ammonium hydroxide mobile phase modifier

[pham_sci]

Hello,

I would like to use ammonium hydroxide as a mobile phase modifier. It can generally be ordered as aqueous solutions at various concentrations however due to its volatile nature the concentrations generally falls within a rather large range. Does anyone use ammonium hydroxide frequently? Do you find changes in your chromatography with lot to lot changes in ammonium hydroxide solution? Can I generate more controlled ammonium hydroxide concentrations by using ammonium chloride in water? Any concerns with then having HCl present in the solution?

Thanks!

[Consumer Products Guy]

Years ago I used dilute ammonium hydroxide as the aqueous phase (10ml ammonium hydroxide per liter of HPLC water), but made it fresh daily. The organic was CH3OH, on RP-18, the assay was for thiabendazole, from K. Isshiki, S. Tsumura, T. Watanabe, "High Performance Liquid Chromatography of Thiabendazole Residues in Bananas and Citrus Fruits", JAOAC, Vol. 63, No. 4 (1980), pp. 747 749.

[Bruce Hamilton]

If it's a real concern, then acid-base titration is simple and would confirm concentration. I've used NH4OH quite often for prep HPLC, and I make up to typical concentration ( eg 0.05% ) directly from stock every few days.

I just dilute AR grade 25% solution - which is more consistent, and less affected by storage conditions, than AR grade 880 ( 32% ).

[Uwe Neue]

Why do you need ammonia? A reasonable alternative is to use ammonium bicarbonate.

[pham_sci]

Thanks for all the feedback. I'm trying to avoid bicarbonate because I get horrible baselines. I'm running a gradient elution with UV detection at 215 nm.