About the use of two ionic pair agents

[Tequila]

Dear members of this list,

I would like to get information about the possibility to use two pair ionic agent as sodium salt of hexansulfonic acid and triethylamine. I try to get information and in every places where I read, always use one of both.
The reason is I have an organic acid and organic base solid formulation and I think the use of both agents is the best solution. If it is possible, I would like to know the concentration and pH of work.
Thanks in advance for your help,

Diego Delmonte

[Uwe Neue]

This is not likely to work. The oppositely charged ion-pair reagent will compete with the oppositely charged analyte that you are trying to retain with your ion-pair reagent. Of course, it may help you in manipulating the retention of this analyte.

[SIELC_Tech]

Tequila,

We have column which has two ion-pairing reagent embedded on the surface of silica - one for retention of cation and another one for the retention of anions. This is a new column we have introduced recently. Primesep AB column is a reverse phase column with embedded ion-pairing reagents, it provides the retention based on RP and ion-exchange mechanisms.

Contact us if you have more quastions:

http://www.allsep.com/

[Uwe Neue]

Wow, SIELCTECH, this is the first time I heard somebody say that sodium chloride is an acid and a base...

[SIELC_Tech]

Dear Uwe,

Would you please show where did I state that sodium chloride is a base and an acid? But you agree that sodium (plus) and chloride (minus) are strong base and strong acid? I am not making up the story about the column with two ion-pairing reagents. As far as I know chromatography is about equilibriums so you can use it to you advantage if you know how to shift them and how to create a ligand on the surface. I know that it is something new but time will tell if this concept will gain users. So far we have people who used and were able to retain compounds otherwise unretainable. But the beauty of choice is, that scientist can choose the approach and if they like Atlantis columns (or any other column) better I have no beef about it.

regards,

[SIELC_Tech]

Another point is that you probably have hydrochloric acid and sodium hydroxide in you lab staying close to each other, but you need to mix them in 1:1 ratio to get sodium chloride, otherwise you don't have sodium chloride. It is the matter of how the ligand is designed and placed on silica.

[HW Mueller]

How did we get into this? Actually, assigning compounds to acids or bases is not that easy.
The Arrhenius definition, that bases give OH- and acids H+ in H2O, do not describe Na+ or Cl-.
The Bronsted definition, that acids can dissociate H+ while bases like to accept a proton, doesn´t apply either.
The Lewis definition that an acid can accept an electron pair from a base ....hm. The Cl- can donate an electron pair, but not so freely, at least in water. But Na+ accept an electron pair to form a covalent bond?.... Well, yes if a super donator is around and if you stretch "covalent".
Both ions have inert gas electronic structure which appears to be a relatively stable configuration. But nevertheless, Cl- is close to OH- as a nucleophile (which is sort of a basic property) in non-aqueous media....
etc., etc.
(Actually, I would rather debate some more about the do it all column concept.)

[JA]

is this a hypothetical situation or have you got a real sample to play with? Why not take the traditional method development steps and see if you can get adequate retention and selectivity with simple pH control (low then intermediate or high pH).

Failing that, ionise one analyte for ion-pairing with pH control, neutralising the other.. eg. 20 mM NaH2PO4 pH 2.3 (check column) + 5 mM alkylsulfonate IP reagent. Or maybe 20 mM Na2HPO4 pH 7 or 8 + 5 mM tetrabutylammonium salt for opposite case.

Or is your case too complex for those simple steps

[Uwe Neue]

Sieltech: the point was that you can either use a cation exchange mechanism or an anion exchange mechanism, and not both at the same time.

[Newman768]

Uwe, it is possible.
Since the surface of the column is that big, it is a very interesting idea packing two different charged ligands on it.
But I guess it is easier to mix 50% of material contaning ligands with acidic groups and 50% of material containing ligands with basic groups. Or the relation can be shifted to one side or the other.
To copy Mr. Spock: fascinating... I remember someone had tested such a concept with different ligands for RP - giving them the column with the needed selectivity to seperate all the peaks...

[SIELC_Tech]

Newman,

We have tried both approaches and decided to put two ligands on the surface instead of mixing two dufferent materials. You still can adjust the ratios and create variations of basic/acidic IP embedded silicas within the particle, we sometimes doing it for our customers-creating a custom made stationary phase (still reproducible within the required range) when people want to cange order of elution for analytical and prerarative runs.

regards,