Table 1 Recommendations to obtain high A_m in C-11 and F-18 productions

Use highly pure target gas 6.0

Use only highly pure target gas and flush gas (purity: 6.0, 99.9999%) to avoid carrier CO₂ in target. Via isotope exchange in target the A_m of the final product will decrease. The target gas mixture should be analysed for carbon < 0.1 volume per million (VPM) of CO₂ and CO (detection limit). The use of gas purification cartridges may also be advantageous. Low volume targets are to be preferred to obtain high A_m/A_s

Use highly pure target flush gas 6.0 (Helium, Nitrogen or Argon)

Target flush or push gas transports [¹¹C]CO₂ from target to synthesis module. Use only highly pure target flush gas 6.0 (99.9999%) to avoid non-radioactive CO₂ accumulation in the CO₂ trap. Note: if Argon is used as push gas beware it condenses at − 150 °C

Insert a molecular sieve (CO₂ trap) in line before target

Most suitable inline CO₂ trap is an Ascarite® column. CO₂ will be converted to carbonate under basic conditions and sticks in the column. This process can influence the performance of the column and therefore important to replace the column frequently

Prefer inert tubing to the target and from target to hotcell (stainless steel, PEEK)

The choice for the appropriate inert material, depends on the situation of the lab. For instance, PEEK tubing must be replaced frequently and if stainless steel tubing’s are used, there must be a possibility for frequent rinsing of these lines to remove carrier carbon

Use inert target and target seals

Carrier carbon could be released and migrate from target metal and seals into target body

Fill the target directly after irradiating with target gas

The target must be filled to avoid isotope exchange of carbon with highly pure target gas from the surrounding area

Dump irradiation each morning

Because of possible minor leaks into the gas handling system, like valves and tubing, the first irradiation provides lower A_m compared to the following irradiations. Keep in mind that air contains 380 ppm carbon dioxide. It can be advantageous to flush the target and tubing to the radiosynthesis system several times with high purity gas (e.g. helium) to remove carrier carbon

Use of glovebox for solvent storage and dissolving precursor

Glove box filled with highly pure gas (preferred to use argon) avoids accumulation of CO₂ in the solvent used to dissolve precursors

Use highly pure enriched water ([¹⁸O]H₂O) and check certificate of analysis (COA) of enriched water for fluoride content

To avoid trace of carrier cold fluoride (¹⁸F is diluted with ¹⁹F), and will decrease the A_m

Use highly pure target push gas 6.0 (Helium, Nitrogen or Argon)

To avoid trace of carrier fluoride. See comments in previous table

Use inert tubing from target to hot cell (like PEEK, PTFE)

To avoid trace of carrier fluoride. See comments in previous table above. Selection of inert tubings must be done carefully and the selection of materials are site specific

Clean target

Clean according to an approved cleanings procedure to avoid possible accumulation of carrier fluoride in target. See for procedures in IAEA document https://www-pub.iaea.org/MTCD/Publications/PDF/Pub1563_web.pdf

Radiotracer production

Notice that a radio-synthesis starting with [¹¹C]CO₂ and using reagents that are reactive at ambient temperatures, often yield products with low A_m. E.g. radiosynthesis with Grignard reagents and organolithium compounds

Use inert materials for cassettes, tubing, valves etc.

Selection of inert materials must be done carefully and the selection of materials are site specific

Use pure precursors (99%)

To obtain radiotracers with high A_m it is important to avoid traces of carrier during the synthesis

Use high purity chemicals and gasses (e.g. acetonitrile, potassium carbonate, Helium, Nitrogen etc.)

See above

Use minimising amounts of starting materials/reagents

Minimising added carrier as contaminants could be beneficial to obtain high A_m