CBE Interdisciplinary Glossary

Experimental Equipment and Methods

ATTENUATED TOTAL REFLECTION FOURIER TRANSFORM INFRARED SPECTROSCOPY (ATR/FT-IR) Collects an infrared spectrum from an interfacial region within one micrometer of a substratum: typically germanium or germanium-coated with a thin film. Infrared spectra of organic compounds are used for identification and yield information on molecular composition, bonding, conformation, and orientation with respect to the interface. Biomolecules which can be identified in spectra of biofilms include proteins, RNA/DNA, carbohydrates and lipids.

BUFFERING CAPACITY MONITOR An instrument which measures the buffering capacity of an aqueous solution by quantitively generating hydrogen and/or hydroxyl ions and measuring the amount necessary to produce a change of one pH unit in the solution. The quantity C/pH is defined as the buffering capacity at the pH of the solution. The instrument consists of an immersible probe and associated electronics.

QUARTZ CRYSTAL MICROBALANCE An instrument which measures gain or loss of mass at the surface of a quartz crystal resonating element. The device is capable of measuring nanogram changes in mass per square cm of surface area. The change in mass, as a function of resonance frequency, is independent of the composition of the material and is described for simple systems by the Sauerbrey equation. The instrument consists of: 1) a thin quartz crystal disk plated on opposite sides with electrodes; and 2) the resonance element (which is immersible in aqueous solutions), part of a stable oscillator circuit whose center frequency is measured by a sensitive frequency counter.

VIBRATING PLATINUM ELECTRODE A device for measuring electric fields caused by ion gradients in aqueous solutions. When a temporary localized non-uniformity in ion distribution (separation of charge) exists, for example, due to reactions in biological systems or corrosion at metallic surfaces, fluxes of ions occur to cancel the imbalance. The vibrating platinum microelectrode rapidly samples potentials over a small vertical distance and converts the variation into an alternating voltage. The device consists of an insulated platinum microelectrode, a one-dimensional vibration actuator, an AC amplifier, and a lock-in amplifier.

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