An apparatus for providing a sensitive volume for single-sided NMR includes: (i) at least one first permanent magnet for providing a first magnetic field at the sensitive volume; and (ii) at least one of the following means for superimposing at least one second magnetic field for homogenizing the first magnetic field in the sensitive volume: (A) at least one shim magnet, (B) at least one pair of shim magnets, and (C) at least one electrical conductor being connectable to an electric current source. The at least one second magnetic field is adjusted such that the magnetic field homogeneity in the sensitive volume is corresponding to a line width of hydrogen (1H) of less than 10 ppm.