ICP instruments

The nebulization concept has been known for many years and is commonly used in hair and paint spays and similar devices. Greater control is needed to introduce a sample to an ICP instrument. For example, if the highest sensitivities of detection are to be maintained, most of the sample solution should enter the flame and not be lost beforehand. The range of droplet sizes should be as small as possible, preferably on the order of a few micrometers in diameter. Large droplets contain a lot of solvent that, if evaporated inside the plasma itself, leads to instability in the flame, with concomitant variations in instrument sensitivity. Sometimes the flame can even be snuffed out by the amount of solvent present because of interference with the basic mechanism of flame propagation. For these reasons, nebulizers for use in ICP mass spectrometry usually combine a means of desolvating the initial spray of droplets so that they shrink to a smaller, more uniform size or sometimes even into small particles of solid matter (particulates). 

AA and ICP instruments can be equipped with multiple detectors that allow for analysis of more than one element at a time [3,25-29], Recently, an ICP instrument that used microwaves and air or nitrogen as the supporting gas has been made commercially available. Because argon gas is relatively expensive, microwave-based instruments should prove to be significantly less expensive to operate. 

Unlike a flame, in which only a very limited number of metals emit light because of the low temperature, virtually all metals present in a sample emit their line spectrum from the ICP torch. Not only does this make for a very broad application for ICP, but it also means that a given sample may undergo very rapid and simultaneous multielement analysis. With this in mind, it is interesting to consider the options for the optical path for the ICP instrument. 

FIGURE 9.20 An illustration of the optical path for an ICP instrument that utilizes a monochromator for the sequential measurement of spectral lines. 

To exploit the possibility of rapid multi element determinations by modem sequential ICP instruments the pre-concentration procedure must be carried out off-line. Knapp et al. [4i] have developed a microprocessor-controlled preconcentration instrument that performs various preconcentration regimes. In order to demonstrate the options available, trace elements have been concentrated in brines and in standard reference... 

Previous experience in arc and spark emission spectroscopy has revealed numerous spectral overlap problems. Wavelength tables exist that tabulate spectral emission lines and relative intensities for the purpose of facilitating wavelength selection. Although the spectral interference information available from arc and spark spectroscopy is extremely useful, the information is not sufficient to avoid all ICP spectral interferences. ICP spectra differ from arc and spark emission spectra because the line intensities are not directly comparable. As of yet, there is no atlas of ICP emission line intensity data, that would facilitate line selection based upon element concentrations, intensity ratios and spectral band pass. This is indeed unfortunate because the ICP instrumentation is now capable of precise and easily duplicated intensity measurements. 

ICP instruments are limited to the analysis of liquids only. Solid samples require some sort of dissolution procedure prior to analysis. The final volume of solution should be at least 25 mL. The solvent can be either water, usually containing 10% acid, or a suitable organic solvent such as xylene. 

The requirement that the sample presented to the instrument must be a solution necessitates extensive sample preparation facilities and methods. More than one sample preparation method may be necessary per sample depending on the range of elements requested. Spectral interferences can complicate the determination of trace elements in the presence of other major metals. ICP instruments are not rugged. 

Fig. 4.7 Schematic diagram of the HPLC-cold vapour ICP instrumentation...

Except for a few laboratory-made units and some devices marketed by other firms, most applications of ultrasonic nebulization (USNn) in atomic spectrometry have been developed with two commeroial devioes from CETAC Technologies viz. the U-5000AT+ and U-6000AT+). It should be noted that these two commercial ultrasonic devices were originally designed for ICP instruments but have been used with other types of detectors [20]. 

ICP instrument[14]. The data after normalization and the results obtained by... 

ICP instruments are designed for input of aqueous solutions, but many archaeological samples such as lithics and ceramics are not easily put into solution. Thus a laser is sometimes used on the front-end of the ICP-MS ( laser ablation, or LA-ICP-MS). The laser is focused upon a small spot on the sample and ablates a smaU part of the material into a gas stream that flows into the plasma. 

Approximately 0.2g of catalyst sample was taken in platinum crucible and silicon was removed by adding HF/HCIO4 and heating over hot plate to dryness. Traces of residual HF, if any, was neutralized by adding 1 ml of 4% boric acid solution and dried again. 10 ml of cOnc.HCl was added to the crucible and heated till clear solution was obtained. The solution was made to 100 ml with distilled water. Blank was prepared under identical condition. In the blank solution itself standards were prepared and ICP instrument (Atom Comp-1100, Jarrell Ash USA) was calibrated to analyze the catalyst samples. Catalyst samples were analyzed in triplicate after sample preparation and results were averaged. Further, for comparative evaluation of precision, four samples were analyzed five times in different days over a span of eight weeks. 

ICP spectroscopy was used to confirm that the potassium ions indeed are present in a toluene solution of PWnCo. Because our ICP instrument can only be used for studying aqueous solutions, we looked for the presence of K ions in the aqueous solution of PWnCo obtained by back transfer from toluene into water, using NaCI04. Pure aqueous NuCIOa showed zero concentration of K ions, while the aqueous solution of the Na salt of PWnCo obtained by back transfer from toluene solution, showed a 1 20 ratio of K to Co. Since most likely not all K ions were back transferred into aqueous solution, the real concentration of K ions in toluene solution was probably higher. 

The ablation devices for solids described in Section 8C-2 are also available from several makers of ICP instruments, With these tvpes of sample-introduction systems, the plume of sapor and particulate matter produced by interaction of the sample with an electric arc or spark or with i laser beam are Iransporled h a tlow of argon into the torch where lurther alomizaiion and esciiaiion occur. 

Figure 7.33 (a) The components of a liquid sample introduction system for ICP glass concentric nebulizer, demountable three piece quartz torch, torch body, and glass cyclonic spray chamber, (b) The components assembled for use. This torch design is typical of that used in Jobin Yvon ICP instruments. [Courtesy of Glass Expansion Pty, Ltd., Australia (www.GEICP.com).]... 

Figure 1. Schematic diagram of the total HPLC-HY-ICP Instrumentation. Reproduced with permission from Ref, 28. Copyright 1984, Marcel Dekker.

A direct reader ICP excels at the rapid analysis of multi-element samples. Common sample types analyzed by ICP include trace elements in polymers, wear metals in oils, and numerous one-of-a-kind catalysts. ICP instruments are limited to the analysis of liquids only. Solid samples require some sort of dissolution procedure prior to analysis. The final volume of solution should be at least 25 mL. The solvent can be either water, usually containing 10% acid, or a suitable organic solvent such as xylene. ICP offers good detection limits and a wide linear range for most elements. With a direct reading instrument multi-element analysis is extremely fast. 

The torch positioning in the ICP instrument can be either radial or axial. Some instruments allow for switching between these two positions. In general, axial torch positioning allows for lower analyte detection limits. However, matrix effects are much more pronounced in this torch geometry. 

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