According to the recent IPCC report (1), climate change as a result of global warming is estimated to proceed at a faster
rate than previously assumed. Consequently, easy and efficient monitoring of the greenhouse gases methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) is becoming an increasingly important issue. The analytical challenges that surround this approach are the varying concentration
ranges of the components in ambient air, ranging from high ppm levels for carbon dioxide, low ppm to ppb levels for methane,
and trace levels below 100 ppb for nitrous oxide. So far, a rather complex GC system including two or three detectors was
needed to fulfill all requirements. With the new Barrier Ionization Discharge Detector (BID), this approach can be simplified
to a gas chromatography (GC) system with one detector and one column only.
The BID detector belongs to the family of helium ionization detectors. It is a universal detector able to measure all types
of organic and inorganic compounds except for helium and neon. Because of the novel plasma technology, the BID detector combines
the high detection sensitivity of the helium ionization technique with robustness and long-term stability.
Gas injection was carried out using a two-position six-port VALCO valve with a 1 mL sample loop. Chromatographic separation
was performed on a 2 m Restek ShinCarbon ST micropacked column with a 1 mm inner diameter and 1/16" outer diameter. The column
was selected because of its sample capacity, and therefore its ability to obtain sufficient separation of methane from the
ambient air matrix peak, even with a 1 mL injection volume. Figure 1 shows the chromatogram of an ambient air sample taken
in the vicinity of a larger city. This is why carbon monoxide is also present in the chromatogram.
Figure 1: Ambient air chromatogram sampled at the southern edge of the city of Duisburg (Germany). Results are shown in Table
The separation of matrix air requires a temperature programme starting at 30 °C, then hold for 5 min, and a temperature increase
at a rate of 10 °C/min to 120 °C. Helium with a purity of 6.0 or better was used as carrier gas and discharge gas for the
BID detector. The carrier gas flow over the ShinCarbon ST column was 14 mL/min. The BID was operated at 250 °C with a discharge
gas flow of 80 mL/min.
Table 1: Quantitation results from the chromatogram in Figure 1.