/ Chemical and surface analysis

Chemical and surface analysis

GCM Lab offers numerous chemical analysis techniques that each have its benefits and limitations. In order to make a choice, one should consider those four fundamental factors: the type of materials that can be analyzed (organic and/or inorganic), the type of information that can be obtained (molecular or elementary), the precision (quantitative or qualitative), the detection limit (%, ppm or ppb) and the depth of analysis (mm, microns or nanometers).

Some techniques are limited to the analysis of solids or liquids. For example, techniques performed under vacuum are not suitable for the study of liquids.

In addition, most techniques can be used to study either organic OR inorganic materials. In that organics are limited to carbon compounds and a few other elements while inorganics include the other ones, the requirements for a good identification can be very different. For instance, a FTIR spectrometer identifies the chemical groups present in organic materials but is almost ineffective for other materials. On the contrary, EDX analysis only gives elemental information (carbon, oxygen, copper) and thus offers limited assets for the analysis of organics .

A chemical analysis aims to obtain the sample’s elementary or molecular composition. For example, a 100g pyrite analysis will reveal approximately 46.5g of sulfur and 53.4g of steel or 100g of the molecule itself (FeS2).

For a simple inorganic sample, an elementary analysis can sometimes be all that is necessary. However, very often it is not the case for organic or more complex samples. Indeed, elementary analysis of polyethylene would only reveal the presence of carbon and hydrogen, which is not enough information to identify the chemical compound.

Furthermore, industrial samples often contain more than a dozen elements, making molecular analysis extremely useful. For example, in the case of a metallurgical residu containing lead sulphate (PbSO4), copper oxide (CuO) and copper arsenide (Cu3As), the elemental composition will only give a limited information about the compounds present.

Obviously, the precision of measurements is often critical. Analytical techniques can be:

Qualitative: Presence or absence of an element or molecule (no numerical answer)

Semi-quantitative: Numerical results with a large error  (ex: 30% +/- 10%)

Quantitatives: Numerical results with a small error (ex: 30% +/- 1%)

Obviously, higher precision is always a plus but in practice, qualitative measurements are often sufficient.

The detection limit of an instrument is the lowest amount of a molecule or element that can be detected from a blank signal. This limit varies significantly between samples and instruments. For example, the detection limit is approximately 0.1 atomic % for XPS, above 5% for FTIR and between ppm and ppb for TOF-SIMS.

The chemical information obtained by an instrument can originate from the first atomic layers (extreme surface), the surface (nanometers) or volume (microns and above). Surface information is extremely specific but also subject to contamination. However, it is well-suited to the characterization of thin films or to the creation of concentration depth profiles. Furthermore, different methods can be used to clean surfaces before analysis or remove contamination during data analysis.

S'inscrire à notre infolettre mensuelle et/ou suivre notre flux rss.