Conditions prone to salt crystallization

For some background information please see I have crystals, but are they salt?.

This list shall not include instances when significant drying of the drop occurred. This list should not be taken to mean that the given conditions always produce salt crystals, but they apparently sometimes do.

Screen and #	Condition	Protein buffer	Confirmed by diffraction	Signature and comment
Hampton PEG/ion #1	0.2M NaF, 20% PEG3350, pH7.1	10mM Tris pH7.5, 150mM NaCl	yes	I've seen this condition produce salt crystals at least twice.--Ed 16:18, 23 May 2008 (CEST) Ditto - NaF has caused me trouble many times - buyer beware! DaveB 11:01, 24 May 2008 (CEST)
Qiagen Plate 3 MembFac & Natrix equivalent	1M Ammonium Sulfate, 0.1M Sodium Acetate	25mM NaPO4 pH8, 150mM NaCl	yes	Crystals reproduced with proteins and with buffer alone at least twice --Emeric.gueneau 18:21, 16 July 2008 (CEST)
Qiagen/Nextal Anions #5 and #6	0.3 M and 0.6 M NaF in NaOAc pH 4.6	20mM Hepes pH7.5, 150mM NaCl	yes	Gives hexagon shaped crystals every time- see line one - beware with NaF --Tom Brett 15:35, 23 July 2008 (CEST)
Hampton Crystal Screen #38	0.1 M Hepes pH 7.5, 1.4 M Sodium Citrate		no	Sodium Citrate crystallizes at cold room temp
JCSG+ #1 (A1)	0.2M Li2SO4, 0.1M NaOAc pH 4.5, 50.0% v/v PEG-400		No	Mixture must be made by adding water first, else precipitates. Also, crystallizes/precipitates with 10mM CaCl in protein buffer, perhaps even less. Others report needle crystals in well solution.
Hampton stockoptions salt as additive	NaF >0.24M, 100mM sodium citrate pH<5.6	20 mM Tris, 150 mM NaCl, 5 mM DTT	Yes	I would expect NaF to be more soluble at low pH (if anything) because of a secondary equilibrium with HF. Nothing in the reservoir, only in the drop; anything under 5.6 gives a few hexagons. If equilibration is slow it will give thick birefringent rods. I'm thinking even minimal contamination by phosphate could give rise to something like fluorapatite, since NaF crystals would be cubic I would think. I have also seen higher concentrations of ammonium fluoride cause the drop to spread all the way over the cover slip and give rise to concentric rings of hexagons (NH4F is actually a hexagonal crystal though as opposed to NaF). Glass etching due to insufficient siliconization? Anyway, beware fluorides in general
Nextal Classics #6 = Hampton Crystal Screen #24	0.2M CaCl2, 0.1M Na acetate pH4.6, 20% isopropanol	20 mM Tris, 5 mM DTT	Yes	Nice-looking crystals observed for two different proteins. I suspect DTT may play some part.
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