Which one is the best method of degassing, is it HPLC (Waters) in-line degasser? or manually degass with sonicator? Please give some facts and reasons.
If I have HPLC with in-line degasser and also sonicator too, did I make a big mistake if I recommend to analyst to do not degas with sonicator but directly using HPLC with in-line degasser? Thanks anyway
About sonication:
"HPLC Mobile Phases – 10 bad habits to avoid.
10. Using sonication to degas mobile phase
It’s great for making sure all your buffer salts have dissolved, but it’s the least effective method of degassing AND it quickly heats up the mobile phase causing the organic portion to evaporate. Save yourself problems later – take 5mins to vacuum filter your mobile phase – it degasses and filters in a single step."
source: chromacademy.com
online degassing is a best system, but you can use a sonicator also
We used to just sparge with helium before the invention of the in-line degasser which is pretty much included with all HPLC/UPLC systems nowadays.
So if you are looking at a cheap alternative in lieu of purchasing a sonicator or in-line degasser just sparge with helium - it should do the trick.
I have been using various LC systems and especially with organic mobile phases, sonication in a sonicating water bath is likely to be the best method. In one of the machines, we have an in-line degasser however I sonicate the mobile phase before use because I once saw a air bubble escape through the in-line degasser during purge, though I havent seen the same problem ever again.
I always used to de-gas my mobile phase solvents via vacuum-filtration through a suitable 0.45 micron pore-size membrane filter. Thereafter, I would de-gas daily, or before changing mobile phase, using an ultrasonic bath into which a round-bottomed flask containing the mobile phase was clamped, to which a vacuum equivalent to 1 atmosphere negative pressure was applied (via a 'mity-Vac' manual pump with vacuum gauge) until no further bubbles rose on releasing the vacuum. This was the least expensive alternative available at the time - and you can buy an inexpensive ultrasonic bath that will accommodate a 1L flask (the sort marketed for cleaning jewellery) for less than £50. Even when working in the far-UV spectrum (195-215nm) I rarely had problems with air bubbles. However, use of an in-line 'bubble trap' ahead of the injector is an inexpensive way of catching any air bubbles that might be accidentally introduced to the solvent path - you can draw-off the air before there is any risk of it reaching the injector or column.
Please, what is the suitable time for degassing using ultrasonic because after long time, the temp will be raised causing evaporating of organic solvent
Dear Amal,
I always used no more than 5-10minutes at about -15psi vacuum (-1 atmosphere, or about -1 Bar) which didn't significantly weaken my MeOH:aqueous/buffer or MeCN:aqueous/buffer mobile phase(s), even after subsequent repeated de-gassing.
The "Best" method (scientifically tested by monitoring oxygen) is to use continous helium sparging. Helium is not soluble in the solution and displaces all gases. A low pressure continuous sparge of He results in stable baseline with very low absorbance and excellent pump operation. No question, this has always been the best technique to use (and still is).
Ultrasonic baths and Vacuum: Placing bottles in ultrasonic baths to degass the liquid has many drawbacks and is not recommended. Solvent can evaporate during the process and change the composition. Heat is added to the solution. And the number one reason why sonication is not recommended is that once you remove the bottle from the bath, the gas slowly begins to diffuse back into the solution. In fact, it does this slowly over about 1 hour or more which results in your baseline drifting the whole time... and then the solution needs to be sonicated (degassed) all over again (and a drifting baseline may lead to poor quality integration and quantitation).
Inline electronic vacuum degasser modules: These module have added a great deal of convenience to the problem of reducing the amount of dissolved gas in mobile phase solutions. Unlike helium sparging, no gas tanks need to be used. Unlike sonication or vacuum filtration, the degassing level can be kept constant over time which is very important to control baseline drift. They work very well, but not as well as continuous helium sparging. They also have some chemical compatibility problems where certain common HPLC solutions can not be run through them without causing damage or contamination to the system (helium sparging is compatible with just about everything). The chamber volume of each channel contributes to extra mobile phase volume which needs to be flushed out every time a bottle or solution is changed to flush out the old solution (and the extra associated tubing too). In ultra-modern analytical systems this volume is very low, but in many older systems it can be 10, 20, 30 or even 50 mls/channel! The inline degassers require regular maintenance, just like the rest of the HPLC modules, but for some reason degasser modules are often ignored and left running broken. This often results in contamination of the mobile phase (and detectors, esp MS) in the system.
You will find additional article related to HPLC degassing at the links below:
- "INLINE HPLC DEGASSING MODULES"; http://hplctips.blogspot.com/2011/02/inline-hplc-degassing-modules.html
- "An Often Ignored HPLC & LC/MS Contamination Source. Did you check your Vacuum Degasser?"; http://hplctips.blogspot.com/2015/08/an-often-ignored-hplc-lcms.html
- "HPLC Solution Degassing, Sparging With the Wrong Gas (Gas Choice Matters)"; https://hplctips.blogspot.com/2013/05/hplc-solution-degassing-sparging-gas.html
http://hplctips.blogspot.com/2011/02/inline-hplc-degassing-modules.html
http://hplctips.blogspot.com/2015/08/an-often-ignored-hplc-lcms.html
https://hplctips.blogspot.com/2013/05/hplc-solution-degassing-sparging-gas.html
Exactly, Bill.
One thing to consider, though, is the price/availability of helium. As of late 2016 the "dire" shortage problem may have been alleviated a little (link below), but still... In many places people try to safe (on) helium.
I recently lost touch with this particular topic of solvent degassing, hence my question: would argon sparging be a suitable substitute for helium?
https://www.wired.com/2016/06/dire-helium-shortage-vastly-inflated/
Hi Jacek: The orginal poster asked what the "Best" method was. Yes Helium can be expensive and was subject to a shortage in the past. Luckily, as presented, we do have alternatives. If you want the "best", then it is a slow, continuous sparging of helium. The most convenient method though is certainly the AC line powered, inline vacuum degasser.
BTW: The use of Argon gas for degassing HPLC mobile phase solutions goes against the very fundamentals of degassing a solution. *Never use Argon gas for degassing HPLC mobile phase. Please see link below, "HPLC Solution Degassing, Sparging (Gas Choice Matters)", for more information.
http://hplctips.blogspot.com/2013/05/hplc-solution-degassing-sparging-gas.html
Good afternoon,
I would recommend the use sonicator
30 minutes of sonication is usually enough
Kind regards
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