Thanks for those who have replied my message.
I have done the following before I sent my message:
reinput base frequency with 'cf',
run experiment using diiferent spectral windows of 20,40,60ppm,
I got same chemical shift value, 8.18ppm. So, the problem is not caused by
folded peak or wrong base frequency. The magnetic field should be same as
before because 2H lock sinal is correct. I guess we could win a nobel
prize if we solve this problem.
Thanks,
Quincy
>Hi, All -
>I have a strange problem with our Bruker AC300. The chemical shift value
>of the instrument is wrong. I used a sample containing TMS and CHCl3 in
>CDCl3. The CHCl3 peak has a chemical shift value of 8.18ppm referenced to
>the TMS peak at 0.0ppm. The frequency difference is 2454 Hz. That means
>that reference frequency has to be 337.55 MHz (instead of 300.13MHZ) in
>order to obtain 7.27ppm (2454/7.27=337.55). I have checked the parameters
>called from a standard parameter file. Also, the same test sample was used
>on our AC250. It gives correct CHCl3 chemical shift (7.27ppm). So, the
>sample is fine. Does anyone have any idea what is wrong with the
>instrument?
>Thanks a lot.
>
>Quincy
>Univ of Georgia
Received on Wed Feb 09 2000 - 18:06:03 MST