Frederick R. van de Voort

Automated FTIR Analysis of Free Fatty Acids or Moisture in Edible Oils

An FTIR spectrometer coupled to an autosampler and attendant methodologies for high-volume automated quantitative analysis of free fatty acids (FFA) or moisture in edible oils are described. Samples are prepared by adding 20 g of oil to a 50 ml screw-capped vial, to which is added either a methanol/NaHNCN solution or dry acetonitrile in a I:I (w/v) ratio for FFA or H2O analysis, respectively. After capping with Mylar-lined septum caps, the vials are loaded into an autosampler tray, which is then agitated vigorously to extract the constituent of interest from the oil into the oil-immiscible solvent, and are then left to stand for ∼ 10 min to allow for phase separation. The upper solvent layer in each vial is aspirated successively into the IR cell, with the Mylar seal allowing facile autosampler needle penetration into the vials. The spectra of the sample extraction solvents serve as spectral backgrounds in addition to being used in monitoring cell path length and verifying cell loading. FFA and H2O analyses are carried out using 100 and 500 μm CaF2 cells, respectively. For FFA analysis, quantification is achieved using the ν (COO) band at 1573 cm−1, while moisture is determined using water absorption bands at 3629 or 1631 cm−1, depending on the moisture range of the samples. Calibration procedures and data are presented. The spectrometer and autosampler are controlled using proprietary Universal Method Platform for InfraRed Evaluation software, which provides a simple user interface and automates the spectral analysis; the output data can also be sent to a Laboratory Information Management System. Validation and performance data obtained with this automated system demonstrate that it is capable of analyzing >60 samples/h, a rate commensurate with the throughput required by commercial contract or high-volume process control laboratories.

A new fourier transform infrared method for the determination of moisture in edible oils

A rapid, practical, and accurate Fourier transform infrared (FT-IR) method for the determination of moisture content in edible oils has been developed based on the extraction of water from oil samples into dry acetonitrile. A calibration curve covering a moisture content range of 0–2000 ppm was developed by recording the mid-infrared (MIR) spectra of moisture standards, prepared by gravimetric addition of water to acetonitrile that had been dried over molecular sieves, in a 500 μm ZnSe transmission flow cell and ratioing these spectra against that of the dry acetonitrile. Water was measured in the resulting differential spectra using either the OH stretching (3629 cm−1) or bending (1631 cm−1) bands to produce linear standard curves having standard deviations (SDs) of approximately ±20 ppm. For moisture analysis in oils, the oil sample was mixed with dry acetonitrile in a 1:1 w/v ratio, and after centrifugation to separate the phases, the spectrum of the upper acetonitrile layer was collected and ratioed against the spectrum of the dry acetonitrile used for extraction. The method was validated by standard addition experiments with samples of various oil types, as well as with oil samples deliberately contaminated with alcohols, hydroperoxides, and free fatty acids to investigate possible interferences from minor constituents that may be present in oils and are potentially extractable into acetonitrile. The results of these experiments confirmed that the moisture content of edible oils can be assessed with high accuracy (on the order of ±10 ppm) by this method, thus providing an alternative to the conventional, but problematic, Karl Fischer method and facilitating the routine analysis of edible oils for moisture content.

Edible oil analysis by FTIR spectroscopy

Fourier-transform infrared (FTIR) spectroscopy offers a new way of approaching edible oil analysis and is well on its way to being developed into a utilitarian quality control tool. This paper provides a brief overview of FTIR spectroscopy, the key elements associated with developing a suitable fats and oils analytical system (sample handling, calibration development, validation, calibration stability and transfer, programming and automation), some methods that have been implemented, and the basic elements of a typical fats and oils FTIR analytical package. It is foreseen that a number of standard AOCS methods will be replaced by this technology, allowing a variety of chemical and physical analyses to be carried out on neat fats and oils in under 2 minutes per sample.

Chapter 4 Fourier transform infrared spectroscopy: Principles and applications

Publisher Summary This chapter focuses on the application of Fourier transform infrared (FTIR) spectroscopy in the quantitative analysis of foods. It discusses the fundamental principles of IR spectroscopy, and describes the instrumentation, data handling techniques, and quantitative analysis methods employed in FTIR spectroscopy. Mid-infrared (IR) sampling techniques are most useful in FTIR analysis of foods. Molecular absorption of electromagnetic radiation in the IR region of the spectrum promotes transitions between the rotational and vibrational energy levels of the ground electronic energy state. An infrared spectrometer essentially consists of a source of continuous IR radiation, a means for resolving the IR radiation into its component wavelengths, and a detector. Radiation from the IR source is divided into a sample beam and a reference beam and passes through the sample and a reference, placed in the respective beams.

Analysis of Base Content in In-Service Oils by Fourier Transform Infrared Spectroscopy

An automated FTIR method for the determination of the base content (BCpKa) of oils at rates of > 120 samples/h has been developed. The method uses a 5% solution of trifluoroacetic acid in 1-propanol (TFA/P) added to heptane-diluted oil to react with the base present and measures the ν(COO−) absorption of the TFA anion produced, with calibrations devised by gravimetrically adding 1-methylimidazole to a heptane-TFA/P mixture. To minimize spectral interferences, all spectra are transformed to 2nd derivative spectra using a gap-segment algorithm. Any solvent displacement effects resulting from sample miscibility are spectrally accounted for by measurement of the changes in the 1-propanol overtone band at 1936 cm−1. A variety of oils were analyzed for BC0.5, expressed as mEq base/g oil as well as converted to base number (BN) units (mg KOH/g oil) to facilitate direct comparison with ASTM D2896 and ASTM D974 results for the same samples. Linear relationships were obtained between FTIR and D2896 and D974, with the ASTM methods producing higher BN values by factors of ~1.5 and ~1.3, respectively. Thus, the FTIR BC method correlates well with ASTM potentiometric procedures and, with its much higher throughput, promises to be a useful alternative means of rapidly determining reserve alkalinity in commercial oil condition monitoring laboratories.