A magnetic stirrer spins a PTFE-coated bar inside your vessel with a rotating magnet under the plate, so there is no shaft, seal or contact with the sample. Choose by three numbers: the volume you stir, how thick the liquid is, and whether you also need heat. Everything else is convenience.
Which magnetic stirrer fits your sample volume?
Pick the model whose rated capacity comfortably exceeds your largest batch, and remember the rating is for water. ERE carries Hanna Instruments and OHAUS stirrers that span 1 L to 200 L.
| Typical job | Stirrer | Rated capacity | Speed range |
|---|---|---|---|
| Titration, pH or conductivity beaker on a crowded bench | Hanna HA-180 mini-stirrers (137 mm diameter, five colours) | 1 L | 100 to 1000 rpm |
| Exothermic reactions, spill-prone benches | Hanna HA-190M / HA-200M mini-stirrers (ABS or AISI 316 stainless cover; 12 V DC option) | 1 L | 100 to 1000 rpm |
| Repeatable speed with a readout, reversing to improve mixing | Hanna HA-304N auto-reverse stirrer | 2.5 L | Low 100 rpm / high 800 to 1000 rpm |
| Several samples at once (jar tests, leaching, dissolutions) | OHAUS multi-position stirrers (4 x 1 L or 9 x 250 mL) | 4 x 1 L / 9 x 250 mL | 60 to 1400 rpm |
| Carboys and drums of standards or reagent | OHAUS large-volume stirrers | 25 L, 100 L, 200 L | 60 to 1400 / 100 to 1800 / 100 to 1650 rpm |
The OHAUS multi-position range comes in analog and digital versions; the digital ones add a timer from 1 second to 160 hours, per the product record.
When do you need a hotplate stirrer instead?
You need one when the sample must be heated while it is stirred, for digestions, dissolving salts or evaporating to concentrate. The OHAUS Guardian 5000 and Guardian 7000 are the two ranges to compare; the Guardian 2000 (analog) and 3000 (digital) sit below them in the stirrers collection.
| Guardian 5000 (e-G52) | Guardian 7000 (e-G71) | |
|---|---|---|
| Heating range | Ambient +5 to 550 °C (7 x 7 in), 500 °C (10 x 10 in), 360 °C (round) | Ambient +5 to 500 °C (ceramic), 380 °C (aluminum round) |
| Speed | 50 to 1800 rpm | 60 to 1600 rpm |
| Capacity (water) | 20 to 22 L | 15 to 20 L |
| Probe control | PT100 / PT1000 Class A; run-dry protection | Temperature probe included |
| Safety features | SafetyHeat, SmartHeat upper limit, run-dry shut-off, IP32 | SafetyHeat, SmartPresence shut-off if no user is detected, SmartHeat |
| Data | Built-in RS232 for logging | USB; 5 stored multi-step programs |
Figures are from the OHAUS datasheets for each series. Plate and probe accuracy depend on the vessel and sample, so the maker recommends a single-point calibration.
Is a magnetic stirrer enough for viscous samples?
Usually not past the limit of the magnetic coupling: the bar decouples and starts to jump instead of spin. Datasheet capacities are quoted in water, so derate for thick slurries and sludges. OHAUS positions its large-volume drive as able to mix highly viscous materials, but if the bar cannot hold, move to a shaft-driven unit.
The OHAUS Achiever 5000 overhead stirrer offers up to 200 Ncm torque and up to 100 L volume in five models, with an IP54 sealed design. For open tanks and vats, ERE also lists stainless and polypropylene stirring paddles in the stirrers collection.
Which stir bar should you buy?
Buy PTFE-coated bars sized to the vessel base: long enough to span most of the flask bottom but short enough to spin freely. ERE stocks Bel-Art Spinbar PTFE bars, including octagon bars with a molded-on pivot ring, polygon bars from 12.7 x 8 mm to 50 x 8 mm, and colour-coded red, yellow or blue bars for keeping reagents separate. Bars are sold individually, so order spares; they are the part that gets lost or scratched.
How do you stir and heat safely in a lab?
Match the plate to the liquid and never leave a heated flask unattended. CCOHS notes that stirring and agitating flammable liquids can build static charge that acts as an ignition source, and advises keeping them away from heat, hot surfaces and sparks (English page; French version at cchst.ca). For flammables, use a non-heating stirrer or a model with probe control and a set maximum temperature.
- Choose the vessel and bar first, then the stirrer; the vessel base should sit within the plate.
- Start at low speed and ramp up so the bar stays coupled.
- Set the maximum temperature (SmartHeat on the Guardian series) below the liquid's flash point and boiling point.
- Use a probe in the liquid, not the plate reading, when the sample temperature matters.
- Label hazardous contents under WHMIS laboratory requirements (CCOHS summary; French version at cchst.ca).
- Let the plate cool before moving or storing the unit.
Stirrers usually sit next to other bench instruments. See our pH meter buyer's guide, laboratory balance buyer's guide and moisture analyzer guide when you are equipping a whole bench.
Need help choosing a stirrer or hotplate?
ERE Inc. has been Canada's environmental equipment specialist for 30+ years. Tell us your vessel size, sample viscosity and whether you need heat, and we will quote the right model.
→ Request a Quote | 1-888-287-EREC | Browse Stirrers | sales@ereinc.com
Frequently Asked Questions
What is a magnetic stirrer used for?
It mixes liquids without a shaft or seal by spinning a PTFE-coated bar with a magnet under the plate. It is used for titrations, pH and conductivity work, preparing standards, dissolving solids and keeping suspensions mixed.
What is the difference between a magnetic stirrer and a hotplate stirrer?
A hotplate stirrer adds a heated plate. Compact magnetic stirrers like the Hanna HA-180 have no heater and are meant for room-temperature work.
How fast should I stir?
Start low and increase until you see a shallow vortex without the bar jumping. Speed ranges differ by model, for example 100 to 1000 rpm on the Hanna mini-stirrers and 50 to 1800 rpm on the Guardian 5000.
Why does my stir bar stop spinning or jump?
It decouples when the liquid is too viscous, the speed is ramped too fast, or the bar is too small for the vessel. Slow down, use a longer bar, or move to an overhead stirrer for thick samples.
Can I stir flammable solvents on a hotplate stirrer?
Treat it as a hazard. CCOHS says stirring flammable liquids can generate static, and that they should be kept from hot surfaces. Use a non-heating stirrer or a probe-controlled model with a set maximum temperature, and follow your site's procedures.
Related articles
Lire en français : Agitateur magnétique : guide de choix par volume, vitesse et chauffage