Aromatic compound mapping - ToF-SIMS

Animal health is closely linked to human health. These species share the same ecosystems. It is therefore essential to ensure that they are well constituted, which sometimes means resorting to medicinal treatments. The different texture and taste of drugs compared to their usual food can be unpleasant for animals, making them difficult to administer.

To solve this problem, some drugs are formulated to look, smell and taste attractive to pets.

Veterinary laboratories are developing new types of food products containing active ingredients. Chewing gum against fleas and ticks, for example, can be flavored with beef to mask the scent of drugs.

To maintain optimum texture and uniform taste throughout the gum, it is important to ensure that the active ingredients and excipients are evenly distributed.

ToF-SIMS in ion imaging mode will map the various elements and molecular compounds present on chewing gum sections, with submicron lateral resolution. The primary ion beam, reduced to a small diameter spot, scans the surface of the sample to be imaged.

Secondary ion extraction and mass analysis optics enable chemical images to be reconstructed by synchronizing the detection of the secondary signal with the scanning of the primary beam. The lateral resolution of the images depends on the size of the micro-beam (from 100 nm to 3 µm in diameter, depending on the analysis conditions).

ToF-SIMS can detect trace elements down to ppb at the extreme surface (< 1 nm), and in profile mode down to 20 µm in depth on vacuum-compatible samples of all types.

A pulsed source of mono- or multi-atomic primary ions (Ga+, Bin+, Au+, C60+, ...) with an energy of a few keV bombards the sample surface. The secondary ions resulting from the interaction between the primary ions and the sample are accelerated with the same kinetic energy towards the time-of-flight analyzer, which separates them according to their m/z ratio with very good mass resolution (M/ΔM > 10,000 at mass 28). The mass spectra thus obtained represent the number of secondary ions as a function of their travel time to the detector, which is proportional to the square root of the m/z ratio.

TESCAN ANALYTICS has over 20 years' expertise in the use of ToF-SIMS on all types of materials, whether insulating or conducting... With state-of-the-art instruments, our team of experts works with all industrial sectors.

Figure 1: 2D ToF-SIMS images of the superposition of ions characteristic of beef flavor, phosphates and starch for batch 1


Figure 2: 2D ToF-SIMS images of the superposition of ions characteristic of beef flavor, phosphates and starch for batch 2

First, ToF-SIMS molecular analysis of the raw materials used in chewing gum formulation was carried out. This is used to identify the tracer ions in the ingredients, and to determine the best polarity to use for chemical imaging (in this case, negative polarity).

Two chemical maps (4 x 4 mm²) were therefore produced using negative polarity on two sections of the two batches of chewing gum. Figures 1 and 2 show the superposition of tracer ions for beef flavoring (red), phosphates (green) and starch (blue).

The chemical images and mass spectra obtained on the chewing gum sections show that :

• significant differences in ingredient distribution between the two batches,
• phosphate and starch intensities are higher for batch 1,
• in addition to the raw materials, the samples show high levels of phosphate ions, which may be associated with beef flavoring.

In this example, the ToF-SIMS imaging mode revealed visual information on the micron-scale distribution of chewing gum ingredients.

ToF-SIMS can map the distribution of the various elements and compounds present in a sample with sub-micron resolution.

In other work, ToF-SIMS has been used to map 2D contaminants on the surface of technical parts (steel, ceramics, glass, etc.) or biological materials (animal fiber, skin, mouse brain, etc.).

For more analysis applications with ToF-SIMS or other techniques offered by TESCAN ANALYTICS, visit our topics page.

Other complementary techniques can also be used to study the surface structure of a sample (TEM, SEM) and to analyze its chemical composition (EDX, XPS).