Dear Charlie,
First, the INEPTRD sequence (refocused inept in Bruker-speak) has fairly significant advantages over DEPT for any experiment where J is small, because the INEPTRD sequence is significantly shorter than DEPT [ <= 1/J versus 3/(2J), respectively]. The time savings improves as the number of neighbor protons increases (as with TMS). We observe significant improvements using INEPTRD for 29Si with J < 20Hz over DEPT.
It turns out that Bruan, et al., do have a problem in their write-up for the 29Si experiment, in both the 100 and 150 Exps editions, and it's a fairly serious error at that. They did fix one error in going from the 100 to 150 editions, in changing the label correctly in eq (1) from d2opt to d3opt.
But in both editions, d3opt is 2x too large. The total final delay in an INEPTRD sequence is delta, which is split into two delta/2 periods, each equal to d3. Braun, et al., are using in eq (1) the optimum value for delta, not d3. Thus, eq (1) in section 9.4 should be:
d3opt = (2*pi*J)^-1 arcsin (n)^1/2
The error is a big one, because twice the d3opt, as stated in the book, is a _very_ non-optimal value (approaching a null!). You should see good INEPTRD data with this corrected setting, and J~8Hz for TMS. The DEPT experiment may be too long for your sample; it may work ok for degassed samples, where relaxation is longer.
Cheers,
Charlie
At 04:51 PM 7/2/2003 -0400, you wrote:
>Dear Ammrlists
>
>
>I'm in one of those mind raveling situations trying to run
>something very simple which does not appear to work at all,
>even after multiply rechecking EVERYTHING.
>
>Particularly I am trying to get Expt 9.4 "29Si NMR
>Spectroscopy with DEPT" in Berger's '150 & More..' to run, in order
>to decrease spectrometer time and get rid of the glass signal.
>This expt also appears in the earlier version of the book
>so surely it is right as writ...but maybe not.
>
>In my hands doing straight decoupled 29Si on my TMS sample I
>get s/n 900 in a single scan. With the Berger DEPT sequence
>I get only 250 after jiggering the final delay.
>
>I have quadruply checked my pulse calibrations for 29Si and 1H,
>being sure my '90s' are not 270s, that I have not reversed powers
>or labels for the two nuclei/pulses, that my constants and
>multipliers are right (his example is TMS!) that I have his
>pulse sequence correctly translated, correct phase cycles,
>etc., etc. etc!!!
>
>I was puzzled at the discussion in the Comments for Expt 9.4
>on the length of the final delay ...for INEPT which this is not.
>When I do vary that delay at least I get some Si signal but
>nothing like the predicted enhancement.
>
>I am hoping some lab is out there which does a lot of routine
>29Si can straighten me out on applying DEPT to 29Si. I am
>running xwinnmr 2.5 on an AVANCE600.
>
>Thanks in advance
>
>Charlie Dickinson
>
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Charles G. Fry, Ph.D. Tel: (608)262-3182
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Received on Mon Jul 07 2003 - 17:26:36 MST