[Show abstract][Hide abstract] ABSTRACT: Introduction The quality or status of a lubricant is directly related to the performance and reliability of machinery and the importance of condition monitoring so as to avoid excessive wear and downtime of equipment and critical components has been recognized (1). The chemical and physical parameters analyzed for are largely based on standardized analytical methods to provide an overall indication of the status of a lubricant. However, key ASTM chemical methods such as the determination of Total Acid Number (TAN), Total Base Number (TBN) and moisture (H 2 O) are troublesome to carry out, being tedious, time consuming and trouble prone even in their automated forms. Today, there is more emphasis on structured condition monitoring to provide trending data so that one can take preventive action on the one hand, but not take unnecessary action on the other. This approach may extend drain intervals and reduce lubricant disposal and maintenance and failure costs. On the other hand, extensive testing is required and data management can become complex. FTIR Spectroscopy In this context, an instrument that has become increasingly prominent in lubricant analysis is the infrared spectrometer, specifically the Fourier transform infrared (FTIR) spectrometer. This analytical instrument effectively provides a spectral snapshot of the base oil and other constituents present. Its power is based on the fact that specific molecular functional groups absorb in unique regions of the mid-infrared spectrum, allowing identification of additives, contaminants and breakdown products. Although IR spectral information is meaningful to a spectroscopist, its meaning is not necessarily apparent to the non-expert. Even with this limitation, IR spectroscopy is still a very powerful tool, simply because it can provide substantial information about oil condition using a single instrument. Indications about the state of oxidation, nitration and sulfation and levels of soot, moisture, glycol and various additives, among others, is available. Extensive IR studies of lubricants and fuels have led to the establishment of standardized protocols to monitor selected condition parameters under the guise of the Joint Oil Analysis Program (JOAP). These protocols, and similar protocols under consideration by the ASTM, provide a comprehensive means of monitoring the condition of lubricants using a single analytical technique.
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: 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.
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