Gas Chromatography Systems

Analysts interested in quantifying volatile organic compounds like disinfection byproducts in liquid samples should consider using the gas chromatography system. There are two gas chromatography (GC) systems in the laboratory. The Agilent 6890 Series Gas Chromatography System uses an electron capture detector (ECD) to quantify analytes, and the Agilent 7890A Series Gas Chromatography System uses either and ECD or a flame ionization detector (FID) for analytical quantification. Each gas chromatography system works by heating and volatilizing liquid samples. The volatilized sample is carried through the system into a stationary phase column with an inert gas. The stationary phase separates analytes based on their size and/or polarity. After exiting the stationary phase column the sample enters either an ECD or FID.The ECD contains radioative nickel that emits beta particles, and electrodes on each side of the detector measure the current.  A constant flow of nitrogen gas enters the ECD, and the beta particles ionize the gas releasing a cloud of electrons. A baseline current from the nitrogen electrons is determined by the detector. When compounds in the sample containing electronegative groups (halogens) enter the ECD, electrons are “captured” or bound by the sample. The software creates peaks based on the current reduction/change created by each analyte passing through the detector. The FID contains a positive and negative electrode. The negative electrode above the ionizing flame attracts the negatively charged hydrocarbons to a collector plate. When ions hit the collector plate, a current is induced that is proportional to the concentration of hydrocarbons.The software creates peaks based on the current of each analyte. Analyte concentrations are determined by comparing sample results to a set of standards analyzed during the analytical run for both ECD's and FID's. Current methods for both GC's are for quantifying disinfection byproducts in wastewater and drinking water. The Agilent 6890 Series Gas Chromatography System is setup for haloacetic acids (HAA's) analysis, and the Agilent 7890A Series Gas Chromatography System is setup for trihalomethane (THM's) and haloacetonitrile (HAN's) analyses. If researchers are interested in other organic compounds, they may develop methods for those analytes.