Hettmann Elena, Brand Willi A, Gleixner Gerd
Max Planck Institute for Biogeochemistry, Jena, Germany.
Rapid Commun Mass Spectrom. 2007;21(24):4135-41. doi: 10.1002/rcm.3304.
A low dead volume oxygen scrubbing system was introduced in a commercially available liquid chromatography/isotope ratio mass spectrometry (LC/IRMS) interface to enhance the analytical capability of the system. In the LC/IRMS interface carbon from organic samples is converted into CO(2) inside the mobile phase by wet chemical oxidation using peroxodisulfate (Na(2)S(2)O(8)). After passing the hot reaction zone, surplus oxygen (O(2)) remains dissolved in the liquid phase. Both CO(2) and O(2) diffuse through a transfer membrane into the helium carrier and are transferred to the mass spectrometer. The presence of O(2) in the ion source may have detrimental effects on measurement accuracy and precision as well as on filament lifetime. As a remedy, a new on-line O(2)-removing device has been incorporated into the system. The new O(2) scrubber consists of two parallel hot copper reduction reactors (0.8 mm i.d., active length 120 mm) and a switch-over valve between them. One reactor is regenerated using He/H(2) while the other is actively scavenging O(2) from the gas stream. The capacity of each reduction reactor, expressed as usage time, is between 40 and 50 min. This is sufficient for a single LC run for sugars and organic acids. A further increase of the reduction capacity is accompanied by a peak broadening of about 100%. After switching to a freshly reduced reactor the oxygen background and the delta(13)C values of the reference gas need up to 500 s to stabilize. For repeated injections the delta(13)C values of sucrose remain constant (+/-0.1 per thousand) for about 3000 s. The long-term stability for measurements of sucrose was 0.11 per thousand without the reduction oven and improved slightly to 0.08 per thousand with the reduction oven. The filament lifetime improved by more than 600%, thereby improving the long-term system stability and analytical efficiency. In addition the costs per analysis were reduced considerably.
一种低死体积氧气洗涤系统被引入到市售的液相色谱/同位素比率质谱联用仪（LC/IRMS）接口中，以增强该系统的分析能力。在LC/IRMS接口中，有机样品中的碳通过过二硫酸盐（Na₂S₂O₈）的湿化学氧化在流动相内转化为CO₂。通过热反应区后，过量的氧气（O₂）仍溶解在液相中。CO₂和O₂都通过传输膜扩散到氦气载气中，并被传输到质谱仪。离子源中O₂的存在可能会对测量的准确性和精密度以及灯丝寿命产生不利影响。作为一种补救措施，一种新型在线O₂去除装置已被纳入该系统。新型O₂洗涤器由两个平行的热铜还原反应器（内径0.8毫米，有效长度120毫米）以及它们之间的切换阀组成。一个反应器使用He/H₂进行再生，而另一个则从气流中积极去除O₂。每个还原反应器的容量，以使用时间表示，在40到50分钟之间。这对于糖类和有机酸的单次LC运行来说已经足够。还原容量的进一步增加会伴随着约100%的峰展宽。切换到新还原的反应器后，氧气背景和参考气体的δ¹³C值需要长达500秒才能稳定。对于重复进样，蔗糖的δ¹³C值在约3000秒内保持恒定（±0.1‰）。在没有还原炉的情况下，蔗糖测量的长期稳定性为0.11‰，使用还原炉后略有改善，为0.08‰。灯丝寿命提高了600%以上，从而提高了系统的长期稳定性和分析效率。此外，每次分析的成本大幅降低。
