Converting a C18 into a mixed-mode column

[adam]

Let me ask one last question. This is for both Vlad and Bverma

Do either of you have applications where a mixed mode column can separate a variety of analytes - in isocratic mode.

(there's a reason why I'm asking about isocratic, but it is not worth going into the long story).

If you have any examples can you attach them here.

Much Thanks!

[bverma]

Yes, we have many applications where analytes have been separated using isocratic elution. If you go to our website, http://www.imtaktusa.com/, and then go to the "technical library" tab, then "full application library," and then type in the compound name that you are working with in the keyword search, you can find all of the applications for that type of compound. If you are looking for isocratic in our mixed mode columns, type in "Scherzo" in the keyword search and all of the Scherzo column applications will pop up. You can browse through the applications by clicking on the number at the left, and see which ones have isocratic separation. Some example Scherzo isocratic applications are below:

http://www.imtaktusa.com/site_media/fil ... TI703E.pdf
http://www.imtaktusa.com/site_media/fil ... TI698E.pdf
http://www.imtaktusa.com/site_media/fil ... I689E_.pdf
http://www.imtaktusa.com/site_media/fil ... TI681E.pdf
http://www.imtaktusa.com/site_media/fil ... TI679E.pdf

There are many more examples on the website.

If you have any questions, feel free to email me at bverma@imtaktusa.com. Thanks!

[Vlad Orlovsky]

Most of our applications are isocratic:

http://www.sielc.com/Application-HPLC-S ... Sinus.html
http://www.sielc.com/Application-HPLC-S ... isc-R.html
http://www.sielc.com/Application-Simult ... -Acid.html
http://www.sielc.com/Application-HPLC-A ... ation.html

If you understand mechanism of interaction, know structures of compounds you can develop isocratic method in 90% cases. If you have specific mixture I can help you to develop a method. We also offer free method development screening for everybody. Turned around time is usually 1-2 days and you don't have obligation to buy anything

http://www.sielc.com/Services_MethodDev ... tForm.html

Don't pay attention to exact structures of compounds in any method. Look at functional groups which are available for interaction. I don't care about structures at all, because it is irrelevant in 99% of cases.

Here are benefits of mixed-mode:
http://www.sielc.com/Technology_2D_Properties.html

and here is step-by-step guide:
http://www.sielc.com/MethodDevelopment_ ... dType.html

[tlahren]

(SIELC) are using second and third generation mixed-mode columns which incorporate a single particle/ligand design which carries two or three functionalities (reversed-phase, cation- and anion-exchange).

Vlad,

I am interested in your three functionality columns. We are running a method for As species. Some inorganic and some organic based. We were able to push through some initial data using an older method from literature using a Hamilton PRP-200 ion exchange column. This worked only OK and I would like to try a mixed-mode column in the future.

Do you think I would get adequate separation of 6 As species with one of these columns? (Arsenate, Arsenite, MMA, DMA, Arsenobetaine and Arsenocholine). On this column my first two peaks (AsIII and MMA) are basically unretained and very difficult to separate. Lets say I got lucky so far, but I had very very poor reproducibility from column to column. Out of 3 columns only 1 could adequately separate all components. I am using 20 mM HNO3 as mobile phase A with a HNO3/NH4NO3 buffered solution B for gradient. Oh, I'm using ICP-MS for a detector.

[Vlad Orlovsky]

Ty,

Do you know pKas of aresenate/arsenite and what are MMA/DMA (monomethylarsinate and dimethylarsinate?) in your case? Can you see/monitor both cations and anions in your system? My guess is that Obelisc R column should work, but I prefer to try it in the lab. Do you have any restriction on mobile phase? If you can send me samples we will run this in the lab using ELSD. I need 5-10 mg of individual sample to develop a method. PRP-200 is cation-exchange column and you are not going to retain acidic molecules. You might have some retention but it is not related to main mechanism of retention and that is why you don't have reproducibility.

P.S. Found pKas for As acids, they are slightly weaker than phosphoric acid.

[tlahren]

I need 5-10 mg of individual sample to develop a method. PRP-200 is cation-exchange column and you are not going to retain acidic molecules. You might have some retention but it is not related to main mechanism of retention and that is why you don't have reproducibility.

Vlad,

Could you contact me via email? I might be able to send you some of the materials in the near future.
lahren(dot)tylor@epa(dot)gov

Thanks.