I Elemental Composition

Table I. Elemental compositions of asphaltenes precipitated by different flocculants from various sources (16)...

Table I. Elemental Composition of the Water-Insoluble Lignin...

Table I. Elemental Compositions of Asphaltene Fractions Precipitated by Different Solvents...

Table I. Elemental composition and peak areas for quantitative NMR spectra of fulvic and humic acids.

The column was 25 cm long, 4.6 mm I.D. and packed with Partisil 10. It is seen that linear curves were obtained for three different solutes and two different moderators in n-heptane. Scott and Beesley [14] obtained retention data for the two enantiomers, (S) and (R) 4-benzyl-2-oxazolidinone. The column chosen was 25 cm long, 4.6 mm I.D. packed with 5 mm silica particles bonded with the stationary phase Vancomycin (Chirobiotic V provided by Advanced Separations Technology Inc., Whippany, New Jersey). This stationary phase is a macrocyclic glycopeptide Vancomycin that has a molecular weight of 1449.22, and an elemental composition of 54.69% carbon. 

Fig. 3. (a) Thermal expansion coefficients a for the inclusion (f), matrix (m), mesophase (i) and composite (c) of a typical iron-epoxy particulate composite, with 5 percent volume fraction for the inclusions, versus temperature, (b) the reduced longitudinal expansion of the same elements, normalized to the unit-length versus temperature (diameter of inclusions df = 150 pm)... 

M.15 In addition to determining elemental composition of pure unknown compounds, combustion analysis can be used to determine the purity of known compounds. A sample of 2-naphthol, C)0H7OH, which is used to prepare antioxidants to incorporate into synthetic rubber, was found to be contaminated with a small amount of LiBr. The combustion analysis of this sample gave the following results 77.48% C and 5.20% H. Assuming that the only species present are 2-naphthol and I.iBr, calculate the percentage purity by mass of the sample. 

The quadrupole is classified as a low-resolution device, i.e. it is capable of measuring the m jz ratio of an ion to the nearest integer value, and thus is unable to provide the elemental composition of an ion. 

A limited number of pure substances are available from NIST, primarily clini-cally-relevant compounds such as cholesterol, urea, uric acid, creatinine, glucose, cortisol, tripalmitin, and bilirubin (NIST SRM website). These compounds are certified for purity (greater than 99 %) and are used as primary calibrants in definitive methods for these clinical analytes (see below). Several additional pure substances are available for specific applications such as microchemistry, i.e. elemental composition (acetanilide, anisic acid, cystine nicotinic acid, o-bromobenzoic acid, p-fluoro-benzoic acid, m-chlorobenzoic acid), polarimetric standards (sucrose and dextrose), acidimetric standard (benzoic acid and boric acid). Only three pure substance NIST RMs are available for environmental contaminants, namely the chlorinated pesticides, lindane, 4,4 -DDT, and 4,4 -DDE. 

Applications With the current use of soft ionisation techniques in LC-MS, i.e. ESI and APCI, the application of MS/MS is almost obligatory for confirmatory purposes. However, an alternative mass-spectrometric strategy may be based on the use of oaToF-MS, which enables accurate mass determination at 5 ppm. This allows calculation of the elemental composition of an unknown analyte. In combination with retention time data, UV spectra and the isotope pattern in the mass spectrum, this should permit straightforward identification of unknown analytes. Hogenboom et al. [132] used such an approach for identification and confirmation of analytes by means of on-line SPE-LC-ESI-oaToFMS. Off-line SPE-LC-APCI-MS has been used to determine fluorescence whitening agents (FWAs) in surface waters of a Catalan industrialised area [138]. Similarly, Alonso et al. [139] used off-line SPE-LC-DAD-ISP-MS for the analysis of industrial textile waters. SPE functions here mainly as a preconcentration device. 

While these silylamide-catalyzed reactions provided a good way to solve the problem of the low ceramic yield in the pyrolysis of [(CH3SiH)x (CH3Si)y]n, the problem of the elemental composition of the ceramic product remained (i.e., the problem of Si/C ratios greater than one) since only catalytic quantities of the silylamide were used. 

In modern terms, asphaltene is conceptually defined as the normal-pentane-insoluble and benzene-soluble fraction whether it is derived from coal or from petroleum. The generalized concept has been extended to fractions derived from other carbonaceous sources, such as coal and oil shale (8,9). With this extension there has been much effort to define asphaltenes in terms of chemical structure and elemental analysis as well as by the carbonaceous source. It was demonstrated that the elemental compositions of asphaltene fractions precipitated by different solvents from various sources of petroleum vary considerably (see Table I). Figure 1 presents hypothetical structures for asphaltenes derived from oils produced in different regions of the world. Other investigators (10,11) based on a number of analytical methods, such as NMR, GPC, etc., have suggested the hypothetical structure shown in Figure 2. 

Borszeki J, Kepes J, Koltay L, Sarudi I (1986a) Classification of paprika quality using pattern recognition methods based on elemental composition. Acta Alimentaria 15 93... 

The possibility to have well resolved peaks allows the measurement of the accurate mass of an ion, i.e. m/z values significant to four decimals, and to calculate its elemental composition. 

It should be emphasized that the deviations from the logarithmic correlation obey the normal distribution statistics, allowing one to apply convenient statistical procedures to analytical measurement results. As will be shown below, the logarithmic linear correlation rule was observed for all types of geo-chemical samples, i. e., snow, air, water, and soil. The correlation analysis of the elemental composition of melted-snow fractions showed with confidence level 95% that no significant discrepancy exists between the element composition within the correlation curves (see Table 1) and the corresponding variances are thus homogeneous for any two randomly chosen samples (i. e., points of the territory). 

Reiche, I., Favre-Quattropani, L., Calligaro, T., et al. (1999). Trace element composition of archaeological bones and postmortem alteration in the burial environment. Nuclear Instruments and Methods in Physics Research B 150 656-662. 

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