Agilent The 500 MHz OneNMR Probe Manual
Contents
1. and parameterization used for each experiment were identical The experiment time for each data set was less than 5 minutes Conclusions These results clearly demonstrate that data collection of routine organic chemistry spectra using the Agilent 500 MHz OneNMR probe can be accomplished without sample to sample tuning This procedure impacts neither the functionality of the NMR system nor the ability of the chemist to collect practical interpretable NMR data Furthermore the ability to operate the OneNMR probe without sample specific tuning saves the user time wear and tear on the system and mechanical complexity www agilent com Agilent shall not be liable for errors contained herein or for incidental or consequential damages in connection with the furnishing performance or use of this material Information descriptions and specifications in this publication are subject to change without notice Agilent Technologies Inc 2011 Printed in the USA March 18 2011 SI 1599 7 Agilent Technologies2. ratio of 3 7 Until now the only means available to correct this situation was to retune the NMR probe for every sample Since tuning the probe is a mechanical operation long term considerations of wear and tear must be considered Manual tuning is time con suming and prohibits the use of the spectrometer in an automated fashion The Agilent ProTune accessory allows automated probe tuning but this entails adding mechanical complexity to the system and more work is required when changing probes The 500 MHz OneNMR probe The Agilent 500 MHz OneNMR probe is very forgiving with respect to sample dielectric constant Repeating the experiments described above with the OneNMR probe demonstrates the outstanding sample tolerance of this system In this case the carbon pulse widths were observed to change by only 8 6 and the 13C sensitivity even using the default pulse calibrations was still 94 of optimum Table 2 Table 2 Relative Probe Performance 5 mm OneNMR Probe 90 degree pulse width 2Signal to Noise 13 13 Probe tuned to chloroform 6 95 us 1 00 Probe tuned to 200 mM salt 7 55 ps 0 94 2Both signal to noise measurements were made using the pulse width and power levels calibrated for the accurately tuned sample Given the C performance results presented above and the excellent H specifica tions of the Agilent OneNMR probe one might anticipate that the proton channel would suffer from this type of intentionally m
3. The Agilent 500 MHz OneNMR Probe Technical Overview Sample Dielectric Tolerance Advantage Statement The Agilent 500 MHz OneNMR probe is very tolerant of the differences in the dielectric properties of common NMR solvents thereby eliminating the need for sample tuning in the routine H and 13C environment This feature allows high quality data collection on typical organic chemistry samples without the cost in time wear and tear and complexity required to actively tune the probe for each sample Introduction NMR samples interact electromagnetically with the RF coils in the NMR probe The magnitude of this interaction is proportional to the dielectric constant of the sample When placed into the probe samples with a high dielectric constant such as ionic solutions couple strongly to the RF coils increasing the capacitance of the circuit and thereby changing the tuning of the probe Unless the probe is re tuned for this new condition the length of the 90 degree pulse width can suffer dramati cally Conversely a probe tuned appropriately for a high dielectric sample will not perform as well if the sample has a comparatively low dielectric constant for example chloroform n y Agilent Technologies The performance cost for running the NMR system in a poorly tuned state is significant for a typical NMR probe To demonstrate this effect a standard 500 MHz 5 mm Dual Broadband probe was tuned accurately on an organic chem istry sa
4. is optimized tune experiment This is not the case When the same worst case set of tuning experiments were repeated using the high frequency channel on the 500 MHz OneNMR probe the performance changes between the well tuned probe and the poorly tuned probe were negligible The proton 90 degree pulse width increased by 5 9 while the S N ratio decreased by only 5 3 These experiments plainly display the superior ability of the OneNMR probe to remain effectively tuned even with a large change in the dielectric constant of the sample Practical Application of the One NMR Probe s Sample Tolerance The ability of the OneNMR probe to accept a wide range of solvents with minimal change in probe tuning means that for routine organic chemistry applications at 500 MHz the OneNMR probe can be used to collect high quality data without adjustment of the tuning circuit from sample to sample The typical NMR solvents used in organic chemistry do not represent a large range of dielectric constants Chloroform is on the lower end of the scale with water on the upper side of the series Figure 1 Given this situation one could easily tune the 500 MHz OneNMR probe to the middle of the frequency shift band and simply leave it there The full range of organic NMR solvents would then be available for use without any need to retune the probe while maintaining essentially all of the excellent performance of the OneNMR probe Benzene S Chlorofor
5. m 2 Acetone 2 Water 3 200 mM Salt 2 Frequency Figure 1 Relative frequency shifts for various solvents as measured in the Agilent OneNMR probe The HSQC experiment is a cornerstone NMR experiment for organic chemistry It is also one of the more challenging experiments with respect to the quality of the NMR pulses used to collect the data This makes it a perfect test experiment to demonstrate the ability of the OneNMR probe to yield high quality data without the need for careful tuning adjustments Figure 2 displays two gHSOQC data sets obtained on a mixture of two alkaloids in deuterochloroform using the 500 MHZ OneNMR probe These data show that running a demanding 2 D experiment without tune optimiza tion has little effect on sensitivity In fact comparison of the first increment of two adiabatic HSQC experiments with the probe tuned versus detuned as described above yielded a S N change of less than 9 4 5 3 5 2 5 1 5 4 5 3 5 2 5 1 5 F2 ppm F2 ppm Figure 2 gHSQC data spectra acquired on a mixture of two alkaloids in deuterochloroform using the OneNMR probe The data in the left panel were obtained with the RF coils carefully tuned to the sample The data in the right panel were obtained on the same sample but with both the proton and carbon RF coils tuned on a sample of 200 mM NaCl in D 0 No attempt was made to compensate for the mis optimization of the RF pulses in the second experiment the pulse widths power levels
6. mple dissolved in deuterochloroform Carbon spectra were acquired to establish baseline performance for the 90 degree pulse width and sensitivity An aqueous 200 mM NaCl sample was then inserted into the probe and the system was tuned to this sample Using this tune setting the chloroform sample was returned to the magnet and the pulse width and sensitivity data were once again collected The results are shown in Table 1 Table 1 Relative Probe Performance 500 MHz 5 mm Dual Broadband Probe 90 degree pulse width Signal to Noise 3e 3e Probe tuned to chloroform 10 75 us 1 00 Probe tuned to 200 mM salt 15 00 us 0 59 1Both signal to noise measurements were made using the pulse width and power levels calibrated for the accurately tuned sample The NMR probe performance was degraded significantly by the poor tuning condi tion Moreover if a user attempted to operate the NMR in this condition using default system calibrations the pulse width expected to yield a 90 degrees tip angle would actually yield only 64 5 degrees of spin rotation An attempt was made to acquire HSQC data under these conditions but as would be predicted based on the effective tip angles the experiment failed to yield useful information As expected for the Dual Broadband probe configuration the H coil is not as strongly coupled to the sample Similar experiments carried out on the proton channel yielded a pulse width increase of 5 1 with a concomitant loss in S N
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Agilent The 500 MHz OneNMR Probe Manual