WET CHEMICAL ANALYSIS

The possibilities of destructive chemical analysis on metallic materials are completed with instruments capable of investigating items with irregular shapes or powders or shavings by means of mineralization in microwaves and the subsequent determination of the composition using ICP-OES and ICP-MS. The two techniques work in the liquid phase and allow to determine the concentration of almost all the elements present on the periodic table with higher accuracies than normal spark applications that work in the solid state. The possibility of working independently from the geometry of the product then makes it possible to analyze all those items of small dimensions or with irregular surfaces, low thicknesses or complex geometries that would not otherwise be analyzed.

ICP-OES is based on phenomena similar to those exploited by spark instruments. The elements present in solution are excited by plasma with subsequent light emission. Decomposition of the generated light spectrum in single wavelengths make possible to directly determine elemental composition of the alloy in terms both qualitative (type of element) and quantitative (concentration). One of the main advantages of working with ICP instead of spark-based instrument, lies in the possibility of working with a liquid obtained by mineralization of the alloy with a consequent greater specimen homogeneity. Sample isotropy guarantees more reproducible data and low measurement uncertainties.

The ICP-MS technique maintains the ability to work on liquids but is not based on light interactions but on ionic currents. The mineralized specimen is first ionized by a plasma and then accelerated by electric and magnetic fields (quadrupolar field) capable of passing only one type of ion at a time on the basis of its precise mass / charge ratio. The ability to select the desired element setting electro-magnetic parameters makes possible to exclude interference due to other elements present in high concentration and consequently increases the analysis sensitivity and selectivity. The technique is particularly suitable for the determination of trace elements where their concentration would be scarcely quantifiable with optical methods or where strong interference phenomena are present.

The ICP-OES and ICP-MS techniques have in common the preparation of the specimen but are therefore complementary to each other in terms of concentrations analyzed due to the different principles on which they are based. The former is mainly used for elements with a high alloy concentration while the latter is preferred for the determination of trace concentrations.

Almost all of the elements present on the periodic table can be analyzed with ICP techniques except for C, O, N, H, P and S.