QIAquick Nucleotide Removal Kit

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.

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).

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.

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

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.