Sample solid samples

Atomization and Excitation Atomic emission requires a means for converting an analyte in solid, liquid, or solution form to a free gaseous atom. The same source of thermal energy usually serves as the excitation source. The most common methods are flames and plasmas, both of which are useful for liquid or solution samples. Solid samples may be analyzed by dissolving in solution and using a flame or plasma atomizer. 

Infrared Sample Preparation Liquid Samples Solid Samples... 

Quantitative analysis MS is used extensively for the quantitative determination of the organic components of liquid and gas samples. Solid samples can be analyzed using laser ablation. 

Problematic samples Scattering samples, solid samples, gaseous samples... 

Some techniques that combine the properties of extraction and cleanup are supercritical fluid extraction (SEE) and matrix solid-phase dispersion (MSPD). Supercritical fluids, i.e., at a temperature and pressure in excess of their critical point, have unique properties for selective extraction of analytes from a sample. Solid samples are mixed with an inert dispersant, such as hydromatrix, and the mixture packed into the cell of the SEE apparatus. The sample is extracted with supercritical CO2, with or without addition of organic modifier, and the extracted analytes may be collected inline or offline on suitable adsorbents (Figure 3). Further cleanup of the sample extract may be performed using SPE. MSPD is based on intimate mixing of animal tissue sample with a bonded silica, such as Cig, and packing of the blended material into a column from which interferences can be eluted by washing with solvents and the analytes eluted using a selective solvent. 

Determination of placenta and autopsy material may be done with various techniques, e.g., FAAS, ICP, GFAAS, all after destmction of the sample. Solid sampling GFAAS can determine the sample directly. The last technique is very suitable for both screening of the whole organ (e.g., the liver) or locating hot spots (e.g., in the kidney cortex). Examples are described in Ref. 23 and in Chap. 14. 

It is also typically used in the digestion process of turbid water samples, sludge samples, solid samples as well as other types of unique samples which require elemental analysis via ICP-MS, ICP-OES, ICP-AES, GFAA and FAA. Typically these digestions use a 50% solution of the purchased HNO3 mixed with Type 1 DI Water. 

Gaseous samples Liquid samples Solid samples... 

The direct analysis of dry solid samples (solid sampling) is even more straightforward than that of slurries and it also constitutes an excellent approach for sample materials that are hard to dissolve. Even for materials that are not so difficult to take into solution, solid sampling offers advantages. Obviously, the necessary amount of sample pre-treatment is decreased, such that the speed of analysis is increased and the risk of contamination and/or analyte losses is reduced. Since the sample is not diluted, lower limits of detection are attainable. Sample manipulation. 

LIF is also used witii liquid and solid samples. For example, LIF is used to detect lJO ions in minerals the uranyl ion is responsible for the bright green fluorescence given off by minerals such as autunite and opal upon exposure to UV light [23],... 

Even for a single radical tire spectral resolution can be enlianced for disordered solid samples if the inliomogeneous linewidth is dominated by iimesolved hyperfme interactions. Whereas the hyperfme line broadening is not field dependent, tire anisotropic g-matrix contribution scales linearly with the external field. Thus, if the magnetic field is large enough, i.e. when the condition... 

IR spectra can be recorded on a sample regardless of its physical state—solid liquid gas or dissolved m some solvent The spectrum m Eigure 13 31 was taken on the neat sample meaning the pure liquid A drop or two of hexane was placed between two sodium chloride disks through which the IR beam is passed Solids may be dis solved m a suitable solvent such as carbon tetrachloride or chloroform More commonly though a solid sample is mixed with potassium bromide and the mixture pressed into a thin wafer which is placed m the path of the IR beam... 

When working with a solid sample, it often is necessary to bring the analyte into solution by dissolving the sample in a suitable solvent. Any solid impurities that remain are removed by filtration before continuing with the analysis. 

Typical examples of solid samples include large particulates, such as those found in ores smaller particulates, such as soils and sediments tablets, pellets, and capsules used in dispensing pharmaceutical products and animal feeds sheet materials, such as polymers and rolled metals and tissue samples from biological specimens. 

Sample Preservation Without preservation, many solid samples are subject to changes in chemical composition due to the loss of volatile material, biodegradation, and chemical reactivity (particularly redox reactions). Samples stored at reduced temperatures are less prone to biodegradation and the loss of volatile material, but fracturing and phase separations may present problems. The loss of volatile material is minimized by ensuring that the sample completely fills its container without leaving a headspace where gases can collect. Samples collected from materials that have not been exposed to O2 are particularly susceptible to oxidation reactions. For example, the contact of air with anaerobic sediments must be prevented. 

Second, the majority of analytical techniques, particularly those used for a quantitative analysis, require that the analyte be in solution. Solid samples, or at least the analytes in a solid sample, must be brought into solution. 

Many continuous extractions involving solid samples are carried out with a Soxhiet extractor (Figure 7.18). The extracting solvent is placed in the lower reservoir and heated to its boiling point. Solvent in the vapor phase moves upward through the tube on the left side of the apparatus to the condenser where it condenses back to the liquid state. The solvent then passes through the sample, which is held in a porous cellulose filter thimble, collecting in the upper reservoir. When the volume of solvent in the upper reservoir reaches the upper bend of the return tube, the solvent and any extracted components are siphoned back to the lower reservoir. Over time, the concentration of the extracted component in the lower reservoir increases. 

A second approach to gravimetry is to thermally or chemically decompose a solid sample. The volatile products of the decomposition reaction may be trapped and weighed to provide quantitative information. Alternatively, the residue remaining when decomposition is complete may be weighed. In thermogravimetry, which is one form of volatilization gravimetry, the sample s mass is continuously monitored while the applied temperature is slowly increased. 

Solid samples are separated by particle size using one or more sieves. By selecting several sieves of different mesh size, particulates with a narrow size range can be isolated from the solid matrix. Sieves are available in a variety of mesh sizes, ranging from approximately 25 mm to 40 )j,m. 

A solid sample is known to consist of approximately equal amounts of two or more of the following soluble salts. 

Transparent solid samples can be analyzed directly by placing them in the IR beam. Most solid samples, however, are opaque and must be dispersed in a more transparent medium before recording a traditional transmission spectrum. If a suitable solvent is available, then the solid can be analyzed by preparing a solution and analyzing as described earlier. When a suitable solvent is not available, solid samples may be analyzed by preparing a mull of the finely powdered sample with a suitable oil. Alternatively, the powdered sample can be mixed with KBr and pressed into an optically transparent pellet. 

Fundamentally, introduction of a gaseous sample is the easiest option for ICP/MS because all of the sample can be passed efficiently along the inlet tube and into the center of the flame. Unfortunately, gases are mainly confined to low-molecular-mass compounds, and many of the samples that need to be examined cannot be vaporized easily. Nevertheless, there are some key analyses that are carried out in this fashion the major one i.s the generation of volatile hydrides. Other methods for volatiles are discussed below. An important method of analysis uses lasers to vaporize nonvolatile samples such as bone or ceramics. With a laser, ablated (vaporized) sample material is swept into the plasma flame before it can condense out again. Similarly, electrically heated filaments or ovens are also used to volatilize solids, the vapor of which is then swept by argon makeup gas into the plasma torch. However, for convenience, the methods of introducing solid samples are discussed fully in Part C (Chapter 17). 

In some cases, it may be convenient to dissolve a solid and present it for analysis as a solution that can be nebulized and sprayed as an aerosol (mixed droplets and vapor) into the plasma flame. This aspect of analysis is partly covered in Part B (Chapter 16), which describes the introduction of solutions. There are vaporization techniques for solutions of solids other than nebulization, but since these require prior evaporation of the solvent, they are covered here. There are also many solid samples that need to be analyzed directly, and this chapter describes commonly used methods to do so. 

These data are typical of lasers and the sorts of samples examined. The actual numbers are not crucial, but they show how the stated energy in a laser can be interpreted as resultant heating in a solid sample. The resulting calculated temperature reached by the sample is certainly too large because of several factors, such as conductivity in the sample, much less than I00% efficiency in converting absorbed photon energy into kinetic energy of ablation, and much less than 100% efficiency in the actual numbers of photons absorbed by the sample from the beam. If the overall efficiency is 1-2%, the ablation temperature becomes about 4000 K. 

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