Source ICP-OES

An easy calibration strategy is possible in ICP-MS (in analogy to optical emission spectroscopy with an inductively coupled plasma source, ICP-OES) because aqueous standard solutions with well known analyte concentrations can be measured in a short time with good precision. Normally, internal standardization is applied in this calibration procedure, where an internal standard element of the same concentration is added to the standard solutions, the samples and the blank solution. The analytical procedure can then be optimized using the internal standard element. The internal standard element is commonly applied in ICP-MS and LA-ICP-MS to account for plasma instabilities, changes in sample transport, short and long term drifts of separation fields of the mass analyzer and other aspects which would lead to errors during mass spectrometric measurements. 

The Inductively Coupled Plasma (ICP) has become the most popular source for multielement analysis via optical spectroscopy since the introduction of the first commercial instruments in 1974. About 6000 ICP-Optical Emission Spectrometry (ICP-OES) instruments are in operation throughout the world. 

Calibration curves must be made using a series of standards to relate emission intensities to the concentration of each element of interest. Because ICP-OES is relatively insensitive to matrix effects, pure solutions containing the element of interest often are used for calibration. For thin films the amount of sample ablated by spark discharges or laser sources is often a strong function of the sample s composition. Therefore, either standards with a composition similar to the sample s must be used or an internal standard (a known concentration of one element) is needed. 

J. W. Olesik. Analyt. Chem. 63, 12A, 1991. Evaluation of remaining limitations and potential sources of error in ICP-OES and ICPMS. 

Different analytical techniques such as ICP-OES (optical emission spectrometry with inductively coupled plasma source), XRF (X-ray fluorescence analysis), AAS (atomic absorption spectrometry) with graphite furnace and flame GF-AAS and FAAS, NAA (neutron activation analysis) and others, are employed for the trace analysis of environmental samples. The main features of selected atomic spectrometric techniques (ICP-MS, ICP-OES and AAS) are summarized in Table 9.20.1 The detection ranges and LODs of selected analytical techniques for trace analysis on environmental samples are summarized in Figure 9.15.1... 

Flames and plasmas can be used as atomisation/excitation sources in OES. Electrically generated plasmas produce flame-like atomisers with significantly higher temperatures and less reactive chemical environments compared with flames. The plasmas are energised with high-frequency electromagnetic fields (radiofrequency or microwave energy) or with direct current. By far the most common plasma used in combination with OES for analytical purposes is the inductively coupled plasma (ICP). 

For a given ICP-OES instrument, the intensity of an analyte line is a complex function of several factors. Some adjustable parameters that affect the ICP source are the radiofrequency power coupled into the plasma (usually about 1 kW), the gas flow rates, the observation height in the lateral-viewing mode and the solution uptake rate of the nebuliser. Many of these factors interact in a complex fashion and their combined effects are different for dissimilar spectral lines. The selection of an appropriate combination of these factors is of critical importance in ICP-OES. This issue will be addressed in Chapter 2, where experimental designs and optimisation procedures will be discussed. Many examples related to ICP and other atomic spectrometric techniques will be presented. 

In contrast, OES techniques (particularly those using a hot spectrochemical source such as an ICP) are intrinsically multielemental and this offers the possibility of a very high sample throughput in routine analysis. To counterbalance such a clear advantage, AAS techniques are simpler and cheaper than ICP-OES. 

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. 

Furthermore, it is desired that atomization and excitation occur in an inert chemical environment to minimize possible interferences. Different flame, spark, and arc somces have been used as the excitation sources since the beginning of the twentieth century however, none of these approximates the fiiU fist of conditions fisted above. It was not until mid-1960s when the analytically useful plasma sources were developed, subsfantially improving fhe capabilities of OES. The first commercially available inductively coupled plasma optical emission spectrometry (ICP-OES) was introduced in 1974 and since then the revival of OES can be noted. 

P. W. J. M. Boumans ed., Inductively Coupled Plasma Emission Spectroscopy , John Wiley Sons, New York, 1987—basic source book on ICP-OES. 

C. Vandecasteele and C. B. Block, Modem Methods for Trace Element Determination , 1st edition, John Wiley Sons, Chichester, 1993—very good source book on the principles of ICP-OES and ICP-MS. 

The plasma sources commonly available for trace elemental analysis are DCP-OES and ICP-OES of which the latter is more popular due to being the most studied and user-friendly and its compatibility with hyphenated accessories. The MIP mainly uses helium... 

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