Simultaneous determination of chromium and manganese in alumina by slurry sampling graphite furnace atomic absorption spectrometry using NbC and NaF as modifiers

Abstract

This paper reports a method for the direct and simultaneous determination of Cr and Mn in alumina by slurry sampling graphite furnace atomic absorption spectrometry (SiS-SIMAAS) using niobium carbide (NbC) as a graphite platform modifier and sodium fluoride (NaF) as a matrix modifier. 350 mg of Nb were thermally deposited on the platform surface allowing the formation of NbC (mp 3500 C) to minimize the reaction between aluminium and carbon of the pyrolytic platform, improving the graphite tube lifetime up to 150 heating cycles. A solution of 0.2 mol L À1 NaF was used as matrix modifier for alumina dissolution as cryolite-based melt, allowing volatilization during pyrolysis step. Masses (c.a. 50 mg) of sample were suspended in 30 ml of 2.0% (v/v) of HNO 3 . Slurry was manually homogenized before sampling. Aliquots of 20 ml of analytical solutions and slurry samples were co-injected into the graphite tube with 20 ml of the matrix modifier. In the best conditions of the heating program, pyrolysis and atomization temperatures were 1300 C and 2400 C, respectively. A step of 1000 C was optimized allowing the alumina dissolution to form cryolite. The accuracy of the proposed method has been evaluated by the analysis of standard reference materials. The found concentrations presented no statistical differences compared to the certified values at 95% of the confidence level. Limits of detection were 66 ng g À1 for Cr and 102 ng g À1 for Mn and the characteristic masses were 10 and 13 pg for Cr and Mn, respectively.

Atomic Spectroscopy

“…Exemplarily, the determination of Cr, Cu, Fe, K, Mn, Sb, and Zn in powdered aluminum nitride down to 0.05 (Zn) and 80 ng g –1 for Fe has been described . For these types of refractory matrixes, the use of modifiers also may be useful, as shown in the examples of the determination of Cr and Mn in alumina by slurry nebulization under the use of NbC and NaF as the modifier . Other applications of slurry sampling under the use of modifiers were the determination of Sn in marine sediments under the use of Ir/W/Nb mixtures as a permanent modifier and the determination of Zn in marine sediments under the use of Pd/Mg mixtures as a permanent modifier and slurry sampling .…”

“…29 For these types of refractory matrixes, the use of modifiers also may be useful, as shown in the examples of the determination of Cr and Mn in alumina by slurry nebulization under the use of NbC and NaF as the modifier. 30 Other applications of slurry sampling under the use of modifiers were the determination of Sn in marine sediments under the use of Ir/W/Nb mixtures as a permanent modifier 31 and the determination of Zn in marine sediments under the use of Pd/Mg mixtures as a permanent modifier and slurry sampling. 32 For the aim of matrix modification also, electrodeposition on a platform can be successful.…”

Simultaneous determination of Cr, Fe, Ni and V in crude oil by emulsion sampling graphite furnace atomic absorption spectrometry

“…During the drying and pyrolysis steps it is possible to carry out the in situ sample pretreatment, such as digestion to eliminate organic matrix components. 13 Additionally, the availability of simultaneous atomic absorption spectrometry with conventional light source (SIMAAS) 14 or with high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS AAS) 15 allowed the development of multi-element methods, improving the analytical frequency, reducing the cost related to instrument maintenance, sample and high purity reagents.…”