Patent Application
20190011421
The embodiments described herein relate generally to detection techniques for chemical substances, and, more particularly, to contacting a doped membrane with a substance of interest, thereby increasing the detection sensitivity and/or selectivity for the substance of interest. More specifically, the methods and systems include contacting a substance of interest with a doped membrane comprising at least one semi-permeable medium doped with an acid. The systems and methods further include desorbing the doped membrane to release the substance of interest and performing an analysis on the substance of interest to detect the substance of interest.
Certain substances of interest (e.g., narcotics, energetic materials, explosives such as home-made explosive (HMEs)) have low vapor pressures and high melting points, making their detection a challenge using conventional trace detection systems and methods. In some instances, it is desirable to increase the volatility of the substance of interest (such as through chemical modification) for improved detection. For safety reasons, it is desirable to provide methods and systems for increased substance of interest volatility that presents minimal chemical exposure risk to users/operators and other contacted items. In some instances, it is additionally advantageous to increase substance of interest volatility without requiring significant alteration or adaptation of conventional trace detection system hardware or sample throughput.
There is a need, therefore, for trace detection systems and methods that utilize a sensitive, low-cost approach for detecting substances of interest having low volatilities with little to no modification of instrument hardware or throughput, while minimizing chemical exposure. The present disclosure achieves these benefits by utilizing doped membranes to contact and modify a substance of interest, effectively increasing its volatility and improving detection thereof. In particular, chemical modification for increased volatility of a substance of interest may be achieved through contact with a doped membrane, such as a semi-permeable medium doped with an acid.
In one embodiment of the present disclosure, a device for detecting a substance of interest is disclosed. The device includes a doped membrane, wherein the membrane comprises at least one semi-permeable medium and is doped with at least one acid.
In another embodiment of the present disclosure, a method for detecting a substance of interest is disclosed. The method includes contacting a substance of interest with a doped membrane, wherein the membrane comprises at least one semi-permeable medium and is doped with at least one acid. The method also includes heating the substance of interest and the doped membrane in a desorber. The method further includes performing an analysis of the substance of interest and detecting the substance of interest.
In yet another embodiment of the present disclosure, a system for detecting a substance of interest is disclosed. The system includes an inlet configured to receive a substance of interest. The system also includes a doped membrane, wherein the membrane comprises at least one semi-permeable medium and is doped with at least one acid. The system further includes a desorber and an analysis device coupled in flow communication with the inlet and the desorber, wherein the analysis device is configured to perform an analysis on the substance of interest.
Trace detection systems are utilized for analyzing, detecting, and identifying various substances of interest, such as explosives and narcotics. In some embodiments of the present disclosure, a doped membrane is contacted with the substance of interest to increase detection sensitivity and/or selectivity of the substance of interest by increasing its volatility. In some embodiments, the substance of interest includes at least one of an explosive, an energetic material, a taggant, a narcotic, a toxin, a chemical warfare agent, a biological warfare agent, a pollutant, a pesticide, a toxic industrial chemical, a toxic industrial material, a homemade explosive, a pharmaceutical trace contaminant and combinations thereof. In some embodiments, a substance of interest comprises an inorganic salt such as an inorganic oxidizer salt, which is becoming increasingly prevalent in various home-made explosives (HMEs) and poses a significant detection challenge in trace detection systems that rely on vaporization of the sample or substance of interests for detection, due to their low volatilities and high melting points.
The doped membrane is comprised of at least one semi-permeable medium that is doped with at least one acid. In some embodiments, the membrane is an ion exchange membrane. In some embodiments, the semi-permeable medium is a polymer or copolymer. For example, in some embodiments, the semi-permeable medium is a polybenzimidazole (PBI) copolymer. The at least one acid is an organic acid or an inorganic acid. In some embodiments, the organic acid is at least one of trifluoroacetic acid and formic acid. In some embodiments, the organic acid is a strong organic acid with a low molecular weight. In some embodiments, the inorganic acid is at least one of phosphoric acid and polyphosphoric acid. In some embodiments, the inorganic acid is an inorganic acid having an acidity lower than that of phosphoric acid (i.e., pKa1 of from about 2.10-2.20, or about 2.14). The semi-permeable medium is doped with the acid at a concentration of from about 0.50 weight percent to about 20 weight percent of the acid. In some embodiments, the semi-permeable medium is doped with the acid at a concentration of from about 1 weight percent to about 5 weight percent of the acid.
Once doped and thermally treated, the acid has a slow diffusion rate at ambient/room temperatures (see Tables 1a and 1b) and is not released from the semi-permeable medium. Consequently, the doped membrane has generally neutral surface pH. For example, the diffusion rates of phosphoric acid in PBI membranes are a function of the water content, temperature and phosphoric acid content of the PBI membrane. The molecular/ionic species that are diffusing in the membrane change with temperature, water content and molar ratio of the phosphoric acid versus the repeated subunit of the polymer, such as benzimidazole units in the PBI membrane. As the water content decreases, phosphoric acid condenses to larger polyphosphoric acids. These are primarily dimers and trimers having higher acidity, higher viscosity, and lower hygroscopicity than that of phosphoric acid.
Because phosphoric acid is a weak acid (pKa of 2.1), a mixture consisting of free acid, polyphosphoric acids and the corresponding ions is present in aqueous solutions. Perchloric acid (pKa−10) and chloric acid (pKa−1) are strong acids with a Ka>1, and completely dissociate in aqueous solution. Generally, protons move to the stronger conjugate base, the phosphate anion, yielding phosphoric acid instead of forming the inorganic oxidant acids. However, if phosphoric acid condensation takes place on the surface during drying of the membrane after doping or during the desorption process, dimers (pyro-phosphoric acid, pKa 0.8 to −0.5) and trimers (tri-phosphoric acid, pKa 0.5 to −0.5) are formed with a much higher acidity, thus pushing the protonation in the direction of inorganic oxidant acid formation.
Removal of hydration water inside the membrane together with a polycondensation step makes water available to solvate or dissolve any inorganic oxidants on the surface of the doped membrane during the initial stage of the desorption. The energy of the subsequent proton exchange step is lowered by lowering the energy required for separating cation and anion of the inorganic oxidant salt. Polyphosphoric acids or polyphosphoric acid cations supply the protons to form a volatile conjugate acid of the inorganic oxidant (i.e., a modified form of the substance of interest). The formation of the active, highly acidic, polyphosphoric acid can be controlled. Because the polycondensation primarily takes place at elevated temperatures, the weakly acidic phosphoric acid is present during the sample collection prior to desorption. This is in contrast to Nafion polymer based ion exchange membranes and conventional sample swabs.
Continuing with the present example, the phosphoric acid loading of a PBI membrane shows a clear stepwise increase in membrane conductivity reflecting the protonation of the first benzimidazole nitrogen followed by protonation of the second nitrogen. This is a basic group titration process that takes time at ambient/room temperature (e.g., hours) as the phosphoric acid has to penetrate the polymer network. The corresponding phosphate anions remain bonded to the doubly protonated imidazole group of the membrane and do not take part in either phosphate or proton diffusion. After the neutralization of the basic groups, further phosphate uptake is observed as a result of hydrogen bonding with the phosphate groups bound to the PBI backbone. In some embodiments, PBI membranes can be loaded with up to 20 phosphate groups per benzimidazole group. Loading above 20 phosphate groups per benzimidazole group causes the membrane to become unstable. The amount of water present in the membrane determines the transfer mechanism of protons and phosphoric acid species and thereby the diffusion rate of these species.
Tables 1a and 1b show proton and phosphate diffusion rates, respectively, for phosphoric acid at relatively low concentrations. The diffusion rate of phosphoric acid inside the PBI copolymer goes up by three orders of magnitude at 240° C. in comparison to the diffusion rate at ambient temperature (25° C.). For instance, the diffusion rate of phosphoric acid at 25° C. is 10−8 cm2 sec−1, while at 240° C. the diffusion rate of phosphoric acid is 10−5 cm2 sec−1 (see Table 1b). Accordingly, the effect of temperature on the diffusion rate of phosphoric acid within a PBI membrane is significant.
In accordance with the present disclosure, the doped membrane described herein has a generally neutral surface pH of from about 6.0 to about 7.0. This feature is beneficial for safety reasons, presenting minimal risk of chemical (e.g., acid) exposure to anyone handling the doped membrane or to other items contacted by the doped membrane (e.g., sampled luggage, cargo, freight, packages, mail, etc.). In some embodiments, the surface pH of the doped membrane is 6.5. The doped membrane has a thickness of from about 10 μm to about 1000 μm. In some embodiments, the thickness of the doped membrane ranges from about 25 μm to about 900 μm, from about 50 μm to about 750 μm, from about 75 μm to about 500 μm, or from about 100 μm to about 250 μm.
The doped membrane is used to contact and modify a substance of interest to increase its volatility and thereby improve detection selection and/or sensitivity by a trace detection system. Analysis of the modified substance of interest by the trace detection system results in detection and identification of the corresponding un-modified substance of interest that was originally sampled. In some embodiments, the trace detection system includes one or more libraries for identifying substances of interest based on the analysis of the modified, more volatile substance of interest.
In some embodiments, the substance of interest includes at least one of an explosive, an energetic material, a taggant, a narcotic, a toxin, a chemical warfare agent, a biological warfare agent, a pollutant, a pesticide, a toxic industrial chemical, a toxic industrial material, a homemade explosive, a pharmaceutical trace contaminant and combinations thereof. In some embodiments, the substance of interest includes an inorganic salt. For example, the inorganic salt includes at least one of a nitrate, a chlorate, a perchlorate, nitrites, a chlorite, a permanganate, a chromate, a dichromate, a bromate, an iodate, and combinations thereof.
In some embodiments, the doped membrane is incorporated into a sample swab and comprises at least a portion of an outer surface of the sample swab. The sample swab with incorporated doped membrane is used to collect a sample containing at least one substance of interest, and is introduced into a trace detection system inlet. In some embodiments, the substance of interest is chemically modified upon contact with the doped membrane to a more volatile form. The trace detection system includes a desorber which desorbs the sample swab with incorporated doped membrane and releases the modified, more volatile substance of interest for subsequent analysis and detection by the trace detection system.
In some embodiments, the doped membrane is not incorporated into the sample swab. Rather, the doped membrane is positioned within the desorber of the trace detection system. A sample swab is used to collect a sample containing at least one substance of interest and is introduced into the inlet and desorber of the trace detection system. The doped membrane comes into contact with the substance of interest within the desorber by contacting the sample swab (or other sample media). For instance, in some embodiments, the doped membrane is coupled to a mechanical arm that is configured to move the doped membrane for contact with the sample swab. In other embodiments, the mechanical arm is coupled to the sample swab, or is coupled to both the sample swab and doped membrane, such that the doped membrane and the substance of interest on the sample swab come into contact with each other. In some embodiments, a desorption cycle is initiated following contact between the doped membrane and the substance of interest (via contact with the sample swab). In some embodiments, a desorption cycle is initiated after the sample swab has been introduced into the desorber, yet prior to contacting the substance of interest with the doped membrane within the desorber. In these embodiments, the desorption cycle is begun prior to contacting the substance of interest with the doped membrane in order to minimize any potential alteration of the desorption process of other substances of interest (e.g., more conventional explosives) that might be present on the sample swab. Accordingly, the sample swab is contacted with the doped membrane after a suitable amount of time in the desorption cycle and/or after a suitable desorption temperature has been reached.
Once a doped membrane has contacted a substance of interest, the doped membrane and substance of interest are heated in a desorber and the modified, more volatile substance of interest is released for subsequent analysis and detection by the trace detection system. In some embodiments, the substance of interest is released by heating the desorber to a temperature of from about 150° C. to about 270° C.
The substance of interest can be detected using at least one of an ion mobility spectrometer (IMS), an ion trap mobility spectrometer (ITMS), a drift spectrometer (DS), an aspiration ion mobility spectrometer, a non-linear drift spectrometer, a field ion spectrometer (FIS), a radio frequency ion mobility increment spectrometer (IMIS), a field asymmetric ion mobility spectrometer (FAIMS), an ultra-high-field FAIMS, a differential ion mobility spectrometer (DIMS), a differential mobility spectrometer (DMS), a trapped ion mobility spectrometer (TIMS), a traveling wave ion mobility spectrometer, a semiconductor gas sensor, a raman spectrometer, a laser diode detector, a mass spectrometer (MS), a gas chromatograph (GC), an electron capture detector, a photoionization detector, a chemiluminescence-based detector, an electrochemical sensor, an infrared spectrometer, a lab-on-a-chip detector and combinations thereof.
The bottom spectrum shows a stronger intensity response for KClO4 (approximately over 6000 arbitrary intensity units) within the range of interest. Accordingly, KClO4 is successfully detected using a doped membrane for increasing volatility and improving detection.
In some embodiments, desorber 808 begins heating the doped membrane 806 following contact between the doped membrane 806 and the substance of interest (via contact with the sample swab 804). In other embodiments, desorber 808 begins heating after the sample swab 804 has been introduced into the desorber 808, yet prior to contacting the substance of interest (collected on sample swab 804) with the doped membrane 806 within the desorber 808. In these embodiments, desorption heating is begun prior to contacting the substance of interest with the doped membrane 806 in order to minimize any potential alteration of the desorption process of other substances of interest (e.g., more conventional explosives) that might be additionally present on the sample swab 804. In some embodiments, the sample swab 804 is contacted with the doped membrane 806 after a suitable amount of time in the desorption cycle and/or after a suitable desorption temperature has been reached. In some embodiments, the desorber 808 is heated to a temperature range of from about 150° C. to about 270° C. In some embodiments, the desorber 808 is heated to a temperature range of from about 200° C. to about 250° C. Analysis device 810 is configured to perform an analysis on the substance of interest and detect the substance of interest.
In some embodiments of the present disclosure, the substance of interest detected by the detection system 700 or 800 includes at least one of an explosive, an energetic material, a taggant, a narcotic, a toxin, a chemical warfare agent, a biological warfare agent, a pollutant, a pesticide, a toxic industrial chemical, a toxic industrial material, a homemade explosive, a pharmaceutical trace contaminant, an inorganic salt, a nitrate, a chlorate, a perchlorate, a nitrite, a chlorite, a permanganate, a chromate, a dichromate, bromates, an iodate, and combinations thereof.
In some embodiments of the present disclosure, the analysis devices 710 and 810 include at least one of an ion mobility spectrometer (IMS), a reverse ion mobility spectrometer, an ion trap mobility spectrometer (ITMS), a drift spectrometer (DS), an aspiration ion mobility spectrometer, a non-linear drift spectrometer, a field ion spectrometer (FIS), a radio frequency ion mobility increment spectrometer (IMIS), a field asymmetric ion mobility spectrometer (FAIMS), an ultra-high-field FAIMS, a differential ion mobility spectrometer (DIMS), a differential mobility spectrometer (DMS), a trapped ion mobility spectrometer (TIMS), a traveling wave ion mobility spectrometer, a semiconductor gas sensor, a raman spectrometer, a laser diode detector, a mass spectrometer (MS), a gas chromatograph (GC), an electron capture detector, a photoionization detector, a chemiluminescence-based detector, an electrochemical sensor, an infrared spectrometer, a lab-on-a-chip detector, and combinations thereof.
Exemplary embodiments of detection systems for determining the presence of substances of interest, and methods of operating such systems are not limited to the specific embodiments described herein, but rather, components of systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein. For example, the methods may also be used in combination with other systems requiring determining the presence of substances of interest, and are not limited to practice with only the substance detection systems and methods as described herein. Rather, the exemplary embodiment can be implemented and utilized in connection with many other substance detection applications that are currently configured to determine the presence of substances of interest.
Although specific features of various embodiments of the disclosure may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the disclosure, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing.
Some embodiments involve the use of one or more electronic or computing devices. Such devices typically include a processor or controller, such as a general purpose central processing unit (CPU), a graphics processing unit (GPU), a microcontroller, a reduced instruction set computer (RISC) processor, an application specific integrated circuit (ASIC), a programmable logic circuit (PLC), and/or any other circuit or processor capable of executing the functions described herein. The methods described herein may be encoded as executable instructions embodied in a computer readable medium, including, without limitation, a storage device and/or a memory device. Such instructions, when executed by a processor, cause the processor to perform at least a portion of the methods described herein. The above examples are exemplary only, and thus are not intended to limit in any way the definition and/or meaning of the term processor.
This written description uses examples to disclose the disclosure, including the best mode, and also to enable any person skilled in the art to practice the disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
