Three embodiments of an improved photo acoustic cell for use in analyzing solid and quasi-solid samples are disclosed. Each cell includes a sample holding chamber having one wall or portion of one wall thereof made from a light transparent material. The sample holding chamber in each embodiment is connected to a microphone by a thin tube which renders the cell, which includes the chamber tube and microphone, an acoustical resonant structure at a frequency within the response characteristics of the microphone. In one embodiment, means are disclosed for pressuring the inside of the cell as well as equalizing the pressure on the outside of the tube. In a second embodiment, the sample to be analyzed forms a portion of the cavity walls and means are provided for reducing the pressure in the cavity to hold the sample securely to the remaining structure for defining the cavity. In this embodiment a fiber optic element brings the light into the chamber. In the third embodiment the cell is mounted relative to a support structure so that different portions of the sample can be brought into relationship with can advantageously be employed to analyze plates, paper or the like which result from chromatographic techniques.
A heatable cell for photoacoustic tests. The cell includes a specimen chamber which is connected with the microphone chamber of a detector microphone, and is provided with a specimen receiving portion and light admission window located across therefrom. A recess is located in the chamber closure and serves as the specimen receiving portion. The sealing surface of the chamber closure is sealingly pressed against a sealing surface of the chamber. At least one heating winding is provided on the chamber and/or on the chamber closure, and a thin-wall connecting tube having poor heat conducting characteristics is provided between the specimen chamber and the microphone chamber, which is arranged lower than the specimen chamber to prevent convection.
A photoacoustic cell for analyzing solid and quasi-solid samples and which includes a table for holding a sample to be analyzed and which is movably disposed in the cell housing and positioned in a sample test position to form a part of the cell chamber in which the sample is to be analyzed or tested. The cell chamber is formed having a window through which a light source may pass onto the sample whereby energy is released inside said cell chamber characteristic of the light source and is sufficient to provide a signal characteristic of the absorbance of the sample and which is sensed by a microphone in said chamber. At the completion of the sample test, the table may be moved to a sample load/unload position for discharge of the tested sample and preparatory to having a subsequent sample placed thereon for analysis.
A method for enhancing the intensity of a photoacoustic signal by surrounding a solid with a gas having a normal boiling point at least about 25.degree. C. below the temperature at which the photoacoustic effect is being measured and a critical temperature not less than about 2.degree. C. By utilizing a second gas, selected from the permanent gases having a critical temperature not greater than about -73.degree. C., the surface area of a solid can be measured in accordance with procedures and relationships herein described.
A cell for photoacoustic spectroscopy has a metal heat conductive rod immersed at one end in a liquid coolant and another end forming part of the sample-receiving cell for accurate control of the temperature to eliminate thermal distortion of the measurements.
Resonant optoacoustic cells are used in measurements of the concentration and composition of a gas or aerosol. Such apparatus is improved by providing a small absorption cell acoustically coupled to a resonant acoustic cavity so that the time delay associated with the flow of a gas or aerosol through the absorption cell is greatly reduced.
