Mass spectroscopy, hydrocarbon analysis

Acetylene Derived from Hydrocarbons The analysis of purified hydrocarbon-derived acetylene is primarily concerned with the determination of other unsaturated hydrocarbons and iaert gases. Besides chemical analysis, physical analytical methods are employed such as gas chromatography, ir, uv, and mass spectroscopy. In iadustrial practice, gas chromatography is the most widely used tool for the analysis of acetylene. Satisfactory separation of acetylene from its impurities can be achieved usiag 50—80 mesh Porapak N programmed from 50—100°C at 4°C per minute. 

As already mentioned, it is the volatile constituents that serve to identify fruit type and variety. Broadly speaking, qualitative analysis will identify the principal substances present in the volatiles fraction as representative of a particular fruit type, but it is the relative proportions of these substances that will reflect the variety. Alcohols, volatile acids, esters, carbonyl compounds, and low-boiling hydrocarbons are the principal groups represented. Analysis by GC-MS (gas chromatography coupled with mass spectroscopy) can be used to provide quantification and identification of the various constituents. 

Multiphoton ionization combined with mass spectroscopy has been proposed as a sensitive tool for analysis of trace gases to a detection limit of 2 parts in 10 . Flashlamp- and nitrogen-laser-pumped dye lasers have been used for REMPI detectors for gas chromatography. Aromatic hydrocarbons could be detected at the 10 pg level. The necessity for constant peak energy as well as CW power, for multiphoton ionization studies has been discussed. ... 

Historically, mass spectroscopy was developed to separate atoms and to determine the masses of isotopes accurately [1]. The predecessor of magnetic sector field mass spectrometers was built in 1918 by Dempster [2]. Later, some of the first instruments for the analysis of molecules [3] were used by analytical chemists in refineries to determine hydrocarbons (the first article in the first issue of the journal Analytical Chemistry dealt with mass spectrometry of a mixture of hydrocarbons [4]). Combinations of infrared and mass spectroscopy were reported shortly afterwards [5]. 

Microwave enhanced CVD. UV-vis, IR, and mass spectroscopies of the solute and raw soot material formed via the MW-CVD method indicate a complex assortment of various carbons and hydrocarbons. For example, in the UV-vis spectra of soot material dissolved in ether or hexane, the absorption band at 250 nm is routinely observed. Since corannulene has a pronounced absorption peak at 250 nm (26), it is possible that corannulene is a precursor of fullerenes in the MW-CVD method. However positive identification of the individual species will require extraction, purification, and further analysis. 

More sophisticated detection methods for gas chromatography are also employed in the analysis of hydrocarbons gas chromatography-mass spectrometry (EPA 8270C) and gas chromatography-Fourier transform infrared spectroscopy (EPA 8410). These procedures have a significant advantage in providing better characterization of the contaminants and thus are of particular use where some environmental modification of the hydrocarbons has taken place subsequent to soil deposition. 

An alternative method for fractionating and purifying petroleum hydrocarbons prior to GC or HPLC separation has been developed (Theobald 1988). The method uses small, prepacked, silica or Cjg columns that offer the advantage of rapid separation (approximately 15 minutes for a run) good recovery of hydrocarbons (85% for the Cjg column and 92% for the silica column) reusability of the columns and for the silica column in particular, good separation of hydrocarbon from non-hydrocarbon matrices as may occur with environmental samples. Infrared analysis and ultraviolet spectroscopy were used to analyze the aromatic content in diesel fuels these methods are relatively inexpensive and faster than other available methods, such as mass spectrometry, supercritical fluid chromotography, and nuclear magnetic resonance (Bailey and Kohl 1991). 

Naito et al. studied hydrogenation with use of adsorption measurements, mass spectrometry, and microwave spectroscopy for product analysis. In the room temperature deuteriation of propene, butene, and 1,3-butadiene, the main products were [ H2]-propane, [ H2]-butane, and l,2-[ H2]-but-l-ene, respectively. They showed, using mixtures of H2 and D2, that deuterium was added in the molecular form and at a rate proportional to the partial pressure of D2, as opposed to D surface coverage the reaction rates were zero order in hydrocarbon. They proposed, therefore, in contrast to the model of Dent and Kokes for ethene (but note in this case that reaction rate was 0.5 order in hydrogen pressure and proportional to ethene surface coverage), that hydrogenation proceeded by interaction of adsorbed hydrocarbon with gas-phase D2, that is by an Eley-Rideal mechanism. 

The hydrocarbon ("oil") fraction of a coal pyrolysis tar prepared by open column liquid chromatography (LC) was separated into 16 subfractions by a second LC procedure. Low voltage mass spectrometry (MS), infrared spectroscopy (IR), and proton (PMR) as well as carbon-13 nuclear magnetic resonance spectrometry (CMR) were performed on the first 13 subfractions. Computerized multivariate analysis procedures such as factor analysis followed by canonical correlation techniques were used to extract the overlapping information from the analytical data. Subsequent evaluation of the integrated analytical data revealed chemical information which could not have been obtained readily from the individual spectroscopic techniques. The approach described is generally applicable to multisource analytical data on pyrolysis oils and other complex mixtures. 

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