Abstract: The preconcentration device for N2O analysis was upgraded and assembled by a series of components, including air pressure bar, gas control valve, stainless steel cyro trap, fused silica capillary cyro trap, dewar, chemi
cal trap and etc. The function of Gasbench II was extended to control the lifting of cyro traps while the gas circuit,
sampling syringe, and sample plate were altered to realize the on-line determination with N2O preconcentration de
vice, Gasbench II and IRMS. Nitrate was chemically converted to N2O to build the method for analysis of N and O
isotope in seawater nitrate. Our results showed that the developed method has a very good precision. The standard
 deviation of 15N,18Oand peak area of nitrate was less than 1% , 3% and 5%, respectively. Tlie N and O iso
topes of nitrate in seawater collected from the Piydz Bay, Antarctica, were measured with this method. The values
 of 15N,18O of nitrate obtained were agreed well with literature reports, The profiles of 15N, 18O of nitrate in 
the Prydz Bay showed the typical characteristics of the ocean. The developed technique for analyzing N and O iso
topes of seawater nitrate was feasible.