*2.2. Analytical Methods*

An analytical HPLC unit (Agilent 1200 Series, Agilent Technologies Germany GmbH) was used to characterize the solid standards, to quantify the CUR, DMC and BDMC contents in the crude mixtures as well as in the final crystallization products. The reversed phase method reported by Jadhav et al. [40] was adjusted as follows: the mobile phase composition was fixed to 50/50 (vol/vol) acetonitrile/0.1% acetic acid in water. Before usage water was purified via Milli-Q Advantage devices (Merck Millipore). The eluent flow-rate was set to 1 mL/min. Solid samples preliminarily dissolved in acetonitrile were injected (injection volume 1 μL) in the column (LUNA C18, 250 × 4.6 mm, 10 μm, Phenomenex GmbH, Germany, column temperature 25 ◦C) and analyzed at a wavelength of 254 nm. Figure 2 shows chromatograms of the solid standards of BDMC, DMC and CUR compared to a ternary mixture of CURDs (exemplarily crude solid No. 3).

X-ray powder diffraction (XRPD) was applied to characterize the purchased solid standards, solid fractions obtained during the solubility studies and the crystallization products. For the measurements, solid samples were ground in a mortar and prepared on background-free Si single crystal sample holders. Data were collected on an X'Pert Pro diffractometer (PANalytical GmbH, Germany) using Cu-Kα radiation. Samples were scanned in a 2Theta range of 4 to 30◦ with a step size of 0.017◦ and a counting time of 50 s per step.
