Helium ionisation detector

HID Helium ionisation detector HT-ToFMS Hadamard transform time-of-flight... 

Ar. Ns This detector employs a source of P radiation (usually 6JNi-cf. helium ionisation detector). The 1000-10.000 velocities of the high energy electrons are reduced to thermal velocities by coOisioo with atoms of inert gas with which the detector chamber is purged. When a sample of a gas with a greater election affinity than the inert gas is introduced into the ccC some of the electrons are captured and form negative ioas. 

PDHID Pulsed discharge helium ionisation detector... 

Plasmas compare favourably with both the chemical combustion flame and the electrothermal atomiser with respect to the efficiency of the excitation of elements. The higher temperatures obtained in the plasma result in increased sensitivity, and a large number of elements can be efficiently determined. Common plasma sources are essentially He MIP, Ar MIP and Ar ICP. Helium has a much higher ionisation potential than argon (24.5 eV vs. 15.8 eV), and thus is a more efficient ionisation source for many nonmetals, thereby resulting in improved sensitivity. Both ICPs and He MIPs are utilised as emission detectors for GC. Plasma-source mass spectrometry offers selective detection with excellent sensitivity. When coupled to chromatographic techniques such as GC, SFC or HPLC, it provides a method for elemental speciation. Plasma-source detection in GC is dominated by GC-MIP-AES... 

In both systems the flow of helium carrier gas through the columns was 0.7-0.8 ml min-1, with a septum purge of 0.5 ml min-1 and a split valve flow of 4-4.5 ml min-1. The injection ports were maintained at 260°C and the detector ovens at 240° C. The detector employed was either a flame ionisation or a nitrogen-specific NPD-40 thermionic detector (Erba Science (UK) Ltd) and the output was recorded on a HP 3390 integrator (Hewlett Packard Ltd, Wokingham, UK). 

Sporek, K. F. New type of argon ionisation, helium electron capture detector for gas chromatography. US-At. Energy Comm. Rpt. Conf-650, 809 (1966). — Anal. Abstr. 14, 3715 (1967). 

Bourke, P. J., Dawson, R. W. The sensitivity to oxygen of an ionisation detector with helium and neon at the carrier gases. Nature 211, 409 (1966). 

Adlard and Matthews [16] applied the flame photometric sulphur detector to pollution identification. A sample of the oil pollutant was submitted to gas chromatography on a stainless steel column lm><3mm packed with 3% of OV-1 on AW-DMCS Chromosorb G (85-100 mesh). Helium was used as carrier gas (35rnLmin ) and the column temperature was programmed from 60 to 295°C and 5°C per minute. The column effluent was split between a flame ionisation and a flame photometric detector. Adlard and Matthews [16] claim that the origin of oil pollutants can be deduced from the two chromatograms. The method can also be used to measure the degree of weathering of oil samples. 

Ci-C4 mono-, di- and trialkylamines, Onuska [73] adjusted the pH of the sample to between 5 and 8. A lpL aliquot of the filtrate was injected on to a stainless steel column (185cmx2mm id) packed with 28% of Pennwalt 223 and 4% of potassium hydroxide on Gas-Chrom R (80-100 mesh) and maintained at 134°C A dual-flame ionisation detector was used and the carrier gas was helium (flow rate 52.2ml min-1). The detector response was rectilinear between lOng and at least lOOpg of dimethylamine, and the reproducibility was good. The column could be regenerated by increasing the column temperature to greater than 180°C. 

Figure 2.13. Schematic of helium-specific mass spectrometer leak detector H uniform magnetic field N ionisation chamber K ion collector, Sp entrance of ions, S2 exit of ions...

The working principle of a helium-specific mass spectrometer leak detector is as follows [7], The mass spectrometer mainly consists of three parts an ion source, a deflection system and an ion collector. When the atoms pass the ionisation chamber of the detector, they are ionised to become positive ions. When these ions are then accelerated in the ionisation chamber, they obtain sufficient energy and enter into the magnetic field of the detector. These positive ions travel in a specific mbit in the magnetic field. As different ions have specific orbit radii only ions with the same orbit radius as that of the spectrometer can pass a narrow gap, as indicated by K in Figure 2.13, and reach the ion collector K to form an ion stream. 

Gas chromatography has been applied437 to the determination of the low-molecular-weight portion in poly(dimethylsiloxane). Polymers of molecular weight up to 700 in poly(dimethylsiloxane) can be determined on a column packed with OV-1 on Chromosorb W AW-HP with helium as carrier gas and a flame ionisation detector. 

Catalytic activity measurements were carried out with a fixed bed flow reactor. The reactor was a quartz tube. The flow rates were adjusted using Brooks mass flow controller units. The composition of the effluents was analyzed by gas chromatography using a dual CTRl column fi-om Alltech (porapak for CO2, N2O, molecular sieve for O2, N2, CO) with a thermal conductivity detector and a porapak Q column with a flame ionisation detector for hydrocarbons. The mixture was analyzed every 13 minutes. NO and NO2 amounts were measured continuously on-line by means of Rosemount Infi-ared Analyzers. Helium was used as carrier gas as well as diluent gas. 

In this technique, bulk dried samples are heated in an inert helium atmosphere, where upon thermo-vaporization and pyrolysis, hydrocarbons are quantified by flame-ionisation detection. Compounds occurring as free gases and liquids in sediments are separated from those that occur in bound form, or as particulate organic matter by temperature control. The S [-detector signal records free hydrocarbons, which are thermo-vaporizable at 300°C, and the S2-detector signal measures those compounds liberated during programmed pyrolysis from 300 to 550°C. 

Operation showed that it was necessary to install within the main helium circuit an additional device for measuring the accrueing special gaseous impurities, that is hydrocarbons and oil vapor. For this purpose a "flame-ionisation-detector" was provided and proved successfiil. 

Crompton and co-workers [32, 33] have extended the gas chromatographic technique to the determination in polystyrene of styrene and a wide range of other aromatic volatiles in amounts down to the 10 ppm level. In this method a weighed portion of the sample is dissolved in propylene oxide containing a known concentration of pure -undecane as an internal standard. After allowing any insolubles to settle an approximately measured volume of the solution is injected into the chromatographic column which contains 10% Chromosorb 15-20M supported on 60-70 BS Celite. Helium is used as carrier gas and a hydrogen flame ionisation detector is employed. 

Krishen [78] used a dual flame ionisation chromatograph equipped with a 1 mV recorder. Two stainless steel columns each 1.8 m x 13 mm od packed with 10% UCW-98 on 60-80 mesh Diatoport S were employed in the dual operation mode. The initial column oven temperature was 100 °C and after 4 minutes of isothermal operation, the temperature was programmed at a rate of 8 C per minute to a maximum of 330 C. The final temperature was held constant for 8 minutes. The injection block and the detector were maintained at 270 °C. The helium, hydrogen, and air pressures were 0.4 (Flowrator 0.8), 0.09, and 0.2 MPa, respectively. 

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