Nitrogen thermionic detector

One of the major advantages of SFC is its compatibility with both GC and HPLC detectors. GC flame detectors, such as the flame ionization detector (FID) [11,12], nitrogen thermionic detector [12,13], and flame photometric detector [14] have all been interfaced with SFC systems using a capillary restrictor which, while maintaining supercritical conditions in the column, also effectively decompresses the fluid to ambient pressure just before it enters the flame tip [10,15]. HPLC detectors such as ultraviolet and fluorescence detectors are employed when pure organic mobile phases or modified mobile phases are used. With these detectors, analytes are detected spectroscopically in a flow-through cell prior to decompression [16]. 

Among the various detectors specific for nitrogen, the NPD (Nitrogen Phosphorus Thermionic Detector) we will consider, is based on the following concept the eluted components enter a conventional FID burner whose air and hydrogen flows are controlled to eliminate the response for hydrocarbons. 

Other Detectors Two additional detectors are similar in design to a flame ionization detector. In the flame photometric detector optical emission from phosphorus and sulfur provides a detector selective for compounds containing these elements. The thermionic detector responds to compounds containing nitrogen or phosphorus. 

SPME has been utilized for deterrnination of pollutants in aqueous solution by the adsorption of analyte onto stationary-phase coated fused-siUca fibers, followed by thermal desorption in the injection system of a capillary gas chromatograph (34). EuU automation can be achieved using an autosampler. Eiber coated with 7- and 100-p.m film thickness and a nitrogen—phosphoms flame thermionic detector were used to evaluate the adsorption and desorption of four j -triazines. The gc peaks resulting from desorption of fibers were shown to be comparable to those obtained using manual injection. 

The alkah flame-ionisation detector (AFID), sometimes called a thermionic (TID) or nitrogen—phosphoms detector (NPD), has as its basis the fact that a phosphoms- or nitrogen-containing organic material, when placed ia contact with an alkaU salt above a flame, forms ions ia excess of thermal ionic formation, which can then be detected as a current. Such a detector at the end of a column then reports on the elution of these compounds. The mechanism of the process is not clearly understood, but the enhanced current makes this type of detector popular for trace analysis of materials such as phosphoms-containing pesticides. 

EC = electrical conductivity detector ECD = electron capture detector FPD = flame photometric detector GC = gas chromatography HPLC = high performance liquid chromatography NPD = nitrogen phosphorus detector TID = thermionic detector UV = ultraviolet spectroscopy... 

Gas chromatograph fitted with a thermionic nitrogen-specific detector Gas chromatograph fitted with a quadrupole mass-selective detector... 

NPD nitrogen-phosphorus detector (also known as a thermionic detector)... 

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). 

Carlsson H, Robertsson, G, Golmsjo. 2001. Response mechanisms of thermionic detectors with enhanced nitrogen selectivity. Anal Ghem 73 5698. 

MS, Mass spectrometry El, electron impact Cl, chemical ionization MID, multiple ion detection PICI, positive-ion chemical ionization NICI, negative-ion chemical ionization SIM, selected ion nmonitoring TSP, thermospray PPINICI, pulsed positive ion-negative ion chemical ionization ECD, electron-capture detector NPD, nitrogen/phosphorous detector NSTD, nitrogen-selective thermionic detector FT-IR, Fourier transform infrared spectrometry. 

Gas chromatographic methods have been successfully used for the determination of penicillin molecules bearing neutral side-chains in milk and tissues (95, 97), but cannot be used for amphoteric -lactams. Gas chromatography of penicillin residues is further complicated by the necessity for derivatization with diazomethane. This derivatization step is particularly important because it not only leads to formation of the volatile penicillin methyl esters but also improves their chromatographic properties (thermal stability and decreased polarity). Using a fused-silica capillary column in connection with a thermionic nitrogen-selective detector, excellent separation and sensitivity figures were obtained. 

However, by no means are microbore HPLC columns nonoptimal when sample volumes are limited. Because of the substantially reduced mobile-phase volumes necessary to carry out a given separation, microbore columns are more easily interfaced to many useful detection systems, for example, electron-capture detectors, nitrogen-specific thermionic detectors, and mass spectrometers. 

Nitrogen-phosphorus detector (NPD), thermionic detector, alkali flame ionization detector... 

G. Verga, High resolution gas chromatographic determination of nitrogen and phosphorus compounds in complex organic mixtures by tunable selective thermionic detector, J. Chromatogr., 279 657-665 (1983). 

The most popular thermionic detector (TID) is the nitrogen-phosphorus detector (NPD). The NPD is specific for compounds containing nitrogen or phosphorus. The detector uses a thermionic emission source in the form of a bead or cylinder composed of a ceramic material impregnated with an alkyl-metal. The sample impinges on the electrically heated and now molten potassium and rubidium metal salts of the active element. Samples which contain N or P are ionized and the resulting current measured. In this mode, the detector is usually operated at 600-800°C with hydrogen flows about 10 times less than those used for flame-ionization detection (FID). 

The alkali flame-ionization detector, sometimes called an NP or nitrogen-phosphorus detector, contains a thermionic source, such as an alkali-metal salt or a glass element containing rubidium or other metal, that results in the efficient ionization of organic nitrogen and phosphorus compounds. It is a selective detector that shows little response to hydrocarbons. 

The nitrogen phosphorus detector (NPD) (sometimes called the thermionic detector) is another sensitive, but, in this case, a specific detector, that is based on the FID. Physically the sensor appears to be similar to the FID but, in fact, operates on an entirely different principle. A diagram of an NPD detector is shown in figure 9. 

Ives and Guiflfrida ° investigated the applicability of the potassium chloride thermionic detector and the flame ionization detector to the determination of organoarsenic compounds in the presence of organophosphorus and nitrogen-containing compounds. 

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