Evacuating a sample chamber

#This disclosure is related to the field of chemical analysis and detection, and more particularly to the use of a sample collection and introduction system that utilizes a sample collector inserted into a sample chamber and chamber evacuation techniques to increase the concentration of a sample introduced to a detection device such as a mass spectrometer.

#Chemical analysis tools such as gas chromatographs (“GC”), mass spectrometers (“MS”), ion mobility spectrometers (“IMS”), and various others, are commonly used to identify trace amounts of chemicals, including, for example, chemical warfare agents, explosives, narcotics, toxic industrial chemicals, volatile organic compounds, semi-volatile organic compounds, hydrocarbons, airborne contaminants, herbicides, pesticides, and various other hazardous contaminant emissions.

#Most explosives, however, have very low volatility indices and as such, emit a very low amount of vapor into the surrounding air, typically below the detection limit of most analysis instruments. For this reason, detection typically involves the use of a swab or pad to capture the sample, and in some cases, involves heating the collector to release or vaporize the sample, thereby releasing it into an ambient gas matrix (e.g., air) before being transferred into the chemical detector.

#FIG. 1 is a system diagram of an exemplar chemical detection system.

#FIGS. 2, 3, and 4 are cross-sectional views of exemplar sample chambers.

#FIG. 5 is a system diagram of another exemplar chemical detection system.

#Like reference symbols in the various drawings indicate like elements.

#In the description below, for the purposes of explanation, specific examples related to detecting particulates/chemicals captured in or on a collector and analyzed using a mass spectrometer have been set forth in order to provide a thorough understanding of the implementations of the subject matter described in this specification. It is appreciated that the implementations described herein can be utilized in other capacities as well and need not be limited to mass spectrometers, but may be used to improve the operation of other detection instruments and techniques used in series or in parallel with a mass spectrometer. Accordingly, other implementations are within the scope of the claims.

#Mass spectrometers are particularly well suited for chemical analysis due to the high resolution measurements that can be realized and because mass spectrometers measure a fundamental property of chemicals that are introduced into the instrument. Other forms of chemical analysis instrumentation such as ion mobility spectrometers, surface acoustic wave devices, electrochemical cells, and similar instruments measure the constituents of a sample by inferring their presence from measurements of related phenomena such as resonant frequency changes, voltage changes, and drift time measurements. In addition, while other analytical instruments typically operate at approximately one atmosphere of pressure, mass spectrometers typically require a vacuum environment (e.g., pressures of 10−6-10−3 Torr) for proper operation. Because mass spectrometers operate at pressures well below that of atmospheric pressure, fewer molecules are present per unit volume in the instrument than for those instruments that operate at higher pressures. This is well described by the Ideal Gas Law: pV=nRT where p is the pressure inside the analysis chamber of an instrument, V is the volume of the analysis chamber, n is the number of molecules present, R is a constant equal to 8.314 J mol−1 K−1, and T is the temperature of the sample.