Journal - Association of Official Analytical Chemists最新文献

Liquid chromatographic (LC) analysis of desulfated derivatives of rapeseed glucosinolates has been carried out under isocratic elution conditions with different CN-bonded stationary phases. The effects of the eluant composition (water, acetonitrile, and methanol) with the stationary phase (Zorbax CN, Lichrospher CN, and Ultrasphere CN) and temperature (20 and 50 degrees C) are described. An isocratic LC method performed at room temperature using a Lichrospher CN column and water as mobile phase is proposed. The chromatographic analysis can be done in less than 12 min, and it is easier and less expensive than the traditional gradient mode. Four commercial samples of rapeseed containing various quantities of other cruciferous seeds (wild mustard and stinkweed) as an admixture have been analyzed to determine the total glucosinolate content. Relative standard deviations of repeatability of the isocratic and gradient LC methods ranged from 0.4 to 1.7% and from 2.7 to 4.7%, respectively. Comparison of the results showed good agreement between the 2 methods (beter than 98%).

Percentage ingredient labeling has been proposed for baby foods. We determined whether or not the potassium content of baby foods could be used to verify the quantity of fruit when the characterizing ingredients were apricots or bananas, fruits rich in potassium. Official values for potassium in fruit (USDA Handbook No. 8-9) did not agree well with actual analyses. The potassium levels of products of known composition were accurately predicted from analyses of the actual ingredients used to make the foods. For banana-containing monofruit products of variable or unknown composition, potassium analysis led to fruit level estimates consistent with either the known composition or the label declaration. For products of unknown composition made with apricot concentrate, however, potassium analysis led to fruit level estimates lower than the probable fruit content. The quantity of fruit in baby foods made with potassium-rich fruits can be estimated from the potassium content if the potassium value for the fruit is representative of the actual ingredients used to make the product. If potassium analysis is to be used to verify compliance with percentage ingredient labeling, there must be statutory specification of the single-strength fruit level for fruit reconstituted from concentrate.

Acrolein (2-propenal) and other low molecular weight aldehydes (LMWAs) formed by degradation of the frying medium (triglycerides) were monitored by liquid chromatography (LC) during preparation of fried items. LMWA contents of coatings from codfish and of doughnuts and their volatiles that codistill with steam are monitored by trapping the vapors and distillate from the food matrix in a 2,4-dinitrophenylhydrazine solution. The resulting hydrazones are partitioned from the aqueous phase, first into isooctane and then into acetonitrile for LC analysis. The hydrazones are separated and quantified on a C18 reversed-phase column with acetonitrile-water as the mobile phase. LMWAs are confirmed by gas chromatography/mass spectrometry. No difference was found in LMWA content in coatings from fish fillets fried at 182 or 204 degrees C. Cake doughnuts were higher in acrolein content than yeast-raised doughnuts prepared under similar conditions. Freshness of the frying medium, frying time, and batch size did not seem to influence LMWA production from doughnuts. Results indicated that most of the LMWAs formed codistilled with steam during frying rather than remaining with the food item.

An improved method has been developed for quantitative determination of polynuclear aromatic hydrocarbons (PAHs) in pharmacopoeial paraffin and medicinal white oil samples. This new method combines 2 liquid-liquid partition and adsorption chromatography procedures with a 2-step purification on Sephadex LH 20 and liquid chromatography with fluorometric determination. Selective elution of PAHs results in absence of background fluorescence. The minimum detectable level ranges from 0.2 ppt for benzofluoranthene isomers to 200 ppt for acenaphthene. Recoveries of PAHs added at 7 ppm varied from 92.1 to 111.4%. When a variety of medicinal white oil samples were analyzed by this improved method, 27 PAHs were identified, including 11 suspected carcinogens. Their identities were confirmed by capillary gas chromatography.