Checking Ethanol for Fluid-preserved Specimens

The majority of MVZ fluid-preserved specimens are stored in 70% ethanol. Because of evaporation, it is important to periodically check the level and concentration of ethanol in jars. In addition, older smooth black Bakelite lids need to be replaced with white polypropylene lids that provide a better seal. These tasks ensure that the fluid-preserved specimens are kept in good condition, and are typically performed by students enrolled in the Undergraduate Research Apprentice Program.

The Setup

The following tools and materials are required for checking ethanol concentrations: a hydrometer, graduated cylinder, large pipette, forceps, China red wax markers for labeling, replacement lids, 70% ethanol, 95% ethanol, and a waste ethanol container. All supplies are available in the MVZ Herp Lab.

Fill two one-gallon jars with 70% and 95% ethanol, respectively. Label an additional empty jar with “working ethanol”, which will serve as the container for waste ethanol when working with jars with concentrations above 70%. Working ethanol is collected in jugs in the Herp lab and is
later recycled.

Basic setup for checking ethanol concentrations.

Identifying Jars to Check

Jars that are low on ethanol (fluid level is not to the top of the jar) should be checked for the appropriate concentration and refilled as needed.

Jars with a black lid also need the ethanol level checked and lid replaced, because those lids become ineffective in sealing the jar over time. Remove the plastic liner of the old lid before tossing the lid, and put a liner in a new white lid to help cut down on evaporation.

Jar with low ethanol level and a smooth black lid.

Checking the Ethanol Concentration

Using the large pipette, transfer 100 mL of ethanol from the jar to the graduated cylinder. Place the hydrometer in the graduated cylinder and note the concentration; it should be at 70%. If it is below 70%, then add 95% ethanol to bring the concentration back up to 70%. Keep in mind that it doesn’t take much to raise the concentration. If the concentration is above 70%, replace the ethanol with new ethanol from the 70% jar. When you are finished, use the red wax marker to write the date on the lid and be sure to put the jar back where you found it on the shelf (label facing forward). 

Ethanol concentration below 70%.
Ethanol concentration at 70%.