Investigating the Sensitivity Limits of 13C-Detected 1H–13C Chemical Shift Correlation Sequences with Modern Microprobe and Microtube Technology

✍ Scribed by William F. Reynolds; Margaret Yu; Raul G. Enriquez

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 365 KB
• Volume: 35
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/(sici)1097-458x(199709)35:9<614::aid-omr146>3.0.co;2-x

✦ Synopsis

The sensitivity limits for 13C-detected 13C-1H shift correlation sequences were evaluated using a microprobe in combination with 3 mm microtubes Ðtted with susceptibility plugs which allow for further restriction of the sample volume. For an absolute value BIRD-decoupled HETCOR spectrum acquired in 4-5 h, the sensitivity limit for compounds with non-equivalent groups in ca. 3 lmol of sample, with signiÐcantly lower limits for compounds CH 2 with only CH and/or groups. For an absolute value n-bond spectrum acquired with the FLOCK sequence in CH 3 16 h, a similar amount of sample is barely adequate to observe cross peaks from singlets while a spectrum CH 3 showing a large number of n-bond peaks to CH, and protons requires about 15 lmol of sample. Further CH 2 CH 3 sensitivity gains could be realized by using phase-sensitive versions of the two sequences. While these experiments still fall considerably short of the corresponding limits for HMQC and HMBC using a similar 1H-optimized microprobe, the 13C-detected experiments can give signiÐcantly better 13C resolution, hence they may still be advantageous for organic structure elucidation in cases where 13C resolution is critical.