362.3 or 363.3 m/z

[pliva]

dear all,
we have API 3200 SCIEX Applied biosystem. yestearday i scan ciprofloxacine for which the molecular weight is 331.35. i was expecting my parent ion as 332.35. but i got a sharp peak of 331.5 along with the 332.5. the intensity of 331.5 is almost double the 332.5. can i take 331.5 as my parent ion? i check the isotopes of fluorine also but the isotopic abundace is negligible. then i fragment the 332.5 parent ion and got 288.1 as daughter but the intensity was not that much stable. i confirm the precursor scan of 288.1, its ok. just tell me how to get a stable freagmen.

[sassman]

Maybe you need to tune and calibrate the instrument. It is possible that you mass calibration is off. I think cipro should be at 332 in positive ion mode. For fragmentation, you want to infuse the compound into the mass spec using a syringe and use tune to adjust the parameters which give best fragmentation.

[kuldeep_mica]

I agree with sassman regarding the shift in MS. You can check for the mass shift of instrument by injecting any other standard. Also for scaning of your compound, you can try to scan your compound in acidic media. We have observed that tuning a compound in slightly acidic media (e.g. 0.1% Formic acid in methanol) gives better results then in plain solvent solution.

[bert]

We have observed that tuning a compound in slightly acidic media (e.g. 0.1% Formic acid in methanol) gives better results then in plain solvent solution.

Dear kuldeep_mica,

What do you mean with better results??

regards Bert