Spectroscopic analysis Emission Spectrometry

Owing to their superior fluorescent yield, heavy elements ordinarily yield considerably more intense XRF bands than the light elements. This feature can be exploited to determine the concentration of inorganic species in a sample, or the concentration of a compound that contains a heavy element in some matrix. Many potential XRF applications have never been developed owing to the rise of atomic spectroscopic methods, particularly inductively coupled plasma atomic emission spectrometry [74]. Nevertheless, under the right set of circumstances, XRF analysis can be profitably employed. 

Each spectroscopic method has a characteristic application. For example, flame photometry is still applicable to the direct determination of Ca and Sr, and to the determination of Li, Rb, Cs and Ba after preconcentration with ion-exchange resin. Fluorimetry provides better sensitivities for Al, Be, Ga and U, although it suffers from severe interference effects. Emission spectrometry, X-ray fluorescence spectrometry and neutron activation analysis allow multielement analysis of solid samples with pretty good sensitivity and precision, and have commonly been applied to the analysis of marine organisms and sediments. Recently, inductively-coupled plasma (ICP)... 

An inductively-coupled plasma (ICP) is an effective spectroscopic excitation source, which in combination with atomic emission spectrometry (AES) is important in inorganic elemental analysis. ICP was also considered as an ion source for MS. An ICP-MS system is a special type of atmospheric-pressure ion source, where the liquid is nebulized into an atmospheric-pressure spray chamber. The larger droplets are separated from the smaller droplets and drained to waste. The aerosol of small droplets is transported by means of argon to the torch, where the ICP is generated and sustained. The analytes are atomized, and ionization of the elements takes place. Ions are sampled through an orifice into an atmospheric-pressure-vacuum interface, similar to an atmospheric-pressure ionization system for LC-MS. LC-ICP-MS is extensively reviewed, e.g., [12]. 

The very low concentrations expected in the analysis of trace elements in offshore and coastal Antarctic sea water can be also detected thanks to the high detection power of spectroscopic techniques such as Electrothermal Atomic Absorption Spectrometry (ETA-AAS) and Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) or ICP-MS. However, the saline matrix which constitutes the ideal medium in which to perform electrochemical measurements poses severe problems to the direct analysis of sea water because of possible signal suppression and/or undesired matrix effects. 

Part V covers spectroscopic methods of analysis. Basic material on the nature of light and its interaction with matter is presented in Chapter 24. Spectroscopic instruments and their components are described in Chapter 25. The various applications of molecular absorption spectrometric methods are covered in some detail in Chapter 26, while Chapter 27 is concerned with molecular fluorescence spectroscopy. Chapter 28 discusses various atomic spectrometric methods, including atomic mass spectrometry, plasma emission spectrometry, and atomic absorption spectroscopy. 

The oldest of the spectroscopic radiation sources, a flame, has a low temperature (see Section 4.3.1) but therefore good spatial and temporal stability. It easily takes up wet aerosols produced by pneumatic nebulization. Flame atomic emission spectrometry [265] is still a most sensitive technique for the determination of the alkali elements, as eg. is applied for serum analysis. With the aid of hot flames such as the nitrous oxide-acetylene flame, a number of elements can be determined, however, not down to low concentrations [349]. Moreover, interferences arising from the formation of stable compounds are high. Further spectral interferences can also occur. They are due to the emission of intense rotation-vibration band spectra, including the OH (310-330 nm), NH (around 340 nm), N2 bands (around 390 nm), C2 bands (Swan bands around 450 nm, etc.) [20], Also analyte bands may occur. The S2 bands and the CS bands around 390 nm [350] can even be used for the determination of these elements while performing element-specific detection in gas chromatography. However, SiO and other bands may hamper analyses considerably. 

There are three main atomic spectroscopic techniques that are used for the analysis of acid digests atomic absorption spectrometry (AAS), inductively coupled plasma-atomic emission spectrometry (ICP-AES) and atomic fluorescence spectrometry (AFS). Of these, AAS and ICP-AES are the most widely used. Our discussion will deal with these techniques and also an affiliated technique, inductively coupled plasma mass spectrometry (ICP-MS). 

Electrothermal atomic absorption represents a suitable instrumental technique for the analysis of elements in petroleum products [1-5]. The technique shows very low detection limits, similar to or even better than those found for other spectroscopic techniques, such as Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) [6] and ICP-Mass Spectrometry (ICP-MS) [7-12]. Some problems were evidenced in the use of ETAAS when elements like Ni [3] and Pb [13] are analyzed, due to the different behavior of organo-metallic species during the thermal treatment of standards and samples. 

The earliest methods for tin analysis, namely, gravimetric and titrimetric methods, are now mainly of historical interest. Being essentially macro methods, laborious in application, they are limited and mainly useful for levels of tin in food in the 50-100 ppm range or above. The use of colorimetric analysis is associated with problems of specificity, sensitivity, and stability of the tin complexes formed. Nowadays, methods for tin analysis in biological media include the various atomic spectroscopic techniques (atomic absorption spectrometry, atomic emission spectroscopy, and inductively coupled plasma atomic emission spectrometry) as well as electrochemical and neutron activation procedures. 

The oldest spectroscopic radiation sources operate at low temperature (Section 21.5.3.1), but have good spatial and temporal stability. They readily take up wet aerosols produced by pneumatic nebulization. Flame atomic emission spectrometry [162] is still a most sensitive technique for determination of the alkali metals, e.g., for serum analysis. With the aid of hot flames such as the nitrous oxide - acetylene flame, a number of elements can be effectively excited, but cannot be determined at low concentration. Interference arising from the formation of stable compounds is high. 

Nearly every area of measurement science can boast of progress in measuring ever-smaller quantities of chemicals, but several stand out in their stunning trace-analysis capabilities. Trace-metal analysis has come to be dominated by methods that volatilize the sample and then either measure its spectroscopic emission or absorption, or measure the masses of the gaseous metal ions using mass spectrometry. Volatilization is accomplished by various thermal means that include flames, furnaces, and inductively coupled or microwave plasmas. The com-... 

GFAAS = graphite furnace (flameless) atomic absorption spectroscopy TLC = thin layer chromatography HFP-AES = high frequency plasma-atomic emission spectroscopy NAA = neutron atomic analysis ICP-AES = inductively coupled plasma-atomic emission spectroscopy AAS = atomic absorption spectrometry GSE = graphite spectroscopic electrode UV = ultraviolet spectrophotometry PD = photodensitometer and (3,5-diBr-PADAP) = 2(-3,-5-dibromo-2-pyridylazo)-5- diethyl-ami nophenol. 

Mass spectrometry (MS), also covered in this chapter, is not a spectroscopic technique, because it does not measure absorption or emission of light. A mass spectrometer bombards molecules with electrons and breaks the molecules into fragments. Analysis of the masses of the fragments gives the molecular weight, possibly the molecular formula, and clues to the structure and functional groups. Less than a milligram of sample is destroyed in this analysis. 

Various spectroscopic techniques such as flame photometry, emission spectroscopy, atomic absorption spectrometry, spectrophotometry, flu-orimetry, X-ray fluorescence spectrometry, neutron activation analysis and isotope dilution mass spectrometry have been used for marine analysis of elemental and inorganic components [2]. Polarography, anodic stripping voltammetry and other electrochemical techniques are also useful for the determination of Cd, Cu, Mn, Pb, Zn, etc. in seawater. Electrochemical techniques sometimes provide information on the chemical species in solution. 

In both total and sequential dissolutions, the result is a solution containing the components of rocks and soils. This solution is then analyzed by different methods. Mostly, spectroscopic methods are used atomic absorption and emission spectroscopic methods, ultraviolet, atom fluorescence, and x-ray fluorescence spectrometry. Multielement methods (e.g., inductively coupled plasma optical emission spectroscopy) obviously have some advantages. Moreover, elec-troanalytical methods, ion-selective electrodes, and neutron activation analysis can also be applied. Spectroscopic methods can also be combined with mass spectrometry. 

More common methods for elemental analysis - to determine the elemental contents of a sample - include spectroscopy and spectrometry. Spectroscopy measures changes in atoms that cause a specific light photon to be either absorbed (absorption spectroscopy) or emitted (emission spectroscopy). This light has a precise wavelength or energy, characteristic of a specific element in the periodic table. The simplest (and oldest) form of elemental analysis was not spectroscopic, in fact, but colorimetric. This method was based on the reaction of a strongly colored chemical in a solution. The appearance of a specific color in the solution revealed the identity of the element of interest. If the color intensity is proportional to the amount of that element present, the method can also be used to estimate the amount of the element present. 

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,... 

The application of microtron photon activation analysis with radiochemical separation in environmental and biological samples was described by Randa et al. (2001), and both flame and plasma emission spectroscopic methods are also widely used. A more recently developed technique is that of laser-excited atomic fluorescence spectrometry (LEAFS) (Cheam et al. 1998). 

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