[newbie!]

using this bad boy! XD

erm so yeah this week in the lab we are doing an experiment using that thing above.
something like we run nitrogen over a sample (we're using alumina) and then helium and we measure the adsorption/desorption from the thermal conductivity. then we have to use the BET isotherm or something.
i'm not sure.
would anyone care to explain how this works?

[Borek]

You must be joking. You will be doing something like something over something and you expect us to explain to you what you will be doing? Ger real. Get your book, check if there is a protocol for the lab, check what are the prelab questions, come to ask for the help once you will hit the wall, not before you even tried to move your finger.

[newbie!]

no i was asking for a bit of background info on how the machine work, i've read my lab manual but i dont understand it clearly and allgoogle throw up is sites trying to sell me the equipment.
so NO i wasnt (yet) looking for how my experiment is going to work, i simply asked generally along which lines do machines like this run.
there is a difference in those questions.

[Arkcon]

Like Borek: anticipated, I have no idea what you're talking about.  So I typed 'BET isotherm' into Goggle and I get a Wikipedia page: http://en.wikipedia.org/wiki/BET_theory

BET theory aims to explain the physical adsorption of gas molecules on a solid surface and serves as the basis for an important analysis technique for the measurement of the specific surface area of a material

Now, often an HPLC column, which I have used, will give a specification for surface area of the media.  So the quote above makes sense to me, in that regard.

Did you need something more?  Its unlikely a student in a classroom was dropped in front of this machine with no information at all.  What have you been doing in class recently?  Why not try to read the rest of the Wikipedia entry to see what insights you can gain, so you'll be ready when the time comes -- either lab work, or examination.

[quantachromeinst]

Like Borek: anticipated, I have no idea what you're talking about.  So I typed 'BET isotherm' into Goggle and I get a Wikipedia page: http://en.wikipedia.org/wiki/BET_theory

BET theory aims to explain the physical adsorption of gas molecules on a solid surface and serves as the basis for an important analysis technique for the measurement of the specific surface area of a material

Now, often an HPLC column, which I have used, will give a specification for surface area of the media.  So the quote above makes sense to me, in that regard.

Did you need something more?  Its unlikely a student in a classroom was dropped in front of this machine with no information at all.  What have you been doing in class recently?  Why not try to read the rest of the Wikipedia entry to see what insights you can gain, so you'll be ready when the time comes -- either lab work, or examination.

I know that this is an old topic but seeing how the op's question actually went unanswered among all the criticism for not reading or researching himself beforehand, I figured I would chime in. The OP is asking about the instrument's working theory and not about BET theory itself. Essentially, the link provided by the mod is actually useless for the purpose of the OP.

The instrument works by gas sorption via flow method (gas sorption systems can be categorized in either static/vacuum-volumetric or flow). The Quantasorb is a flow system that basically will allow you to perform a single point BET experiment with a gas of a premixed concentration (N2 in He with the latter being the carrier gas). The gas flows through a TCD before coming in contact with the sample and a thermal conductivity of the mixture is recorded. As the gas flows over the sample, the concentration of N2 will be reduced since some N2 molecules will be adsorbed by the sample. As the gas leaves the sample, it will go through a second TCD which will also record the thermal conductivity of the exiting gas. This value will be different from the one originally measured. The difference between the two can be used to calculate the concentration of gas adsorbed by the sample, and from there, the amount of volume adsorbed. With the volume information, one can easily use the BET equation to calculate the surface area at relative pressure (P/P0) of 0.3.

Again, I know this is old and the OP will likely not read this, but this is just for posterity.

@OP, if you happen to read this.... where are you studying??? The Quantasorb is at least a 20 year old instrument. I wonder who still uses it.

[quantachrome_lab]

Thank you for your answer. I'm not OP, but I happen to have the same lab and it gave me some insight into it. Also, I study in Estonia and here Quantasorb is used only for student labs.