Formaldehyde Solution for molecular biology

Product No. 47608

CAS RN 50-00-0
Synonyms: Formalin

Product Description

This product is a solution of approximately 37% by weight of formaldehyde gas in water. The product contains 10% methanol as a stabilizer to prevent polymerization. But it can anyway contain precipitate from paraformaldehyde. Solutions may become cloudy on standing (especially in the cold), and upon exposure to very low temperatures, a precipitate of trioxymethylene may form. In the air, this product slowly oxidizes to formic acid. When evaporated, some formaldehyde escapes, but most of it is changed to trioxymethylene.1

It is designated as a molecular biology reagent, tested for electrophoresis of RNA in agarose gels. Is free of DNase, RNase, Proteases and Phosphatases.5

When used as a bactericidal agent, the relative humidity of the environment is critical for optimal activity of this product.2

Precautions and Disclaimer

This product is for R&D use only, not for drug, household, or other uses. Please consult the Safety Data Sheet for information regarding hazards and safe handling practices. 

Preparation Instructions

To raise the pH of the formaldehyde solution above pH 4, treat it with a small amount of mixed bed resin (Product No. M8032). Do not simply try to raise the pH with base such as NaOH. The pH of the formaldehyde solution is raised to above pH 4, since there is no breakdown of RNA above pH 4 compared to a solution at or below 4.

There are several recipes for fixatives. In general a 10-fold dilution is made for fixation of cells.3

Product Profile

Molecular Formula: CH2O
Molecular Weight: 30.03 g/mol
pH: 2.8 - 4.01
Molarity: >13 M
bp: 96 ºC1
Specific Gravity: 1.081-1.085 at 25 ºC1
Refractive Index: 1.3746 at 20 ºC1


This product is soluble in water. Dilute solutions are stable at 2 °C for 1 week.4




  1. The Merck Index, 12th ed., Entry# 4262.
  2. Disinfection, Sterilizationand Preservation, 4th ed., Block, S.S., ed., Lea & Febiger (Philadelphia, PA: 1991), pp. 582-583.
  3. Staining Procedures, 4th ed., Clark, G., ed., Williams and Wilkins (Baltimore, MD: 1981), pp. 13-14.
  4. Dawson, R.M.C., et al., Data for Biochemical Research, 3rd ed., p. 39., Oxford University Press, New York, (1986).
  5. Fluka quality control


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