Patent Description:
Detection kits might contain several reagents or host compounds to cover a wider range of classes of explosives and to differentiate between them. Chemical methods usually need sample preparation. There are several methods for the chemical detection of nitrogen-based explosives; however, there is only a limited number of colorimetric detection methods for peroxide-based explosives:
<CIT> (Ehud Keinan und Harel Itzhaky) describes a colorimetric method and kit for the detection of peroxide based explosives (cyclic peroxides), such as triacetone peroxide (TATP), diacetone peroxide (DADP) and hexamethylene triperoxide diamine (HMTD). Peroxide detection is based on a two-step process. The first step involves dissolution of the suspected material in an organic solvent and the hydrolysis of the cyclic peroxide with strong acids into acetone and hydrogen peroxide. In the second step, the acidic solution is neutralized with a buffer and the hydrogen peroxide is detected by the color change of a redox active dye oxidized by the hydrogen peroxide and a peroxidase enzyme. The patent includes a kit for the practical use of the invention including an organic solvent, a strong acid, a solution of the buffer, a peroxidase enzyme and the redox active dye. The reason for this rather complicated detection procedure is the fact that a strong acid is needed for the cleavage of the cyclic peroxide (explosive), however, the actual colorimetric detection can only be performed at neutral pH. Therefore, neutralization of the solution is necessary as an intermediate step.

<NPL>) for colorimetrically detecting TATP describe a process in which a gaseous sample flows through a bed of the acid form of a sulfonated highly cross-linked polystyrene ion-exchange resin Amberlyst <NUM> to achieve acid hydrolysis, with subsequent contacting the reaction products with an array of redox dyes. Since the acid is immobilized in the porous, solid resin, and cleavage of the cyclic peroxide occurs in the gas phase inside the resin, a separate neutralization step is avoided. However, the disadvantage of this procedure is the fact, that only volatile explosives (TATP and DADP) can be detected. Moreover, to develop a sufficient vapour pressure for detection, TATP and DADP must be placed in a container or at least at a place with minimal air exchange. Hexamethylene triperoxide diamine (HMTD), which has a higher sublimation point and a lower vapor pressure as compared to TATP and DADP, cannot be detected. Advantage of the method is the fact that TATP can be discriminated from other oxidizing agents such as hydrogen peroxide and hydroperoxides by exposing the vapor after solid acid hydrolysis to an array of redox active dyes with different reactivities.

Amisar in <CIT> described a method for the detection of chlorate, bromate and/or organic peroxides. The detection kit includes two containers, including an organic solvent, strong acid, an aromatic amine and a transition metal ion.

In a follow-up patent <CIT> Amisar describes a sequential procedure that includes several steps and several reagents to detect <NUM>. perchlorates, <NUM>. nitroaromatic compounds, <NUM>. nitramines, nitroester, chlorate and bromate, <NUM>. peroxides, <NUM>. nitrates from the same sample.

<NPL>) for detecting TATP or HMTD describe the addition of catalase to a liquid test sample for removal of free hydrogen peroxide, followed by extraction with acetonitrile to remove the catalyst, and subsequently irradiating the sample with UV in order to decompose the peroxide-based compounds, and in an enzyme-catalysed reaction colorimetrically detecting the hydrogen peroxide generated by the decomposition reaction.

<CIT>, Detection of explosives and other species, describes the detection of peroxide-based explosives by acid or light induced decomposition to hydrogen peroxide and subsequent detection of the hydrogen peroxide by reaction with oxalic acid esters and detection of the chemiluminescence thereof.

<NPL> describes synthesis of Ni-porphyrins (Ni-tetra(<NUM>-hydroxyphenyl)porphyrins).

<NPL> describes the detection of cyanide (CN-), fluoride (F-) and picric acid using as sensor compound Ni-porphyrins (Ni-tetra(<NUM>-hydroxyphenyl)porphyrins).

<CIT> according to a machine translation describes a Ni-porphyrin carrying a sulfonic acid group or a carboxylic acid group for detecting hydrogen peroxide by measuring the absorption spectrum or the fluorescence in aqueous p-hydroxyphenyl acetic acid at pH <NUM>-<NUM>.

<NPL>) describes analytical methods for detecting neurotoxin such as VX, sarin and especially paraoxon using porphyrin, which can form a complex with Ni2+, embedded in organosilicate.

Without relation to use in detecting explosives<NPL>) describes perhalogenated Ni-porphyrin compounds.

Without relation to use in detecting explosives, <NPL> describes Ni-porphyrin compounds, which when substituted with an acid group have a pKa <NUM>.

Without relation to use in detecting explosives, <NPL> describes the interaction of an acid substituted porphyrin (meso-tetra(<NUM>-carboxyphenyl) porphine) with model membranes.

Optical detection methods of nitroaromatics, nitramines and nitrate esters are reviewed in "<NPL>). Methods to detect nitrogen-based explosives such as inorganic nitrates, organic nitrates and nitramines have been described in: <NPL>), <CIT> and <CIT>.

<CIT> (Determination of explosives including RDX) presents methods to detect nitramines, e.g. RDX and PETN using dyes such as <NUM>,<NUM>-didehydroacridine or <NUM>,<NUM>-didehydroanthracene derivatives that act as a hydride donors upon irradiation with UV light, reducing the nitramines, thereby being converted to fully conjugated acridine or anthracene derivatives. Detection is performed by observation of changes in absorption or emission.

<CIT> (Detection of analytes including nitro-containing analytes) describes a variation of <CIT> wherein the decomposition products after irradiation with UV light react via electrophilic aromatic substitution of electron rich aromatic compounds. Detection is based on an optical signal, which may be a change in absorption or emission.

<NPL> describes that nitrotoluenes, e.g. <NUM>,<NUM>-dinitrotoluene (DNT) or <NUM>,<NUM>,<NUM>-trinitrotoluene (TNT), immediately give rise to a blue (DNT) or a purple color (TNT) upon treatment with an organic superbase.

None of these papers or patents describes a general colorimetric method (detection based on an optical signal) to detect peroxide-based explosives, nitramines, nitrate esters and/or nitrate salts with the same reagent. None of the published methods reports on a colorimetric method to detect peroxide-based explosives (cyclic peroxides) in one stage without a separate activation step using acid, base or UV light.

It is an object of the invention to provide an analytical process for detecting peroxide- and nitrogen-based explosives, with high sensitivity and with only one step of pretreatment of a sample prior to a color reaction that can be detected visually, preferably without spectrophotometric detection. The analytical process preferably can be performed at ambient conditions within a short time, e.g. within <NUM>, within <NUM>, within <NUM>, or less. A further object is to provide a simple-to-use kit-of-parts containing the reactants for use in the analytical process.

The invention achieves the object by the features of the claims, and especially provides an analytical process according to claim <NUM> for detecting explosive compounds in a sample by a color reaction, including contacting the sample with a composition comprising a Ni-porphyrin and a free acid having a pKa of -<NUM> to <NUM>, after pretreatment of the sample with a superbase. The process does not comprise a separate step of hydrolysing the sample suspected of containing a peroxide-based explosive prior to contacting the sample with the composition containing the Ni-porphyrin. For the detection of nitramine-based explosives, the two-step procedure is necessary. The sample is treated with an organic superbase first, and in a second step the sample is contacted with the composition containing the Ni-porphyrin as described above. Pretreatment with the organic superbase does not interfere with the detection of peroxide, nitrite ester and nitrate salts, and it does not impede their detection. So all compounds mentioned above can be detected by the two-step procedure, as for the detection of nitramines, the pretreatment with organic superbase is required. Further, the invention provides a kit-of-parts according to claim <NUM>, suitable to carry out the analytical process.

The analytical process and the kit-of-parts have the advantage of allowing a differentiation between the explosives, as peroxide-based explosives are indicated by the Ni-porphyrin finally generating green color, and that nitrate-based explosives and nitramine-based explosives are indicated by the Ni-porphyrin initially generating green color and finally generating brown color.

Further disclosed is the use of a device in the analytical process, the device comprising the composition comprising or consisting of a Ni-porphyrin, an acid and preferably an acid-stable solvent and preferably a carrier, e.g. a porous carrier, which carrier holds the Ni-porphyrin, acid and acid-stable solvent, wherein the carrier e.g. is a porous and/or swelling liquid adsorbing material that forms a gel, e.g. a membrane of an acid-stable material, e.g. of a synthetic polymer or cellulose, so that the carrier forms a supporting material for a liquid composition.

The process of the invention has the advantage of detecting explosives, because the Ni-porphyrin is acid-stable and the acid decomposes the peroxide-based explosive to generate a hydroperoxide, or hydrogen peroxide, and the nitramine or nitrate esters are decomposed to generate the nitronium ion and/or nitrogen dioxide, which react with the Ni-porphyrin to change its color. Nitramines (e.g. hexogen and octogen) react slowly under these conditions. Therefore, according to the invention, nitramines are first treated with an organic superbase (B) to eliminate nitrite according to the reaction mechanism: (-N(NO<NUM>)-CH<NUM>- + B → -N=CH- + BH+ + NO<NUM>-). After several seconds, e.g. less than <<NUM> reaction time, the procedure described above is applied to detect the generated nitrite (NO<NUM>-).

It was found that the process is extremely sensitive towards peroxides, because it is catalytic in peroxide, e.g. one TATP molecule will result in the conversion of ca. <NUM> Ni-porphyrin molecules to the corresponding cation, which gives a color change from red to green. Nitrogen-based explosives as well accept two electrons per NO<NUM> -group. For instance, nitroglycerine and hexogene are capable of oxidizing <NUM> equivalents of Ni-porphyrin. A high sensitivity is also provided by the fact that Ni-porphyrins exhibit extremely high molar extinction coefficients of their Soret bands. Therefore, only small amounts of the porphyrin need to be used in the invention for visual detection of a color change.

In contrast to the prior art using separate activation of the explosives, e.g. by separate acid or base hydrolysis or UV irradiation, with subsequent detection by a color reaction, the analytical process of the invention detects the above listed explosives in a reaction that only requires contacting the sample suspected of containing the peroxide- or nitrogen based explosive, after the superbase pretreatment, with the composition comprising or consisting of Ni-porphyrin, the acid and optionally acid-stable solvent.

According to the invention, the acid is a free acid that is present in admixture with the Ni-porphyrin and with the optional solvent, but which free acid is not covalently linked to the Ni-porphyrin. The free acid, e.g. in the form of a liquid acid, is one acid or a mixture of at least two acids. Further, the free acid can be in the form of an acid linked to a matrix, which matrix may be the carrier. The acid linked to a matrix can e.g. be a strongly acidic cation exchanger. An acid is generally active to decompose cyclic peroxides, nitramines, nitrate esters and/or nitrate salts, especially a peroxide-based explosive, a nitrate-based explosive or a nitramine-based explosive. The strong base, which is used to activate nitramines is an organic superbase, either in pure form or as a solution in an inert solvent such as acetonitrile. The pKa of this organic superbase preferably is at or above <NUM>.

The Ni-porphyrin, preferably in at least one meso position, has electron-donating substituents, which are aryl groups, e.g. aromatic groups containing at least one phenyl ring, which optionally are substituted with at least one methoxy group, or substituted amino group, or alkyl groups, each having e.g. <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> carbon atoms, linear or branched or cyclic. The Ni-porphyrin can have its meso positions unsubstituted, or the Ni-porphyrin can have one, two, three or all four of its meso positions substituted, preferably with an electron-donating group, which can be the same or independently a different one for each meso position.

According to the invention, the free acid has a pKa value of -<NUM> to <NUM>.

Generally, the acid in all embodiments preferably has a pKa value of at maximum <NUM>, e.g. a pKa value of below <NUM>, e.g. of -<NUM> to <NUM>. For example, p-toluenesulfonic acid has a pKa value of -<NUM>, trichloroacetic acid has a pKa value of <NUM>. Generally preferred, the acid has a pKa in the range from -<NUM> to <NUM>. The pKa value preferably is determined at <NUM> in water. A pKa value of at maximum <NUM> is preferred, because it results in decomposition of peroxide-based explosives that have a cyclic structure such as TATP within <NUM> or shorter, e.g. at <NUM>. At a pKa of the acid below -<NUM> (e.g. triflic acid pKa -<NUM>) the Ni-porphyrin could decompose.

In an embodiment, the acid is a compound, which is in admixture with the Ni-porphyrin, preferably in an acid stable solvent. The acid is a strong acid, e.g. having a pKa of -<NUM> to <NUM> or to <NUM>. The acid preferably is selected from trifluoroacetic acid (pKa <NUM>), pentafluoro propionic acid (pKa <NUM>-<NUM>), heptafluoro butyric acid (pKa <NUM>) or perfluoropentanoic acid (pKa <NUM>-<NUM>) preferably perfluoropentanoic acid, or trifluoroacetic acid, and mixtures of at least two of these.

The acid stable solvent preferably is a solvent that stabilizes cations and radical cations. The acid stable solvent can be an organic halogenated solvent, e.g. methylene chloride, chloroform, <NUM>,<NUM>-dichloroethane, <NUM>,<NUM>,<NUM>-trichloropropane, <NUM>,<NUM>,<NUM>-trichloropropane, <NUM>,<NUM>,<NUM>,<NUM>-tetrachloropropane, <NUM>,<NUM>,<NUM>,<NUM>,<NUM>-pentachloropropane, <NUM>,<NUM>,<NUM>,<NUM>,<NUM>-pentachloropane, fluorinated C<NUM>-to C<NUM>-alcohols, preferably hexafluoro isopropanol (HFIP), or sulfolane or mixtures of at least two of these.

In chlorinated solvents, the acid preferably is trifluoroacetic acid (TFA), pentafluoro propionic acid, heptafluorobutyric acid, or perfluoropentanoic acid. In chlorinated solvents, in fluorinated alcohols, e.g. in HFIP, or in sulfolane the acid can be toluenesulfonic acid. Preferentially, higher boiling solvents are combined with higher boiling acids to prevent rapid evaporation in some embodiments.

Generally, the composition comprising the Ni-porphyrin and acid and optionally a solvent can be held on, e.g. adsorbed on or contained in a solid carrier, which can for example be a porous substance or a gel. The porous substance can e.g. be silica or zeolite or cellulose. The gel can e.g. be an acid stable polymer such as polyvinyl alcohol (PVA) or polyvinyl pyrrolidone (PVP). Preferentially, a gel is used, which contains the acid in the polymer backbone. These gels are commercially available as strongly acidic cation exchange resins such as Amberlite® R-<NUM> or Dowex® <NUM> WX-<NUM>.

The organic superbase should be a neutral base that is soluble in organic solvents and should have a pKa ><NUM> in acetonitrile. These bases are from the families of amidines, guanidines, phosphazenes (Schwesinger bases), guanidinophosphazenes or proazaphosphatranes (Verkade's bases). An example for a suitable amidine is <NUM>,<NUM>-diazabicyclo[<NUM>. <NUM>]undec-<NUM>-ene (DBU, pKa <NUM>). Guanides with sufficient base strengths are for instance <NUM>-t-bu-<NUM>,<NUM>,<NUM>,<NUM>-tetramethylguanidine (pka <NUM>), <NUM>-H-<NUM>,<NUM>,<NUM>-triazabicyclo[<NUM>. <NUM>]dec-<NUM>-ene (pKa <NUM>), <NUM>-methyl-<NUM>,<NUM>,<NUM>-triazabicyclo[<NUM>. <NUM>]dec-<NUM>-ene (pKa <NUM>) or <NUM>,<NUM>-bis(tetramethylguanidino) naphthalene (pKa <NUM>). Most efficient are phosphacene bases (Schwesinger bases), such as t-bu-hexamethylphosphorimidtriamid (P<NUM>-t-Bu, pKa <NUM>) or <NUM>,<NUM>-(dimethylethyl)tris[tris(dimethylamino) phosphoranylidene]phosphorimidic triamide (P<NUM>-t-Bu, pKa <NUM>). <NUM>,<NUM>,<NUM>,<NUM>-Tetramethylguanidine (pKa <NUM>) is not strong enough a base to react with nitramines (hexogene or octogene) (pKa<<NUM>, see above). Aqueous solutions of NaOH or KOH are not suitable as well because of long reaction times even at elevated temperatures.

As an alternative to holding the composition on a carrier, the composition can be contacted in the form of droplets with the sample, e.g. by spraying a liquid composition containing the Ni-porphyrin, preferably contacting the composition on a solid carrier, preferably a white carrier, which can e.g. be a wall of a container suspected of containing a sample containing an explosive, or a paper, a plastic, or a glass surface arranged inside the sample or in the vicinity of the sample.

As a carrier containing free acid in the form of a matrix-bound acid, test stripes can be produced by using a strongly acidic cation exchange resin impregnated with the Ni-porphyrin dissolved in halogenated solvent. Dipping the test stripes into the headspace of TATP or EGDN, or direct contact with traces of peroxide- or nitrogen-based explosives, such as triacetone triperoxide (TATP), diacetone diperoxide (DADP), hexamethylene triperoxide diamine (HMDT), methyl ethyl ketone peroxide (MEKP), potassium nitrate (KNO<NUM>), ammonium nitrate (NH<NUM>NO<NUM>), urea nitrate (NH<NUM>COHNH<NUM>+·NO<NUM>-), nitro glycerine (NG), ethylene glycole dinitrate (EGDN), pentaerythritol tetranitrate (PETN), hexogene (RDX), octogene (HMX), <NUM>,<NUM>,<NUM>-trinitrophenylmethylnitramine (tetryl) or nitrourea (NH<NUM>CONHNO<NUM>) leads to a color change from red to green. In case of the nitrogen-based explosives a subsequent color change from green to brown is observed. Detection of explosives is also possible in mixtures such as black powder (KNO<NUM>/sulphur/charcoal) or pyrotechnic compositions (e.g. KClO<NUM>/Al-powder).

In another aspect of the invention, acid stable porous polymer membranes such as polypropylene membranes, PVC membrane filters, or porous polyvinylidene fluoride, or cellulose, impregnated with the Ni-porphyrin dissolved in pure acid such as trifluoroacetic acid or preferentially higher boiling acids e.g. pentafluoro propionic acid are used as test stripes.

Generally, test stripes can comprise an inert base material, e.g. a plastic stripe, with an attached porous substance or gel for accommodating the Ni-porphyrin in mixture with a free acid. The test stripes can be in combination with free acid and/or an acid stable solvent contained in a container suitable for dispensing liquid, optionally in combination with a superbase, preferable is a separate container suitable for dispensing liquid, as a kit-of-parts. In the alternative to the Ni-porphyrin being comprised in a test stripe, the Ni-porphyrin in mixture with a free acid can be present in a liquid composition, preferably in an acid-stable solvent, optionally in combination with a superbase in a separate container suitable for dispensing liquid, as a kit-of-parts. A kit-of-parts according to the invention as claimed contains the required compounds and is suitable for carrying out the analytical process of the invention.

Dipping the test stripes into the headspace of TATP or EGDN or direct contact with traces of peroxides, nitrate salts, nitrate esters or nitramines leads to a color change from red to green.

The Ni-porphyrin can comprise or consist of Structure <NUM>, wherein Structure <NUM> shows an embodiment in which the Ni-porphyrin is substituted with aryl substituent groups (Ar) in all four of the meso positions. Exemplary aryl substituent groups can be independently selected from a phenyl or other aromatic rings (Ar), which aryl group optionally is further substituted by at least one electron donating group, herein shown as a methoxy group, e.g. as shown one methoxy group or three methoxy groups, and shown as three methyl groups. Exemplary aryl groups (Ar) are the phenyl group, a methoxy phenyl group, a tri-methoxy phenyl group, and a trimethyl phenyl group. The aryl group can be bound by any of its carbon atoms to the carbon in meso position of the Ni-porphyrin.

In an embodiment, although less preferred, the aryl substituent groups do not carry an electron donating group. In this embodiment of the aryl substituent groups being free from electron donating groups, the analytical process is slower to generate the indicating color, and the process is less sensitive.

Structure <NUM> is suitable for an embodiment, in which the composition comprises the Ni-porphyrin and, as a compound in admixture with the Ni-porphyrin, an acid, optionally a solvent.

At present, the reaction mechanism is assumed to be as depicted in <FIG>, wherein in the reaction with the peroxide (R-O-O-R), the reactive Ni<NUM>+ (NiII) of the Ni-porphyrin is shown with only a portion of the porphyrin. For the sake of simplicity, the unpaired electron and the positive charge of the porphyrin radical cation are shown as being located at the pyrrole nitrogen, and not delocalized over the π system of the porphyrin.

Therein, the color change is based on a one-electron oxidation of the porphyrin. Each peroxide unit upon reaction accepts <NUM> electrons and hence one molecule of TATP or HMTD, including <NUM> peroxide units, oxidizes <NUM> porphyrin molecules. Further enhancement of the sensitivity involves a radical chain reaction initiated by RO· and involving ambient air oxygen as the oxidizing agent. Oxidizing species in case of the detection of nitramines and nitrate esters are the protonated species or the nitronium ions eliminated thereof. The acid cleavage corresponds to the reverse process of the synthesis of nitramines and nitrate esters. The nitronium ions (NO<NUM>+) thereby are reduced to nitrogen dioxide (NO<NUM>), which oxidizes another equivalent of the red porphyrin to the green porphyrin radical cation and being reduced the nitrite anion (NO<NUM>-). When the red porphyrin is consumed, the nitrogen dioxide reacts with the green porphyrin radical cation via radical recombination forming a brownish β nitrated porphyrin. (see e.g. <NPL>) This explains the color change by the process and kit-of-parts of the invention when in contact with a peroxide-based explosive generates a change of color from red to green, and when in contact with a nitrate-based or a nitramine-based explosive, a change of color from red to green and finally to brown, which is characteristic only for the nitrogen-based explosives, and which allows to distinguish between peroxide- and nitrogen-based explosives (see examples).

In order to discriminate between hydrogen peroxide and cyclic peroxides such as TATP and HMTD, a weaker acid such as dichloroacetic acid (pKa <NUM>) can be employed, which is not able to hydrolyse the cyclic peroxides but which is strong enough to activate hydrogen peroxide. To avoid false positives from hydrogen peroxide in practical applications, two test stripes are used: one with a strong acid to detect all peroxides and one with a weaker acid to detect only hydrogen peroxide. The weak acid can e.g. have a pKa of <NUM> to <NUM>.

Optionally, the process can consist of contacting the sample with the composition, or the process can comprise an additional step of destroying free hydrogen peroxide from the sample prior to contacting the sample with the composition in order to reduce or eliminate the influence of free hydrogen peroxide. For hydrolysing free hydrogen peroxide, prior to contacting the sample with the composition comprising Ni-porphyrin, the sample can be contacted with a reactant having activity to disintegrate free hydrogen peroxide. Accordingly, the device can optionally comprise a flow path in which the composition comprising the Ni-porphyrin is arranged to receive a sample, wherein upstream of this composition there is arranged a reactant having activity to disintegrate free hydrogen peroxide. The reactant can e.g. be an inorganic catalyst, e.g. KMnO<NUM> or MnO<NUM>. The reactant can be immobilized on a porous carrier that optionally spans the cross-section of the flow path.

A flow path can e.g. be provided by a wicking action material, e.g. a porous material, and/or by a duct through which a sample can migrate, e.g. by capillary action or by positive or negative pressure applied to the duct.

The invention is described in greater detail by way of examples with reference to.

A plastic stripe (<NUM> x <NUM>) equipped with a cellulose pad (<NUM> x <NUM>) at one end, impregnated with Ni-tetrakis(<NUM>,<NUM>,<NUM>-trimethoxyphenyl)porphyrin by dropping <NUM>µL of a <NUM> solution of the porphyrin in toluene onto the cellulose pad and then the solvent is removed by evaporation. The stripe prepared in this way is moistened with a drop of <NUM>-<NUM>µL of perfluoropentanoic acid. The addition of the acid to the Ni-porphyrin compound of the invention herein is also referred to as activating the Ni-porphyrin or the stick. The activated stick is brought into close proximity, ca. ~ <NUM> to crystals of TATP present on an uncovered surface or into the headspace of TATP present in a small glass vial. After <NUM> the red color of the pad turns into green. Assuming a saturation vapour pressure in the head space of the solid explosive and a volume of <NUM> of gas, <NUM> nmol of TATP can be detected.

Traces of these compounds, PETN, EGDN, NG, and nitrate salts (e.g. NH<NUM>NO<NUM>, KNO<NUM>, NaNO<NUM>) each separately present on an uncovered surface, or in a small glass vial are treated with a drop (<NUM>-10µl) of perfluoropentanoic acid. After several seconds, the activated plastic stripe prepared as in Example <NUM> is brought into close proximity (~<NUM>) to one of the compounds present on the surface or into the head space of the glass vial. The color of the pad turns from red to brown. The detection of nitrate salts by the invention is obtained also when the nitrate salts are present in solution or in a dry mixture, e.g. with sulfur and charcoal as in black powder.

Separately, traces of solid nitramines on a surface or in a small glass vial are moistened with a drop (<NUM>-<NUM>µl) of a solution of an organic superbase (e.g. <NUM> vol. % P<NUM>-t-Bu in dissolved in acetonitrile). Then a drop (<NUM>-<NUM>µl) of perfluoropentanoic acid is applied to the same spot. The activated stripe prepared as in Example <NUM> is brought into close proximity (~ <NUM>) of the suspension of one of the nitramine compounds in the organic superbase on the surface or into the headspace of the glass vial. The color of the pad immediately turns from red to brown.

The activated stripe (prepared as in Example <NUM>) is separately brought into contact with traces of solid HMDT or TATP by swiping a contaminated surface. The color of the stripe immediately changes from red to green at the spots, where the pad comes into contact with traces of the solid explosive. These green spots spread out and within about <NUM> seconds the pad turns green. <NUM>µl of a <NUM> solution of TATP dissolved in dichloromethane were dropped as a round spot onto the previously prepared test stripe. After one minute the test stripe turned light green. Using this method, it is possible to detect <NUM> nmol (<NUM> ng) TATP.

<FIG> shows a plastic stripe with a terminally attached cellulose pad impregnated with Ni-porphyrin according to the invention, prior to contact with a compound to be detected (fresh (red)), and a plastic stripe containing the same Ni-porphyrin, activated by adding acid and after contact with peroxide (peroxide (green)), and a plastic stripe containing the same Ni-porphyrin activated by adding acid and after contact with nitrate (nitrate (brown)).

The activated stripe prepared as in Example <NUM> is brought into contact with separate traces of solid nitrate salts or organic nitrates (PETN is a solid, EDGN and NG are liquids) by swiping a contaminated surface. The color of the stick immediately changes from red to green at the spots, where the pad comes into contact with traces of the explosive. These green spots turn brown and spread out over the pad.

Separately, traces of solid nitramines are moistened with a drop (<NUM>-<NUM>µl) of a solution of an organic superbase (e.g. P<NUM>-t-Bu) in acetonitrile (<NUM> vol. % P<NUM>-t-Bu). The activated stripe (prepared as in Example <NUM>) is brought into contact with the suspension. The color of the pad immediately turns from red to brown.

Separate traces of these explosives, e.g. of <NUM>,<NUM>-dinitrotoluene or of <NUM>,<NUM>,<NUM>-trinitrotoluene, are brought into contact with an organic superbase (e.g. a solution of <NUM> vol. % of P<NUM>-t-Bu in acetonitrile). The solution turns immediately from colorless to deep violet (TNT) or deep blue (DNT). In this case the activated stripe is not needed.

For detection of HMTD and/or TATP in solution, <NUM>µL of Ni-tetrakis(<NUM>,<NUM>,<NUM>-trimethoxyphenyl) porphyrin (<NUM> in CH<NUM>Cl<NUM>) and <NUM>µL trifluoroacetic acid (<NUM>) were transferred into a sample tube. After adding <NUM>µL of a <NUM> solution (HMTD or TATP separately in CH<NUM>Cl<NUM>), the solution turned green within several minutes due to the formation of the porphyrin π-radical cation. It was calculated that the process can detect <NUM> nmol (<NUM> ng) TATP or (<NUM> ng) HMTD as a color change from red to green.

Analogously, the detection limit of ammonium nitrate (NH<NUM>NO<NUM>) was determined as <NUM> ng.

A plastic stripe (<NUM> x <NUM>) is equipped with a cellulose pad (<NUM> x <NUM>) at one end. The pad is moistened with a solution of the Ni-porphyrin in an organic solvent. The solvent is evaporated leaving the dry pad uniformly impregnated with the red colored porphyrin. This stick is storable for extended periods of time (> <NUM> years at room temperature in a dry environment). Prior to application, the stripe is activated with a drop (<NUM>-<NUM>µL) of perfluoropentanoic acid applied onto the pad. The stripe now remains active and ready to use for about <NUM>. The acid can be applied from a dropper bottle, or released from a reservoir above the pad by mechanical force. In these examples, the following detection limits could be determined: for TATP: ~ <NUM> ng, for NH<NUM>NO<NUM>: - <NUM> ng, for urea nitrate: ~<NUM> ng, for HMTD: - <NUM> ng.

For comparative purposes, electron rich Ni-porphyrins (Ni-tetra(<NUM>-hydroxyphenyl)porphyrins) have been prepared according to <NPL> and used as sensors for cyanide (CN-), fluoride (F-) and picric acid according to <NPL>. To the Ni-porphyrins used in these publications, trifluoroacidic acid (TFA) and TATP and HMDT was added. After one minute at room temperature an unspecific reaction took place. Hence, these porphyrins described by Chahal et al. are not suitable for the detection of peroxide-based explosives.

Claim 1:
Analytical process for detecting explosive compounds by a color reaction, comprising contacting a sample suspected of containing a peroxide-based compound, a nitrate-based compound, a nitrotoluene-based compound, or a nitramine-based compound with a composition comprising a Ni-porphyrin and a free acid having a pKa of -<NUM> to <NUM>, wherein the sample is first treated with a superbase before contacting the sample with the Ni-porphyrin and the acid.