Memory effect versus Source contamination

[jasontomas]

Dear all,

I am trying to learn more about calibration of ESI instruments and i am confused and stuck on a few facts.

From a book called Analytical Method Validation and Instrument Performance Verification, Edited by Chung Chow Chan, Herman Lam, Y. C. Lee, and Xue-Ming Zhang.

It writes that "The right calibrants for LC-ESI-MS should (1) not give memory effects; (2) not cause source contamination through the introduction of nonvolatile material; (3) be applicable in both positive- and negative-ion mode. "

However what is the difference between memory effects and source contamination? From what i have gathered source contamination is one of the reasons of memory effect and they should be the same am i right to say so?

[JMB]

Absolutely !!

"Memory effect" is just a hand-waving, catch-all description of contamination from previous analyses.

Injection port/sample delivery lines/ionization source etc. are all possible sites of contamination.

[jasontomas]

Hi JMB,

Thanks for helping me out . For cases where the calibrant is "sticky" and difficult to remove from the column / require more than reasonable amount of rinse time, is there a term for such calibrants?

If i rephrase the statement to say "The right calibrants for LC-ESI-MS should (1) not be "sticky" resulting in memory effects; (2) not cause source contamination through the introduction of nonvolatile material; (3) be applicable in both positive- and negative-ion mode."

Would it be more correct?

[JMB]

Yes, I think that your rewrite is acceptable, but if you keep your phrasing I would insert a comma ........"sticky",.....

You might consider rephrasing to something similar to

........should (1) be easily washed from the system, otherwise memory effects may result, (2)....

which avoids the use of the term "sticky".

Another requirement for mass calibrants is that they should also be readily available in a high state of purity; this usually implies a crystalline solid.

As a practical point, mass calibrants are usually injected downstream of the HPLC column via an injection port.