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Is Your Rotovap Too Slow?

Can 15 more RPMs have an impact on productivity and operator satisfaction in your lab?

In running your lab experiments, you might find it challenging to increase your work speed while keeping your procedures efficient.

We understand you! Running your experiments over and over again can be tiring. Long hours of waiting while something like a rotary evaporator spins around can make it tiring plus boring, double frustration! What more when you deal with solvents in large amounts, right?

So what if there is a way to save 25 minutes of boring solvent recovery time in a day?

A typical rotovap in most industrial markets has a maximum of 280-300 rpms. 

But don’t you think it would be a game-changer if there’s a model that can spin up to 315 rpms? That added speed could help you recover your solvents 25-minutes faster. It can be enough time to indulge yourself in a massage chair.

You’ll know more about this later. First things first, here are some things we want you to learn to help you better understand your rotary evaporators, boost productivity at your lab, and save more time.

How does a rotovap work?

Rotary evaporators, or rotovaps, are widely used in labs to remove volatile solvents from your reaction mixtures after an evaporation or distillation process.:

  1. A motor moves your flask in a circular motion to increase the surface area of your sample. As the flask turns, the liquids are stretched by the shape of the flask and the motion, increasing surface area.
  2. A vacuum pump to minimize the pressure on your system. Reducing pressure lowers the boiling temperature, resulting in faster evaporation.
  3. A bath to heat or boil your sample.
  4. A condenser to hold your coolant mixture, like dry ice and acetone.
  5. A mechanical or motorized system to lift your evaporation flask from the heating bath or sink it as your experiment process requires (for larger sample sizes).

What does a rotovap do?

Well, there could be many ways to make use of your rotovap. It can facilitate processes of evaporation, concentration, drying, crystallization, and of course, solvent recovery. In many fields, it operates through the continuous distillation of large volumes of volatile solvents under reduced pressure. Sometimes, the solute from the mixture is the interest of some experiments. In this case, the removed solvent is still collected to serve another purpose in later experiments or if we run another experiment where we use the removed solvents from our current mixture.

Rotary evaporation uses the principle that solvents will have a lower boiling point at reduced pressure. In this state, evaporation of solvents is done by rotating its container flask at a constant speed. As it spins, the sample is formed into a large area of the uniform thin film in motion at the inner wall of the flask holding your solvents. The rotating flask is simultaneously heated by a water or oil bath at the temperature where your solvent, with now a lower boiling point, becomes capable of evaporating rapidly under vacuum conditions. Your solvent steam is then recycled by way of your receiving flask being cooled in a high-efficiency glass condenser. Pretty complex, but your end product simply– is your solvent separated from your mixture.

This equipment is essential for manufacturing biological, pharmaceutical, chemical, and, lately, even food-making materials. For example, in the drug recovery process, your rotovap will function by extracting the bioactive substances or compounds in your, for instance—plant sample, which is then utilized to develop a novel medicine. 

In chemical laboratories, your supervisor or colleague probably showed you a few times extracting chemical substances to be further applied in other chemical procedures to create something useful for science.

You see, rotovaps are generally useful in research and manufacturing labs, but each equipment component is a powerful tool that will help you:

  1. Accommodate the volume of your mixtures to as large as 2-3 liters.
  2. Avoid your solvent from freezing during the evaporation process.
  3. Remove your solvents through a vacuum system and collect your solvent in a flask for easy reuse or disposal.
  4. Control your mixture’s boiling temperature and rotation speed to avoid bumping and unwanted reactions in your sample.

When you’re choosing a rotovap for your lab, there are a few standard features you’ll find regardless of your manufacturer:

  • Rotation speed
  • Vessel size
  • Bath
  • Vacuum

But what are these features exactly?

How to easily separate features you need from those you don’t.

Rotation Speed 

Having precise control of the rotation speed in your evaporation flask is important. The rotating motion agitates your solution and the water bath, accelerating the heat transfer between the flask and your solvent. 

But, maybe you will want to consider this according to the needs of your solvent and sample’s consistency, flask size, and volume, which may require higher or lower rotational speed than usual.

Flask/Vessel Size

The size of the flask in your rotovap also influences the surface area of your mixture. It will improve the heat transfer and evaporation rate of your solvents. Large holders would also prevent spillage, considering that in a rotovap set-up, your flask is tilted.

Large flasks also help prevent foaming, a negative effect of rushed boiling or bumping. But on certain occasions, smaller flasks could also be advantageous for obtaining a specific amount of solvents if you want to observe or assess the residue of your sample after the evaporation. Hence, you should carefully decide according to the needs of your applications.

Water Bath Temperature

As reduced pressure helps speed up evaporation, the water bath does the same thing. As it heats your solvent, evaporation takes place. However, you should monitor the temperature carefully to avoid bumping and unwanted reactions such as too much solvent in your vapor which could degrade the quality of your sample.

As compared to their boiling point at ambient pressure, here’s some of the solvents and their adjusted boiling point when there is reduced pressure through a vacuum system that is worth taking note of (see table below):

Solvent

Boiling Point

At ambient pressure

(760 torr)

Rotovap vacuum system

(40 torr)

acetonitrile

81.8 oC

7.7 oC

diethyl ether

34.6 oC

-27.7oC

ethanol

78.4 oC

19 oC

ethyl acetate

77.1 oC

9.1 oC

hexane

68.7 oC

-2.3 oC

heptane

98.4 oC

22.3 oC

methanol

64.7 oC

5.0 oC

water

100 oC

34.0 oC

Vacuum 

While your goal is to gradually increase the temperature to facilitate evaporation, it is also your goal to control the boiling temperature of your solvent by reducing the pressure within its system through the vacuum. But you should still be diligent in increasing your vacuum level, as a rapid increase in a vacuum could also risk an implosion of your flask.

Again, that’s speed, size, temperature, and pressure. You should carefully evaluate these features when you plan to upgrade or purchase your rotovap.

What is bumping in a rotovap?

Bumping sucks. It can cause sample loss, possible contamination, and the need to repeat your entire day’s work— a waste of your time, effort, and resources! 

Hence, here’s what you can do to eliminate the risk. 

Bumping could happen when your sample boils excessively or super fast due to a rapid increase in your temperature rate or vacuum level. It can cause bubbles, which could expel or blow the sample out of your flask and damage your whole procedure. Not to mention your beautiful face.

You have two things to remember: Control and trap

You must monitor your temperature and vacuum level closely and increase both gently so you do not trigger bumps and foams. You should also remember that the volume of your sample should be less than half of your flask so enough surface area can mitigate rapid boiling.

Meanwhile, trap refers to a hack sometimes called bump trump. You should place another glassware before your flask so your mixture will not necessarily spill out of it when bumping.

The formation of foams is difficult to avoid. You should consider the careful application of vacuum and opening and closing of your stopcock to release pressure whenever the foam clumps together.

  • In choosing a flask, select one that accommodates approximately twice the starting volume of your solvent.
  • The moderate spinning of your flask increases your surface area and prevents the nucleation of bubbles. This lowers the chances of accidentally bumping.
  • Carefully choose a temperature appropriate for the solvent being evaporated. 
  • Boiling is not the same as bumping.
  • If the boiling bubbles reach the flask's neck, reduce pressure immediately and gently in multiple steps.

How to choose rotary evaporator flask size?

As mentioned above, your flask's size affects your solution's surface area. So here’s what you should consider in choosing your rotovap flask.

Evaporation performance is directly proportional to the size of the flask you are using.

What does this mean?

A larger flask size may be useful if your application requires high-performance evaporation. But if you run an experiment that observes solvent after evaporation, using smaller flasks may be useful. 

But maybe, depending on your resources, purchasing both large and small flasks could give you more productivity. After all, a little investment for a 25-minute more of your time sounds good, right?

What’s the difference between A glass and B glass?

One of the very crucial parts of running rotary evaporators is the glassware that you use. With increasing heat and flask spinning, you cannot afford breaking your glassware and mess up your entire procedure. That’s why you should take careful consideration in choosing your glasses. 

Currently, laboratory glasswares available in the market are classified into two: Class A and B. At first glance, it will be difficult to notice the differences between the two. But, these glasswares vary in terms of purpose, design, especially when it comes to heat tolerance and calibrations.

Class A glassware is your superior one. It has a high accuracy level, impressive thermal and chemical resistance properties. This is due to the fact that its material is made from borosilicate that contains boron trioxide which is capable of a very low coefficient of thermal expansion. To put simply, Class A glasswares are durable because they will not easily crack under extreme temperature changes unlike other regular glasses. This glassware is very ideal if you are running procedures that require evaporation of substances with high evaporating/boiling temperature points.

Class B glasses on the other hand is made from soda-lime which is commonly used for making commercial glasswares. They are used in laboratories for general purposes like holding or storing substances. This glass can be susceptible to shock and may not handle extreme temperature changes as Class A, but this glassware is durable for sure at normal temperatures.

It’s worthy to also know that Class B glassware is way cheaper and can be your affordable option if your budget for your glassware is tight for now. But if you value running procedures on a high-temperature substance often, then it may be a good investment to select Class A glassware. 

So yes, it really matters that you know a little or two about these differences to help you assess which glassware best suits your needs and capabilities. 

Yamato Rotovap

But after reading this far, it’s here. The 25-minute extra time that we’ve been talking about.

Your Yamato RE202-A / REV202M-A Rotary Evaporator is about space and power. It features an evaporation capacity of 23 ml per minute, saving you extra time. It has a different speed range at 5~315 rpm with water or oil bath. That’s 15 more rpms than other rotovaps you can find in the market!

Finally, your Yamato rotovap has flexible glassware and bath position. You can put them on the left or ride side depending on your dominant hand or the unit's location. Talking about inclusivity, yes, if you are a left-handed scientist, then this is yours.

Now, enough of your reading. Get that rotovap and kickstart your application!