  A gas cell for in-situ measurements of Volatile Organic Compounds (VOCs) and
their adsorption behavior on different surfaces by means of X-Ray Fluorescence
(XRF) and X-ray Absorption Fine-Structure (XAFS) spectroscopy has been
developed. The cell is especially designed to allow for the efficient
excitation and detection of low-Z elements such as carbon, oxygen or nitrogen
as main components of VOCs. Two measurement modes are available. In the surface
mode, adsorption on a surface can be studied using XAFS by fluorescence
detection under shallow angles of incidence. The transmission mode enables the
simultaneous investigation of gaseous samples via XAFS in transmittance and
fluorescence detection modes. Proof-of-principle experiments were performed at
the PTB plane grating monochromator beamline for soft x-ray radiation at the
synchrotron radiation facility BESSY II. The flexible design and high
versatility of the cell are demonstrated with the investigation of ethanol
(EtOH) as one of the most abundant VOCs. The comparison of Near-Edge X-ray
Absorption Fine-Structure (NEXAFS) spectra under transmission and fluorescence
detection in the gas phase with measurements of adsorbed molecules on a
Si-wafer surface both at the C and O-K absorption edges proves the
applicability of the cell for the monitoring of adsorption processes.
