15 % loading of a proprietary stationary phase and 1% of phosphoric acid supported on 100/120 Chromosorb W AW, a processed diatomite. The column was made of glass, 6 ft long, 4 mm I.D. and operated isothermally at 145˚C. Helium was used as the carrier gas at a flow rate if 60 ml/min. and 15 ml of the ether extract was injected onto the column. The three different types of bacteria gave quite different volatile fatty acid profiles. Furthermore it would appear that the acid profile; could be used as a means of identification. Courtesy of Supelco Inc. Chromatogram provided to Supelco by K.J. Hauser, Department of Pathology, Mount Sinai Medical Center, Milwaukee, WI. Figure 40 Volatile Fatty Acid Profiles from Different Bacteria

were extracted with chloroform/methanol (2+1) containing 2, 6-di-tert-butyl-4-methylphenol as an antioxidant. The extract was separated on a thin layer plate using n-hexane-diethyl ether-acetic acid (70+30+1) as a solvent. The phospholipid, triglyceride and free fatty acid spots were scraped off the plates and the lipids removed by eluting with a chloroform methanol mixture(2+1). The phospholipids and triglycerides were trans-esterified (21) using sodium methoxide in methanol and the free fatty acids were methylated with diazomethane.   It was found that for satisfactory operation the column must have a very low level of bleed. Although the use of polymer coated capillary columns would appear to be ideal for this work, the resolution was inadequate and the best stationary phase was found to be a Carbowax polymer column (polyethylene glycol). The combination of retention data with mass spectrum gave virtually unambiguous fatty acid identification.  

nbsp; Courtesy of Supelco Inc. 1/ n-Valeric Acid 2/ n-Caproic Acid 3/ n-Caprylic Acid 4/ n-Capric Acid 5/ n-Lauric Acid 6/ n-Myristic Acid 7/ n-Palmitic Acid 8/ n-Stearic Acid 9/ n-C16-1 ene 10/ n-Oleic Acid 11 /n-Linoleic Acid 12/ n-Linolenic Acid. Figure 42. The Separation of the Free Fatty Acids from Milk If an external standard is used, then the extract is merely diluted to a known volume (e.g., 10 ml)

, the FID was held at 250 oC (50oC) above the maximum column temperature . The sample size was 0.1 ml which was split 100-1 onto the column and so the total charge on the column was about 1 mg. Helium was used as the carrier gas at a linear velocity of 20 cm/sec. The value of the open tubular column is clearly demonstrated. Free Fatty Acids from Milk An example of the use of the packed column in natural product analysis is the separation and determination of the free fatty acids in whole milk. An example of such an analysis is shown in figure 42. This analysis requires a rather lengthy procedure for sample preparation but, at the same time, avoids a derivatization procedure that can easily give incorrect, low values for the fatty acid content. Due to their relatively high volatility, the lower fatty acids can be lost as vapor during the procedure. Losses can also occur as a result of their incomplete derivatization. The sample preparation developed by

for terms hydrophobic and hydrophilic, and, as such, might be considered somewhat irrelevant. These terms stemmed from the early days of the soap industry when soap was prepared by boiling a vegetable oil with an alkaline solution obtained from leaching wood ash with water. The alkaline product from the wood ash was a crude solution of sodium and potassium carbonates called lye. The result of boiling vegetable oil with the lye was the soap (sodium and potassium salts of long-chained fatty acids) which, due to the dispersive interactions between the fatty acid alkane chains, separated from the lye and, consequently, was calledlyophobic. Itfollows, thatlyophobic, is synonymous to "hydrophobic", and thus lyophobic interactions are dispersive. The other product from soap-making is glycerol, which, being strongly polar, remained in the lye and was consequently termed lyophilic. Glycerol is very polar because of its many hydroxyl groups and is completely miscible with

meaning fear of lye) and "lyophilic" (meaning love of lye) are a little more obscure. The terms originated in the early days of the soap industry when soap was prepared by boiling a vegetable oil with an alkaline solution obtained from leaching 'wood ash' with water. The alkaline product from the wood ash was a crude solution of sodium and potassium carbonates called "lye". On boiling the vegetable oil with the lye, the soap (sodium and potassium salts of long-chained fatty acids) separated from the lye due to the dispersive interactions between the fatty acid alkane chains and were thus called "lyophobic". It follows that "lyophobic", from a physical chemical point of view, would be the same as "hydrophobic", and interactions between hydrophobic and lyophobic materials are dominantly dispersive. The other product of the soap-making industry was glycerol, which remained in the lye and was consequently termed "lyophilic