Skip to main content
ARS Home » Research » Publications at this Location » Publication #160452
Title: ANALYSIS OF TRIGLYCERIDE ISOMERS BY SILVER-ION HPLC: EFFECT OF COLUMN TEMPERATURE ON RETENTION TIMES

Author
item ADLOF, RICHARD
item LIST, GARY

Submitted to: Journal of Chromatography A
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/2/2003
Publication Date: 2/1/2004
Citation: Adlof, R.O., List, G.R. 2004. Analysis of triglyceride isomers by silver-ion HPLC: effect of column temperature on retention times. Journal of Chromatography A. 1046:109-113.

Interpretive Summary: Silver ion high performance liquid chromatography (Ag-HPLC) has shown itself to be a useful technique for analyzing a variety of fats and oils. The authors demonstrated, for the first time that, using but a single solvent and a chiller/heater to control column temperatures, triglycerides actually eluted more rapidly at lower column temperatures. This effect is just the opposite to that observed in gas chromatography, but could be utilized to develop a single-solvent, temperature-programmed Ag-HPLC system which, like gas chromatography, could be used to rapidly analyze a wide range of samples, with the improved reproducibility and sample separation(s) required for the development of standard methods. The authors' discovery has not been documented before and will help silver ion chromatography become a standard method for the more rapid analysis of fats and oils.

Technical Abstract: Silver ion chromatography (Ag-HPLC), utilizing columns packed with silver ions bonded to a silica or similar substrate, has proven to be a tremendously powerful technique for the analytical separation of cis and trans geometric and positional fatty acid methyl ester (FAME) and triacylglycerol (TAG) isomers. In this manuscript we utilized a HPLC column chiller/heater to study the effects of Ag-HPLC column temperatures on retention of TAG isomers. Two Varian ChromSpher Lipids© columns connected in series and an isocratic solvent system of 1.0% acetonitrile (ACN) in hexane were used to analyze a mixture of 1,3-distearoyl,2-monolinolenoyl- and 1,2-distearoyl,3-monolinolenoylglycerols. Unexpectedly, retention times of these TAG isomers were found to have increased by approximately 50% when column temperatures were increased from 10 deg.C to 40 deg.C, a result just the opposite to the temperature effects (shorter sample elution times at higher temperatures) noted in gas chromatography (GC). One possible explanation may be a temperature-induced change in the partition coefficient between ACN and hexane. In GC, the increased rate of exchange between the sample and the stationary phase of the GC column has been used to explain the more rapid elution of FAME and TAG isomers as column temperatures increased. In Ag-HPLC, the ACN competes with double bond electrons of the eluting sample for the immobilized silver ions on the LC substrate. As solvent temperature decreases, the ACN co-solvent becomes less soluble in the hexane and more readily available for competition with the eluting sample for silver ions (analogous to a higher concentration of ACN in the eluting solvent) and more rapid sample elution. Studies utilizing other solvent systems and temperature programming are underway.