Hotplate Stirrers Frequently Asked Questions
What is the best laboratory hotplate stirrer?
Selecting the perfect hotplate stirrer for your applications from the thousands of models available can be overwhelming. To ensure optimal stirring of your solutions, it is important to find a hotplate stirrer that is suitable not only for the types of samples you are working with, but also for all your application needs. Consider the pros and cons of each and think about what additional features you may need in the future. Get the best-fit hotplate stirrer for your lab protocols with our interactive selection guide.
Why should you use an external temperature sensor?
A probe that is placed within your sample shows you the actual sample temperature. Without a probe, the unit will show the plate temperature that may differ from the sample temperature. Your sample absorbs and stores heat according to its physical properties. The thermal conductivity of the plate or heating vessel and the room conditions can also influence the temperature of your sample.
How can I reduce overshoot?
To minimise overshoot use a metal container instead of glass. Set your target temperature lower than necessary and increase it once it is stable. If temperature stability is important, it is recommended to use a water bath.
Can hotplate stirrers be operated over a longer period or is there a maximum duty cycle?
Hotplate stirrers can be operated 24 hours a day for several days. There is no maximum duty cycle specified.
At what speed should you set the hotplate stirrer?
The optimal speed depends on several factors, e.g. on the application and your sample. It is important to ensure a uniform mixing. Therefore the speed should not be too low. The most common applications require speeds between 400 and 800 rpm.
Can hotplate stirrers process liquids with high viscosity?
No, a hotplate stirrer is made to work with aqueous solutions or low viscosity media up to 100 mPa. Solutions with high viscosity or high density are barely mixed using this method. Overhead stirrers are usually required to handle higher viscosities.
What is a hotplate stirrer with hotplate used for?
The hotplate stirrer (or hotplate stirrer) is used for mixing and heating aqueous solutions for a great variety of chemical, biological and microbiological applications. If you do not need heating for your application, look for magnetic stirrers.
What is the difference between a ceramic top plate and a stainless-steel top plate?
Ceramic plates have excellent chemical resistance and are therefore ideal if you work with corrosive chemicals that could splash onto the plate surface. They can withstand higher temperatures of up to 450°C and are easy to wipe clean. The white surface of the ceramic top plates is well suited for titrations or other work where clear visibility of the colour is required. Ceramic hotplates have cool edges. This may not be suitable if you need heating all over the plate surface. Another disadvantage is that ceramic hotplates must only be used to heat glassware.
A stainless-steel top plate does not generate eddy currents (like aluminium) and therefore ensures very strong coupling and agitation. Aluminium top plates are more robust and resist accidental impacts better than ceramic plates. They provide an even temperature across the entire plate. Metal hotplate stirrers can also be used to heat metal vessels. So, if you are working with stainless steel beakers or other metal vessels, this is the best choice.
How can hotplate stir bars be sterilised?
Most stir bars (also known as magnetic fleas) are coated with PTFE and can be sterilised by autoclaving or treating with alcohol.
How do I choose a hotplate stir bar?
Choosing the right size and shape of hotplate stir bar ensures efficient mixing and reduces wear and tear on the PTFE coating. The length should be equal to 2/3 of the diameter of the vessel bottom. The power of the bar is dependent on the diameter of the magnet. Regarding the shape, we have the following recommendations based on the vessel:
- Straight bars for flat-bottomed vessels
- Bars with a central ring for slightly convex-bottomed vessels
- Oval bars for balloon-shaped vessels
- Triangular bars for dissolving solids and sediments (where the flat surface of the bar can scrape the bottom of the vessel).
What are the different types of hotplate stirrer to consider?
- Analog stirrers
Analog stirrers feature electronic speed control for constant speed even with changes in sample load and usually have low thermal stability. - Digital stirrers
Units either have LCD or LED displays that show rotation speed and temperature, allowing easy adjustment until the appropriate target values are reached to ensure speed and heat control and maintenance. - Multi-position stirrers
This type can stir multiple beakers or flasks on the platform at the same time.