Hybrid Inductively Coupled Plasma Techniques

Direct introduction of a sample into an ICP produces information only on the total element content. It is now recognised that information on the form of the element present, or trace element speciation, is important in a variety of applications. One way of obtaining quantitative measurement of trace element speciation is to couple the separation power of chromatography to the ICP as a detector. Since the majority of interesting trace metal speciation problems concern either nonvolatile or thermally unstable species, high-performance liquid chromatography (HPLC) becomes the separation method of choice. The use of HPLC as the separation technique requires the introduction of a liquid sample into the ICP with the attendant sample introduction problem. 

2 Flow Injection with Inductively Coupled Plasma 

3 Inductively Coupled Plasma with Atomic Fluorescence Spectrometry 

Atomic fluorescence is the process of radiation activation followed by radiation deactivation, unlike atomic emission which depends on the collisional excitation of the 

Good results have been obtained using a high-power (6 kW) ICP as a source and a low-power ( 1 kW) plasma as an atomiser. 

Atomic fluorescence is the process of radiational activation followed by radiational deactivation, unlike atomic emission, which depends on the collisional excitation of the spectral transition. For this, the ICP is used to produce a population of atoms in the ground state and a light source is required to provide excitation of the spectral transitions. Whereas a multitude of spectral lines from all the accompanying elements are emitted by the atomic emission process, the fluorescence spectrum is relatively simple, being confined principally to the resonance lines of the element used in the excitation source. 

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Besides the universal detector systems, for example electron capture, flame ionisation and thermal conductivity usually coupled with gas chromatographic columns, various other detectors are now being used to provide specific information. For example, the gas chromatograph/mass spectrometer couple has been used for structure elucidation of the separated fractions. The mechanics of this hybrid technique have been described by Message (1984). Other techniques used to detect the metal and/or metalloid constituents include inductively coupled plasma spectrometry and atomic absorption spectrometry. Ebdon et al. (1986) have reviewed this mode of application. The type and mode of combination of the detectors depend on the ingenuity of the investigator. Krull and Driscoll (1984) have reviewed the use of multiple detectors in gas chromatography. 

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. 

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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