MIDI Flex Tube Kit, 6-8KDa MWCO

Model Number IB48024

  • Item Description
  • Specifications
  • Protocol
  • Technical Information
  • Accessories
  • MWCO: 6-8KDa
  • FlexTube Volume: 800µl
  • Dialysis Volume: 50-800µl
  • Minimum Sample Size for Extraction: 0.5µg
  • Maximum Gel Slice: 1cm x 0.5cm
  • Comes with (2) MIDI FlexTubes and (1) Dialysis Float (4-place)

IBI MIDI FlexTubes are typically used for the following applications: dialysis, gel extraction, electro-elution, and de-salting. The design of the FlexTube allows for easy loading and unloading with a standard pipette tip and screw-cap top. Multiple tubes can be placed in one buffer tank for high-throughput applications with minimal hands-on time.

The FlexTube membrane is constructed of regenerated cellulose and is 18 - 42µm thick. The membrane dimensions for the MIDI FlexTube is 0.9 x 1cm.

For the MIDI FlexTube, the minimum sample size is 0.5µg, the maximum gel slice is 1cm x 0.5cm, and the dialysis volume is 50-800µl. The MIDI FlexTube is offered with the following Molecular Weight Cut-Offs (MWCO): 1KDa, 3.5KDa, or 6-8KDa.

When used for dialysis or buffer exchange, the MIDI FlexTubes can be used with DNA, RNA, proteins, and Oligonucleotides (>15nt) for small volumes of 50-800µl. Simply load the sample into the tube with a standard pipette, load into the FlexTube float, and place in a stirred beaker of desired buffer.

When used for gel extraction, the FlexTubes can be used with proteins, RNA, DNA, or oligonucleotides (>20nt) from polyacrylamide, agarose, or any other gel matrix in a running buffer. The tubes are ideal for protein-nucleic acid complexes and large size DNA fragments (>100Kb) from agarose or polyacrylamide gels. DNA recovery from polyacrylamide or agarose gels is typically greater than 90%. See manual for more approximate times.

Isolation of proteins from a gel using the FlexTube delivers up to 70% recovery yield. After the protein gel extraction, the sample can remain in the tube for SDS removal*. The combination of SDS-PAGE, electro-elution with the FlexTube, and SDS removal buffer can give you a more accurate determination of a protein’s molecular mass due to the high recovery yield and purity of the sample. This also results in a MALDI-MS analysis with greater sensitivity**.

The same FlexTube can also be used for Oligo PAGE Electro-Elution and De-Salting. This method is a vast improvement over the Diffusion Method, which is a lengthy over-night process that typically produces low yields. The FlexTube will allow the extraction of the protein from the gel followed by de-salting of the sample by dialysis in the same FlexTube. The easy-to-follow protocol will save you valuable lab time.

IBI MIDI FlexTubes are tested by using them in the extraction of proteins, RNA, or DNA fragments of various sizes from either agarose or polyacrylamide gels. IBI MIDI FlexTube kits are also tested for simple dialysis of salts or buffer exchanges. The quality of the isolated protein, RNA, or DNA fragments, or of the sample after dialysis, is checked by several assays commonly used for proteins, nucleic acids, and dialysis.

The FlexTube is a single-use product.

*To use the FlexTubes for protein gel extraction, Quick Blue protein stain (extraction grade) must be used. Coomassie blue fixes the proteins in the gel, whereas, Quick Blue does not. Therefore, Quick Blue Protein Stain is necessary for protein gel extraction. Quick Blue Protein Stain is an environmentally friendly stain with high sensitivity and does not contain methanol or acetic acid. Quick Blue does not require use of hazardous solvents for destaining.

**MS Buffer must be used for precipitation of protein for analysis by MALDI-MS. Product numbers are IB48500 (3ml) and IB48501 (5ml).

Molecular Weight Cut-Off (MWCO): 6-8KDa
FlexTube Volume: 800µl
Dialysis Volume: 50-800µl
Minimum Sample Size for Extraction: 0.5µg
Maximum Gel Slice: 1cm x 0.5cm
Yield of Molecule Recovery: 90% from an agarose or polyacrylamide gel; 70% from an SDS-PAGE gel
Membrane: Ultra-clean, sulfur- and heavy metal-free. EDTA-treated.

FlexTube Membrane Solvent Compatibility Table

The elution time depends on the size of protein molecule to be eluted, the applied voltage, the size of gel slice, the ratio of the polyacrylamide:bisacrylamide and the percentage of the polyacrylamide gel. Electro-elution time at the elution step has to be adjusted for each individual sample.


Table 1: Minimum time needed to extract different-sized proteins from 10% SDS-polyacrylamide gel (29:1 polyacrylamide:bisacrylamide) at 100V.
Protein Size (KDa) Elution Time (Minutes)
14 35-45
19-26 45-55
29 55-65
40 60-70
45 65-75
50 75-85
66 85-95
81 105-115
116 120-130
128 140-150


The elution time depends on the size of the nucleic acid fragment, the concentration of the gel, the size of the gel slice, the ratio of the polyacrylamide:bisacrylamide and the applied voltage. Electro-elution time at the elution step needs to be adjusted for each individual sample.


Table 2: Minimum time needed to extract various DNA or RNA fragments from native or denatured 4% polyacrylamide gel (29:1 polyacrylamide:bisacrylamide) at 100-150V.
DNA Fragment Size (bp) RNA Fragment Size (bp) Elution Time (Minutes)
100 10-20
300 100 15-25
500 20-30
822 400 25-35
1044 20-30
600 35-45
2700 1000 45-55


Table 3: Minimum time needed to extract DNA fragments from 1% agarose gel at 80-110V.
DNA Fragment Size (bp) Elution Time (Minutes)
100-200 10-20
500-700 15-20
1000 20-30
4361 25-35
6557 45-55
9416 55-65
23130 70-80


Why do my FlexTubes have water in them and in the bag they came in? Some FlexTubes are shipped with water inside of the tube to protect the membrane. Some water might leak through the membrane and water is added to the bag as well.

Can I tape another tube to the electro-elution tray to run more FlexTubes at one time? Yes, as long as the arrow on the tube is facing up, and the membranes are facing the electric field.

What Molecular Weight Cut Off do I need? Anything below the listed MWCO can travel through the membrane. To calculate the MW of a nucleic acid: 330 Da  MW of 1 base 660 Da  MW of 1 base pair

What type of stain do I need if I want to electro-elute protein from an acrylamide gel? Quick Blue Stain (Extraction) grade is needed because it won’t fix the proteins in the gel. Stains such as Coomassie Blue will fix the proteins in the gel and the proteins will not come out during electro-elution.

Can I concentrate my sample in the Flextube by centrifugation? No, if the Flextube is centrifuged, the fluid will leak out of the membrane.

After electro-elution, can I use the same tube for dialysis of my sample? Yes, remove gel from tube and then dialyze against a large amount of water. However, some gel residue may still be in the sample from electro-elution. Look at the Oligo protocol for further information.

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