PLIS Operation

The operation of PLIS is based on a specific sample volume that is moved through seals from the sample stream (load position) to the inject position. This movement is controlled by a timed event resident in the gc time table.

PLIS has a Stem that is attached to a pneumatic piston and this Stem runs from the top of PLIS through the PLIS body and exits on the bottom side of the lower seal just above the injection port. When 90 psi air pressure is applied to the bottom side of the pneumatic piston, the piston moves up and moves the Stem groove to the load position. In the load position, the Stem groove is positioned in the sample stream and right in the middle of the sample chamber. Sample comes in on one side of the sample chamber and exits the opposite side. When fresh sample has purged the sample chamber of the previous sample, the flow is stopped with a plug valve on the outlet side of the sample chamber.

The sample in the sample chamber is pressurized up to the sample cylinder pressure so as to ensure the sample is in single liquid phase. At this point, the gc Start button is pressed which activates a solenoid and applies 90 psi air pressure to the top side of the pneumatic piston. This drives the piston down and moves the sample/Stem in the Stem groove into the vapourizer adapter which is secured to the gc injection port with the big black nut. Carrier gas enters PLIS at the small lower 1/16" brass union and flushes the vapourized sample from the Stem groove into the injection port liner and then into the column.

The vapourizer adapter derives its heat from the injection port it is attached to. In the case of HPLIS the Stem groove volume is heated to approximately 450C for about 1.25 seconds. The Stem is left in the inject position for 20 seconds and then automatically retracted into the load position.

After the analysis is complete, the cycle can be repeated. This makes PLIS very adaptable to On-Line applications.