Chapter 5 69
Operation
Testing the PFPD Performance
The performance of the PFPD should be tested only after it has been optimized for
the desired detectivity and selectivity. This presumes that suitable filters have been
installed, the PMT voltage has been set correctly for detecting the analyte, the H
2
to Air 1 flow ratio and integration gate settings have been optimized, and the
correct detection mode has been specified and selected in the WinPulse software.
The following additional measures are necessary for the correct operation of the
PFPD.
1. Configure the data integration system to display a detector baseline with
sufficient resolution to measure the noise of the PFPD. Collect data for a time
that is sufficient to accurately measure the detector noise and peak-to-peak
noise level (see Appendix D).
2. Prepare a standard test solution containing a hydrocarbon, a compound
containing sulfur, and a compound containing phosphorus. Set the relative
concentrations of hydrocarbon, sulfur, and phosphorus in the standard to an
appropriate level(s) for the specific test to be done. If the PFPD and the PMT
have been configured for the sulfur mode, sulfur sensitivity can be tested
using a standard mix containing sulfur (1 ng S/µL), high levels of hydrocar-
bon (100 ng C/µL), and phosphorus (1 ng P/µL). If the configuration is for the
phosphorus mode, a standard mix containing 100 pg P/µL, 10 ng C/µL, and
10 ng S/µL should be used.
3. Inject the standard test solution into the GC injector and simultaneously start
the data integration system. Note the amount of sample injected into the
column and calculate the amount of sulfur and phosphorus for each analyte in
the sample.
4. Ensure that the range and attenuation parameters are set to provide sufficient
noise resolution (see Appendix D). The PMT voltage may also require some
adjustment (default is 600 V) so that the output signal does not exceed the
PFPD’s signal handling capacity. Alternatively, if the output signal is low, the
PMT voltage can be increased to increase the signal. See step 14 of “Starting
the PFPD System” in this chapter for information on optimizing the PMT
voltage.
5. Monitor the chemiluminescence emission in WinPulse to ensure that the
emission does not exceed the maximum signal handling capacity of the
electronics of the PFPD (i.e., emission peak remains below 50,000 counts in
WinPulse). If this does occur, reduce the sample concentration or reduce the
range setting in WinPulse, and rerun the test. The upper limit of 65,000 counts
is observed only if all the dwell times under the gate are saturated. Normally,
saturation begins when only a portion of the signal under the gate is saturated.
This will produce a partially saturated signal at lower than 50,000 counts.
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