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 whi ch a single compound is used to quantitate other compounds within a sa mple. Gas chromatography with atomic emission detection (AED) is one t echnique in which CIC can theoretically be applied. Reports are presen t in the literature, however, that both support CIC and indicate depen dence of the AED response on compound structure. In this investigation , the effects of two gas chromatographic parameters (injection mode an d 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 thr ee detection wavelengths (C at 179 nm, H at 486 nm, and N at 174 nm) w ere used in this work to explore CIC with GC-AED, When on-column injec tion was used, the calibration plots for the seven compounds fell on t he 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 injecto r. The now rate dependence of AED response was demonstrated through st udies performed with on-column injection and constant now rates of 1.0 , 2.8, and 5.0 mL/min. All three conditions produce compound-independe nt 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 se ven compounds became more variable due to the change in now rate durin g a temperature-programmed chromatographic experiment. Thus, the exper imental parameters of injection mode and column now rate must be consi dered in order to prevent apparent compound dependence of AED response .