Wire loop atomization

C4. Chauvin, J. V., Newton, M. P., and Davis, D. G., Determination of lead and nickel by atomic absorption spectrometry with a flameless wire loop atomizer. Anal. Chim. Acta 65, 291-302 (1973). 

The preconcentration of metals by electrodeposition onto a tantalum strip for flameless AAS has not been described and though similar to the wire-loop atomizer, the greater stability and malleability attainable with tantalum should make it possible to extend the method more readily to other metals. In fact, the... 

A microsampling system known as the Delve s cup is a hybrid of flameless and flame techniques. The sample is placed in a small crucible, which is held in the flame by means of a wire loop. The sample is ashed in a cooler part of the flame and then moved to the hotter part in order to cause the rapid vaporization of the element. The cup is held beneath an opening in a nickel or aluminium tube which is in the light path of the instrument. The atomic vapour... 

Fig. 3.4 (c) Penn State design tip exchange setup ffor an FIM or a pulsed-laser atom-probe with a vacuum lock. The tip can be heated by passing a current through the wire loop. The tip is mounted on an internal gimbal and is cooled through a copper braid by a refrigerator. 

In order to bring the sample rapidly into a hot environment, use is often made of the platform technique, as was first introduced in atomic absorption spectrometry by L vov [179]. Here the very rapid heating may enable the formation of double peaks to be avoided, which are a result of various subsequent thermochemical reactions, all of which have their own kinetics. Also the high temperature avoids the presence of any remaining molecular species, which are especially troublesome in the case of atomic absorption spectrometry. Thin platforms can be made of graphite, which have a very low heat capacity, or from refractory metals. In the latter case wire loops, on which a drop can easily be previously dried, are often used. 

Davis and co-workers (N2, C4) described a new preconcentrating sampling technique for flameless atomic absorption spectroscopy in which a tungsten alloy wire loop is soaked in the sample solution for a specified period of time. Metal ions are concentrated on the surface of the wire loop, apparently by an ion exchange mechanism. The wire... 

More recently, Newton and Davis (779) used 10-mil tungsten-rhenium wire (3% Re) and preelectrodeposition times of 200 sec and were able to obtain absolute detection limits in AAS for 19 metals (Ag, As, Au, Be, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mn, Ni, Pb, Sb, Se, Sn, V, and Zn, without regard to specia-tion), which were lower than flame atomization and comparable to the carbon-rod atomizer. Spontaneous preconcentration was reported when the wire loop was immersed in the solution in the absence of an applied potential. The... 

Liquid samples have also been introduced directly into the ICP carried on a tungsten wire loop [17]. The approach has been used with both AES and MS variants of detection. A 10-p,L sample is pipetted onto the loop and then advanced into the torch using a programmable stepping motor. This allows a temperature sequence of drying, ashing, and atomization steps as the plasma is approached and then entered, reminiscent of furnace atomic absorption spectrometry. 

Transport phenomena occur particularly when transporting the vapors themselves. They disappear completely when the sample is inserted directly into the signal generation source, where it is evaporated thermally. This approach is known from work with graphite or metal probes in atomic absorption, where for example W wire cups and loops are used. The technique is also used in plasma spectrometry with the inductively coupled plasma (ICP), both in atomic emission [189-191] and in mass spectrometry [192]. Its absolute power of detection is extremely high and the technique can be used both for the analysis of dry solution residues as well as for the volatilization of microamounts of solids. 

The ion beam is produced in the following way U atoms are evaporated from an oven at a temperature of typically 400 C, and are ionized and excited to the metastable 2 5 state by electron impact, when leaving the oven aperture. The electrons are emitted from a little ring-shaped tungsten wire cathode which is placed horizontally several millimeters above the oven exit. The cathode is held at ground potential, the oven at +200 V. The electrons are accelerated directly onto the oven aperture thus counterpropa-gating to the ions which are accelerated in the same electric field. The ions pass the cathode loop and are formed into a well-collimated beam by an electrostatic lens system. 

The chemical shift exists because the applied magnetic field Bq causes electrons in atoms and molecules to circulate around the nuclei. Somewhat like an electric current in a loop of wire, the swirling electrons generate a small local magnetic field that... 

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