How does carbon load on an LC column relate to retention? | Trust your Science 1
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How does carbon load on an LC column relate to retention? | Trust your Science 1

February 25, 2020


[Jonathan] What do we got in the
inbox today for myths? [Kim] Ah, well we actually
have a really good one. This is one that comes up a lot. This scientist is wondering how carbon load on a column relates to the overall retentivity that you can expect to see with a column. And that’s a really
difficult question to answer. So I think that this is one
we should definitely look at. – Cool. I love looking at retention myths. Because they’re so easy to remember. Ha ha, get it? – Yes. What do you think we should do for this? – So, since this myth
obviously involves carbon load, we can look at some of the
columns we may have looked at before that have the
different carbon load values. And we can run those columns
under the same set of conditions and just take a look at
the overall retentivity and see if it pans out, see if we can find some
sort of correlation between carbon load and retention. – That sounds really good. Why don’t we get those columns
and then take it to the lab? – Sounds great. – Okay. – All right Kim, that was
a pretty straightforward set of experiments. We just ran the same columns
under the same conditions. – That’s probably the
most boring experiment I’ve ever done in my life. – But we needed the data. So we had to do it. – Yeah. – So getting back to
looking at the results from percent carbon and
overall retentivity. We ran a bunch of columns, able to track the overall
retentivity of those columns. How does the data look? – Okay, let’s take a look. So when we look at the overall retentivity of all these different columns, we can see that there’s
really no correlation at all between the percent carbon and the overall retention. The highest retentive phase that we see out of the columns we tested had a middle of the road
percent carbon of only 13%. And that was again the
highest retentive base. So you’ll also notice that
the lowest retentive column, percent carbon value is only 5%, but this phase is not
three times less than that with a carbon load of 15%, so there’s really no direct
correlation we can draw between retentivity
and the percent carbon. – Yeah, I see that, Kim. It’s easy to notice. – So since there’s no correlation, what’s really important here? What has the effect? – Yeah, Kim, that’s a great question. So what really drives
retention is what’s known as the phase ratio of the base particle. And what that is is really just a ratio of the pore volume and
the overall surface area in it’s most simplest forms. So here we ran a couple of columns just as an example of two columns that have the same pore volume
and different surface areas. But they had the same
overall bonded phase coverage or percent carbon load. And as you can see from
the chromatography, when you look at the HSS C18, compared to the BEH C18, you’ll see that the HSS C18 has much higher retention based on the fact that that phase ratio of that base particle is much higher. – So it’s really great
to have all this data showing the comparison between
all these different columns with all their different
percent carbon values because that’s one of those questions that comes up pretty frequently from a lot of scientists just like this. – Yeah, Kim, there’s so many other factors in this chromatography,
in the base particles, that dictate the overall
retentivity of the phase. Like you said, we talked
about phase ratio, pore volume, surface area. If you’re not familiar
with all this stuff, it’s kind of confusing. – It is. So when you’re trying to choose a column, if you’re looking at
USP designations, right, like the L 1, or if you’re looking at percent carbon. Really just doesn’t tell the whole story. – Doesn’t tell the whole
story, that’s right. – All right, so I think we
need to email this customer and let him know that
the percent carbon load doesn’t really tell him how retentive the column’s actually gonna be. – Yeah, based on percent
carbon alone, Kim, this myth is busted. – I think it is. – It’s really hard to
track or to correlate overall retentivity with just the carbon. – It is. – It’s just, there’s other things in play. Like I said, pore volume, surface area, they’re all important, too. – [Kim] You’d like your
question to be answered on a future episode, please feel free to email us
at [email protected]

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  1. I dig science videos, you guys just need to get rid of that hum. It's a bigger deal than you may think, also you could cut some of the written dialogue transitions, "that's a great question Kim." it hurts the immersion, slows things down, and when written poorly makes the film seem amatuer. We know we are watching a video/ presentation, you don't need to try to make it a conversation, in my opinion. I hope you guys do really well in the future! Good luck!

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