QIAquick Gel Extraction Kit – Purification du gel

Buffer PE did not contain ethanol

Ethanol must be added to Buffer PE (concentrate) before use. Repeat procedure with correctly prepared Buffer PE.

Inappropriate elution buffer

DNA will only be eluted efficiently in the presence of low-salt buffer (e.g., Buffer EB: 10 mM Tris·Cl, pH 8.5) or water. Elution efficiency is strongly dependent on the salt concentration and pH of the elution buffer. Contrary to adsorption, elution is most efficient under basic conditions and low salt concentrations. DNA is eluted with 50 or 30 µl of the provided Buffer EB (10 mM Tris·Cl, pH 8.5), or water. The maximum elution efficiency is achieved between pH 7.0 and 8.5. When using water to elute, make sure that the pH is within this range. In addition, DNA must be stored at –20°C when eluted with water since DNA may degrade in the absence of a buffering agent. Elution with TE (10 mM Tris·Cl, 1 mM EDTA, pH 8.0) is possible, but not recommended because EDTA may inhibit subsequent enzymatic reactions.

Elution buffer incorrectly dispensed

Add elution buffer to the center of the QIAquick membrane to ensure that the buffer completely covers the membrane. This is particularly important when using small elution volumes (30 µl).

• Add 1/10 volume of 3 M Na-Acetate pH 5.2, and 2 to 2.5 volumes of ice-cold 100% ethanol to the DNA sample
• Mix, and store at –20°C for at least 1 h to precipitate the DNA
• Recover the precipitated DNA by centrifugation at full speed in a microcentrifuge for 15–20 min
• Pour off the ethanol and wash the pellet twice with room-temperature 70% ethanol
• Allow the DNA pellet to air-dry
• resuspend the DNA in a suitable volume of sterile TE buffer or distilled water

Based on our experience, the QIAquick PCR Purification Kit removes SYBR Green dye efficiently from PCR reactions.

We strongly assume that the QIAquick Gel Extraction Kit will be equally efficient in removing this dye, however, we recommend a 5 min incubation with wash Buffer PE on the QIAquick spin column at step 10 of the QIAquick Gel Extraction Kit Protocol. Efficiency of SYBR Green dye removal has to be validated by the enduser.

Yes, please follow the Supplementary Protocols 'High-throughput gel extractions using the QIAquick 96 PCR Purification Kit' (QQ03).  Please contact your local QIAGEN Technical Service for this protocol.

Yes. The QIAquick Gel Extraction Kit for extraction of DNA from gels can also be used for RNA gel extraction. Please see a user-developed procedure below, which was kindly provided by J. Knobloch, Heinrich Heine University, Düsseldorf, Germany. Note that this protocol has not been thoroughly tested and optimized by QIAGEN. QIAquick Gel Extraction Kits are not guaranteed to be RNase-free.

1. Excise the RNA fragment from the formaldehyde agarose gel with a clean, sharp scalpel.
2. Weigh the gel slice, and record the weight. Soak the gel slice in TE buffer for 25 min at room temperature with gentle shaking.
3. Remove the gel slice from the TE buffer, and place it in a colorless tube. Add 6 volumes of Buffer QG to 1 volume of gel, based on the gel weight (100 mg ~ 100 µl).
4. Incubate at 58°C for 25 min. To help dissolve the gel, mix by vortexing the tube every 2–3 min during the incubation.
5. Continue the QIAquick Gel Extraction Kit Protocol (using a microcentrifuge) in the QIAquick Spin Handbook, beginning with step 4.

Figure 1:

A. Total RNA was isolated from the parasitic blood fluke Schistosoma mansoni using the RNeasy Mini Kit and run on a formaldehyde agarose (1.2%) gel. (Note: The 28S rRNA in S. mansoni contains a break site so that the rRNA splits into two parts, which run on a gel at the same size as the 18S rRNA.) The rRNA bands were excised and treated as described above (left lane) or using 10 volumes of Buffer QG in step 3 (right lane).

B. The extracted RNA was then analyzed on a new formaldehyde agarose gel. (Data kindly provided by J. Knobloch, Department of Genetic Parasitology, Heinrich Heine University, Düsseldorf, Germany).

DNA fragments purified with the QIAGEN DNA Cleanup Systems, i.e., the QIAquick PCR Purification Kit, the MinElute Reaction Cleanup Kit, the QIAEX II Gel Extraction Kit etc. may float out of the loading wells of agarose gels due to residual ethanol carried over from the wash step with Buffer PE (despite the addtition of glycerol-containing loading buffer).

Use either of the following options to remove residual ethanol from the eluate:

• re-purify the sample using a QIAquick-, or MinElute column, or QIAEX II resin
• incubate the eluate at 56°C for 10 min to evaporate the ethanol
• dry down the sample in a vacuum centrifuge, and resuspend the pellet in a small volume of sterile water

As a rule of thumb, single-stranded DNA binds to silica with approximately half the affinity of a double-stranded DNA fragment of the same length under the buffer conditions used in the QIAquick and MinElute Kits. Even though no systematic experimental data exists, we expect that recovery of ssDNA fragments of approximately 200 nucleotides and below will not be very efficient after cleanup using the QIAquick PCR Purification Kit or MinElute PCR Purification Kit. By comparison, it should be possible to purify fragments longer than 140 nucleotides using the QIAquick Gel Extraction Kit.

Note that recovery of single strand DNA is influenced to some degree also by factors such as base composition and secondary structure. It has to be determined empirically by the researcher if cleanup of single-stranded DNA with QIAquick columns yields satisfactory results.

The composition of Buffer EB is:

• 10 mM Tris-Cl, pH 8.5

Buffer EB is the elution buffer used in the QIAquick PCR, Gel Extraction, Nucleotide Removal Kits, and MinElute Kits for DNA cleanup, and the QIAprep Miniprep Kits for small-scale plasmid purification. The purified DNA can also be eluted in TE (10 mM Tris-Cl, 1 mM EDTA, pH 8.0), but the EDTA may inhibit subsequent enzymatic reactions.

Occasionally, DNA fragments eluted from the silica matrix of QIAquick, MinElute or QIAEX II Kits will contain denatured single-stranded DNA (ssDNA), appearing as a smaller band on an analytical gel. Under certain conditions, chaotropic agents (present in all silica-based DNA purification methods) can denature DNA fragments. This is a rare event that may be influenced by sequence characteristics such as the presence of inverted repeats or A–T-rich stretches.

Because salt and buffering agents promote renaturation of DNA strands, the following tips are recommended:

• use the eluted DNA to prepare your downstream enzymatic reaction, but omit the enzyme. Incubate the reaction mix at 95°C for 2 minutes to reanneal the ssDNA, and allow the tube to cool slowly to room temperature before adding the enzyme and proceeding
• alternatively, the DNA can be eluted from the silica-gel membrane or resin in 10 mM Tris buffer containing 10 mM NaCl. However, the salt concentration of the eluate must then be taken into consideration in downstream applications.

The QIAquick Spin Columns (100) (cat. no. 28115) in the QIAquick PCR Purification, Gel Extraction, Nucleotide Removal and PCR & Gel Cleanup kits are also sold separately from the kits.

The MinElute columns in the MinElute PCR Purification, Gel Extraction and Reaction Cleanup kits are not sold separately.

We always provide extra buffers in our kits so you can scale up reactions, add extra washes or allow for spillage.

Always dispose of potentially biohazardous solutions according to your institution’s waste-disposal guidelines. Although the lysis and binding buffers in QIAamp, DNeasy, and RNeasy kits contain chaotropic agents that can inactivate some biohazardous material, local regulations dictate the proper way to dispose of biohazards. DO NOT add bleach or acidic solutions directly to the sample-preparation waste. Guanidine hydrochloride in the sample-preparation waste can form highly reactive compounds when combined with bleach.
Please access our Material Safety Data Sheets (MSDS) online for detailed information on the reagents for each respective kit.

The QIAEX II and QIAquick Gel Extraction Kit can be used to extract DNA from polyacrylamide gels.

The QIAEX II Handbook contains a protocol for Polyacrylamide Gel Extraction. A specialized User-Developed Protocol (QQ05) is available when using the QIAquick Gel Extraction Kit for this purpose.

Both protocols require the preparation of a diffusion buffer and a disposable plastic column or syringe barrel containing a Whatman GF/C filter or siliconized glass wool. To ensure optimal diffusion, cut the gel slices as small as possible, and use 2 volumes of diffusion buffer per 1 volume of gel. Increasing incubation time (protocol step 3) may result in higher yields.