Detector Systems
Flame photometric detector (FPD)
Flame photometric detector (FPD)
Optimizing FPD sensitivity and selectivity
FPD sensitivity and selectivity are affected by several important parameters. These are listed below, with suggested ways to optimize for each application.
A.FPD Flow Rates. FPD flow rates are the most critical for optimizing either sensitivity or selectivity (these do not necessarily have the same optimal conditions). The most critical flow parameter is the hydrogen/air (or hydrogen/oxygen) ratio. Less critical are the auxiliary nitrogen/carrier combined flows.
A suggested way to set near•optimalflows is to begin with recommended flow rates located in the HP 5890 Operating Manual. Then vary each gas until a local maximum is reached. Optimize hydrogen first, then air (or oxygen), and lastly the auxiliary nitrogen flows. This may require a couple of iterations (tries). Adjusting these flows is most easily done by just varying the supply pressure regulator setting. Figure 7•11 plots approximate FPD flows versus supply pressure for all FPD gases.
Note: Take care that adjusting the supply gas pressure does not change some other flow supplied by the same regulator.
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