Analysis of Elements

The efficient recovery of volatile nitrosamines from frankfurters, followed by gc with chemiluminescence detection, has been described (133). Recoveries ranged from 84.3 to 104.8% for samples spiked at the 20 ppb level. Methods for herbicide residues and other contaminants that may also relate to food have been discussed. Inorganic elements in food can be deterrnined by atomic absorption (AA) methods. These methods have been extensively reviewed. Table 8 Hsts methods for the analysis of elements in foods (134). 

THE LIFE-TIME ANALYSIS OF ELEMENTAL COMPOSITION OF HUMAN LIVER PUNCTURES (SRXRF)... 

Both XRF and EPMA are used for elemental analysis of thin films. XRF uses a nonfocusing X-ray source, while EPMA uses a focusing electron beam to generate fluorescent X rays. XRF gives information over a large area, up to cm in diameter, while EPMA samples small spots, (om in size. An important use of EPMA is in point-to-point analysis of elemental distribution. Microanalysis on a sub- lm scale can be done with electron microscopes. The penetration depth for an X-ray beam is normally in the 10-(om range, while it is around 1 (om for an electron beam. There is, therefore, also a difference in the depth of material analyzed by XRF and EPMA... 

Rutherford Backscattering (RBS) provides quantitative, nondestructive elemental depth profiles with depth resolutions sufficient to satisfy many requirements however, it is generally restricted to the analysis of elements heavier than those in the substrate. The major reason for considering depth profiling using FIXE is to remove this restrictive condition and provide quantitative, nondestructive depth profiles for all elements yielding detectable characteristic X rays (i.e.,Z> 5 for Si(Li) detectors). 

The type of interaction along the interface will exert a great influence on the various properties of the composite materials. Therefore, to improve the performance of a composite material, it is absolutely necessary to characterize the structures of the interface. Some of the methods for analysis of the interface are ESCA, AES, IR-FTIR, SIMS, and SEM, etc. At present, ESCA is widely used in the surface analysis of elements and the qualitative analysis of functional groups. Figure 11 shows the ESCA spectrum of polyethylene treated with... 

Grating, use in analysis of elements near carbon, 220, 318, 319 Ground and bent crystals, 119, 122-124... 

In a competitive process, the excess energy can be dissipated by emission of a second or Auger electron from an outer shell of the atom, leaving it in a doubly ionised excited state. The relative importance of AES and XRF depends upon the atomic number (Z) of the element involved. High Z values favour fluorescence, whereas low Z favours AES. This fact, taken together with X-ray absorbance in air, makes XRF into a method which is not very sensitive for elements with atomic numbers below Z 10. Measurements of solid samples are normally made under vacuum, as the absorption of air renders analysis of elements lighter than Ti impossible. 

An indirect method for the determination of lead by coupling reactions was developed based on the replacement of Fe(II) by Pb(II) from the Fe(II)-EDTA complex. The subsequent CL reaction was based on the Fe(II)-luminol-02 system. The method was used to determine lead in polluted water samples [75], Such methods may be extended to other ions with proper complex constants as compared to the Fe(II)-EDTA complex, after HPLC separation. Analysis of elements based on indirect reactions is summarized in Table 4. 

Table 4 Analysis of Elements Using Coupling Reactions...

Lambert, J.B., Simpson, S.V., Buikstra, J.E. and Hanson, D. (1983). Electron microprobe analysis of elemental distribution in excavated human femurs. American Journal of Physical Anthropology 62 409 -23. 

In short, emission spectroscopy is considered to be the most accurate, precise and reliable means of quantitative analysis of elements as on date. If proper skill, precautions and wisdom are applied together this method may be adopted safely and conveniently to analyze approximately seventy elements from the periodic table at a concentration as low as 1 ppm. 

Atoms can be excited using the high energy levels associated with inductively coupled plasma (ICP) instead of a flame. Such a method of excitation is far more effective and permits the analysis of elements beyond the scope of simple... 

Figure 8. XPS analysis of elemental composition as a function of sputter depth (a) zinc phosphated steel (b) interfacial substrate surface of zinc phosphated steel after adhesion failure of epoxyester coating in cathodic polarization testing. Reproduced from Ref. copyright 1983, American Chemical Society.

The analytes and matrices are chosen for their prominence in cross-border trade and environmental or political issues, and they include substances such as rice, wine, water, fuel, and human serum. Table 5.2 is a list of 1MEP rounds up to the end of 2006. The majority of analytes are elements. This reflects the history of 1RMM, which has been prominent in the measurement of atomic weights and the development of IDMS as a primary method for the analysis of elemental amounts. 

Ultra-vioteFphotoelectron spectroscopy (UPS) UV-hgH Valence electrons Qualitative and quantitative analysis of elements Depth profiling... 

The flames commonly used as atomisers have temperatures in the range 2000-3000 K allowing for the analysis of elements such as Na, K and Cs by OES. The flame temperatures are not high enough to excite many other elements, so other atomisers such as spectroscopic plasmas have to be used. 

Very little data have been reported on the analysis of elements in whole coal and mine dusts in particular. Kessler, Sharkey, and Friedel analyzed trace elements in coal from mines in 10 coal seams located in Pennsylvania, West Virginia, Virginia, Colorado, and Utah (5). Sixty-four elements ranging in concentration from 0.01 to 41,000 ppm wt were determined. Several surveys published previously have provided data on the concentration of minor elements in ashes from coals rather than a direct determination on the whole coals or mine dusts. Previous investigations include studies by Headlee and Hunter (6), Nunn, Lovell, and Wright (7), Abernethy, Peterson, and Gibson (8), and others (9, 10, 11,12). 

---