Sample preparation elemental analysis

There are other advantages to the SEM, including ease of sample preparation, elemental analysis by energy-dispersive X-ray analyzer, and usually excellent specimen contrast. The light mieroscope is still important beeause an SEM costs 10-50 times the cost of an adequate light microscope. Secondly, there are many routine surface examinations easily performed by light optics that do not justify use of the SEM. 

CF-IRMS provides reliable data on micromoles or even nanomoles of sample without the need for cryogenic concentration because more of the sample enters the ion source than in DI-IRMS. CF-IRMS instruments accept solid, liquid, or gaseous samples such as leaves, soil, algae, or soil gas, and process 100-125 samples per day. Automated sample preparation and analysis takes 3-10 min per sample. The performance of CF-IRMS systems is largely determined by the sample preparation technology. A variety of inlet and preparation systems is available, including GC combustion (GC/C), elemental analyzer, trace gas pre-concentrator and other. The novel... 

Many of the fabric structures from which these samples were taken have been described in other publications (1-3). In experimenting with appropriate methods for preparation of samples for elemental analysis, fibers are of limited value because they cannot be proven to belong to the textile object in the box. For experimental purposes, these fabrics served well as representative brittle, fragile, and minute fibrous samples for preparation and analysis. 

White Jr., R.T. Open reflux vessels for microwave digestion botanical, biological, and food samples for elemental analysis. In Kingston, H.M., lassie, L.B. (eds.) Introduction to Microwave Sample Preparation. Theory and Practice. ACS, Washington, DC (1988)... 

Many researchers have attempted to determine mercury levels in the blood, urine, tissues, and hair of humans and animals. Most methods have used atomic absorption spectrometry (AAS), atomic fluorescence spectrometry (AFS), or neutron activation analysis (NAA). In addition, methods based on mass spectrometry (MS), spectrophotometry, and anodic stripping voltametry (ASV) have also been tested. Of the available methods, cold vapor (CV) AAS is the most widely used. In most methods, mercury in the sample is reduced to the elemental state. Some methods require predigestion of the sample prior to reduction. At all phases of sample preparation and analysis, the possibility of contamination from mercury found naturally in the environment must be considered. Rigorous standards to prevent mercury contamination must be followed. Table 6-1 presents details of selected methods used to determine mercury in biological samples. Methods have been developed for the analysis of mercury in breath samples. These are based on AAS with either flameless (NIOSH 1994) or cold vapor release of the sample to the detection chamber (Rathje et al. 1974). Flameless AAS is the NIOSH-recommended method of determining levels of mercury in expired air (NIOSH 1994). No other current methods for analyzing breath were located. 

The recovery of spiked metals was close to 100% for most elements. It shows that this method is acceptable and that the results are reasonably accurate. The percentage recovery for Pb, Cr and Ni is close to 100%. This test shows that none of the listed toxic elements are present or lost during the sample preparation or analysis. The level of toxic metals in PVC, PCM, epoxy, CA and PU are negligible compared with levels in the CPU boards. These are a cause for concern and care should be taken when disposing of all obsolete CPU boards containing these metals, particularly those made for electronic components in the early days of computer manufacturing. These boards have the highest levels of toxic metals present, as shown in Table 4.17. 

The determination of small quantities of azide and the analysis of single crystals require sensitive but nonsubjective methods of analysis. This section discusses relevant methods of sample preparation and analysis as they relate to small samples the next section discusses techniques suitable for trace-element analysis. 

To appreciate the different approaches available for the preparation of solid samples for elemental analysis. 

The ASTM has already published a preamble to oil identification (19) and methods on preservation of samples (20), elemental analysis (21), and infrared analysis (22), in addition to the GC and FL methods (4,5) and sample preparation methods (3) previously mentioned. Widespread adoption of these carefully developed methods and their under-... 

X-ray fluorescence spectrometry, gas chromatography and neutron activation analysis (NAA). An older book edited by Hofstader, Milner and Runnels on Analysis of Petroleum for Trace Metals (1976), includes one chapter each on principles of trace analysis and techniques of trace analysis and others devoted to specific elements in petroleum products. Markert (1996) presents a fresh approach to sampling, sample preparation, instrumental analysis, data handling and interpretation. The Handbook on Metals in Clinical and Analytical Chemistry, edited by Seiler,... 

The method of sample preparation and analysis will depend on the form of the metal (ore, complex, metal, etc.), its concentration, and the presence of potentially interfering species. If noble metals are mixed with base metals, the latter must be removed first, followed by noble metal separation. The chemistry of noble metal separation is similar to that used in the refining of the metals, but it can be greatly simplified by knowning what elements are present. 

The concentration of inorganic components in forage crops varies according to crop maturity, temperature, and soil pH and composition. The analyses of mineral content can reveal soil or management deficiencies as well as optimum harvest time for proper crop management. Actual mineral analyses are used to determine the amount of mineral supplementation to be added to an animal ration for proper nutritional balance. Reference methods of analysis include inductively coupled argon plasma (ICP), atomic absorption spectroscopy (AAS), and x-ray fluorescence spectroscopy (XRF). These techniques are well established for the analysis of mineral elements in whole-plant material. The exact procedures for sample preparation and analysis are well documented. Copies of the procedures may be obtained from instrument manufacturers or are readily found using basic texts for each analytical technique. 

The determination of rare earth elements was one of the very first applications that attracted geochemists to ICP-MS, mainly because of the lengthy sample preparation and analysis times involved with previously used techniques such as ICP-OES and NAA. However, even though ICP-MS offered significant benefits over these techniques, it was not without its problems, because of the potential of spectral interferences from other rare earth elements in rocks or natural water samples. For that reason, instrument parameters have to be optimized, depending on the rare earth elements being determined and the kinds of interferents present in the sample. For example, plasma power and nebulizer gas flows must be adjusted to minimize the formation of oxide species. This is necessary because an oxide or hydroxide species of one rare earth element can spectrally interfere with another rare earth element at... 

Due to difficulties in theoretical and experimental assessment of the effect exerted by various factors on dissolution of solid phases, chemists have lost interest in detailed investigation of such processes. Thus, in modem analytical chemistry of inorganic substances, dissolution is considered as a stage in the preparation of samples to elemental analysis, their dissection , and is described just qualitatively as complete or incomplete, fast or slow, easy or difficult process. The problem of separation and identification of solid phases in multielement multiphase substances is generally neglected this problem is not presented in university manuals of analytical chemistry. 

A major advantage of this hydride approach lies in the separation of the remaining elements of the analyte solution from the element to be determined. Because the volatile hydrides are swept out of the analyte solution, the latter can be simply diverted to waste and not sent through the plasma flame Itself. Consequently potential interference from. sample-preparation constituents and by-products is reduced to very low levels. For example, a major interference for arsenic analysis arises from ions ArCE having m/z 75,77, which have the same integral m/z value as that of As+ ions themselves. Thus, any chlorides in the analyte solution (for example, from sea water) could produce serious interference in the accurate analysis of arsenic. The option of diverting the used analyte solution away from the plasma flame facilitates accurate, sensitive analysis of isotope concentrations. Inlet systems for generation of volatile hydrides can operate continuously or batchwise. 

The complex of the following destmctive and nondestmctive analytical methods was used for studying the composition of sponges inductively coupled plasma mass-spectrometry (ICP-MS), X-ray fluorescence (XRF), electron probe microanalysis (EPMA), and atomic absorption spectrometry (AAS). Techniques of sample preparation were developed for each method and their metrological characteristics were defined. Relative standard deviations for all the elements did not exceed 0.25 within detection limit. The accuracy of techniques elaborated was checked with the method of additions and control methods of analysis. 

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