NITROGEN/PHOSPHOROUS DETECTOR ( NPD )
NPD/DELCD COMBINATION DETECTOR

The Nitrogen Phosphorus Detector ( NPD ) is similar in design to the FID, except that the hydrogen flow rate is reduced to about 3 ml/min and an electrically heated thermionic bead ( NPD bead ) is positioned near the jet orifice. Nitrogen or phosphorus containing molecules exiting the column collide with the hot bead and undergo a catalytic surface chemistry reaction. The ions created in this reaction are attracted to a collector electrode, amplified, and output to the data system.

The NPD is commonly used to detect pesticides, herbicides, and drugs of abuse because it responds to N-P compounds about 100,000 stronger than normal hydrocarbons, making it very selective. When combined with the chlorine/bromine selective DELCD, the combined detector is ideal for pesticide screening since the NPD selectively detects the organo-phosphate pesticides, while the DELCD detects only the chlorinated species. Together all pesticides can be detected, and the relative responses can help to identify pesticide species.

The SRI ceramic NPD bead is exceptionally rugged and long-lasting, offering service from 100-1000 hours depending on operating conditions.

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