Preparation of Reference Materials for Carbon and Nitrogen Isotopes of Organic Materials

OBJECTIVESThe carbon and nitrogen isotope reference materials used by laboratories and researchers are generally obtained by the International Atomic Energy Agency (IAEA). However, in recent years, with the widespread use of carbon and nitrogen isotopes in laboratory quality control, method evaluation, and instrument calibration, the market demand continues to increase, and the types and quantities of carbon and nitrogen isotope reference materials developed by IAEA are gradually unable to meet the rapid development of scientific research. The development of national standard materials for carbon and nitrogen isotopes of organic matter that are suitable for the current analytical technology level for quality control, method evaluation, and instrument calibration are urgently needed in China.

OBJECTIVESTo prepare carbon and nitrogen isotope reference materials for organic matter.

METHODSIn order to ensure the accuracy of the transmission of the value, 4 stable carbon and nitrogen isotope reference materials of organic chemical materials were developed, of which 3 were urea samples and 1 was L-glutamic acid.

RESULTSAccording to the homogeneity test results, no statistically significant heterogeneity was found based on F test. The verified results by variance analysis for four samples showed very good homogeneity for the series. Nearly one-year stability analysis of δ¹³C and δ¹⁵N values confirmed that no statistically significant instability was found. The certified values of the reference materials were determined by an interlaboratory comparison of 12 participating laboratories. Carbon and nitrogen stable isotope ratios were measured using an elemental analyzer coupled with an isotope ratio mass spectrometer. The δ¹³C and δ¹⁵N values of the series of reference materials had a gradient distribution. The δ¹³C values ranged from -40‰ to 0‰, and the δ¹⁵N value from -10‰ to 30‰, covering the range of organic carbon and nitrogen stable isotope composition in natural samples in China. The extended uncertainty of the series of standard materials was not greater than 0.08‰ for δ¹³C and not greater than 0.09‰ for δ¹⁵N, and the fixed value level was equivalent to that of the international standard materials. This series of reference materials had been approved by the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China as the national first-level reference materials (GBW04494-GBW04497).

ConclusionThe series of reference materials can be used for analysis and monitoring, instrument calibration, method evaluation, quality assurance and quality monitoring in the determination of δ¹³C and δ¹⁵N ratios of various samples in geology, ecology and environment.