Table 3

Notes on fixatives

Fixative

Notes

neutral-buffered formalin (10% NBF)

Formalin = 37% formaldehyde solution (aq.).

Normally used at 10% dilution in phosphate buffer at pH 7.0

Commercial formalin usually contains about 10% methanol.

The most common, but rarely the best fixative. [23,24]

paraformaldehyde

Polymerized formaldehyde, usually dissolved in buffer (e.g. PBS) at 4% w/v when a chemically-controlled fixative is required.

Action is generally similar to 10% NBF. [23,24]

gluteraldehyde

Strong cross-linking fixative, often prepared in cacodylate buffer or a less toxic alternative such as HEPES. Common fixative for electron microscopy. [23,24]

4F1G

4% (or 3.7%) formaldehyde + 1% gluteraldehyde in phosphate buffer.

Takes advantage of the faster penetration of formaldehyde and the superior fixing action of gluteraldehyde. Common fixation for electron microscopy. [25]

Bouin's fluid

75 parts (v/v) saturated aqueous picric acid,

25 parts formalin (37% formaldehyde),

5 parts glacial acetic acid.

A standard and excellent histological fixative. [24]

alcoholic Bouin's

Refers to either a mixture of Bouin's fluid and ethanol (1:1), or to the fixative also known as Bouin-Duboscq-Brasil [24]. The two are similar in final composition.

The alcoholic solutions penetrate more readily and are sometimes favored for arthropods.

glyoxal

A cross-linking dialdehyde (OCHCHO) prepared in acidic buffers and marketed as formalin substitutes: Prefer (Anatech Ltd.; http://www.anatechltdusa.com webcite) and Shandon Glyo-Fixx (Thermo Scientific; http://www.thermo.com webcite).

Much less volatile and toxic than formaldehyde.

Very good tissue preservation; especially good for immunostaining.

Dent's fixative

80% methanol, 20% DMSO

Rapid dehydrating fixative. Expect some tissue shrinkage. Often used for immunostaining.

hot alcohol

Samples are dropped into 70% ethanol at about 60°C.

Mainly used for fixing soft-bodied animals, such as insect larvae and pupae.

In general, the best fixative for microCT scanning will be the best histological fixative for the particular tissues under investigation.

Metscher BMC Physiology 2009 9:11   doi:10.1186/1472-6793-9-11