Laser-excited atomic fluorescence of atoms produced in a graphite furnace

Abstract

25) Win@, R. K.; Peterson, v. J.; Fassei, v. A. APPl. sPectKJsc. 1979, 33, 206.Laser-excited atomlc Huotescence in a graphne furnace gives detection IbnHs for Pb, Cu, Mn, Sn, AI, In, LI, and Pt, in the pkogram to sub-picagram range. The linear dynamk range for these elements varles from 3 to 7 orders of magnnude. A graphlte rod, a plain graphite cup, and a slotted graphite cup are compared as the cuvette In the fluorescence system.Detection lhnlts for a pyrolytic coating, a tantalum foil liner, and a tantalum carbide coating of the graphlte cuvette are compared. A hydrogen-argon atmosphere, a low-pressure atmosphere, and an argon atmosphere are compared as the atmosphere s u r r o w the graphite cuvette. Lastly, Cu and Yn are determined In several standard reference materials.Laser-excited atomic fluorescence using a graphite furnace has been shown to give very low detection limits (1-9). Bolshov et al. (5) achieved excellent detection limits for Pb, Fe, Na, Pt, Ir, Eu, Cu, Ag, Co, and Mn, using a Nd:YAGpumped dye laser system. These results ranged from 1.5 fg for P b to 300 pg for Eu. Tilch et al. (7) utilized a nitrogenpumped dye laser system to obtain similar detection limits for some of the same elements as well as a few others. Probably the most impressive reaulb have been the femtogram detection limits for Pb. Besides Bolshov and Tilch (5, 7) Human et al. (6) also obtained a detection limit in the femtogram range for Pb.Pulsed lasers offer several advantages for atomic fluorescence such as wide tunability and high peak powers. However, these lasers are less than optimum when using electrothermal atomization because of the low repetition rate (e.g., 20 Hz) of the lasers. The pulsed laser must be synchronized so that there is a laser pulse during the time when atoms are present in the laser path. This problem can be overcome somewhat by using a computer to synchronize the laser pulse with the formation of atoms during the atomization stage or by confining the atomic vapor within a tube atomizer to increase the residence time. An alternative is to operate the pump laser at higher frequencies if possible, e.g., by use of a copper vapor laser pumped dye laser system a t ca. 6 kHz. The atomizer requires a special design for atomic fluorescence since the fluorescence is viewed at 90' to the laser beam. A graphite cup (5, 7), a Massmann cup (IO), a graphite tube with holes cut in the sides (9), and a graphite rod ( I , 6), are several designs that have been tried. The simplicity of the graphite rod makes it attractive for use with volatile elements. On the other hand, the graphite cup offers an improvement over the graphite rod because the sample is in a semienclosed 0003-2700/86/0358-2598$01.50/0 environment, which gives more of a "furnace" effect. However, the atoms still must emerge from the furnace into the cooler atmosphere before being excited by the laser. As the atoms vaporize out of the hot furnace they have more of a chance to react with interferents, such as 02. In principle, the best atomizers are those...

Laser-Excited Atomic Fluorescence Spectrometry in a Pressure-Controlled Electrothermal Atomizer

“…Fluorescence was detected at 180°to the direction of the laser beam, in a scheme called front surface illumination. 26 An off-axis ellipsoidal mirror (Aero Research Associates Inc., Port Washington, NY), with an aluminum reflective surface and a magnesium fluoride overcoat, 27 was used to reflect the fluorescence from the graphite furnace onto the slit of a monochromator (ISA, Model H-10, Metuchen, NJ). For tellurium, platinum, and phosphorus, fluorescence was detected at 238.4, 241.0, and 253.5 nm, respectively.…”

Laser-induced double resonance fluorescence of lead with graphite tube atomization

“…(3), tast polarography (4), normal pulse polarography ( 5), neopolarography (6) (or convolution voltammetry (7)), discretely convolved staircase voltammetry (8), and steady-state voltammetry at inlaid disk microelectrodes (9). The output may be a steady-state current (2, 9), an averaged current (3), a sample current (4, 5), or a current processed by semiintegration (6,7) or by some other convolution (8b In what follows, any such output will be represented by /.…”

“…It was also shown previously (8,11) that no special atomizer design is required for the observation of the fluorescence emission, which can be efficiently collected by the combination of a plane mirror, having a hole in the center to allow exiting by the laser beam, positioned at 45°with respect to the longitudinal axis of the tube and a lens positioned so as to image the center of the tube into the entrance slit of the fluorescence monochromator. Such an arrangement has the advantage that the graphite furnace and its inherent electrical characteristics are not modified, and as a result, one should take full advantage of the very significant amount of analytical knowledge and experience gained by analysts in the use of the furnace in atomic absorption spectrometry (12).…”