ETV-ICP-OES: a useful technique for homogeneity study of trace element in metals—application to the homogeneity study of 23 elements in electrolytic copper

Abstract

Solid sampling techniques can perform multi-elemental determination on large number of samples in repeatable conditions without sample preparation, making them valuable tools for the homogeneity testing of reference materials. Even if techniques like glow discharge mass spectrometry are often used for large samples, the application to small chips was not well documented due to the small sample mass. This study compares two analytical methods for homogeneity studies of Ag, Al, As, Au, Bi, Cd, Co, Cr, Fe, In, Mg, Mn, Ni, P, Pb, Sb, Se, Si, Sn, Te, Ti, Zn and Zr in two electrolytic copper materials in the format of chips (ERM-EB074C and ERM-EB075C): (a) digestion methods: acid dissolution followed by ICP-MS or ICP-OES and (b) solid sampling method using electrothermal vaporization coupled with inductively coupled plasma optical emission spectrometry (ETV-ICP-OES). The same 10 units were analysed in 3–5 replicates by the different methods. ETV-ICP-OES was more precise than digestion methods with relative standard deviations of less than 8 % for most elements. The between-unit uncertainties determined by ETV-ICP-OES were lower than the values reported by the digestion methods. ETV-ICP-OES is a very interesting alternative to the digestion methods for large homogeneity study involving large number of trace elements. Also, the intrinsic sample inhomogeneity (minimum sample intake) was re-evaluated using the results of ETV-ICP-OES (sample intake: 3 mg) for the two materials. The minimum sample intake of several elements (e.g. Au Pb, Se and Te) was evaluated to be lower than the 10 mg reported for the two materials.