A process for the preparation of a composition comprising one or more compounds of formula (I) is provided: wherein R1 and R2 independently represent H or -NO, provided that at least one of R1 and R2 is -NO； wherein the process comprises the steps of (i) reacting 1,2-propanediol with a source of nitrite, optionally in the presence of a suitable acid, wherein: (a) when the nitrite is an organic nitrite, step (i) is performed in a suitable organic solvent； and (b) when the nitrite is an inorganic nitrite, step (i) is performed in a bi-phasic mixture comprising an aqueous phase and an non-aqueous phase. The nitrite is preferably sodium nitrite or tert-butyl nitrite. The acid is preferably sulfuric acid. A substantially non-aqueous composition comprising (a) one or more compounds of formula (I)； and (b) 1,2-propanediol is provided. A pharmaceutical formulation； a kit of parts and a combination product comprising the substantially non-aqueous composition are provided. The composition, pharmaceutical formulation, kit of part or combination product for use in the treatment of a condition wherein administration of nitric oxide (NO) has a beneficial effect is provided.
