Full Vacuum FTIR Spectrometer for Quantitative Trace Gas Analysis (H2O in N2 Gas)

Download PDF June 13, 2017

Introduction

FT/IR-6800FV full vacuum Gas Analysis FTIR
FT/IR-6800FV full vacuum Gas Analysis FTIR

Trace gas analysis requires the use of long path length gas cells, this has been been reported in a separate application note, however, it can be difficult to accurately quantitate gases at low concentrations when the absorption peaks of the target gas overlap with the peaks of atmospheric water vapor or, when the target gas itself is H2O or CO2, which are present in the atmosphere. This is because even with a vacuum FTIR spectrometer, it was not possible to evacuate the sample chamber with the long path length cell present. The FT/IR-6000 Series full vacuum gas analysis system introduced in this application note has a special gas cell integrated into the sample chamber, allowing the entire light path to remain under full vacuum with the gas cell in place. This full vacuum  model makes it possible to quantitate concentrations of H2O even at levels as low as 0.2 ppm.

Experimental

For the measurement, a manifold with several vacuum lines is used  for independent evacuation of the FT/IR-6800FV interferometer, detector chamber and sample compartment, as well as the gas cell. Adding a vacuum gauge to the gas cell makes it possible to control the loading of extremely low concentrations of gas samples.

Cell Specifications

Cell TypeMulti-pass white cell
Path Length10 m
Cell BodyStainless-steel
Cell Inner SurfaceElectrochemically Polished
Mirror MaterialStainless-steel
Mirror SurfaceGold
O-ringViton
WindowCaF2
Cell Volumeapprox. 2 L
Gas In/Out Ports1/4" VCR
HeatingAvailable 100 deg C Max.

Keywords

230-TR-0199

Results

The quantitation of a trace levels of water vapor (H2O) in CO2 in a cylinder was attempted. Water vapor with a concentration of 15.0 ppm was diluted by monitoring the pressure gauge during dilution of the standard samples with concentrations of 1.5, 3.0, 4.5, 6.0, 7.6 and 9.12 ppm. Figure 2 shows the IR spectra of water vapor for each concentration. The lowest detection limit calculated from the Signal to Noise ratio was approx. 0.2 – 0.3 ppm. The calibration curve in Figure 3 was created using the absorption peak at 1734 cm-1. As seen, the precise quantitation of low concentration can be made with this system.

About the Author

John Burchell is a seasoned JASCO veteran adept with chromatography and spectroscopy products. He is currently the business development manager for both instruments.