The open-access automated NMR facilities comprise a Bruker DPX200 spectrometer (first floor), and four Bruker automated AV400 spectrometers; the AVG400 and AVH400 on the ground floor, the AVF400 on the first floor and Hg400 on the second floor. The purpose of the open-access facilities is to allow researchers in the CRL rapid and simple access to routine spectra of proton, carbon, fluorine, phosphorus and selected other nuclei. They are geared towards fast turnover and hence rapid sample throughput.
The open-access spectrometers are configured in such a way that they are very easy to use for routine 1D and 2D spectroscopy; the configurations of the various instruments are summarised below, and details of available experiments are summarised on in this table. Samples that require more complex analysis should be submitted to the NMR service or you may be trained by the NMR staff to do this yourself. You will be shown how to run spectra when you attend a basic training session, which you must do before using these instruments.
Bruker DPX200 [Organic]: This operates automatically but with manual sample insertion, providing 1D 1H NMR only.
Bruker AVIII400 (AVF400) [Organic]: This spectrometer operates automatically and provides: 1D 1H, 13C, DEPT, 19F and 31P; 2D 1H-1H COSY and 1H-13C HSQC. Between 1pm and 6pm proton, phosphorus and some fluorine experiments have priority. The current status of the automation run and whether your sample has been completed can be checked through its automation history web page: http://flounder-crl:8015/ (log in using avf400 as log-in and password).
Bruker AVIII400 (AVG400) [Organic]: This spectrometer operates automatically and provides quick 1H spectra during the day (8am – 7pm) and also 13C, DEPT, COSY and HSQC experiments overnight. The current status of the automation run can be checked through its automation history web page: http://turbot-crl:8015/ (using avg400 as log-in and password).
Bruker AVIII400 (AVH400) [Organic]: This spectrometer operates automatically and provides quick 1H, 19F and 31P spectra during the day (9am – 9pm) and also 13C, DEPT, COSY and HSQC experiments overnight. The current status of the automation run can be checked through its automation history web page: http://halibut-crl:8015/ (using avh400 as log-in and password).
Bruker AVIII400 (Hg400) [Inorganic]: This spectrometer operates automatically and provides quick 1H, 7Li, 11B, 19F, 27Na, 27Al, 31P and COSY during the day (8am – 7pm) and also HMBC experiments overnight. The autosampler will accept both normal and Young’s tap NMR tubes.
Sample preparation and handling
The open-access spectrometers attempt to automate some of the more troublesome aspects of spectrometer operations. The automatic lock and shim systems are quite effective, but in order for these to be reliable, to make subsequent operations straightforward and to obtain a good quality spectrum, care must be exercised when preparing samples. This is of utmost importance! Remember: Junk in, Junk out! The following points are most important:
- Precision 5 mm tubes must be used (available from stores, as are deuterated solvents). These should be periodically checked for cracks and for scratches around the bottom of the tubes, and discarded if necessary.
- Tubes that are shorter than 7 inches are already broken and should be discarded.
- Samples must be made up to a solvent depth of 4.0-4.5 cm. This is an extremely important point! If you allow the liquid column to fall below 4 cm, the instrument will find it more difficult to lock and shim. Making samples too deep, although less detrimental, will dilute your sample and waste solvent.
- Care should be taken to ensure that sample tubes are clean on the outside before placing them in the instrument. Contamination of the probe, either by transfer of external dirt or by a sample breakage in the probe, is a very serious matter. You will be shown how to insert a sample correctly into a turbine and then into the magnet or sample changer during your training session. If you break a tube whilst loading a turbine, clear up the mess with some methanol. DO NOT USE chlorinated solvents as these destroy the depth gauge plastic.
- When preparing samples you will typically require the following sample quantities for acceptable results:
ca. 5 mgs for a proton spectrum
ca. 50 mgs or more for a carbon spectrum
ca. 2 mgs for a proton spectrum
ca. 20 mgs or more for a carbon spectrum
When handling oils, the quantity drawn up into a pipette by capillary action should be sufficient for a proton spectrum. It is good practice to filter your samples before placing them in the NMR tube as floating debris or a cloudy solution can be guaranteed to give a poor result.