Spark ablation ICP-OES

Tab. 6. Analytical precision of spark ablation ICP-OES for a BAS 410/1 steel sample, ccu = 3.6 mg/g. Line pair leu 324.7 nm/lfe 238.2 nm- 400 Hz medium voltage spark, 1.5 kW argon ICP, transport gas flow 1.2 L/min, 0.5 m Paschen-Runge spectrometer, measurement time 10 s [213],...

Approximately 70 different elements are routinely determined using ICP-OES. Detection limits are typically in the sub-part-per-billion (sub-ppb) to 0.1 part-per-million (ppm) range. ICP-OES is most commonly used for bulk analysis of liquid samples or solids dissolved in liquids. Special sample introduction techniques, such as spark discharge or laser ablation, allow the analysis of surfaces or thin films. Each element emits a characteristic spectrum in the ultraviolet and visible region. The light intensity at one of the characteristic wavelengths is proportional to the concentration of that element in the sample. 

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. 

Fig. 100. The analysis of Al and AlSi alloys by spark ablation coupled with ICP-OES. 3 kW argon-nitrogen I CP, Spectrovac 1000 and 1 kV spark at 25 Hz. (Reprinted with permission from Ref. [100].)...

Kehden A., Flock J., Vogel W. and Broekaert J. A. C. (2000) Direct solids atomic spectrometric analysis of metal samples by laser induced argon spark ablation coupled to ICP-OES, Appl Spectrosc, in press. 

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... 

With advanced Nd YAG lasers at atmospheric pressure, as utilized when coupling with ICP-OES or MS, selective volatilization is moderate. However, in the case of brass, it is as high as in spark ablation and causes problems in calibration [257]. In recent work, favorable working conditions in laser ablation studies were also shown to apply at reduced pressures of around 10-100 mbar [255, 258, 259]. In a number of cases, analytes in very different matrices were found to give signals which fitted astonishly well with the same calibration curves from OES, and a nearly matrix-independent calibration could be applied. This would be very welcome in the analysis of compact ceramics, for which no other direct analysis methods exist. By careful optimization of the laser working conditions, it is now possible to obtain very reproducible sample material from plastics, as shown by Hemmerlin and Mermet [260]. 

Preferred methods in trace determination of the elements include atomic absorption spectrometry (AAS), optical emission spectrometry (OES) with any of a wide variety of excitation sources [e.g., sparks, arcs, high-frequency or microwave plasmas (inductively coupled plasma, ICP microwave induced plasma, MIP capacitively coupled micro-wave plasma, CMP), glow discharges (GD). hollow cathodes, or laser vaporization (laser ablation)], as well as mass spectrometry (again in combination with the various excitation sources listed), together with several types of X-ray fluorescence (XRF) analysis [51]. 

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