Fatty acids, oxidation total, quantitation

Hydrolysis of polyamide-based formulations with 6 N HC1 followed by TLC allows differentiation between a-aminocaproic acid (ACA) and hexamethylenedi-amine (HMD) (hydrolysis products of PA6 and PA6.6, respectively), even at low levels. The monomer composition (PA6/PA6.6 ratio) can be derived after chromatographic determination of the adipic acid (AA) content. Extraction of the hydrolysate with ether and derivatisa-tion allow the quantitative determination of fatty acids (from lubricants) by means of GC (Figure 3.27). Further HC1/HF treatment of the hydrolysis residue, which is composed of mineral fillers, CB and nonhydrolysable polymers (e.g. impact modifiers) permits determination of total IM and CB contents CB is measured quantitatively by means of TGA [157]. Acid hydrolysis of flame retarded polyamides allows to determine the adipic acid content (indicative of PA6.6) by means of HPLC, HCN content (indicative of melamine cyanurate) and fatty acid (indicative of a stearate) by means of GC [640]. Determination of ethylene oxide-based antistatic agents... 

Semm cholesterol exists as a mixture of fatty acid esters and free cholesterol. Quantitation of total cholesterol involves the initial conversion of the esters to free cholesterol, followed by the total conversion of free cholesterol to its oxidation product. This reaction is coupled to the familiar dye-peroxidase indicator reaction. The parameter A50o measurements using stock cholesterol solutions provide a calibration curve. A reagent blank solution is prepared using all components except cholesterol, and this value is subtracted from all measured A50o values, correcting for any background oxidation of the dye. 

To understand the sensitivity of the extracts to artifact formation it is informative to review the volatiles in kiwifruit. Quantitatively, peroxidation products of unsaturated fatty acids (11, 12), which include (E)-2-hexenal (77.87%), (E)-2-hexen-l-ol (6.80%), 1-hexanol (3.40%), hexanal (1.78%), (Z)-2-hexenal (0.87%), (E)-3-hexen-l-ol (0.32%) and (Z)-3-hexen-l-ol (0.17%), constitute over 90% of the total volatiles. Other major constituents include the esters, methyl butanoate (2.54%) and ethyl butanoate (3.52%). The presence of large amounts of saturated and unsaturated aldehydes in the extract is noteworthy since they are quite susceptible to free-radical oxidation. We therefore expected that at least some of the artifacts were the products of autoxidation. 

---