NPD - Nitrogen/Phosphorus Detector
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DETECTORS Nitrogen/Phophorus Detector - NPD The SRI Nitrogen-Phosphorus Detector (NPD) has a linear response selective to organic compounds containing nitrogen and/or phosphorus. The NPD also responds to normal hydrocarbons, but approximately 100,000 times less than nitrogen or phosphorus containing compounds. Due to its selectivity and sensitivity, the NPD is often used to detect pesticides, herbicides, drugs of abuse, and other trace compounds. Nitrogen is the carrier gas of choice for the NPD detector, but helium is often used, especially when other detectors are installed on the same GC as the NPD. The NPD is similar in design to the FID, except it uses a The NPD is similar to the FID in design. thermionic NPD bead to generate ions in a hydrogen and air plasma. Like the FID, the NPD uses a stainless steel jet to deliver sample-laden carrier gas and hydrogen gas to the detector, and a positively charged collector electrode that also serves as the detector exhaust. The NPD bead is positioned between the jet and the collector electrode. The tip of the NPD jet is slightly different from that of the FID jet. The NPD may be combined with the DELCD for pesticide screening. The NPD detects Organo-phosphate pesticides and the DELCD detects the chlorinated pesticides.

DETECTORS Nitrogen/Phophorus Detector - NPD Theory of Operation NPD jet Detector viewport cap nut Positively charged collector electrode Area where ionization takes place NPD bead (the tip is inside the ionization area of the detector body) Electrical lead to amplifier Electrical leads provide current to the NPD bead to maintain the hydrogen-air plasma Inside the NPD detector body, an electrically heated thermionic bead (NPD bead) is positioned between the jet orifice and the collector electrode. The bead is coated with an alkali metal which promotes the ionization of compounds that contain...

Expected Performance The following chromatograms are from an SRI GC equipped with NPD, DELCD and FID detectors. Since the NPD is not the only detector, helium carrier gas was used instead of nitrogen. The first chromatogram shows a separation of200ppm Organophosphorus pesticide standard, Mix 8270. The second chromatogram shows both the NPD and DELCD responses to a mixture of 100ppm Mix 8270 and 100ppm Organochlorine pesticide standard, Mix 8081. Other than the sample and length of time, the analytical parameters were the same for both runs. The NPD has a much smaller response to the...

Expected Performance This chromatogram shows the NPD response to an isothermal analysis of a 10ppm malathion sample. Compare the NPD response to the 100% hydrocarbon solvent with the response to the 10ppm malathion sample. Acqumlion Help Results: Component Solvent Malathion Sample: 1 pL 10ppm malathion Column: 15-meter MXT-5 Carrier: helium at 10mL/min NPD gain: HIGH NPD temperature: 250oC NPD bead current: -380 Injector temperature: 200oC Temperature program: Initial Hold Ramp Final 200oC 100.00 0.00 200oC The following chromatogram shows an NPD noise run using helium carrier gas and an...

DETECTORS Nitrogen/Phophorus Detector - NPD Note: Most SRI NPDs are installed on a GC with one or more other detectors. Therefore, SRI tests its NPD detectors with helium carrier gas. General Operating Procedures NPD Detector 1. Set the NPD amplifier gain switch to HIGH for most applications. 2. The approximate pressures required for the correct hydrogen and air flows are labeled on the right-hand side of the GC chassis under “GAS FLOW RATES.” Set the hydrogen flow to 3mL/minute and the air flow to 100mL/minute using the trimpots on the top edge of the GC’s front control panel. To adjust a...