irm-EAMS (δ13C and δ15N)
CO2 in-air (δ13C and δ18O)
O2/N2 in air (+ δ18O of O2 in air or Ar/N2)
Laser Ablation
GasBench
TC/EA ('Pyrolysis', δ2H and δ18O)
Acid reaction and air mixing system (ARAMIS) (δ13C and δ18O)

GasBench

Gasbench measurements

The Gasbench II is an interface that couples an autosampler (PAL80, CTC) on-line with an IRMS ('Bianca') for isotopic analysis from the headspace of septum sealed vials. In our case, the volume of the vials is 10 ml ('Exetainer') and we have utilized the system for isotopic analysis of CO2 in air samples. The setup has the advantage that a large number of samples can be taken in the field within a short period of time. Without special sampling equipment. Disadvantages are the presence of the septum that can alter the isotopic composition of the analyte and the reduced precision of about 0.1‰ for δ13C. Storage time of the samples is limited to a couple of days only. A single measurement sequence can hold up to 96 samples which are processed in a fully automated mode. The samples are pierced with a double-hole needle. Helium enters the sample and slowly carries the analyte through a sampling loop at about 0.2 ml/min. The sampling loop is switched to a GC repeatedly and CO2 is fed to the mass spectrometer via an open split. Two Nafion dryers prevent moisture from entering.

The system has mainly been used by the Buchmann group for studying diurnal and annual cycles of CO2 within ecosystems like the Hainich. In 2001 and 2002, a total of 5000 analyses have been made on the system, with 57% samples and 43% reference air and test runs.

Recent experiments with the GasBench are reported in

Alexander Knohl, Roland A. Werner, Heike Geilmann and Willi A. Brand, Improved storage time of canopy air samples in 10-mL vials for CO2- δ13C analysis using Kel-f discs, Rapid Comm. Mass Spectrom., (2004) 18: 1663-1665

Alexander Knohl, Roland A. Werner, Willi A. Brand, Nina Buchmann, Short-term variations in δ13C of ecosystem respiration reveals link between assimilation and respiration in a deciduous forest, Oecologia, (2005) 142: 70-82