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a query again? I recorded an DQF on deuterated solid sample. The basic pulse programme taken from bruker, optimised the pulse and kept the proper short delay between the last two 90 pulses? phase cycling is same as mentioned in bruker? I got empty spectrum with very poor diagonal and no cross peaks? what could possibly go wrong ? does these delays depend on higher magnetic field strengths? or pulse imperfections cause collapsed spectrum or empty spectrum? the spectra i recorded on 700 MHz with 14 KHz MAS. regards anup |
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I forgot to add it is DQF COSY with MAS on solids |
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Few questions for you please. What nucleus is being detected? I would try synchronizing the delay between the final two 90's to a half-rotor period. You could check 'high-resolution NMR techniques in organic chemistry', Claridge 1e. for basics on COSY, I am guessing half-rotor periods based on this discussion. Good Luck! Dear The detected nucleus is 13C. 1D of 13C is good.linewidth reduced to 2.5 Hz for the solid sample. i did not look for simple cosy. i am using microcrystalline protein. the delay between the first two pulse was 490 us.the t1 delay between scans is 7s. the last two pulses short fixed delay of 4us. - anup chowdhury (Nov 21 '11 at 07:25) 13C detected 1D is a normal direct polarisation without CP with low decoupling of 1H and 2H in my sample.comparable linewidths with that of standard adamantane.all the pulses are 5.5us each.the last two 90 pulses was not rotor synchronised. - anup chowdhury (Nov 21 '11 at 07:32) but on the other hand, i have got the 2d spectrum with dqfcosy at 400MHz with 20KHz MAS.it was informational with the desired multiplet formation(quite resolved and medium S/N). but as field increased to 600 and 700, the spectrum is empty. kindly suggest. thanks for the above suggestions. - anup chowdhury (Nov 21 '11 at 07:34) |
