The Faculty of Science of the University of Ottawa is seeking a technician for its very active Nuclear Magnetic Resonance (NMR) facility. This rapidly growing NMR facility serves more than 25 active research groups and consists of 7 NMR instruments ranging in field from 200 to 500 MHz. The facility conducts a wide range of modern NMR experiments on both solids and liquids as well as MRI. As the NMR technician, you must hold at least a B.Sc. degree in chemistry or a related field (M.Sc. preferred) with at least two years experience in either one or both high resolution or solid state NMR spectroscopy. You must be enthusiastic, highly motivated and work well both independently and in groups. Extensive computer experience is mandatory. As you will be interacting daily with students and faculty, you must have excellent interpersonal skills as well as excellent oral and written communication skills. Reporting to the NMR facility manager, you will collect routine NMR data as a service, assist students and answer questions, train new users of the equipment, help with equipment maintenance (including cryogen fills), maintain a data archive, keep accurate time and usage records, and assist the NMR facility manager in the general operation of the facility. French/ English bilingualism is a definite asset. The position is open for one year starting August 15, 2010 and will be renewable, availability of funds permitting. The annual salary range for this position is $38,862 - $51,504. For consideration, please email your CV and cover letter to the Human Resources Service firstname.lastname@example.org and refer to competition number TSCI9583NEP. Please also have three letters of recommendation emailed or sent to:
Dr. Glenn A. Facey
NMR Facility Manager,
Department of Chemistry, University of Ottawa
10 Marie Curie, Ottawa, Ontario, K1N 6N5
ph. (613) 562-5800 ext 6077
fax. (613) 562-5170
The deadline for applications is Friday June 25 at 5:00 pm.
More information is available at the following web site:
Thursday, May 27, 2010
Wednesday, May 26, 2010
Despite my best efforts in teaching students how to properly use NMR spectrometers, invariably a new user will, on occasion, drop a sample spinner into a magnet without a sample. This is usually done in our undergraduate laboratory by inexperienced students who have finished collecting their data and feel a need to return the empty spinner to the magnet. The problem is that ejecting the empty spinner with the eject air is not possible as the air passes through the spinner. In the past I have removed empty rotors from magnets on Varian spectrometers by removing the upper barrel of the magnet. On Bruker spectrometers, I have removed the probe and inserted a semi-rigid NONMAGNETIC plastic hose in the bottom of the magnet and pushed the spinner to the top of the upper barrel where it can be removed by a helper. In either case, the entire operation took between 5 minutes (Varian) and 30 minutes (Bruker) depending on how much reshimming was required. To avoid this tedious chore, I had our machine shop make a plastic tool for empty rotor removal shown below.
This tool consists of a pole with a diameter slightly less than that of the spinner. On the end of the pole is a tapered prong with a diameter of 4 mm at the tip and 6 mm at the base. This tool is inserted in the top of the magnet and gently lowered until the prong gets wedged into the empty spinner. The spinner is removed with the tool. The entire operation takes less than 10 seconds and no reshimming is required.
Thursday, May 20, 2010
Shaped excitation pulses can replace the non-selective hard pulses typically used in a one-pulse measurement to achieve selective excitation. Another method of achieving selective excitation is the gradient spin echo using a selective 180° pulse. This technique is demonstrated in the figure below. A non-selective hard 90°x pulse is first given followed by a pair of identical pulsed field gradients sandwiching a soft selective 180° pulse about the y axis. The hard 90° pulse rotates all spin vectors onto the -y axis. During the first gradient pulse the spin vectors dephase and evolve according to their offset frequencies. The soft 180°y pulse flips a single resonance 180° about the y axis leaving all other resonances untouched. During the second gradient pulse, the "selected" resonance is rephased and its offset frequency evolution is refocused. The unselected resonances dephase more and continue to evolve according to their offset frequencies. The receiver is then turned on to collect the FID of the "selected" resonance, all others are dephased and therefore suppressed. This is demonstrated in the figure below which shows 1H NMR spectra for a mixture of methylence chloride and acetone. The bottom trace shows a standard one-pulse measurement. The middle and top traces show results from a selective gradient spin echo measurement with the selective 180° pulse set for methylene chloride and acetone, respectively.