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Quantitative determination of hydroperoxides by fourier transform infrared spectroscopy with a disposable infrared card
Author(s) -
Ma K.,
Voort F. R.,
Ismail A. A.,
Sedman J.
Publication year - 1998
Publication title -
journal of the american oil chemists' society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.512
H-Index - 117
eISSN - 1558-9331
pISSN - 0003-021X
DOI - 10.1007/s11746-998-0296-0
Subject(s) - analytical chemistry (journal) , infrared , normalization (sociology) , fourier transform infrared spectroscopy , chemistry , infrared spectroscopy , calibration , triphenylphosphine oxide , triphenylphosphine , chromatography , optics , organic chemistry , mathematics , physics , statistics , sociology , anthropology , catalysis
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 KCI 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.