. Mansor 《Journal of the American Oil Chemists' Society》2011,88(2):187-192
Fourier transform infrared (FTIR) spectra at mid infrared regions (4,000–650 cm−1) of lard and 16 edible fats and oils were compared and differentiated. The chemometrics of principal component analysis and
cluster analysis (CA) was used for such differentiation using FTIR spectra intensities of evaluated fats and oils. With PCA,
an “eigenvalue” of about 90% was achieved using four principal components (PCs) of variables (FTIR spectra absorbances at
the selected frequency regions). PC1 accounted for 44.1% of the variation, while PC2 described 30.2% of the variation. The
main frequency regions that influence the separation of lard from other evaluated fats and oils based on PC1 are 2,852.8 followed
by 2,922 and 1,464.7 cm−1. Furthermore, CA can classify lard into its group based on Euclidean distance. 相似文献
4.
New FTIR method for the determination of FFA in oils 总被引:3,自引:0,他引:3
A rapid, practical, and accurate FTIR method for the determination of FFA in edible oils was developed. Analogous to the AOCS
titration procedure, the FTIR FFA determination is effected by an acid/base reaction but directly measures the product formed
rather than utilizing an end point based on an electrode potential or color change. A suspension of a weak base, potassium
phthalimide (K-phthal) in 1-propanol (1-PrOH), is used to convert the FFA present in oils to their carboxylate salt without
causing oil saponification, and differential spectroscopy is used to circumvent matrix effects. Samples are first diluted
with 1-PrOH, then split, with one-half treated with the K-phthal reagent and the other half with 1-PrOH (blank reagent), their
spectra collected, and differential spectra obtained to ratio out the invariant spectral contributions from the oil sample.
Quantification of the percentage of FFA in the oil, expressed as %oleic acid, based on measurement of the peak height of the
ν (COO−) absorption of the FFA salt formed, yielded a calibration with an SE of <0.020% FFA over the range of 0–4%. The method was
validated by standard addition and the analysis of Smalley check samples, the results indicating that the analytical performance
of the FTIR procedure is as good as or better than that of the standard titrimetric procedure. As structured, the FTIR procedure
is a primary method, as calibration is not dependent on reference values provided by another method, and has performance criteria
that could lead to its consideration as an instrumental AOCS procedure for FFA determination. The FTIR portion of the analysis
is automatable, and a system capable of analyzing ∼60 samples/h was developed that could be of benefit to laboratories that
carry out a large number of FFA analyses per day. 相似文献
5.
Meghan Allendorf Anand Subramanian Luis Rodriguez-Saona 《Journal of the American Oil Chemists' Society》2012,89(1):79-88
This study evaluated the capabilities of a handheld mid-infrared (MIR) spectrometer combined with multivariate analysis to
characterize oils, monitor chemical processes occurring during oxidation, and to determine fatty acid composition. Vegetable
oils (corn, peanut, sunflower, safflower, cottonseed, and canola) were stored at 65 °C for 30 days to accelerate oxidation
reactions. Aliquots were drawn at 5 day intervals and analyzed by benchtop and portable handheld mid-infrared devices (4,000–700 cm−1) and reference methods (IUPAC 2301 [1], 2302 [1]; AOCS Cd 8-58 [2]; and Shipe 1979 [3]). PLSR and soft independent modeling of class analogy (SIMCA) models were developed for oil classification and estimation
of oil stability parameters. Models developed from MIR spectra obtained with a benchtop spectrometer equipped with a 3-bounce
ATR device resulted in superior discriminative performances for classifying oils as compared to those obtained from handheld
spectra (single-bounce ATR). Models developed from reference tests and handheld spectra showed prediction errors (SECV) of
1 meq/kg for peroxide value, 0.09% for acid value and 2% for determination of unsaturated fatty acids in different oils. Spectral
regions ~3,012–2,850 cm−1 (C–H stretching bands/shoulders of fatty acids), ~1,740 cm−1 (C=O stretching of esters), and ~1,114 cm−1 (–C–O stretching) were found to be important for prediction. Handheld-FTIR instruments combined with multivariate-analysis
showed promise for determination of oil quality parameters. Portability and ease-of-use makes the handheld device a great
alternative to traditional methods. 相似文献
6.
Stoichiometric determination of hydroperoxides in fats and oils by fourier transform infrared spectroscopy 总被引:1,自引:0,他引:1
K. Ma F. R. van de Voort J. Sedman A. A. Ismail 《Journal of the American Oil Chemists' Society》1997,74(8):897-906
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. 相似文献
7.
T. Verleyen R. Verhe A. Cano A. Huyghebaert W. De Greyt 《Journal of the American Oil Chemists' Society》2001,78(10):981-984
A rapid and direct Fourier transform infrared (FTIR) spectroscopic method using a 25-μm NaCl transmission cell was developed
for the determination of free fatty acids (FFA) in six important vegetable oils (corn, soybean, sunflower, palm, palm kernel,
and coconut oils) that differ in fatty acid profile. The calibrations were established by adding either standard FFA (oleic,
lauric acids) or a representative mixture of FFA obtained after saponification of the refined oils. For all oils, up to a
FFA level of 6.5% for coconut oil, the best correlation coefficient was obtained by linear regression of the free carboxyl
absorption at 1711 cm−1. All correlation coefficients were greater than 0.993, and no significant difference between the calibration methods could
be detected. Upon validation of the calibration, no significant difference (α=0.05) between the “actual” and the “FTIR predicted”
FFA values could be observed. The calibration models developed for the six oils differed significantly and indicate the need
to develop a calibration that is specific for each oil. In terms of repeatability and accuracy, the FTIR method developed
was excellent. Because of its simplicity, quick analysis time of less than 2 min, and minimal use of solvents and labor, the
introduction of FTIR spectroscopy into laboratory routine for FFA determination should be considered. 相似文献
8.
A new FTIR approach was investigated for assessing edible oil oxidative stability with the use of polymer IR (PIR) cards as
sample holders. This approach allows oil oxidation to be monitored at moderate temperatures owing to the fairly rapid rate
at which unsaturated oils oxidize on the PIR cards. To assess the FTIR/PIR card method, pure TAG—triolein, trilinolein, and
trilinolenin—were loaded onto cards and placed in a chamber where warm air (55°C) flowed over them continuously to facilitate
oxidation. At periodic intervals, individual cards were removed and their FTIR spectra scanned, after which they were replaced
in the aeration chamber. All spectra were normalized to compensate for variations in PIR card path lengths or oil loadings,
and for each card the initial spectrum recorded (t=0) was subtracted from all subsequent spectra taken over time to produce differential spectra. With the use of a peak-find
algorithm, the absorbance minimum in the cis region (3017–3000 cm−1) and the absorbance maxima in the hydroperoxide (3550–3200 cm−1), isolated trans (977–957 cm−1), and conjugated trans regions (995–983 cm−1) were measured in the differential spectra and plotted as a function of time. For all three TAG, the loss of cis double bonds was linearly related to the development of hydroperoxides and isolated trans bonds for much of the oxidation process, whereas for the polyunsaturated TAG a similar relationship also existed for conjugated
trans species. Based on experimentally determined hydroperoxide (ROOH) absorbance slope factor (0.06 mAbs/PV), ROOH absorbance
changes were converted to PV, allowing direct PV monitoring as a function of time using the PIR cards. Trilinolenin, trilinolein,
and triolein attained a PV of 100 mequiv/kg oil after, 43,98, and 2889 min, respectively, their relative reaction rates being
similar to ratios published in the literature. The assessment of the FTIR/PIR card method using TAG indicates that it may
be a practical and rapid means of oxidizing lipids and tracking their oxidative state in terms of PV so as to provide a measure
of their oxidative stability. 相似文献
9.
The application of in situ Raman, IR, and UV-Vis DRS spectroscopies during steady-state methanol oxidation has demonstrated
that the molecular structures of surface vanadium oxide species supported on metal oxides are very sensitive to the coordination
and H-bonding effects of adsorbed methoxy surface species. Specifically, a decrease in the intensity of spectral bands associated
with the fully oxidized surface (V5+) vanadia active phase occurred in all three studied spectroscopies during methanol oxidation. The terminal V = O (∼1030 cm−1) and bridging V–O–V (∼900–940 cm−1) vibrational bands also shifted toward lower frequency, while the in situ UV-Vis DRS spectra exhibited shifts in the surface
V5+ LMCT band (>25,000 cm−1) to higher edge energies. The magnitude of these distortions correlates with the concentration of adsorbed methoxy intermediates
and is most severe at lower temperatures and higher methanol partial pressures, where the surface methoxy concentrations are
greatest. Conversely, spectral changes caused by actual reductions in surface vanadia (V5+) species to reduced phases (V3+/V4+) would have been more severe at higher temperatures. Moreover, the catalyst (vanadia/silica) exhibiting the greatest shift
in UV-Vis DRS edge energy did not exhibit any bands from reduced V3+/V4+ phases in the d–d transition region (10,000–30,000 cm−1), even though d–d transitions were detected in vanadia/alumina and vanadia/zirconia catalysts. Therefore, V5+ spectral signals are generally not representative of the percent vanadia reduction during the methanol oxidation redox cycle,
although estimates made from the high temperature, low methoxy surface coverage IR spectra suggest that the catalyst surfaces
remain mostly oxidized during steady-state methanol oxidation (15–25% vanadia reduction). Finally, adsorbed surface methoxy
intermediate species were easily detected with in situ IR spectroscopy during methanol oxidation in the C–H stretching region
(2800–3000 cm−1) for all studied catalysts, the vibrations occurring at different frequencies depending on the specific metal oxide upon
which they chemisorb. However, methoxy bands were only found in a few cases using in situ Raman spectroscopy due to the sensitivity
of the Raman scattering cross-sections to the specific substrate onto which the surface methoxy species are adsorbed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
10.
F. R. van de Voort A. A. Ismail J. Sedman J. Dubois T. Nicodemo 《Journal of the American Oil Chemists' Society》1994,71(9):921-926
A rapid method for the quantitative determination of peroxide value (PV) of vegetable oils by Fourier transform infrared (FTIR)
transmission spectroscopy is described. Calibration standards were prepared by the addition oft-butyl hydroperoxide to a series of vegetable oils, along with random amounts of oleic acid and water. Additional standards
were derived through the addition of mono- and diglyceride spectral contributions, as well as zero PV spectra obtained from
deuterated oils. A partial least squares (PLS) calibration model for the prediction of PV was developed based on the spectral
range 3750–3150 cm−1. Validation of the method was carried out by comparing the PV of a series of vegetable oils predicted by the PLS model to
the values obtained by the American Oil Chemists Society iodometric method. The reproducibility of the FTIR method [coefficient
of variation (CV)=5%)] was found to be better than that of the chemical method (CV =9%), although its accuracy was limited
by the reproducibility of the chemical method. The method, as structured, makes use of a 1-mm CaF2 flow cell to allow rapid sample handling by aspiration. The spectrometer was preprogrammed in Visual Basic to guide the operator
in performing the analysis so that no knowledge of FTIR spectroscopy is required to implement the method. The method would
be suitable for PV determinations in the edible oil industry and takes an average of three minutes per sample. 相似文献
11.
Rapid Method for the Determination of Moisture Content in Biodiesel Using FTIR Spectroscopy 总被引:1,自引:0,他引:1
Mohamed E. S. Mirghani Nasreldin A. Kabbashi Md. Zahangir Alam Isam Y. Qudsieh Ma’an F. R. Alkatib 《Journal of the American Oil Chemists' Society》2011,88(12):1897-1904
A new, rapid, and direct method was developed for the determination of moisture content in biodiesel produced from various
types of oils using Fourier transform infrared (FTIR) spectroscopy with an attenuated total reflectance (ATR) element. Samples
of biodiesels used in this study were produced using sludge palm oil (SPO). The calibration set was prepared by spiking double-distilled
water into dried biodiesel samples in ratios (w/w) between 0 and 10% moisture. Absorbance values from the wavelength regions
3,700–3,075 and 1,700–1,500 cm−1, and the partial least square (PLS) regression method were used to derive a FTIR spectroscopic calibration model for moisture
content in biodiesel samples. The coefficient of determinations (R
2) for the models was computed by comparing the results obtained from FTIR spectroscopy against the values of the moisture
concentrations (%) determined using the American Oil Chemists’ Society (AOCS) oven method Ca 2d-25. Same comparison was done
using International Union of Pure and Applied Chemistry (IUPAC) distillation method 2.602. R
2 was 0.9793 and 0.9700 using AOCS and IUPAC methods, respectively. The standard error (SE) of calibration was 1.84. The calibration
model was cross validated within the same set of samples, and the standard deviation (SD) of the difference for repeatability
(SDDr) and accuracy (SDDa) of the FTIR method was determined. With its speed and ease of data manipulation, FTIR spectroscopy
is a useful alternative method to other methods for rapid and routine determination of moisture content in biodiesel for quality
control. 相似文献
12.
Determination of olive oil free fatty acid by fourier transform infrared spectroscopy 总被引:2,自引:0,他引:2
Enriqueta Bertran Marcelo Blanco Jordi Coello Hortensia Iturriaga Santiago Maspoch Ivan Montoliu 《Journal of the American Oil Chemists' Society》1999,76(5):611-616
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). 相似文献
13.
Biodiesel derived from camelina as well as other feedstocks including palm, mustard, coconut, sunflower, soybean and canola
were prepared via the conventional base-catalyzed transesterification with methanol. Fatty acid profiles and the fuel properties
of biodiesel from different vegetable oils were analyzed and tested in accordance with ASTM D6751. Camelina biodiesel contains
10–12%, 37–40%, and 48–50% saturated, monounsaturated and polyunsaturated components, respectively. Some fuel properties of
camelina biodiesel are comparable to that of sunflower biodiesel including kinematic viscosity (40 °C), flash point, cloud
point, cold filter plugging point, and oil stability index. However, camelina biodiesel exhibited the poorest oxidative stability,
highest distillation temperature and has the highest potential to form coke during combustion, all of which are attributed
to the high amounts of n-3-fatty acids in camelina oil. While neat camelina biodiesel may exhibit undesirable fuel properties,
it is very comparable with soybean biodiesel at the B20 level. 相似文献
14.
Free fatty acid formation and lipid oxidation on milled rice 总被引:2,自引:0,他引:2
Henry S. Lam Andrew Proctor Jean-François Meullenet 《Journal of the American Oil Chemists' Society》2001,78(12):1271-1275
Milled rice was stored at 37°C and 70% humidity and sampled regularly for 50 d. Rice surface lipid was extracted with isopropanol
and analyzed for free fatty acids (FFA) and conjugated diene (CD) contents. Diffuse reflectance Fourier transform infrared
(DRIFTS) spectra of the rice samples were also obtained. FFA and CD levels increased together during rice storage and exhibited
three distinct phases. DRIFTS identified a decrease in intensity at 1746 cm−1 (ester, −C=O) and increases in intensity at 1731 cm−1 (aldehyde, −CO) and 1714 cm−1 (fatty acid, −C=O) during storage, which correlated well with the chemical analysis data. DRIFTS spectral data were analyzed
by a partial least squares regression method to identify spectral regions that correlate strongly with measured FFA and construct
prediction models. Overall, the mid-infrared region (4000–400 cm1) gave the best model (R=0.98, root mean square error of cross-validation=0.05) and also predcted the FFA content of milled rice well. The DRIFTS
technique has potential for use in studying qualitative chemical changes on the milled rice surface lipids and for predicting
FFA on milled rice. 相似文献
15.
Gerhard Knothe 《Journal of the American Oil Chemists' Society》2001,78(10):1025-1028
Biodiesel, defined as the alkyl esters (usually methyl esters) of vegetable oils, is miscible with conventional diesel fuel
at all blend levels. Until the present time, no rapid and reliable analytical method has existed for determining the blend
level of biodiesel in conventional diesel fuel. In the present work, near-infrared (NIR) and nuclear magnetic resonance (NMR)
spectroscopies were used to determine the blend level of biodiesel in conventional diesel fuel. Several regions in the NIR
region (around 6005 cm−1 and 4800–4600 cm−1) are suitable for this purpose. The method is rapid and easy to use, and does not require any hardware changes when using
the same instrument for monitoring the biodiesel-producing transesterification reaction and determining biodiesel fuel quality.
In 1H NMR spectroscopy, the integration values of the peaks of the methyl ester moiety and the aliphatic hydrocarbon protons in
biodiesel and conventional diesel fuel were used for determining blend levels. The results of NIR and NMR blend level determinations
are in good agreement. 相似文献
16.
Elizabeth M. Kirby Marra J. Evans-Vader M. Adele Brown 《Journal of the American Oil Chemists' Society》1965,42(5):437-446
The length of polymethylene chains is determined by counting the number of, or measuring the position of, methylene vibration
peaks in the 1070–710 cm−1 and/or the 1380–1170cm−1 regions of the IR spectrum of salts of fatty acids. Plotting this peak position against the phase relationship of the vibration
in adjacent methylenes gives a curve which is independent of the chain length. (Thephase relationship, Φ/π=k/(m+1); where φ is the phase difference in radians between adjacent methylenes in a chain;m is the number of methylenes in the chain;k=1,2,3,…m, withk=1 generally assigned to the in-phase vibration.) Separate curves are obtained for methylene wagging and for two arrays of
coupled twisting-rocking vibrations.
Coupled twisting-rocking vibrations give as many as one peak per methylene group in the 1070–710 cm−1 region with silver, sodium, potassium and barium salts of saturated acids. Lead salt peaks split. These peaks show the total
length of salts of both saturated andtrans-unsaturated acids, but only the length of the carboxylate segment in salts ofcis-unsaturated acids. (The carboxylate segment comprises the carbons from the carboxylate carbon to the first unsaturated carbon,
inclusive.)
Wagging vibrations in the 1380–1170 cm−1 region show the total chain length of saturated salts and the length of the carboxylate segment in unsaturated salts, bothcis andtrans. This region also has peaks for twisting-rocking vibrations, and they are most conspicuous in the spectra of silver and barium
salts.
Presented in part at the AOCS meeting in Toronto, Canada, 1962. 相似文献
17.
João Pires Beatriz Brasil M. Eduarda M. Araújo 《Journal of the American Oil Chemists' Society》2013,90(4):555-561
Biodiesel is a biofuel obtained from vegetable oils. The oils used as raw materials are usually refined edible vegetable oils. Nonedible acidic oils are unsuitable for biodiesel production unless reduction of the high content in free fatty acids (FFA) of these materials had been achieved. Obtaining a good raw material from unprofitable oils becomes an important research field. Additionally clays have a long history in industrial sorption and catalysis, some being commercially available and with properties that can be modified. In this work we present the results of the use of the montmorillonite clay K10 and two acid modified clays K10(I) and K10(II), in the esterification of stearic acid with methanol and 95 % of methyl stearate was obtained with K10(II). These clays were then used for the first time to reduce the acidity of enhanced FFA sunflower oil and they show to be very effective. Reduction of FFA from 11 to 4 % was obtained with K10(II) mainly due to 94 % conversion of FFA into fatty acid methyl esters (FAME). These clays were also tested with two waste oils, one from domestic use and the other gathered from different restaurants, and showed their ability to lower the acidity of these oils. Reactions were followed by 1H NMR as well as quantitative determination of FFA and FAME. Clays were characterized by FTIR and XRD. 相似文献
18.
Emily Birkel Luis Rodriguez-Saona 《Journal of the American Oil Chemists' Society》2011,88(10):1477-1483
Trans fat poses serious health risks to consumers. In order to meet the FDA labeling requirements for trans fatty acids, development of fast, accurate, easy-to-use analytical methods for oils, fats and related products is desirable.
Fourier transform infrared spectroscopy (FTIR) is a well-established analytical technique for quantifying trans fats, and the development of handheld FTIR units over the past decade presents new application opportunities. Our objective
was to evaluate the performance of a handheld FTIR sensor for measuring trans fat content between 0.1 and 20% trans (w/w) in edible saturated and unsaturated oils. Calibration models were built by measuring height of the band at 966 cm−1 and by partial least squares regression (PLSR) using benchtop FTIR as a reference method. Predictive accuracy of the models
was validated with an independent test set of commercial edible oils. Calibration models developed using PLSR and linear regression
of band heights gave correlation coefficients R
2 > 0.98. Multivariate analysis for the handheld unit gave standard error of prediction (SEP) of approximately 1%, comparable
to values obtained with benchtop systems. This study demonstrates that handheld FTIR spectroscopy coupled with chemometrics
is a suitable method for quantitation of trans fat content. 相似文献
19.
Hadjiivanov Konstantin Concepción Patricia Knözinger Helmut 《Topics in Catalysis》2000,11(1-4):123-130
Adsorption of NO on vanadia–titania samples pre-subjected to different reduction treatments has been studied by FTIR spectroscopy.
When the NO adsorption is performed at 85 K on oxidized samples, antisymmetric NONO species, typical for V5+ sites, are detected and characterized by bands at 1779 and 1686 cm−1. At ambient temperature, however, adsorption is negligible and only with time reactive adsorption occurs producing NO+ (2120 cm−1), nitro/nitrato species (bands in the 1650–1100 cm−1 region) and weakly adsorbed NO (broad band at 1915 cm−1). Adsorption of NO at ambient temperature on reduced samples results in the formation of two types of species: (i) V4+(NO)2 dinitrosyls characterized by νs(NO) and νas(NO) at 1903–1880 and 1769–1753 cm−1, respectively, and (ii) V3+(NO)2 complexes, which give rise to νs(NO) at 1834–1822 cm−1 and νas(NO) at 1697–1685 cm−1. At low temperature the dinitrosyls are transformed into species in which more than one (NO)2 dimer is attached to one cationic site. Addition of O2 to NO, preadsorbed on reduced vanadia–titania samples, results in a fast oxidation of the V3+(NO)2 species, whereas the V4+(NO)2 complexes are more stable and do not disappear completely in the presence of oxygen. The results obtained suggest that NO
is a convenient probe molecule for the analysis of the oxidation state of vanadium in vanadia–titania catalysts. To prevent
oxidation of reduced vanadium sites, low equilibrium pressures of NO and registration of the IR spectrum soon after the NO
admission are recommended.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
20.
M. Jafarian R.B. Moghaddam M.G. Mahjani F. Gobal 《Journal of Applied Electrochemistry》2006,36(8):913-918
The electro-catalytic oxidation of methanol on a Ni–Cu alloy (NCA) with atomic ratio of 60/40 having previously undergone 50 potential sweep cycles in the range 0–600 mV vs. (Ag/AgCl) in 1 m NaOH was studied by cyclic voltammetry (CV), chronoamperometry (CA) and impedance spectroscopy (EIS). The electro-oxidation was observed as large anodic peaks both in the anodic and early stages of the cathodic direction of potential sweep around 420 mV vs. (Ag/AgCl). The electro-catalytic surface was at least an order of magnitude superior to a pure nickel electrode for methanol oxidation. The diffusion coefficient and apparent rate constant of methanol oxidation were found to be 2.16 × 10−4 cm2 s−1 and 1979.01 cm3 mol−1 s−1, respectively. EIS studies were employed to unveil the charge transfer rate as well as the electrical characteristics of the catalytic surface. For the electrochemical oxidation of methanol at 5.0 m concentration, charge transfer resistance of nearly 111 Ω was obtained while the resistance of the electro-catalyst layer was ca. 329 Ω. 相似文献