Optimization of chemiluminescent nitrogen detection for packed column supercritical fluid chromatography with methanol-modified CO2

A chemiluminescent nitrogen detector was optimized for packed-column supercritical fluid chromatography. Methanol modifier concentrations of 15% or less, an ozone now of 5.8 mL/min, and a decompressed CO2 now between 240 and 310 mL/min were found to exhibit a maximum sensitivity of 5 ng for sulfamethazine (1 ng of N). The addition of a membrane drier to the ''optimized'' system further decreased the minimum detectable quantity (MDQ) to 0.5 ng (0.1 ng of N). In addition, by using a microbore column (2 mm i.d.) instead of an analytical scale column, the postcolumn decompressed now split could be eliminated, further reducing the MDQ to 0.125 ng of sulfamethazine (0.025 ng of N).