An improved interface for universal acoustic flame detection in modified supercritical fluid chromatography

A novel method of interfacing the acoustic flame detector (AFD) with modified supercritical fluid chromatography (SFC) is presented. By applying resistive heating directly to the burner region between the restrictor outlet and the acoustic flame, infrequent severe noise, baseline drifting, and peak deformations that can occasionally be observed with the AFD are eliminated. For example, by increasing the interface temperature only a few hundred degrees Celsius, such sporadic noise in the detector can be reduced nearly ten-fold resulting in smooth stable operation of the AFD. Further, for various levels of methanol modified supercritical carbon dioxide mobile phase examined, the interface was observed to reduce detector noise in each to a common minimal range near 10-25 Hz when an appropriate temperature was achieved. The method is simply assembled, inexpensive to construct, and robust in its daily operation. Overall, the heated interface developed and presented facilitates reliable AFD operation in modified SFC, and supports further exploration and implementation of this sensor as an alternative universal detector in separations requiring an organic cosolvent in the mobile phase.