Cowie G, Lloyd D
Microbiology Group (PABIO), University of Wales, Cardiff, UK.
J Microbiol Methods. 1999 Feb;35(1):1-12. doi: 10.1016/s0167-7012(98)00090-6.
The use of an ion trap mass spectrometer with three different membrane inlet probes is described. Two methods of removing water from the sample are compared. One is the use of a PTFE-silicone rubber double membrane, PTFE is relatively impermeable to water and so reduces the amount entering with the gas sample (Probe A). The second is the use of a silicone rubber membrane covered long probe, which condenses water out of the sample (Probe B). Response times (100%) for dissolved N2O, O2, Ar and CO2 without He in the chamber vary from between 158 and 684 s with Probe A. For the same probe with He, the response times were between 283 and 551 s. In the gas phase response times were between 99 and 153 s with He and 117 and 122 s without He. Probe B had 100% response of between 122 and 152 s for dissolved gases. Further extension of the probe by 2 m slowed response times as did increasing the ionisation time. Response times for Probe B increased to between 99 and 340 s when ionisation time increased from 1000 to 24,930 microseconds. Plots of output against concentration showed the steepest line of response for the short single membrane covered probe with 1000 microseconds ionisation time. Increasing the ionisation time, extending the probe and the use of a double membrane all reduced the gradient of output against concentration for every gas tested. In an intact sediment core, concentrations of O2, N2O and CO2 rose at the start and the concentration of N2 fell. As the disturbed sediment settled, this was reversed. The initial increase in O2 concentration stimulated respiration and inhibited the final pathway in dentrification producing higher concentrations of N2O and reducing the concentration of N2.
描述了使用带有三种不同膜进样探头的离子阱质谱仪。比较了两种从样品中去除水分的方法。一种是使用聚四氟乙烯 - 硅橡胶双层膜，聚四氟乙烯对水相对不渗透，因此减少了随气体样品进入的水量（探头A）。第二种是使用覆盖有硅橡胶膜的长探头，它能将样品中的水冷凝出来（探头B）。对于腔室内不含氦气的溶解态N₂O、O₂、Ar和CO₂，探头A的响应时间（100%）在158至684秒之间。对于同一探头在有氦气的情况下，响应时间在283至551秒之间。在气相中，有氦气时响应时间在99至153秒之间，无氦气时在117至122秒之间。探头B对溶解气体的100%响应时间在122至152秒之间。探头再延长2米会减慢响应时间，增加电离时间也会如此。当电离时间从1000微秒增加到24930微秒时，探头B的响应时间增加到99至340秒之间。输出量与浓度的关系图显示，对于电离时间为1000微秒的短的单膜覆盖探头，响应曲线最陡。增加电离时间、延长探头以及使用双层膜都会降低所测试的每种气体的输出量与浓度的梯度。在完整的沉积物岩心中，O₂、N₂O和CO₂的浓度在开始时上升，N₂的浓度下降。随着受扰动的沉积物沉降，情况逆转。O₂浓度的初始增加刺激了呼吸作用，并抑制了反硝化作用的最终途径，从而产生更高浓度的N₂O并降低了N₂的浓度。
