A microfluidic high-resolution NMR flow probe based on a novel stripline detector chip is demonstrated. This tool is invaluable for the in situ monitoring of reactions performed in microreactors. As an example, the acetylation of benzyl alcohol with acetyl chloride was monitored. Because of the uncompromised (sub-Hz) resolution, this probe holds great promise for metabolomics studies, as shown by an analysis of 600 nL of human cerebrospinal fluid.

We present a new technique that combines the versatility of magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy with the superior sensitivity provided by very small detection coils. This opens the way for NMR studies of solid samples with nanoliter volumes. Furthermore, the very strong radio frequency (rf) fields that can be generated by these microcoils facilitate a much broader excitation bandwidth and/or decoupling efficiency.Although solid-state NMR is the method of choice for investigating local structure, alignment, and dynamics of nonsoluble and noncrystalline functional materials, its feasibility for studying chemically and biologically relevant systems is often hampered by sensitivity. For sensitivity reasons, microcoil technology was introduced in liquid-state NMR for mass-limited samples 1 and highresolution, small-volume MRI experiments 2 , based on the observation that the efficiency of a solenoid coil scales inversely with its diameter. 1,3 By reciprocity, this also allows the generation of very high rf fields with limited amount of power, which has been exploited for static wide-line NMR studies in solids. 4 Two important pillars underpin the success of solid-state NMR as an analytical tool in materials science: first, sample rotation about the so-called "magic angle" 5 needed to average anisotropic contributions to the resonance lines and second, polarization transfer from abundant nuclei (e.g., protons) to less-abundant nuclei with low gyromagnetic ratios such as 13 C or 15 N. 6,7 The evolution of a variety of techniques for studying internuclear distances, bond angles, molecular orientation and dynamics, spin diffusion, and chemical exchange processes, is built on these foundations.Here we describe a microMAS design, featuring microcoilbased resonators with either 400/300 µm outer/inner diameter or 335/235 µm outer/inner diameter coils and sample holders down to 170/125 µm outer/inner diameter (10 nL sample volume), mounted on a regular commercially available MAS unit ( Figure 1). The microcoil resonator is a solenoid coil integrated into a capacitor similar to that developed for static experiments 4 leaving a 220 µm opening (30 nL internal volume) for the rotor. The advantage of this design is its mechanical stability and minimization of signal losses. Compared to regular millimeter-sized coils with only a few windings, our microcoil design with over 10 windings allows for a better B 1 homogeneity over the sample volume, thus improving efficiency. Using microcoils, susceptibility broadening can be a serious issue that limits the resolution. In the present design, this is not the case, as these effects are averaged by MAS. The resolution of most solids spectra is, therefore, determined by the intrinsic spin interactions in the materials. Low-rf-power operation combined with the fact that only a small homogeneous B 0 volume is needed may help to fulfill the promise of tabletop NMR equipment. Low-power requirements and the absence of frictional heating in combination with th...

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Longer coherence life times (i.e. smaller homogeneous linewidths) can be achieved for carbon resonances which are strongly coupled to protons with high rf field heteronuclear decoupling in micro magic angle spinning NMR. Better proton decoupling enhances the sensitivity and resolution of two-dimensional through-bond correlation experiments for mass-limited samples with uniform carbon labeling.