Interface electrothermic

Gunn et al. [44] described the apphcation of a graphite-filament electrothermal vaporization apparatus as a sample introduction system for optical emission spectroscopy with an inductively coupled argon plasma source. Good detection levels were reported for the elements, and details of the interfacing requirements between the ICP and the graphite filament were explored. 

To optimize the applicability of the electrothermal vaporization technique, the most critical requirement is the design of the sample transport mechanism. The sample must be fully vaporized without any decomposition, after desolvation and matrix degradation, and transferred into the plasma. Condensation on the vessel walls or tubing must be avoided and the flow must be slow enough for elements to be atomized efficiently in the plasma itself. A commercial electrothermal vaporizer should provide flexibility and allow the necessary sample pretreatment to introduce a clean sample into the plasma. Several commercial systems are now available, primarily for the newer technique of inductively coupled plasma mass spectroscopy. These are often extremely expensive, so home built or cheaper systems may initially seem attractive. However, the cost of any software and hardware interfacing to couple to the existing instrument should not be underestimated. 

Because of its capability for rapid multielement analysis, ICP-MS is particularly suited to sample introduction methods which give rise to transient signals. For example, electrothermal vaporization, flow injection and chromatographic methods can be interfaced and many elements monitored in a single run (see Chapter 7). 

The response is indicative of die electrothermal behavior of die bridgewire-explosive interface. Bridgewir.es which deviate from the characteristic heating curve have been dissected and examined to determine the cause of die abnormality. Deliberate faults have been fabricated into squibs. The relationship of the specific abnormality and the fault associated with.it have been demon strated (Ref 1, abstracted in Ref 3)... 

Fig. 10 (a) Electrothermic and (b,c) optoelectrothermic interfaces for the control of temperature-sensitive hydrogels based (a) on resistive heaters according to (Richter et al. 2003 Arndt et al. 2000), (b) on a laser beam according to (Wiinschmann et al. 2002) and (c) on controlled light projection according to (Richter and Paschew 2009)... 

As resistive heating elements of this electrothermic interface thin film platinum resistors and surface mount technology (SMT) resistors are used (Richter et al. 2003, 2009a). The hydrogel components can be heated and cooled also by Peltier elements (Yu et al. 2003b Luo et al. 2003a). 

The power of this MS technique has driven the development of methods to interface ICP/MS instruments with various sample introduction systems. Specialized sample introduction systems include ion chromatography (Seubert, 2001), gas chromatography (Vonderheide et al., 2002), and capillary electrophoresis (Costa-Fernandez et al., 2000). Other techniques are hydride generation (used to volatilize selected species and obtain some matrix/elemental separation) (Reyes et al., 2003) (Bings et al., 2002) laser ablation (Gonzalez et al., 2002 Heinrich et al., 2003 Russo et al., 2002), and electrothermal vaporization (Richardson, 2001 Vanhaecke and Moens, 1999). 

The best-known technique based on a combination of methods is ICP-MS. Here, the excited atoms are introduced upon their return to a lower energy level, through an interface into the ion source of a quadru-pole of a mass spectrometer. The ICP thus acts as an ion source and the mass spectrometer as the ion detector. The latest development in atomic spectrometry is the electrothermal evaporation-ICP-MS technique, where a graphite furnace is coupled to an ICP-MS. In this case, use is made of the most remarkable property of a graphite furnace (elimination of matrix interferences) by a graphite tube atomizer and subsequent transport of the atomic phase into the plasma and quadrupole. 

As for any other sample introduction system, the ICPMS working parameters need to be optimized when an electrothermal vaporizer is used. These parameters include the lens voltages, the different gas flow rates (normally Ar), the plasma radiofrequency (RF) power, the position of the torch with respect to the interface, and most importantly, the data acquisition parameters. 

The plasma-based techniques can also serve as detectors for laser ablation (LA) and electrothermal vaporization (ETV). These techniques are well-suited for the analysis of solid samples. ETV can also be used to analyse liquid and slurry samples. Both techniques use small quantities of material and, when interfaced with ICP-MS, are quite sensitive. A cool plasma accessory can also be interfaced with the ICP-MS. This allows for the removal or minimization of interferences caused by the formation of molecular species in the plasma, permitting the determination of Li, Na, Ca, K, Fe and Cr which can not be analysed successfully by conventional ICP-MS. Such analyses exhibit the same sensitivity as afforded by FAAS. 

Shen,W-L., Caruso,J.A., Fricke, E L.,and Satzger,R.D. (1990). Electrothermal vaporisation interface for sample introduction in inductively coupled plasma mass spectrometry. J. Anal. At. Spectrom. 5(6), 451. 

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