2.2.4 Biological Samples
Biological tissue samples are undoubtedly the most difficult to extract and analyze. During the extraction process, the analytes need to be effectively transferred from the outside and inside of cellular matter to the solvent phase. The approaches used are as diverse as the high number of sample tissue types. Common approaches include (1) drying the tissue, followed by grinding, and Soxhlet extraction and (2) a combination of grinding and sonication, followed by liquid extraction. Whichever method is used, extensive sample cleanup (the removal of interfering substances and analytes) is necessary since the analyst should not inject non-volatile biological material into a GC.
An additional point should be made here. Gas chromatography is only used for analytes with boiling points below approximately 300 °C and this limits the utility of GC analysis for both the organic and analytical chemist (HPLC was developed for most other non-volatile compounds). However, some analytes can be reacted with derivatizing agents to remove functional groups that tend to make them nonvolatile. A common derivatizing agent (also referred to as a silylating agent) is N,O-bis (trimethylsily) acetamide which converts groups such as -OH, -COOH, -NH2, =NH, and -SH to a -O-Si(CH3)3 group that renders the compound volatile. It should be noted that derivatizing agents are very hazardous and usually carcinogenic.
| Frank's Homepage |
©Dunnivant & Ginsbach, 2008