Here are a couple of questions I have saved up for the experts. (1) I have been asked to quantitate drug substances suspended in corn oil (as a vehicle for insoluble oral candidates). We already have RPLC methods for analyzing these compounds as solids or in solution; any thoughts any thoughts about getting rid of the darn corn oil? (2) Has anyone out there ever used bromide salts in mobile phase preparations? In our compounds, Mn(II) is bound to five amine nitrogens, and associated with 2 very exchangeable chloride ions. All our mobile phases are high in chloride salt concentration, to maintain the compound in the "chloride form". If we substitute another counterion for chloride, that version of our compound forms, often eluting as a single peak. Perhaps "bromide forms" might exhibit interesting changes in selectivity, resolution, etc. Thanks very much for any help.

Jim,

I'm not sure I can help you much on the first question although it seems like you should be able to use SPE to remove the corn oil assuming your drug substance is significantly more polar than corn oil.

Regarding your second question, Dionex produces a column (the Cryptand A1 Column) which, as the name implies, contains an immobilized cryptand based macrocycle. It has proven to be quite useful for separation of anions. The nature of the cation complexed with the macrocycle affects both the capacity and selectivity. You can even change capacity on the fly by switching cations during a chromatographic separation. Based on what we observe with this macrocycle, I would expect you to find increased stability of the complex in the presence of bromide. I agree that you will likely see changes in resolution and selectivity with bromide but since bromide absorbs much more strongly in the UV than chloride so you probably won't be able to get away was putting it in the eluent.

With respect to the first question, a beter choice could be NP. Oil disolves better in hexane/chloroform etc better. You could load much more samples. Oil would be eluted first. I assume that you are analysing gels or non-aq. solutions. Look at Practical HPLC Method Development and you will find a UV transparent MP.

SPE is usually not a good choice as lower than perfect recovery and /or additional impurity could result from it. Do you work under GMP?

Regards,

J L Shen

Jim,
EPA used to have a cleanup method for pesticides using a size exclusion column (sorry I don't remember the details) but you might get a library search for this cleanup method and see if it will work. The calibration mix for the method, so one knew where to collect fractions, had corn oil as one of the ingredients. The pesticides were collected either before or after the corn oil was eluted.

Regards,
Mark