D-4The detector uses a stable low-voltage DC current to pulse discharge in helium gas as an ionization source, and the tail blown discharge helium gas is excited into metastable helium gas as it flows through the discharge area. The target sample is carried into the detector by a carrier gas after being eluted from the chromatographic column, and the sample molecules or atoms are collisional ionized by metastable helium molecules to generate electrons. The emitted electrons are captured by the collection electrode under the action of a bias electric field, forming a voltage signal. This signal, after amplification, becomes the chromatographic peak of the sample.

In electronic capture mode,PDDTo select detectors for monitoring high electron affinity compounds such as Freon, chlorine containing insecticides, and other halogen compounds. For this type of compound, the detection limit is the lowest（MDQ）do“femtogram”（10^-5）Or Pike（10^-12）Grade.PDDCompared to conventional radiationECDThe sensitivity and response characteristics are similar, and can reach up to400℃Operate at the specified temperature. Working in this mode,HeandCH₄It is introduced in reverse flow from the column outlet.

In helium photoionization mode,PDDFor a universal, non-destructive, high-sensitivity detector. Both inorganic and organic compounds exhibit linearity over a wide rangefixedThe reaction of gas is positively charged（Stable current increases）Detection limitMDQas low asppbGrade.

Under helium photoionization modePDDAn excellent alternative product for flame ionization detectors in petrochemical or refinery environments, but it has issues with the use of flames and hydrogen gas. In addition, when helium discharge gas is mixed with appropriate inert gases such as argon, krypton, or xenon（Determined by the expected deadline）When mixed,PDDIt can be used as a special photoionization detector for selective detection of aliphatic compounds, aromatic compounds, amines, and other substances.

D4The detector is essentially a highly sensitive non-destructive detector（0.01-0.1%Ionization). The linear range of the detector's response to organic matter is as high as10⁵， The detection limit of Zui is as low as10^-12gHigh response to specific gases (increased stagnation), with minimal detection concentrationppbv.

D4The detector is a universal detector, except for neon gas (ionization energy)21.6eV）All substances outside have a response. Due to the near metastable ionization energy of neon gasHe*The ionization energy of atoms（19.8eV）But much larger than diatomic heliumHe₂The photon energy in the spectrum and the ionization efficiency of neon are relatively low, so the detector response is very limited.

Mixing some other gases into helium, such as adding argon when detecting organic substances, adding krypton when detecting unsaturated components, adding xenon when detecting polycyclic aromatic hydrocarbons, etc,D4The detector can selectively operate in the mode of the photoionization detector.

PDD D-4type—Helium photoionization

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The most optimal detector for trace analysis in hydrogen photoionization mode

The detector is specifically designed for 110VACItem number 230VACItem number