High spatial resolution analysis of ferromanganese concretions by LA-ICP-MS†

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

Development and application of a calibration technique for laser ablation - ICP - MS

Laser Ablation - Inductively Coupled Plasma - Mass Spectrometry (LA-ICP-MS) is a powerful analytical technique for the direct elemental analysis of solid samples, with spatial resolution down to a few microns. However, calibration remains the limiting factor in obtaining quantitative analysis by LA-ICP-MS for a wide range of sample types. No universal method exists as yet and the ones that are currently used tend to employ matrix-matched solid standards. Matrix-matched solid standards are not available for many types of sample, such as polymers, biological materials, fluid inclusions, etc. The need for a universal method of calibration that involves standards that are easy to prepare and suitable for any type of sample is required. Additional to matrix-matching, internal standards are widely used in LA-ICP-MS for quantitative analyses. The internal standard compensates for the different ablation yields from the sample and the standard and for the laser shot-to-shot variation. Given that the use of an internal standard is required to obtain reliable results, the need for matrix-matching might be regarded as questionable. This project has focused on the development and application of a new method of calibration for LA-ICP-MS. It involves the use of aqueous standards whose absorption characteristics are modified by the addition of a chromophore to the solution. Additives were selected for ablation with KrF excimer, and Nd:YAG lasers. The influence of the additive concentration on the ablation yield was investigated for different laser energies. Response curves were obtained showing that as the additive concentration was increased, less energy was required to ablate the modified standard solutions efficiently. A general procedure was then defined for the preparation and use of the modified standard solutions for a given sample. The new method of calibration was used for the quantitative analysis of different sample types: low density polyethylene (LDPE), polyketone (PK), polyethylene thin film as well as gels contained in the thin film, and stainless steel. (author)Available from British Library Document Supply Centre-DSC:DXN043623 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo