To gain maximum use of your analysis time a proper sample preparation is essential. Samples which apparently not meet the requirements will not be analysed.
Potential sample material
Dry, solid organic and inorganic (including metallic) materials can be analyzed. Examples:
- Microorganisms and particles on filters
- Thin sections or polishes cuttings of samples
- Thin sections or polished cuttings of resin embeded samples. Please use high-vacuum resistant resin (e.g. araldite).
Different sample holders are availiable. Round samples of different diameters (2.54 cm, 1.25 cm, 1 cm, 0.5 cm) can be mounted. The outer millimeter of the sample is covered by the sample holder and not analyzable. Best results are received from Spots in the middle. If you provide several samples please consider employing 1 cm or 0.5 cm samples because more mounting places are available for these diameters. Filters can be cut in the lab directly before the transfer in the vacuum. The height of sample including mounting material for e.g. thin section should not exceed 0.5 cm.
Essential requirements for analysis
During the analysis process charging of the sample occurs due to the flow of charged particles. To enable continuous discharging the sample needs to be conductible. Non conductible samples can be covered by a layer of metal or graphite.
- Vacuum resistance
The sample needs to withstand a vacuum of down to 1.0*10-10 mbar. Thus, samples are not allowed to have remains of oil or particles on it. The use of gloves is essential. Resin embedded samples need to be thin enough to facilitate the outgassing of the resin. Resin embedded samples should be delivered at least one week prior to analysis to make sure the required vacuum can be reached.
- Surface quality
The maximum height of the sample on the carrier material (e.g. filter) should be 10 µm at maximum to receive a homogenous secondary ion yield and homogenous angular emission. Flat samples enable a fast and accurate analysis. Thin sectioning of samples can be advantageous.
The sample is introduced to a strong electric field. The electrostatic lens system employs + and - 8000 V and has a distance of less than a Millimeter to the sample. Under these conditions no sample parts or particles are allowed to ablate from the sample because arcing can occur and pollute or destroy the lens system.
- Identification of the spot of interest
The location designated for analysis needs to be easily identifiable to make maximum use of the analysis time. An overview-Map with markieng of the desired analysis spots is recommended. A laser-dissecting-microscope is availiable at the IOW to perfom laser marking of spots of interest as well as overview pictures.
To enable measurement under high vacuum conditions the water needs to be removed from biological samples. Simple drying is one options but to prevent redistibution of the elements of interest an fixation might be needed. For immobile, not soluble elements chemical fixation can be used. For mobile/souble elements cryo-fixation is recommended.