To that end, low-resolution and high-resolution pfg-NMR were
combined. Whereas the former provides a more practical and less
expensive approach for measuring water diffusion, the latter
enables water soluble compounds to be monitored as well
[13,14]. Hindmarsh et al. [15] and Guan et al. [10] reported on
the permeation rate of water through an oil film of about 20 s1
as measured at 17–20 C, whereas the permeation rate of charged
and non-charged molecules of similar size (i.e. about 100 g/mol)
through a hydrophobic membrane at 25 C amounted to only
0.17 s1 and 2.5 s1
, respectively [13]. As a further consequence,
concurrent spectrally-resolved diffusion NMR analysis of aqueous
dissolved molecular species and water molecules in W/O emulsions
can demonstrate the effect of molecular exchange during
droplet size analysis. Tetramethylammonium chloride was
selected as it is highly water soluble, it gives a single and intense
signal in a specific NMR region without overlap with water or oil
and because of its low permeability through the oil phase due to
its ionic nature [14,1