# Links between chapters: Characterization methods

Pairs are written once. The direction runs from the finding that needs the other, or whose papers are later, to the finding that supplies its basis, caution or check. The two chapters are [Solid-state methods](solid-state-methods/index.md) and [Solution methods](solution-methods/index.md). Citation keys are in [sources.md](sources.md).

| from | to | relation | why |
|---|---|---|---|
| [Solid-state methods F16](solid-state-methods/findings.md#f16) | [Solution methods F4](solution-methods/findings.md#f4) | builds on | Purohit and Taylor calibrated prodan and pyrene in solid films after probes had been used for drug-rich phases in supersaturated solutions, and Raina and co-workers published the six-probe solvent calibration in the same year [purohit2015b C4; raina2015a C8]; the film order (probucol 418 against procaine 448 nm) repeats the solvent direction of shorter wavelength in less polar media [purohit2015b R1; raina2015a R1]. |
| [Solid-state methods F17](solid-state-methods/findings.md#f17) | [Solution methods F4](solution-methods/findings.md#f4) | same mechanism | Both read a lipophilic probe moving into a drug-rich region: the pyrene ratio of ritonavir–PVP at 97% RH fell from 1.60 to 1.30 and that of nifedipine in solution from about 1.8 to about 0.76, with probe partitioning inferred and not measured in both [purohit2015b R6, C3; raina2015a R16, X17]. |
| [Solid-state methods F19](solid-state-methods/findings.md#f19) | [Solution methods F4](solution-methods/findings.md#f4) | builds on | The itraconazole–HPMC test reads pyrene I1/I3 against pure-drug and pure-polymer references (1.39 and 1.54) on the premise that pyrene partitions into the drug-rich phase, the premise calibrated in solvents and in drug-rich phases of solution [purohit2017a R7, C7; raina2015a R1, C26]. |
| [Solution methods F9](solution-methods/findings.md#f9) | [Solid-state methods F17](solid-state-methods/findings.md#f17) | same mechanism | Crystallization returns the probe signal towards its aqueous value in both states: the prodan emission of probucol–PVP rose to 434.5 nm after birefringent crystals appeared at 21 h, and the pyrene ratio of nifedipine rose from about 0.76 to about 1.60 as particles appeared; only the film was confirmed by a second method [purohit2015b R4, R5, C9; raina2015a R16, C23, X15]. |
| [Solution methods F10](solution-methods/findings.md#f10) | [Solid-state methods F18](solid-state-methods/findings.md#f18) | conditions differ | Leftover 50:50 ritonavir–PVP film read by pyrene moved from about 1.565 to about 1.29 at 30 min, whereas the 50% ritonavir–Kollidon VA64 dispersion left 19 µM in the supernatant and formed no drug-rich phase; separation in the wetted film is not a drug-rich phase in the medium at high loading [purohit2015b R11; tres2018 R6, R9; purohit2017b C54]. |
| [Solution methods F10](solution-methods/findings.md#f10) | [Solid-state methods F17](solid-state-methods/findings.md#f17) | conditions differ | For ritonavir at 50% loading the polymer order reverses: under humidity PVP separated (pyrene 1.60 to 1.30) and HPMCAS did not (1.42 to 1.47), whereas in dissolving films LLPS occurred at 10–20% PVP but not at 30–50%, and HPMCAS reached it at every loading [purohit2015b R6, R13, R15; purohit2017b C33, C34, C37]. |
| [Solution methods F11](solution-methods/findings.md#f11) | [Solid-state methods F18](solid-state-methods/findings.md#f18) | explains | In the 50% lopinavir run the PRODAN lifetime rose to about 1.23 ns because of undissolved ASD particles and fell to 1.00 ns after 1 µm filtration [tres2018 R11, R13, C33]; the film readings of F18 are taken on undissolved material and the card names selective PVP loss as an alternative reading [purohit2015b X5] (synthesis: the same kind of confound cannot be excluded for them). |
| [Solution methods F3](solution-methods/findings.md#f3) | [Solid-state methods F11](solid-state-methods/findings.md#f11) | conditions differ | Extinction cannot tell a liquid drug-rich phase from crystals, and the authors separated them by haze and polarized light [raina2015a R4, C9, P7]; SHG is dark for liquids and glass and answers only for non-centrosymmetric crystals above about 100 nm [kestur2012 C4, C34; wanapun2010 R13]. |
| [Solution methods F9](solution-methods/findings.md#f9) | [Solid-state methods F10](solid-state-methods/findings.md#f10) | conditions differ | Both date the start of crystallization by the first response of a read-out: SHG saw flutamide crystals at 11 days against 53 days by XRPD [correasoto2017 R1], whereas the induction times from probe return and UV fall in solution were never compared with a crystal-selective method [jackson2014 R17; raina2015a X15; tres2017 X6; tres2018 X5]. |
| [Solution methods F5](solution-methods/findings.md#f5) | [Solid-state methods F7](solid-state-methods/findings.md#f7) | conditions differ | Limits for crystals in polymer span about 10 ppm (SHG, calculated) to 1% or more, whereas the extinction, probe and thermodynamic onsets of five of six dihydropyridines lay within a factor of 1.0–1.7; the solution values are plot readings and same-system checks [kestur2012 R7, R8; correasoto2017 R8; raina2015a R11, X9, X12]. |

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