Plasma sources linear dynamic range

In the past, much atomic emission work has been performed on atomic absorption instruments which use a flame as the excitation source. However, these have been surpassed by instruments which utilise a high-temperature plasma as the excitation source, owing to their high sensitivity and increased linear dynamic range. 

The advantages of using plasma emission sources include the ability to perform multi-element analysis, a calibration linear dynamic range of more than three orders of magnitude and for some elements the limits of detection are comparable to those found by GFAAS. The ability to perform multi-element analysis is essential when the purpose of the experiments is to study element interaction effects. 

Linearity And Dynamic Range. There is extensive evidence that emission intensities of many atomic lines excited in an ICP source are linearly related to concentration of the corresponding analytes over a range of at least one million. Trace and major constituents are therefore determinable without changes in the operating condition of the plasma. Ideally, the detection system should have a comparable linear dynamic range performance. As previously discussed (45), there are several definitions of dynamic range that are applicable to the SPD detection system. 

The major disadvantage of arc/spark emission spectroscopy is the instability of the excitation source. This problem can be virtually eliminated by the use of a plasma torch. The most common commercially available method uses an inductively coupled plasma (ICP), which is also called RF plasma, to excite the sample (13-19). The resulting spectrometers (Fig. 4) can simultaneously measure up to 60 elements with high sensitivity and an extraordinarily wide linear dynamic range. 

The objectives of this study were to quantify the trace metals in PM2 5 of Eastern and Western Canada, to analyze their annual and seasonal trends and identify their source origin, by evaluating a database of trace metal concentrations obtained over a 2-year period (May 2004-December 2006) from the NAPS network. Over 1000 PM2 5 samples collected at seven selected sites were analyzed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) after microwave assisted acid digestion. This technique offers low detection limits, wide linear dynamic range, multielement capability, ability to measure isotope ratios and high sample throughput. Principal Components Analysis (PCA) was used to identify sources of trace metals at each sampling site. 

The first commercial plasma atomic fluorescence spectrometer was developed by Demers and Allemand. Hollow cathode lamps are used as radiation sources and an inductively coupled plasma torch as an atomizer. Detection limits are reported for more than 30 elements. The linear dynamic range is normally 10 to 10. ... 

Since the intensity of the source does not affect sensitivity, but does influence the noise, the high-intensity source increases the DLs of this system by a factor of 2-5 over conventional AAS. The linear dynamic range of the system is 5-6 orders of magnitude, much broader than conventional AAS and similar to inductively coupled plasma-optical emission (ICP-OES) (discussed in Chapter 7). 

In spark ablation, a spark at constant density is obtained in a matter of seconds, and thus, particularly in the case of small spark chambers, prebum times are accordingly low. In plasma emission as well as in plasma mass spectrometry a linear dynamic range of more than four orders of magnitude can be obtained and RSDs are a few percent in the case of absolute measurements. However, as shown by the results in Table 6, they can easily fall to below 1%, when using an internal standard element (Fe in the case of steel samples). The matrix effects from the sampling source are low, as will be shown in combination with ICP-OES (see Refs. [242, 248]). They are lower than in arc ablation, as here differences stemming from the thermal volatility of the elements and their compounds play a lesser role. The... 

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