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- Posts: 17
- Joined: Thu Oct 21, 2004 9:08 am
When you have got a ESI probe, is it useful to have a APCI probe to analyse small organic molecules?
Is it a good investment?
Is it a good investment?
It can be, for molecules more toward the nonpolar end. But don't get me wrong, it won't work for the nonpolar extremes (such as hydrocarbons). For that, you want photoionization (APPI). I don't have experience using APPI, but this would be something else to look into, depending on your needs.
If you find yourself analyzing compounds that ionize poorly or not at all, due to lack of acidic or basic sites, APCI might be something worthwhile. It can also be useful with certain volatile mobile phase additives that aren't friendly to electrospray, such as TFA or TEA.
For example, free amino acids work well by ESI(+), but some don't retain well on a C18 column. One solution is to add TFA to the mobile phase and use APCI(+), which is less affected by the TFA. Also, there can be differences in ion suppression when analyzing for targets in a biological matrix. Some have reported that APCI has less problems with ion suppression in these situations.
Another example: Suppose you want to analyze for carboxylic acids and their esters in the same run. ESI might only work for the acids, while APCI will work for both (assuming you can switch polarity during the run).
Without APCI, you may still be able to analyze some neutral compounds by adding micromolar quantities of sodium salt to the mobile phase and looking for the sodium adducts in ESI(+).
