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Hi, Most people tend to use a lower d1 for 2D than for 1D. Help me understand why. Furthermore, supposing you know your T1 value, what do you think is the "best" (or most effective while having the shortest experiment time) value for d1 in a 2D experiment? I'm not even sure my question makes any sense. |
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Hi, Your question makes perfect sense! In 2D experiments we are usually more concerned about sensitivity than how quantitative the spectrum is. For experiments where we effectively use a 90 degree excitation pulse, which is the case for most 2D, the maximum signal per unit experiment time is obtained when the relaxation delay =1.3xT1. Such a short relaxation delay would lead to significant intensity distortions so is not ideal for 1D spectra (you want to be able to compare the size of integrals in a proton spectrum, for example). You may want to go even shorter if S:N is not an issue (e.g. COSY), simply to reduce the experiment time. Additionally, for HSQC spectra you excite and observe protons directly bonded to C13 - the dipolar coupling provides an efficient relaxation mechanism for those protons. So they have usually a rather shorter T1 than the main peaks in the proton spectrum (usually <1s, and often quite a lot less). So for HSQC a relaxation delay of 1s or less is common, whereas for HMBC (where we excite and detect protons not bonded to C13) we usually use longer. |
