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Improved isotope ratio measurement performance in liquid chromatography/isotope ratio mass spectrometry by removing excess oxygen
Author(s) -
Hettmann Elena,
Brand Willi A.,
Gleixner Gerd
Publication year - 2007
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.3304
Subject(s) - chemistry , isotope ratio mass spectrometry , mass spectrometry , analytical chemistry (journal) , oxygen , chromatography , volume (thermodynamics) , surface area to volume ratio , chemical engineering , organic chemistry , physics , quantum mechanics , engineering
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 δ 13 C values of the reference gas need up to 500 s to stabilize. For repeated injections the δ 13 C values of sucrose remain constant (±0.1‰) for about 3000 s. The long‐term stability for measurements of sucrose was 0.11‰ without the reduction oven and improved slightly to 0.08‰ 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. Copyright © 2007 John Wiley & Sons, Ltd.