H-1-NMR SPECTROSCOPY ON THE NANOLITER SCALE FOR STATIC AND ONLINE MEASUREMENTS

NMR spectroscopy is one of the most powerful methods available for str uctural elucidation and for determination of the physical environment of an analyte. However, there has been limited success in scaling NMR to work with smaller volume samples. We report the development of nano liter-scale NMR detection cells, formed by wrapping a radio frequency microcoil directly around a fused silica capillary. This creates 5-200 -nL volume NMR detection cells from an similar to 1 mm length of 75-53 0-mu m-i.d. fused silica capillary. The design and construction of opt imized coils are described in detail. Using such NMR detection cells i n a static mode, <50-ng limits of detection for amino acids are achiev ed for 1-min data acquisition times. The NMR line widths are in the se veral hundred hertz range for thin-walled (30-mu m walls) fused silica capillaries but can be reduced to under 10 Hz using thick-walled (140 -mu m walls) capillaries. Such small-volume cells allow on-line NMR de tection for capillary electrophoresis separations. The complex depende nce of the NMR band intensities on electrophoretic current, applied po tential, and dynamic flow are also described.