Atomic emission spectroscopy selectivity

Colorimetric procedures are often used to determine copper in trace amounts. Extraction of copper using diethyldithiocarbamate can be quite selective (60,62), but the method using dithhone is preferred because of its greater sensitivity and selectivity (50—52). Atomic absorption spectroscopy, atomic emission spectroscopy, x-ray fluorescence, and polargraphy are specific and sensitive methods for the deterrnination of trace level copper. 

When the problem has been defined and needed background information has been studied, it is time to consider which analytical methods will provide the data you need to solve the problem. In selecting techniques, you can refer back to the other chapters in this book. For example, if you want to measure the three heavy metals (Co, Fe, and Ni) that were suspect in the Bulging Drum Problem, you might immediately think of atomic absorption or inductively coupled plasma atomic emission spectroscopies and reread Chapter 8 of this book. How would you choose between them Which would be more accurate More precise Does your lab have both instruments Are they both in working order What if you have neither of them What sample preparation would be needed ... 

Nickel is normally present at very low levels in biological samples. To determine trace nickel levels in these samples accurately, sensitive and selective methods are required. Atomic absorption spectrometry (AAS) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES), with or without preconcentration or separation steps, are the most common methods. These methods have been adopted in standard procedures by EPA, NIOSH, lARC, and the International Union of Pure and Applied... 

Eluate from a chromatography column can be passed through a plasma to atomize and ionize its components and measure selected elements by atomic emission spectroscopy or mass spectrometry. An atomic emission detector directs eluate through a helium plasma in a microwave cavity. Every element of the periodic table produces characteristic emission that can be detected by a photodiode array polychromator (Figure 20-14). Sensitivity for sulfur can be 10 times better than the sensitivity of a flame photometric detector. 

P. B. Farnsworth, M. Wu, M. Tacquard and M. L. Lee, Background correction device for enhanced element-selective gas chromatographic detection by atomic emission spectroscopy , Appl. Spectr. 48 742-746 (1994). 

P. Uden, Element-selective chromatographic detection by atomic emission spectroscopy, Chromatogr. Forum, 17-26 (Nov.-Dee. 1986). 

Table 11.5 Detection Limits (ng/mL = ppb) for Selected Elements by Atomic Absorption Spectroscopy (AAS), Atomic Emission Spectroscopy (AES), and Atomic Fluorescence Spectroscopy (AFS) [6]...

Atomic absorption and atomic emission spectroscopies are praised for their high selectivity in the determination of a wide variety of metal and non-metal elements. On the... 

Actual metal contents were determined by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Metal particles were examined by X-ray diffraction, transmission electron microscopy and CO chemisorption. Details about the procedures used can be found elsewhere [9]. In the case of Pd-Ag/C catalysts, the combination of these three techniques enabled us to obtain the metal particles size and their bulk and surface composition [9, 13]. Finally, the Pt/C catalysts were tested for benzene hydrogenation, and the Pd-Ag/C catalysts were used to study mass transfer in the support during a well-known reaction the selective hydrodechlorination of 1,2-diehloroethane into ethylene. 

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). 

Frank, A. and Petersson, L.R. (1983). Selection of operating conditions and analytical procedure in multi-metal analysis of animal tissues by d.c. plasma-atomic emission spectroscopy, Spectrochim. Acta, 3S, 207. 

The combination of gas chromatography and atomic emission spectroscopy has been used for element selective investigations. The measurements were carried out with an HP G2350A Atomic emission detector (Hewlett Packard Inc.). For structural elucidation the channels carbon (C), hydrogen (H), arsenic (As), chlorine (Cl), oxygen (O) and sulfur (S) have been investigated. Spectral background correction was performed for elimination of interferences. 

Inconspicuous instrumental, environmental, or chemical effects often cause a loss of instrument response. In atomic emission spectroscopy, for example, sensitivity is affected by such instrumental factors as flame temperature, aspiration rate, and slit width. In amperometric measurements, diffusion currents vary with temperature, and a significant loss in sensitivity may occur with a drop in sample temperature. In ion-selective electrode measurements, sensitivity may be affected by chemical effects, such as changes in ionic strength or pH. 

Inductively coupled plasma-atomic emission spectroscopy (ICP-AES) is used for multi-element determinations in blood and tissue samples. Detection in urine samples requires extraction of the metals with a polydithiocarbamate resin prior to digestion and analysis (NIOSH 1984a). Other satisfactory analytical methods include direct current plasma emission spectroscopy and determination by AAS, and inductively coupled argon plasma spectroscopy-mass spectrometry (ICP-MS) (Patterson et al. 1992 Shaw et al. 1982). Flow injection analysis (FIA) has been used to determine very low levels of zinc in muscle tissue. This method provides very high sensitivity, low detection limits (3 ng/mL), good precision, and high selectivity at trace levels (Fernandez et al. 1992b). 

Spectral interference has been well studied and are probably best understood in atomic emission spectroscopy. The usual remedy to alleviate a spectral interference is to either increase the spectral resolution of the spectrometer (which often is not possible with a given type of instrument) or to select an alternative emission line. Three types of spectral interference can be discriminated 1. Direct wavelength coincidence with another emission line, 2. partial overlap of the hne under study with an interfering line in close proximity, 3. a linear or non-linear increase or decrease in background continuum (see Fig. 12.33). 

The metal chelate LLE was much more common 25 years ago when it was the principal means to isolate and recover metal ions from aqueous samples of environmental interest. The complexes were quantitated using a visible spectrophotometer because most complexes were colored. A large literature exists on this subject (14). The technological advances in both atomic absorption and inductively coupled plasma-atomic emission spectroscopy have significntly reduced the importance of metal chelate LLE to TEQA. However, metal chelate LLE becomes important in processes whereby selected metal ions can be easily removed from the aqueous phase. 

ETV may also serve as sample introduction for inductively coupled plasma (ICP)-atomic emission spectroscopy (AES)/MS providing the possibility of in situ sample preparation by selective vaporization of different sample components, using appropriate heating programs. By the reduction/elimination of matrix components, spectral interferences can be minimized and matrix effects in the plasma decreased. 

Numerous specialized liquid chromatography (LC) systems and ion-exchange chromatography in particular have been used to determine a wide selection of minor components that include selenium, arsenic, molybdenum, chromium, and boron. Various detection systems have been employed, including AAS, ICP-atomic emission spectroscopy, electrochemical, and conductivity. A concentrator column can also be included inline. 

Analytical methods AAS, atomic absorption spectroscopy ICP-AES, inductively coupled plasma-atomic emission spectroscopy ICP-MS, inductively coupled plasma-mass spectrometry 1C, ion chromatography ISE, ion selective electrode TEM, transmission electron microscopy. 

In the atomic spectroscopy experiment in Figure 20-1, a liquid sample is aspirated (sucked) through a plastic tube into a flame that is hot enough to break molecules apart into atoms. The concentration of an element in the flame is measured by absorption or emission of radiation. For atomic absorption spectroscopy, radiation of the correct frequency is passed through the flame (Figure 20-2) and the intensity of transmitted radiation is measured. For atomic emission spectroscopy, no lamp is required. Radiation is emitted by hot atoms whose electrons have been promoted to excited states in the flame. For both experiments in Figure 20-2, a monochromator selects the wavelength that will reach the detector. Analyte concentrations at the parts per million level are measured with a precision of 2%. To analyze major constituents, a sample must be diluted to reduce concentrations to the ppm level. Box 20-1 describes an application of atomic emission for space exploration. 

Field measurement of bulk soil lead by XRF instruments will typically require confirmation analysis through some randomly selected subset of further testing by some reference technique in the laboratory A AS, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), or ICP-mass spectrometry (ICP-MS). Other methods are electrochemical in nature, such as ASV and differential pulse polarography. Many soil samples are processed and analyzed directly in the laboratory. 

Quimby, B.D, Diyden, P.C. Sullivan, J.J. (1991), A selective detection of volatile nickel, vanadium and iron porphyrins in crude oils by gas chromatography atomic emission spectroscopy, /. High Res. Chromatogr., 14,110-116. 

Atomic emission spectroscopy is one of the most useful and commonly used techniques for analyses of metals and nonmetals providing rapid, sensitive results for analytes in a wide variety of sample matrices. Elements in a sample are excited during their residence in an analytical plasma, and the light emitted from these excited atoms and ions is then collected, separated and detected to produce an emission spectrum. The instrumental components which comprise an atomic emission system include (1) an excitation source, (2) a spectrometer, (3) a detector, and (4) some form of signal and data processing. The methods discussed will include (1) sample introduction, (2) line selection, and (3) spectral interferences and correction techniques. 

Typical biological fluids include blood and blood serum, blood plasma, urine and saliva. Measurement of calcium in serum was the first analysis to which the technique of AAS was applied and is an obvious example of how FAAS is useful for biomedical analysis. Other specimens e.g. dialysis fluids, intestinal contents, total parenteral nutrition solutions, may be analysed on rare occasions. Elements present at a sufficiently high concentration are lithium and gold when used to treat depression and rheumatoid arthritis respectively, and calcium, magnesium, iron, copper and zinc. Sodium and potassium can be determined by FAAS but are more usually measured by flame atomic emission spectroscopy or with ion selective electrodes. Other elements are present in fluids at too low a concentration to be measured by conventional FAAS with pneumatic nebulization. With other fluids, e.g. seminal plasma, cerebrospinal fluid, analysis may just be possible for a very few elements. 

Of the different techniques for atomic emission spectroscopy (AES) only those which use a flame or an ICP are of any interest for analysis of biomedical specimens. Flame AES, also called flame photometry, has been an essential technique within clinical laboratories for measuring the major cations, sodium and potassium. This technique, usually with an air-propane flame, was also used to determine lithium in specimens from patients who were given this element to treat depression, and was employed by virtually all clinical laboratories throughout the world until the recent development of reliable, rapid-response ion selective electrodes. Biological fluids need only to be diluted with water and in modern equipment the diluter is an integral part of the instrument so that a specimen of plasma or urine can be introduced without any preliminary treatment. 

---