Lvov platform

Further improvements in the technique [706] includes the use of a LVov platform to achieve a temperature that is constant in time, and improved py-rolytically coated graphite tubes. To achieve improved performance requires... 

ET-AAS with graphite furnace tubes constituted the analytical support for the speciation analysis of Al and the concomitant determination of Al (III) in tea infusions, as described by Alberti and coworkers [141], Lvov platforms incorporated into the graphite furnace atomizers enabled the authors to attain an LoD of 2 xg l-1 Al. The determination was not impaired by the relatively high solid contents. Adsorption of Al on ion Chelex-100 resin was employed to estimate the free metal content and the concentration and stability constants of complexed Al species. The metal is reported to be present in total concentrations from 0.09 to 0.26 mM, but mainly linked to strong complexes. Strong complexation is demonstrated by the inability of Chelex-100 to dissociate the complexes. These results are considered by the authors as an explanation of the low toxicity of the Al associated with tea infusions. The concentration of free Al was found to be very low (at the nM level). No structural or chemical information about the ligands was obtained from the method. 

Wavelength 193.7 nM Background correction Lvov platform yes yes Argon flow rate 80 mL/min Lamp EDL Slit 0.7nM ... 

Wavelength 324.8 nM Background correction no LVov platform yes Argon flow rate 200 mL/min Lamp HCL Slit 0.7 nM ... 

Figure 20-5 (a) Electrically heated graphite furnace for atomic spectroscopy. Sample is injected through the port at the top. LVov platform inside the furnace is heated by radiation from the outer wall. Platform is attached to the wall by one small connection hidden from view. [Courtesy Perkin-Elmer Corp., Norwalk, CT.] (b) Heating profile comparing analyte evaporation from wall and from platform. 

Sample is injected onto the Lvov platform inside the furnace in Figure 20-5a. Analyte does not vaporize until the furnace wall has reached constant temperature (Figure 20-5b). If sample were injected directly onto the inside wall of the furnace. 

If the concentration of cadmium in a sample solution is too low for quantitation by this flame AAS analytical technique, and the sample is to be averaged with other samples for TWA calculations, aliquots of the sample and a matrix modifier are later injected onto a Lvov platform in a pyrolytically-coated graphite tube of a Zeeman atomic absorption spectrophotometer/graphite furnace assembly for analysis of elemental cadmium. The matrix modifier is added to stabilize the cadmium metal and minimize sodium chloride as an interference during the high temperature charring step of the analysis (5.1., 5.2.). 

Autosampler capable of accurately injecting 5 to 20 [iL sample aliquots onto the Lvov Platform in a graphite tube... 

Pyrolytically coated graphite tubes containing solid, pyrolytic Lvov platforms. 

Set up the autosampler to inject a 5- i,L aliquot of the working standard, sample or reagent blank solution onto the Lvov platform along with a 10- i,L overlay of the matrix modifier. 

The typical features of chemical modifiers used in graphite furnace AAS are exemplified by the use of hydrofluoric acid as a modifier in the determination of Cu and Mn in seawater [328], and by the use of CaCl2 and ZrOQ2 as modifiers in the determination of B [329]. Tsalev et al. [330] determined Cd and Pb with stabilized phosphate deposited on permanently modified platforms, while Pereira-Filho et al. [331] used Zr and Pd + Mg as modifiers in the determination of Al, Cd, and Pb in biological slurry samples dispensed on Lvov platforms. They studied the elemental distributions of P, S, Ca, Ti, Fe, Zr, Hf, and Pd on these platforms by micro synchrotron radiation X-ray fluorescence and the morphology of the platforms by scanning electron microscopy. 

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