Inductively coupled plasma detectors atomic-emission spectrometry

There is also a standard test method for determination of major and minor elements in coal ash by inductively coupled plasma (ICP)-atomic emission spectrometry (ASTM D-6349). In the test method, the sample to be analyzed is ashed under standard conditions and ignited to constant weight. The ash is fused with a fluxing agent followed by dissolution of the melt in dilute acid solution. Alternatively, the ash is digested in a mixture of hydrofluoric, nitric, and hydrochloric acids. The solution is analyzed by (ICP)-atomic emission spectrometry for the elements. The basis of the method is the measurement of atomic emissions. Aqueous solutions of the samples are nebulized, and a portion of the aerosol that is produced is transported to the plasma torch, where excitation and emission occurs. Characteristic line emission spectra are produced by a radio-frequency inductively coupled plasma. A grating monochromator system is used to separate the emission lines, and the intensities of the lines are monitored by photomultiplier tube or photodiode array detection. The photocurrents from the detector... 

Five different detectors are common in HPLC (1) UV, (2) refractive index (RI), (3) conductivity, (4) inductively coupled plasma atomic emission, and (5) mass spectrometry. A UV detector passes a specific wavelength of UV light... 

L. Ebdon, M. Foulkes and K. O Hanlon, Optimised simultaneous multielement analysis of environmental slurry samples by inductively coupled plasma atomic emission spectrometry using a segmented array charge-coupled device detector. Anal. Chim. Acta, 311, 1995, 123-134. 

AAS = atomic absorption spectrometry GC/FID = gas chromatography/f1ame ignition detector GC/FPD = gas chromatography/f1ame photometric detector ICP/AES = inductively coupled plasma atomic emission spectroscopy ICP/MS = inductively coupled plasma with mass spectrometric detection... 

Ultraviolet-visible (UV-Vis) spectrophotometric detectors are used to monitor chromatographic separations. However, this type of detection offers very little specificity. Element specific detectors are much more useful and important. Atomic absorption spectrometry (AAS), inductively coupled plasma-atomic emission spectroscopy (ICPAES) and inductively coupled plasma-mass spectrometry (ICP-MS) are often used in current studies. The highest sensitivity is achieved by graphite furnace-AAS and ICP-MS. The former is used off-line while the latter is coupled to the chromatographic column and is used on-line . 

As noted earlier, USNs have been employed for sample insertion into atomic spectrometers suoh as flame atomio absorption spectrometry (FAAS) [9,10], electrothermal atomic absorption speotrometry (ETAAS) [11], atomic fluorescence spectrometry (AFS) [12,13], induotively ooupled plasma-atomic emission spectrometry (ICP-AES) [14,15], inductively coupled plasma-mass spectrometry (ICP-MS) [16,17] and microwave induced plasma-atomic emission spectrometry (MIP-AES) [18,19]. Most of the applications of ultrasonic nebulization (USNn) involve plasma-based detectors, the high sensitivity, selectivity, precision, resolution and throughput have fostered their implementation in routine laboratories despite their high cost [4]. 

Much more sensitive and less time-consuming techniques such as mass spectrometry, atomic emission, and atomic absorption are needed for the analysis of pollutants. Detectors such as graphite furnace-atomic absorption spectrometer (GF-AAS), inductively coupled plasma-mass spectrometer (ICP-MS), or inductively coupled plasma-atomic emission spectrometer (ICP-AES) seem to be ideal candidates for the analysis of trace metals because of their very low detection limits. The high temperatures used avoid the need for tedious digestions in many samples. FFF-gas chromatography-mass spectrometry could perhaps be used in the analysis of particular organic molecules. 

Research developing environmental methods might consider the use of AA detection. Perhaps some of the more interesting are detectors that use inductively coupled plasma (ICP) as an energy source and either atomic emission (AE) or mass spectrometry (MS) as the detector. ICP-AE and ICP-MS are well-developed analytical tools. Once of the major advantages of these techniques is that mixture of metals can be analyzed without the need for separation. Thus, workers who use these instruments normally do not think about their use as detectors. However, ICP-AE and ICP-MS cannot determine the oxidation or chemical state of a particular metal ion. Some samples are quite important from a toxicological and environmental standpoint since the... 

As shown in the discussion above, there are a multiplicity of desirable and undesirable features of OID s that impact their general application as detectors in analytical atomic emission spectrometry. It is therefore appropriate to compare, in a critical and objective sense, the experimental figures of merit of these devices vis-a-vis the classical polychromator photomultiplier approach. These comparisons should be performed virtually on a continuing basis because of advances in performances, not only of the array detectors themselves but also in the associated spectroscopic excitation sources. An evaluation of the overall performance figures of merit of OID s when they are employed in conjunction with induction-coupled plasma excitation is of particular current interest because of the popularity that this source is attaining for the simultaneous determination of the elements at all concentration levels. In this paper we present such an evaluation for self-scanned, photodiode array detectors... 

AAS = atomic absorption spectrometry APDC = ammonium pyrrolidine dithiocarbamate APHA = American Public Health Association EPA = Environmental Protection Agency FPD = flame photometric detection ICP/AES = inductivity coupled plasma atomic emission spectroscopy MED = microwave emission detector MIBK = methyl isobutyl ketone NIOSH = National Institute for Occupational Safety and Health XRF = x-ray fluorescence... 

The gas chromatograph may be interfaced with atomic spectroscopic instruments for specific element detection. This powerful combination is useful for speci-ation of different forms of toxic elements in the environment. For example, a helium microwave induced plasma atomic emission detector (AED) has been used to detect volatile methyl and ethyl derivatives of mercury in fish, separated by GC. Also, gas chromatographs are interfaced to inductively coupled plasma-mass spectrometers (ICP-MS) in which atomic isotopic species from the plasma are introduced into a mass spectrometer (see Section 20.10 for a description of mass spectrometry), for very sensitive simultaneous detection of species of several elements. 

In some instances other detectors may be preferred over TCDs. Windsor and Denton [174], e.g., applied inductively coupled plasma atomic emission spectrometry to the elemental analysis of GC effluents. 

Over the years, in trace and major element analysis in general, three detectors which are especially suitable for element-specific detection have been developed inductively coupled plasma mass spectrometry (ICP-MS), inductively coupled plasma atomic emission spectrometry (ICP-AES) and graphite furnace atomic absorption spectrometry (GFAAS). 

Elemental speciation is becoming more and more important, since the environmental toxicity and biological importance of many elements depend on their oxidation states and different chemical forms. It is accepted today that the most reliable approaches for speciation are tandem techniques, such as hybrid analytical methods involving interfeced chromatography/atomic emission spectrometry (AES) or chromatography/inductively coupled plasma-mass spectrometry (ICP-MS). The low level det ion capability of ICP-MS makes it especially attractive as an element-specific chromatographic detector in chromatography. 

In this vein, many appHcations have appeared in the literature on speciation of oxidation states, such as Cr(m)/Cr(VI), Fe(n)/Fe(m), As(III)/As(V), Se(IV)/ Se(VI). Also, FIA techniques have been used to preconcentrate Sn, Hg, and Pb organometallics mainly from natural waters, sediment, and soil extracts. In particular great interest has been focused into the speciation of chromium oxidation states in water samples at very low level (nanograms per liter). A FI system with a minicolumn of acidic preconcentration and inductively coupled plasma optical emission spectrometry (ICP-OES) for final detection was developed for a rapid speciation of Cr(VI) and Cr(III) in waters. On sample injection, Cr(VI) is retained in the alumina column whilst Cr(III) is not passing directly to the atomic detector. Afterwards, the retained Cr(VI) is eluted by injection of ammonium hydroxide, as shown in Figure 5, and its analytical signal of emission in the ICP-OES is registered. 

A range of chromatographic techniques coupled to element specific detectors has been used in speciation studies to separate individual organometallic species (e.g., butyltins, arsenic species) and to separate metals bovmd to various biomolecules. The combination of a chromatographic separation with varying instrumental detection systems are commonly called coupled, hybrid, or hyphenated techniques (e.g., liquid chromatography inductively coupled plasma-mass spectrometry (LC-ICP-MS), gas chromatography-atomic absorption spectroscopy (GC-AAS)). The detection systems used in coupled techniques include MS, ICP-MS, atomic fluorescence spectrometry (AFS), AAS, ICP-atomic emission spectrometry (ICP-AES), and atomic emission detection (AED). 

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