Multicenter Evaluation of Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) Spectroscopy-Based Method for Rapid Identification of Clinically Relevant Yeasts.

Fourier transform infrared (FTIR) spectroscopy has demonstrated applicability as a reagent-free whole-organism fingerprinting technique for both microbial identification and strain typing. For routine application of this technique in microbiology laboratories, acquisition of FTIR spectra in the attenuated total reflectance (ATR) mode simplifies the FTIR spectroscopy workflow, providing results within minutes after initial culture without prior sample preparation. In our previous central work, 99.7% correct species identification of clinically relevant yeasts was achieved by employing an ATR-FTIR-based method and spectral database developed by our group. In this study, ATR-FTIR spectrometers were placed in 6 clinical microbiology laboratories over a 16-month period and were used to collect spectra of routine yeast isolates for on-site identification to the species level. The identification results were compared to those obtained from conventional biochemical tests and/or matrix-assisted laser desorption/ionization-time of flight mass spectrometry. Isolates producing discordant results were reanalyzed by routine identification methods, ATR-FTIR spectroscopy, and PCR gene sequencing of the D1/D2 and internal transcribed spacer (ITS) regions. Among the 573 routine clinical yeast isolates collected and identified by the ATR-FTIR-based method, 564 isolates (98.4%) were correctly identified at the species level, while the remaining isolates were inconclusive with no misidentifications. Due to the low prevalence of Candida auris in routine isolates, additional randomly selected C. auris (n = 24) isolates were obtained for evaluation and resulted in 100% correct identification. Overall, the data obtained in our multicenter evaluation study using multiple spectrometers and system operators indicate that ATR-FTIR spectroscopy is a reliable, cost-effective yeast identification technique that provides accurate and timely (∼3 min/sample) species identification promptly after the initial culture.

Antimicrobial activity of various essential oils and their application in active packaging of frozen vegetable products.

Essential oils (EOs) have potential utility as clean-label food preservatives due to their antimicrobial and antioxidant properties. In this study, various EOs were screened for their antimicrobial activities against Listeria grayi in vitro. The susceptibility of L. monocytogenes to select EOs was compared with that of L. grayi. The effectiveness of the selected EOs in inhibiting the growth of L. grayi on vegetable products was also investigated. The results showed that cinnamon and oregano EOs and carvacrol were effective in the vapor phase in inhibiting the growth of L. grayi as well as L. monocytogenes, with the susceptibility of L. monocytogenes to cinnamon EO being slightly higher than that of L. grayi. The packaging of green peppers with cellulose stickers impregnated with cinnamon EO at 556 µL/Lheadspace reduced the Listeria count to 1 log CFU/g after 2 days of storage as compared to 7.5 log CFU/g for controls.

Reagent-Free Identification of Clinical Yeasts by Use of Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy.

Invasive fungal infections by opportunistic yeasts have increased concomitantly with the growth of an immunocompromised patient population. Misidentification of yeasts can lead to inappropriate antifungal treatment and complications. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy is a promising method for rapid and accurate identification of microorganisms. ATR-FTIR spectroscopy is a standalone, inexpensive, reagent-free technique that provides results within minutes after initial culture. In this study, a comprehensive spectral reference database of 65 clinically relevant yeast species was constructed and tested prospectively on spectra recorded (from colonies taken from culture plates) for 318 routine yeasts isolated from various body fluids and specimens received from 38 microbiology laboratories over a 4-month period in our clinical laboratory. ATR-FTIR spectroscopy attained comparable identification performance with matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). In a preliminary validation of the ATR-FTIR method, correct identification rates of 100% and 95.6% at the genus and species levels, respectively, were achieved, with 3.5% unidentified and 0.9% misidentified. By expanding the number of spectra in the spectral reference database for species for which isolates could not be identified or had been misidentified, we were able to improve identification at the species level to 99.7%. Thus, ATR-FTIR spectroscopy provides a new standalone method that can rival MALDI-TOF MS for the accurate identification of a broad range of medically important yeasts. The simplicity of the ATR-FTIR spectroscopy workflow favors its use in clinical laboratories for timely and low-cost identification of life-threatening yeast strains for appropriate treatment.

Principles, performance, and applications of spectral reconstitution (SR) in quantitative analysis of oils by Fourier transform infrared spectroscopy (FT-IR).

Spectral reconstitution (SR) is a dilution technique developed to facilitate the rapid, automated, and quantitative analysis of viscous oil samples by Fourier transform infrared spectroscopy (FT-IR). This technique involves determining the dilution factor through measurement of an absorption band of a suitable spectral marker added to the diluent, and then spectrally removing the diluent from the sample and multiplying the resulting spectrum to compensate for the effect of dilution on the band intensities. The facsimile spectrum of the neat oil thus obtained can then be qualitatively or quantitatively analyzed for the parameter(s) of interest. The quantitative performance of the SR technique was examined with two transition-metal carbonyl complexes as spectral markers, chromium hexacarbonyl and methylcyclopentadienyl manganese tricarbonyl. The estimation of the volume fraction (VF) of the diluent in a model system, consisting of canola oil diluted to various extents with odorless mineral spirits, served as the basis for assessment of these markers. The relationship between the VF estimates and the true volume fraction (VF(t)) was found to be strongly dependent on the dilution ratio and also depended, to a lesser extent, on the spectral resolution. These dependences are attributable to the effect of changes in matrix polarity on the bandwidth of the ν(CO) marker bands. Excellent VF(t) estimates were obtained by making a polarity correction devised with a variance-spectrum-delineated correction equation. In the absence of such a correction, SR was shown to introduce only a minor and constant bias, provided that polarity differences among all the diluted samples analyzed were minimal. This bias can be built into the calibration of a quantitative FT-IR analytical method by subjecting appropriate calibration standards to the same SR procedure as the samples to be analyzed. The primary purpose of the SR technique is to simplify preparation of diluted samples such that only approximate proportions need to be adhered to, rather than using exact weights or volumes, the marker accounting for minor variations. Additional applications discussed include the use of the SR technique in extraction-based, quantitative, automated FT-IR methods for the determination of moisture, acid number, and base number in lubricating oils, as well as of moisture content in edible oils.

Analysis of base content in in-service oils by fourier transform infrared spectroscopy.

An automated FTIR method for the determination of the base content (BC(pKa)) 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 2(nd) 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 BC(0.5), 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.

A new direct Fourier transform infrared analysis of free fatty acids in edible oils using spectral reconstitution.

A new transmission-based Fourier transform infrared (FTIR) spectroscopic method for the direct determination of free fatty acids (FFA) in edible oils has been developed using the developed spectral reconstitution (SR) technique. Conventional neat-oil and SR calibrations were devised by spiking hexanoic acid into FFA-free canola oil and measuring the response to added FFA at 1,712 cm(-1) referenced to a baseline at 1,600 cm(-1)(1,712 cm(-1)/1,600 cm(-1)). To compensate for the known oil dependency of such calibration equations resulting from variation of the triacylglycerol ester (C═O) absorption with differences in oil saponification number (SN), a correction equation was devised by recording the spectra of blends of two FFA-free oils (canola and coconut) differing substantially in SN and correlating the intensity of the ester (C═O) absorption at the FFA measurement location with the intensity of the first overtone of this vibration, measured at 3,471 cm(-1)/3,427 cm(-1). Further examination of the spectra of the oil blends by generalized 2D correlation spectroscopy revealed an additional strong correlation with an absorption in the near-infrared (NIR) combination band region, which led to the development of a second correction equation based on the absorbance at 4,258 cm(-1)/4,235 cm(-1). The NIR-based correction equation yielded superior results and was shown to completely eliminate biases due to variations in oil SN, thereby making a single FFA calibration generally applicable to oils, regardless of SN. FTIR methodology incorporating this correction equation and employing the SR technique has been automated.

Rapid identification of community-associated methicillin-resistant Staphylococcus aureus by Fourier transform infrared spectroscopy.

The emergence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) carrying Panton-Valentine leukocidin is a worldwide problem. Their identification is based currently on costly and complicated molecular methods. This article describes a simple method for differentiating CA-MRSA from hospital-associated (HA) epidemic MRSA pulsed-field gel electrophoresis types using Fourier transform infrared (FTIR) spectroscopy. The 47 CA-MRSA isolates included 3 Southwest Pacific (resembling USA1100), 24 CMRSA7 (resembling USA400/MW2), 19 CMRSA10 (resembling USA300), and 1 European ST80, while HA-MRSA were represented by 27, 16, 11, 15, 7, and 8 Canadian epidemic isolates CMRSA1 through CMRSA6 respectively, plus 25 nontyped Canadian HA-MRSA. Principal component analysis (PCA), self-organized maps (SOMs), and the K-nearest neighbor (KNN) method were used to cluster the isolates based on chemometric analysis of FTIR spectra of dried films of stationary-phase cells grown on Que-Bact® Universal Medium No. 2 (Quelab Laboratories, Montreal, QC, Canada). First-derivative normalized data from a single narrow spectral region (1361-1236 cm(-1), suggesting differences in protein amide III and nucleic acid phosphodiester contents) allowed 98% correct classification by KNN, 93% by SOMs, and 92% by PCA. FTIR spectroscopic analysis of cells grown on Que-Bact® Universal Medium No. 2 offers a rapid and simple alternative to molecular methods for routine identification of CA-MRSA epidemic isolates.

Effect of dissolved oxygen on two bacterial pathogens examined using ATR-FTIR spectroscopy, microelectrophoresis, and potentiometric titration.

The effects of dissolved oxygen tension during bacterial growth and acclimation on the cell surface properties and biochemical composition of the bacterial pathogens Escherichia coli O157:H7 and Yersinia enterocolitica are characterized. Three experimental techniques are used in an effort to understand the influence of bacterial growth and acclimation conditions on cell surface charge and the composition of the bacterial cell: (i) electrophoretic mobility measurements; (ii) potentiometric titration; and (iii) ATR-FTIR spectroscopy. Potentiometric titration data analyzed using chemical speciation software are related to measured electrophoretic mobilities at the pH of interest. Titration of bacterial cells is used to identify the major proton-active functional groups and the overall concentration of these cell surface ligands at the cell membrane. Analysis of titration data shows notable differences between strains and conditions, confirming the appropriateness of this tool for an overall charge characterization. ATR-FTIR spectroscopy of whole cells is used to further characterize the bacterial biochemical composition and macromolecular structures that might be involved in the development of the net surficial charge of the organisms examined. The evaluation of the integrated intensities of HPO(2)(-) and carbohydrate absorption bands in the IR spectra reveals clear differences between growth protocols. Taken together, the three techniques seem to indicate that the dissolved oxygen tension during cell growth or acclimation can noticeably influence the expression of cell surface molecules and the measurable cell surface charge, though in a strain-dependent fashion.

Evaluation of Fourier transform infrared spectroscopy for the rapid identification of glycopeptide-intermediate Staphylococcus aureus.

OBJECTIVES: To evaluate Fourier transform infrared (FTIR) spectroscopy as a rapid method for distinguishing glycopeptide-intermediate Staphylococcus aureus (GISA) from glycopeptide-susceptible methicillin-resistant S. aureus (MRSA) and to compare three data analysis methods. METHODS: First-derivative normalized spectra of dried films of bacterial growth on Que-Bact Universal Medium No. 2 were examined by singular value decomposition to identify key spectral regions. Region selection was analysed by principal component analysis (PCA), self-organizing maps (SOMs) and the K-nearest neighbour (KNN) algorithm. The initial data set included 35 GISA (including GISA Mu50 and heterogeneous GISA Mu3) and 25 epidemic MRSA. The regions were then tested using enlarged data sets that included 22 sporadic and 85 additional epidemic MRSA. RESULTS: Epidemic MRSA and GISA/hGISA were separated into two distinct clusters on the basis of spectral data from regions 1352-1315 and 1480-1460 cm(-1), the former providing 100% correct classification by all three analyses and the latter providing 96.67% correct by PCA, 98.34% by SOM and 100% by KNN. The 1480-1460 cm(-1) region was more effective for distinguishing GISA/hGISA from a set combining sporadic and epidemic MRSA, with two GISA/hGISA and four sporadic MRSA misclassified by PCA and SOM (92.69% correct), while the KNN method misclassified three of the four sporadic MRSA (93.90% correct). The addition of 85 other epidemic MRSA this set increased the fraction of correctly classified isolates to 96.41% and 97.01% by PCA, SOM and KNN, respectively. CONCLUSIONS: As only 6 of 167 isolates were misclassified, FTIR spectroscopy may provide means of rapid and accurate identification of GISA and hGISA among isolates of MRSA.

Improved determination of isolated trans isomers in edible oils by Fourier transform infrared spectroscopy using spectral reconstitution.

A substantially more sensitive and accurate alternative to the single-bounce attenuated total reflectance (SB-ATR) Fourier transform infrared spectroscopic method of AOAC/American Oil Chemists' Society (AOCS) was developed for determination of isolated trans isomers, based on transmission measurements using a technique called spectral reconstitution (SR). The method involves the 1:1.5 dilution of an oil with odorless mineral spirits (OMS) containing a spectral marker. The resulting reduction in sample viscosity facilitates the use of a transmission flow cell, with the spectral marker serving to determine the precise dilution ratio. This allows the spectral contributions of the OMS to be eliminated and a facsimile of the neat oil spectrum to be mathematically reconstituted. The transmission-SR (T-SR) procedure was initially evaluated relative to SB-ATR to track changes in the trans content of mixtures of unhydrogenated canola and a highly hydrogenated sunflower oil (0-30% trans). The results indicated that the T-SR procedure had the potential to serve as the basis of an accurate quantitative method. A subsequent T-SR calibration based on the spectral ratioing principle of the SB-ATR AOACIAOCS method was developed by gravimetrically adding trielaidin (0-4%) to extra virgin olive oil (EVO), producing an excellent linear response with a standard deviation (SD) of < 0.04% trans. Subsequent comparison of SB-ATR and T-SR calibrations developed for 5 oils of different types, each spiked with low levels of trielaidin (0-1.2% trans), clearly indicated that SB-ATR was signal-limited, whereas the T-SR procedure performed well. The EVO calibration was subsequently used to predict the added trans content of these spiked oils, after the spectrum of the corresponding unspiked oil had been ratioed out. The resulting plot of predicted versus added trans was linear, with a slope of 1.02 and an overall SD of <0.05% trans. When the spectra of these oils were ratioed against the spectrum of EVO, the trans predictions for some of the oils were offset by 2-3 percentage points, emphasizing the need for the appropriate trans-free reference oil to perform accurate analyses. If the latter condition is met, then T-SR provides a very simple technique, with the potential for automation, for analysis of oils by transmission spectroscopy, with approximately 20x the sensitivity of the AOAC/AOCS SB-ATR method.

Epidemiological typing of methicillin-resistant Staphylococcus aureus strains by Fourier transform infrared spectroscopy.

A rapid and simple typing system is needed for controlling the spread of epidemic methicillin-resistant Staphylococcus aureus (MRSA), currently one of the most widespread multi-resistant nosocomial pathogens in Canadian hospitals. Fourier transform infrared (FTIR) spectroscopy was used to subtype 85 isolates representing five strains of epidemic Canadian MRSA (CMRSA). Spectral fingerprints of whole cells grown on Que-Bact(R) Universal Medium No. 2 were transformed to first derivative peak-height normalized files and examined visually and by singular-value decomposition (SVD). Distinguishing spectral regions were processed by principal component analysis (PCA), self-organizing map and K-nearest neighbor supervised cluster analysis. Among the visually identified regions, 1070-1050 and 1155-1137 cm(-1) were found suitable for discrimination of CMRSA-4 and CMRSA-2 respectively, while CMRSA-1, CMRSA-3, and CMRSA-5 each exhibited distinctive spectral profiles in the 1123-1094 cm(-1) region. The combination, 1123-1094, 1174-1154 and 2904-2864 cm(-1) separated the five CMRSA with 84.6% correct classification by PCA. Five clusters were also obtained using the SVD-selected regions 1096-1066, 1118-1090 and 2914-2880 cm(-1), with 87.8% correct classification based on visual examination of the PCA scores plot and 97% based on supervised cluster analysis. These results demonstrate that FTIR spectroscopy has considerable potential as a rapid (1-hour) and simple method for MRSA strain typing and monitoring in clinical settings.

An automated FTIR method for the routine quantitative determination of moisture in lubricants: An alternative to Karl Fischer titration.

An accurate primary Fourier transform infrared (FTIR) method for the determination of moisture in mineral and ester based lubricants has been developed based on the extraction of moisture into dry acetonitrile. FTIR evaluation of acetonitrile extracts from new and used lubricants as well as common lubricant additives and contaminants which might co-extract indicated that phenolic constituents interfered significantly with moisture measurements. By measuring moisture at 3676cm(-1) on the shoulder of the asymmetric OH stretching band, spectral interferences from extracted phenolic constituents were minimized. The spectra of calibration standards (0-2100ppm), prepared by gravimetric addition of water to dry acetonitrile, were recorded in a 1000-mum CaF(2) transmission flow cell and produced linear standard curves having an S.D. of approximately +/-20ppm. Lubricant sample preparation involved the vigorous shaking (20min) of a 1:1.5 (w/v) mixture of lubricant and dry acetonitrile, centrifugation to separate the phases, acquisition of the FTIR spectrum of the upper acetonitrile layer, and subtraction of the spectrum of the dry acetonitrile used for extraction. A Continuous Oil Analyzer and Treatment (COAT((R))) FTIR system was programmed to allow the automated analysis of acetonitrile extracts, and the methodology was validated by analyzing 58 new and used oils, independently analyzed by the Karl Fischer (KF) method. Linear regression of FTIR versus KF results for these oils produced a linear plot with a between-method S.D. of +/-80ppm. As implemented on the COAT((R)) system, this FTIR method is capable of analyzing 72 acetonitrile extracts/h and provides a high-speed alternative to the KF titrimetric procedures for the determination of water in lubricants.

Rapid identification of coagulase-negative staphylococci by Fourier transform infrared spectroscopy.

Coagulase-negative staphylococci (CNS), frequently associated with both community-acquired and nosocomial bloodstream infections, must be distinguished from Staphylococcus aureus for clinical purposes. Conventional methods are too laborious and time-consuming and often lack sensitivity to CNS. Fourier transform infrared (FTIR) spectroscopy combined with the use of a universal growth medium (Que-Bact Universal Medium No. 2) and chemometrics was evaluated for its potential as a rapid and simple clinical tool for making this distinction. FTIR spectra of 11 methicillin-sensitive and 11 methicillin-resistant CNS isolates as well as 25 methicillin-sensitive, 47 methicillin-resistant, 34 borderline oxacillin-resistant and 35 glycopeptide intermediate S. aureus isolates were obtained from dried films of stationary-phase cells grown on the universal medium. Principal component analysis (PCA), self-organizing maps, and the K-nearest neighbor algorithm were employed to cluster the different phenotypes based on similarity of their FTIR spectra. PCA of the first-derivative normalized spectral data from a single narrow region (2888-2868 cm(-1)) yielded complete differentiation of CNS from both methicillin-sensitive and methicillin-resistant S. aureus. The rate of correct classification was somewhat reduced, from 100% to 90%, after inclusion of borderline oxacillin-resistant and glycopeptide intermediate S. aureus strains in the data set. Differentiation based on the data in broader spectral regions was much less reliable. The results of this study indicate that with proper spectral region selection, FTIR spectroscopy and cluster analysis may provide a simple and accurate means of CNS species identification.

Differentiation of group I and group II strains of Clostridium botulinum by focal plane array Fourier transform infrared spectroscopy.

A method was developed for whole-organism fingerprinting of Clostridium botulinum isolates by focal plane array Fourier transform infrared (FPA-FTIR) spectroscopy. A database of 150,000 infrared spectra of 44 strains of C. botulinum was acquired using a FPA-FTIR imaging spectrometer equipped with a 16 x 16 array detector to evaluate the ability of FTIR spectroscopy to differentiate the 44 strains. The database contained strains from C. botulinum groups I and II producing botulinum neurotoxin of serotypes A, B, E, and F. All strains were grown on each of three agar media (brain heart infusion, McClung Toabe agar base, and universal) prior to spectral acquisition. Given the dependence of the infrared spectra of microorganisms on the composition of the growth medium, the spectra were initially separated into three subsets corresponding to the three growth media employed. However, the replicate spectra of all strains, regardless of growth medium, were properly clustered by hierarchical cluster analysis based on differences in their infrared spectral profiles in three narrow spectral regions (1,428 to 1,412, 1,296 to 1,284, and 1,112 to 1,100 cm(-1)). The dendrogram generated from the FTIR data revealed complete separation between group I and group II strains. The spectral differences between group I and group II strains allowed accurate classification of C. botulinum strains at the group level in two blind validation studies (n = 40). These results demonstrate that FPA-FTIR spectroscopy has the potential for rapid discrimination of group I and group II C. botulinum strains in less than 3 min per sample.

Heterospectral two-dimensional correlation spectroscopy of mid-infrared and Fourier self-deconvolved near-infrared spectra of sugar solutions.

The mid- and near-infrared (mid-IR and NIR) spectra of aqueous solutions of glucose and fructose, fructose and galactose, and glucose and galactose were recorded and analyzed by heterospectral two-dimensional correlation spectroscopy (H2D-CS) to determine characteristic NIR wavelengths for each sugar. Fourier self-deconvolution (FSD) was applied to the NIR spectra prior to H2D-CS analysis to help resolve the strongly overlapping sugar absorptions. Examination of the H2D-CS data gave characteristic absorption wavelengths for glucose, fructose, and galactose. The wavelengths identified by H2D-CS were then used to develop multiple linear regression (MLR) calibrations for the quantitative analysis of mixtures of the three sugars in solution. This approach gave comparable results to MLR calibrations based on wavelengths selected by examination of the first- and second-derivative spectra of solutions of the individual sugars.

Fourier transform infrared study of lipoxygenase conformation in organic solvent media.

The secondary structure of commercially purified soybean lipoxygenase (EC 1.13.11.12) was investigated in selected monophasic organic solvents, including chloroform, methanol, acetonitrile, hexane, and octane. The Fourier transform infrared (FT-IR) spectra of the enzyme obtained in chloroform, methanol, and acetonitrile showed an absorption band at 1617 cm(-1) indicative of significant protein aggregation, whereas spectra of lipoxygenase in hexane and octane exhibited substantially less aggregate formation. Variable-temperature infrared studies of lipoxygenase in D(2)O show that the predominately alpha-helical structure of the protein undergoes an irreversible transition to intermolecular beta-sheet at and above 65 degrees C. Chemical imaging technology employing an FT-IR spectrometer equipped with an infrared microscope and a focal-plane array detector was used to examine the changes in the secondary structure of lipoxygenase at the water-hexane interface in the presence and absence of substrate. The secondary structure of lipoxygenase at the hexane-water interface was comparable to that of the structure of lipoxygenase in D(2)O after exposure of lipoxygenase solution to hexane.

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 microm 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.

Investigation of the potential utility of single-bounce attenuated total reflectance Fourier transform infrared spectroscopy in the analysis of distilled liquors and wines.

A new Fourier transform infrared (FTIR) spectroscopic method based on single-bounce attenuated total reflectance (SB-ATR) spectroscopy was developed for the analysis of distilled liquors and wines. For distilled liquors, a partial least-squares (PLS) calibration was developed for alcohol determination based on the SB-ATR/FTIR spectra of mixtures of ethanol and distilled water. An independent set of 12 different distilled liquor samples was predicted from the PLS calibration, and a standard deviation of the differences for accuracy (SDD(a)) between actual and predicted values of 0.142% (v/v) was obtained. The potential utility of SB-ATR/FTIR spectroscopy for the analysis of wines was initially evaluated based on a comparison with Fourier transform near-infrared (FT-NIR) spectroscopy and FTIR spectroscopy using a flow-through transmission cell. PLS calibrations for alcohol, total reducing sugars, total acidity and pH were developed using pre-analyzed wine samples (n = 28), and for SB-ATR/FTIR spectroscopy, the SDD(a) for the leave-one-out cross-validation statistics were of the order of 0.100% (v/v), 0.707 g L(-1), 0.189 g L(-1) (H2SO4), and 0.230, respectively. Overall, the SB-ATR/FTIR results were better than those obtained using FT-NIR spectroscopy and comparable to those obtained with transmission FTIR spectroscopy. A PLS calibration based on preanalyzed wine samples (n = 72) for the prediction of 11 different components and parameters in wines by SB-ATR/FTIR spectroscopy was subsequently developed and validated using an independent sample set (n = 77). Good coefficients of correlation between the reference and predicted values for the validation set were obtained for most of the components and parameters except citric acid, volatile acids, and total SO2. The results of this study demonstrate the suitability of SB-ATR/FTIR spectroscopy for the routine analysis of distilled liquors and wines.