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Since ROESY uses a cw spin-lock, is it safe to set up a mixing time of 500ms? If I want a roesy spin-lock strength of 2.5kHz, its corresponding optimized power level turns out to be about 25dB. In the bruker pulse program roesyph, p15 is the duration of the spin-lock and is equal to the mixing time (200ms). How is p15 related to the spin-lock strength? |
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Hi Visi, 2.5kHz RF field means a 100us 90 degree pulse. The typical proton CPD pulse would be shorter than that (higher power), and you would use that for the entire AQ in a carbon experiment. So basically any mixing time is safe at this level. In case you do not have CORTAB (in edasp, look for the green dot next to the routing path that indicates cortab is present - if so you are fine), then you should really check that the power level of 25dB does give a 100us 90 degree pulse. Without CORTAB, if you increase the attenuation by 6dB relative to the hard pulse, the change in power is not really as much as 6dB, so you have more power than you expect. I'm not sure from your question if you already did this, if you did then obviously that power level is fine. The relationship between max spinlock time and rf field is not specified for all probes, but for room temperature 5mm TXI probes 500/600MHz the spec was max 200ms for a 90 degree pulse length of 25us (10kHz rf field) or if you want longer than that 400ms is OK with 35us 90 degree pulse (just over 7kHz). At a power corresponding to 80us 90, there is no limit. For cryoprobes the typical pulses sheet that comes with the probe specifies the limits. Hope that helps! |
