| Nitric oxide (NO) is a small gaseous molecule and free radical, and it is widely present in animals, plants and microorganisms and other biological organisms. The research on nitric oxide has attracted great attention of researchers from different fields including Chemistry, Molecular Biology, and Medicine at present. However, the research about nitric oxide in Oceanological field is very scarce. It is necessary to study nitric oxide in marine for elucidating the influence of nitric oxide on oceanic ecological system and understanding the function and significance of nitric oxide on oceanic nitrogen cycle system.This paper was designed to take nitric oxide in seawater as the research object, the following several aspects were carried out: (1) Established the determination method of nitric oxide in seawater—the fluorometric method and the chemiluminescence method, and found out the optimal conditions of each method; (2) Studied on the distribution, diurnal variation and the issue of sources-sinks of nitric oxide in the surface seawater in Jiaozhou Bay and its adjacent area by the use of flurometric method for the first time.The main results were summarized as follows:1. The study of the flurometric determination of nitric oxide in medium of seawaterBased on the specific reaction of nitric oxide with 2, 3-diamino naphthalene (DAN) and the strong fluorescence of the production under alkaline condition, this paper established the method of purge-and-trap pretreatment combined with fluorometric determination to measure nitric oxide in seawater, and optimized the fluorometric determination conditions and the purge-and-trap conditions. The results were as follows: excitation wavelength of 383nm, emission wavelength of 410nm, the reaction temperature of 1020℃, purging flow rate of 400mL/min, purging time of 30min. Under the optimized experimental conditions, the detection limit is 6.7×10-11mol/L, the linear range is 1.4×10-101.9×10-8mol/L, have a good correlation, the average recovery is 83.8%, the precision is 7.2%.2. The study of the chemiluminescence determination of nitric oxide in medium of seawaterBased on the principle of the luminol-hydrogen peroxide mixed solution reacting with nitric oxide to emit light signal, this paper established a chemiluminescence method of nitric oxide in the medium of seawater, and discussed the disturbance for the chemiluminescence probe of nitric oxide in seawater. The result showed that a number of ions in seawater had some impact on the determination of nitric oxide, but this impact may be decreased to the allowable error range by adding the EDTA. Besides, we have optimized the experimental conditions。The results were as follows: carbonate solution was proved to be the optimal buffer system, and chemiluminescence peak area and S/N were the strongest when its pH was 9.2, luminol concentration of 8.4×10-5mol/L, H2O2 concentration of 1×10-2mol/L, measured temperature of 20℃, EDTA optimal concentration of 1×10-3mol/L. The detection limit was 3.4×10-12mol/L, the linear range of 9.8×10-10 1.4×10-12mol/L, the correlation coefficient R2 = 0.995, relative standard deviation (RSD) of 13.6%.3. Method comparisonThe concentrations of nitric oxide in the algae culture of Platymonas subcordiformis and Skeletonema costatum during the exponential growth period was measured by both fluorometric method and chemiluminescence method. Through a comparison of the results of both methods, fluorometric method and chemiluminescence method were proved to be feasible to determinate the concentration of nitric oxide in algae culture. Moreover, due to their low detection limits, these methods could be used to determinate the concentration of nitric oxide in field seawater at low concentration levels.4. The distribution of nitric oxide in Jiaozhou Bay and its adjacent areaThe distribution of nitric oxide in the surface seawater was determined in Jiaozhou Bay and its adjacent area during November 2009 and August 2010. The results showed that, the concentration of nitric oxide in the period of 2009 was 0.26±0.14 ( 0.50±0.01) nmol/L, that in the period of 2010 was 0.47±0.25 (0.27 1.27) nmol/L. The horizontal distribution of nitric oxide presented certain characteristics in the area investigated. The average concentration inside Jiaozhou Bay was higher than that outside Jiaozhou Bay, and the highest value was in the north of Jiaozhou Bay A2 station, while outside Jiaozhou Bay the high value area was in the east of the survey area. The diurnal variation generally showed that, the nitric oxide concentration was relatively higher in the daytime, while during the night the nitric oxide concentration was lower, which indicated that the concentration of nitric oxide in the surface seawater was significantly affected by light. Correlation analysis showed that there was a significant negative correlation between the nitric oxide concentration and the content of dissolved oxygen, there was also certain positive correlation between NO and NO2- in the daytime. The study on NO sources and sinks showed that the ocean was the source of atmospheric NO during the day in investigated sea area in November 2009, and it was unclear of NO sources and sinks due to lack of the NO concentrations during the night; that the ocean was the source of atmospheric NO in investigated sea area in Augest 2010.The results of the study provide the detection method of nitric oxide in the field of seawater. The preliminary study on the distribution of nitric oxide in Jiaozhou Bay and its adjacent area is the experimental basis of further study on the function and status of nitric oxide in marine nitrogen cycle, which has important significance to its biogeochemistry research. |
PDF Full Text Request