Cold-Probe Users Manual - University of Colorado Denver
Contents
1. z el j Compressor O Inlet psi 213 0 Htr Res Ohms F 40 j Valve 2 Channel 9 1 Cool Pack Errors F valve 3 Channel 2 Eject Air O lon Pump Torr Mda Mas Eoaea S Valve 4 Channel a8 Turbo Torr 2 31E 8 z Ion Pump O Ion Valve Channel 44 High Limit w 10 00 Accelerate Warm Up ie acon Test Valves F4 Sars TA Low Limit Y X CoolPack Configuration Enable Eject Air on Error Load Config F5 Disable Eject Air on Error Potente a Ion Pump On Error Path 9 C CryobayErrors Ion Pump Off Data Path amp C CryobayData Exit Enable Yacuum Error Checking Save Config F6 Disable Vacuum Error Checking Error amp Data File Paths Figure 4 The layout of the CryoBay Monitor Window During routine operation the region outlined in red should be monitored carefully Temp is the temperature of the cold head inside the probe and is essentially the temperature of the RF coil This value should not change by more than 0 5 K when an experiment starts Once steady state has been reached this value should be stable at 25 K Heater is the amount of power in Watts required to heat the super cooled He gas to 25 K This value should not change by more than 1 Watt compared to its starting value If too much power is used during an experiment then the probe will not be able to maintain a steady temperature and damage may occur to the probe and your sample Timer is th2. Before starting your acquisition with the cold probe you should do the following e dsp i or dsp to make sure that it is set to i qcomp y or qcomp to check oversamp 16 or oversamp to check rof2 2 4 not gt 5 gradientshaping y CHECK your decoupling and spin lock powers decoupling and spin lock times and your acquisition time to be sure that you do not exceed the limits specified for the probe Seeprevious page e After starting your acquisition CLOSELY monitor the CryoBay Monitor window paying close attention to the Heater power and the Temperature You should monitor this for at least 5 minutes after the acquisition begins e Ifthe heater drops more than 1 2 Watts from the baseline i e if Heater drops from 3 9 to 2 7 ABORT the acquisition aa and check your decoupler powers spin lock powers decoupling times and spin lock times see above Remember that in most cases the acquisition time at also represents a decoupling time e For long multi day experiments check the information in the CryoBay Monitor Window each time you check on your acquisition 10
3. channels tune only no match adjustment the cabling for probe tuning is the same as for a conventional probe Cold Probe Operation on the 600 4 Setting Up Experiments Variable Temperature Sample Temperature e The cold probe has a VT range of 0 to 50 degrees Celsius DO NOT EXCEED THESE LIMITS e Do not set the FTS below 15 degrees C e ALWAYS ensure that there is VT gas flow to the probe 20 L min This is very important to prevent the sample from freezing Radiofrequency Power Handling Issues As with any probe using too much Rf power for too long a time can damage the probe The cold probe is more efficient in terms of B1 field vs Rf power therefore the user must be cognizant of the correct calibrations for this probe The power levels for the cold probe must be adjusted from those values used in experiments performed on the regular probe The values below represent safe operating limits for C and N Decoupling and H Spin Locks If multiple spin locks and multi nucleus decoupling is used you must adjust your pulse sequence parameters so that you do not too put much power into the probe e Standard Pulse Widths 1H 8 2 us at 55 dB 13C 14 us at 59 dB 15N 40 us at 60 dB e Safe levels for C Decoupling dowr 43 pw 80 4 us 3 1 KHz field for a maximum of 12 Omsec dowr 45 pw 63 9 us 3 9 KHz field for a maximum of 60 msec e Safe levels for C Spinlock owr 52dB 8 7 KHz for a maximum of 25 msec e Safe l
4. particularly those obtained from Lewis Kay in Toronto do not use this parameter Damage to the probe may occur if you use one of these experiments without any modification Cold Probe Operation on the 600 Instrument Cabling The preamplifer for the proton observe channel is now located inside the cryogenically cooled region of the probe Consequently a different receiver pre amplifier module called a Cryopreamp Driver has replaced the original preamp The way this system is setup for operation and probe tuning is different Probe Tuning In addition to cabling issues the cold probe has a different user interface for probe tuning A single brass knob is used to tune all channels A larger knob is used to position the tuning stick to engage the tuning element for each channel Tuning channels are available for H Tune H Match C Tune N Tune and H Tune Cold Probe Operation on the 600 2 Description of the Cold Probe System The layout of the cold probe system and the individual components are shown in Figure 2 The basic theory of how this woks and what each component does is as follows Figure 2 Layout of the Cold Probe System Close Cycle Chiller He refrigerator r ae N Vibration Cryogenic Vibration isolation plate damping pier probe e Cryobay o Helium gas is compressed by a compressor inside the CryoBay and this is fed into the e Closed Cycle Chiller CCC which is the box located in the
5. pit of the 600 where it undergoes thermal expansion e Closed Cycle Chiller o Inside the CCC thermal expansion of the He gas is used to cool the cold head to below 25 Kelvin A small amount of the Helium gas is routed through the cold head in the CCC where it is cooled to below 25 Kelvin and then flows through the flexible stainless steel line to the side arm of the probe and up through the probe Sample tube e Probe o Within the probe the cold He gas is used to Cryo cooled r f coil cool the tuning elements the coils and the Cryogenic heat exchanger receiver pre amplifier to 25 K Figure 3 The coldhead probe contains a vacuum chamber at 10 10 Torr to thermally isolate the cryogenic Vacuum chamber circuit from the outside world As a result the probe body sample and the magnet are kept at or near room temperature while the probe is at 25 K Hniena oneee saptar w e A WARNING Even though the sample is relatively well cold He E insulated from the cryogenic temperatures inside the gas supply P probe it is imperative that dry air or nitrogen is kept Warm He gas return flowing through the VT port in the probe Without VT Vacuum chamber valve air flow the sample will cool at a rate of 1 C per minute until it freezes Figure 3 Diagram of the Cold Probe e The Intelligent Temperature Controller o The ITC is located inside the cryobay and can be seen at the back of the cryobay It uses a va
6. the Tuning VT Assembly of the Cryo Probe Right Photo of the tuning assembly installed in the probe with the tuning selector set to C and the tuning rod in the down position Rotate the Function Selector until the desired channel is visible in the Indicator Window Cable the Preamp Tune Interface as required described above Selected the appropriate channel number on the reflected display meter as usual Push the brass Tune Match knob up until it seats fully into the slot Turn the brass knob to tune and minimize the reflected power on the tuning meter Proton Channel Tuning e Rotate the Function Selector to 1H T 1H Tune Push the brass Tune Match knob up until it is fully seated Adjust the 1H Tune for minimum reflected power LOWER the Brass Tune Match knob pull down Rotate the Function Selector so that 1H M is in the window Push the brass knob up to engage and adjust the 1H Match for minimum reflected power Repeat until the probe is optimally tuned and matched Note that the tuning dip is extremely sharp with these probes therefore the sensitivity of the tuning is very high In contrast the match is very broad and may need to be turned some distance Typically proton will tune to a reflected power of 2 and C and N to values 4 10 It takes a patience anda careful touch to properly tune these probes e After the probe is tuned be sure to re cable the system for normal operation e For tuning the C and N
7. Using the Cold Probe on the Varian Inova 600 NMR Spectrometer Original material March 2004 by Rich Shoemaker Dept of Chemistry University of Colorado at Boulder Modified by David Jones Univ of Colorado Health Sciences Center September 2006 WARNING Read through the whole manual before using the cold probe Failure to follow the guidelines in this handout could result in severe damage to the Cold Probe and to your sample All NMR experiments must be modified to account for the substantial differences in the technology of cold probes If you are using the cold probe for the first time make sure that you check with the manager that your experiments are acceptable for use on the cold probe Failure to do so will require that your group pay for any repair costs that are incurred due to damage caused by your experiment If you have any doubts about how to run the cold probe ASK it is better to spend 10 minutes figuring it out than 3 months waiting for the probe to come back from the repair shop Cold Probe Operation on the 600 1 Overview This manual is intended for users who are experienced at operating Varian NMR spectrometers at a relatively high level of proficiency The intent is to point out the issues pertaining to the cold probes how the use of the cold probe differs from a conventional probe and the issues that directly affect how one does spectroscopy with these probes and how to avoid damage to the probe are highl
8. adient amplitudes can lead to a loss in gradient reproducibility and a reduction in signal to noise WARNING Only pulse sequences that use the zgradpulse statement to apply gradients will use gradient shaping A number of earlier pulse sequences particularly those obtained from Dr Lewis Kay s group in Toronto use the rgradient parameter to apply gradients DO NOT USE THESE experiments on the cold probe They must be edited to have all the rgradient statements replaced with the zgradpulse statement Data Acquisition Issues Your data acquisition with the cold probe is affected by the long ring down times of the Rf pulses To deal with this a new global flag parameter called qcomp is used in conjunction with oversampling dsp 1 Make sure that dsp i dsp The parameter qcomp should be set to y by typing qcomp y The parameter rof2 should be set to 2 4 usec lf digital signal processing is turned off at any time dsp n then gcomp will also be set to n lt must be reset to y manually after dsp l is executed The software will reset the oversampling any time the spectral window sw is adjusted The parameter oversamp indicates the amount of oversampling being used If oversamp is too large acquisition errors can occur e BEFORE STARTING YOUR ACQUISITION type oversamp to check the amount of oversampling being used There is no real reason for it to be greater than 16 Summary
9. cold probe assembly to support or steady yourself while working under the probe The probe is under a high vacuum and any disturbance to this vacuum will cause the probe to shut down and warm up to room temperature e Atthe probe the process of tuning is significantly different Refer to Figure 8 below for the following description which shows the tuning assembly at the bottom of the probe e The tuning assembly consists of two parts the first part is a small brass tuning knob which is used to tune the selected channel IMPORTANT the tuning knob slides up and down into the probe to engage the actual tuning rods inside the probe The tuning knob MUST BE PULLED DOWN before a different channel can be selected Cold Probe Operation on the 600 e Before starting tuning make sure that the tuning knob is pulled all the way down Figure 8 e Use the function selector knob to select which part of the probe circuit is being tuned The window in the side of the function selector shows which part is being tuned The options are 1H M Proton Match 1H T Proton Tune 2H Deuterium Tune 13C Carbon Tune 15N Nitrogen Tune Temperature controller gas flange screw Temperature iar one of three controller LN e connector hg y Heater Function a Va assembly selector knob Label carrier Flow cell port 2 plug removed be gt Function Tune Match _ i indication selector knob window Figure 8 Above Diagram of
10. e amount of time left until the probe will be ready for us if it is in cool down mode B Sample Insertion and Ejection The cold probe can accommodate both round and rectangular NMR tubes Rectangular tubes are used to reduce noise when the sample contains high concentrations of salt There are two different spinners for these probes The spinner for the rectangular tubes has a rectangular slot as you might expect The spinner for the round tubes has a slot cut into the bottom of the spinner See Figure 1 Cold Probe Operation on the 600 There is a danger of your sample freezing and causing damage to the probe if there is a loss of temperature regulation if the VT gas flow is turned off Therefore the probe is equipped with an emergency sample eject system As part of this system the top of the bore tube on magnet has been modified to include a Sample Catcher This consists of a small brass toggle switch that will prevent the sample going into the magnet In an emergency the sample is very forcefully ejected from the probe so that it pops up above the catcher and as it drops back down is caught on the lip of the catcher To insert your sample place the spinner into the bore tube so that it sits on the lip of the sample catcher Slide the brass nut on the front of the catcher to the Off position Figure5 your sample should slip down over the catcher and float freely on the stream of eject Figure 5 Sample Catcher for air Th
11. ecise temperature by using an Intelligent Temperature Controller ITC to heat super cooled helium gas to a stable temperature of 25 0 Kelvin under normal operation When RF power is inserted into the probe especially when using broadband decoupling i e N and C this causes heating of the probe and this is compensated by changing the power in the heater controlled by the ITC The heater power in Watts is displayed in the CryoBay Monitor window As the net RF power in an experiment increases the heater power will drop to maintain a steady probe head temperature of 25 0 Kelvin If too much power is used such that lowering the heater power cannot maintain the probe head temperature then the tuning will be lost and ultimately damage to the probe or the receiver pre amplifier in the probe could occur Pulsed Field Gradient Performance The inductance of the gradient coil in these probes is much higher Adjustments have been made to the gradient amplifier to compensate for this in addition the software has built in rudimentary shaping of the rise fall times of the gradient pulses to further improve the gradient performance esp the amplitude stability A new parameter called gradientshaping a global flag parameter is used to activate the shaping of the gradient pulses WARNING Gradient shaping only works for pulse sequences that use the zgradpulse statement to control gradients Many early experimental pulse sequences
12. en slide the switch back to the On position Emergency Eject System You can then proceed as normal WARNING The sample catcher must be in the On position if a sample is in the magnet Serious damage to your sample and the probe may result if the catcher is left in the Off position C Instrument Probe Cabling TE P Cabling for C N and H is the same as a conventional eres probe including the location of the bandpass filters H From HB Amplifier cabling is different Refer to Figure 6 and the following J5303 instructions to ensure that the system is cabled properly ee e The cable from the High Band Transmitter plugs into the To Probe H CY top port HB XMTR J5303 e HBPROBE XMTR J5331 goes to the 1H port on the probe e HB PROBE PREAMP J5335 connects to the 1H RCVR port on the probe J5331 e OUTPUT J5302 is connected to the same cable as a Ae PREBE BREEN normal pre amplifier Output cable connects to the mixer From Probe Fa in the magnet leg interface H Premap ee Signal path To HB pa The transmitter pulse is routed to the probe from port RCVR nd J5331 on the cryopreamp driver to the probe This cable a fat cable also carries the DC voltage for gating the Transmit Receive Switch Figure 6 Cryoprobe Preamp Driver h a J5304 After pulsing the NMR signal is amplified in the pre amplifier located inside the probe and this signal come
13. evels for N Decoupling dowr 2 42 pw 306 us 0 8 KHz field fora maximum of 120msec e Safe Levels for H Spin Locks TOCSY spin lock pwr 44 pw 29 4 us 8 5 KHz field for a maximum of 80 msec ROESY spin lock pwr 34 2 6 KHz field for a maximum of 450msec e Safe Levels for H Decoupling ow and dpwr 3 48 dB pw 400 us field strength 0 6 KHz for a maximum of 60 msec NOTE For C decoupling you should use WURST 40 decoupling schemes instead of GARP wherever possible This will reduce the amount of probe heating On the CryoBay Monitor there is a value for HEATER This represents the number of watts being used in the heater to maintain the probe temperature of 25 Kelvin As more RF power is delivered to the probe the HEATER wattage will drop PAY ATTENTION to this heater power when an experiment is started If the heater power drops by more than 1 2 Watts STOP YOUR ACQUISITION aa Adjust your power levels spin lock times acquisition times and relaxation delays to reduce this Cold Probe Operation on the 600 Using Pulsed Field Gradients To improve the stability of gradient pulses with the cold probe all gradients are implemented as shaped gradients so that the gradient is turned on and off in a smoothed fashion albeit somewhat crude This shaping is turned on for all experiments by setting the parameter gradientshaping y lt is recommended that all gradient amplitudes used are less than 18 000 Larger gr
14. ighted Note Some of the figures have been used with permission from Varian Doing NMR spectroscopy with a cold probe is essentially the same as with a conventional probe however certain properties of the cold probe must be understood to obtain optimal results Each of these will be address in further detail later in this document The primary issues that should be understood are View from Sample Spinners bottom The salt tolerant cold probe can accept square tubes as well as round tubes To allow this to happen there are new spinners for use on the cold QO probe The spinner for square tubes is obvious the spinner for round tubes has a slot cut into the bottom See Figure 1 Use of other spinners will mean that your sample will not get into the probe Figure 1 Spinner for use with cold probe Rf Pulse Ringdown Times Due to the high Q Quality factor of these probes the ring down time of the RF coil after a pulse is significantly longer This means that the delay between the end of the pulse and start of signal detection is longer Since pre acquisition delays can adversely effect the appearance of the spectrum mostly in frequency dependent phase errors and other baseline issues there are new parameters that deal with this problem The parameter qcomp for Q compensation is used and is dependent upon the settings of the dsp parameter Rf Power Handling The coil in the probe is maintained at a pr
15. riable heater inside the probe to maintain the desired temperature at the coldhead 4 Cold Probe Operation on the 600 3 Preparing for NMR Experiments on the Cold Probe Doing NMR is not much different than a normal probe The main issues are associated with how much power you can use in your experiments for decoupling and spin locking etc A Monitoring the Status of the Cold Probe Before starting an experiment check the status of the probe in the CryoBay monitor window Figure 4 Note the value of Temp and Heater readings in the box outlined in red You need to know the values of these settings when the probe is not in use so that you can judge how much power you are using in your experiments I gt CrunRaw Front Danol WY 2 rri 4 me selector oo ak CryoBay Monitor Mass flow SLPM VARIAN Settings l 2 26 28 Enable ITC Te m p 2 5 O 4 Cold loop impedance Disable ITC j na Timer Te C L 1 1 8 Cooling Configuration DAQ Configuration Errors j Device 1 LabVIEW Errors CI P Cooling ee N Exhaust Ch pre Error 5012 occurred at an ose rane n unidentified location Total Time Mi Snlet___ F3 H eate r 3 12 saeh Mass Flow Ch massflow Possible reasons PSI Time Sec CCC P1 Psi Ton Pump Ch Jonpump_ Fault Vacuum CCC P2 Psi IMG Yacuum Ch oe z Scan Rate 4500 Set Point k z Purge In O Off Temp k NScans 250 pees Exhaust psi 181 9 ee Pn Weare 7
16. s back to J5335 on the cryopreamp driver The signal is further amplified and sent to the mixer RCVR via the OUTPUT J5302 port Cold Probe Operation on the 600 D Probe Tuning For C N and H channels the cabling to tune the probe is the same as with a normal probe The Probe connector on the tune interface connects to the appropriate channel on the probe and the cable connected to the Output port of the BROADBAND Pre Amplifier is connected to the Output port of the tune interface For the H channel THE CABLING SETUP FOR TUNING IS DIFFERENT Figure 7 e Disconnect the thick cable connected to the top port of the cryopreamp driver J5303 Figure 7 A and B e Using a short BNC cable connect the now empty port J5303 Figure 7B to the PROBE port of the tune interface module Figure 7C Move the cable from J5202 OUTPUT to the OUTPUT port of the tune interface DO NOT REMOVE the cables going to the H channel of the probe J5331 The system is now ready to tune the H channel of the probe Figure 7 Cabling of 1H Preamp for normal operation and tuning A Normal operation B After removing HB transmitter cable and C After bridging HB transmitter and Probe connector on Tune interface CAUTION Extreme care must be exercised when working under the magnet Be very careful not to touch the side arm or any of the vacuum connections on the probe Do not lean on pull or otherwise press on any part of the
Download Pdf Manuals
Related Search