Midi Horizontal Gel Electrophoresis System

What is the Midi Horizontal Gel Electrophoresis System?

A mid-size horizontal tank for gels of roughly 15 x 15 cm that holds 20–40 samples and gives sharper resolution than mini formats. It suits routine genotyping and restriction mapping where more lanes and longer separation distance are needed.

Overview

The midi system sits between mini and large tanks. A gel of about 15 x 15 cm offers roughly 15–20 cm of electrode spacing, so fragments that differ by a few percent in length can be separated more clearly than on a mini gel. Comb options of 20, 30 or 40 teeth, and double-sided combs for two rows of samples, raise throughput without changing the footprint much. Buffer volume is typically 500–900 mL. Because runs last 45–90 minutes at 100–150 V, cooling is rarely an issue, and most models accept standard 300 V power supplies. The midi format is widely used for genotyping by fragment length, restriction fragment mapping and screening of clones where a mini gel is too crowded.

How does it work?

In a horizontal system the agarose gel is cast in a tray, placed in a tank and submerged a few millimetres below running buffer, usually TAE or TBE. When voltage is applied between the platinum or stainless-steel electrodes, negatively charged nucleic acids migrate toward the anode through the pores of the agarose. Shorter fragments move faster, so the bands sort by length, and a size ladder allows estimation of fragment size. The buffer carries current and conducts away Joule heat, which is why voltage per centimetre of electrode spacing is limited, typically to 5–10 V/cm. Bands are visualised with intercalating dyes such as ethidium bromide or safer alternatives under UV or blue light. Key components are the tank, gel tray, combs that form wells, electrode leads and a safety lid.

What are the key features?

• Gel area of about 15 x 15 cm gives longer migration distance for closely sized fragments
• Comb set of 20, 30 and 40 teeth plus double-sided combs raises lane count
• Buffer recirculation ports or level marks help keep conductivity uniform across long runs
• Sealed casting gates allow pouring gels in the tank without tape
• Transparent lid with interlock and shrouded leads improves electrical safety
• Removable electrode assemblies simplify cleaning and replacement

What are the technical specifications?

A typical midi horizontal gel electrophoresis system configuration offers gel size (W x L) of 15 x 15 cm, buffer volume of 500–900 mL, electrode spacing of approx. 20 cm, maximum voltage of 300 V DC, sample capacity per gel of 20–40 samples (up to 80 with double-row combs) and typical run time of 45–90 min at 100–150 V. Values are indicative of the product class; the exact figures for each configuration are confirmed on the quotation and the calibration documents supplied with the instrument.

Which applications is it used for?

The Midi Horizontal Gel Electrophoresis System is used in genotyping by fragment length, restriction fragment mapping, clone screening and medium-throughput PCR analysis. Across the wider Horizontal Electrophoresis class, laboratories also deploy it for PCR product verification, restriction digest analysis and RNA integrity checking.

Which standards and certifications apply?

Relevant standards and methods include IEC 61010-1, IEC 61326-1, ISO 17025 and Ph. Eur. 2.2.31. Certification candidates for this model are CE, ISO 9001 manufacturing and RoHS; each is to be confirmed for the specific configuration before shipment, and certificates are supplied only where they have been issued.

Place the tank on a level, vibration-free bench away from sinks and keep the power supply outside the splash zone. Replace running buffer regularly, because ion depletion and pH drift degrade resolution after repeated runs. Clean tanks with mild detergent and rinse with deionised water; avoid solvents that craze acrylic. Inspect electrodes for corrosion and check that lid interlocks and lead insulation remain intact. Handle ethidium bromide and UV sources under local chemical and optical safety rules, or switch to safer stains. Electrical safety should follow IEC 61010-1. Record voltage, time, gel percentage and buffer batch for traceability, and use ladders appropriate to the fragment range.

How do I select the right Midi Horizontal Gel Electrophoresis System?

Select a midi tank when mini gels are too crowded or fragment sizes are too close for a short run, but you do not need 96-well loading. It uses more buffer and time than a mini. Specify gel dimensions, comb teeth, maximum voltage, buffer volume and whether double-sided combs are required.

How does it compare with other Horizontal Electrophoresis variants?

Choose the gel size first, because it fixes run time, sample number and resolution. Mini tanks give fast checks of a few samples, midi and standard formats balance throughput and resolution, and wide-format tanks accommodate multi-channel pipetting for 96-well workflows. Check the maximum voltage and buffer volume, as a larger tank needs a bigger power supply and more buffer. Consider whether dual trays or removable casting systems help speed. Pulsed-field systems are only needed for fragments above roughly 50 kb, such as genomic DNA typing. Also confirm comb thickness and tooth options, electrode material, lid interlock design and chemical resistance of the polycarbonate or acrylic body, and whether replacement trays and combs are easy to source.