179 - 2007 - Determination of Peroxide Value of Edible Oils by FTIR spectroscopy with the use of the Spectral Reconstitution Technique. (original) (raw)
Related papers
Talanta, 2007
Spectral reconstitution (SR), a technique that has been developed to facilitate mid-FTIR transmission analysis of inherently viscous samples, was applied to simplify and automate a previously reported FTIR method for the determination of peroxide value (PV) of edible oils. The basis of the PV determination is the rapid reaction of triphenylphosphine (TPP) with the hydroperoxides present in an oil to produce triphenylphosphine oxide (TPPO), which exhibits a readily measurable absorption band at 542 cm −1. In the SR procedure, the viscosity of oil samples is reduced by mixing them with a diluent, which allows them to be readily loaded into a flow-through transmission cell. The spectra of the neat oil samples are then reconstituted from those of the diluted samples by using the absorption of a spectral marker present in the diluent to determine the dilution ratio. For the SR-based PV method, the TPP reagent was added to the diluent, which consisted of odorless mineral spirits (OMS) containing methylcyclopentadienyl manganese tricarbonyl (MMT) as the spectral marker. Sample preparation for PV analysis involved mixing ∼10 ml of oil with ∼25 ml of the TPP-containing diluent; accurate weighing or delivery of precise volumes was not required because the dilution ratio was determined spectroscopically from the intensity of the ν(CO) absorption of MMT at 1942 cm −1 in the spectrum of the diluted sample relative to that in the spectrum of the diluent. Calibration standards, prepared by gravimetric addition of TPPO to a peroxide-free oil, were handled in the same manner, and a linear calibration equation relating the concentration of TPPO (expressed as the equivalent PV) to the absorbance of TPPO at 542 cm −1 relative to a baseline at 530 cm −1 in the reconstituted spectra was obtained, with a regression S.D. of ±0.15 meq/kg oil. PV determinations on two sets of validation samples, spanning PV ranges of 0-20 and 0-2 meq/kg oil, were carried out in parallel by the AOCS titrimetric and SR-based FTIR procedures, and comparison of the results of duplicate analyses by the two methods indicated that the latter was more reproducible and slightly more sensitive. The SR-based PV method, when implemented on an autosampler-equipped FTIR system, allowed for the automated analysis of ∼90 samples per hour.
123 - 1997 - Stoichiometric determination of hydroperoxides in fats and oils by FTIR spectroscopy.
J. Am. Oil Chem. Soc. 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 KCl 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. JAOCS 74, 897-906 (1997) . Differential spectra of TPP/hexanol (A), TPPO/hexanol (B), TBHP (C), and reacted TBHP and TPP/hexanol (D) in canola oil over the spectral range of 3750-3350 cm −1 . Spectra A-C have been ratioed against the spectrum of canola oil; spectrum D has been ratioed against the spectrum of TBHP in canola oil. Owing to hydrogen bonding in triglyceride-based oils, the OH absorptions are shifted from their positions in mineral oil , the hexanol solvent band appearing at 3579 cm −1 . In the differential spectrum of the reaction mixture (D), the TBHP band at 3460 cm −1 (C) is negative, confirming the reaction of TBHP with TPP. See for abbreviations. 902 K. MA ET AL. JAOCS, Vol. 74, no. 8 (1997) FIG. 4. Differential spectra of TPP/hexanol (A), TPPO/hexanol (B), TBHP (C), and reacted TBHP and TPP/hexanol (D) in canola oil over the spectral range of 775-475 cm −1 .
Analytical Sciences 25(5) 627-632.
This paper described an FTIR spectrometer coupled to an auto-sampler and some attendant methodologies for a direct free fatty acid (FFA) method and triphenylphosphine (TPP)-based method for determination of FFA and peroxide value (PV) of edible oils by FTIR spectroscopy using spectral reconstitution. The viscosity of oil samples is reduced by mixing them with a diluent; such lowered viscosity allows them to be readily loaded into a flow-through transmission cell. The spectra of the neat oil samples are then reconstituted from those of the diluted samples by using the absorption of a spectral marker present in the diluent to determine the dilution ratio. For the direct FFA analysis, quantification is achieved using the (COO -) band at 1712 cm -1 , while PV is determined using triphenylphosphine oxide (TPPO) absorption bands at 542 cm -1 . Calibration procedures and data are presented. Validation and performance data obtained with this automated system demonstrate that it is capable of analyzing ~90 samples/h, a rate commensurate with the throughput required by commercial contract or high-volume process control laboratories.
106 - 1994 - The determination of peroxide value by Fourier Transform infrared (FTIR) spectroscopy.
J. Am. Oil Chem. Soc. 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 of tbutyl 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 diglyeeride 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-k 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' S(~ciety iodometric method. The reproducibility of the FTIR method [coefficient of variation (CV) = 5%)] was found to be better than that of the chemical method ICV = 9%), although its accuracy was limited by the reproducibility of the chemical method. The method, as structured, makes use of a l-ram 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.
Determination of peroxide value by fourier transform near‐infrared spectroscopy
Journal of the American Oil Chemists' Society, 2000
A Fourier transform‐near infrared (FT‐NIR) method originally designed to determine the peroxide value (PV) of triacylglycerols at levels of 10–100 PV was improved upon to allow for the analysis of PV between 0 and 10 PV, a range of interest to the edible oil industry. The FT‐NIR method uses convenient disposable glass vials for sample handling, and PV is determined by spectroscopically measuring the conversion of triphenylphosphine (TPP) to triphenylphosphine oxide (TPPO) when reacted with hydroperoxides. A partial‐leastsquares calibration was developed for 8 mm o.d. vials by preparing randomized mixtures of TPP and TPPO in a zero‐PV oil. The method was validated with samples prepared by gravimetric dilution of oxidized oil with a zero‐PV oil. It was shown that the American Oil Chemists’ Society primary reference method was quite reproducible (±0.5 PV), but relatively insensitive to PV differences at lower (0–2) PV. The FT‐NIR method on the other hand was shown to be more accurate o...
143 - 2000 - Monitoring peroxide value in fat liquor manufacture by FTIR spectroscopy.
JAOCS 77 (6) 681-685.
A Fourier transform infrared (FTIR) spectrometer equipped with an attenuated total reflectance (ATR) sample handling accessory was used to rapidly monitor the peroxide value (PV) of oils undergoing catalytic oxidation to produce sulfonated fatliquors used in the leather industry. PV quantitation was based on the stoichiometric reaction of triphenylphosphine (TPP) with hydroperoxides to produce triphenylphosphine oxide (TPPO). By using a germanium ATR accessory that has a very short effective pathlength, the spectral contributions of the base oil could be subtracted out, eliminating any oil-dependent interferences as well as providing a facile means of observing the spectral changes associated with the TPP/TPPO reaction. A calibration was devised by adding a constant amount of TPP-saturated chloroform to oils containing varying amounts of tert-butyl hydroperoxide (TBHP) to produce TPPO that had a measurable band at 1118 cm −1 . This band was linearly related to TBHP concentration, and the calibration devised had an SD of ~3.4 PV over the range of 0-250 PV. The ATR-PV method was standardized and the spectrometer programmed using Visual Basic to automate the analysis. The automated FTIR-ATR method was found to be a convenient means of tracking PV of oils undergoing oxidation, and the results correlated well with the PV values obtained using the AOAC iodometric method (r = 0.94). The FTIR-ATR PV methodology provides a simple means of monitoring the PV of oils undergoing rapid oxidation and could serve as a quality-control tool in the production of sulfonated oils for the leather industry.
J. Am. Oil Chem. Soc. 75 (9) 1095-1101.
Disposable polyethylene infrared cards (3M IR cards) were investigated for their suitability for the quantitative determination of peroxide value (PV) in edible oils relative to a conventional transmission flow cell. The analysis is based on the stoichiometric reaction of triphenylphosphine (TPP) with hydroperoxides to produce triphenylphosphine oxide (TPPO). Preliminary work indicated that the cards, although relatively consistent in their pathlength (±1%), had an overall effective pathlength variation of ±~5%, caused by variability in loading of the oil onto the cards. This loading variability was reduced to <0.5% by developing a normalization protocol that is based on the peak height of the ester linkage carbonyl overtone band at 3475 cm −1 , which allowed one to obtain consistent and reproducible spectra. The standard PV calibration approach, based on the TPPO peak height at 542 cm −1 , failed because of unanticipated card fringing in the region where the measurements were being made. However, the development of a partial-least-squares (PLS) calibration provided a means of eliminating the interfering effect of the fringes and allowed the TPPO band to be measured accurately. An alternate approach to the standardized addition of TPP reagent to the oil was also investigated by impregnating the 3M IR cards with TPP, thus allowing the reaction to take place in situ. The spectral analysis protocols developed (normalization/calibration) were programmed to automate the PV analysis completely. The 3M card-based Fourier transform infrared PV methods developed were validated by analyzing oxidized oils and comparing the PV predictions obtained to those obtained in a 100-µm KCl flow cell. Both card methods performed well in their ability to predict PV. The TPP-impregnated 3M card method reproduced the flow cell PV data to within ±1.12 PV, whereas the method with an unimpregnated card was accurate to ±0.92 PV over the calibrated range (0-25 PV). Our results indicate that, with spectral normalization and the use of a PLS calibration, quantitative PV data, comparable to those obtained with a flow cell, can be provided by the 3M IR card. With the analytical protocol preprogrammed, the disposable 3M card provides a simple, rapid and convenient means of carrying out PV analyses, suitable for quality control laboratories, taking about 2-3 min per analysis.
Applied Spectroscopy, 2020
The peroxide value (PV) of edible oils is a measure of the degree of oxidation, which directly relates to the freshness of the oil sample. Several studies previously reported in the literature have paired various spectroscopic techniques with multivariate analyses to rapidly determine PVs using field portable and process instrumentation; those efforts presented 'best-case' scenarios with oils from narrowly defined training and test sets. The purpose of this paper is to evaluate the use of nearand mid-infrared absorption and Raman scattering spectroscopies on oil samples from different oil classes, including seasonal and vendor variations, to determine which measurement technique, or combination thereof, is best for predicting PVs. Following PV assays of each oil class using an established titration-based method, global and global-subset calibration models were constructed from spectroscopic data collected on the 19 oil classes used in this study. Spectra from each optical technique were used to create partial least squares regression (PLSR) calibration models to predict the PV of unknown oil samples. A global PV model based on near-infrared (8 mm optical path length-OPL) oil measurements produced the lowest RMSEP (4.9), followed by 24 mm OPL near infrared (5.1), Raman (6.9) and 50 μm OPL mid-infrared (7.3). However, it was determined that the Raman RMSEP resulted from chance correlations. Global PV models based on low-level fusion of the NIR (8 and 24 mm OPL) data and all infrared data produced the same RMSEP of 5.1. Global subset models, based on any of the spectroscopies and olive oil training sets from any class (pure, extra light, extra virgin), all failed to extrapolate to the non-olive oils. However, the near-infrared global subset model built on extra virgin olive oil could extrapolate to test samples from other olive oil classes.
JAOCS 76 (1) 19-23.
A near infrared (NIR) spectroscopic method was developed to measure peroxide value (PV) in crude palm oil (CPO). Calibration standards were prepared by oxidizing CPO in a fermentor at 90°C. A partial least squares (PLS) calibration model for predicting PV was developed based on the NIR spectral region from 1350 to 1480 nm with reference to single-point baseline at 1514 nm. The optimization of calibration factors was guided by the predicted residual error sum of squares test. The standard error of calibration obtained was 0.156 over the analytical range of 2.17-10.28 PV and the correlation coefficient (R 2 ) was 0.994. The method was validated with an independent set of samples which was prepared in the same manner on a different day. A linear relationship between the American Oil Chemists' Society and the NIR methods was obtained with R 2 of 0.996 and standard error of performance of 0.17. This study has demonstrated that the prediction of PV in the NIR region is possible. The method developed is rapid, with total analysis time less than 2 min, is environmentally friendly, and its accuracy is generally good for quality control of CPO.