The use of calibration approaches for quantitative GC/MS analysis-secobarbital example

One-point, Linear, Hyperbolic and Polynomial calibration approaches were adopted to elucidate the quantitative effectiveness of standard solutions of 10 to 800 ng/mL secobarbital by comparing theoretical and observed concentrations. Different concentrations of internal standard(IS), 50 and 200 ng/mL, were added to standard solutions for comparison purpose. Two GC column temperature programs, a high ramp rate of 20 °C per minute and a low ramp rate of 2 °C per minute, were used to generate different degrees of peak-overlap and ion cross-contributions to evaluate the most appropriate application for each calibration approach. The ion cross-contribution deriving from IS to analyte leads to the significantly positive observed concentration at low concentration levels while using One-point calibration. This phenomenon is clearly exhibited by ion pairs containing the higher ion cross-contribution, the larger added IS magnitude, and the higher ramp rate of temperature programming. One-point calibration is appropriately used for the quantitation that concentrations of analytes are close to that of the calibrator. In addition to the ion cross contribution, the “non-proportional over-all change in ionization efficiency” phenomenon will also affect the effectiveness under Linear calibration. Thus, it can be adopted by using appropriate derivatization, IS and/or its magnitude, and temperature programming along with the suitable concentration range of standard solutions. The Hyperbolic calibration can be generally used for determining analytes at various concentration levels without interference from ion cross-contribution factor. The Polynomial approach can completely fit in ion-pair intensity ratios of standard solutions for each ion-pair yielding the ideal observed concentrations.