tag:blogger.com,1999:blog-3300702123878659843.post2358100173903974447..comments2024-03-26T05:25:50.831-04:00Comments on University of Ottawa NMR Facility Blog: Pure-Shift HSQCGlenn Faceyhttp://www.blogger.com/profile/05146575170575279335noreply@blogger.comBlogger4125tag:blogger.com,1999:blog-3300702123878659843.post-4135151745776410762018-12-08T07:21:16.846-05:002018-12-08T07:21:16.846-05:00Hi Pete,
Thank you for your thoughtful and informa...Hi Pete,<br />Thank you for your thoughtful and informative response. <br />GlennGlenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-15009209162558816862018-12-07T18:33:47.797-05:002018-12-07T18:33:47.797-05:00Hi Jasper, Glenn,
In this case the only losses ar...Hi Jasper, Glenn,<br /><br />In this case the only losses are due to relaxation during the refocusing blocks and imperfect refocusing. The BIRD pureshift works by selecting only the protons bonded to 13C and decoupling them from those bonded to 12C, but in the HSQC you already only see the 13C bonded protons so there is in principle no loss. So in practice for CH/CH3 protons the overall gain in S:N is significant. For CH2 protons the gain is usually less because the 2J coupling remains, but in my experience you still don't really lose anything compared to the non pureshift version.<br /><br />This is in contrast to the 1D case where compared to a simple proton spectrum you really lose a factor of 100 for BIRD and significant but usually rather lower factors for e.g. PSYCHE.<br /><br />However:<br />Long AQ may mean you need longer D1 than for the non-pureshift version to mitigate sample heating effects (although this is not really true for X-optimised probes at lower fields where the decoupling power is quite low)<br />You really need a multiple of 2 scans for the pureshift version, whereas 1 scan is usually OK for the non-SI sequences without pureshift.<br /><br />So the minimum experiment time is usually longer, and the signal:noise per unit time may not be as much higher as you would guess by comparing otherwise identical pureshift and non-pureshift versions.Petenoreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-71096032210463395642018-11-16T09:12:21.658-05:002018-11-16T09:12:21.658-05:00Jasper,
In my limited experience with this method,...Jasper,<br />In my limited experience with this method, I find that the SNR gain attained in the Pure Shift HSQC due to the collapse of 1H-1H coupling compensates any other loss in SNR associated with Pure Shift methods. The gain in SNR is however signal dependent. Your question may be better directed to the NMR methods group in Manchester.<br /><br />GlennGlenn Faceyhttps://www.blogger.com/profile/05146575170575279335noreply@blogger.comtag:blogger.com,1999:blog-3300702123878659843.post-18956004222803337402018-11-16T05:00:23.662-05:002018-11-16T05:00:23.662-05:00Hi Glenn,
Does the increased S/N ratio gained by ...Hi Glenn,<br /><br />Does the increased S/N ratio gained by the collapse of multiplets compensate for the loss in sensitivity normally associated with Pure-Shift experiments?<br /><br />Kind regards,<br /><br />JasperAnonymoushttps://www.blogger.com/profile/17857267707111060976noreply@blogger.com