Analytical Method For N₂O In Seawater And Sediment With Room Temperature Purge And Trap-Gas Chromatography

Nitrous oxide (N₂O) plays an important role in the nitrogen cycle. Atmospheric N₂O directly contributes to the greenhouse effect, and affects the ozone layer through various photochemical reactions. Since the industrial revolution, the increase in N₂O abundance is reported as 0.2%/yr. Ocean is the important source of N₂O. Through the study of temporal and spatial distribution of N₂O in ocean, the flux of N₂O between sea and atmosphere is evaluated. Therefore, analytical methods for N₂O in the seawater and sediment are significant. In this dissertation, the analytical methods for N₂O in seawater and sediment had been developed and applied to measure denitrifaction rate of microenvironment. The detail information is as follows:(1) Establishment of analytical method for N₂O in seawater with room temperature purge and trap-gas chromatography (PT-GC)Experimental parameters, including different sorbent, GC column temperature, trap temperature, desorbing temperature, purge time and purge flow rate, were optimized. 80¹00 mesh 5? molecular sieve was chosen as the optimal sorbent. The method detection limit, linearity of N₂O calibration curve, RSD of 5 calibration curve slopes and average recovery were 2.8×10-10 mol/L, 3.4～39.2×10(-9) mol/L, 2.84% and 93.93±3.1% (n=5), respectively.N₂O was trapped at room temperature by 80¹00 mesh 5A|°molecular sieve. The method was found to be economical, sensitive, simple and repeatable.(2) Establishment of analytical method for N₂O in sediment with room temperature purge-trap and gas chromatography (PT-GC)Based on the established method for N₂O in seawater samples, a novel room temperature PT-GC method with purge-trap autosampler system had been developed for the determination of N₂O in sediment. Experimental parameters, including purge flow rate, purge time and purge temperature, were optimized. The method detection limit, linearity of N₂O calibration curve, RSD of 5 parallel samples and average recovery were 4.5×10(-9) mol/L, 0.42～21.06×10^-7 mol/L, 3.5% and 75.1±3.3% (n=3), respectively.The method, which simplifies experimental procedures through using purge-trap autosampler system, showed advantages of high sensitivity and reproducibility.(3) Application of room temperature purge-trap and gas chromatography on the study of denitrification rate of microenvironmentMicroenvironments were established in the laboratory. The analytical methods of N₂O in seawater and sediment were applied on the study of denitrification rate of microenvironment. Acetylene (C₂H₂) was used to inhibit key enzymes involved in nitrification and denitrification (N₂O reductases). Then denitrification rate was evaluated from the data of N₂O accumulation rate.