[MARMAM] New publication: Evaluation of two lipid removal methods for stable carbon and nitrogen isotope analysis in whale tissue

Kerri J. Smith smithkerrij at gmail.com
Thu Jun 4 10:31:18 PDT 2020

Dear all,

We are pleased to share our recent publication on lipid extraction methods
for stable isotope analysis of beaked whale tissue.

Smith, KJ, Trueman, CN, France, CAM, Peterson, MJ. Evaluation of two lipid
removal methods for stable carbon and nitrogen isotope analysis in whale
tissue. *Rapid Commun Mass Spectrom*. 2020.

The presence of lipids in animal tissues can influence the interpretation
of stable isotope data, particularly in lipid‐rich tissues such as the skin
and muscle of marine mammals. The traditionally employed
chloroform:methanol delipidation protocol has the potential to alter δ15N
values in proteinaceous tissues. Our objective was to determine whether
cyclohexane is an alternative extraction method, effectively removing
lipids without altering δ15N values. Kidney, liver, muscle, and skin
samples were collected from beach‐cast Sowerby's beaked whales (*Mesoplodon
bidens *). Control subsamples were processed without delipidation
extraction, and duplicate subsamples were extracted with either
chloroform:methanol or cyclohexane. δ13C, δ15N, and C:N values were
determined by continuous‐flow elemental analysis isotope ratio mass
spectrometry. Paired Wilcoxon tests were used to evaluate the change in
isotope ratios after extraction, and unpaired Wilcoxon tests were used to
evaluate difference in isotope ratios between extractions. Cyclohexane is
an effective delipidation technique for tissues with low and moderate lipid
content. Chemical delipidation influenced δ15N values; extracted samples
generally showed an increase in δ15N values which varied from 0.0‰ to 1.7‰.
Chloroform:methanol extraction resulted in alterations to δ15N values
greater than the analytical precision for all analyzed tissues. Changes to δ
15N values after cyclohexane extraction were at or near the analytical
precision in liver and muscle but greater than the analytical precision for
kidney and skin. We recommend processing duplicate subsamples for stable
isotope analysis, one with and one without extraction in order to obtain
accurate values for each isotope ratio. Prolonged chemical extractions are
not necessary to effectively remove lipids. When samples are limited, we
suggest using cyclohexane for tissues with low or moderate lipid content,
and chloroform:methanol for lipid‐rich tissues.


*--Kerri J. Smith, Ph.D.*
Postdoctoral Researcher- Laboratory of Ecological and Adaptational
Research Fellow - Smithsonian Institution
Website <https://kerrijsmith.wordpress.com/>

“The love for all living creatures is the most noble attribute of man.”
-Charles Darwin
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