The Preparation of Carbon and Nitrogen Stable Isotopes Reference Materials Using Sediments from the Bohai and East China Seas

The stable isotope of carbon and nitrogen (δ¹³C and δ¹⁵N) in marine sediments have received much attention as they can be used to trace the sources of organic matter and are helpful in understanding the carbon cycle, climate change and the transformation of organic matter in the ambient environment. However, during stable carbon and nitrogen isotopic analysis and testing, the standard reference materials for quality control are limited. Three reference materials of carbon and nitrogen stable isotope (MSCNI-1, MSCNI-2 and MSCNI-3) have been developed from marine sediments in the Bohai Jinzhou Bay, the coast of Fujian and Zhejiang in the east part of the China sea and the ocean through Okinawa within the East China Sea, respectively. All of these reference materials have certified values of the total carbon and nitrogen isotope (δ¹³C-TC, δ¹⁵N-TN) and organic carbon and nitrogen isotope (δ¹³C-C_org, δ¹⁵N-N_org) which were determined by an inter-laboratory comparison of 8 participating laboratories, using Element Analysis-Isotope Ratio Mass Spectrometry (EA-IRMS). The analytical results indicate that three reference materials were homogeneous (in Table 1) and stable (in Table 2) as the certified values had no statistically variations within a year. The standard uncertainties of δ¹³C and δ¹⁵N were less than 0.15% and 0.24% (in Table 4), respectively. Both of the certified values and uncertainties are within acceptable limits. The reference materials of natural carbon and oxygen isotopes were initially developed based on marine sediments in China. The test method was accurate and reliable, thus it is anticipated that it can be used for instrument calibration, method evaluation and quality control in related laboratories such as marine, geological and environmental fields.