I would advise against it though it might be interesting to find out what if anything happens to the stable isotope signatures, in particular 13C by comparing aliquots of a samples where the A sample was kept frozen and the B sample was kept in 70% EtOH.

The reason why I would advise caution has to do with the fact that polar solvents (especially in the presence of water) have the potential to react with one's sample. Even if that does not happen, getting samples that were soaked in EtOH/H2O absolutely dry will require exhaustive drying under oil pump vacuum. See our paper on “Influence of precursor solvent extraction on stable isotopic signatures of methamphetamine prepared from pseudo-ephedrine extracted from over the counter medicines using the Moscow and Hypophosporous routes”; Anal. Bioanal. Chem., 405 (9), 2931-2941; DOI: 10.1007/s00216-012-6600-8.

My advice would be never to add anything to one's samples that has the potential to result in compromise the actual or original stable isotopic composition of one's samples. I would suggest you freeze-dry your samples and store them in glass vials (or Eppendorf caps) in a -20C freezer.

Alessandro

I have contributed to a similar thread in the past that covers the key issues in this discussion. The fact you are interested in muscle and the discussion was on inverts is largely irrelevant. The link is below but In short be careful as EtOH prservation will unperdicatbly partially extract lipids shifting d13C and many preservations also impact d15N

https://www.researchgate.net/post/Can_we_store_benthic_invertebrates_in_ethanol_for_stable_isotope_analysis

Also the below reference may be of interest and is specifically on fish muscle and EtOH

Tissue and fixative dependent shifts of delta C-13 and delta N-15 in preserved ecological material, C. J. Sweeting, N. V. C. Polunin, S. Jennings, Rapid Communications in Mass Spectrometry 01/2004; 18(21):2587-2592. · 2.79 Impact Factor

Hello Alessandro,

I understand that ethanol can be a convenient preservative, especially in the field. In my experience with sea turtle tissues, ethanol is generally safe to use. Check out the following publication, as it demonstrates there is no significant effect of ethanol preservation on stable isotope values of turtle tissue samples. That doesn't necessarily mean the same holds for fish tissue and insects, and I see the other replies are quite cautionary. In the appendix of this paper, there is also has a nice summary of other preservation studies if you can find species/tissues similar to what you will be using or if you want to consider other methods.

Effects of Preservation Method on Stable Carbon and Nitrogen Isotope Values

Lindy M. Barrow, Karen A. Bjorndal, and Kimberly J. Reich

Physiological and Biochemical Zoology

Vol. 81, No. 5 (September/October 2008) (pp. 688-693)

Of course, the best thing to do would be to do a trial study to compare ethanol-preserved vs. frozen tissue as suggested above.

One of our papers deals with this question.

The Effects of Ethanol Preservation on Fish Fin Stable Isotopes: Does Variation in C:N Ratio and Body Size Matter?

Carmella Vizza; Beth L. Sanderson; Douglas G. Burrows; Holly J. Coe

Transactions of the American Fisheries Society

Vol. 142, No. 5, (2013), p. 1469-1476

There are plenty of references showing presence or abscence of effects in EtOH or other preservatives, however, there are very few that actually offer a mechanistic explanations for positive or negative effects, particularly for 15N...