Graphite furnace, temperature program

Cvetkovic and coworkers [74] evaluated a mixed Ni and Sr nitrates matrix modifier for the determination of Se in wines by Zeeman ET-AAS. Samples were heated on a boiling water bath with small amounts of HNO3 and H2O2. To eliminate interferences, especially sulfates and phosphates, Se was complexed with APDTC and extracted into methylisobutyl ketone (MIBK) and the graphite furnace temperature program was optimized for both aqueous and organic solutions. Selenium concentrations up to 0.93 pg l-1 were detected in wines from the Republic of Macedonia. 

Table 8.1 Graphite furnace temperature program for the determination of lead in sorbent extraction eluate...

The graphite furnace temperature program was optimised by response surface methodology (RSM) using a Doehlert design for three variables. 

FIGURE 9.17 An illustration of a temperature program for a graphite furnace experiment (left), and the absorbance signal that results (right). The absorbance signal corresponds to the third temperature plateau. See text for a more detailed explanation. 

Describe the temperature program applied to a graphite furnace and explain each of the processes involved. 

Figure 14.9—Thermoelectric atomisation device, a) Graphite furnace heated by the Joule effect b) example of a graphite rod c) temperature program as a function of time showing the absorption signal. The first two steps of this temperature program are conducted under an inert atmosphere (argon scan).

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. 

Electrothermal vaporization. With ETV/ICP-MS, a small amount of solid sample ( lmg) is introduced into a graphite furnace and subjected to a multi-step temperature program for atomization. Additionally, a modifier can be used for thermal stabilization of the analytes or to improve the matrix mineralization. The vapours produced during the vaporization step are transferred into the plasma by argon carrier gas. 

In electrothermal atomization methods, the microcomputer also controls the furnace temperature, a key factor for this technique. Guevremont and Whitman used a microcomputer based on a Z80 microprocessor for the automatic control and data acquisition from a graphite furnace [13] they could heat the furnace from 0 to 2500 C In about 3 s, with an approximate gain In precision of 50% under the control of the microprocessor. The system Is shown schematically In Fig. 10.9. The automatic functions afforded are data acquisition, measurement of the furnace temperature and calibration, temperature programming, control of the gas flow, control of the sampler and delivery of results. 

Modern graphite furnace atomizers have a separate power supply and programmer that control the electrical power, the temperature program, the gas flow, and some spectrometer functions. For example, the spectrometer can be programmed to read , that is, collect absorbance data, only when the furnace reaches the atomization temperature. This saves data storage space and data processing time. 

Figure 6.18 Typical temperature program for a graphite furnace atomizer. [From Beaty and Kerber, used with permission of PerkinElmer, Inc. (www.perkinelmer.com).]...

Fig. 12.10 (a) Schematic temperature program of the graphite furnace (1, Ar flow on 2, drying ... 

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