Feb 26, 2010

MPLC vs Flash Chromatography

Yesterday an old argument reemerged in the lab. On discussing the use of an auto-column and the ways in which we can implement it in the lab and the ways in which time will be saved one of us mentioned that an auto-column MPLC would never be as good as a good ol' hand worked flash column. 

Well, this discussion, I am sure, has been brought up in a number of scientific circles since the emergence of these new-fangled contraptions. Most notably, the Biotage Isolera (Image 1) and the Teledyne CombiFlash (Image 2) as well as the Kyle Finchsigmate's MPLC for the people (Image 3). But, are they as good as the good ol' hand column.

Well, here are the pros and cons that I can think of and I am sure some equally chemically minded person will come through with many more.

  • Set it up and walk away (do another experiment in the time it takes to run)
  • Set up a solvent gradient to allow for greater separation.
  • In the case of the Industrial machines, use of software to duplicate Rf separation from TLC plates is reportedly possible.
  • Ready-made cartridge columns mean you don't have to worry about packing your column.
  • Loading the column requires little to no time and doesn't require you to reach high up in the hood under the sash and try load your column without disturbing the silica.
  • Small scale to large scale, it doesn't matter.
  • Auto collection of samples with ELSD tech to let you know where your compounds are and in which fractions.
  • Reusable columns (simply flush with methanol)
  • Reverse phase simply requires a different column pack.
  • Column can be set to not collect until it identifies a compound.
  • Can be networked and allow for notification of completion.
  • Higher pressure means faster run columns.
  • Some setup time required to start the column.(Probably simply comes with time and use of the machine the user should get faster.)
  • Works better with small Rf separations rather than large.
  • ELSD doesn't work without a chromaphore in your compound (duh).
  • TLC mimic tech doesn't always work.
  • Churns through a lot of solvent (but can be optimized with Isolera "Gradient Optimization").
  • Any blockage may cause detrimental effects and lots-o-mess. 
  • One column at a time for the basic apparatus and this can cause lab fights (grrr)
  • Someone's gotta look after the bloody thing or else it'll turn to sh!t.
Ol' Faithful
  • Usually able to be run fairly quickly once you are proficient.
  • Can usually get a good separation especially with large Rf differences
  • Close to hand and no wait time in the lab.
  • Can be relaxing and give you some time to reflect on some of the finer points in your thesis.

  • Time consuming running a big column and no free hands to do other work.
  • Silica is often not recycled and discarded.
  • TLCing your fractions only to find it hasn't come off yet is such a biatch.
  • No automatically made solvent gradients means you pretty much make up a solution of a certain polarity and run it like that.
  • Loose silica is bad for your lungs (like Cancer bad)
  • Loading columns can be tedious
  • Packing columns can be tedious
  • Exploding glass columns, rare but can happen
  • Ground joints on goose necks fusing to the joint on the column, so annoying
  • Tubes flying off from too much pressure

Feb 23, 2010

What the Heck...

I've always found ACIEE abstracts fascinating, not just because they describe exciting research but because they always have some quirky (and sometimes really lame) one-liners. For example this one (DOI 10.1002/anie.200906818):

I always thought "What the Heck" was my joke... apparently it was also one of Professor Weinreb's too. That's an impressive looking compound too, and I'll certainly take a closer look at this once I put this reduction/oxidation on.

Feb 18, 2010

Pushing hard

Well, over the last week or so I have been struggling to form this damn strecker product on a particularly bitchy aldehyde (read F@rking HORRIBLE). Anyway, after failing miserably numerous times I have decided to modify my aldehyde to make it a bit more stable and possibly allow me to follow some literature procedure a bit more closely.

Unfortunately, this means PCC (pyridinium chlorochromate) yummy! and the boss wants me to use this due to the literature. I am seriously not cool with the whole thing. I mean seriously, Ley's oxidation was working quite well on the less stable compound and is a bit less nasty. But anyway, I have to admire the simplicity in setting up a reaction of this sort. Reminds me of cooking a little bit.

Not that I taste my reaction or anything but I mean the whole way it is just like measure out the ingredients (Alcohol, Molecular sieves, Dry DCM, PCC) and then bung them all together, sonicate and stir. There is barely any fussing around, just have to be careful weighing out the PCC and then you just spoon it into the stirred solution of sieves and alcohol in DCM (~0.05-.25M).

The workup is a bit of a bitch cuz you have all that nasty nasty floating around but you really just have to add some silica and some Ether and filter through some silica, wash it and then move on to column or just take it through to the next step. Pretty nice, but at the same time kinda deadly, like a portugese man of war.

Anyway, time to "Get in the Lab". Wooh! Gotta love slave labor as a PhD student. $4/hr is a totally amazing pay rate! (SARCASM!)

Feb 11, 2010

Corrosives cabinet = Clean'd

Well, it cost me some time and some lungs but after finally getting a good gas mask I was able to really get in there and clean out the corrosives cabinet. Mainly because of the stupid inventory we had to do. Anyway, the cabinet is clean but all the bottles in the cabinet are really not. They still stink of whatever the crap it was that spilt in there. I tried cleaning them off but the labels are basted in the stuff and probably need to be fully removed and replaced for there to be any improvement. (I am so not doing that btw)

The cabinet looks a hell of a lot better now though and I am pleased with the tidiness inside now. All the bottles are stacked neatly according to height and size and there should be no problems with retrieving something from that cabinet. That said, there is probably some sort of health risk by just going near the cabinet but we can't do anything about that right now really. So, today it's continuing on with the inventory, moving into the flammables and then the fridge (which also smells). WOO! More death! 

Feb 5, 2010

Why we don't like Arkivoc, an oldy but a goody.

Today my good friend Labchimp messaged me a nice little reminder of how crap some free publishers are when you don't have decent peer review.


Say hello to two new pentavalent carbon compounds. So awesome. NOT!

Feb 4, 2010

Corrosives cabinet

Well today P, MSG and me as well as our new PhD student attempted a rescue of the destroyed corrosives cabinet that we use for storing our acids. As we speak I feel I have inhaled about a litre of the brown liquid that coats every inch of that damn cabinet. The stuff is everywhere, and its all because some stupid foreign exchange student broke a goddamn bottle of bromine or something in there and didn't tell us about it. We found it cracked and leaking about 3 months after she left.

So P and MSG finally wrangled me into helping them pull the contents of the cabinet and then relabel and seal them all with parafilm. So after clearing the top shelf we decided that starting this at 3pm was probably a bad idea but we kept on and I decided to wipe out the cabinet. The paper towel was covered in a brown/orange liquid and the more I wiped it out the more there seemed to be.

So now, we have a terribly abused corrosive cabinet and its still not clean. The stuff just won't stop oozing from the pores of the cabinet. We are pretty much calling it a write-off I think. But now I feel like shit.