How Do I Choose a Magnetic Bead Separation Rack for 1.5 mL Tubes or a 96 Well Plate?

Magnetic bead cleanups show up in DNA and RNA extraction, PCR cleanup and library prep. The beads only work if the magnet holds them firmly against the wall while you pipette. A rack that is the wrong size for your tubes, or uses magnets that are too small, turns a two minute step into a guessing game. Here is how to choose one, and what DC Additive Pros, an additive manufacturing company in the USA, builds for labs that want a simple bench rack.

Which magnetic rack do I need for 1.5 mL tubes or a 96 well plate?

Match the rack to the format you pipette from most: a tube rack for 1.5 mL or 2.0 mL microcentrifuge tubes, or a plate separator for 96 well PCR plates. A tube rack holds tubes in rows with magnets running between them, so each tube has a magnet beside it at the lower part of the tube. A 96 well plate separator sits under the plate and places magnets between the wells, so beads are drawn toward the side of every well at once.

If you process a handful of samples at a time, a 16 place tube rack is a common size. If you run full plates, a plate separator saves you from moving samples into tubes at all.

How do I check that my tubes will fit?

Use the tube body width in millimeters, measured just under the cap, rather than the volume printed on the tube. Published maker dimensions for standard 1.5 mL microcentrifuge tubes run about 10.2 to 10.8 mm across the body, and about 38 to 41 mm long. Published 2.0 mL tubes run about 10.5 to 11.0 mm across. A few tenths of a millimeter is the difference between a tube that drops in and one that binds or wobbles.

We checked published dimensions from several makers before sizing our racks, and we only list a brand when its numbers fit our design. For example, the 1.5 mL rack lists:

• Compatible with Eppendorf Safe-Lock 1.5 mL
• Compatible with Fisherbrand Premium 1.5 mL
• Compatible with Sarstedt 1.5 mL reaction tubes
• Compatible with SSI 1.5 mL (1210-00)

The full list for each size is in the builder. If your brand is not listed, measure a tube with calipers. Set snap cap tubes with the hinge facing out toward the rack edge so neighboring caps open freely.

Should I choose a slider or fixed magnets?

Choose a slider if you want to turn the pull on and off without moving tubes, and fixed magnets if you are happy to lift tubes out to release the beads. On a slider rack a magnet bar runs between the two rows of tubes. Slide it in and the beads collect on the tube wall; slide it out and you can mix or resuspend in place. On a fixed rack the magnets are always on, so you set tubes in to pellet and lift them out to resuspend.

The slider is our most popular style. The fixed rack has no moving parts, which some benches prefer for simple wash steps.

Want to see the price for your exact setup? Build your magnetic rack in the N52 Magnetic Rack Builder →

Why does the magnet grade matter?

Neodymium magnets are graded by a number such as N35, N42 or N52, and at the same size a higher grade is a stronger magnet. The number tracks the magnet's maximum energy product. Magnet size matters too: a small disc of a high grade can still be weak if it is tiny or set far from the tube.

When you compare racks, ask three things. What grade are the magnets? What size are they? Are they sealed inside the rack so they cannot slip, chip or touch your samples? Every rack in our builder uses N52 grade neodymium disc magnets, 12 x 2 mm, fully enclosed. Customers told us racks with small or weak magnets were not good enough, so we do not use them.

Pull time still depends on your bead kit, buffer and volume. We do not publish a speed number. Follow your kit protocol and wait until the liquid is clear before you remove the supernatant.

What should I check on a 96 well plate magnetic separator?

Check that it is built to the ANSI SLAS footprint and that it lists your plate style: skirted or semi skirted. The ANSI SLAS 1-2004 standard sets the plate footprint at 127.76 x 85.48 mm. A skirted PCR plate rests on its full skirt inside the separator. A semi skirted plate has a short half skirt, and its well tips seat in shallow guides in the separator. Non skirted and deep well plates locate differently, so check the maker's list before you buy.

Our separator lists:

• Compatible with Axygen PCR-96-BRF and PCR-96-EPF (skirted)
• Compatible with SSI 3450 and Axygen PCR-96-EPS (semi skirted)

Can I autoclave a printed magnetic rack?

No. Our printed magnetic racks are not autoclavable. Keep them away from heat sterilization, hot water baths, dishwashers and warm drying ovens. For cleaning, wipe with mild soap and water or a quick 70 percent isopropyl alcohol wipe and let the rack air dry. Do not soak it in alcohol, bleach or solvents, and keep phenol and chloroform off it. Magnetic racks live on the bench at room temperature, so this covers normal use.

How do I order a rack sized for my lab?

Open the builder, pick your product, size and color, confirm the fit, and pay by card at checkout. Free US shipping is already in the price you see, and the price shown is the price you pay. Racks are made to order in the USA and usually ship in 3 to 5 business days. For 0.2 mL PCR strips, 15 mL or 50 mL conical tubes, our custom magnetic bead separation rack builder covers those sizes, and the tube rack size guide explains hole sizes for plain storage racks.

Frequently asked questions

Will my 1.5 mL tubes fit a magnetic rack?
Most standard 1.5 mL microcentrifuge tubes have a body about 10.2 to 10.8 mm across, based on published maker dimensions. Our 1.5 mL racks are sized for that range. Measure just under the cap if your brand is not on the compatible list.

Is a slider rack better than a fixed magnet rack?
Neither is better for every lab. A slider lets you switch the pull on and off without moving tubes, which helps when you resuspend beads often. A fixed rack keeps the magnets always on, so you move tubes in and out instead.

Can I autoclave a 3D printed magnetic rack?
Not ours. These racks are not autoclavable and should not see heat sterilization, hot water baths or dishwashers. Wipe them clean with mild soap and water or a quick 70 percent isopropyl alcohol wipe.

Which 96 well plates fit a magnetic plate separator?
Look for skirted or semi skirted 96 well PCR plates with the ANSI SLAS footprint of 127.76 x 85.48 mm. Check the separator maker's compatible list, since non skirted and deep well plates locate differently.

Build your N52 magnetic rack

Slider or fixed racks for 1.5 mL and 2.0 mL tubes, plus a 96 well PCR plate separator, all with N52 neodymium 12 x 2 mm magnets, fully enclosed. Free US shipping included. For Research Use Only.

Open the N52 Magnetic Rack Builder (from $32.95) →