Ionization detector thermal argon

The purpose of the detector is to determine when and how much of a compound has emerged from the column. Although the goal of all detectors is to be as sensitive as possible, many detectors are designed to be selective for certain classes of compounds. Dozens of different types of detectors have been developed, but only a few are used routinely. Those are thermal conductivity (TC), thermionic (N/P), electron capture (ECD), flame photometric (FPD), Hall electroconductivity detector (Hall or ELCD), hydrogen flame ionization detector (FID), argon ionization (AI), photoionization (PID), gas density balance (GDB), and the mass spectrometer. Chemists usually select a detector by the following criteria, listed in priority ... 

The connection to an appropriate detector flame ionization detector, thermal conductivity detector, flame photometric detector, nitrogen phosphorous detector (FID, TCD, FPD, NPD, etc.) is achieved via the four- or six-port valve being operated manually or electronically. The carrier gas (helium, nitrogen, argon, artificial air, etc.) flows via the valve only through the sampling column, at low flow rates (e.g., 25 cm /min) held constant during the experiments. 

Total NMOC. Total non-methane organics (NMOC) as a group (i.e., nonspeciated) are commonly measured by cryotrapping the air sample, e.g., in liquid argon, which does not trap CH4. The contents of the trap can then be thermally desorbed directly into a flame ionization detector (FID) (McElroy et al., 1986). 

The development of the ionization detectors by Lovelock that evolved from the original argon detector culminated in the invention of the electron capture detector [2]. However, the electron capture detector operates on a different principle from that of the argon detector. A low energy 3-ray source is used in the sensor to produce electrons and ions. The first source to be used was tritium absorbed into a silver foil but, due to its relative instability at high temperatures, this was quickly replaced by the far more thermally stable Ni source. 

The type of detector to be employed determines the nature of the carrier gas which may be used. Argon is used with the argon ionization detector. Helium is used with flame-ionization, thermal conductivity, thermionic emission, and cross-section detectors. Hydrogen may be used in thermal conductivity detectors to give maximum sensitivity. Probably the commonest and cheapest carrier gas is nitrogen, which can be used with flame-ionization, electron capture, thermal conductivity, and cross-section detectors. Argon-methane mixtures may be used with electron capture detectors. 

Thermal conductivity detectors have been discussed in detail by Ingraham (107), who also described their application to thermodynamic and kinetic measurements. In this same book. Lodding (4) describes the gas density detector as well as several ionization detectors, such as the argon ionization detector, the electron capture detector, and others. Flame ionization detectors have been described in detail by Brody and Chaney (108) and Johnson (109). The latter also discusses other types of detectors. Malone and McFad-den (110) described many different types of special identification detectors, such as those listed in Table 8.3. Numerous texts on gas chromatography describe a wide variety of detectors, many of them useful in EGD and EGA. 

A Perkin-Elmer Auto-system gas chromatograph (GC), which houses a 30-m, 0.53-mm (ID) fused silica capillary column (Carboxen 1010 Plot, Supelco), was used to analyze the gaseous samples from the liquefaction process. Temperature programmed step heating was performed as follows 40°C for 1.7 min, increase by 40°C/min imtil 220°C, and leave at 220°C for 1.8 min. Argon was the carrier gas at a flow rate of 20 ml/min. Two detectors were used for gas analysis a flame ionization detector (FID) for carbon-bearing species and a thermal conductivity detector (TCD) for H2. Uncertainties in reported concentrations are estimated to be within 5% [8]. 

For the thermal conductivity detector, helium is the most popular. While hydrogen is commonly used in some parts of the world (where helium is very expensive), it is not recommended because of the potential for fire and explosions. With the flame ionization detector, either nitrogen or helium may be used. Nitrogen provides slightly more sensitivity, but a slower analysis than helium. For the electron capture detector, very dry, oxygen-free nitrogen, or a mixture of argon with 5% methane is recommended. 

These workers used a prototype spectraspan III dc plasma echelle spectrometer, 510-512, (Spectrametrics Inc., Andover, Mais.). They adapted a Varian 1200 gas chromatograph for on-column injection onto a 6 ft X g in. o.d. stainless steel column packed with 2% Dexsil 300 GC on Chromosorb 750, 100 120 mesh (Johns-Manvilie Corp., Denver, Col.). Column effluent was split by an approximately 1 1 ratio between the flame ionization detector of the gas chromatograph and a heated, thermal, and electrically insulated 1/16-in. o.d. stainless steel transfer line to the dc plasma. Preheated argon sheath gas was required in addition to the argon supplied to sustain the plasma, in order to optimize spectral sensitivity. The column and injection port temperature were set at 130 and 160 C, respectively, and the interface temperature was 170 0. Helium carrier gas flow rate was 25 ml/min. 

Carrier Gas— Hdium or hydrogen for use on thermal conductivity detector unit or nitrogen, helitun, or argon for use on ionization detector units. 

Carrier Gas—A carrier gas appropriate to the type of detector used should be employed. Helium or hydrogen may be used with thermal conductivity detectors. Nitrogen, helium, or argon may be used with ionization detectors. The minimum purity of any carrier should be 99.95 mol %. 

Carrier (ray—Helium (Warning—See Note 3.) or hydrogen (Warning—See Note 4) for use with thermal conductivity detectors or nitrogen, (Warning—See Note 3.) helium, or argon for use with flame ionization detectors. 

Detectors are either concentration sensitive or mass flow sensitive. The signal from a concentration-sensitive detector is related to the concentration of the solute in the detector and is decreased by dilution with a makeup gas. The sample is usually not destroyed. Thermal conductivity, argon-ionization, and electron capture detectors are concentration sensitive. In mass-flow-sensitive detectors, the signal is related to the rate at which solute molecules enter the detector and is not affected by the makeup gas. These detectors usually destroy the sample, such as flame ionization and flame thermionic detectors. Sometimes two-column GC is used to increase resolution, by taking cuts of eluents from an initial column and directing them to a second column for secondary separation. The first detector must be nondestructive or else the eludnt split prior to detection, with a portion going to the second column. 

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