Comparing Methods of Determining Formalin Concentration in Fluid Preservatives

Formalin (3.7% weight/weight [w/w], 4% weight/volume [w/v] aqueous formaldehyde) is commonly used as a fixative to prevent postmortem changes in the tissues of a specimen. The specimen is then either maintained in formalin or transferred to another fluid preservative, such as ethanol or isopropanol, for long-term preservation. Residual formalin often remains in the preservation fluid. As formaldehyde is a known carcinogen, it is important to know the concentration present in preservation fluids. A titration method has been developed to determine formalin concentration in fluid preservatives. It utilizes sodium sulfite to react with formaldehyde in solution. An adjustable, repeating pipette and a digital titrator allow for the rapid determination of formalin concentrations in small samples (<1 ml). This method of titration is compared with three commercially available methods of determining formaldehyde and formalin concentration: two brands of formaldehyde test strips, Quantofix® (Machery-Nagel GmbH) and MQuant® (EMD Millipore Corp), and a drop count titration test kit (Hach® formaldehyde test kit, model FM-1). A comparison and evaluation are made on the effectiveness of each method in determining the concentration of formalin in preservation fluids.