Chapter 5 67
Operation
Maximizing Phosphorus to Sulfur Selectivity
1. Use an optical filter in the PMT assembly that is optimal for detecting phos-
phorus (see Appendix D). This will minimize the sulfur response. However, if
another filter that allows detection of both phosphorus and sulfur is in place,
the following steps will still increase phosphorus selectivity.
2. Since HPO emission is optimized at a more oxygen-rich flame than sulfur, set
the phosphorus H
2
to Air 1 flow ratio at the phosphorus optimal detection
flow rate.
3. Optimize the PFPD for phosphorus response as described in “Maximizing
Phosphorus Response.” Since phosphorus emits earlier than sulfur, an earlier
gate termination improves the phosphorus to sulfur selectivity. Use a 3-mm
combustor and set the PFPD to 300°C.
4. In addition, it may be desirable to activate the PFPD’s dual gate capability to
enhance selectivity between phosphorus and sulfur without large adjustments
to gate settings for optimal phosphorus detectivity (see Appendix C for further
details).
Maximizing Sulfur to Phosphorus Selectivity
1. Use an optical filter in the PMT assembly that is optimal for detecting sulfur
(see Appendix A). Using a BG-12 filter (Part #282947) greatly reduces any
phosphorus response. However, if another filter that allows detection of both
phosphorus and sulfur is in place, the following steps will still increase sulfur
detection.
2. Set the H
2
to Air 1 flow ratio at the sulfur detection optimal flow rate.
3. Optimize the PFPD for sulfur sensitivity as described in “Maximizing Sulfur
Response.” Since sulfur emits later than phosphorus, increased gate delay
improves the sulfur to phosphorus selectivity. Use a 2-mm combuster and set
the PFPD to 220°C.
4. Since delaying the gate can reduce detectivity, it may be desirable to activate
the PFPD’s dual gate capability to enhance selectivity without large adjust-
ments to gate settings for optimal sulfur detectivity. This enables the operator
to adjust for phosphorus responses within the detectivity-optimized time
domain of Gate A (see Appendix B for further details).
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