Natural History Wet Collections: Observations on PH Readings from the Use of Different Ethanol and Label Types

We examined the effects of different types of specimen labels and tags on pH of different concentrations of ethanol typically used for fluid preservation in natural history collections. Labels were immersed in three different concentrations of ethanol, 96% pure undenatured ethanol (EtOH), 96% EtOH denatured with methyl-ethyl ketone (MEK), and 99.8% pure undenatured EtOH, with or without the presence of insect specimens, and the solutions were evaluated after 26 months for changes over time in pH reading. In general, pH readings of all label trials with 96% and 99.8% ethanol increased over time, except for trials of denatured alcohol, which demonstrated lower pH readings in almost all treatments, regardless of label type. Samples that contained labels with ordinary, nonstandardized, not explicitly acid-free printing paper had higher pH readings compared after the trial. Our observations are a good starting point for further experiments to answer research questions related to chemical interactions with labels in ethanol-preserved specimens, including tissue samples for molecular analyses, which can guide collection staff in their daily work.