Powder <t>XRD</t> diffractograms of <t>OCP</t> (red) and OCP-citrate (blue). The shift of the (100) reflection from 4.85° to 4.09° between OCP and OCP-citrate, respectively, is indicative of the expansion of the OCP unit cell along the a axis resulting from incorporation of the citrate within the hydrated layer of OCP in the latter compound. The principle reflections for OCP are labeled; other signals consist of a superposition of several reflections.