Laboratory Stirring & Mixing

Lab stir plates for mixing samples

Mixing is used in research labs and industrial labs for blending, dissolving, or other purposes. A variety of devices are available for stirring and mixing solutions and samples.

Stir Rods and Spatulas

Stir rods and spatulae are used to mix solutions manually. Stir rods should be selected based on dimensions and material. PTFE and polypropylene stir bars are autoclavable and offer good heat resistance. Polyethylene and steel rods provide both chemical and temperature resistance. Borosilicate glass rods can be used for general purpose stirring or for use with mixtures that are reactive with plastics or steel. Laboratory spatulas are useful for scooping and scraping, and are available with heads in various shapes to accommodate different vessels or samples with varying levels of sedimentation.Mixing is used in research labs and industrial labs for blending, dissolving, or other purposes. A variety of devices are available for stirring and mixing solutions and samples.



Vortexers

Vortex mixers use circular motion to form vortices in liquids and fluids that uniformly mix the solution. Vortexers are available with touch activation or continuous mode operation, fixed and adjustable speeds, and platforms that support different types of vessels and containers ranging from small tubes to large plates. The orbit diameter of the vortexer or orbital shaker determines which vessels can be used. Smaller 3 mm orbits are suited for microplates, microfuge tubes, and other small vessels. Mid-size 15 mm - 25 mm orbits are good for cell culture dishes, flasks, and beakers. Larger orbits (>30 mm) are recommended for large volume or wide vessels.

Magnetic Stir Bars

Magnetic stir bars should be selected based on shape, size, and material.

Shape: The shape of the stir bar can affect degree of agitation and vessel compatibility.

  • Round stir bars are typically used with flat-bottom beakers and vessels.
  • Slide round stir bars have a pivot ring around the center to reduce vibrations and friction and work well in containers that have curved or uneven bottoms.
  • Spherical stir bars are used in tubes and vials.
  • Elliptical stir bars are ideal for use in round-bottomed beakers.
  • Cross-shaped spin bars stabilize stirring at high speeds and are recommended for turbulent solutions or solutions with sedimentation.
  • Crown stir bars are used in cuvettes or test tubes.
  • Bone-shaped stir bars are recommended for use in containers with slightly convex bottoms.
  • Triangular stir bars are good at scraping and preventing sedimentation and are recommended when increased turbulence is required for mixing.

Size: Stir bars should be small enough so that they do not touch the walls of the vessel during stirring. Maximizing the size of the stir bar enables more motion and better mixing. Curved vessels will require smaller stir bars to prevent snagging on the sides of the flask.

Material: Magnetic stir bars are typically made from alloys of aluminum, nickel, and cobalt. Samarium cobalt stir bars couple more strongly with the internal stir magnet of the plate stirrer or stir mantle. Stir bars are typically coated with PTFE, which has high chemical and temperature resistance. The coating material should be compatible with your sample.

Plate Stirrers and Stir Mantles

Stir bars are used with stir mantles or plate stirrers that contain internal magnets for mixing. Stir mantles are used with round bottom tubes and flasks. Stir plates have platforms compatible with beakers, flasks, and other flat bottom vessels. Hot plate stirrers and heating stir mantles are also available, providing controlled heating and stirring for dissolution.

Impellers and Stir Blades

Impellers use shear force, vortex, or aeration to mix samples when combined with compatible shafts or blades. Impellers should be selected based on flow, diameter, viscosity, and material. Axial flow is recommended for liquid blending. Radial flow provides higher shear and turbulence and is recommended for dispersion and emulsion mixing. Tangential flow is recommended for mixing high viscosity samples. Impellers are typically made from different grades of stainless steel or PTFE for applications involving harsh or corrosive samples.

Overhead Stirrers

Overhead stirrers are positioned above the sample and use impellers to mix samples. They should be selected based on stirring speed, volume, torque, and viscosity. Higher torque is recommended for mixing higher viscosity mixtures. Overhead stirrers are available with a variety of options including reversible directional stirring, programming for automatic shutdown, data logging, and overload/overheat protection.