MEPS 328:17-28 (2006)  -  doi:10.3354/meps328017

ABSTRACT: We compared effects of different sample preparation techniques on the stable carbon and nitrogen isotope values of fish muscle, whole crustaceans and particulate organic matter (POM). Comparisons were also made to untreated (i.e. dried and homogenised) samples. Relatively carbonate-rich samples treated with weak acid (0.1 N HCl), either by quickly wetting or acid dampening, were on average 1.3‰ more enriched in ¹³C than duplicates soaked in 2 N HCl for 5 min, indicating incomplete carbonate removal with the weaker acid. In comparison, no differences in δ¹⁵N values were found between acid treatments, and a following water rinse had no effect on the δ¹³C or δ¹⁵N values. Chloroform-methanol (2:1 by volume) extraction overnight removed less lipids than Soxhlet extraction with 7% methanol in dichloromethane for 2 h, resulting in ~1.2‰ difference in δ¹³C values between treatments of lipid-rich duplicates. Different lipid-extraction methods did not lead to consistent differences in δ¹⁵N values, however. Depending on the lipid and carbonate content, untreated samples were depleted in ¹³C by 0.8 to 4.4‰ and in ¹⁵N by 0.6 to 1.4‰ compared to treated duplicates. We conclude that δ¹³C and δ¹⁵N values of samples with low lipid and carbonate content are highly comparable among studies regardless of pre-treatment methods, whereas the δ¹³C values of relatively lipid- and/or carbonate-rich samples must be carefully considered based on the pre-treatment applied to samples. In comparison, δ¹⁵N values are relatively robust to differences in carbonate and lipid-removal methods, and δ¹⁵N values of untreated vs. carbonate- and lipid-treated samples are comparable within ±1.0‰.

KEY WORDS: Sample pre-treatment · δ¹³C · δ¹⁵N · Lipids · Carbonates · C:N