which lithium salt is UV transparent?

[GC_Cf]

I need a UV transparent (~220nm) lithium salt at high concentration (> 0.1M) yet still soluble in mixtures of water/methnaol. Thanks!

[Markus Laeubli, Metrohm]

I would suggest LiCl.

[GC_Cf]

Dr. Laeubli, thank you! How does LiCl compare to LiNO3 and LiClO4 in terms of ionic strength and UV transparency?

I would suggest LiCl.

[carls]

nitrate has significant UV absorbance

Is your question about ionic strength referring to ion pairing character, chaotropic/lyotropic character or are you asking about differences in the activity coefficients?

Chloride is thought to attack the stainless steel components in standard HPLC systems and therefore it is avoided. Some systems, i.e. ion exchange or biocompatible, do not have stainless in the flow path and chloride is OK with them. I do not a have a reference specifically about chloride damage in HPLC systems but perhaps someone else on this forum can provide one.

[HW Mueller]

There is a lot of material on Cl- and stainless in this forum. In short, only acidic Cl- attacks SS, so formally it is HCl, not Cl- that is deleterious.
I used LiSCN once when I wanted a chaotropic salt.

[carls]

The pH of ocean water is ~8 yet it is very corrosive to SS. Are you (anyone) aware of any references showing Cl- is ok with HPLC systems?

[GC_Cf]

I need a salt like LiNO3 to negate interactions between samples and column. I guess maybe it is more related to chaotropic/lyotropic, since the sample is neutral. Maybe I should try LiSCN as well. Please help explain how activity coefficients is related to RP-HPLC here. Really appreciate all the help here.

[HW Mueller]

One should use activities not concentrations when actions of salts are involved. In HPLC the salt concentrations are usually low enough to assume that concentrations equal activities. Note also that somewhere below 0.1 molar about all salts are equally chaotropic, even the highly lyotropic Na2SO4.

carls, check the archives.