Osmometer tech – Vapor or Freezing point?
I’ve used Wescor Vapro osmometers for a long time. Specifically, the model pictured above. They’re nice machines. But now I think freezing point osmometers are better. In this post I’ll talk about why.
The Wescor Vapro machines are the only game in town when it comes to vapor pressure osmometers (due to patent issues). It used to be that freezing point osmometers were priced 30% or more over their vapor pressure cousins. This let the Wescor machines take over significant market share. However, recently that price gap has narrowed. This is the new Wescor.
The technology is the same. But now they’ve added more consumables (and more stuff that can break). Wescor also informed me that they’ve redesigned the thermocouple enough (even though the tech and specs are the same) that they are going to stop supporting the older model and will not sell replacement parts in the future.
With that in mind, the relative merits of the two technologies should be re-evaluated.
1. Freezing point osmometers offer more reproducible and reliable measurements
Vapro machines have to coddled in order to be reliable. Daily recalibration is common. They’re very sensitive to ambient temperature and humidity. By contrast, freezing point osmometers are tanks. Their measuring mechanism is pretty violent compared to vapor pressure osmometers (there’s a loud bang when a measurement is made), but the signal to noise is so high that they still nail their measurements under challenging conditions. The freezing point measurement is simply more robust and higher signal-to-noise than the vapor pressure measurement.
Check out this machine. It looks WWII surplus. But you can yank it out of deep storage, run three 290 mosm standards in series, and it nails 290 all three times. It’s the Jeep of osmometers.
2. Less maintenance
I haven’t much experience with freezing point osmometers, so for the comparison I’m relying on the testimony of my colleagues. But as I mentioned at the beginning of this post, I have a lot of experience with the Wescor Vapro. Cleaning the thermocouple, replacing the thermocouple, sending it back to the factory for repair… the machines I’ve used have needed all of this. The freezing point machines need maintenance, but it’s markedly less than the Vapros.
3. Wescor isn’t what it used to be
EliTech bought Wescor in 2007. So Wescor, naturally, is not the same company.
If freezing point osmometers are better than vapor point osmometers, why did all the labs I trained in have the vapor point osmometers. One reason: price. Vapor point osmometers used to be 30% cheaper. But now they’re not. And given the advantages of freezing point osmometers, it’s worth reconsidering.
The Fiske, above, is great, but a bit loud even when in standby. This one’s quieter.
Hi, thanks for your review, there’s not much like this out there.
I just would like to know if the freezing point osmometers are also able to read tissue samples. We are looking for an osmometer, actually we were looking for the Wescor 5520 model, because we want to assess leaf tissues. Do you think that a freezer point osmometer will be as good as Wescor for tissues?…
Thanks
Can you provide a link/document with a method to process leaf tissue samples using the 5520?
I recommend that you call the manufacturers. They can be surprisingly helpful.
Thanks so much for this. I was going to buy a Wescor vapro, because of famaliarity. I will know consider alternatives.
Thank you so much for this post. I know that I am not alone with my feelings! Although I used the freezing point osmometer rarely, I am regreting that my recent lab does not have this machine. The vapor one is terrible!!! The temperature drift, the calibration and the termocuple cleaning! Nightmare! I must spend half a day just to deal with the above before starting to patch! I am really missing Losing.
Good luck with your Wescor!
Yes, this has been my experience as well. So as we gear up to buy a freezing point, my Vapro 5520 is acting up. Anyone know the basis of the “IOT ERROR”?
Iv been using Wescor 5600, and it works really well, and can do test on most of samples that other machine cant . and used just a 10uL of sample volume,auto calibration,, operating temperature should be 15 and 37 degree celcius with maximum relative humidity of 85%. Our company bought this from singapore, email this Wescor (elitech group) product specialist whom we purschased, he can really explain and provide you details; julius@unimed.com.sg
Thanks for the above material……we are in a dispute whether to opt for vapros or freezing point osmometers…In fact we are using a freezing point one which needs replacement….anyways needs to ponder over now
The Wescor vapor pressure based output is in mmol/kg whereas some freezing point depression osmometers such as Advanced Instruments 3250 outputs osmolality in mOsm/kg. Since these are both based on colligative properties these units should be interchangeable right? Since ultimately it is the amount of dissociated particles that matters and not the known concentration of pre-dissociated molecules?
I’m wondering what the motivation was to post this blog? It seems slanted towards what is wrong with vapor pressure, but doesn’t tout any advantages of freezing point osmometors. My Wescor lasted almost 20 years without any issues until a student hit the thermocouple. we are only buying a new one bc they discontinued the 5520. Otherwise it was a rock. If freezing point osmometors are more reliable day in day out with no calibration, I’d love to see some data showing that. It’d make a decision on what to choose very easy.
Thanks for sharing your experience.
Agreed. We’d like to see more data on reliability for different systems too.
I’m not sure of the accuracy of the information provided. The vapor pressure method determines osmolality at room temperature with the sample in natural equilibrium. This precludes cryoscopic artifacts due to high viscosity, suspended particles, or other conditions that can interfere with freezing point determinations, giving Vapro a much broader range of error-free applications. With freezing osmometers you often have to stir the sample and even then can run into problems with particulate as it freezes. Most electrophysologists tend to use vapor pressure osmometers for the simplicity and durability of the instrument.
For artificial cerebrospinal fluid and intracellular patch clamp pipette solutions, we have not had problems with the freezing point system we have in the lab. That’s just our experience.
Following advice for this post we bought a freezing point (Gonotech Osmomat 3000 Basic) on sale after receiving a quote from Elitech to replace our Vapro’s motherboard and thermocouple head. The new Osmomat was marginally more money than Elitech’s quoted repair, and has been a regret-free purchase. After years of using VAPROs in various labs (daily calibration required), we’ve been impressed that the Osmomat has not yet needed recalibration. We just test it from time to time with a standard, but so far no change at all over one year of use. Also, the results are very consistent run to run (the same every time!) compared to Vapro. The only downside is the sample containers, which are annoyingly expensive specially-sized eppendorf tubes… Thanks to this post and good experience with Osmomat, we are now squarely in the “freezing-point” camp of osmometers for standard ephys stuff.
It’s good to hear that your lab’s experience was good with it.
We don’t intend to create converts to any technology or products. We just want to share our experience, as you did.
Thanks for sharing!
I have used both – a older Wescor 5200 (I think) that I inherited from another lab for many years in Baltimore (~1993-1999) – it was working well when I left there but we couldn’t move it (university asset). We went with an Advanced Osmometer in the more recent lab (1999 until it died – electronics failure – in about 2011). We went back to the Wescor (Vapro 5600) when we finally bought the replacement in about 2015. We have been happy with both, as long as you are careful with them. On both it is useful to make measurements in triplicate, but my sense is that the vapor pressure unit is a bit more consistent. Both required regular checks on the calibration, which is just plain good practice. The self-cleaning feature of the newer models is also very nice. Main use is electrode solutions for patching and a variety of “ACSF” solutions of varying composition for slicing and recording, and usage is not quite daily.
I used both – a new Wescor Vapro and freezing once (Knauer and Precision systems). Freezing once are less reliable for my specific need, since I work with high concentration protein solutions. First – it’s hard to get a reading (no freeze is usual error), second – the osmolality is sky rocket with increasing protein concentration and dose not represent the true value. Even Vapro overestimates osmolality, but it’s readings are lower and almost never with errors.
Hi, could you share your thoughts on what is the alternate to Freezing point depression technique to measure osmolality of viscous samples. Would Vapour pressure technique work?
I had tried with AI’s Osmometer 3250 to measure the osmolality of a viscous samples, and it displays “Sample did not freeze”.
We need to measure osmolarity of our sample solution at 37 C (37degree centigrade). Is it possible to measure osmolarity at 37C on both instruments?
I am curious if anyone has used the Precision Systems Model 6002 Osmette, especially the reliability and how often it needs calibration. Thanks!
I am also eager to see reviews/comparisons of the 6002 Osmette? Anyone have experience with this machine?