Electrothermal atomizers tantalum

N1 and Zn from a graphite rod were significantly lower than from a tantalum filament, suggesting that these free metal atoms can be liberated by chemical reduction of their respective oxides, rather than by direct thermal dissociation. Findlay et al (19) emphasized the hazards of preatomlzatlon losses of trace met s In electrothermal atomic absorption spectrometry, when the ashing temperature Is permitted to exceed the minimum temperature for vaporization of the analyte. 

Nonflame atom reservoirs have been developed for specific atomic spectrometric techniques. Electrothermal atomizers (carbon rods, carbon furnaces, or tantalum ribbons) have been developed for AAS or AFS since they require the generation of ground state atoms, whereas... 

Atomic absorption spectrometry, belonging to a class of techniques also defined as optical atomic spectrometry, has been for some four decades - and continues to be - one of the most important, dominant determinative techniques. It includes flame atomic absorption spectrometry (FAAS), electrothermal atomization atomic absorption spectrometry (ETAAS) (including graphite furnace AAS (GFAAS), carbon rod AAS, tantalum strip AAS), and gaseous generation (cold vapor AAS for Hg, hydride gener-... 

Carbon furnaces and cups have been utilized as electrothermal atomizers but these tend to be rather complex and most work has been with metal strips or filaments of platinum, tantalum, or tungsten. 

One of the advantages of electrothermal atomization is that some materials can be atomized directly, thus avoiding the solution step. For example, liquid samples such as blood, petroleum products, and organic solvents can be pipetted directly into the furnace for ashing and alomization. Solid samples, such as plant leaves, animal tissues, and some inorganic substances. can be weighed directly into cup-type atomizers or into tantalum boats for introduction into tube-type furnaces. Calibration is. however, usually difRcult and requires standards that approximate the sample in composition. 

Electrothermal atom cells have changed radically since their inception in the late 1950s. The majority of electrothermal devices have been based on graphite tubes that are heated electrically (resistively) from either end. Modifications such as the West Rod Atomizer (a carbon filament) were also devised but were later abandoned. Tubes and filaments made from highly refractory metals such as tungsten and tantalum have also been made, but they tend to become brittle and distorted after extended use and have poor resistance to some acids. Their use continues, however, in some laboratories that need to determine carbide-forming elements. For example, silicon reacts with the graphite tube to form silicon carbide, which is both very refractory and very stable. The silicon is therefore not atomized and is lost analytically. Use of a metal vaporizer prevents this. 

Only few data are available in the literature that deal with the measurement of Gd in biological fluids and tissues. Some workers used atomic emission spectrometry (AES) for the determination of Gd in tissues [4] after digesting samples with nitric acid. Others used radiolabeled Gd to study the biodistribution of the element [14]. ICP-MS has been used for the determination of Gd in serum and urine. With this method samples are simply diluted in water [16]. To our knowledge the method described by the group of D Haese [28] is the only report that exists on the determination of Gd in biological fluids and tissues by electrothermal AAS (ETAAS). With this procedure the element can be accurately determined in serum, urine, blood, bone, and tissues after extraction into methyl isobutyl ketone followed by reextraction in hydrochloric acid. Atomization of the element for AAS determination is performed from a tantalum boat. 

Electrothermal vaporizers, which were described briefly in the previous section, are also used for various types of solid samples. The sample is heated conduc-tively on or in a graphite or tantalum rod or boat. The vaporized sample is then carried into the atomizer by an inert carrier gas. 

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