Atomization cell graphite furnace

In order to derive a quantitative relation between emission Intensity as measured by EMI and actual metal content, cell samples were subjected to graphite furnace atomic absorption (GFAA) analysis (14). Atomic absorption experiments were performed both on cells which had been stained with a fluorescent reagent and on cells not exposed to a lumlnophore. After EMI analysis, 50 fiL of cell suspension were withdrawn from the 0.30 mL of sample used for EMI and were digested In 150 iiL of concentrated HNO3 for 90 minutes at 85° . These solutions were then diluted to 1/10 of their concentration with deionized water, and the 150 liL of these diluted... 

Willie et al. [17] used the hydride generation graphite furnace atomic absorption spectrometry technique to determine selenium in saline estuary waters and sea waters. A Pyrex cell was used to generate selenium hydride which was carried to a quartz tube and then a preheated furnace operated at 400 °C. Pyrolytic graphite tubes were used. Selenium could be determined down to 20 ng/1. No interference was found due to, iron copper, nickel, or arsenic. 

Describe a typical electrothermal atomizer for atomic absorption spectrometry. Critically compare graphite furnaces, air-acetylene flames, and nitrous oxide flames as atom cells for atomic absorption spectrometry. 

The recommended procedure for the determination of arsenic and antimony involves the addition of 1 g of potassium iodide and 1 g of ascorbic acid to a sample of 20 ml of concentrated hydrochloric acid. This solution should be kept at room temperature for at least five hours before initiation of the programmed MH 5-1 hydride generation system, i.e., before addition of ice-cold 10% sodium borohydride and 5% sodium hydroxide. In the hydride generation technique the evolved metal hydrides are decomposed in a heated quartz cell prior to determination by atomic absorption spectrometry. The hydride method offers improved sensitivity and lower detection limits compared to graphite furnace atomic absorption spectrometry. However, the most important advantage of hydride-generating techniques is the prevention of matrix interference, which is usually very important in the 200 nm area. 

Even a technique of higher detection power as ET-AAS may require some sort of previous analyte enrichment for difficult elements. In the determination of As and Se in mineral waters described by Hudnik and Gomiscek [23], coprecipitation of both elements on hydrated Fe(III) oxide was employed to improve LoDs, otherwise impaired by matrix effects. A graphite tube furnace was the atomization cell, with the atomic vapor sampled with element electrodeless discharge lamps. After treatment of the sample with Fe(III) solution at the appropriate pH, the oxide precipitate was filtered and dissolved and the solution volume reduced to 5 mL of 0.2 M H2SO4. Ten-microliter volume aliquots of sample and standard solutions were injected into the furnace. Reported LoDs were 0.2 and 0.5 p,g l-1 for As and Se, respectively. 

In 1955, A. Walsh recognized this and showed how the absorption from the great preponderance of unexcited molecules could be exploited analytically.Thus, in atomic absorption spectroscopy (AAS) the light from a (usually modulated) somce emitting the spectrum of the desired analyte element is passed through a sample atomization cell (such as a flame or graphite tube furnace), a monochromator (to isolate the desired somce emission line) and finally into a detector to allow measmement of the change in somce line... 

Several types of atomization cell are available flame, graphite furnace, hydride generation and cold vapour. Flame is the most common. In the premixed laminar flame, the fuel and oxidant gases are mixed before they enter the burner (the ignition site) in an expansion chamber. The more commonly used flame in FAAS is the air-acetylene flame (temperature, 2500 K), while the nitrous oxide-acetylene flame (temperature, 3150K) is used for refractory elements, e.g. Al. Both are formed in a slot burner positioned in the light path of the HCL (Fig. 27.4). 

The atomization cell is the site were the sample is introduced the type of atomization cell can vary (flame or graphite-furnace) but essentially it causes the metal-containing sample to be dissociated, such that metal atoms are liberated from a hot environment. Such an environment of the atomization cell is sufficient to cause a broadening of the absorption line of the metal. By utilizing the narrowness of the emission line from the radiation source, together with the broad absorption line, means that the wavelength selector only has to isolate the line of interest from other lines emitted by the radiation source (Figure 11.9). This... 

Detection systems employed with hydride generation approaches are conventional AA spectrometers, usually fitted with intense electrodeless discharge or hollow cathode lamp sources. Quartz tube cells are of suitable dimensions to be compatible with the optical systems of all modem spectrometers. Background correction is usually achieved in double-beam optics using deuterium sources, and Zeeman-effect background correction can be implemented when the graphite furnace is used as the atomization cell. 

The atom cell converts the sample into gaseous atoms. Generally, it is necessary to convert all standards and samples into solution form by the use of acids or other reagents before introduction into the atom cell. Commonly used atom cells for AFS include cold vapor (CV) cells, flames, and ETAs (graphite furnaces). 

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