Two positions were possible: In position A (Figures 1-3),
valves V2, V3, and V4 were opened and V5 was closed. Helium
pressure was regulated by PR1. Helium reached the interface
through two lines (the normal gas inlet and the split exit), and
the flow in each path could be controlled by its respective needle
valve (N1 or N2). Helium exited through the ST tubing and the
GC column. In position B (Figure 4), valves V2, V3, and V4 were
closed and V5 was opened. Pressure was regulated using PR2.
Helium reached the interface only by the normal gas inlet of the
PTV injector.
(b) Operation Mode.Initially, the TOTAD interface temperature was stabilized at 80°C and valves were positioned as in
Figure 1. The helium flows were 1800 mL/min (regulated by N2)
and 900 mL/min (regulated by N1). A 50µL aliquot of the sample
was injected into the LC system. Initially the eluate coming from
the HPLC system was sent to waste. When the fraction of interest
was in the TT tube, the pump flow was changed from 1 to 0.1
mL/min.