General FAQs

No. Microwaves heat polar material like water and alcohol, and don’t heat non-polar material like paraffin and fats. This is why we strongly encourage users to incorporate Polar Heat™ Sheets into their paraffin processing steps. Some fats are actually emulsions or other associations with polar components, so they can heat. Materials like Pyrex can be slightly polar and can absorb microwave energy, and metal can cause “arcing” (sparking).

“Microwave transparent” isn’t synonymous with “optically transparent.” It means the material allows the passage of microwaves without converting a significant portion to heat. Many materials that we wouldn’t think of as “transparent,” like opaque white Teflon are, in fact, “microwave transparent.”

Yes, usually. Larger amounts of metal are to be avoided. With staples, do ensure that multiple staples aren’t right next to each other, and that no staple is close to a metal temperature probe, or arcing can occur. Occasionally staples can overheat, however. Make very sure they stay immersed in solution to minimize this effect.

No. Microwave radiation is not ionizing radiation like X-Rays. Microwave energy is more akin to radio waves, is not mutagenic, and effects are not cumulative. And equipment standards have been developed to assure safety, assuming that your microwave has been properly maintained and regularly inspected, and is not damaged.

It produces hazardous vapors at room temperature, and gets worse when heated. Eliminating xylene should be a goal; it’s now an officially recognized hazard to pregnant women and unborn babies. Also, it’s as non-polar as paraffin, and wouldn’t heat efficiently.

Not with the majority of tissue types, and not usually for the relatively short timeframes involved. Also, the tissue has already been fixed, dehydrated, and defatted; while you certainly don’t want to burn or cook the tissue, 82°C isn’t extreme in this context.

Vacuum can be used for any paraffin step Vacuum can be especially beneficial when processing thick (>4mm), fatty, or thick and fatty samples. It’s used to help lower the boiling point of isopropyl alcohol remaining from the previous step, and assist its replacement by paraffin.

Ideally, the laboratory microwave should have its own dedicated circuit, with nothing else plugged in. High energy demand instruments should not share the same circuit as the microwave. This can cause a severe drop in magnetron output of the microwave, producing inconsistent results.

Almost always. Agitation promotes even heating of reagent, preventing uneven distribution of solutes, suspensions, etc. A good example is the pink meniscus ring that forms in microwave PAS staining procedures, when agitation is omitted. This layer rises to the top due to vaporization of SO2, and agitation helps prevent this. Rarely, you may find a protocol that warns against the “damaging effects of bubbling,” for example, but we have seen no evidence supportive of this claim and much evidence to the contrary. Of course, when applying vacuum to your samples during the paraffin infiltration step, air agitation should not be used.

You can check out a quick LabPulse® microwave comparison here.

Doing so is not advisable. If you insist on using zinc formalin, make sure that the temperature probe is kept clean of zinc build-up or arcing may result.

No. LabPulse Microwave Processors come complete with microwave stirrers built so the microwave cavity is evenly heated. This coupled with the very short power cycles (1-2 seconds), and air agitation ensures even heating of your samples.

Maintenance for the laboratory microwaves requires very little effort. Routine cleaning of the internal cavity, door seal, air intakes, and hinges is recommended. Inspect and clean the temperature probe (if equipped) as well. You may also decide to inspect the unit with a microwave leakage detector to ensure your unit is working at peak performance.