Reason for C18
Posted: Sun Mar 16, 2008 2:57 am
What is reason behind that why C18 only why not C19 or C16 is there any scinetific story?
Chromatography Forum
Chromatography Forum is a public discussion group where you can post questions, news, or messages of interest to chromatographers everywhere, but you must be registered to participate (registration is FREE). If you are a registered user, please log in.
http://www.chromforum.org/
Reason for C18
Page 1 of 1
Posted: Sun Mar 16, 2008 6:27 pm
first one popularly used, tradition.
Posted: Mon Mar 17, 2008 1:31 am
Consumer Products Guy is right. A more verbose version goes like this:
Many years ago, when bonded-phase technology was being developed, octadecyltrichlorosilane was commercially available in "food grade" purity at reasonable cost. As CPG said, they tried it and it worked. As it happens, the effect of chain length on chromatography is essentially exponential, so a small change has very little effect (the most common columns are C18, C8, C4). There wasn't much point is using a specially made (and thus very expensive) reagent to make a C19 column that wasn't a whole lot different from the easily available C18.
Many years ago, when bonded-phase technology was being developed, octadecyltrichlorosilane was commercially available in "food grade" purity at reasonable cost. As CPG said, they tried it and it worked. As it happens, the effect of chain length on chromatography is essentially exponential, so a small change has very little effect (the most common columns are C18, C8, C4). There wasn't much point is using a specially made (and thus very expensive) reagent to make a C19 column that wasn't a whole lot different from the easily available C18.
Posted: Mon Mar 17, 2008 7:46 pm
Tom,
I am intrigued when you use the phrase "food grade".
What uses were made of this reagent in the food industy? I remember being told a long time ago that the reagent was used to silylate the glass on cola bottles, to render the surface hydrophobic and make the drops stand out on the surface in an attractive fashion. I thought this explanation rather incredible at the time, but now you have got me thinking with the reference to food grade....
I am intrigued when you use the phrase "food grade".
What uses were made of this reagent in the food industy? I remember being told a long time ago that the reagent was used to silylate the glass on cola bottles, to render the surface hydrophobic and make the drops stand out on the surface in an attractive fashion. I thought this explanation rather incredible at the time, but now you have got me thinking with the reference to food grade....
Posted: Mon Mar 17, 2008 7:57 pm
That's the story I'm referring to (minor difference: the silanization of the outside of the bottle was allegedly to minimize spalling of the glass in contact with the steel "pincers" in the vending machines of the day).I remember being told a long time ago that the reagent was used to silylate the glass on cola bottles, to render the surface hydrophobic and make the drops stand out on the surface in an attractive fashion.
In detail, it's probably apocryphal, but I'm sure there's a grain of truth in there somewhere!
The pertinent point is that a 1 or 2-carbon change in chain length makes little difference.Posted: Fri Mar 21, 2008 3:36 pm
I could imagine that the origin for the C18 chain is the corresponding fatty acid, because that would make the raw material very cheap.
Fatty acids are essentially even-numbered, hence 18, and not 19.
Of course, there are also C16, C12 etc. fatty acids. But maybe C18 would be the most prevalent?
Fatty acids are essentially even-numbered, hence 18, and not 19.
Of course, there are also C16, C12 etc. fatty acids. But maybe C18 would be the most prevalent?