Compound-specific isotope analysis (CSIA) of organic compounds with a gas chromatograph - isotope ratio mass spectrometer (GC-IRMS) has been employed as one of the most powerful techniques in molecular isotope studies. This analysis is applicable not only for volatile and non-polar compounds (e.g., hydrocarbons), but also for non-volatile and polar compounds (e.g., alcohols and fatty acids) when such low volatility and high-polarity are reduced by derivatization. However, derivatization frequently causes isotopic fractionation, which considerably reduces the accuracy on the isotope ratios determined. In the present study, we investigated change in the carbon isotope ratio (δ¹³C value) of 1-hexadecanol that acetylated with a variable molar balance between substrate and derivative reagent, to illustrate the fractionation of carbon isotopes during acetylation of alcohols. The results illustrate that the δ¹³C values of acetyl group of the 1-hexadecanol derivative asymptotically change from −38.8‰ to −60.8‰, with the molar balance decreasing from 1:10 to 1:30000 in the acetylation. Moreover, the isotopic fractionation factor (α) calculated is 0.9711 if the Rayleigh fractionation model is applied. Thus, we demonstrated that there is a large fractionation of carbon isotopes in the acetylation of alcohols, and that the degree of fractionation is correlated with the molar balance between substrate and derivative reagent of the acetylation.

Difference in the stable nitrogen isotope ratio (δ¹⁵N value) between two types of amino acids within a single organism has been employed as a powerful tool for estimating the trophic position (TP) of the organism in food webs. However, accuracy of the TP values estimated relies on the consistency of trophic elevation in the δ¹⁵N value across diverse organisms and among diverse environments. Indeed, little is known the applicability of this tool for organisms found in cold environments. In the present study, we determined the δ¹⁵N values of amino acids for 10 species collected in a coastal marine environment of Hokkaido, a humid continental climate zone in Japan, to evaluate whether this tool is applicable to marine species found in cold regions. The δ¹⁵N values of glutamic acid and phenylalanine determined in the present study illustrate diverse TP values for the species, as 0.7-1.0 for primary producers (i.e., macroalgae), 1.9-2.3 for herbivores (e.g., zooplankton and sea urchin), and 2.3-3.7 for omnivores and carnivores (e.g., crab and fish). These results indicate that the TP values estimated in the present study are basically consistent with actual TP for producers and herbivores and with the literature TP values for the same or similar species of omnivores and carnivores from temperate regions, and thus provide evidence that this tool is basically applicable to estimate the TP of marine species found in cold regions. On the other hand, low TP value was estimated for one species, goby, suggesting that further studies will be required, particularly for identifying mechanisms responsible for the low TP values estimated for such species.

Trophic position (TP) estimates of organisms using compound-specific isotope analysis (CSIA) of nitrogen within amino acids allow us to trace the trophic transfer of organic materials in food webs and its dynamics in biogeochemical cycles. However, accuracy of the estimates is potentially affected by natural variation in the body size within a species, because the isotope ratios of amino acids primarily correlate with metabolic activities in organisms. In the present study, we therefore determined the δ¹⁵N values of amino acids for two species of juvenile fish (the cresthead flounder Pleuronectes schrenki and the sunrise sculpin Pseudoblennius cottoides) that have a variation in the body size in a natural coastal marine environment, to evaluate the effects of body size on the TP values estimated for these juvenile fish. Because the juvenile fish investigated were a couple of months old and grew together in a natural coastal marine environment for each species, variation in the body size within species can be explained primarily by diet amounts and/or metabolic activities at the individuals. However, the results illustrate that variation in the TP value estimated is negligible (i.e., ±0.08 for cresthead flounder and ±0.05 for sunrise sculpin) even though there is a large variation in the body length within species (28-54 mm and 19-34 mm, respectively), and clearly indicate that the effects of body size are negligible to the δ¹⁵N values of amino acids and associated TP estimates at least for juvenile fish of two species investigated. These results will be useful for reducing the sample size of CSIA and for expanding application in further trophic food web studies, as well as for better understanding the factors controlling for natural variation in the body size within a species.

Non-methane hydrocarbons (NMHC) in the atmosphere are raw materials for photochemical oxidants, and many measurements of the NMHC gases have been performed. The treatment for concentration of the NMHC is required for its measurement. The author has concentrated the NMHC by passing air through a concentration tube containing quartz sand cooled with liquid nitrogen. In this treatment, it was confirmed that the recovery rate of pure air-based NMHC was likely to decrease even if nitrogen-based NMHC could be concentrated with a sufficient (close to 100%) recovery rate depending on experimental conditions for the concentration. Non-methane hydrocarbons (NMHC) in the atmosphere are raw materials for photochemical oxidants, and many measurements of the NMHC gases have been performed. The treatment for concentration of the NMHC is required for its measurement. The author has concentrated the NMHC by passing air through a concentration tube containing quartz sand cooled with liquid nitrogen. In this treatment, it was confirmed that the recovery rate of pure air-based NMHC was likely to decrease even if nitrogen-based NMHC could be concentrated with a sufficient (close to 100%) recovery rate depending on experimental conditions for the concentration.