Chapter 5 65
Operation
3. Set the detector temperature to 250°C. Higher temperatures can be used for
some applications if needed, resulting in a small decrease in sensitivity.
4. Set the combustor gas composition to the optimum H
2
-rich mixture.
5. Set the fine adjust needle valve so that the needle valve is half a turn counter-
clockwise from the point in which the PFPD goes out of tick-tock.
Optimizing for Selectivity
Increasing selectivity for a specific heteroatom can greatly simplify a chromato-
graphic analysis. WinPulse allows the operator to specify gate settings that mini-
mize or eliminate interferences from other analytes (heteroatoms), thus increasing
selectivity for the analyte of interest. Selectivity for analytes with overlapping
chemiluminescence lifetimes can also be enhanced through the use of the dual gate
capability of the software (see Appendix C for detailed discussion). The dual gate
capacity is particularly useful for maximizing sulfur to carbon, phosphorus to
carbon, sulfur to phosphorus, and phosphorus to sulfur selectivity. Figure 5.7
shows possible gate settings for selecting phosphorus and sulfur.
Figure 5.7. C
2
*, OH*, CH*, Phosphorus, and Sulfur Emissions With Gate
Settings for Phosphorus and Sulfur (Note: Phosphorus emission
was obtained using 400 V PMT voltage, and sulfur emission was
obtained using 600 V PMT voltage.)
Phosphorus Gate
Sulfur Gate
Phosphorus
Sulfur
C
2
*, OH*, CH*
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