Gas separation: processes – Selective diffusion of gases – Selective diffusion of gases through substantially solid...
Reexamination Certificate
1999-11-10
2001-10-02
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
Selective diffusion of gases
Selective diffusion of gases through substantially solid...
C095S082000, C095S090000, C096S004000, C096S101000, C096S108000
Reexamination Certificate
active
06296685
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns a diffusion collector for the so-called passive sample-taking of gaseous analytes or analytes dissolved in a liquid (dispensing phase) with a semipermeable, transport-controlling diffusion membrane, which prefers the analytes, and an analyte-selective ad- or absorption means for the purpose of increasing the analyte concentration (collecting or receiving phase).
The main area of application of the device according to the invention is the monitoring of environment-relevant substances, mainly in air and water samples (or the collection of volatile analytes in soil samples). The advantages of the passive sample-taking, such as simplicity (construction of badges) and no energy requirement whatsoever are sufficiently well known. For the purpose of monitoring the environment there is a large demand for simply constructed passive sample collectors, that are easy to use, which can collect the materials (analytes) of interest in a substantially shorter time, so as to be able to determine short-term peak values as well. For monitoring the work place, correspondingly suitable collecting badges are needed, which can be easily carried on the human body and which can perform satisfactorily without electrically driven pumps and nevertheless permit the taking of samples in comparable time intervals.
Commercially available diffusion sample-taking devices for collecting volatile materials are mainly based on the use of activated charcoal as an adsorption means of low specificity, which, for example, is strongly adversely affected by water vapor (moisture). The size of the diffusion surface is between 2 and 20 cm
2
, and the diffusion path amounts to about 10 mm, These result in material-specific absorption rates of only 5 to 50 cm
3
/min. Because the analytes can be almost completely desorbed again from the activated charcoal by a solvent eluation process, during which process, however, a dilution by the solvent takes place, these collectors are almost exclusively suitable for high analyte concentrations and long sample-taking periods (several hours to a number of weeks).
The diffusion sample taking devices, which are based on organic polymers or the like, where in addition to the solvent desorption usually the more effective thermal desorption is also possible, are almost all based on glass tubes of the type known from the active sample-taking process involving the use of a pump. These collectors, however, have only a small diffusion cross-section(about 0.1 cm
2
), and with a diffusion path of <<10 mm, very low absorption rates of less than 0.5 cm
3
/min result from it, which do not permit any short-term measurements. This means that the limits of detection, which can be achieved with these systems, are not sufficient for the analysis of environmental trace quantities.
2. Description of the Related Art
In the EP 0 714 020 A3 a device for the sample-taking of volatile materials including a diffusion body and a means for the adsorption of volatile materials to be collected is described. Here a radially-symmetrical arrangement of a central collector phase, which is placed concentrically within a cylindrical diffusion body, is disclosed. The diffusion path has been substantially shortened with respect to conventional devices, which, it is true, results in a better ratio of surface to diffusion path, but the diffusion path still amounts to more than one millimeter and contains no provisions for the increase of the selectivity of the analytes to be collected. In particular, in the case of this device the moisture, which will have a strong adverse effect during the subsequent analysis, gets unhindered into the collector phase. Furthermore, a design involving a central collector cartridge and open side surfaces (steel wire grid) is complicated and makes it harder to use fine-pored or liquid collector phases, which will then fall out through the metal grid. For reasons of stability, the large surface regions of the collecting phase are, in this case, covered by the metal and reduce the effective diffusion surface. Moreover, this device must be taken apart during the subsequent thermal desorption, in order to heat the collector phase rapidly and effectively by close contact with heated surfaces. During this process the interfering components can enter and distort the result. Due to the air gap between the cylindrically shaped outer plastic body and the centrally symmetrical collecting tubes, this device cannot be used for the passive taking of samples in the case of liquid samples. If one needs to conduct a solvent eluation due to heavy volatile analytes, then, in this case it is necessary, because of the tube-shaped adsorption cartridge with an open perimeter, to use once more an exactly fitting eluation container, which prevents that the solvent escapes through the metal weave. But this results in the formation of small cracks and gaps, which, because they generate a so-called dead volume, delay the washing away of the collected analytes and achieve the desired quantitative transfer to an analysis system only with a high degree of dilution.
From the DE 37 35 307 a diffusion collector is known, which contains a collector phase which is in contact with the phase containing the analytes to be detected by way of a channel-shaped settling path, which is bounded by walls. In this case, the housing can be equipped with perforations, which permit the introduction of water vapor for expelling the substance, the concentration of which was increased in the collector phase.
From WO 96/07885 A1 a collector for chemical analyses is known, in which the receiving part for analytes is covered with a membrane, and where at opposite ends of the receiving part an inlet and an outlet are present. In the case of this collector, however, it only involves a filter, with which a membrane-specific separation can be carried out and where the separated materials can be passed on to a device with which a chemical analysis can be conducted.
By J. A. Johnson and L. Mathiasson in “Supported liquid membrane techniques for sample preparation and enrichment in environmental and biological analysis”, Trends in Analytical Chemistry; 11 (1992) March; No. 3, Amsterdam pp. 106-114 possibilities for the collection, preparation and enrichment of analytes are described. In this context a liquid membrane as well as a donor-acceptor complex are used in order to achieve a targeted separation by means of the membrane, which is at least supported by the specific donor-acceptor complex. Furthermore, the transport of material through the membrane is supported by pumps, so that in this case it only involves extremely limited and passively implemented processes, which cannot be used indiscriminately at just any location under the most varied conditions. Thus, for example, neutral material components can only reach equal concentrations on both sides of the membrane.
Starting with the disadvantages of the state of the art, the invention is based on the task of creating a diffusion collector and a process for taking samples in a passive way by means of a. diffusion collector which are not very susceptible to being contaminated, can also be used in liquids and permit a quantitative evaluation of the collected sample. The device should have a compact construction and be usable in a versatile manner.
This objective is being achieved by a diffusion collector for gaseous analytes contained in fluid phases comprising a housing which includes at least one indentation in the form of a channel, the at least one channel being provided with an inlet pipe and an outlet pipe and a hydrophobic diffusion membrane permeable for the analyte and covering the at least one indentation, wherein a collector phase is stored in the at least one indentation. This objective is also achieved by a process for the passive taking of samples by means of a diffusion collector wherein the gaseous analyte is diffused through a hydrophobic membrane, which is permeable for the analyte, from the fluid
Brendel Thomas
Cammann Karl
Cammann Karl
Marshall & Melhorn LLC
Spitzer Robert H.
LandOfFree
Device and method for sampling in liquid phases using a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Device and method for sampling in liquid phases using a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Device and method for sampling in liquid phases using a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2576822