My background is in geology/geochemistry so I have never dealt with preserved organic specimens before. I recently acquired some preserved modern crinoids that I would like to process and analyze for major/trace element concentrations (mainly Ca, Mg, Sr, Mn) and calcium isotopes. I will be analyzing the mineralized skeleton of the crinoids, which are composed of high-Mg calcite, and have an established procedure to eliminate the organic mater from the samples involving a multi-step treatment with HCl and hydrogen peroxide. However, this procedure was established for calcified algal mats that were stored in water in a fridge, and not alcohol/formaldehyde.
These crinoid samples were collected in the early 90s and have been sitting in alcohol/formaldehyde for the past ~30 years. While alive many crinoids are brilliant in colour (reds, oranges, yellows, etc); however the preserved samples I have are dull brown or pale white in colour. Does this mean the preservation solution has leached or broken down some of the organic pigments? If the preservation solution is leaching/breaking down the organic matter, would it also affect the mineralized skeleton? I will be analyzing the crinoid sample on an ICP-OES, so maybe it would be worth it to analyze some of the preservation solution?
Thanks for any help or insight!
Alcohol and formaldehyde preservation solutions are commonly used in the preservation of skeletal carbonates. However, there is a concern that these solutions may leach elements from the skeletal carbonates, which could potentially affect the accuracy of isotopic and elemental analyses.Several studies have investigated the effects of alcohol and formaldehyde preservation solutions on skeletal carbonates. One study found that formaldehyde preservation did not significantly affect the stable isotopic composition of skeletal carbonates, but it did result in a slight decrease in calcium concentration. Another study found that alcohol preservation did not significantly affect the stable isotopic composition or elemental concentrations of skeletal carbonates. However, some studies have reported that both alcohol and formaldehyde preservation solutions can leach elements from skeletal carbonates. For example, one study found that alcohol preservation caused a significant loss of magnesium from coral skeletons. Another study found that formaldehyde preservation caused a significant loss of strontium from bivalve shells. Overall, the effects of alcohol and formaldehyde preservation solutions on skeletal carbonates appear to be dependent on several factors, including the type of carbonate, the concentration and duration of exposure to the preservation solution, and the specific element being analyzed.
Most formaldehyde and alcohol solutions contain enough water to cause possible leaching. Even though carbonates have low solubility in water, e.g., 0.011 g/ 1L (18 °C) for SrCO3, this would still be sufficient to overwhelm an oroginal seawater signal of 8ppm of Sr for all surface areas and porous elements in contact with the solution.
You could try testing a low porosity denser interior portion of the crinoid test not in direct contact with the volume of the solution. You could also try using the ions that remain dissolved in solution to estimate the extent of leaching, but that could wind up being unexpectedly complicated.
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