Using Theoretical Correction Factors for Quantitative Analysis of Sterols and Sterol Concentrates

A common detector for the analysis of sterols and sterol concentrates by gas chromatography is the flame ionization detector (FID). The detector measures the response of ions from a molecule as it is pyrolyzed in a hydrogen flame. The response is relative to the number of hydrogen and carbon atoms in a molecule and it gives different responses for the same amounts of different analytes. Theoretical correction factors (TCF) can be used to account for these differences during data analysis and are based upon the number of active carbons in a molecule and can be calculated from known structures. TCF have been used to provide a more reproducible approach to the analysis of sterol concentrates in raw materials. Use of empirical correction factors (ECF) requires determination of relative responses for each analyte and also a high purity standard (and determination of that purity), which can be expensive or difficult to obtain for the more uncommon sterols. Experiments have been conducted to determine ECF for Ergost-5-en-3-ol, (3 beta,24R), commonly known as campesterol, Stigmasta-5,22-dien-3-ol, (3 beta,22E), commonly known as stigmasterol, and Stigmast-5-en-3-ol, (3 beta), commonly known as beta-sitosterol and compared to the calculated TCF for these same sterols. The experiments evaluated differences in concentration, standard purity, and injection technique and found that all three factors had an effect on the determination of ECF. It was also found that cool on column injections gave more accurate ECF values and are preferable for quantitative analysis of sterols.