Diluents & Preservatives < Extractopedia

Diluents & Preservatives

When making dilutions from the concentrate vial, a number of diluents can be used.

Normal Saline with Phenol (NSP)

NSP is the same solution that is used to extract Aqueous extracts. It is a buffered solution of sodium chloride (0.9%) with phenol (0.4%) as a preservative. NSP offers limited stability protection for dilute allergens.

Human Serum Albumin (HSA)

HSA is a high protein solution that has been shown to provide added stability to dilute extract vials. High protein concentration is thought to protect allergen stability by preventing dilute allergens from sticking to the vial’s wall.


While 50% Glycerin has been shown to be the ideal solution for protecting allergen stability, it is known to cause injection pain at concentrations above 25%.


10% Glycerin is available from certain manufacturers as an alternative to HSA for protecting dilute vials.

Preservative - Phenol

Phenol is a bacteriostatic agent that is required by the FDA for use in aqueous extracts to inhibit microbial growth and maintain sterility.


While 50% Glycerin has also demonstrated bacteriostatic properties, once it is diluted below 50% it no longer offers sterility protection. Phenol must be added to dilute glycerin vials.