HCl/NaOH; acid base catalyzed forced degradation, you should neutralized the media sample before injection. HCl excess shall denature the LC column, also excess NaOH is harmful. Ferrous ions shall precipitated on the ESI ion source as black spots. H2O2 excess shall decomposed at ESI.

Inject blank experiment to identify the gust peaks due to reagent or reaction byproducts of reagent with column stationary phase.

Thank you Mr Khedr. Thank you Mr Khedr.

Do you belive that de products generated by forced degradation are stable after neutralization?

best regard

Actually As is a structural analog of  P.   The difficulty with LC-MS of As and P is speciation.  If you do not do this correctly, you can get an incomplete and sometimes inaccurate/misleading answer.   Please check out attachment.   It is incorrect that for metals and organometallics that MS results are mass ions.  They are always mass/charge.  Thus unless one know what the net charge is, one can totally lose and/or misinterpret MS data.   As easily can be arsenite or arsenate and the charge on each ion can be -1, -2, or sometimes -3.  

Dr. Schmidt I cannot see the connection between either the first or second question and your comments about m/Z.

From the chemicals your question is on it appears you are doing Fenton oxidation. As long as both Fe2+/Fe(III) and H2O2 is in solution the oxidation will continue.

The fastest procedure to stop the reaction I know of is to add excess NaCO3 to raise the pH to 10 which will precipate iron. This might also be needed as pretreatment to LC-MS.

If you experience problems with stability you can additionally add 0.1% methanol which react with the radicals. For some analysis like COD H2O2 interferes with the quantitation and then H2O2 can be destroyed by catalase at neutral pH.

The question is about speciation.   Which forms of Arsenic are present initially is obviated / changed / disrupted by the chemical treatment.  The chemistry is to force all arsenic to be one form upon LC-MS analysis.   My question was about  1) what happens if and when the chemical reaction does not go  100% to completion,  and 2) what if one were actually interested in speciation prior to chemical treatment.  It seems to me LC-MS is a very powerful technique, and in this analysis, one is using only a fraction of its potential.   Why in fact is it necessary to do the chemical treatment except to get all arsenic into a single form?  Why with all this highly expensive technology is one settling for only total Arsenic?    The simplest answer is that one cannot find the Arsenite peak or the Arsenate peak if one does not know what the charge is at any particular pH. ...  .

I still cannot follow you Dr Schmidt. Why do you talk about arsenit/arsenate? They are not pharmaceuticals!

Sorry.   The redox reaction listed is routinely used to convert  As+5 to As+3.

Misinterpreted the As representation of an organic compound as referring to the chemical element As.

Dear Andersen, thank you about your answer. was a great contibution!!

best regard