Analytical methods mass spectrometry

Keywords Chlorinated paraffins, Short chain chlorinated paraffins (SCCPs), Medium chain chlorinated paraffins (MCCPs), Analytical methods, Mass spectrometry... 

Analytical applications Mass spectrometry has been applied to a variety of analytical problems related to expls, some of which have already been mentioned. Identification of the principal constituents of expls has been attempted from electron impact cracking patterns (Refs 34, 50 58), as well as chemical ionization spectra (Refs 69,70 71). Such methods necessarily include vapor species analysis and are directed to detection of buried mines (Refs 50, 58, 61,... 

As one of primer analytical techniques, mass spectrometry (MS) developed from nineteenth-century physics, starting with the pioneering work of J. J. Thomson on the electrical discharges in evacuated tubes. In 1913, Thomson wrote I feel sure that there are many problems in Chemistry which could be tackled with far greater ease by this than any other method. The method is surprisingly sensitive— more so than that of Spectrum Analysis—requires infinitesimal amount of material, and does not require this to be specially purified Indeed, MS offers speed, high sensitivity and isotopic specificity. This... 

The four Py-MS spectra — for pollen, bee feces, and two of the unknowns — presented as a figure in this report (but not shown in this chapter) clearly showed distinct differences, but the authors found that the complexity present in the 93 spectra made visual classification of the samples impossible. A discussion of the data analysis techniques used for the classification of these samples is beyond the scope of this chapter, but a brief summary of the results can be made. (Those readers with interest in statistical methods for analysis of data generated by analytical pyrolysis-mass spectrometry should find this paper interesting and may also want to read more recent work in this area. - )... 

In this chapter, quantitative applications of mass spectrometry were discussed. In this respect, mass spectrometry is distinctly superior over most other analytical techniques. Mass spectrometry-based methods are more specific and highly sensitive. In combination with high-resolution separation devices, the task of quantitation of real-world samples becomes much easier. A mass spectrometry signal is acquired in the SIM or SRM mode. In SIM, the ion current due to one or more compound-related ions is recorded, whereas in SRM, precursor-product... 

Various types of analytical information about the analyzed molecule can be obtained using mass spectrometry. The determination of the molecular weight is one of the most common goals. The observation of molecular species (molecular ions, molecular adducts, or ions formed by a loss of specific neutrals from the analyzed and ionized molecule) are often sufficient proof for the presence of the desired molecule. Accurate mass measurements of molecular species provide information about the elemental composition of ions and their precursor molecules consequently, mass spectrometry has largely replaced traditional elemental analysis. Mass spectrometry is a powerful technique for both qualitative and quantitative analyses. GC, HPLC, TEC, and CE are separation techniques compatible with mass spectrometry. When combined with such chromatographic methods, mass spectrometry becomes a unique method for the identification of submicromolar quantities of analytes. 

Classical or wet chemistry analysis techniques such as titrimetry and gravimetry remain in use in many laboratories and are still widely taught in Analytical Chemistry courses. They provide excellent introductions to the manipulative and other skills required in analytical work, they are ideal for high-precision analyses, especially when small numbers of samples are involved, and they are sometimes necessary for the analysis of standard materials. However, there is no doubt that most analyses are now performed by instrumental methods. Techniques using absorption and emission spectrometry at various wavelengths, many different electrochemical methods, mass spectrometry, gas and liquid chromatography, and thermal and radiochemical methods, probably account for at least 90% of all current analytical work. There are several reasons for this. 

Analytical characterization Mass spectrometry is suitable for detecting triethylcyclotriboroxane (base peak m/z = 139) in tetraethyldiboroxane (base peak m/z = 125). 0.5% Triethylcyclotriboroxane (5hb PP ) triethylborane (6iig = 86 ppm) in tetraethyldiboroxane (6ng = 53.3 ppm) can be identified by B-NMR spectroscopy. Triethylcyclotriboroxane or triethylborane amounts can be determined quantitatively by finding the Be-values using the trimethyl-amine A -oxide method in conjunction with the combined pyridine A/ -oxide/ trimethylamine A -oxide method and the total boron content. 

In the internal standard (IS) method, a known amount of a known compound called the internal standard is added to the sample and all calibration samples/solutions. The internal standard must be chromatographically separated from the analytes, unless mass spectrometry (MS) detection is utilized. A calibration curve is established based upon fortified samples, where the concentration of the analyte is varied, while the amount of IS is kept constant (Figure 10.7). 

Non-exhaustive summary of analytical methods using mass spectrometry. 

Mass spectrometry (Section 13 22) Analytical method in which a molecule is ionized and the vanous 10ns are exam ined on the basis of their mass to charge ratio... 

Following the movement of airborne pollutants requires a natural or artificial tracer (a species specific to the source of the airborne pollutants) that can be experimentally measured at sites distant from the source. Limitations placed on the tracer, therefore, governed the design of the experimental procedure. These limitations included cost, the need to detect small quantities of the tracer, and the absence of the tracer from other natural sources. In addition, aerosols are emitted from high-temperature combustion sources that produce an abundance of very reactive species. The tracer, therefore, had to be both thermally and chemically stable. On the basis of these criteria, rare earth isotopes, such as those of Nd, were selected as tracers. The choice of tracer, in turn, dictated the analytical method (thermal ionization mass spectrometry, or TIMS) for measuring the isotopic abundances of... 

To examine a sample by inductively coupled plasma mass spectrometry (ICP/MS) or inductively coupled plasma atomic-emission spectroscopy (ICP/AES) the sample must be transported into the flame of a plasma torch. Once in the flame, sample molecules are literally ripped apart to form ions of their constituent elements. These fragmentation and ionization processes are described in Chapters 6 and 14. To introduce samples into the center of the (plasma) flame, they must be transported there as gases, as finely dispersed droplets of a solution, or as fine particulate matter. The various methods of sample introduction are described here in three parts — A, B, and C Chapters 15, 16, and 17 — to cover gases, solutions (liquids), and solids. Some types of sample inlets are multipurpose and can be used with gases and liquids or with liquids and solids, but others have been designed specifically for only one kind of analysis. However, the principles governing the operation of inlet systems fall into a small number of categories. This chapter discusses specifically substances that are normally liquids at ambient temperatures. This sort of inlet is the commonest in analytical work. 

Aerosols can be produced as a spray of droplets by various means. A good example of a nebulizer is the common household hair spray, which produces fine droplets of a solution of hair lacquer by using a gas to blow the lacquer solution through a fine nozzle so that it emerges as a spray of small droplets. In use, the droplets strike the hair and settle, and the solvent evaporates to leave behind the nonvolatile lacquer. For mass spectrometry, a spray of a solution of analyte can be produced similarly or by a wide variety of other methods, many of which are discussed here. Chapters 8 ( Electrospray Ionization ) and 11 ( Thermospray and Plasmaspray Interfaces ) also contain details of droplet evaporation and formation of ions that are relevant to the discussion in this chapter. Aerosols are also produced by laser ablation for more information on this topic, see Chapters 17 and 18. 

When mass spectrometry was first used as a routine analytical tool, El was the only commercial ion source. As needs have increased, more ionization methods have appeared. Many different types of ionization source have been described, and several of these have been produced commercially. The present situation is such that there is now only a limited range of ion sources. For vacuum ion sources, El is still widely used, frequently in conjunction with Cl. For atmospheric pressure ion sources, the most frequently used are ES, APCI, MALDI (lasers), and plasma torches. 

Fox, A., Morgan, S.L., Larsson, L., and Oldham, G., Analytical Microbiology Methods Chromatography and Mass Spectrometry, Plenum Press, New York, 1990. 

Quantitative mass spectrometry, also used for pharmaceutical appHcations, involves the use of isotopicaHy labeled internal standards for method calibration and the calculation of percent recoveries (9). Maximum sensitivity is obtained when the mass spectrometer is set to monitor only a few ions, which are characteristic of the target compounds to be quantified, a procedure known as the selected ion monitoring mode (sim). When chlorinated species are to be detected, then two ions from the isotopic envelope can be monitored, and confirmation of the target compound can be based not only on the gc retention time and the mass, but on the ratio of the two ion abundances being close to the theoretically expected value. The spectrometer cycles through the ions in the shortest possible time. This avoids compromising the chromatographic resolution of the gc, because even after extraction the sample contains many compounds in addition to the analyte. To increase sensitivity, some methods use sample concentration techniques. 

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