Operating variables in the analysis of tall oil acids by capillary gas chromatography

Factors influencing the analysis of fatty and resin acid methyl esters by capillary gas chromatography have been investigated. Methods to calculate equivalent chain length (ECL) values and their limitations are first discussed. Retention data, expressed as equivalent chain lengths (ECL) were determined on SE-30, SP-2100 and Carbowax 20M columns. The medium length (20–30-m) polysiloxane columns, SE-30 and SP-2100, provided overall better resolution and shorter retention times than the more polar Carbowax 20M column of similar length. The temperature dependence of ECL values was investigated for all three columns in the range 180–210 C. Retention times and ECL values were more temperature-dependent for the Carbowax 20M than for the other two stationary phases. The effects of split ratio and method of injection on the precision and accuracy of the analysis were also examined. Using optimal conditions of analysis established in this paper, the difference between measured and actual weights of an internal standard added to two tall oil samples was determined to be less than 3%.