Thermionic ionization detector

Figure 3.10 Thermionic ionization detector (Perkin-Elmer),...

The flame ionization detector Is the most popular of the flame-based detectors. Apart from a reduction in sensitivity compared to expectations based on gas chromatographic response factors [138] and incompatibility with the high flow rates of conventional bore columns (4-5 mm I. 0.), the flame ionization detector is every bit as easy to use in SFC as it is in gas chromatography [148,149]. It shows virtually no response to carbon dioxide, nitrous oxide and sulfur hexafluoride mobile phases but is generally incompatible with other mobile phases and mixed mobile phases containing organic modifiers except for water and formic acid, other gas chromatographic detectors that have been used in SFC include the thermionic ionization detector (148,150], ... 

Thermionic ionization Ionization Type Detectors Alkali salt vapors cause P, N. X 23... 

Separation of hydrazine and dimethylhydrazines from environmental samples is by acid extraction when necessary. Air samples are usually collected in a bubbler with acid or on an acid-coated silica gel (NIOSH 1977a, 1977b, 1984). When GC is employed, detection may be by electron capture detector (ECD), FID, nitrogen-specific detector (NSD), thermionic ionization detector (TID), and/or MS as described above (Section 6.1). 

ECD = electron capture detection FID = flame ionization detector GC = gas chromatography MS = mass spectroscopy NSD = nitrogen specific detector TID = thermionic ionization detector... 

Flame-Ionization Detector or Flame-Thermionic Ionization Detector... 

At the temperatures and pressures generally used in gas chromatography the common carrier gases employed behave as perfect insulators. In the absence of conduction by the gas molecules themselves, the increased conductivity due to the presence of very few charged species is easily measured, providing the low sample detection limits characteristic of ionization based detectors [259]. Examples of ionization detectors in current use include the flame ionization detector (FID), thermionic ionization detector (TID), photoionization detector (PID), the electron-capture detector (ECD), and the helium ionization detector (HID). Each detector employs a different method of ion production, but in all cases the quantitative basis of detector operation corresponds to the fluctuations of an ion current in the presence of organic vapors. 

Modem thermionic ionization detectors evolved out of earlier studies of alkali-metal-doped flame ionization detectors [253]. Adding an alkali metal salt to a flame enhanced the response of the detector to compounds containing certain elements, such as N, P, S, B, as well as some metals (e.g. Sb, As, Sn, Pb). In its early versions, however, the detector response was unreliable and critically dependent on experimental parameters. Recent studies involving the continuous introduction of alkali metal salt solutions or aerosols into the flame demonstrated more reliable performance but have not been taken up [268,269]. 

All modem thermionic ionization detectors (TED) employ a solid surface, composed of a ceramic or glass matrix doped with an alkali metal salt in the form of a bead or cylinder, molded onto an electrical heater wire as the thermionic source [254,270,271]. 

The popularity of the BCD can be attributed to the high sensitivity to organohalogen compounds, which include many compounds of environmental interest, including polychlorinated biphenyls and pesticides. It is the least selective of the so-called selective detectors but has the highest sensitivity of any contemporary detector. The NPD or thermionic ionization or emission detector is a modified FID in which a constant supply of an alkali metal salt, such as rubidium chloride, is introduced into the flame. It is a detector of choice for analysis of organophosphorus pesticides and pharmaceuticals. The FPD detects specific luminescent emission originating from various excited state species produced in a flame by sulfur- and phosphorus-containing compounds. 

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