Samples transported over the colder months risk being frozen if they are not packed and shipped properly. Even 10% buffered neutral formalin will freeze in harsh winter weather. To help mitigate freezing of fixed samples, you can mix alcohol with the buffered neutral formalin at a ratio of 10 parts formalin to 1 part alcohol. Everclear or other high proof, clear, alcohol is best. (Do not use wood alcohol as it will cause the tissues to become brittle and they will lose antigenicity.)
Buffered Neutral Formalin recipe
- Commercial Formaldehyde (37-40%) - 100 ml
- Distilled water - 900 ml
- Sodium phosphate monobasic - 4.0 g
- Sodium phosphate dibasic (anhydrous) - 6.5 g
To prevent fresh samples from freezing, even in insulated containers, add room temperature (unchilled) cold packs to increase the ambient temperature mass in the box. This will reduce the temperature decline during transit, however is not a guarantee against freezing if extended cold exposure occurs.
For critical samples that cannot be exposed to extreme cold, consider delaying the shipment or find alternative means to deliver the specimens to the laboratory.