The significant spectral overlap in the conventional 1 H NMR spectrum (Figure ) is largely avoided in the PSYCHE-iWG spectrum (Figure ). The WG elements completely suppress the solvent signal while retaining solute signals that are close in frequency (e.g. H9 in atropine). The API signals (in black) are immediately evident due to their higher intensity, and full assignment is provided in Figure . With the improved spectral resolution observed in Figure , the impurity signals, no longer eclipsed by the more intense API signals, are easier to identify. The identification of degradation products is of importance as it provides insight into the stability of the API. Hydrolysis of the ester bond cleaves atropine into tropine and tropic acid (Figure ; peaks assigned in grey in Figure ). It is possible to use these signals as markers to assess the shelf life of the eye-drop solution. A further impurity, partially assigned in brown, is attributed to reversible rearrangement of the NMe group. The preferred configuration of the NMe group is equatorial (NOEs between H17 and H12, H13 prove this), and the minor configuration axial (NOEs between H17 and H10, H15 are seen). The reversible rearrangement was confirmed by NOESY experiments which showed exchange peaks between atropine signals and this rearrangement product (data not shown).