Ionization detection systems

Fia. 15. Separation of tryptamine-related indole bases. The compounds are N,N-dimethyltiyptamine (DMT), eneamine (acetone condensation product) from tiypt-amine (TRYPT-SB), 7-trimethylsilyloxy-JV,iV-dimethyltryptamine (7-OH-DMT-TMSi), 4-trimethylsilyloxy-iV,i r-dimethyltryptaniine (4-OH-DMT-TMSi), 5-tri-methylsilyloxy-iV,JV-dimethyltryptamine (5-OH-DMT-TMSi), 6-trimethylsUyloxy-JV, iV -dimethyltryptamine (6-OH-DMT-TMSi), and the eneamine (acetone condensation product) from 5-trimethylsilyloxytryptamine (5-OH-TRYPT-TMSi-SB). Conditions 7% F-60, 1% EGSS-Z, on 100-120-mesh Gas Chrom P, 182 C, 18 psi argon ionization detection system. Reproduced from Homing et al. (H15), with permission. 

A flame ionization detection system optimized for use with packed columns and capable of the following ... 

In order to increase the sensitivity of TLC and also to allow the rapid quantification of a variety of separated lipids, efforts have been made to apply flame ionization detection systems. The most successful method involves separating small amounts of lipid mixtures on quartz rods to which a thin silica gel has been fused. After separating the mixtures, the rods are... 

For IBSCA analysis, standard HV or, better, UHV-equipment with turbomolecular pump and a residual gas pressure of less than 10 Pa is necessary. As is apparent from Fig. 4.46, the optical detection system, which consists of transfer optics, a spectrometer, and a lateral-sensitive detector, is often combined with a quadrupole mass spectrometer for analysis of secondary sputtered particles (ions or post-ionized neutrals). 

Figure 12.7 Cliromatograms of a polycarbonate sample (a) microcolumn SEC ti ace (b) capillary GC ti ace of inti oduced fractions. SEC conditions fused-silica (30 cm X 250 mm i.d.) packed with PL-GEL (50 A pore size, 5 mm particle diameter) eluent, THE at aElow rate of 2.0ml/min injection size, 200 NL UV detection at 254 nm x represents the polymer additive fraction ti ansfeired to EC system (ca. 6 p-L). GC conditions DB-1 column (15m X 0.25 mm i.d., 0.25 pm film thickness) deactivated fused-silica uncoated inlet (5 m X 0.32 mm i.d.) temperature program, 100 °C for 8 min, rising to 350 °C at a rate of 12°C/min flame ionization detection. Peak identification is as follows 1, 2,4-rert-butylphenol 2, nonylphenol isomers 3, di(4-tert-butylphenyl) carbonate 4, Tinuvin 329 5, solvent impurity 6, Ii gaphos 168 (oxidized). Reprinted with permission from Ref. (14).

Figure 12.9 Typical pyrolysis chromatogram of fraction from a styrene-acTylonitiile copolymer sample obtained from a miciocolumn SEC system 1, acrylonitrile 2, styrene. Conditions 5 % Phenylmetliylsilicone (0.33 p.m df) column (50 m X 0.2 mm i.d.) oven temperature, 50 to 240 °C at 10 °C/min carrier, gas, helium at 60 cm/s flame-ionization detection at 320 °C make-up gas, nitrogen at a rate of 20 mL/min. P indicates tlie point at which pyrolysis was made. Reprinted from Analytical Chemistry, 61, H. J. Cortes et ai, Multidimensional cliromatography using on-line microcolumn liquid cliromatography and pyrolysis gas cliromatography for polymer characterization , pp. 961-965, copyright 1989, with permission from tlie American Chemical Society.

An on-line supercritical fluid chromatography-capillary gas chromatography (SFC-GC) technique has been demonstrated for the direct transfer of SFC fractions from a packed column SFC system to a GC system. This technique has been applied in the analysis of industrial samples such as aviation fuel (24). This type of coupled technique is sometimes more advantageous than the traditional LC-GC coupled technique since SFC is compatible with GC, because most supercritical fluids decompress into gases at GC conditions and are not detected by flame-ionization detection. The use of solvent evaporation techniques are not necessary. SFC, in the same way as LC, can be used to preseparate a sample into classes of compounds where the individual components can then be analyzed and quantified by GC. The supercritical fluid sample effluent is decompressed through a restrictor directly into a capillary GC injection port. In addition, this technique allows selective or multi-step heart-cutting of various sample peaks as they elute from the supercritical fluid... 

Harden T.C. Imeson, Detection and Identification of Trace Quantities of Organic Vapors in the Atmosphere by Ion Cluster Mass Spectrometry and the Ionization Detector System ,... 

The electrical conductivity detector is probably the second most commonly used in LC. By its nature, it can only detect those substances that ionize and, consequently, is used frequently in the analysis of inorganic acids, bases and salts. It has also found particular use in the detection of those ionic materials that are frequently required in environmental studies and in biotechnology applications. The detection system is the simplest of all the detectors and consists only of two electrodes situated in a suitable detector cell. An example of an electrical conductivity detector sensing cell is shown in figure 13. 

This technique detects substances qualitatively and quantitatively. The chromatogram retention time is compound-specific, and peak-height indicates the concentration of pollutant in the air. Detection systems include flame ionization, thermal conductivity and electron capture. Traditionally gas chromatography is a laboratory analysis but portable versions are now available for field work. Table 9.4 lists conditions for one such portable device. 

The effort required to establish identity of a nitrosamine in an environmental sample depends on the nature of the problem and the specificity of the primary detection system. TEA response is much stronger evidence of identity than response from a flame ionization or nitrogen-specific detector. If TEA response is supported by chemical (9) or ultraviolet photolysis (8) supporting data, identification is adequate for many... 

Universal and selective detectors, linked to GC or LC systems, have remained the predominant choice of analysts for the past two decades for the determination of pesticide residues in food. Although the introduction of bench-top mass spectrometers has enabled analysts to produce more unequivocal residue data for most pesticides, in many laboratories the use of selective detection methods, such as flame photometric detection (FPD), electron capture detection (BCD) and alkali flame ionization detection (AFID) or nitrogen-phosphorus detection (NPD), continues. Many of the new technologies associated with the on-going development of instrumental methods are discussed. However, the main objective of this section is to describe modern techniques that have been demonstrated to be of use to the pesticide residue analyst. 

The MS detection system can be such that the full mass spectrum is observed (at least five peaks) or just selected ions monitored (SIM) with three or four identification points. For some analyses, it may be necessary to use MS-MS" techniques [8]. In LC-MS, it is important to make sure that ionization of the compounds of interest has been achieved. For all of these approaches, the criteria for matching of the analyte with the standard should be established during validation studies. 

Gas chromatography can also be used with other detection systems, e.g. electron-capture detection (GC-ECD) and flame-ionization detection (GC-FID). The optimization will have been carried out during validation studies. The peak separation criterion is the same as that given for LC above. Once again, cochromatography can be used for confirmation. 

E. C. Homing, M. G. Homing, D. I. Carroll, I. Dzidic, and R. N. Stillwell. New Picogram Detection System Based on a Mass Spectrometer with an External Ionization Source at Atmospheric Pressure. Anal. Chem., 45(1973) 936-943. 

Some substances, known as fluors or scintillants, respond to the ionizing effects of alpha and beta particles by emitting flashes of light (or scintillations). While they do not respond directly to gamma rays, they do respond to the secondary ionization effects that gamma rays produce and, as a result, provide a valuable detection system for all emissions. 

Negative atmospheric pressure chemical ionization (APC) low-energy collision activation mss spectrometry has also been employed for the characterization of flavonoids in extracts of fresh herbs. Besides the separation, quantitative determination and identification of flavonoids, the objective of the study was the comparison of the efficacy of the various detection systems in the analysis of flavonoids in herb extracts. Freeze-dried herbs (0.5g of chives, cress, dill, lovage, mint, oregano, parsley, rosemary, tarragon and thyme) were ground and extracted with 20 ml of 62.5 per cent aqueous methanol. After sedimentation the suspension was filtered and used for HPLC analyses. Separations were carried out in an... 

A gas chromatography-flame ionization detector system can be nsed for the separation and detection of nonpolar organic componnds. Semivolatile constitnents are among the analytes that can readily be resolved and detected nsing the system. If a packed column is used, four pairs of compounds may not be resolved adequately and are reported as a quantitative sum anthracene and phenanthrene, chrysene and benzo[a]anthracene, benzo[/ ]fluoranthene and benzo[/ ]fluoranthene, and dibenzo[a,/i]anthracene and indeno[l,2,3-cd]pyrene. This issue can be resolved through the use of a capillary column in place of a packed column. 

Photoionization a gas chromatographic detection system that uti-hzes an ultraviolet lamp as an ionization source for analyte detection. It is usually used as a selective detector by changing the photon energy of the ionization source. 

Carroll, D.I. Dzidic, I. Stillwell, R.N. Homing, M.G. Homing, E.C. Subpico-gram Detection System for Gas Phase Analysis Based Upon Atmospheric Pressure Ionization (API) MS. Anal. Chem. 1974,46, 706-704. 

Fluorescence excitation techniques provide a more sensitive detection system in which fluorescent X-ray photons (a fraction of the ionized absorbing atoms relax by emission of a fluorescent X-ray photon) are counted as the photon energy is scanned. The signal generated is proportional to the absorption coefficient, p, of the absorbing atom. 

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