Application Examples
There are many examples of quantitative GC and LC analyses in the literature all of which are readily available for referral. Consequently only two examples will be given here that have been chosen to illustrate some atypical applications of GC and LC analyses.
The Extraction and Analysis of Carbonyl Compounds from Natural Products
Lipid hdroperoxides decompose to form aldehydes and their presence can identify lipid peroxidation. The medium and short chain aldehydes are the source of the unpleasant odor of rancid fat rich foods (23). In addition, carbonyl compounds can be considered as toxic messengers heralding free radical peroxidation (24) and their assay can identify and measure he extent of peroxidation. Aldehyde assay will involve liquid/liquid extraction or solid phase extraction. Stashenko et al. (25) used the two techniques to determine aldehydes in vegetable oil and human urine after ingestion of beer over a two hour period.
Two milliliters of vegetable oil was placed in a capped tube and heated for one hour at 259oC. When cool, the sample was derivatized at room temperature with 2 ml of pentofluorophenylhydrazine solution (0.22 M in 0.1 M hydrochloric acid for three hours. The pentofluorophenyl-hydrazine deruvatives were extracted from the aqueous layer three times with 2 ml of hexane and the bulked extracts reduced to 1 ml by evaporation in a stream of nitrogen. The solid phase extraction (SPE) was carried out by passing the aqueous layer through an (SPE) cartridge containing an octadecyl bonded packing and the extract was eluted with 2 ml of hexane which was reduced to one ml by evaporation.
Two columns were used; one was 50 m long, 0.24 mm I.D. coated with a film of poly dimethyl siloxane 0.2 mm thick; the other column was 60 m long, 0.25 mm I.D. coated with a film of 5% phenylpolydimethyl siloxane 0.33 mm thick. Both column were held isothermally at 100oC for 5 min. and then programmed up to 200oC at 2.5oC/min. then held at 200oC for 10 min and finally programmed up to 259oC at 5oC/min.
