Plasma emission spectroscopy interferences

An example of the application of dynamic ion-exchange chromatography for the direct separation of rare earths is shown in Fig. 1.22. The sample was a sodium hydroxide leach solution from an aluminium processing operation and contained high concentrations of sodium, iron and aluminium. Due to matrix interference, these solutions could not be accurately analysed by inductively coupled plasma emission spectroscopy. Fig. 1.22 shows the chromatogram when the sample was separated by dynamic ion-exchange... 

Several methods are available for the determination of total aluminum in biological and other materials. Chemical and physicochemical methods are in most practical situations insensitive and inaccurate X-ray fluorescence is specific but lacks sensitivity neutron activation analysis is complex and subject to interferences, although it is a very sensitive technique. Nuclear magnetic resonance spectroscopy is not very sensitive but useful to get information on speciation [33]. Graphite furnace atomic absorption spectrometry (GFAAS) is the most widely used technique and can produce reliable results, provided that the matrix effects are recognized and corrected. Savory and Wills [19] reviewed chemical and physicochemical methods for the determination of aluminum in biological materials, e.g. X-ray fluorescence, neutron activation analysis, atomic emission spectrometry, flame emission, inductively coupled plasma emission spectroscopy, and AAS. 

Several different methods have been utilized for measuring iron in these biological samples. However, spectrophotometry is the most widely used because it does not require unusual equipment and is readily amenable to automation. Atomic absorption spectrometry is effectively used for tissue and urine analyses [33-35], but unreliable results are obtained with serum due to sensitivity limitations as well as matrix and hemoglobin interferences [35]. Other methods utilizing inductively coupled plasma emission spectroscopy [36], coulometry [37], proton induced X-ray emission [38], neutron activation analysis [39], radiative energy attenuation [40], and radiometry with Fe [41] have been described but, with the exception of coulometry, have not become standard procedures in the clinical chemistry laboratory, inasmuch as sophisticated and expensive instrumentation is required in some instances. However, some of them, e.g., neutron activation, may be the method of choice for definitive accurate analysis. 

Kola H, Peramaki P, Valimaki I. Correction of spectral interferences of calcium in sulfur determination by inductively coupled plasma optical emission spectroscopy using multiple hnear regression. J. Anal. At. Spectrom. 2002 17 104-108. 

The inductively coupled plasma13 shown at the beginning of the chapter is twice as hot as a combustion flame (Figure 21-11). The high temperature, stability, and relatively inert Ar environment in the plasma eliminate much of the interference encountered with flames. Simultaneous multielement analysis, described in Section 21 1. is routine for inductively coupled plasma atomic emission spectroscopy, which has replaced flame atomic absorption. The plasma instrument costs more to purchase and operate than a flame instrument. 

Metals can be conveniently determined by emission spectroscopy using inductively coupled plasma (ICP). A great advantage of ICP emission spectroscopy as applied to environmental analysis is that several metals can be determined simultaneously by this method. Thus, multielement analysis of unknown samples can be performed rapidly by this technique. Another advantage is that, unlike atomic absorption spectroscopy, the chemical interference in this method is very low. Chemical interferences are generally attributed to the formation of molecular compounds (from the atoms) as well as to ionization and thermochemical effects. The principle of the ICP method is described below. 

For ICP-OES-MS (inductively coupled plasma-optical emission spectroscopy-mass spectroscopy) work, the desolvator will remove oxide and hydride polyatomic ion interferences, i.e. ArO+ is reduced 100 fold, which allows for improved detection of Fe. The solvent loading reduction is caused by volatiles passing through the walls of a tubular microporous Teflon PTFE membrane. The argon gas removes the solvent vapour from the exterior of the membrane. Solvent-free analytes remain inside the membrane and are carried to the plasma for atomisation and excitation. 

C-3 Interferences in Plasma and Flame Atomic Emission Spectroscopy... 

Argon plasma offers a number of advantages as a source for emission spectroscopy. Argon is an inert gas and will not react with the sample so chemical interference is greatly reduced. At plasma temperatures, atomization is complete and elemental spectra do not reflect molecular components. Detection limits are high for most elements. Accuracy and precision are excellent. In addition, ICP/OES requires less sample preparation and less sample amount than other techniques. 

Inductively coupled plasma (ICP) emission techniques can be used to measure selenium concentrations in air. ICP techniques offer multielement capabilities, but instrumentation is costly and background interference can be a problem (Koirtyohann and Morris 1986). The NIOSH-recommended method for determining selenium in air is inductively coupled argon plasma atomic emission spectroscopy (NIOSH... 

Once in solution, the preferred method for measurement of boron is inductively coupled plasma atomic emission spectroscopy (ICP-AES) or inductively coupled plasma mass spectrometry (ICP-MS). The most widely used nonspectrophotometric method for analysis of boron is probably ICP-MS because it uses a small volume of sample, is fast, and can detect boron concentrations down to 0.15 pgL . When expensive ICP equipment is not available, colorimetric or spectrophotometric methods can be used. However, these methods are often subject to interference (e.g., nitrate, chloride, fluoride), and thus must be used with caution. Azomethine-H has been used to determine boron in environmental samples (Lopez et al. 1993), especially water samples. Another simple, sensitive spectrophotometric method uses Alizarin Red S (Garcia-Campana et al. 1992). 

In atomic emission spectroscopy flames, sparks, and MIPs will have their niche for dedicated apphcations, however the ICP stays the most versatile plasma for multi-element determination. The advances in instrumentation and the analytical methodology make quantitative analysis with ICP-AES rather straightforward once the matrix is understood and background correction and spectral overlap correction protocols are implemented. Modern spectrometer software automatically provides aids to overcome spectral and chemical interference as well as multivariate calibration methods. In this way, ICP-AES has matured in robustness and automation to the point where high throughput analysis can be performed on a routine basis. 

Inductively coupled plasma (ICP) ionization has currently assumed a more prominent role in the field of elemental and isotopic analysis [1,2,14]. It is apphcable to solid-state as well as to solution-phase samples. A plasma is defined as a form of matter that contains a significant concentration of ions and electrons. The heart of this technique is a plasma torch, first developed as an efficient source for optical emission spectroscopy (OES) [15,16]. Multielement analysis with OES has, however, some serious shortcomings, such as complicated spectra, spectral interferences, high background levels, and inadequate detection of some rare-earth and heavy elements. The high ionization efficiency (>90%) of ICP for most elements is an attractive feature for its coupling to mass spectrometry. 

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. 

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