Inorganic sampling

The infonuation that can be extracted from inorganic samples depends mainly on tlie electron beam/specimen interaction and instrumental parameters [1], in contrast to organic and biological materials, where it depends strongly on specimen preparation. 

Organics produce no useful positive ions, but the ions produced by inorganic samples are remarkably free from background interference, and the resulting mass spectra are relatively simple. The ion currents derived from the positive sample ions at each m/z value, being free from background ions, represent an accurate measure of the amount of each element. 

TXRF is an ideal tool for microanalysis [4.21]. The analytical merits are that TXRF has a broad range of linearity (lO -lO atoms cm ) and it is extremely surface-sensitive and matrix-independent. TXRF can be applied to a great variety of different organic and inorganic samples such as water, pure chemicals, oils, body fluids and tissues, suspended matters, etc., down to the picogram range. 

Toxic Pollutant Metals and Inorganics Samples Detections >10 gg/L Range Median Mean... 

Spark source mass spectrometry is used for the examination of non-volatile inorganic samples and residues to determine elemental composition. An RF spark of about 30 kV is passed between two electrodes, one of which may be the sample itself, causing vaporization and ionization. Powdered samples or residues from ashed organic materials can be formed into an electrode after mixing with pure graphite powder. 

Dynamic SIMS is used for depth profile analysis of mainly inorganic samples. The objective is to measure the distribution of a certain compound as a function of depth. At best the resolution in this direction is < 1 nm, that is, considerably better than the lateral resolution. Depth profiling of semiconductors is used, for example, to monitor trace level elements or to measure the sharpness of the interface between two layers of different composition. For glass it is of interest to investigate slow processes such as corrosion, and small particle analyses include environmental samples contaminated by radioisotopes and isotope characterization in extraterrestrial dust. 

This appendix describes briefly the dissolution procedures for some of the more common inorganic sample types. The use of an internal standard is discussed in Section 13.3. 

Table 14.5 Single-vessel dissolution of inorganic sample using HF HN03 H20...

For minerals and inorganic samples, low temperature is almost useless to improve structure solution and only marginally relevant to improve the refinement, unless dealing with host-guest materials like zeolites. In facts, for harder materials ambient temperature is already quite comparable and sometimes lower than the Debye temperature. Therefore, resolution is seldom a limitation for structure refinement of minerals at ambient temperature. On the contrary, for macromolecules and especially for proteins, the low temperature significantly increases the number of... 

Mass spectrometry has gradually become an irreplaceable method for the investigation of compound structures. It is also applied to the determination of the elemental composition of inorganic samples (ICP/MS). When combined with chromatography for the separation of compounds, MS can be used to study mixtures of molecular species. The on-line coupling of these techniques, GC/MS, constitutes one of the best methods of analysis for mixtures and samples containing trace amounts of analyte. 

A wide range of chemical changes are possible. For inorganic samples, controlling the pH can be useful in preventing chemical reactions. For example, metal ions may oxidize to form insoluble oxides or hydroxides. The sample is often acidified with HNO3 to a pH below 2, as most nitrates are soluble, and excess nitrate prevents precipitation. Other ions, such as sulfides and cyanides, are also preserved by pH control. Samples collected for NH3 analysis are acidified with sulfuric acid to stabilize the NH3 as NH4SO4. 

Inorganic samples, soils, sediments, ores, rocks, and minerals may be digested in dilute or concentrated acids or mixtures of acids, which may be sufficient to leach out the analytes. However, if total dissolution is required,... 

The choice of acid to be used depends on the sample. Relatively soluble inorganic samples, salts, active metals, or alloys may be dissolved in water or dilute acid. Electropositive metals will also dissolve in dilute acid, although aluminum may need a trace of mercuric chloride added to prevent the formation of an impervious oxide layer. 

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