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NMR has traditionally lagged behind other analytical techniques when it comes to sensitivity. As a consequence, anything that can decrease the amount of sample needed for NMR analysis will in turn increase the utility of NMR, and that's exactly what MicroFlow NMR does. On a mass basis at a given spectrometer field strength, the CapNMR probe provides a 10-fold increase in sensitivity for a given sample mass compared to conventional 5-mm NMR probes. The CapNMR probe rivals cooled probes for mass sensitivity, and often provides better data quality.
Performance |
Common 5mm |
LC Flow |
Specialty Trace |
CapNMRTM |
Spectral Resolution (Hz) |
< 1 |
< 1 |
< 1 |
< 1 |
S/N (fixed mass) |
1 |
1.3 |
2 |
10 |
Relative Data Acquisition Time |
100 |
59 |
25 |
1 |
Salt Tolerance |
ok |
ok |
ok |
excellent |
To achieve the same level of sensitivity increase by the traditional route that NMR sensitivity gains have been made over the last 20 years (by increasing magnet field strength) it would take a 2,300-MHz NMR spectrometer using a conventional 5 mm sample to yield what you would get with CapNMR at 500 MHz. In other words, you'll have to wait a long, long time to get NMR sensitivity gains if you rely on magnet field strength increases. In addition, cooled probes may provide similar mass sensitivity, but unlike the CapNMR probe they are vulnerable to salty samples, and large solvent residual signals.
A benefit of the capillary NMR scale is that the relative concentration of sample to solvent is much higher that in conventional probes. This results in spectra with less interference from solvent resonance lines and solvent impurities and a cleaner NMR spectral baseline. Recent comparisons of CapNMR to cryogenic probe data show that for a given mass, CapNMR provides consistently cleaner data from these solvent interferences. In addition, CapNMR probes are considerably more salt tolerant than other probes, especially cryogen probes.
The CapNMR is just like any other NMR flow probe, except it's more sensitive. Once a spectroscopist becomes familiar with handling a few microliters of sample, operation becomes routine. CapNMRTM probes do not require a dedicated instrument as compared cryogenic NMR probes: you can add CapNMRTM to any system knowing that you can swap it in and out in a few minutes just like any other non-cryogen probe. This is an important point as it allows a spectroscopist to use a full range of probes to solve specific NMR problems and not be locked into a system where a probe change is a headache and a long and perhaps risky procedure.
CapNMR probes are easy on the budget, costing 3 to 4 times less than cryogenic high sensitivity probes. This means that you could outfit more NMR systems with a high sensitivity CapNMR probe giving the spectroscopy lab a bigger productivity multiplier (more bang for the buck). A further advantage is that all the spectrometer equipped with CapNMR still can do all the former work they were doing AND they become high-sensitivity capable ... you don't lose any productivity or flexibility.
