Solid atomic emission spectroscopy

To examine a sample by inductively coupled plasma mass spectrometry (ICP/MS) or inductively coupled plasma atomic-emission spectroscopy (ICP/AES) the sample must be transported into the flame of a plasma torch. Once in the flame, sample molecules are literally ripped apart to form ions of their constituent elements. These fragmentation and ionization processes are described in Chapters 6 and 14. To introduce samples into the center of the (plasma) flame, they must be transported there as gases, as finely dispersed droplets of a solution, or as fine particulate matter. The various methods of sample introduction are described here in three parts — A, B, and C Chapters 15, 16, and 17 — to cover gases, solutions (liquids), and solids. Some types of sample inlets are multipurpose and can be used with gases and liquids or with liquids and solids, but others have been designed specifically for only one kind of analysis. However, the principles governing the operation of inlet systems fall into a small number of categories. This chapter discusses specifically substances that are normally liquids at ambient temperatures. This sort of inlet is the commonest in analytical work. 

For inductively coupled plasma atomic emission spectroscopy (ICP-AES) the sample is normally in solution but may be a fine particulate solid or even a gas. If it is a solution, this is nebulized, resulting in a fine spray or aerosol, in flowing argon gas. The aerosol is introduced into a plasma torch, illustrated in Figure 3.21. 

Fig. 2. Solid-phase arsenic in ppm versus depth in m from a continuous core. The core consists of clayey silt to depth of 28 m, and fine sand thereafter with a silt horizon at 34 m depth. As was measured by digestion with an HCI-HNO3-H2O aqua regia solution followed by inductively coupled plasma mass spectrometry and inductively coupled plasma atomic emission spectroscopy analysis.

The amount of polymer adsorbed on each sample was measured by pressure filtration through a 0.1 m filter, followed by analysis of the filtrate for residual polymer by gel permeation chromatography with refractive index determination. Particle zeta potentials were measured by taking a small sample of the solids from the centrifuge and re-suspending them in the supernatant prior to analysis in a Malvern Instruments Zetasizer . The concentration of all other types of ions in the supernatant was analysed by ICP atomic emission spectroscopy. 

Tin is readily measured in multielement analyses of air, water, and solid waste samples by inductively coupled plasma atomic emission spectroscopy. For individual analyses of tin, direct aspiration atomic absorption spectroscopy is usually used. Organotin can be extracted from environmental samples and determined by atomic spectrometric methods or gas chromatography, usually after derivatization. 

Figure 11.4 Ion binding to a P4-P6 mutant that does not exhibit specific Mg2"1" binding in the ion core. The number of excess Mg2"1" ions was measured using a fluorescence indicator (circles) and atomic emission spectroscopy (squares) by Das et al. (2005) in 2 M NaCl background. Theoretical predictions were obtained from PB calculations using the PDB coordinates (dun, solid lines) or the reconstructed bead model with uniformly assigned charges (Lipfert et al., 2007b) (thick, dashed lines). Figure adapted from reference Bai et al. (2007).

Many metal analyses are carried out using atomic spectroscopic methods such as flame or graphite furnace atomic absorption or inductively coupled plasma atomic emission spectroscopy (ICP-AES). These methods commonly require the sample to be presented as a dilute aqueous solution, usually in acid. ICP-mass spectrometry requires similar preparation. Other samples may be analyzed in solid form. For x-ray fluorescence, the solid sample may require dilution with a solid buffer material to produce less variation between samples and standards, reducing matrix effects. A solid sample is also preferred for neutron activation analyses and may be obtained from dilute aqueous samples by precipitation methods. 

An example of a noncovalent attachment of a metal-phosphine complex to a solid support is presented in Figure 31, as reported by Bianchini et al. (120). The complex is attached via a sulfonated variant of the "triphos" ligand, which is known for its successful application in several catalytic reactions. The ligand is attached to the silica by an ionic bond, which is stable in the absence of water. The catalyst was used for the hydroformylation of styrene and of hex-1-ene in batch mode and showed moderate activity. The triply coordinated rhodium atom is strongly boimd although the conditions were rather harsh (120 °C, 30 bar) the concentration of leached metal measured by atomic emission spectroscopy was at most at the parts per million level. However, for commercial applications, for example, in a process such as hydroformylation of bulk products, these concentrations should be less than 10 ppb 111,121). 

In the application of atomic emission spectroscopy for quantitative analysis, samples must be prepared in liquid form of a suitable solvent unless it is already presented in that form. The exceptions are solids where samples can be analysed as received using rapid heating electro-thermal excitation sources, such as graphite furnace heating or laser ablation methods. Aqueous samples, e.g. domestic water, boiler water, natural spring, wines, beers and urines, can be analysed for toxic and non-toxic metals as received with... 

The catalyst employed in this work was a commercial Ru/C catalyst (Aldrich, ref 20,618-0). Inductive coupled plasma-atomic emission spectroscopy (ICP-AES) was used to measure the ruthenium content in the catalyst after dissolution of the solid in an acidic solution, and for the determination of the concentration of various metal ions in the solution after the oxidation treatment. The sizes of ruthenium particles were measured by high resolution electron microscopy (JEOL JEM 2010). 

Chapter 11 details the relevant methods of analysis for both metals and organic compounds. For elemental (metal) analysis, particular attention is given to atomic spectroscopic methods, including atomic absorption and atomic emission spectroscopy. Details are also provided on X-ray fluorescence spectrometry for the direct analysis of metals in solids, ion chromatography for anions in solution, and anodic stripping voltammetry for metal ions in solution. For organic compounds,... 

EPA. 1986b. Inductively coupled plasma atomic emission spectroscopy—method 6010. In Test methods for evaluating solid waste. 3rd ed. SW-846. Washington, DC U.S. Environmental Protection Agency, Office of Solid Waste and Emergency Response. 

The separation of yttrium from the lanthanides is performed by selective oxidation, reduction, fractionated crystallization, or precipitation, ion-exchange and liquid-liquid extraction. Methods for determination include arc spectrography, flame photometry and atomic absorption spectrometry with the nitrous oxide acetylene flame. The latter method improved the detection limits of yttrium in the air, rocks and other components of the natural environment (Deuber and Heim 1991 Welz and Sperling 1999).Other analytical methods useful for sensitive monitoring of trace amounts of yttrium are X-ray emission spectroscopy, mass spectrometry and neutron activation analysis (NAA) the latter method utilizes the large thermal neutron cross-section of yttrium. For high-sensitivity analysis of yttrium, inductively coupled plasma atomic emission spectroscopy (ICP-AES) is especially recommended for solid samples, and inductively coupled plasma mass spectroscopy (ICP-MS) for liquid samples (Reiman and Caritat 1998). 

Since only the electronic levels of the sample are probed with this technique, many parameters of interest to the material cannot be direcdy assessed. For example, morphology or structural information of the material cannot be determined through luminescence measurements. In addition, the specific nature and location of the observed defects described above cannot be determined without more sophisticated luminescence microscopy measurements. Also, the material must be inherently luminescent to provide any useful information from this technique. This luminescence may not be visible at ambient temperatures, however some sample cooling might be required to obtain usable data. With these limitations in mind, however, the solid-state luminescence technique has many benefits. Many of these advantages are also commonly profiled in molecular or atomic emission spectroscopy treatments. Luminescence is one of the most sensitive of analytical techniques, with a large linear concentration range and very low limits of detection. 

The following ionization sources are used mainly in inorganic (atomic) MS, where the elemental composition of the sample is desired. The glow discharge (GD) and spark sources are used for solid samples, while the inductively coupled plasma (ICP) is used for solutions. All three sources are also used as atomic emission spectroscopy sources they are described in more detail with diagrams in Chapter 7. 

The most common analytical procedures for measuring cadmium concentrations in biological samples use the methods of atomic absorption spectroscopy (AAS) and atomic emission spectroscopy (AES). Methods of AAS commonly used for cadmium measurement are flame atomic absorption spectroscopy (FAAS) and graphite furnace (or electrothermal) atomic absorption spectroscopy (GFAAS or ETAAS). A method for the direct determination of cadmium in solid biological matrices by slurry sampling ETAAS has been described (Taylor et al., 2000). 

Although most samples are commonly presented as liquids for atomic emission spectroscopy, direct solid sample analysis has the advantage that no major pretreatment or dissolution steps are required [44]. This minimises dilution errors or contamination from reagents and reduces the reagent and manpower cost per sample. In addition, improved detection Hmits may be obtained if microsamples or microanalysis are possible without any further dilution. However, the analyst has to ensure that the solid material sampled is representative of the bulk material. ICP-AES has generally a remarkable tolerance for total dissolved sohds compared to ICP-MS or flame AAS so that, depending on the overall matrix, between 2 and 25 % suspended sohds can be coped with. Therefore, most of the sohd sample introduction devices described below are dedicated for ICP-AES. 

The second approach named laser-induced breakdown spectrometry (LIBS) is based on atomic emission spectroscopy. In this method, a laser is focused on a solid sample and forms a microplasma that emits light characteristics of the elemental composition of the sample. The emitted light is collected, spectrally resolved, and detected to monitor concentrations of elements via their unique spectral signatures. When calibrated, the method can also provide quantitative measurements. 

Figure 7.7 (a) Diagram of a direct current arc source. The solid sample is packed into the cupped end of the lower graphite electrode. The graphite counterelectrode is also shown. (From Hareland, W., Atomic emission spectroscopy, in Ewing, G.W. ed.. Analytical Instrumentation Handbook, 2nd edn., Marcel Dekker, Inc., New York, 1997. With permission.) (b) A schematic of the lower electrode used to hold the sample. 

Figure 6.36 shows a variety of gas-phase techniques that have been used to synthesize 0-D nanoparticles. Radio frequency plasma sources have long been used for quantitative analysis by atomizing component species in liquid or solid samples - a technique referred to as inductively-coupled plasma atomic emission spectroscopy (ICP-AES). The extreme energy of an ICP may also be exploited to vaporize precursor sources to afford the growth of nanoparticles (Figure 6.36a). In this system, the nanoparticle size/morphology would be mostly controlled by the concentration of precursor in the plasma, and the rate of cooling - a function of its distance from the plasma source.

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