Effect of column flow rate and sample injection mode on compound-independent calibration using gas chromatography with atomic emission detection

Compound-independent calibration (CIC) is a theoretical concept in which a single compound is used to quantitate other compounds within a sample. Gas chromatography with atomic emission detection (AED) is one technique in which CIC can theoretically be applied. Reports are present in the literature, however, that both support CIC and indicate dependence of the AED response on compound structure. In this investigation, the effects of two gas chromatographic parameters (injection mode and column now rate) on the atomic emission detector elemental response factor (ERF, peak area per nanogram of element injected) were studied. Seven compounds containing various nitrogen functional groups and three detection wavelengths (C at 179 nm, H at 486 nm, and N at 174 nm) were used in this work to explore CIC with GC-AED, When on-column injection was used, the calibration plots for the seven compounds fell on the same line (R = 0.9995), indicating that CIC was possible. However, when splitless injection was employed, an apparent compound dependence of the AED response was observed due to discrimination at the injector. The now rate dependence of AED response was demonstrated through studies performed with on-column injection and constant now rates of 1.0, 2.8, and 5.0 mL/min. All three conditions produce compound-independent response, yet the average ERFs varied with the different now rates. When a constant head pressure of 30 psi was used, the ERFs for the seven compounds became more variable due to the change in now rate during a temperature-programmed chromatographic experiment. Thus, the experimental parameters of injection mode and column now rate must be considered in order to prevent apparent compound dependence of AED response.