CPMG and Red Blood Cells

In a previous post it was shown how one could discriminate against broad NMR lines and emphasize sharp NMR lines by using a CPMG T₂ filter.  This technique has tremendous power for getting detailed information from difficult samples.  Biological samples containing in-tact cells can be difficult because they contain semi-solid components with extremely short T₂'s and liquid components with dissolved compounds having much longer T₂'s.  The CPMG technique was used as early as 1988 to study red blood cells.*  The figure below shows 600 MHz ¹H NMR data collected at uOttawa on a sample of in-tact red blood cells.  The sample, obtained from centrifuged human blood, was paste-like and contained no solvent.  The magnet was shimmed using proton gradient shimming and the data were collected without the deuterium lock.

The top panel of the figure shows the result obtained with a standard one-pulse measurement. Clearly, the spectrum shows very little detail and is dominated by the water resonance.  The bottom panel shows the CPMG spectrum obtained after 350 echos using an echo delay time (2τ = 640 µsec).  One can clearly see the suppression of all the broad signals (including the water signal) with short T₂'s leaving the incredibly detailed and high resolution spectrum of the soluble compounds dissolved in the liquid component of the red blood cells (amino acids, sugars etc...).  The water signal is almost completely suppressed.

Thank you to Madeleine Adam of Dr. Robert Ben's research group at uOttawa for providing the sample.

* D.L. Rabenstein, K.K. Mills and E.J. Strauss, Analytical Chemistry, 60(24), 1380 A, (1988).