Nitrogen-selective thermionic

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. 

An increase of sensitivity with some GC detectors can largely be attributed to their selective response. As shown by Adams et al. [487], a substantial response enhancement is realized while using the nitrogen-selective thermionic detector. The availability of various fluorine-containing derivatives is highly beneficial in work with the electron capture detector as well as the high-sensitivity mass-spectral measurements. For example, Petersen and Vouros [504] have estimated the detection limit for heptafluorobutyryl methyl esters of the thyroid hormones to be around 500 fg-... 

Besides the universal FID-detector, the selective electron capture (ECD), nitrogen-selective thermionic (NPD) and flame photometric (FPD) detectors have been used for the measurement of PAH, and nitrogen or sulfur containing heterocyclic analogs respectively (Wakeham (26), Willey et al. (29)). 

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

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. 

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). 

A selective thermionic specific detector (TSD) was developed by Albert (107) but it is more commonly referred to as a nitrogen-phosphorous detector (NPD). It is basically an alkali FID. Figure 13.36 compares the TSD and the microcoulometric detector. More resolution is obtained through the TSD with elimination of the mixing in the transfer line, reactor tube, and titration cell of the... 

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. 

The most common selective detectors in use generally respond to the presence of a characteristic element or group in the eluted compound. This is well illustrated by the thermionic ionisation detector (TID) which is essentially a flame ionisation detector giving a selective response to phosphorus- and/or nitrogen-containing compounds. Typically the TID contains an electrically heated rubidium silicate bead situated a few millimetres above the detector jet tip and below the collector electrode. The temperature of the bead is maintained... 

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

PDMS = polydimethylsiloxane. PA = polyacrylate. CW = Carbowax. DVB = divinylbenzene. FID = flame ionization detection. NPD = nitrogen-phosphorus detection. TSD = thermionic-specific detection. LOQ = limit of quantitation. LOD = limit of detection. TCA = trichloroacetic acid. PICI-MS = positive ion chemical mass spectrometry. SIM = selected ion monitoring. 

For amines absorption in an acid solution, or preferably adsorption onto an acid ion exchange column (acidified divinylbenzene-styrenesulfonic acid copolymer) is used. 10-50 1 of ambient air is sent over a wet 100 mmx 3 mm I.D. column the ion exchange polymer is put into a vial, made alkaline and the water solution is analysed on packed Carbowax-KOH GC-column with a thermionic selective detector (TSD), which is specific for nitrogen- and phosphorus-compounds. Trimethylamine is detected easily at 1 ppb. 

The thermionic or alkali flame ionization detector (FID) is a variant of the FID that has enhanced sensitivity to nitrogen (N) and phosphorous (P) containing compounds. It is essentially a hydrogen flame around a pellet of an alkali metal salt with an electric potential across the flame. Organic compounds in the air are drawn into the flame and ionized. The alkali metal enhances the response to N and P-containing compounds and, since many chemical agents contain N and P, it is selective for their detection. This detector is rarely used without prior separation by GC. 

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. 

Myers and Smith [133] showed that in identifying biological substances by Py-GC use should be made of a rubidium thermionic detector selective towards nitrogen-containing pyrolysis products of proteins and nucleic acids, because when a conventional flame-ionization detector is employed most characteristic structures are masked by the pyrolysis products of carbohydrates and lipids. 

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