Sequential ICP-OES

Bauer G, Wegscheider W, Ortner HM (1991b) Selectivity and error estimates in multivariate calibration application to sequential ICP-OES. Spectrochim Acta 46B 1185... 

In Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), a gaseous, solid (as fine particles), or liquid (as an aerosol) sample is directed into the center of a gaseous plasma. The sample is vaporized, atomized, and partially ionized in the plasma. Atoms and ions are excited and emit light at characteristic wavelengths in the ultraviolet or visible region of the spectrum. The emission line intensities are proportional to the concentration of each element in the sample. A grating spectrometer is used for either simultaneous or sequential multielement analysis. The concentration of each element is determined from measured intensities via calibration with standards. 

The plasma is maintained at a temperature of 10 000° C by an external radio frequency current, as described in Section 3.3. At this temperature, many molecular species are broken down, and approximately 50% of the atoms are ionized. So far this is identical to ICP-OES, but for ICP-MS we are not interested in the emission of electromagnetic radiation, but rather in the creation of positive ions. To transfer a representative sample of this plasma ion population to the mass spectrometer, there is a special interface between the plasma and the mass spectrometer. This consists of two sequential cones... 

ICP-OES is an analytical system that can do simultaneous or sequential determination of up to 50 elements at all concentration levels with a high degree of accuracy and precision. Excellent vaporization-atomization-excitation-ionization is obtained with an argon-supported ICP operated at atmospheric pressure. The emitted spectra is observed with a polychromator or a scanning spectrometer may be used depending on whether simultaneous or sequential determinations are desired. This atomization-excitation process does not exhibit interelenent effects often seen in AAS, and ppb range detection is routine. Effective nebulization of samples needs to be improved on however, ICP and direct-current (DC) plasmas are extremely effective atomization sources that provide the most effective instrumental technique for simultaneous elemental analysis. 

Fig. 101. Precision achievable in the analysis of high-temperature superconducting powders by sequential and simultaneous ICP-OES [402],...

ICP/OES can be conducted either simultaneously or sequentially. Simultaneous instruments rely on a polychromator or direct-reading spectrometer to read up to 60 elements from the same sample excitation. Sequential analyses use a computer-controlled, scanning monochromator system. The light emitted by the sample in the plasma source is focused on the entrance slit of the monochromator and the spectrum is scanned through the region of interest. Typically, it is possible to determine several elements per minute in the sample in a sequential spectrometer. 

In terms of metals analysis, the availability of inductively coupled plasma mass spectrometry (ICP-MS) is now providing better detection limits for important elements and wider simultaneous determinand suites than ICP-OES, though it is not reliable for the measurement of some contaminants such as mercury. Applied research into sequential extraction methods and physiologically based extraction techniques is informing our understanding of the role and importance of contaminant bioavailability in risk assessments.29,36,37... 

ICP-OES is commercially available as either a scanning instrument (elements determined sequentially) or a fixed-channel instrument (elements determined simultaneously). The simultaneous design is usually faster, but both systems offer exceptional sample throughput capability and can determine up to 20-30 elements in a few minutes. However, when determination of only a few elements are required, ICP probably isn t the best technique because of the relatively long read delay times of60-90 s required to wash-out/wash-in a sample and wait for the signal to reach equilibrium. 

With the aid of an internal standard, fluctuations in sample delivery in particular and, to a certain extent, changes in excitation conditions can also be compensated for. To appreciate the full benefit of internal standardization, the intensities of the analytical line and the internal standard line, and in trace determinations also of the spectral background near the analytical line, should be measured simultaneously, which can easily be done in the case of a CCD spectrometer. The full analytical precision of ICP-OES can thus be obtained. This can be demonstrated by the determination of the main components, as is required in stoichiometric determinations of advanced ceramics. After optimizing the sample dissolution procedure in the case of silicon-boron-carbo-nitride, which can be speeded up by microwave-assisted decomposition with acids [455], silicon at the 60% level could be determined with a sequential spectrometer with an absolute error of analysis (standard deviation including replicated analyses as well as decompositions) of 1% or better. 

A Atomic Absorption Anaiysis and inductiveiy Coupied Piasma Anaiysis The total metal loading of Fe and Ni in the membrane was analyzed using Varian Fast Sequential AA spectrometer (SpectraAA 220/FS) interfaced with SpectraAA V-3.0 for quantitative analysis. The Pd content in the membrane was determined using Varian Vista-Pro Simultaneous ICP-OES machine. The use of ICP for Pd analysis is due to the expected low Pd content in the membrane that required an analytical method with high sensitivity at low detection limit. Five-point linear calibration curves for Fe, Ni, and Pd were constructed and the results were correlated accordingly. The calibration curves were periodically checked with solutions appropriately diluted using standards obtained from Ultra Scientific (Pd = 1000 mg/L) and Fisher Scientific (Fe and Ni = 1000 mg/L). 

---