Quantitative elemental analysis

Here I stands for the intensity of the spectral hnes N is the atom number density in cm Z is the partition function E and y are the energies and degeneracy s of the upper levels, respectively and A and A are the Einstein coefficient and wavelength, respectively, for the observed transitions. When changing the concentration Nt relative to that Nm the line intensities ft and 7m will likewise change, and according to (6.1) one should obtain a cahbration curve with constant slope (Davies et al. 1995 Ciucci et al. 1999 Hou and Jones 2000). 

The way to improve LIBS analytical abilities is double pulse LIBS. It is conducted by using two pulses from the same laser source operated at a single wavelength. By utilizing a modified commercial laser, a proper external trigger circuit allows us to extract two laser pulses with adjustable delay from the same flash-lamp emission, and a relative time delay variable from a few to several tenths of microseconds. The experimental results show that such a technique 

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Thus the quantitative elemental analysis of the fuel establishes an overall formula, (CH O ) , where the coefficient x, related to the average molecular weight, has no effect on the fuel-air ratio. 

Electron Probe X-Ray Microanalysis (EPMA) is a spatially resolved, quantitative elemental analysis technique based on the generation of characteristic X rays by a focused beam of energetic electrons. EPMA is used to measure the concentrations of elements (beryllium to the actinides) at levels as low as 100 parts per million (ppm) and to determine lateral distributions by mapping. The modern EPMA instrument consists of several key components ... 

The electron-optical performance of the EPMA system is indistinguishable from that of a conventional scanning electron microscope (SEM) thus, EPMA combines all of the imaging capabilities of a SEM with quantitative elemental analysis using both energy- and wavelength-dispersive X-ray spectrometry. ... 

Three techniques involving the use of X-ray emission to obtain quantitative elemental analysis of materials are described in this chapter. They are X-Ray Fluorescence, XRF, Total Reflection X-Ray Fluorescence, TXRF, and Particle-Induced X-Ray Emission, PIXE. XRF and TXRF use laboratory X-ray tubes to excite the emission. PIXE uses high-energy ions from a particle accelerator. 

The LIMS technique is rarely used for quantitative elemental analysis, since other techniques such as EPMA, AES or SIMS are usually more accurate. The limitations of LIMS in this respect can be ascribed to the lack of a generally valid model to describe ion production from solids under very brief laser irradiation. Dynamic range limitations in the LIMS detection systems are also present, and will be discussed below. 

Quantitative Analysis. Quantitative elemental analysis is possible by measuring an area under the appropriate ionization edge, making allowance for the background intensity. 

Ciucci A., Palleschi V., Rastelli S., Salvetti A., Tognoni E., New procedure for quantitative elemental analysis by Laser Induced Plasma Spectroscopy, Appl. Spectrosc., 1999 53 (8) 960. 

This is a semi-quantitative elemental analysis technique. 

Characteristic X-rays emitted from transitions involving K and L electrons wavelength and emission intensity measurements for qualitative and quantitative elemental analysis respectively. 

Wesley and Wall (19) collected and analyzed airborne dust samples collected from three areas within five Mississippi gins in 1975. The general composition of their samples are summarized in Table IV. These data show the dust to be about 30 percent cellulosic, the remainder being soil and other materials. The quantitative elemental analysis of their samples is detailed in Table V. Although the percentages are different, the constituents in these samples of gin dust are very similar to those listed by Brown (18) in whole plant parts. None of the data presented have identified residues from insecticides or harvest aid chemicals. This may be because they were not specifically sought. 

Optical examination of etched polished surfaces or small particles can often identify compounds or different minerals hy shape, color, optical properties, and the response to various etching attempts. A semi-quantitative elemental analysis can he used for elements with atomic number greater than four by SEM equipped with X-ray fluorescence and various electron detectors. The electron probe microanalyzer and Auer microprobe also provide elemental analysis of small areas. The secondary ion mass spectroscope, laser microprobe mass analyzer, and Raman microprobe analyzer can identify elements, compounds, and molecules. Electron diffraction patterns can be obtained with the TEM to determine which crystalline compounds are present. Ferrography is used for the identification of wear particles in lubricating oils. 

Inorganic analysis was conducted in conjunction with the mineral analysis. Particles analyzed previously for mineral content were analyzed for their inorganic content, and an overall analysis conducted. The resultant EDS spectra output was fed into a spreadsheet software package which was adapted by the authors to allow the calculation of a quantitative elemental analysis. 

Qualitative and quantitative elemental analysis of polymers can be carried out by the conventional methods used for low-molecular-weight compounds. So a detailed description is not needed here. Elemental analysis or determination of functional groups is especially valuable for copolymers or chemically modified polymers. For homopolymers where the elemental analysis should agree with that of the monomer, deviations from the theoretical values are an indication of side reactions during polymerization. However, they can also sometimes be caused by inclusion or adsorption of solvent or precipitant, or, in commercial polymers, to the presence of added stabilizers. The preparation of the sample for... 

Unstable radionuclei result on subjecting the nuclei of some elements to neutron bombardment. During the decay process, in which the radionuclei return to more stable forms, characteristic radiation is emitted. The energy of the radiation is characteristic of the element, and its intensity forms the basis for quantitative elemental analysis. The advantages of NAA for trace analysis include low detection limits, good sensitivity, multi-element capability and relative freedom from matrix effects. However, for successful application of this technique skilled personel are required and because of the low sample throughput the amount of work involved in the analysis of column fractions, for example, is prohibitively high. In addition, it may take up to several weeks before the results are available. Further, only few laboratories have easy access to a neutron source. 

ICP spectroscopy has been applied in quantitative elemental analysis in forensic examinations (57), and for such issues as the determination of source provenance based on these data for materials such as ochre (58) or other pigments. Speakman et al. (59) report on the characterization of archaeological materials with LA-ICP-MS, while others analyzed pigments successfully on pottery from the American Southwest (60), including the Mesa Verde region (61) among others. 

Because the objective of the protocol was not only to get a quantitative elemental analysis, but also to keep the sample size as small as possible, EDS must be considered as preliminary test for elemental analysis by ICP-MS or ICP-OES, thus allowing for the chemical composition of die material to dictate what must be done next... 

Using forensic photography as a precursor to any sample acquisition forms the foundation of the protocol, and allows purposive sampling. EDS should be performed to establish which elements to expect before attempting any quantitative elemental analysis such as ICP-OES/MS. Before working with actual artifacts, a set of replicated materials must be used and a successful trial run using the planned methods of analysis whether ICP-OES/MS, GC-MS or any others, must be achieved, so the methods of preparation can be adjusted properly. To facilitate this, appropriate materials must be replicated, which might mean that plants or minerals must be collected, and dyed or painted comparative standards must be created, so the unknown can be compared to the known. For many of the Old World dye plants these standards already exist. However, for North American dye plants comparative collections are in the early phases and subsequent analysis of colorant constituents have not yet been conducted (68,69). 

Quantitative elemental analysis often limited in practical situations by the combination of an unknown depth distribution over the probing depth, which itself may not be known to better than a factor of 2. 

Fast, semi-quantitative elemental analysis (less accurate than XPS owing to a combination of less well-known cross-sections, and the manner in which the data are usually taken). Simultaneous Ar+ profiling. 

SIMS process not well-understood. Major problem is the huge variation in a given SIMS ion intensity with changes in chemical or physical environment. This makes quantitative elemental analysis difficult. 

Using medium energies (100-300 keV) and double alignment instrumentation becomes a quantitative elemental analysis tool with sub-monolayer sensitivity. It has excellent structural analysis capabilities. 

Table 2 Semi-quantitative elemental analysis of sulphur on photo-sulphonated LDPE films obtained from the EDX spectra...

SEM of the treated films indicated a progressive change in the surface morphology, as seen in Fig. 17. After 5 min of reaction time (Fig. 17b), the surface appeared slightly smoother than that of the control sample (Fig. 17a), upon 10 min exposure (Fig. 17c) submicron-sized blisters appeared and at 30 min (Fig. 17d), the defects covered the entire surface and were of several micron in diameter. The EDX spectra substantiated the presence of sulphur on the treated films and its absence on the control. The results of this semi-quantitative elemental analysis of sulphur on the film surface, computed from the collective EDX spectra, are shown in Table 2. The tabulated results indicate that the relative concentration of sulphur in these films increases with an increase in the reaction time. 

Qualitative and quantitative elemental analysis and elemental maps inside electron microscope. With Be window detector Na —> U, with thin window detector C —> U analyzed. Detection limit 0.1%. 

Qualitative and quantitative elemental analysis inside electron microscope, no elemental mapping. Sharper peaks compared to EDS and no peak overlaps. Detectable elements C —> U, detection limit 0.2%. 

The UV-absorption method, with which quantitative determination of DNA in tissue sections can be done, provided the inspiration for the development of x-ray spectrographic methods at the end of the 1940s. The quantitative x-ray analysis methods were developed to provide quantitative elementary analysis on a histochemical and cytochemical scale, that is, quantitative elemental analysis of tissues in situ and at a subcellular level. Engstrom1 formulated how the problem could be attacked in the following way ... 

Fassel, V. A., "Quantitative Elemental Analysis by Plasma Emission Spectroscopy, Science, 202, 183 (1978). 

Calculation of the Empirical Formula Molecular formulas can be determined by a two-step process. The first step is the determination of an empirical formula, simply the relative ratios of the elements present. Suppose, for example, that an unknown compound was found by quantitative elemental analysis to contain 40.0% carbon and 6.67% hydrogen. The remainder of the weight (53.3%) is assumed to be oxygen. To convert these numbers to an empirical formula, we can follow a simple procedure. 

Analysis schemes developed for identifying clay minerals in the TEM based on EDS spectra (e.g., Murdoch et al.100) are inappropriate for colloidal samples dispersed on polycarbonate filters due to complications associated with the various sample-beam-substrate interactions that differ dramatically from that of ideal samples or standards with smooth polished surfaces.94 96 101 102 Correction procedures that account for the influence of particle size and morphology on x-ray spectra have been widely available for some time,101102 but these techniques have not been applied to the analysis of environmental particulates. To overcome the limitation of quantitative elemental analysis, some research groups have compared the x-ray spectra for sample colloids to the spectra for various minerals of similar size and composition under the same instrumental and sample preparation conditions to calibrate instrumental response.7 24 93 Noting the resolution problems associated with SEM analysis of submicron colloids, several research groups have chosen TEM as the primary discrete particle analysis technique,21 52 103 104 or have combined TEM analysis techniques, such as electron diffraction and x-ray microanalysis, to confirm conclusions drawn from SEM surveys.7,93 105... 

Thanks to the linear relationship between the intensity of the characteristic X-ray radiation generated in the sample by electrons and the concentration of the given element, quantitative elemental analysis is also possible. X-ray microanalysis performed using SEM-EDX is, in principle, point analysis and is suitable for studying very small samples of solid materials that are stable in an electron beam. The X-ray fluorescence method, on the other hand, can be applied to the study of both solids and liquids. The signal reaching the detector always originates from a certain sample volume, and thus it is not point analysis. It is more sensitive than the SEM-EDX method. 

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