[c0ok1e]

WHat is the different in application between C8 and C18 column? I read somewhere that C18 is more hydrophobic because it contains longer carbon chain. Is that the only difference? WHen trying to seprarate a particular compound using column purifcation, both C8 and C18 columns can be used?

[marquis]

It depends on what you are trying to separate.  Both columns can be used.  Depending on the other materials present, one may be dramatically better than the other.  C-18 is usually better for separating out compounds like long chain fatty acids (say oleic acid) as compaired to a relatively small organic compound (say butyric acid).  The applications department or salesman of the vendor can give many more details.  It is a good idea to make contact with their salesman anyway.  Often, he can arrange some samples or put you in contact with others doing the same testing.  That can save time and money.

[c0ok1e]

Sales is handled by the lab helper in my place. But since both columns can be used so it shouldnt be a problem whichever I use right? My compound is an unknown with size lower than 1000 Dalton. Thnx

[marquis]

Actually, it would be best to try them both.  My guess is the c-18 will do the better job. 

[c0ok1e]

Actually I was reading one methods in a journal and the researcher first use c18 column for purification and then continue with some other steps then continue with c8 acidic column and then c8 basic column then c18 column again. So I was confuse why would he switch around c8 and c18 or maybe the reason is his lab have c8 column at that time thats why he sued them. WHat do you think?

[marquis]

You're getting into some extensive chemistry steps.  Without method explanation and the exact steps used, hard to tell.   

[c0ok1e]

Unfortunately they only said that they used the specific column for each step without explaining much. The only difference i notice is that for c18 column it seems to be very general as in just the column alone. But when they use c8 column, they specify acidic and basic condition. Is the acidic and basic condition the only reason they use c8? c18 doesnt have the option to make it acidic or basic?

If c18 column was available, would you think it would give the same result?

[Captain Sci]

Hi there

There are several different types of reverse phases available in the market. These include: C18, C8, C4, C1, C-cyclehyxyl, C-phenyl, C-cyano and C-adamantyl (C-adamantyl is also called C-12).

C18 is by far and away the cheapest of these materials. The main reason for the low cost of C-18 silica gel is the fact that it is produced in the largest quantity by most manufacturers. When a material is produced in large quantities, the cost of this material is reduced.

C18 is often called the "traditional reverse phase matrix". Because it has the highest degree of hydrophobicity, C18 silica gel interacts with the widest range of compounds and the interactions are generally more pronounced. The reason why C-18 is more hydrophobic than the other reverse phases is because the length of the carbon chains are longer (i.e. C18 is longer than C8, and C8 is longer than C4 etc).

In my view, the reason why anybody would choose C8 instead of C18 is because they are looking for a reverse phase matrix that has a lower degree of hydrophobicity. Lower hydrophobicity means faster retention for non-polar compounds, therefore your non-polar compounds would move down the column more readily with C8 than with C18. The C8 sorbent would be particularly useful if your compounds streak on C18 silica gel.

To summarise:
C8 may be used instead of C18 when shorter retention times are required. C4 provides even less retention towards non-polar compounds than both C18 and C8

I don't think acidity (as in your previous message) had anything to do with this. Maybe the chemist was simply looking for a sorbent that would allow the compounds to move faster - hence their use of C8 instead of C18.

If you have any more specific questions I would be happy to help you out - msg me and I will give you my email address.

Best wishes

Athan

[c0ok1e]

Hi there

There are several different types of reverse phases available in the market. These include: C18, C8, C4, C1, C-cyclehyxyl, C-phenyl, C-cyano and C-adamantyl (C-adamantyl is also called C-12).

C18 is by far and away the cheapest of these materials. The main reason for the low cost of C-18 silica gel is the fact that it is produced in the largest quantity by most manufacturers. When a material is produced in large quantities, the cost of this material is reduced.

C18 is often called the "traditional reverse phase matrix". Because it has the highest degree of hydrophobicity, C18 silica gel interacts with the widest range of compounds and the interactions are generally more pronounced. The reason why C-18 is more hydrophobic than the other reverse phases is because the length of the carbon chains are longer (i.e. C18 is longer than C8, and C8 is longer than C4 etc).

In my view, the reason why anybody would choose C8 instead of C18 is because they are looking for a reverse phase matrix that has a lower degree of hydrophobicity. Lower hydrophobicity means faster retention for non-polar compounds, therefore your non-polar compounds would move down the column more readily with C8 than with C18. The C8 sorbent would be particularly useful if your compounds streak on C18 silica gel.

To summarise:
C8 may be used instead of C18 when shorter retention times are required. C4 provides even less retention towards non-polar compounds than both C18 and C8

I don't think acidity (as in your previous message) had anything to do with this. Maybe the chemist was simply looking for a sorbent that would allow the compounds to move faster - hence their use of C8 instead of C18.

If you have any more specific questions I would be happy to help you out - msg me and I will give you my email address.

Best wishes

Athan

Thanks Athan. That seems to be a good explanation for me. Im sure I will have more questions as I progress in my experiment and hopefully can seek you for help