Hello everybody. In our institution we routinely prepare C-11 methionine radiopharmaceutical. Recently after the synthesis we obtained the excess of pH value (pH=9,5) in final sterile solition of C-11 methionine. Normally it should be in the range 4,5-8,5. Can anybody suggest the reason if this?
The only source of OH- ions we have is water-ethanol (60:40) solution of NaOH which used to dissolve the precursor of methionine. After the dissolution of precursor we put an aliquot of 0,3 ml onto solid-phase extraction cartridge Sep-Pak C18 plus (Waters). The last step of radiosynthesis of C-11 methionine is on-column methylation on Sep-Pak C18. After this we elute the radiotracer from cartridge by 0,1M NaH2PO4 solution (7 ml).
Evidently the reason could be the excess of NaOH. Either you put more volume on the cartridge, or concentration of NaOH in the solution was too high. The easy test is, if you mix the 7 ml phosphate buffer with the NaOH solution and measure the pH. By the way, what is the concentration of NaOH?? Do measure the pH of the phosphate buffer as well. It can happen, if somebody uses dinatrium phosphate instead of NaH2PO4.....
- Badges
- Science topic
- Similar topics
- Biological Science
- Biochemistry
- Biochemical Techniques
- Analytical Chemistry
- pH