PM-IRRAS For Floating Monolayer Studies - PMI 550

Quickly and easily determine the orientation and composition of floating or solid monolayers via infrared spectroscopic analysis. The simple construction marks a breakthrough in in situ IR-analysis of monolayers. No more do you need to fiddle with mirrors and prisms in order to get the IR-beam to the interface. The simple goniometer carries a spectrometer on one arm and detector on the other, with simple screw adjustment allowing rapid alignment of the IR-beam. Integrated software allows mouse-click acquisition of spectra at user-defined surface pressures.

Applications

• Lipid films
• Membrane proteins
• Nanoparticles
• Surfactants

The Technique

Infrared Reflection Absorption Spectroscopy (IRRAS) is a powerful method to assess the chemical composition and orientation of molecules at an interface. IRRAS takes advantage of the fact that p-polarized light (perpendicular to the reflective surface) is preferentially absorbed upon reflection, whereas s-polarized light is virtually unabsorbed. In contrast, absorption in isotropic media is independent of polarization, so that any difference between the s- and p-polarized signals can be assigned to surface specific absorption. While it sounds simple in principle, extracting the signal of interest has proved challenging due to instrumental noise, and the interference of water vapor and CO₂ in the measuring chamber. However, recent advances in component design have greatly improved the ability to extract the information of interest. "Polarization Modulation"� (PM) is a method that can be used in conjunction with FTIR spectroscopy where the incoming light is continuously modulated between s- and p- polarization at high frequency. This effectively allows simultaneous measurement of spectra for the two polarizations, the difference providing surface specific information, and the sum providing the reference spectrum. As the spectra are measured simultaneously, the effect of water vapor is largely removed.

The Instrument

The KSV PMI 550 contains a state-of-the-art compact Fourier Transform IR-spectrometer, and PM-Unit on one arm of the goniometer, and a highly sensitive MCT-detector on the other arm. The spectrometer and PM-unit operate at different frequencies, allowing separation of the two signals at the detector. A resolution of 8 cm^-1 allows distinction of most processes of interest in the monolayer. The PM unit consists of a photoelastic modulator (PEM), which is an IR transparent piezoelectric lens that is distorted in different directions using an applied voltage, allowing control of the incident beam polarization.

Software

Possible Measuring Configurations