Effects of distilled water rinsing on stable isotope ratios of acid-treated marine invertebrate (Paguridae) samples.
BACKGROUND
Stable isotope ratios are widely used to infer trophic relationships, although a growing number of studies show that sample pre-treatments (such as acidification to remove carbonates) can cause changes in isotope ratios. Samples are often rinsed in distilled water after acidification, and we examine the effects of this step in particular on the isotope ratios of marine invertebrate samples.


METHODS
Samples of whole hermit crabs (Paguridae) were subjected to one of three treatments: acidification using dilute hydrochloric acid without subsequent distilled water rinsing; acidification with rinsing; and rinsing with no acidification. Continuous-flow isotope ratio mass spectrometry was used to compare the mean carbon and nitrogen stable isotope ratios of treated and untreated material.


RESULTS
Acidification (both with and without subsequent distilled water rinsing) resulted in reductions in mean δ(13)C values (1.939 and 3.146‰, respectively), while rinsing without prior acidification led to a smaller (but still significant) increase. Nitrogen isotope ratios were not affected by acidification, but subsequent rinsing with distilled water caused a decrease of approximately 1‰.


CONCLUSIONS
Acidification of samples is clearly necessary in the presence of carbonates to obtain useful carbon isotope ratio data. However, post-acidification rinsing can result in further (potentially undesirable) changes to both carbon and nitrogen isotope ratios. Ideally, rinsing should be avoided, but the impacts are small enough to be of little concern in many studies. Rinsing (or not) should be considered carefully on the basis of the aims of a study.
National Oceanography Centre Southampton, European Way, Southampton, SO14 3ZH, UK. andrew.guerin@uhi.ac.uk
Andrew J
AJ
Guerin
Antony C
AC
Jensen
Rona A R
RA
McGill
D000143:Acids / Q000494:pharmacology; D053000:Analytic Sample Preparation Methods / Q000379:methods*; D000818:Animals; D033381:Anomura / Q000737:chemistry* / Q000187:drug effects; D002247:Carbon Isotopes / Q000032:analysis*; D013058:Mass Spectrometry; D009587:Nitrogen Isotopes / Q000032:analysis*
D000143:Acids; D002247:Carbon Isotopes; D009587:Nitrogen Isotopes