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TEMED is N,N,N’,N’-tetramethylethylenediamine, the catalyst used with ammonium persulfate (APS) to start the chemical polymerization of acrylamide and bis-acrylamide into polyacrylamide gels. Bio-Rad describes it as a catalyst for polyacrylamide gels. Its age, storage and handling affect whether a gel sets, so it is worth treating as a tracked consumable.
Short answer
TEMED is the catalyst half of the APS/TEMED pair. Bio-Rad’s acrylamide manual states that chemical polymerization is initiated by ammonium persulfate and TEMED. When a gel does not set, the usual suspects are the age of these two reagents, dissolved oxygen, cold solutions and contaminants, each covered below with the manufacturer’s own statements.
Definition and scope
TEMED (also written TMEDA) is the common laboratory abbreviation for tetramethylethylenediamine. Bio-Rad sells it as catalog number 1610800 (5 ml) and 1610801 (50 ml) and describes it as a catalyst for the polymerization of acrylamide and bis-acrylamide. Its main laboratory role is in casting polyacrylamide gels used in electrophoresis; for the technique itself see what gel electrophoresis is and the SDS-PAGE guide. This page covers the reagent, not a casting protocol, and gives no volumes or concentrations.
How TEMED and APS start polymerization in practice
Bio-Rad’s manual for acrylamide solutions and powders states that chemical polymerization is initiated by ammonium persulfate and TEMED. The two are named together as the initiating pair, which is why a failed gel is diagnosed by checking both.
The same manual identifies what slows the reaction down. Oxygen is an inhibitor of free radical polymerization, so degassing the gel solution immediately before pouring is described as critical for reproducibility. Cold solutions have a greater capacity for dissolved oxygen, so Bio-Rad advises bringing the gel solution to room temperature first, and notes that a cold pour has a substantial negative effect on the rate of polymerization. Contaminants in buffer reagents, gel additives and laboratory water can also inhibit polymerization; see the buffer and solution preparation guide for the preparation side.
Storage and shelf life: TEMED compared with APS
The Bio-Rad manual gives storage statements for both reagents. Set side by side, they show why the two age differently.
| Reagent | Form | Storage statement in the Bio-Rad manual |
|---|---|---|
| TEMED | Liquid reagent | Can be stored tightly closed and desiccated at 4 °C or room temperature for at least 6 months. After 10 to 12 months there is a significant reduction in activity. If refrigerated, warm to room temperature before opening. |
| APS (solid) | Powder | Can be stored desiccated at room temperature for at least 1 year. |
| APS (solution) | Dissolved | Make fresh daily, because persulfate in solution decomposes rapidly. |
Why gels fail to set: a sourced checklist
Each item below comes from the Bio-Rad acrylamide manual. Use it alongside the troubleshooting row in the SDS-PAGE guide.
- TEMED age: activity drops significantly after 10 to 12 months; the stated storage window is at least 6 months when tightly closed and desiccated.
- APS solution age: APS in solution decomposes rapidly, so a solution made on an earlier day is a suspect.
- Dissolved oxygen: oxygen inhibits free radical polymerization; degassing right before pouring is called critical.
- Cold solution: cold solutions carry more dissolved oxygen and polymerize more slowly, so the manual says to bring the gel solution to room temperature first.
- Contamination: buffer reagents, gel additives and laboratory water can carry inhibitors.
- Refrigerated TEMED: the manual says it should be warmed to room temperature before opening.
Where it matters for labs and supply decisions
Because the manufacturer gives TEMED a stated activity window, recording the date a bottle is received and opened lets staff judge it against that window, as with other reagents (see reagent lot-to-lot verification). Bio-Rad lists TEMED in 5 ml and 50 ml sizes and flags it as hazardous material on its product page. Hazard classification, storage conditions and handling details belong to the supplier’s safety data sheet for the specific product you hold, so follow that document; how to read a safety data sheet explains its sections.
Common misunderstandings
- “TEMED alone makes the gel set.” Bio-Rad states that polymerization is initiated by APS and TEMED together.
- “If TEMED is fine, an old APS solution is fine too.” The manual says APS solutions should be made fresh daily; the solid keeps far longer.
- “A cold pour only slows things slightly.” Bio-Rad describes a substantial negative effect on the polymerization rate.
- “An old bottle works the same as a new one.” The manual reports a significant loss of TEMED activity after 10 to 12 months.
FAQ
What does TEMED stand for?
N,N,N’,N’-tetramethylethylenediamine, sometimes abbreviated TMEDA.
What does TEMED do in a polyacrylamide gel?
It acts as the catalyst for the polymerization of acrylamide and bis-acrylamide, working with ammonium persulfate as the initiating pair.
How long does TEMED last?
Bio-Rad states at least 6 months when stored tightly closed and desiccated at 4 °C or room temperature, with a significant activity reduction after 10 to 12 months.
Why is my gel not polymerizing?
Check reagent age, APS solution freshness, dissolved oxygen, solution temperature and contaminants, as listed in the checklist above.
Sources
- Bio-Rad Laboratories, TEMED product page, catalog 1610800, bio-rad.com, checked 2026-10-29.
- Bio-Rad Laboratories, Acrylamide Solutions and Powders user manual (copy hosted by manualsdir.com), manualsdir.com, checked 2026-10-29.
