Desorption trace analysis

Tan BL, Hawker DW, Muller JF, Tremblay LA, Chapman HF (2008) Stir bar sorptive extraction and trace analysis of selected endocrine disrupters in water, biosolids and sludge samples by thermal desorption with gas chromatography-mass spectrometry. Water Res 42 404 112... 

Laser desorption/ ionization LDI Photon induced desorption/ ionization Nonvolatile atomic and molecular ions Isotope ratio Trace analysis... 

The ability to recover monolayers and subject them to meaningful analysis has become practical only in recent years because of the development of new methods of trace analysis. High-performance liquid chromatography and vapor phase chromatography allow separation and identification of such small quantities (54a). Attenuated total reflectance techniques for infrared analysis (56) and field desorption mass spectrometry (68) have been applied to the trans-... 

With a focus on trace forensic detection of explosives, especially for use in counterterrorism and to counter narcotics investigations, Fetterolf et al. [75] evaluated the use of ion mobility-mass spectrometry for explosives determinations. In this, explosives residues were collected on a membrane filter by a special attachment on a household vacuum cleaner. Although subsequent thermal desorption and analysis required only 5 s, fimits of detection for most common explosives were as low as 200 pg. The persistence of explosives on hands and transfer to other surfaces were also examined as were post-blast residues of NG on fragments of improvised explosive devices constructed with double-based smokeless powder. Finally, postblast residue from C-4, Semtex, and other explosives was found by IMS analyses on items of forensic and evidentiary value. These few out of many examples demonstrate that mobihty spectrometers are well suited tools for laboratory and on-site investigations, before and after the use of explosives. 

Derivatization After Desorption. Alkanolamines, highly polar basic compounds, present a difficult analytical problem. Although direct gas chromatographic separations can be achieved, this technique is not applicable to trace analysis due to sorption problems at trace concentrations. A derivatization/gas chromatographic procedure has been developed for the determination of alkanolamines in air as low as 100 ppb (54,55). The samples are collected on activated alumina and desorbed with an aqueous solution of 1-octanesulfonic acid. The... 

Kawaguchi, M., R. Ito, N. Endo, et al. 2006. Stir bar sorptive extraction and thermal desorption-gas chromatography-mass spectrometry for trace analysis of benzophenone and its derivatives in water sample. Anal. Chim. Acta 557 272-277. 

Figure 2.12 The so-called complete analysis of TDS data is based on the rigorous application of Expression (2-15) for the rate of desorption. The spectra of Figure 2.11 are integrated to determine points on the spectra corresponding to a fixed coverage, in this example 0.15 of a monolayer (b). This procedure gives a pair of (r,T) values for every desorption trace, from which an Arrhenius plot is made (c). The slope yields the activation energy and the intercept equals In v+n In 9 each corresponding to a coverage of 0.15 ML.

Gas chromatographic (GC) methods also provide possibilities to detect the irreversibly held amounts of a poison (51), although these techniques are less accurate than the gravimetric methods. The number of irreversibly adsorbed molecules can be calculated from the material balance for successively injected pulses of the poison and the eluted amounts. Alternatively, adsorption equilibrium can be attained at low temperature, the adsorbed amount being determined by frontal analysis (51). Desorption may then be carried out at the same temperature and the irreversibly held amount can be calculated either from the difference between adsorbed and desorbed amounts of a first cycle or from the difference of the adsorbed amounts of a first and a second adsorption (52). Desorption temperatures can then be raised stepwise after the first desorption and the dependence of the irreversibly adsorbed amounts on desorption temperature determined from the corresponding desorbed amounts. The accuracy of these GC measurements is limited because of the usually very pronounced tailing of the desorption trace for the systems of interest. 

Oostdijk, J.P., Degenhardt, C.E., Trap, H.C., Langenberg, J.P. (2007). Selective and sensitive trace analysis of sulfur mustard with thermal desorption and two-dimensional gas chromatography-mass spectrometry. J. Chromatogr. A. 1150(1-2) 62-9. 

Solid-phase microextraction (SPME) is a technique that was first reported by Louch et al. in 1991 (35). This is a sample preparation technique that has been applied to trace analysis methods such as the analysis of flavor components, residual solvents, pesticides, leaching packaging components, or any other volatile organic compounds. It is limited to gas chromatography methods because the sample must be desorbed by thermal means. A fused silica fiber that was previously coated with a liquid polymer film is exposed to an aqueous sample. After adsorption of the analyte onto the coated fiber is allowed to come to equilibrium, the fiber is withdrawn from the sample and placed directly into the heated injection port of a gas chromatograph. The heat causes desorption of the analyte and other components from the fiber and the mixture is quantitatively or qualitatively analyzed by GC. This preparation technique allows for selective and solventless GC injections. Selectivity and time to equilibration can be altered by changing the characteristics of the film coat. 

Mass spectrometry is one of the most powerful multielemental determination methods, allowing the estimation of non-pollution levels in a multielement run. In field-desorption MS, 10 pg Tl could be detected in 2, L of non-ashed sample solution (homogenized rat brain) by means of an isotope dilution technique (Schulten et al., 1978), offering possibilities of microlocal trace analysis. Ionization of CHCI3 extracts from plant cytosols with Ar" (secondary ion MS) enabled the detection of dimethylthallium-t- directly in the mass spectrum (Gunther and Umland, 1989). 

Hobbs J. R. and Conde E. P, A simple inexpensive thermal desorption method for the trace analysis of headspace vapors from explosives and organic nitro-Compounds, Proceedings of Interernational Symposium on Forensic Aspects Trace Evidence, FBI Quantico, VA, June 24-28, 1991, 269. Avail. NTIS PB94-145877. 

The rapid development of mass spectrometric technology and the wide field of applications exclude a complete and comprehensive discussion of mass spectrometric possibilities for trace analysis of metals. Therefore, this report will give a brief outline of the principles of mass spectrometry (MS) and the fundamentals of qualitative and quantitative mass spectrometric analysis with emphasis on recent developments and results. The classical methods of analysis of solids, i.e. spark-source MS and thermal ionization MS, as well as newer methods of metal analysis are described. Focal points in this survey of recently developed techniques include secondary ion MS , laser probe MS , plasma ion source MS gas discharge MS and field desorption MS . Here, a more detailed description is given and the merits of these emerging methods are discussed more explicitly. In particular, the results of the FD techniques in elemental analyses are reviewed and critically evaluated. 

The experimental technique for the trace analysis of metals simply involves the production of an emitter of acceptable quality. In general, 10 /im tungsten wires are activated at high temperature with benzonitrile in a multiple activation device. As the result of such an activation process, the tungsten wire is covered with dendrites of partially ordered pyrocarbon. Due to the small radii of curvature of the tips of the microneedles, the field strength is enhanced to a. level suitable for FDMS. These emitters are mechanically stable, which is important for repeated use they can also be chemically and thermally strained. This property is a prerequisite for the pyrolysis of the organic matrix and desorption of the metal cations, and last not least, the surface area of the emitter is sufficient for sample application. 

Mass S >ectrometric Methods for Trace Analysis of Metab TaMe 9. Laser-assisted field desorption mass spectrometry of metals and allo) ... 

Adsorptive stripping (AdSV) can be employed in the trace analysis of a wide variety of organic compounds exhibiting surface active properties. When the given compound contains an electrochemically reducible or oxidizable group, the peak current on the voltammetric curve recorded after completion of the accumulation period then corresponds practically only to the reduction or oxidation of the whole amount of the adsorbed electroactive species. Only tensammetric adsorption/desorption peaks are obtained for electroinactive compounds. 

Thome FA, Heavner DL, Ingebrethsen BJ, Eudy LW, Green CR (1986) Environmental tobacco smoke monitoring with an atmospheric pressure chemical ionization mass spectrometer/mass spectrometer coupled to a test chamber. Proc 79th Annual Meet Air Pollution Control Assoc. Air Pollution Control Assoc, Pittsburgh, paper 86-37.6 Thompson CV, Jenkins RA, Higgins CE (1989) A thermal desorption method for the determination of nicotine in indoor environments. Environ Sci Technol 23 429-435 Thomson BA, Davidson WR, Lovett AM (1980) Applications of a versatile technique for trace analysis atmospheric pressure negative chemical ionization. Environ Health Perspect 36 77-84... 

Several variants of the selective desorption technique has been reported for preparing nanopores in an SAM [60], oligonucleotide attachment and DNA hybridization [62], selective immobilization of enzymes [63, 112], controlled release of biological cells [65], and trace analysis [64, 113,114]. 

Hoffmann, A., and R. Bremer, Design, Performance and Applicability of a Multi-functional Thermal Desorption System for Trace Analysis in Capillary GC, Proc. 16th Int. Symp. on Capillary Chromatography, Riva del Garda, Italy, P. Sandra and G. Devos (eds.), 1994, pp. 1165-1175. 

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