Analysis of alkanes

Smits THM, SB Balada, B Witholt, JB van Beilen (2002) Eunctional analysis of alkane hydroxylases from Gram-negative and Gram-positive bacteria. J Bacterial 184 1733-1742. 

Raner, K. D. Lusztyk, J. Ingold, K. U. Kinetic Analysis of Alkane Polychlorination with Molecular Chlorine. Chlorine Atom/Monochloride Geminate Pairs and the Effect of Reactive Cage Walls on the Competition Between Monochloride Rotation and Chlorine Atom Escape. J. Am. Chem. Soc. 1988, 110, 3519-3524. 

Venter, A., Rohwer, E.R., and Laubscher, A.E. 1999. Analysis of alkane, alkene, aromatic and oxygenated groups in petrochemical mixtures by supercritical fluid chromatography on silica gel. Journal of Chromatography A, 847 309-21. 

The spectroscopic analysis of alkanes will be discussed in Secs. 13.I5-13.16.)... 

Perdih, A. (2000a) On topological indices indicating branching. Part 1. The principal component analysis of alkane properties and indices. Acta Chim. Sloven., 47, 231-259. 

Partitioning of Organic Compounds. Groups of compounds, such as hydrocarbons and chlorinated hydrocarbons, have different k s. For example, each class of hydrocarbons (alkanes, alkenes, cycloalkanes, and aromatics) have different k s. The alkanes partition 95+% into the gas when equal volumes of gas and water are equilibrated. For this reason two, or at most three, equilibrations will transfer all the alkanes present into the gas phase. Thus, it is more accurate and convenient merely to sum the concentrations found in the successive gas phases rather than back-extrapolate. If 5% accuracy is adequate for analysis of alkanes, a single equilibration is sufficient. Two or three equilibrations are also adequate for alkenes and cycloalkanes. 

In the early stages of preparation of the present manuscript I was confronted with a surprise The analysis of alkanes and cycloalkanes has never been reviewed as such. Although the C—C and C—H bonds are the most abundant bonds in organic chemistry, the analysis of compounds constructed solely from these bonds cannot be found in analytical reviews of functional groups. Therefore, I could not relate to previous secondary or tertiary sources of literature. Moreover, the reader of this chapter will find that, although I attempted to stay as objective as possible in presenting the various analytical techniques, most of the advanced applications come from petroleum and other fossil fuels studies. Since the choice of analytical techniques relates to structures of the whole alkane or cycloalkane, the various isomers, enantiomers or conformations are discussed. 

The diversity of alkane isomers is discussed in detail in the chapter by Kier and Hall in this volume. However, we should mention that the C H2 +2 open-chain alkanes can have from a single structural isomer (C —C3) up to 366,319 isomers for C20H42. Hence, the analysis of alkanes is more and more complicated with increasing number of C atoms. 

The analysis of alkanes and cycloalkanes TABLE 1. Normal alkanes 293... 

By the introduction of a molecule into the mass spectrometer it will be charged. In most cases we study the positive ions, which can be produced by various ionization methods. The El method is most commonly used for the analysis of alkanes. When the energy of the electron beam is greater than the ionization potential of the substrate, the following processes may occur ... 

Table 3 gives IP values and heats of formation for selected alkanes and cycloalkanes. It is clear that the IP differences are not large enough to render these as diagnostic tools for the analysis of alkanes and cycloalkanes. Since the IP measures the energy needed... 

In general, the analysis of alkanes and cycloalkanes by GC is based on boiling point... 

The use of MS as a detector for both HPLC and GC added a new dimension to the analysis of alkanes, and even more so to the identification of complex cycloalkanes. 

The basic concepts have already been presented in this review. However, the study of single compounds does not require an interface between the chromatographic unit and the MS. The analysis of mixtures by MS relates not only to GC/MS or HPLC/MS . The popularity of GC/MS systems can be examined by the nuihber of relevant publications. These were less than 100 in 1968, rose to a peak of 2000 papers in 1979, dropped to 1500-1750 yearly until 1988, when they rose again to 2000. The use of MSD for HPLC (also called LC/MS) also rose from a few publications in 1975 to a few hundred in 1988. A method, less used for hydrocarbon analysis, SFC (Super-critical Fluid Chromatography)/MS, was initiated only in 1985 and is gaining interest slowly. These data are given by Evershed . Obviously it will be impossible to review all these developments in the use of MSD ", even for the analysis of alkanes and cycloalkanes. 

The use of MS in addition to GC/MS includes methods such as capillary zone electrophoresis (CZE/MS), thin layer chromatography (TLC/MS) and others. The major problem in employing these separation-MSD methods is the interface. The very high vacuum required for MS operation requires complete removal of the carrier gas or liquid . Since the present review treats specifically the use of the MSD for the analysis of alkanes and cycloalkanes, we concentrate on the GC/MSD/C (gas chromatography/ mass spectrometry/computerized) method. The MS used can be quadrupole or magnetic and its configuration will, of course, control the power of resolution (PR), the mass range, etc. The ionization mode is also important, e.g. whether El or Cl (see Sections, III.A.l and III.A.2). 

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