Magnetic field drift

When a new superconducting magnet is brought up to field one of the specifications for assessing it is magnetic field drift. A cryomagnet's magnetic field is not constant but changes with time, and if this change is too rapid then the magnet becomes difficult to use. Measuring the drift rate of a new magnet is one criterion for judging its quality.

Sine bell for truncation

The sine bell is a window function commonly used to enhance the appearance of truncated data, such as often recorded for multidimensional NMR spectra. The sine bell ensures the signal decays to zero and fourier transformation will not produce artifacts. Shifting the sine bell also allows some resolution enhancement to be applied.

Gaussian multiplication for resolution enhancement

When processing NMR data a window function, or apodisation, is typically applied to emphasise or deemphasise certain aspects of the spectrum. Numerous window functions are available each with their own benefits and drawbacks. A gaussian multiplication is often applied to 1D data to increase resolution at the expense of sensitivity.

Exponential multiplication for sensitivity enhancement

When processing NMR data a window function, or apodization, is often applied to the raw data before fourier transformation to enhance the appearance of the spectrum. For one dimensional spectra an exponential multiplication is often used. This window function reduces the noise at the expense of resolution.

Sensitivity in reduced diameter tubes

Sensitivity is the bane of NMR. Spectroscopists are always looking for ways of increasing it, particularly when sample is limited. One suggested method to increase sensitivity is to reduce the volume while keeping the amount of material constant, thereby increasing the concentration. This can be done by using a smaller diameter NMR tube, e.g a 3 mm or 1.7 mm tube. I have been skeptical of this method for a long time and finally decided to test how well it works.

Fill volume for 5 and 3 mm NMR tubes

While 5mm NMR tubes are the default size for solution NMR, several alternatives are available. For those with less sample 3mm, 1.7mm, and 1mm NMR tubes are available. The 1.7mm and 1mm NMR tubes really require a microprobe with reduced diameter coils, but 3mm tubes can be used in a 5mm probe. With our 1.7mm probe out of action I purchased a 3mm spinner and ran some spectra to compare the fill volumes of 5mm and 3mm tubes in our 5mm BBI probe.

How much sample do I need for a carbon?

Probably the most common question I get asked is "How much sample do I need for a carbon?" The answer is - it depends on the probe being used, the molecular weight of the compound, and how long you are prepared to run the experiment for. For most people, however, "it depends" is not a very satisfactory answer, so I've tried to find a way to get some numbers to answer the question.