Comment: Important study. Happy to see you tackle the task.
Now questions: How does one determine the concentration of EtOH in a jar or vial of preserved insects? What concentration should be added to a jar of specimens preserved in 95% EtOH? — absolute EtOH is very expensive. Would it be wise to drain out old liquid and replenish with new?
My primary work using liquid preservation is with neuropteran larvae reared from adults. Specimens are first treated with KAAD and then held in shell vials containing 95% EtOH, stoppered with a cotton plug. Vials are stored, inverted, in a museum jar containing EtOH. The larvae are not large in size, but there usually are several larvae per vial. Specimens in the collection range in age from the 1960s to current. They seem to be holding up reasonably well, but I am curious what to expect in the future.
Any advice from the work that you have done or the observations you have made in collections thus far?
Kay Stewart || NHMU || They/Them/Thiers
This is very interesting! Given that replenishing with the same concentration used initially will never raise the concentration to the same value, what do you recommend? How do we balance concentrations for specimens that need particular conditions to maintain?
Genevieve Anderegg
Thank you so much, I really appreciated it!
These are really great questions that depend on the collection as well as the nature of the jar/vial and the specimens preserved inside, the details of which I am trying to determine for my thesis. Methods of determining EtOH (or other alcohol) concentration include 1) traditional glass hydrometers (not expensive), which are only useful for large amounts of fluid (over 100 mL, usually more) because they need to float in the solution, with the surface of the fluid corresponding to numbers on the side of the hydrometer that indicate the concentration/proof; 2) expensive (>$1000) digital density meters/hydrometers that only require 2 drams of fluid to measure concentration and give readings to the nearest 0.01%, very useful for institutions with extensive fluid holdings, but not easy to use with small specimens like minute insects that must be prevented from accidentally being drawn into the device; and 3) other less common methods, like using floating beads that will sink when the solution reaches a certain concentration (cheap but provides very coarse measurement of concentration), or dipping a rag into the solution and then lighting it on fire (not recommended!), which will indicate if a solution is above or below 100 proof/50% concentration.
When topping off a container, determining the concentration of the solution to add (once you know the current concentration) involves a calculation using the concentration and the current container volume, which can be done easily with the formula at the top of this chart here: https://spnhc.biowikifarm.net/w/index.php?title=File:Topping_Up_Protocol_-_Calculator.pdf&page=2 (Chart is specifically for topping off solutions of 70%, but may be adapted for other target concentrations). If you wish to maintain the fluid remaining in the jar/vial, this chart will tell you what concentration to top off with (this may involve pouring off some of the remaining solution if the concentration is very low, and topping off with 95%). Because your collections are preserved in 95%, always top off with additional 95%. However the concentration might lower over time as the ethanol evaporates out of solution, which would not be helped by adding 95% every time, and might require pouring off most if not all of the solution occasionally. While absolute EtOH is very expensive, I would not recommend using denatured ethanol, as it contains unknown proprietary additives that renders ethanol poisonous to drink, but might have unforeseeable effects on specimens.
You might be able to move your specimens to a lower concentration (anywhere from 70 to 95%) if you wish to keep costs down by mixing ethanol with dionized water, but this would involve “laddering” specimens down various specific concentrations over a period of time in order to keep specimens from being damaged by the the influx of water into their tissues.
Often, for small specimens and/or vials where measuring concentration is difficult or impossible, simply pouring off the initial solution and replacing with entirely new ethanol is the easiest and guarantees the correct concentration (but might be more expensive). Again, storing specimens in 95% will always require adding more 95%.
Sounds like a great collection in the care of a dedicated scientist! I’d love to know what the older specimens look like and how they have held up over time. I myself have noticed that specimens that smell strongly and have gained a dark color in addition to having fluid evaporated may be at a lower concentration than other comparable vials of a lighter color and more pleasant odor. Also, vials/jars with a higher proportion of specimen to fluid volume ratio will lower in concentration over time during the first several years of storage as the water leaches out of specimens and into the solution. I would recommend for specimens of this nature checking the solution concentration more frequently during the first several years as topping off may be needed, or just replacing the entire solution more frequently. I also recommend maintaining a ratio of 50:50 ethanol to specimen volume ratio, and avoiding stuffing containers. This effect may be more noticeable in hard-bodied species like large beetles, but this is something I am currently researching, so stay tuned!
Comment: Important study. Happy to see you tackle the task.
Now questions: How does one determine the concentration of EtOH in a jar or vial of preserved insects? What concentration should be added to a jar of specimens preserved in 95% EtOH? — absolute EtOH is very expensive. Would it be wise to drain out old liquid and replenish with new?
My primary work using liquid preservation is with neuropteran larvae reared from adults. Specimens are first treated with KAAD and then held in shell vials containing 95% EtOH, stoppered with a cotton plug. Vials are stored, inverted, in a museum jar containing EtOH. The larvae are not large in size, but there usually are several larvae per vial. Specimens in the collection range in age from the 1960s to current. They seem to be holding up reasonably well, but I am curious what to expect in the future.
Any advice from the work that you have done or the observations you have made in collections thus far?
This is very interesting! Given that replenishing with the same concentration used initially will never raise the concentration to the same value, what do you recommend? How do we balance concentrations for specimens that need particular conditions to maintain?
Thank you so much, I really appreciated it!
These are really great questions that depend on the collection as well as the nature of the jar/vial and the specimens preserved inside, the details of which I am trying to determine for my thesis. Methods of determining EtOH (or other alcohol) concentration include 1) traditional glass hydrometers (not expensive), which are only useful for large amounts of fluid (over 100 mL, usually more) because they need to float in the solution, with the surface of the fluid corresponding to numbers on the side of the hydrometer that indicate the concentration/proof; 2) expensive (>$1000) digital density meters/hydrometers that only require 2 drams of fluid to measure concentration and give readings to the nearest 0.01%, very useful for institutions with extensive fluid holdings, but not easy to use with small specimens like minute insects that must be prevented from accidentally being drawn into the device; and 3) other less common methods, like using floating beads that will sink when the solution reaches a certain concentration (cheap but provides very coarse measurement of concentration), or dipping a rag into the solution and then lighting it on fire (not recommended!), which will indicate if a solution is above or below 100 proof/50% concentration.
When topping off a container, determining the concentration of the solution to add (once you know the current concentration) involves a calculation using the concentration and the current container volume, which can be done easily with the formula at the top of this chart here: https://spnhc.biowikifarm.net/w/index.php?title=File:Topping_Up_Protocol_-_Calculator.pdf&page=2 (Chart is specifically for topping off solutions of 70%, but may be adapted for other target concentrations). If you wish to maintain the fluid remaining in the jar/vial, this chart will tell you what concentration to top off with (this may involve pouring off some of the remaining solution if the concentration is very low, and topping off with 95%). Because your collections are preserved in 95%, always top off with additional 95%. However the concentration might lower over time as the ethanol evaporates out of solution, which would not be helped by adding 95% every time, and might require pouring off most if not all of the solution occasionally. While absolute EtOH is very expensive, I would not recommend using denatured ethanol, as it contains unknown proprietary additives that renders ethanol poisonous to drink, but might have unforeseeable effects on specimens.
You might be able to move your specimens to a lower concentration (anywhere from 70 to 95%) if you wish to keep costs down by mixing ethanol with dionized water, but this would involve “laddering” specimens down various specific concentrations over a period of time in order to keep specimens from being damaged by the the influx of water into their tissues.
Often, for small specimens and/or vials where measuring concentration is difficult or impossible, simply pouring off the initial solution and replacing with entirely new ethanol is the easiest and guarantees the correct concentration (but might be more expensive). Again, storing specimens in 95% will always require adding more 95%.
Sounds like a great collection in the care of a dedicated scientist! I’d love to know what the older specimens look like and how they have held up over time. I myself have noticed that specimens that smell strongly and have gained a dark color in addition to having fluid evaporated may be at a lower concentration than other comparable vials of a lighter color and more pleasant odor. Also, vials/jars with a higher proportion of specimen to fluid volume ratio will lower in concentration over time during the first several years of storage as the water leaches out of specimens and into the solution. I would recommend for specimens of this nature checking the solution concentration more frequently during the first several years as topping off may be needed, or just replacing the entire solution more frequently. I also recommend maintaining a ratio of 50:50 ethanol to specimen volume ratio, and avoiding stuffing containers. This effect may be more noticeable in hard-bodied species like large beetles, but this is something I am currently researching, so stay tuned!
Thanks so much for your interest! Feel free to email me at genevieve.anderegg@colorado.edu !