[coquim]

Hello people! i´ve a doubt and i´d like to know shoul i do...
my sample is at ph 8 (my column is out of range at this ph. The limit is 7,5)
but the mobile phase is at ph 2.5
what would happen in this case? may i inyect the sample and have no consequences with the column? or simply should i keep the sample ph between the ph column work range?

best wishes...

[Arkcon]

You should first off, try to consider if the sample components: analyte, impurities, and solvents all remain soluble when the pH shifts.  Precipitation within the sample loop, the injector rotor, or the column will be ... very bad things (TM).

The effect of a moving slug at pH outside the range of your column may add to wear and tear, which might be significant, or not, depending on the column's quality.  Do consider, if the column is attacked by the sample injection, the pH will shift, and that can also precipitate the analyte.

One thing worth mentioning, columns are a little bit more forgiving of pH than their label might suggest.  First off, if your eluent contains solvent, the effective pH has shifted, generally slightly closer to neutral.  If the pH range allowed is 3 to 7.5, for example, it's not correct for you to expect 1000's of injections lifetimes at pH 7.4, and instantaneous column damage from one run at pH 7.6.  You can make a few runs, a little outside the range, with prompt and careful washing, and still have an O.K. column.  Likewise, the farther you are away from the rated extremes, the longer your column will last.  You have no right to expect maximal lifetime from a column run constantly at the edge of it's rated pH range, yet people still have to do that, or worse, from time to time, to get the work done.  It all boils down to cost of your equipment and your time.

As a side note regarding eluent pH, are you sure extended use at the low pH of 2.5 is acceptable for your column?  For typical reverse phase columns, the hydrocarbon chain is bonded to the silica particles by a Si-O-C bond, which is quite susceptible to hydrolysis at low pH.

[coquim]

Hi Arkcon! thanks for your answer...the column is allow to work at ph 2 to ph 7,5...i know the better range it might be at 4-6 aprox. in order to extend the column lifetime...is´n it?
 
best regards...

[Arkcon]

Hi Arkcon! thanks for your answer...the column is allow to work at ph 2 to ph 7,5...i know the better range it might be at 4-6 aprox. in order to extend the column lifetime...is´n it?
 
best regards...

A correct summary of my lengthy post.   I did want you to have the background of where I was coming from.  The very best results come when the sample is dissolved in the mobile phase.  If that's not possible mimicking it as much as possible is needed -- solvent strength, pH, etc.  You'll encounter problems, if there is slightly better chromatography, from your sample matrix, than from your eluent.  You'll get mixed mode separation, until the injection solvent is diluted.  As a consequence, you'll get different chromatography, depending on sample concentration, injection volume, and retention time of the analyte (early ones more affected than later ones), again, Very Bad Things (TM).

[coquim]

A correct summary of my lengthy post.

    jajaja...i see you have quikly fingers...but i must say, you are very explanatory...and almost seem like a teacher for me...i could say that

I did want you to have the background of where I was coming from

jajaja again..it´s ok....it seems you are coming from the past!...have you developed a time machine and can´t tell us nothing about it, haven´t you??!!  

thanks again for to share your knowledge...