High spatial resolution analysis of ferromanganese concretions by LA-ICP-MS? |
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Authors: | Mikael D Axelsson Ilia Rodushkin Douglas C Baxter Johan Ingri Björn Öhlander |
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Institution: | 1.Division of Applied Geology,Lule? University of Technology,Lule?,Sweden;2.SGAB Analytica,Lule? University of Technology,Lule?,Sweden;3.Division of Inorganic Chemistry,Lule? University of Technology,Lule?,Sweden |
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Abstract: | A procedure was developed for the determination of element distributions in cross-sections of ferromanganese concretions using
laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The effects of carrier flow rates, rf forward power,
ablation energy, ablation spot size, repetition rate and number of shots per point on analyte intensity were studied. It is
shown that different carrier gas flow rates are required in order to obtain maximum sensitivities for different groups of
elements, thus complicating the optimisation of ICP parameters. On the contrary, LA parameters have very similar effects on
almost all elements studied, thus providing a common optimum parameter set for the entire mass range. However, for selected
LA parameters, the use of compromise conditions was necessary in order to compensate for relatively slow data acquisition
by ICP-MS and maintain high spatial resolution without sacrificing the multielemental capabilities of the technique. Possible
variations in ablation efficiency were corrected for mathematically using the sum of Fe and Mn intensities. Quantification
by external calibration against matrix-matched standards was successfully used for more than 50 elements. These standards,
in the form of pressed pellets (no binder), were prepared in-house using ferromanganese concentrates from a deep-sea nodule
reference material as well as from shallow-marine concretions varying in size and having different proportions of three major
phases: aluminosilicates, Fe- and Mn-oxyhydroxides. Element concentrations in each standard were determined by means of conventional
solution nebulisation ICP-MS following acid digestion. Examples of selected inter-element correlations in distribution patterns
along the cross-section of a concretion are given. |
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