Chapter 5 59
Operation
4. Install the end of the GC column into the other inlet of the permeation cham-
ber using a reverse ferrule nut and ferrule.
5. Slowly increase the oven temperature until sufficient chemiluminescence
signal is observed in WinPulse. Do not set the temperature so high that signal
amplitude begins to approach the maximum signal handling capacity of the
PFPD (i.e., the signal should be well below 65,000 counts in WinPulse).
6. If a chemiluminescence signal is not obtained within the recommended
temperature range for the permeation tube, check for gas leaks at the column
connections to the permeation device, injector and detector, and along the
PFPD assembly. If the short section of column was attached to the detector,
ensure that the column has not been inserted too far into the detector body
(i.e., more than 1.5 mm above the top of the combustor support).
7. After a chemiluminescence signal from the diffusion analyte becomes detect-
able in WinPulse, allow 10–15 minutes for the temperature of the oven and
permeation tube to stabilize before optimizing the PFPD’s response. If the
PFPD or GC oven temperatures are changed, the permeation device should
also be allowed to stabilize for 10–15 minutes after the new temperature has
been reached.
8. After the GC oven temperature has stabilized, check the Current Data box on
the main WinPulse screen to ensure that the PFPD is pulsing at about three to
four times per second. When the pulse rate begins to exceed about 4.5 Hz, the
display on the WinPulse screen will turn red indicating that the data generat-
ing frequency has exceeded the PFPD’s data handling capacity. The pulse rate
can be easily changed by adjusting the Air 2 flow rate.
9. For sulfur, the initial H
2
:Air 1 flow ratio should be about 1.15:1.0; for phos-
phorus, the ratio should be about 0.9:1.0. The flow ratio should have been
achieved by the initial H
2
and Air 1 flow settings made prior to starting the
PFPD. If this ratio is correct and a sulfur diffusion tube has been connected, a
chemiluminescence signal similar to that shown in Figure 5.2 should be
observed. In particular, note the start and end of the OH*, C
2
*, and CH*
emission and the start, end, and amplitude of the sulfur emission. If a phos-
phorus diffusion source is used, the start and end of the chemiluminescence
emission will occur considerably sooner than shown in Figure 5.2.
10. If the H
2
to Air 1 ratio is either significantly too high or too low, the sulfur
emission lifetime will rapidly decrease (become shorter in time and ampli-
tude). Adjust the H
2
flow rate to maximize the lifetime and amplitude of the
sulfur emission profile. Maximizing the delayed emission of sulfur is the
primary objective of adjusting the gas flows. Note that as the H
2
to Air 1 ratio
is increased, the amplitude of the OH*, C
2
*, and CH* emission (second peak
from the left) decreases.
It is better to be on the Air 1-rich side of the optimum than on the H
2
-rich side
for better stability and reduced quenching.
11. Check that the detector pulse rate is still in the 3–4 Hz range. Adjust Air 2 if it
is outside of this range.
!
CAUTION: Do
not subject the
permeation
device to more
than 60°C
temperatures.
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