Determination of Ultralow Level 129I/127I in Natural Samples by Separation of Microgram Carrier Free Iodine and Accelerator Mass Spectrometry Detection

摘要

Separation of carrier free iodine from low iodine levelnsamples and accurate measurement of ultralow level 129Inin micrograms of iodine target are essential but anbottleneck in geological dating of terrestrial system andntracer research using naturally produced 129I. In thisnwork, we present a carrier free method using coprecipitationnof AgI with AgCl for preparing microgramsnof iodine target, associated with combustion using antube furnace for separating iodine from solid samplesnand anion exchange chromatography for preconcentratingniodine from a large volume of water. An acceleratornmass spectrometry was used to measurenultralow level 129I in micrograms of iodine target. Thenrecovery of iodine in the entire separation procedurenis higher than 80% and 65% for solid and waternsamples, respectively. One microgram iodine in thentarget (AgI-AgCl) can produce a stable 127I signal fornAMS measurement of 129I/127I, and a detection limitnof this method for 129I is calculated to be 105 atoms.nThis will allow us to accurately determine 129I innprenuclear geological samples of low iodine concentrationnwith 129I/127I of 10-12, such as loess, soil, coral,nrock, sediment, and groundwater. Some samples withnlow iodine content have been successfully analyzed,nand the lowest value of the 129I/127I ratio of 2 × 10-11nwas observed in 23.5 and 63.5 m loess samplesncollected in the Loess Plateau, China. The developednmethod sheds light on a wide application in earthnscience.