适用于测量沉积物pH的金属氧化物微电极

用改进的高温熔融碳酸盐法制备了铱和钨氧化物pH微电极,表征了金属氧化物电极的各项性能.所制备电极对pH有较好的线性响应,斜率在40～60 mV/pH ,接近理想能斯特响应.实验表明,铱氧化物微电极在长时间工作稳定性方面优于钨氧化物微电极,90%响应时间为5 s.铱氧化物微电极受盐度和氧气浓度影响很小,且经Nafion修饰后不受沉积物间隙水中还原性S2-的影响.把铱氧化物微电极应用于测量厦门西海域和九龙江河口的沉积物pH垂直剖面,发现pH在沉积物有氧和无氧深度界面(4～5 mm)达到最小,20 mm以深趋于稳定,符合沉积物生物地球化学规律.

Development of Metal Oxide Microelectrodes for Measuring Sediment pH

Iridium oxide and tungsten oxide pH microelectrodes were fabricated by oxidizing the metal wires in sodium carbonate or lithium carbonate molten at high temperature.Experiments were carried out to characterize their working performance.The microelectrodes show good linear response to pH in buffer solution with a slope between 40 and 60 mV/pH,close to Nernst slope.Experimental results indicate that iridium oxide microelectrode has better performance than tungsten oxide microelectrode in long-time working stability.Iridium oxide microelectrode has a 90% response time of about 5 s,shorter than that of tungsten oxide microelectrode.Iridium oxide microelectrode is little affected by oxygen concentration,salinity,and the reducing agent of S2- ions in the pore water of sediments after being coated with a Nafion film.Iridium oxide microelectrodes were applied to measure pH profiles of sediment cores sampled from Xiamen Western Bay and Jiulong River Estuary.It was found that pH reach minimum values at oxic-anoxic interface of 4～5 mm depths within the sediments and tended to be stable at depths deeper than 20 mm.These results agree with the prediction of biogeochemistry in coastal sediments.