Probeheads inverse

The most commonly used probehead is the inverse dual probehead, which contains an additional coaxial coil that is tuned to resonance frequency, surrounding the detection coil for hetero-... 

As is the case in most gradient-enhanced pulse sequences, GROESY spectra should preferably be obtained with non-spinning samples. In our spectrometer, a Bruker ARX-400 equipped with an inverse broadband probehead incorporating a shielded Z-gradient coil, we have used the following experimental parameters ... 

Triple Inverse 5mm TBI probehead for H and C observation with one additional channel for X observation or decoupling (choice of one nucleus within the range P -" Ag), a Z-gradient coil and operable in the temperature range -50° to -t-80°C. 90° pulselenghts for H and "C were 6.9us (-6dB) and 13us ( dB) respectively. 

Figure 3.63. Gradient recovery after application of a 1 ms square gradient pulse of 0.25 Tm" (50% of maximum output). The sample is chloroform and data were acquired with an actively-shielded 5 mm inverse z-axis gradient probehead.

Figure 3.66. Proton resolution and lineshape tests for a static 3% CHCI3 sample recorded on a 400 MHz spectrometer equipped with a dual H C inverse probehead. The C satellites are clearly seen in (b) at 109 Hz, whereas the artefacts at 20 Hz arise from floor vibrations.

Heteronuclear correlation experiments with IR detection in the direct acquisition period t2 are often called inverse detected experiments. The term "inverse" is also used to describe probeheads that are constructed with the coil as the inner coil and the rf coil for the heteronuclear frequency as the outer coil. The outer coil has a lower sensitivity because of the lower fill factor. This term may also be used to distinguish between two classes of experiments. The HETCOR and COLOC experiments belong to the class of direct detection experiments with take advantage of the coherence transfer from the sensitive nucleus to the relatively insensitive heteronucleus. This type of experiment is illustrated by the first entry in Table 5.22. However experiments in this category are no longer popular and have been superseded by inverse detected experiments, shown in the second entry in Table 5.22. In a comparison of the different types of experiments the IH detected heteronuclear correlation experiments have three distinct advantages over the detected experiment ... 

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