Sciencemadness Discussion Board

Degasser units HPLC (really needed??)

NEMO-Chemistry - 10-10-2017 at 04:12

Hi
Hoe important are degasser units on a HPLC system? I have a chance to buy a HPLC system, but the degasser unit dosnt work apparently.

Considering the normal cost of HPLC i am tempted to get this set up. But it depends if i can get use out of it without the said unit working.

Heavy Walter - 10-10-2017 at 04:59

hi Nemo

Most important when running mixtures with solvents gradient.
Working isocratic (same composition along the run) degassing is less important.
Degasser is a rather simple device. Agilent uses a special plastic tubing permeable to gases and applies vacuum to the external surface of the tubings.
There is an alternative technique bubbling He into the solvents but quite expensive.
About a damaged degassing unit the two typical problems are tube puncturing and small pump damaged (very similar to aquarium pumps).

NEMO-Chemistry - 10-10-2017 at 05:27

Quote: Originally posted by Heavy Walter  
hi Nemo

Most important when running mixtures with solvents gradient.
Working isocratic (same composition along the run) degassing is less important.
Degasser is a rather simple device. Agilent uses a special plastic tubing permeable to gases and applies vacuum to the external surface of the tubings.
There is an alternative technique bubbling He into the solvents but quite expensive.
About a damaged degassing unit the two typical problems are tube puncturing and small pump damaged (very similar to aquarium pumps).


Thx for the info.

I might try and find out more info on what exactly dosnt work mean, i took it to mean that the unit dosnt power up.
Or maybe does power up but dosnt pass self test, they are offering to send the broken unit as part of the package.

Its been offered for sale for a fairly long time, so i am tempted to offer them a fairly low price for it. Looking at the pics of it, it might be a cable issue!

The whole thing comes with full manuals for each of the units. its a tough call, i worked over the summer and saved the money, but at 17 £1,700 is alot of money.

However £1,700 is not much money for the HPLC unit..........Or I just splurg on a rotavap and save money on solvents which at the moment seem to cost a fortune here.

I hate this, when i got no money i know exactly what i would buy if i had the money, when i got some money i can never decide what to spend it on!

Heavy Walter - 10-10-2017 at 12:19

Be aware of obsolescence.
Manufacturers doesn't assure spare parts for old models.
Maintenance and consumables aren't cheap.

S.C. Wack - 10-10-2017 at 13:31

If no one else wants it maybe there's another reason. Degassers are the least expensive module. Can you get another one? Ultrasonic baths have been recommended...while under aspirator vacuum I assume...or just the vacuum for not even a minute according to Agilent.

[Edited on 10-10-2017 by S.C. Wack]

NEMO-Chemistry - 10-10-2017 at 13:49

Thx guys.

the one thing that has made me hesitate is the length of time its been advertised. There is a guy on ebay who was a service engineer for twenty odd years, he worked on Gas chromatographs and HPLC systems.

He fixs them up and sells them on at a reasonable price, i havnt seen him list much for a while, but recently he put a couple of adverts up. It kind of bothers me that he hasnt gone for it and repaired it.

I might contact him and ask his opinion, had he simply dissapered from ebay, i wouldnt be thinking so hard about it, plus it is a old model and not one like agligent or elmer perkins etc. So parts could well be hard to find.

I think the last two comments on this thread have nailed the coffin shut, its cheap for a HPLC, but its a huge amount of cash for me, i think I am going to pass on it.

Thx again, i feel better about letting it go now, even if the unit is easy to sort out, the comment on spares etc have made up my mind.

Chemetix - 10-10-2017 at 13:54

Degasser...we don need no steenking degasser!

Well until a bubble hits a check valve, that's always fun, for an hour of repriming and testing. Oh and columns love a void, you can choose to think of this as not giving inconsistent results, but something that adds character to your data.

Yeah, get that unit though, I always wanted some form of LC and had a Waters Alliance system briefly. Never got to open her up on the open road so to speak.

Dr.Bob - 10-10-2017 at 15:13

It just bubbles N2 or He through the solvent, not essential, we rarely bother with it. Either take the broken one cheap and try to fix it, or live without it. It is like power windows on a car or buying a case for your phone, nice, but not critical.

NEMO-Chemistry - 10-10-2017 at 15:33

Quote: Originally posted by Dr.Bob  
It just bubbles N2 or He through the solvent, not essential, we rarely bother with it. Either take the broken one cheap and try to fix it, or live without it. It is like power windows on a car or buying a case for your phone, nice, but not critical.

The degasser unit is included free apparently. I will try and find the link to the whole HPLC. I tried to look just now and couldnt find it!! (maybe someone else has finally got it lol).

NEMO-Chemistry - 10-10-2017 at 15:38

Ok found it! helps if you dont misspell HPLC!!

http://www.ebay.co.uk/itm/Merck-Hitachi-Transgenomic-HPLC-Sy...

I have just about talked myself out of it, but will see what others think and then sleep on it. Incidentally i have a GC/HPLC interface unit for a pc, i am also pretty sure i can get the software to run it from a pc.

No idea if i would need anything else, but what i would like most of all is one that you can set so it samples at a given point and collects just that fraction.

[Edited on 10-10-2017 by NEMO-Chemistry]

AvBaeyer - 10-10-2017 at 18:16

Like Dr Bob, in my own experience we just very slowly sparged the solvent bottles with N2. Outgassing when solvent mixing is mainly a problem with methanol-water systems. Acetonitrile-water really does not need any degassing. If you are using organic solvents like hexane-ethyl acetate and similar, then degassing is really not important.

AvB

Dr.Bob - 11-10-2017 at 06:02

It also depends on what pressures you go to, if you have a fancy new system that goes to 5000 psi, then it has other issues like oxidation of samples in the column, but for most older HPLCs, that is not an issue, as they are much lower operating pressures. You would also need to super filter solvent and samples on most high pressure HPLCS as well, but older systems not so much.

NEMO-Chemistry - 11-10-2017 at 07:32

Quote: Originally posted by Dr.Bob  
It also depends on what pressures you go to, if you have a fancy new system that goes to 5000 psi, then it has other issues like oxidation of samples in the column, but for most older HPLCs, that is not an issue, as they are much lower operating pressures. You would also need to super filter solvent and samples on most high pressure HPLCS as well, but older systems not so much.


on the filtration side, can those syringe things be used. No idea what you call them, but they have a disk inside and a connector each end. Drug addicts sometimes use them as well I think.

Its a hard choice, the other thing that would help me alot is a rotovap, but obviously its one or the other. The vap would save me money....

[Edited on 11-10-2017 by NEMO-Chemistry]

AvBaeyer - 11-10-2017 at 15:28

NEMO-

You mention that you want to collect fractions. I looked at the pictures of the system on ebay. It is an analytical system and as such will not work well if at all for collecting fractions since the throughput will be in the (sub)milligram range. The system would need the ability to accept (very expensive) preparative columns and also have the flow capacity to operate such columns satisfactorily. Also keep in mind that HPLC systems require considerable solvent expense and that the solvents are not practicably recoverable thus leading to disposal problems. So if you are looking for a system able to provide useful prep runs, this one will probably not suit your needs. If you are interested in preparative chromatography, consider cobbling together a medium pressure system. These are quite practical and cheaper to run. You will still have solvent expense and disposal issues however.

Overall, unless there is a defined need, in my opinion HPLC in the hobby lab is not a practical option. Of course, if you want one just to experiment with that's another story. My advise is to sink your limited funds in a useable roto-vap. It will be much more useful in the long run. Besides, if you get involved in preparative chromatography and have to concentrate large numbers of fractions, you will still need a roto-vap.

Just my thoughts, keep or discard.

AvB

NEMO-Chemistry - 11-10-2017 at 16:14

Quote: Originally posted by AvBaeyer  
NEMO-

You mention that you want to collect fractions. I looked at the pictures of the system on ebay. It is an analytical system and as such will not work well if at all for collecting fractions since the throughput will be in the (sub)milligram range. The system would need the ability to accept (very expensive) preparative columns and also have the flow capacity to operate such columns satisfactorily. Also keep in mind that HPLC systems require considerable solvent expense and that the solvents are not practicably recoverable thus leading to disposal problems. So if you are looking for a system able to provide useful prep runs, this one will probably not suit your needs. If you are interested in preparative chromatography, consider cobbling together a medium pressure system. These are quite practical and cheaper to run. You will still have solvent expense and disposal issues however.

Overall, unless there is a defined need, in my opinion HPLC in the hobby lab is not a practical option. Of course, if you want one just to experiment with that's another story. My advise is to sink your limited funds in a useable roto-vap. It will be much more useful in the long run. Besides, if you get involved in preparative chromatography and have to concentrate large numbers of fractions, you will still need a roto-vap.

Just my thoughts, keep or discard.

AvB


Thanks you have nailed it for me. the full explanation of what I was thinking is as follows...
At the moment i do alot of TLC for plant extractions, they are quick and simple, and cheap to do. the problem is identifying some of the spots.

Most of this is to do with me selling bodycare stuff and soap (all natural), so i look for allergens likely to cause problems and that kind of thing.

I figured if I got a HPLC i could identify more accurately different components, but this would then allow me to separate that fraction and use it as a standard.

So when i did a TLC for a different plant I could look at the RF value and see what I had as a sample that was close. i could then run a TLC with that standard included.

I havnt explained it well, but basically the HPLC was to help me build a library of things I didnt want in material i use, I thought i could isolate and identify and then use in TLC to make the process quicker.

Everything you have said make sense, it isnt going to achieve what i wanted, yes i could run everything through the HPLC, but as you point out that gets expensive with solvents.

So my next option and one I am kind of trying to do now, is look at the drug and compound tests like marquis reagent etc, and use those to test the TLC bands. I am not looking for say Morphine, but some the tests i have found also have a colour change for other plant compounds.

So it looks like the way forward for now is go with the Rotavap option, keep refining my TLC skills and keep learning.

All the stuff I sell gets passed by a lab, its really expensive. So being able to rule out ingredients first, saves alot of money. Actually its not mega expensive, there is a company fairly local, she does the paperwork for around £100.

But sending 4 samples in and having 3 rejected is expensive, so i try and rule out any that wont pass. I am also getting alot better at separating out undesirable stuff via column chromatography.

Again a decent rotavap would help recycle alot of that solvent.

Thx AV, final decision is I ditch the idea. Would be a nice toy to have, but I dont want a toy.