Does anyone know a straightforward method for selectively detecting aliphatic tertiary amines by UV? Post column derivatization is very cumbersome and would rather have precolumn derivatization, but it is not easy to do with tertiary amines. Thanks.

Think about direct detection of aliphatic amines at 230nm in basic conditions. Of course this is not acceptable for silica columns. I detect in such way for example triethylamine, diethylethanolamine or diethanolamine, using polimeric column Astec C18 at pH 8 to 12. Selectivity of detection depends on matrix you have to analyse.

Hamilton Company has a cation exchange column (PRP-X200) which can be used with indirect UV to analyze amines. You can go http://www.hamiltoncompany.com to check all application notes.

I can think of a couple of different suggestions. First, since hydroxide anion absorbs in the UV, a reversed phase separation of tertiary amines under conditions where the amines are separated as the free base should absorb in the UV at low wavelengths (200-210 nm). The best sensitivity will be achieved using the lowest possible mobile phase solvent content in that maximum ionization of the amines occur in high dielectric environments (i.e. pure water). In this case, it would be inadvisable to use a silica based reversed phase column. A number of manufacturers produced polymeric macroporous reversed phase columns including the one mentioned above from Astec. The column that Dionex sells for this purpose is the MPIC NS1 column.

Greater chromatographic versatility could be achieved by combining either ion-pair or ion exchange separations of the tertiary amines in cationic form, followed by a cation suppressor column which will convert the analytes back to free base form which will render them suitable for UV detection (although conductivity detection will generally give significantly higher sensitivity). The best sensitivity achievable for analytes of this sort can be accomplished by Pulsed Amperometric Detection (PAD) but presumably you are only interested in UV detection.

Another possibility which should work well for most tertiary amines is to derivatize them with benzylhalides to a UV absorbing benzyl quaternary ion. While I have not actually done this specific derivatization, we frequently make use of this reaction in the preparation of anion exchange polymers. In particular, benzyl bromide is extremely reactive and should derivatize most tertiary amines in quantitative yield with as little as 10 mole percent excess benzyl bromide. Chromatographic separation of the quaternary derivatives could then be separated by either ion pair or cation exchange chromatography with UV detection. Inasmuch as the product would-be cationic and the reagent is neutral there shouldn't be an interference problem with excess reagent. The reaction is quite exothermic and can probably be done at room temperature in under an hour. The reaction, of course, could be done even more quickly at elevated temperature.

Convert to methanesufonic acid salt, use a cation
exchange column and conductivity detector. This is
a simple direct approach which eliminates the
sampling concerns inherent with low MWt, high
vapor pressure amines