Ion Chromatography - Inductively Coupled Plasma Interfaces (LC/ICP-AAS) 1



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Courtesy of the Hewlett-Packard Company.


Figure 47.Mass Spectrum Showing Multiple Charged Peaks of a Parent Ion


The electrospray interface is very popular but the device does have some drawbacks. The electrospray system may not work well with mobile phases having high water content (and so may not function well under certain circumstances with an ion chromatograph) and as many separations employ reverse phase distribution systems, this limitation can be serious. However, certain interface designs work better than others with aqueous mixtures, and electrospray nebulizers can be designed specifically to handle high water content mobile phases. It follows, that the efficacy of a selected interface for a particular analyses must be ascertained before purchase.


Inductively Coupled Plasma Interfaces (LC/ICP-AAS) (Inductively Coupled Plasma Atomic Absorption Spectroscopy)


The LC/ICP-AAS combined system provides a flexible separating system supported by an element specific detector with very low detection limits, for most elements (usually in the sub ppm concentration levels).. One problem associated with this combination is its intolerance to commonly used organic solvents used in mobile phase mixtures. Consequently, most LC/ICP-AAS systems are employed with ion exchange columns, which largely involve the use of aqueous mobile phase. If mobile phases containing acetonitrile or tetrahydrofuran are to be used, a change in interface design will be necessary to accommodate these solvents.


Figure 48. The Liquid Chromatography/Inductively Coupled Plasma Mass Spectrometer (LC/ICPMS) Instrument


The inductively coupled plasma ionization source is similar to the inductively coupled plasma (ICP) torch employed in atomic spectroscopy. The column eluent is first nebulized and the atomized eluent passes through a spray chamber and then enters an ICP torch. On leaving the jet of the torch, the gas and ions enter an expansion chamber through a cooled sampling cone.