Direct multielement determination of trace elements in boron carbide powders by slurry sampling ETV-ICP-OES

摘要

The use of slurry sampling electrothermal evaporation inductively coupled plasma optical emission spectrometry (S1S-ETV-ICP-OES) for the direct determination of trace elements in boron carbide powders with different particle size distributions was investigated. It was found that the addition of 6 mL min~(-1) of Freon R12 (Cl_2F_2C) to the 500 mL min~(-1) Ar carrier gas flow as a thermochemical reagent resulted in an increase of the net line intensity for Ti by a factor of 25 in SIS-ETV-ICP-OES, when analyzing 20 μL of a slurry containing 1% of the boron carbide powder BC-1. After heating the dry residue of 20 μL of a slurry of 1% of boron carbide for 12 s to 2600 ℃ on a L'vov platform the residues on the platforms were analyzed by total reflection X-ray fluorescence spectrometry (TXRF). The evaporation efficiency for Ti was found to have increased from 12 to 97% by the addition of 6 mL min~(-1) of R12 as compared to evaporation in Ar only. When heating dry residues of boron carbide slurries on L'vov platforms to temperatures ranging from 2000 to 2600 ℃ without adding R12 to the Ar, it could be observed visually that only a small fraction of the boron carbide matrix is evaporated. However, when heating at 2600 ℃ under the addition of R12 almost no residues were found on the platform after the evaporation step. For the analysis of boron carbide powders with S1S-ETV-ICP-OES the limits of detection were found to be between 0.002 and 2 μg g~(-1) for the elements Al, Ca, Co, Cr, Cu, Fe, Mg, Mn, Na, Ni and Ti. For Fe a wide variety of samples could be analyzed by S1S-ETV-ICP-OES with one calibration under the use of R12. This was shown for different samples, namely three boron carbide powders, three boron nitride powders, an aluminium oxide powder (NIST 699), silicon carbide powder (BAM S-003), powdered apple leaves (NIST 1515), a reference sample for trace elements in natural water (NIST 1643d) and an aqueous standard solution. When plotting the net line intensities versus the accepted concentrations a coefficient of determination of 0.990 is obtained. By SIS-ETV-ICP-OES under the addition of R12 the values obtained were found to be between 78 to 128% of the mean of the results of slurry sampling-TXRF and of ICP-OES subsequent to wet chemical digestion. 11 trace elements with concentrations ranging from 0.7 to 370 μg g~(-1) for Co and Fe, respectively, could be determined in two boron carbide powders with particle size distributions of d_(90) = 3.5 μm and d_(90) = 9.2 μm, respectively.