CA2043825A1 - Method of detecting explosives and other substances in samples of ground material - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A method of detecting the presence of substances, such as explosives, environmental pollutants, hydrocarbons and organic materials, in a sample of ground material comprised of soil, a micro layer of soil, liquid, or a combination thereof is presented. The method involves the collecting of a discrete sample of such ground material from an area that may contain said substances and depositing the sample on a teflon filter or other collection medium. The filter is then placed in a sample holding unit adjacent an inlet to an ion mobility spectrometer (IMS) or other suitable instrument for detecting the substances. The sample holding unit is then heated, typically to a temperature of about 180 degrees C
or higher, to vaporize matter from the collected sample atop the filter. The vaporized matter is then entrained in a flow of gas which passes said matter into the IMS, thereby to analyze the vaporized matter and determine the presence of said substances.

Description

2~L38~

RBP File No. 738-416 Title: A METHOD OF DETl~CTING EXPLOSIVE:S
AND OTHER gUBSTANCES IN SANPI~S OF GROUND MATERIAI.

FIELD OF l~IE INVE~TION
The invention relates to a method of detecting the presence of substances in a discrete sample of ground material, whether solid or li~uid.
In particular, matter from the ground material is analyzed by an instrument, such as an ion mobility spectrometer (IMS), to detect substances such as explo ives and their composition, hydrocarbons, organic materials and environmental pollutants.
BaCRGROUND OF THE I~V~TIO~
As environmental laws and requlations become more stringent, the demand grow for effective methods of detecting the presence and composition of surface and subsurface pollutants and otherwise potentially toxic or dangerous substances.
For instance, there is a need for techniques of locating underground "explosive graveyard" sites where explosives are buried or were previously buried and later removed. As well, there is a need to locate surface sites where explosive have been previously stored or manufactured. Numerous sites and large quantities of explosives were created during the two grea world wars, these site~ having been abandoned, diæmantled or destroyed thereafter. With the passage of time and as records are lost, it is becoming increasingly difficul~ to locate these "graveyardsll and surface sites. Such cont~minated sites must, however, be rehabilitated to reduce their threat to the environment, but they must be located first.
No efficient method has yet been de~eloped to detect and locate such site~. Some existing methods consist of deep trenching or drilling operations. These locating methods are dangerous if explosives are : . .
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3~5 -encountered in the process. Other methods include the detonation of small quantities of explosive charges, thereby creating subsurface shock waves which may detonate buried explosives if encountered. These methods may also be dangerous, expensive and time consuming.
There is also a need for effective methods of detecting subsurface hydrocarbons and organic materials, including those associated with mineral deposits. Oil companies engaged in oil and gas exploration are examples of users of existing methods which include drilling and geophysical techniques, and, recently, exploration geochemistry.
Exploration geochemistry is based on the theory that surface soils carry a "chemical signa~ure" or ~imprint" o~ substances found beneath the ear~h's surface.
Exploration geochemistry has been successfully applied to mineral exploration, and more recently to hydrocarbon exploration. It has been recognized that geochemical effects have developed in surface soils overlying qubsurfaces containing oil and gas accumulations. The seepage of oil and gas used as an indicator of the presence of subsurface petroleum accumulations. The technique of exploration geochemistry is aimed at detecting trace levels of these oil~ and gas which have reached the surface. The technique has also been used to detect secondary products of such seepage, such as paraffin dirt formed by microbiological synthesis in soils where natural gas seepage has occurred. In most cases, such seepage is at a trace level, and must be measured by sensitive geochemical analysis.
Various studies show that specific geochemical changes can be idPntified in the surface layer of soils over-lying both minerals and- hydrocarboni. The dynamic effects of macro and micro seepage can also penetrate recen~ly tran ported over burdens. In such studies, a variety of organic and inorganic geochemical parameters have been measured with results that reflect the different . ; , . , : . : . . . . .

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ZO~ 5 chemistry of sedimentaxy basins, either fluids and hydrocarbons and mineral accumulations.
~ he technique of exploration geochemistry consists of collecting surface soil samples and subjecting them to sensitive chemical analysis, and using the information gathered from these tests to help determine the presence, and quantity o~, subsurface hydrocarbons and organic materials. As alluded to above, this technique has been successfully applied to mineral and hydrocarbon exploration, having contributed to the discovery of major oil producing areas. Improvement3 in the productivity and sensitivity of analytical methods are such that surface geochemical surveys have become co~t effective and are applied routinely to surface sample analysis in searches for hydrocarbons and minerals.
The present invention adopts this methodology, and also extends it use to`the realm of location and detection of explosives as previously described.
The movement of subsurface groundwater may deliver to the surface trace amounts of explosive material from its subsurface location. As the groundwater evaporates at the surface, the residue left behind in the surface soil retains the "signature" of the explosive.
The explosives herein discussed have generally been buried for an extended period of time, thus giving the groundwater ample opportunity to act on the subsurface explosives and to transport them to the surface.
Nonetheless, the dynamic effects of macro and micro seepage may also penetrate to the surface of recently transported overburdens. ~huq, the invention may be used in such locations as well.
A further advantage of the invention is that discrete surface soil samples, or a micro layer thereof, may be collected and rapidly analyzed on the spot. Such insitu sampling may employ any number of different instruments for said analysis, including a portable IMS.

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SUM~ARY OF TH~ INYENTION
According to the present invention, there is provided a method of detecting the presence of substances in a sample of ground material, the method comprising the steps of:
(i) collecting a discrete sample of ground material from an area that may contain said substances;
(ii) depositing the collected sample on a collection medium, and then placing the collection medium in a sample holding unit adjacent an inlet to an instrument for detecting the substances;
(iii) heating the collection medium and the sample adjacent the instrument inlet to vaporize matter from the collected sample; and (iv) entraining the vaporized matter in a flow of gas and passing that flow of gas into the instrument, thereby to analyze the vaporized mattex and determine tha presence of said substances.
It is to be appreciated that in this specification, including the claims, the term ~ground material" refers to any matter located at the earth~s surface which can be readily collPcted in discrete samples for purposes of analysis; the ground material can comprise one or more of soil, sand/ clay, water, liquid, etc., or any combina~ion thereof.
One embodiment of the invention is directed to a method of detecting the presence o~ substances in a sample of qround material wherein the instrument for detectin~ the xubstances is an IMS.
The data from the IMS is compared to known mobility spectra of substances to be detected to identify which o~ these substances are present in the sample of matter. Therefore, for example, the invention may be used to detect the presence of various explosives, including plastic explosives, by comparing the data from the IMS to the known mobility spectra for explo~ivs materials such as RDX, HMX, PETN, TNT, DNT, etc. Such comparison may be .. :

2~ 5 done using known modern computer techniques and data analysis.
The invention has broad applications. It may be used to locate and detect subsurface explosives buried many years ago or Yery recently, including land mines and other military devices, as well as surface contamination from explosives manufacturing plants, either existing or decommissioned ones, and from other external sources.
Thus, the invention has forensic applications in the identification of explosives relating to criminal and terrorist activities. For example, it may be used to locate terrorist explosive production fa~ilities or to help evaluate whether an explosion at a location was caused by explosives and, if so, what kind of explosives were used.
The invention may also be used to detect environmental pollutants at the surface, whether they have migrated form the subsurfaces or have been introduced from above-surface sources internal to the site under evaluation. It may further be adapted for use in detecting th~ presence of su~surface hydrocarbons and organic materials, including those associated with mineral deposits.
BRIEF D~SCRIPTIC~ OF ~H~ DRAWI~GS
2S Embodiments of the invention will now be deæcribed, by way of example only, with references to the accompanying drawings, wherein:
Figure 1 is an elevated side view partially in ~ection of an apparatus comprising a portion o the invention;
Figure 2 i~ a plasmagram of a P~TN explosive;
Figure 3 is a plasmagram of an uncontaminated soil sampled;
Figure 4 i5 a plasmagram of a soil sample collected at a PETN contaminated ~ite; and Figure 5 is a plasmagram of a sample comprised of water and sand slurry collected at a P~TN contaminated .

2~43~25 , site.
Referring to Figur~ 1, an IMS analysis instrument is designated with references 3. The instrument 9 has a main body 19, provided with conduits 22 fox the supply and withdrawal of gases necessary for the operation of the IMS. Here, for simplicity, the detailed gas circuitry and gas flow control elements are omitted.
The mains body 19 includes an inlet 7 for a carrier gas bearing a sample. As discussed below, the inlet 7 may optionally include a membrane 17~
Below the main body 19, thexe is a sample holding unit 3, with an o-ring seal 23 for an actual sample holder Z5. The sample holding unit 3 can be dropped by 3.5 mm to permit insert of the sample holder 25. The holder 25 holds a collecting medium or filter 5.
After insertion of the holder 25, the holding uni~ 3 is raised to press it against the instrumQnt 9 and seal the sample within the instxument.
Within the sample holding unit 3, there is a heater 11. The heater is configured to heat a collection medium 5 heating a suitable sample. Conduit 15 is provided for a gas flow, the gas flow being indicated at 13.
Sample 1 may be a ~olid or liquid, a~ detailed below.
A description will now be given of a mode of operation of the instrument 9 of Figure 1. A discrete sample of ground material 1 was coll~cted from an area under investigation that may contain certain suspected substances. The ~ample of ground material 1 may be collected by hand or by any appropriate known mechanical means. The collected sample 1 was ~hen deposited on a collection medium 5 inserted in the sample holder 25, and then inserted above the sample holding unit 3 adjacent ~he inlet 7. ~he process of collecting the sample 1 and depositing it on collection medium 5 may be accomplished with a vacuuming device (not shown) adapted from such a - , : . : : . , - : `;, , .! , : '':, :
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~Oa~3~3Z5 task wherein the sample of ground materi~l i3 vac~umed or withdrawn form the surface of the rare under investigation by an air flow which passes through a porous filter or collection medium 5 to depo^~it said sample thereon.
The collection medium 5 may he comprised of a filter, which filter is capable of withstanding any temperature~ necessary to vaporise said collected sample thereof. The filter may be made of organically inert material, such as teflon. It may be appreciated that the collection medium 5 may be comprised of a plurality of these filters, such that each filter individually can be placed in the holding unit 3 for analysis of the collected sample 1 thereon.
The filter 5 may also be in the form of an elongate tape providing a service of collection mediums that are subsequently moved past a collecting port. ~he tape can si~ilarly be moved sequen$ially past the inlet 7 to the INS in~trument 9.
After having been placed above the sample holding unit 3, the collection medium 5 and the sample 1 are heated by the heater ll to a temperature neces~ary to vaporise matter from the collec~ed sample 1. Thi~
temperature may reach 180 degrees C or higher. This vaporized matter, which is in a gaseous form, may contain the substances being searched for.
The carrier gas flow 13 is then passed through conduit 15 to entrain the vaporised matter in said flow o gas 13. The carrier gas with en~rained vaporised matter then pa88e8 into the main body 19 of the instrument 9 through inlet 7. Once in the instrument 9, the evaporated matter is analyzed, in known manner, to determine the presence of the substances of interest, as detailed below.
The instrument 9 comprises an INS of know configuration. It may or may not have a membrane 17 in the vicinity of inlet 7, or alternatively a fine mesh or screen to capture only solid particles trained in the gas flow. It will be appreciated that the INS must be capable , - " . . ~:
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of high temperature operation to withstand the temperatures of the gas flow 13 entering the IMS, as well as itself capable of being temperatures controlled.
In another aspect to the invention, the instrument 9 which must be sensitive, may be one or more of a mass spectrometer, a gas chromatograph, an optical emission spectrometer, an array spectrometer and an infrared analyzer. --The IMS 9 gives, as an output, plasmagrams, such as are shown in Figure 3, 4 and 5. These are then compared against known mobility ~pectra for substances of interest, such as the plasmagram in Figure 2 for the explosive PETN.
The description and analysis of the plasmagrams in Figure 2, 3, 4 and 5 follows. For all these plasmagrams, the IMS instrument 9 was operated under similar conditions. It was maintained at a temperature of 180 degrees C.
For all these plasmagrams, the similar peak~ are given the same peak number. Peaks l, 3 and 5 correspond to substances which can be used, effectively, for calibrating the individual plasmagrams. Peak 9 is distinctive of DNT with peak lO being distinctive of TNT.
Peak 11 is indicative of RDX, whilst all of peaks 12, 13, 14 and 15 are indicative of the explosive PETN.
In these Figures, the window or time during which the sample is taken is indicated as "Nind" in the top right-hand corner. The drift time is given in millisec. and the reduced mobility is indicated as Red Mobil, in unit~ of cm2/volt.~ec.
Along the bottom of each of these Figures, the Signal Range gives the vertical scale.
The total number of window~ making up the complete window is indicated as "Wnds". ~ach of these 3~ windows comprises a certain number of sweep~ indicated as "Swps" and each spaced at an interval ~T. Each sweep in turn comprises a number of points indicated as "Pts", ' ' .
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~04;~Z5 _ g _ spaced by time interval indicated at ~t. Thus, for Figure 2, the spacing of the points was 25 ys. and there are 780 points in each sweep, for a total tims of 19.5 ms. With 16 sweep~ in each window and a ~t of 20 ms, this give~ a S window length of .32 seconds. This gives a total of 4.48 seconds.
The reduced mobility or Red Mobil of an ion is a parameter that should be monitored Reduced mobilities are calculated from the ratio of the reference peak positionl peak 3 in Figure 2, to the peak of interest on the pla~magram. If the peak is located incorrec~ly then the reduced mobility would be in error.
The reduced mobility of an ion, which i8 an intrinsic property of that ion, is defined as:

Ko= d ToP (cm2V'.s'~
E tD PoT
where: d - drift tube length (cm) (constant for a particular IMS) To - absolute temperahlre (273K) P - opera~ng pressure (torr), function of an environment pressu~e PO - reference pressure (760 torr) T - operating tempera~ preset, but may vary i 4C.
E - elec~ic field in the dr;ft tube region v/cm, may vary slightly (~1%~
tD - ion drift ~ne (s) If any operating parameter such as electric field, temperature, pressure or drift tube length is changed the ion drift time will change; however, the reduced mobilities will remain con~tant.
As noted belo~, some molecules will give a multi-peaked formationO This is due to fragmentation of the original molecule during the ionization process, and molecule/ion clustering. In Figure 2, for example, peak 12 is believed to originate from an electron a~tachment to the PETN molecule, while peaks 13, 14 and 15 are rom a molecular ion cluster formation of P~TN with Cl-NO2 and NO3.
An abundance of ions in the ioniza$ion region with which .
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~0~3825 -- 1 o PETN will form a stable cluster will dictate which particular ion cluster will be dominant. The presence of Cl- reactant tend~ to smooth out these variation~ to ~ome degree.
Where an asterisk is indicated by Red ~obil, this means that the reduced mobility has been fixed to that value and any change in the reference material, a double asterisk by peak 3 position, is due to either tempsrature, pressure or electrical field. The analyte peak is automatically repositioned according to its reduced mobility.
Figure 3 shows a ~ackground plasmagram for an uncontaminated soil sample. Consequently, th~ only peaks of any significance are peak~ l, 3 and 6, showi~g the calibrating substances. The remaining peaksj 9-15 inclusi~e are not present showing that none of the explosive substances of interest are present in the soil sample.
Referring to Figure 4, this shows a plasmagram for a soil sample collected at a PET~ contaminated si$e.
Here, the peaks 1 and 3 are present, although there is no significant peak S. For the explosive DNT, TNT and RDX, the peaks 9, 10 and 11 are insignificant, indica~ing not significant amount of these explosive present. Peak~ 12, 13, 14 and 14, are all clearly visible, thereby giving a clear indication that the sample is contaminated with PETN.
Referring to Figure 5, this IMS plasmagram i form a sand/water slurry sample obtained from a PETN
contaminated there is no significant peak 1. The explo~ives DNT, TNT and RDX, corresponding to peaks 9, 10~
11, respectively are presently absentO Although there i5 was no ~ignificant peak 12, there are significant peaks 13, 14 and 15 indicative of the present of the explosive 35 PE'rN.
It should further be noted that, whilst these plasmagrams are presented give only a qualitative .

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indication of the present of the relevant material, the instrument could be calibrated so as to give a quantity measure of the presence of the substances of interest.
As mentioned, a membrane 17 could be provided although it is preferred for this to be omitted.

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Claims (21)

1. A method of detecting the presence of substances in a sample of ground material, the method comprising the steps of:
(i) collecting a discrete sample of ground material from an area that may contain said substances;
(ii) depositing the collected sample on a collection medium, and then placing the collection medium in a sample holding unit adjacent an inlet to an instrument for detecting the substances;
(iii) heating the collection medium and the sample adjacent the instrument inlet to vaporize matter from the collected sample; and (iv) entraining the vaporized matter in a flow of gas and passing that flow of gas into the instrument, thereby to analyze the vaporized matter and determine the presence of said substances.

2. A method as claimed in claim 1, wherein the instrument is an ion mobility spectrometer (IMS).

3. A method as claimed in claim 2, wherein the IMS
has no membrane.

4. A method as claimed in claims 2 or 3, wherein the temperature of the IMS is controlled.

5. A method as claimed in claims 1, 2, 3 or 4, wherein data from the instrument is compared to known mobility spectra of substances to be detected to identify which of these substances are present in the collected sample.

6. A method as claimed in claim 1, wherein the sample of ground material is collected and deposited during steps (i) and (ii) using a vacuuming device.

7. A method as claimed in claim 1, wherein the collection medium comprises a filter capable of withstanding the temperatures necessary to vaporize the collected sample.

8. A method as claimed in claim 7, wherein the filter is made of material which is organically inert.

9. A method as claimed in claim 8, wherein the filter is made of teflon.

10. A method as claimed in claim 7, wherein the collection medium comprises a plurality of filters.

11. A method as claimed in claim 10, wherein the plurality of filters comprises individual locations along an elongate tape.

12. A method as claimed in claim 11, wherein the tape comprises a teflon tape.

13. A method as claimed in claim 12, wherein sample collection is effected by traversing a ground micro layer with a vacuuming device and depositing samples directly onto the teflon tape, and where the tape is sequentially incremented past the inlet of the instrument.

14. A method as claimed in claim 1, wherein during step (iii) the collection medium is heated to a temperature of about 180 degrees C or higher, and during step (iv) the instrument inlet and the instrument are maintained at a temperature above the ambient air temperature.

15. A method as claimed in claim 14, wherein during step (iv) the flow of gas is maintained at a temperature above the ambient air temperature.

16. A method as claimed in claim 1 or 3, wherein the collected sample comprises at least one of: a sample of soil; a micro layer of soil; and a liquid sample.

17. A method as claimed in claim 16, wherein the method is adapted to detect one or more of the explosives, HMX, RDX, PETN, DNT and TNT, plastic explosives, any other explosives, land-mines and military devices.

18. A method as claimed in claim 17, when applied to the identification and forensic analysis of the origins of explosive compositions and devices.

19. A method as claimed in claim 16, when applied to the detection of toxic materials and other surface contaminants causing environmental pollution.

20. A method as claimed in claim 16, when applied to one of the detection of hydrocarbons, associated with hydrocarbon deposits, and the detection of organic associated with mineral deposits.

21. A method as claimed in claim 16, when applied to the detection of organic compounds associated with mineral deposits.