Optimizing Injection Port Conditions for the Analysis of Semivolatile Organics

Split and splitless injections introduce the sample into a heated injection port as a liquid where it is rapidly and completely vaporized along with the analytes in the sample. The vaporized sample condenses at the head of the column along with the solvent. In split injection mode only a small amount of the vaporized sample is transferred onto the head of the column, the remainder of the sample is removed via the split vent line. The use of split injection minimizes analyte breakdown since compounds spend less time in the hot injection port, however, loss in sensitivity is observed since much of the sample exists the split vent line. In splitless injection the split valve is closed long enough to allow most of the vaporized sample and solvent in the injection port liner to be transferred to the analytical column which can take anywhere between 30 and 90 seconds. Since the split vent valve is closed the sample transfer moves at the speed of the column flow typically in the 1-2 ml/min range. Solvent focusing in splitless mode requires an oven temperature 20°C below the boiling point of the sample solvent allowing the solvent and the analyte to condense and wet the stationary phase. One exception is analyte focusing which can be performed if the difference between the analyte boiling point and solvent boiling point 150°C (2). There are many analyses that use solvents and compounds where solvent focusing and analyte focusing are not possible. This work will demonstrate optimized conditions for a broad range of semivolatile compounds using methylene chloride as a solvent.