-- Dr. Bob Berno Manager - McMaster NMR Facility Department of Chemistry McMaster University 1280 Main St. W Hamilton, ON L8S 4M1 Phone: 905-525-9140 ext. 24158 or 24686 FAX: 905-522-2509 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ "Brian Cherry" <Brian.R.Cherry_at_asu.edu> 28-Jul-2008 17:30 Hi Andy, I?m an used to work for Bruker primarily focusing in solids service and applications. Given that my words could be biased, but I do feel so. In addition to my 3 years at Bruker, I extensively used a narrow bore 4 mm solids probe with a flip type stator. I found them to be rather robust, as long as one understood the design and it?s potential limitations. First, which model of probe do you have? Is this a new Bio-solids H/C/N probe or one of the broadband HX probes? The new HCN is slight better with angle setting. Both probes use a screw to set the magic angle. When the stator is flipped there is a chance that the screw will release tension and change the set point, thus effecting the angle setting. To avoid this, always make your final adjustment in the direction that screws the magic angle set screw out. This method reduces the chance for the set point to slip when the stator is cycled. And time the probe is removed from the magnet, I would verify the angle adjustment. If the probe was handled carefully then the angle could still be fine or very close. But I would always re check it. Also, after initial adjustment I would cycle the stator, you can remove the eject gas line so the sample shoot up and down everytime, this is save you time. Once you?ve cycled set the angle a time or tow it will be reproducible. Hope this helps. Brian Arizona State University ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Dear Andy, I have used Bruker narrow-bore MAS probes on a 500 and 600 for several years. I find them extremely sturdy. Even the magic angle doesn't change any bit after several flip ups and downs. The only trouble is that it is very easy to mess up the stator if you open the probe and do anything with the stator. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Hi Andy, I have a lot of experience with Bruker MAS probes, both wide bore and standard bore. I was a Solid State NMR Applications Scientist for Bruker (USA) for 6 years. One of my current instruments (new in 2004) is a Bruker500 standard bore (SB) with a 4 mm MAS probe. This has the flip-type stator that is common to the SBMAS and HRMAS probes. Prior to working at Bruker, I had more than 10 years' experience with Chemagnetics and Doty probes in wide bore systems. With my Chemag/Doty background I was particularly skeptical of the flip-type stator. I personally tested many SB probes in the course of my work at Bruker. I looked for and did find problems with particular probes (especially with angle instability) and to my great surprise the problems were fixable. My current 4 mm SB MAS probe has worked extremely well. I use it on average about one 24-hour period per month. I run in automation using a solids sample changer (end MAS rate 14 kHz-- limited by my particular samples) and MAS-II unit and it performs reliably. The magic angle setting is fine every time I check it. ***Note, specifically---- By that I mean, after running 24 hours' worth of samples in automation and then storing the probe in a cabinet for weeks, I install the probe and do not have to adjust the angle. That is stable. Insertion/ejection work well with the sample changer. I set up all the samples, come back the next day to a pile of processed spectra and my rotors waiting to be cleaned. This ain't grad-school SSNMR! Having said that, like anything else you buy, you could get unlucky with a particular purchase. Also note that it has to be installed and set up correctly in order to work properly. Make sure that your probe is robust if you buy it. Do not be shy about negotiating your own specs right into the contract before you agree to purchase. I would insist (in contract) on the following very simple test to be demostrated on the new probe in my system with my equipment: Step 1. Insert a rotor packed with KBr (or other angle-test sample of your choice), spin it up to about 5 kHz, adjust the angle if necessary and measure the spectrum. Then spin it up in 5 kHz increments to the maximum specified MAS rate and observe the stability of the spinning rate to make sure it's in spec. Measure a spectrum at the highest MAS rate, if desired, and then drop the MAS rate down to 5 kHz or wherever you started and measure your spectrum again. Compare the spectrum carefully to the first one measured. Does the angle require adjustment? If it does, the probe needs to be repaired and should not be accepted. If the angle does not need adjustment, eject the rotor and go to Step 2. Step 2. Insert the sample again, spin up to the test rate, then measure the spectrum. Do not make any adjustments to the angle setting! Eject the sample. Step 3. Repeat Step 2 at least 10 more times, preferably between other samples. If you want, add a step for removing and reinstalling the probe, but this is not so important. It's very important to eject and insert the rotor between tests. Step 4. Compare all the spectra measured: the envelope of the spinning sideband pattern should be constant. The magic angle should be stable. In a properly installed and working Bruker SBMAS probe it will be stable. If it's not stable, you will have spectral evidence of the instability. Good luck! With best regards, Kelly Kelly L. Moran, Ph. D. Staff Scientist Ashland Inc. Global Technology Analytical Services & Technology http://www.ashlandanalytical.com 5200 Blazer Parkway Dublin, OH 43017 USA 614-790-3936 614-790-4294 (fax) KLMoran_at_Ashland.com ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Hi Andy, I have found that the reproducibility of this type of stator is very good. I would set mine after installation in the magnet and it would be correct for a series of experiment. If I had the probe in for an extended period I would just check it every few days, with a KBr/ Adamantane mix sample. These observations pertain to Hr-MAS and CPMAS probes of the 4mm variety in narrow bore system You could give me a call if you feel you need more info 650.467.8692 Regards Steve Huhn ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 25-Jul-2008 14:03 I have had a Bruker narrow-bore solids probe for over 8 years. It has been very stable and reliable. Although I check it each time I install the probe, it generally requires little or no adjustment of the magic angle. In the past I would check it if I ran multiple samples, but I now have confidence in its stability. I have never had a problem with insertion and ejection of the samples. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 25-Jul-2008 13:46 Andy - I think that this may depend upon the vintage of the probe. We have used an older probe (~ 10years old) and to be honest it wasn't the best. However, with samples like 3-methyl glutaric acid as a setup sample (carbonyl linewidth <15Hz on a 400) it is trivial to verify the angle after each probe change. My concern is the flip between samples. Our probe was OK (not as good as a fixed wide bore) but acceptable for analysis of organic crystalline systems. Where we had problems was with decoupler efficiency. The older narrow bore probes couldn't handle the high power as well and changed performance over time. My understanding is that the newer probes are quite good though. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Dear Andrew, we have been using standard bore 4mm and 3.2mm probes at 750 and 900MHz instruments for a while. Our overall experience with MA stability was quite good. However, it pays off to be careful: you set magic angle on KBr, flip the stator back and forth, check and, if necessary, reset MA till you get reproducible results. Then, you should be ok. I measure MA by (first sideband)/centerband ratio on KBr at 5kHz spinning frq. The maximum ratio is about 15%, you can get reprodicible 12-13% ratio with a standard bore stator. It's enough for C(O). If you run VT experiments, be aware, magic angle setting changes for several hrs till it stabilizes and you need to reset MA at low temperature. Long term and short term performance of high field standard bore probe could be better. So far, we have not been able to achieve fields beyond 90-95kHz on 1H channel and 40-50kHz on 15N/13C channels. Sometimes the probes start arcing immediately, sometimes it takes them 1-3 weeks to start arcing. One 4mm HCN probe has been functioning ok for several months (at power levels mentioned above). ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Hi Andy, We have a 4mm HX MAS probe for a narrow-bore magnet and a 2.5mm HX MAS probe. I swap back and forth between these probes each week and by default run KBr to set the magic angle each time. The 2.5mm probe is fixed at the magic angle and remains remarkable consistent, with my tweaking of the magic angle simply confirming that nothing has changed. As the stator is fixed this is perhaps not a surprise. The 4mm probe flips the stator from vertical(to accept a sample) to the magic angle to run an experiment, then back to the vertical position to eject the sample. The magic angle is not retained as accurately over many sample changes compared to the 2.5mm probe, however, the error is not large and excellent CP-MAS data can be recorded for long experiments(days) and for many short experiments with many sample changes. More demanding sequences such as ST-MAS that require an exact angle will suffer. We run KBr regularly just to reset the magic angle, it is quick, simple and serves as proof that the probe was correctly setup. Variable angle spinning is possible with these probes which allows the reintroduce dipolar couplings and CSA, which can be useful in certain applications. I have used probes that need to be removed from the magnet for each sample change and this usually involved moving the tuning rods. I found these probes far less convenient to use. The 1990s vintage probes from Bruker were occasionally "variable-angle" - drifting away from the magic angle during the same experiment, however, our new 4mm probe arrived here in 2005 and is robust and holds the magic angle reliably over many sample changes for our CP-MAS work. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We've had our HR-MAS probe for ~8-9 years now and not had any problems with it. To be honest, it doesn't get a great deal of use these days (since we stopped doing solid-phase chemistry) and I don't think its been in the magnet for about a year so I can't comment on heavy sample changing performance but when we have put it in it has worked pretty well "straight out of the box". The biggest factor in how well it holds at the magic angle seems to be how careful you are not to catch the adjusting vernier when taking/putting the probe from/into the box - and its very easy to catch it. Hope this helps & let me know if I can be of any further assistance Best Regards Ian Ian Marshall C.Chem. M.R.S.C. Principal Spectroscopist, Selcia Ltd. Tel +44 (0)1277 367017 Fax +44 (0)1277 367099 ian.marshall_at_selcia.com ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ To my excperience (3 years, Bruker Avance, 4 mm NB BB probe) the angle does change in an unpredictable way, so it is advisable to check it after each probe change. However normally I do not check it at each new sample. Otherwise the probe perfoms fairly well, the biggest problems are the rotor crashes, be careful with high density samples. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Cheers, Andy ----------------------------------------------------------- This e-mail was sent by GlaxoSmithKline Services Unlimited (registered in England and Wales No. 1047315), which is a member of the GlaxoSmithKline group of companies. The registered address of GlaxoSmithKline Services Unlimited is 980 Great West Road, Brentford, Middlesex TW8 9GS. -----------------------------------------------------------Received on Tue Aug 19 2008 - 03:42:42 MST
This archive was generated by hypermail 2.4.0 : Wed Jun 14 2023 - 15:15:08 MST