Development of an Automated and Simultaneous Analyzer for Three
Greenhouse Gases
Abstract
We developed a new automated and simultaneous analyzer to measure three major
greenhouse gases (CO2, CH4, and N2O) by one gas sample injection. This simultaneous
measurement was realized by introducing a new packing to totally separate CH4, CO2,
and N2O and using a common carrier gas to detect each gas.
Shigeto Sudo, Greenhouse Gas Mitigation Research Project, Carbon and Nutrient
Cycles Division, National Institute for Agro-Environmental Sciences
Background and Purpose
Since the First Commitment Period of the Kyoto Protocol started in 2008, reducing
greenhouse gas emission from terrestrial ecosystems such as farmland and forest land
becomes more urgent. For this reduction measure target, it is necessary to develop a
method that can measure greenhouse gas with high sensitivity and high frequency.
However, there had been no reports about the simultaneous measurement of these
three greenhouse gases (CO2, CH4, and N2O) until now. Moreover, all gas sample
injections are performed manually. This study arms to develop an automated and
simultaneous analyzer to measure these three gases.
Achievements and Features
A simultaneous analyzer that measures the three greenhouse gas components (CH4,
CO2 and N2O) was developed.
In terms of simultaneous analysis, as shown in the center of the system diagram
(Figure 1), first, by introducing the packing (Unibeads C, GL Sciences Inc), which has a
high separation capacity, in the second stage of the three stages of the gas separation,
the total separation of CO2, CH4, and N2O, which has previously been technically
difficult, took place. Next, for high-sensitive detection of CO2 and N2O, previously
helium and argon (mixed with 5% methane) were used as carrier gases respectively.
However, by adding a mixture of nitrogen and methane into helium as a makeup gas in
the ECD cell, the study, together with obtaining N2O detection sensitivity, which is
equivalent of the conventional method, make it possible to simultaneously analyze CO2
and N2O. Compared with measuring the three gases separately, one of the advantages is
that the measurements of the three gases are free from injection-volume differences
because the same sample is used for all three gas detections. The repeated analytical
precision of the three gases is equal to that of conventional methods.
For sample injection, we modified a commercially available headspace sampler
(HSS-2B, Shimadzu Corporation) and developed an automated injection with a highly
precise gas-tight syringe (2ml, Valco Instruments Co. Inc.). A cone-shaped guide was
also remade for the syringe needle to penetrate a well-sealed butyl rubber lid. With this
auto-injector, the automatic analysis can be made in 10 minutes for one sample with a
maximum of 40 samples.
Although this analyzer (Figure 2) uses a specific maker’s detector and gas
chromatograph, similar products made by other companies can also be used. We expect
that the precision and frequency of greenhouse gas measurement can be greatly
improved by spread of this analyzer.
Figure 1. System diagram of the automated three-greenhouse-gas analyzer
(Unibeads C is used in second phase to realize total three-gas separation (centre).
Mixture gas of nitrogen and methane is added into helium in the ECD cell. Analyzer
obtained the same N2O detection sensitivity of conventional method.)
Figure 2. Overview of the automated three-greenhouse-gas analyzer
New developed auto-injector is located on the top of sample table (left of analyzer).
Figure 3. Chromatography and control software interface
From peak shape and kept time of N2O (center) and CO2 (top), it can consider that these
two gases have been totally separated.