Janet M. Snyder

Analysis of tocopherols by capillary supercritical fluid chromatography and mass spectrometry

Tocopherol-containing mixtures were analyzed by gas chromatography (GC) and capillary supercritical fluid chromatography (SFC). GC analysis of tocopherols required the formation of the silyl derivatives, while SFC analysis of the tocopherol-containing mixtures was accomplished on neat samples. SFC analysis conditions were optimized with respect to column type and density/pressure programming. Enhanced resolution of many components was achieved by using inverse temperature programming during the SFC analyses. Both SFC and GC analyses permitted the separation and quantitation of alpha-, beta-, gamma- and delta-tocopherols. In addition, SFC proved particularly applicable for characterizing the composition of a deodorizer distillate and commercial antioxidant formulation. Coupling of a quadrapole mass spectrometer with a supercritical fluid chromatograph was also achieved; the mass spectrometer provided electron impact mass spectra on the underivatized tocopherol and sterol moieties. Both SFC and SFC/mass spectrometry proved effective for the analysis of complex lipid-containing mixtures, requiring minimal sample preparation prior to analysis.

Fat content for nutritional labeling by supercritical fluid extraction and an on-line lipase catalyzed reaction

A method using sequential supercritical fluid extraction (SFE) and enzymatic transesterification has been developed for the rapid determination of total nutritional fat content in meat samples. SFE conditions of 12.16 MPa and 50 degrees C were utilized to extract lipid species from the sample matrix. The enzymatic transesterification of the lipids by methanol was catalyzed by an immobilized lipase isolated from Candida antarctica. Conversion of the triglycerides to fatty acid methyl esters was monitored by supercritical fluid chromatography, while the fatty acid content of the extract was determined by capillary gas chromatography (GC). Total fat, saturated fat and monounsaturated fat contents were calculated from the GC data and compared to values from traditional extraction and lipid determination methods. Both off-line SFE and automated SFE followed by on-line GC analysis using two different instruments were utilized in this study. The enzymatic-based SFE method gave comparable results to the organic solvent extraction-based method followed by conventional BF3-catalyzed esterification.

On-line supercritical fluid extraction-supercritical fluid reaction-capillary gas chromatography analysis of the fatty acid composition of oilseeds *

SummaryThe versatility of supercritical fluid extraction (SFE) directly coupled with gas chromatography (GC) is further expanded by the addition of an on-line derivatization technique that is performed under supercritical fluid conditions. The integrated extraction and derivatization technique has been applied to the determination of the fatty acid composition of oilseeds. Triglycerides are extracted from seed samples using SC-CO2 and transesterified to methyl esters, in situ, over a solid catalyst. Experimental conditions were selected such that the methyl esters are preferentially eluted from the catalyst. A linear capillary restrictor was used to deposit the effluent from the supercritical fluid extractor/reactor onto a retention gap precolumn in the GC. Applications of the on-line SFE-SFR-GC technique include the analysis of single soybean, evening primrose, and peanut seeds.

Extraction and Enrichment of Pesticides for Analysis using Binary Supercritical Fluid Mixtures

Abstract To improve the extraction selectivity in analytical supercritical fluid extraction (SFE), binary mixtures of supercritical fluids have been used to selectively produce lipid‐free extracts of trace pesticide residues for chromatographic analysis. Mixtures of nitrogen and HC‐134a have been used in conjunction with carbon dioxide to selectively extract both fortified and incurred residues from a variety of fatty foods using both experimental and commercially‐available extraction instrumentation. Extraction of fortified pesticides in butter fat showed high recoveries for both organo‐chlorine and ‐phosphorus pesticides with recoveries declining for specific pesticide moieties at the 1 ppb spiking level for CO2/N2 mixtures. For CO2 and HC‐134a mixtures, there was poor and little improvement in analyte recovery relative to using neat SC‐CO2 for fortified organochlorine pesticides in butter fat at the 0.5–5.0 ppm level. However using a CO2/HC‐134a mixture for organophosphorus pesticides in butter fat improved recoveries (>90%) of the analytes at the 1–3.5 ppm level relative to using neat SC‐CO2. Excellent recoveries were obtained for incurred organochlorine and ‐phosphorus pesticides from a variety of food products at ppb levels using either CO2/N2 or CO2/HC‐134 mixtures. Results from these and additional experiments suggest that binary fluid mixtures can significantly reduce the need for additional sample cleanup prior to chromatographic analysis, allowing in some cases, direct injection of the extract after dilution into the gas chromatograph.

Volatiles from microwave-treated, stored soybeans

Soybeans were microwaved to inactivate enzymes and prevent oil deterioration during storage. Microwave time was varied from 4 to 10 min, in 2-min increments, and the treated and control soybeans were stored for 8 weeks at 40°C. Damage was monitored by analysis of peroxide value and free fatty acid content of the extracted oil and by volatile analysis of the full-fat meal and extracted oil. Volatiles were measured by multiple headspace extraction, and the formation of hexanal was monitored in both oil and meal. During storage of the control beans, peroxide value increased from 0.41 to 1.20 meq/kg, hexanal concentration changed from 29 to 94 ppb and free fatty acid content increased from 0.4 to 1.7%. Oils extracted from soybeans that were microwaved for 4 or 6 min had peroxide values of about 1 meq/kg and hexanal concentrations of 39–44 ppb after storage, indicating partial inactivation of lipoxygenase enzymes. However, soybeans that were microwaved for 8 min or more tended to oxidize during storage to a greater extent than the control soybeans, showing higher peroxide values and greater formation of hexanal in the samples. This suggests that soybeans microwave-treated in excess of 8 min are heat-damaged and susceptible to deterioration during storage. Free fatty acid content of the oils from all of the microwave-treated soybeans was about 0.4% initially, and did not increase with storage, indicating inactivation of hydrolytic enzymes.

An analysis scheme for estimation of crude oil quality

A seed analysis scheme was designed to rapidly estimate the quality of extracted oil. Factors of crude oil quality evaluated were: free fatty acids, oxidative status (Totox value), color, and phosphatides (soybean) or wax (sunflower). Soybean and sunflower seeds subjected to extended storage at varying moisture contents were sampled at incremental time periods to yield fifty storage-damaged samples of each oilseed. Oil was extracted from 50-g lots of each sample and analyzed for the crude oil quality factors according to standard methods. Alternative instrumental and chemical analyses of the quality factors were correlated with the standard methods. Hexanal content, measured by headspace-gas Chromatographie analysis of the ground full-fat meal, was correlated to the oxidative status. Crude oils recovered by rapid extraction, using sonication, and desolventation were monitored by spectrophotometry for color correlation. Free fatty acid content was determined by titration methods and monitored by spectrophotometry. Modified turbidimetric methods estimated the phosphatides (soybean) or wax (sunflower seed) contents. The analysis scheme provides for the rapid estimation of oil quality as impacted by various pre- and post-harvest events that cause deterioration of oilseeds.