Atomic sample transfer efficiency

Atomic absorption spectrometry requires that the species under investigation prevails in the gaseous and atomic state so that absorption of free atoms can be observed. The two most common methods for the production of atoms in the gas phase make use of thermal energy to vaporise and atomise the analyte. The sample transfer efficiency, i. e. how much of the sample is reaching the actual atomisation zone. 

Although electrothermal vaporization has been widely accepted as an extension of atomic absorption, its use in inductively coupled plasma spectroscopy is fairly recent. In this technique the requirement for the vaporizer is somewhat different—the electrothermal vaporizer does not have to double as the atom cell. In fact, it is only needed to effect efficient and reproducible sample transfer from the rod, or a similar device, into the plasma. 

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. 

The interface provides efficient transfer of samples into the Merlin, and, most importantly, a rapid flush-out there is no hold up of mercury (which is a feature of the commonly used atomic absorption techniques). To aid the transfer of mercury vapour, the tin(II) chloride regime is used, together with a gas/liquid separator designed for this task. Mercury is sparged from the reaction vessel into the Merlin Detector. Full automation is provided by using a simple standard DIO card fitted into an IBM compatible computer system with the PSA Touchstone software. This is an easy-to-use menu-driven system which controls the modules used in the instrumentation, calibrates the system, collects, collates and reprints the results, and which finks to host computer systems. 

The use of catalysts in chemistry increases reaction speed and lowers reaction temperatures. Metal catalysts are commonly used in many technologies — the detailed knowledge of catalyzed reaction steps can be used to improve efficiency or find new reaction pathways. Bond formation is the reverse process of bond breaking and constitutes an important basic step in a metal catalyzed reaction. In the simplest case, the transfer of an atom/molecule between the sample and the tip in the vertical manipulation procedure involves both bond breaking and bond formation processes. In this case, the substrate-atom/molecule bond is broken and a new bond between the atom/molecule and the tip-apex atom is formed or vice-versa [45]. Such a bond formation was demonstrated by Lee and Ho [46]. They deposited two CO molecules over an adsorbed Fe atom on a Cu(100) surface using the vertical manipulation procedure. Because an adsorbed Fe atom on this surface can accommodate two CO molecules, an Fe(CO)2 iron carbonyl was produced. 

In 1961, J.E. Lovelock found that the cross-sectional process could be made much more efficient (10 to 100 times more sensitive than an FID) if DRY argon were used as the carrier gas. The /7-particle would produce an excited argon atom that then would transfer its energy to the sample molecules very efficiently. The sequence of reactions is suggested as ... 

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