Quantitative Determination of Linoleic Acid in Infant Formulas by Gas Chromatography

A method has been developed for the quantitative determination of linoleic acid in infant formulas by gas chromatography (GC). A known amount of triheptadecanoin was spiked into the sample. Total lipid was extracted from the product by an ethyl ether-petroleum etherethanol system in a Mojonnier flask. The sample was saponified by methanolic KOH after the solvents were evaporated. Methyl esters of the fatty acids were prepared by boron trifluoride (BF3) in methanol and analyzed by gas chromatography. A glass column packed with 10% SP-2340 (75% cyanopropyl silicone) was used to separate and identify the methyl linoleate and the methyl heptadecanoate. The quantity of methyl linoleate was calculated by comparing the integrated peak areas of these 2 fatty acid methyl esters. This method was satisfactory for both milk protein-based and soy protein-based matrixes. The results obtained by this method are comparable to those obtained by the AOAC spectrophotometric method 28.082- 28.085.

Determination of Nitrilotriacetic Acid in Inland Waters by Gas Chromatography of the Trimethyl Ester

A method for the analysis of low concentrations of nitrilotriacetic acid (NTA) in natural waters was developed. The NTA was converted to the trimethyl ester and determined quantitatively by gas chromatography using methyl heptadecanoate as an internal standard. The lower limit of detection was 25 μg/liter of NTA. The identity of the ester was confirmed using a mass spectrometer–gas chromatograph combination.

EXCRETION OF PHOSPHOLIPIDS BY MEN ON FAT-FREE DIET

The fecal excretion of phospholipids was determined in three adult males during the last 4 days of three 8- to 16-day periods on a fat-free diet. The phospholipids were isolated and identified by column and thin-layer chromatography on silicic acid. The individual phospholipids were quantitatively estimated by gas chromatographic determination of the component fatty acids, using methyl heptadecanoate as internal standard. The range of total excretion of phospholipids was 64–100 mg/day per 100 g of dry feces. In all samples the major phospholipids were tentatively identified as phosphatidyl ethanolamine, phosphatidyl glycerol, and phosphatidyl inositol. Phosphatidyl ethanolamine made up 31–41% of the total excretion. All the phospholipids contained about the same fatty acids (C14–C27), but in somewhat varying proportions. Because of the occurrence of large amounts of the odd carbon number, among both branched and long chain fatty acids, which are not commonly associated with mammalian metabolism, the presence of phospholipids in the feces was attributed to bacterial synthesis.