While a good nmr tube will not guarantee a good spectrum, a bad nmr tube will always result in a "poor" spectrum. A bad NMR tube will introduce large spinning side bands and bad line shape that cannot be compensated for with instrumental adjustments. No matter how long you shim or the number of transients acquired a spectrum obtained with a bad tube will have problems.
The factors that dictate what is a good quality tube are primarily, how straight the tube is (Camber), how uniform is the wall thickness, and how close are the inner and outer surfaces of the tube to perfect cylinders running parallel to each other. The last two factors relate to the "Concentricity". Wilmad defines this as "A measure of the lack of wall uniformity, ...the degree to which the cylinders defined by the inner and outer surfaces of the tube are parallel and overlap". The outer diameter of a tube has to meet exact tolerances. If it is too large it can contact the glass insert protecting the probe coils. If it is too small the tube can move in the spinner turbine when the sample is lowered into the probe, resulting in the tube hitting the bottom of the probe. Either way the probe can be damaged, and the nmr tube can break with loss of the sample.
The first step is to buy good nmr tubes and avoid the bad nmr tubes. The cheap "disposable" or "economy" tubes are adequate on a 200 MHz nmr, but will show limitations when run on higher level instruments. Can you use the cheapest tubes at the higher fields? Yes, BUT you shouldn't. We strongly recommend against the use of the "disposable" tubes on any instrument over 200 MHz. The cheap tubes may fit in the spinner turbine, but they could fail to spin properly or they may damage the probe. They will also be more difficult to shim.
General tube parameters:
For all our instruments and probes you will need NMR tubes with 5 mm outer diameter and 7 or 8 inches in length.
You will see advertisements for thin wall tubes. Unless you have a dramatic need to really maximize your sensitivity, these thin wall tubes are very easy to break and are therefore not recommended.
Because the company Wilmad has been marketing nmr tubes so long it's tube nomenclature has become somewhat of a standard reference. For this note the tube designations are from Wilmad, unless noted otherwise. Each company lists which tubes it recommends for a given magnetic field strength (listed as proton spectrum frequency). The better tubes listed at each class will usually work with routine samples at the next class. Thus, the 528pp listed for 400 MHz work is also fine for most 500 MHz experiments; and the 526pp at 360 MHz is also good on a 400 MHz instrument for most experiments. And, of course, you can always use the higher quality tubes at the lower magnetic fields.
So, what tube(s) should be purchased? The following table represents our recommendations:
Wilmad and Norell tubes can be purchased directly from their manufacturers or through Sigma-Aldrich.
Shigemi tubes are NMR tubes designed to increase the sensitivity of very diluted samples. The glass in these tubes is matched to the magnetic susceptibility of the solvent used. For our instruments you will need either the CMS-005TV (for CDCl3); MMS-005TV (for CD3OD); DMS-005TV (for DMSO-d6) or BMS-005TV (D2O). These tubes can also be purchased from Aldrich.
For routine work on organic samples you will need a deuterated solvent that is at least 99.8% enriched and containing a small quantity of TMS (0.03%). Deuterated chloroform with these specifications corresponds to Cat.No. 225789-100G in the Aldrich catalog.
It is important to take good care of your nmr tubes after purchase. The glass used for nmr tubes is a "soft" glass. Avoid storing the tubes leaning in a beaker or flask. Instead, store them horizontally on a flat surface. Also, avoid exposing the tube to extreme heat. The best way to dry tubes is in a vacuum oven at a temperature below 105 °C, with the tube lying flat on a glass plate. If a vacuum oven is unavailable, use a regular oven set to 125 °C, place the tubes on a flat glass plate, and remove the tubes as soon as they are dry, usually 30-45 minutes.
-Chris Kojiro May 2001, updated March 2003, March 2005.
-E. Alvarado, updated August 2011.
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