Researchers from Spain and France found a complex dependency of the analytical results obtained by inductively coupled plasma optical emission spectrometry (ICP-OES) for silicon from the silicon-compound being present in the sample.
Background: 
The inductively coupled plasma (ICP) is known as a very robust excitation and ionization source for ICP-OES and ICP-MS. One of its often praised features is the absence of any important influence of the analyte species on its response. In general, this allows the use of a single element species as a calibrant for standardization of the element response of the system. This is especially important for quantification in speciation analysis, where even the determination of unknown element species is targeted.
Photo: Optical viewing zones within an ICPThe new study:Researchers from Spain and France investigated the response of different ICP-OES systems with axial and radial viewing optics and also different sample introduction systems for different silicon compounds. To mimic the situation of petrochemical analysis, solutions containing sixteen different silicon organic compounds with the same silicon concentration were prepared in xylene. The studied compounds were: six
siloxanes, nine
silanes and a silicate. Their boiling points ranged from 101 °C (hexamethyldisiloxane) to 310 °C (2,3,4-(epoxycyclohexyl)ethyltrimetoxysilane).
The results they obtained with different sample introduction systems indicated that the ICP-OES signal depended strongly on the silicon compound and the sample introduction system in use. Thus, for a commonly used sample introduction system consisting of a cross-flow pneumatic nebulizer coupled to a Ryton double pass spray chamber, the signal varied by a factor of up to 17, depending on the compound. For most studied cases, some siloxanes yielded higher emission intensities than silanes.
Both aerosol and plasma diagnostic experiments were carried out to elucidate the origin of such behavior. The results indicated that the different response is at least in part a result of differences in the aerosol transport efficiency of the Si-species. The distribution of the analyte species over the gaseous, fine aerosol and coarse aerosol droplets depends on the analyte species. Therefore, spraychambers with a lower transport efficiency such as the double-pass chamber showed more pronounced effects than total consumption systems. The importance of this study also lies in the fact that matrix effects caused on silicon cannot be corrected for by means of internal standardization or standards additions when analyzing petroleum samples.
Since the observed effects could be traced back to the sample introduction system that is shared between ICP-OES and ICP-MS, it is expected that similar effects can be observed also in ICP-MS.
Michael Sperling
Original study:
Raquel Sánchez, José-Luis Todolí, Charles-Philippe Lienemann, Jean-Michel Mermet,
Effect of the silicon chemical form on the emission intensity in inductively coupled plasma atomic emission spectrometry for xylene matrices, J. Anal. At. Spectrom., 24/4 (2009) 391-401.
DOI: 10.1039/b806594m
Related studies:
Raquel Sánchez, José Luis Todolí, Charles-Philippe Lienemann, Jean-Michel
Mermet,
Minimization of the effect of silicon chemical form in xylene on ICP-AESperformance, J. Anal. At. Spectrom., 24/10 (2009) 1382-1388.
DOI: 10.1039/b906568g
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Related EVISA Resources: Brief summary: ICP-MS: A versatile detection system for speciation analysis Link Database: All about silicon
Related EVISA News December 15, 2006, Speciation matters even if the interest is in total element concentration
last time modified: May 22, 2024
