In:
Rapid Communications in Mass Spectrometry, Wiley, Vol. 33, No. 10 ( 2019-05-30), p. 935-945
Abstract:
It is imperative to understand how chemical preservation alters tissue isotopic compositions before using historical samples in ecological studies. Specifically, although compound‐specific isotope analysis of amino acids (CSIA‐AA) is becoming a widely used tool, there is little information on how preservation techniques affect amino acid δ 15 N values. Methods We evaluated the effects of chemical preservatives on bulk tissue δ 13 C and δ 15 N and amino acid δ 15 N values, measured by gas chromatography/isotope ratio mass spectrometry (GC/IRMS), of (a) tuna ( Thunnus albacares ) and squid ( Dosidicus gigas ) muscle tissues that were fixed in formaldehyde and stored in ethanol for 2 years and (b) two copepod species, Calanus pacificus and Eucalanus californicus , which were preserved in formaldehyde for 24–25 years. Results Tissues in formaldehyde‐ethanol had higher bulk δ 15 N values (+1.4, D. gigas ; +1.6‰, T. albacares ), higher δ 13 C values for D. gigas (+0.5‰), and lower δ 13 C values for T. albacares (−0.8‰) than frozen samples. The bulk δ 15 N values from copepods were not different those from frozen samples, although the δ 13 C values from both species were lower (−1.0‰ for E. californicus and −2.2‰ for C. pacificus ) than those from frozen samples. The mean amino acid δ 15 N values from chemically preserved tissues were largely within 1‰ of those of frozen tissues, but the phenylalanine δ 15 N values were altered to a larger extent (range: 0.5–4.5‰). Conclusions The effects of preservation on bulk δ 13 C values were variable, where the direction and magnitude of change varied among taxa. The changes in bulk δ 15 N values associated with chemical preservation were mostly minimal, suggesting that storage in formaldehyde or ethanol will not affect the interpretation of δ 15 N values used in ecological studies. The preservation effects on amino acid δ 15 N values were also mostly minimal, mirroring bulk δ 15 N trends, which is promising for future CSIA‐AA studies of archived specimens. However, there were substantial differences in phenylalanine and valine δ 15 N values, which we speculate resulted from interference in the chromatographic resolution of unknown compounds rather than alteration of tissue isotopic composition due to chemical preservation.
Type of Medium:
Online Resource
ISSN:
0951-4198
,
1097-0231
Language:
English
Publisher:
Wiley
Publication Date:
2019
detail.hit.zdb_id:
2002158-6
detail.hit.zdb_id:
58731-X
SSG:
11
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