The QIAEX II Gel Extraction Kit provides QIAEX II suspension together with binding and wash buffers, and a comprehensive handbook. QIAEX II Suspension is also sold separately. Protocols are provided for purification of DNA from agarose gels, solutions, and polyacrylamide gels.

Batch Gel Extraction
	Size range	No. of samples in parallel	Format	Processing
QIAEX II Gel Extraction Kit	40 bp – 50 kb	1–24	Silica particles	Spin procedure

Principle

Purification of DNA fragments with the QIAEX II system is based on solubilization of agarose and selective adsorption of nucleic acids onto QIAEX II silica-gel particles in the presence of chaotropic salt. QIAEX II separates DNA from salts, agarose, polyacrylamide, dyes, proteins, and nucleotides without phenol extraction or ethanol precipitation. QIAEX II is effective for any type of agarose in either TAE or TBE buffers.

Consistent Recovery from Different Starting Quantities of DNA Fragment

Recovery of various amounts of a 2.9 kb DNA fragment from 1% agarose gels using the QIAEX II Gel Extraction Kit.

QIAEX II particles ensure efficient recovery without shearing, even for large DNA fragments. Optimized buffers permit DNA recovery without sodium iodide, which is difficult to remove from DNA samples, and may affect subsequent reactions. Quantities of DNA from 10 ng to 10 µg are recovered efficiently (see figure "Consistent Recovery from Different Starting Quantities of DNA Fragment"), and the versatile batch procedure can be easily scaled up for preparative purposes up to 15 µg binding capacity using 30 µl QIAEX II suspension.

The solubilization and binding buffer used with the QIAEX II system contains a unique pH indicator. A simple color change indicates whether the pH of the binding mixture is optimal for efficient adsorption of DNA to QIAEX II silica particles (see figure "pH indicator dye"). The colored dye also allows easy visualization of any unsolubilized agarose in the binding mixture, ensuring complete solubilization for maximum yield.

pH indicator dye

pH indicator dye in the solubilization and binding buffer allows easy visual determination of optimal pH for DNA adsorption (pH ≤7.5). An incorrect binding-mixture pH can occur if the agarose gel electrophoresis buffer was frequently used or incorrectly prepared. In this case the pH can be easily adjusted by addition of 10 µl 3 M sodium acetate, pH 5.0.

Size vs recovery with QIAEX II

DNA size Recovery* 44 bp 75% 75 bp 75% 500 bp 95% 7.5 kb 85% 23.5 kb 75% 48.5 kb 60% * From 2 µg loaded on a 1% TAE agarose gel

Binding capacity: 5 µg DNA per 10 µl QIAEX II suspension Recovery: 60–95% of DNA fragments (40 bp – 50 kb) Elution volume: Elution volume: 20 µl

Procedure

QIAEX II silica-gel particles are added to the solubilized gel slice (see QIAEX II Procedure), and the particles collected by a brief centrifugation step. After washing, the pure DNA fragment is eluted in 20 µl of Tris buffer or water.

Downstream applications

DNA purified with the QIAEX II system can be used directly in most applications, including:

• Restriction digestion
• Labeling
• Ligation
• PCR

For a list of references citing uses of the QIAEX II Gel Extraction System, visit the QIAGEN Reference Database online or contact QIAGEN Technical Services or your local distributor.