Establishing a universal swabbing and clean-up protocol for the combined recovery of organic and...

Forensic Science International 223 (2012) 136–147

Establishing a universal swabbing and clean-up protocol for the combinedrecovery of organic and inorganic explosive residues

Nopporn Song-im a,1, Sarah Benson b, Chris Lennard a,*a National Centre for Forensic Studies, University of Canberra, Canberra, ACT 2601, Australiab Forensic and Data Centres, Australian Federal Police, GPO Box 401, Canberra, ACT 2601, Australia

A R T I C L E I N F O

Article history:

Received 1 July 2012

Received in revised form 15 August 2012

Accepted 16 August 2012

Available online 6 September 2012

Keywords:

Explosives

Sampling

Swabs

Alcohol wipes

Solid-phase extraction

Clean-up protocol

Organic residues

Inorganic residues

A B S T R A C T

A single-step solvent extraction and a solid-phase extraction (SPE) clean-up procedure was developed

and optimised in order to establish a universal sampling and clean-up protocol for the combined

recovery of organic and inorganic explosive residues.

Mixtures of three common swabbing solvents (acetone, acetonitrile and methanol) with water, in

various ratios, were assessed for the extraction of four target organic explosives [pentaerythritol

tetranitrate (PETN), 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and

triacetone triperoxide (TATP)] and two inorganic anions (chlorate and nitrate) from alcohol wipes

that were used as a swabbing medium. An efficient, single-step extraction of both organic and inorganic

compounds from the wipes was achieved using 60% v/v methanol/water.

To develop a clean-up procedure, four commercially available SPE cartridges (Oasis HLB, Isolute1 C18,

Bond-Elut1 ENV and ABS ELUT Nexus) and an in-house packed XAD-7 cartridge were firstly evaluated for

their retention capacity toward three organic explosives (PETN, TNT and RDX) in a mixture of methanol

and water. A SPE technique was then developed and optimised from the short-listed sorbents with four

representative organic explosives (including TATP). The Nexus cartridge was found to provide a suitable

sorbent for extract clean-up following swab extraction with 60% v/v methanol/water. By incorporating

the optimised clean-up procedure with the application of a polyester-based alcohol wipe as a sampling

medium, a universal swabbing protocol for the combined recovery of both organic and inorganic

explosive residues was established. The feasibility of the proposed protocol was assessed by collection

and quantitation of the residue from a mixture of TNT, PETN and chlorate deposited on a laminate test

surface.

� 2012 Elsevier Ireland Ltd. All rights reserved.

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Forensic Science International

jou r nal h o mep age: w ww.els evier . co m/lo c ate / fo r sc i in t

1. Introduction

Over the past decade, there has been a general development andoptimisation of analytical methods targeting specific explosiveresidues. However, there is still a demand for a protocol optimisedfor recovering a wide range of explosives, including thosetraditionally encountered in casework (i.e., commercial andmilitary explosives) and emerging threat materials such as organicperoxides and improvised organic/inorganic explosive mixtures.

The key to the successful detection of trace quantities ofexplosives in a highly contaminated environment not only relieson a suitable sampling method (e.g., swabbing) and a sensitive

* Corresponding author. Tel.: +61 0 2 6201 2160; fax: +61 0 2 6201 2461.

E-mail addresses: [email protected] (N. Song-im),

[email protected] (S. Benson), [email protected] (C. Lennard).1 Current address: Forensic Science Laboratory, ChemCentre, PO Box 1250,

Bentley Delivery Centre, WA 6983, Australia.

0379-0738/$ – see front matter � 2012 Elsevier Ireland Ltd. All rights reserved.

http://dx.doi.org/10.1016/j.forsciint.2012.08.017

analytical technique, but also requires effective swab extractionand a compatible extract clean-up procedure. This is to ensure thatall target explosives collected on the sampling medium areefficiently transferred into the extract and that co-extractedinterfering compounds are removed before the extract is subjectedto the final instrumental analysis.

By using a universal swabbing system, both organic andinorganic explosive residues can be targeted for collection on asingle swab. The traditional sequential extraction method usingdifferent polarity solvents is not ideal, as the loss of certaincompounds or groups of compounds is likely to occur, especially ifan incorrect extraction sequence is applied. For the maximumbenefit of utilising a universal swab, an effective single-step swabextraction for both organic and inorganic target compounds needsto be investigated and optimised.

The development of a universal swabbing protocol cannot beachieved without an associated procedure to clean up the swabextract. This crucial element of the protocol needs to be optimisedto permit the purification and concentration of the analytes of


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N. Song-im et al. / Forensic Science International 223 (2012) 136–147 137

interest while ensuring compatibility with the instrumentalanalysis methods commonly used for the detection and identifi-cation of explosive residues.

This study was comprised of three sections. The first partinvolved the determination of the optimum composition ofmixtures of each of three organic solvents (i.e., acetone, acetoni-trile and methanol) and water for the single-step extraction of bothorganic and inorganic explosives from the selected samplingmedium (commercially-available alcohol wipes).

The second part of the project required the evaluation andoptimisation of a clean-up procedure for the swab extracts utilisinga solid-phase extraction (SPE) technique. In this study, a solid-phase extraction technique was not only applied for the removal ofco-extracted interfering compounds and the pre-concentration ofthe compounds of interest, but also for the separation of the swabextract into organic and inorganic components for independentanalyses. The concept is that the sorbent inside the SPE cartridgeretains the organic explosive residues while the inorganiccompounds pass through for collection and analysis. Washingsolvents can then be flushed through the cartridge to removeinterfering compounds and the organic explosives finally elutedfrom the cartridge with the aid of an eluting solvent. The use of SPEfor the two functions of separation and clean-up of explosiveextracts was first proposed by the Forensic Explosive Laboratory(FEL) in the UK [1]. The original FEL protocol used Chromosorb 104as the SPE adsorbent [1,2]. A revised protocol utilising bothChromosorb 104 and Isolute ENV+, to incorporate the recovery oforganic peroxides, has also been reported [3]. However, theChromosorb porous polymer resin referred to in these publicationshad limited availability in Australia at the time of our study and,more recently, is no longer commercially available.

Four commercially available SPE cartridges – namely Oasis HLB,Isolute1 C18, Bond-Elut1 ENV and ABS ELUT Nexus – wereevaluated and compared to results from cartridges packed withXAD-7, which were prepared in-house. Amberlite XAD-7 is anacrylate porous polymer. It was first introduced to recover organicexplosives from hand swabs in 1982 by the Metropolitan PoliceForensic Science Laboratory [4]. A further development of thatmethod in 1985 introduced the use of a form of microcolumnextraction to make the process more convenient [5]. The workconducted by the Israel Police has also demonstrated the successfulapplication of a microcolumn packed with XAD-7 for the purificationof extracts recovered from post-explosion debris [6].

The recovery of explosive compounds using Oasis HLB (acopolymer between divinylbenzene and N-methylpyrrolidone)has already been investigated and it was found that this sorbentprovides good retention of high polarity explosives, such asnitramines, with a cleaner extract compared to other SPE sorbents[7,8].

Although previous studies [8] have demonstrated the poorretention capacity of conventional C18 cartridges, the selectedIsolute1 C18 cartridge contained non-end-capped silica, whichmade it different from other C18s. It was envisaged that improvedretention of polar organic compounds might be achievable withthe additional interactions from the residual silanol group.

Bond-Elut1 ENV is a high-purity styrene-divinylbenzenecopolymer that the manufacturer claims has been optimised forthe extraction of polar organic residues, including herbicides,metabolites and explosives. Also, many studies in the area of traceanalysis of explosives in environmental samples have demon-strated the successful recovery of a wide range of explosives withthis type of polymeric resin [9–11].

ABS ELUT Nexus is a copolymer between methyl methacrylateand divinylbenzene. To the best of our knowledge, Nexus is theonly commercially available prepacked cartridge that contains anacrylate ester functional group, which is close to the functional

group of XAD-7 resin. Also, several studies have demonstrated thatthis resin has the potential for use in the recovery of explosivecompounds either in the gas or liquid phase [12,13].

To establish a universal swabbing and clean-up protocol, thesingle-step swab extraction and optimised clean-up procedurewere combined with the findings from our previous studyregarding the use of alcohol wipes as a universal swab [14].

The third and last section of the study served to demonstratethe feasibility of the proposed protocol via the recovery of amixture of TNT, PETN and chlorate from a laminate test surface. Amixture of TNT, PETN and chlorate represents a combination oforganic and inorganic compounds that may be encountered in anexplosive device; for example, PETN from the detonating cord, TNTas the booster, and chlorate as a component of the main charge. Alaminate surface was chosen due to its common occurrence inhouseholds and offices. In addition, there is limited informationavailable regarding sampling from laminate surfaces whencompared to other common surfaces such as glass and metal.

2. Materials and methods

2.1. Solid sorbents

Isolute1 C18 500 mg packed in a 3 mL cartridge was supplied by BioLab Australia

Pty., Ltd. (Scoresby, VIC, Australia). Bond-Elut1 ENV 60 mg packed in a 3 mL

cartridge and ABS ELUT Nexus 60 mg packed in a 3 mL cartridge both were

purchased from Varian Australia Pty. Ltd. (Mulgrave, VIC, Australia). Oasis1 HLB

60 mg packed in a 3 mL cartridge was purchased from Waters Australia (Rydalmere,

NSW, Australia).

XAD-7 was purchased from Grace Davison Discovery Sciences (Rowville, VIC,

Australia). The XAD-7 resin was washed by being suspended in deionised water

with stirring for one hour. The water was then decanted and the resin suspended in

methanol and stirred for another hour. After decanting the methanol, the washing

process was repeated in the same manner with acetonitrile and then with acetone.

After the final wash with acetone, the resin was allowed to dry in a fume cupboard

overnight then the resin crushed and passed through a sieve. Only the resin with a

particle size between 75 and 150 mm was selected (this was based on the findings

published by Douse [5]). A 60 mg portion of the final resin was finally packed into a

4 mL Extract-CleanTM Empty SPE cartridge that was fitted with 10 mm PTFE frits.

Both the empty cartridge and frits were obtained from Grace Davison Discovery

Sciences. Although the empty cartridge was labelled as being 4 mL in size, after

measuring the dimensions and volume of the packed cartridge, no difference was

found in the volumes between the in-house packed XAD cartridge and the

prepacked cartridges of other sorbents obtained from the vendors detailed above.

2.2. Reagents and standards

TNT (2,4,6-trinitrotoluene) was chosen as a representative nitroaromatic, PETN

(pentaerythritol tetranitrate) as a representative nitrate ester, RDX (hexahydro-

1,3,5-trinitro-1,3,5-triazine) as a representative nitramine, and TATP (triacetone

triperoxide) as a representative organic peroxide. Chlorate and nitrate were

selected as representative inorganic compounds relevant to explosive residue

analysis.

Solutions of TNT, PETN and RDX, each at a certified concentration of 1000 mg/mL

in acetonitrile, were obtained from ChemService (West Chester, PA, USA). TATP, at a

certified concentration of 995 mg/mL in acetonitrile, was obtained from AccuS-

tandard (New Haven, CT, USA).

2-Nitrotoluene (99.5% certified purity, obtained from ChemService, West

Chester, PA, USA) was prepared as a 1000 ppm solution in LiChroSolv1 acetonitrile

(gradient grade for liquid chromatography, supplied by Merck, Kilsyth, VIC,

Australia), and then an aliquot of this solution added as an internal standard for the

quantitative analysis of samples containing both TNT and PETN during the

feasibility study on the proposed universal swabbing protocol.

Sodium chlorate (99.8% purity) and ammonium nitrate (99.5% purity, ACS

reagent grade), purchased from Sigma–Aldrich (Castle Hill, NSW, Australia), were

used to prepare a stock solution of chlorate at a concentration of 2000 ppm in HPLC

grade methanol and a stock solution of nitrate at a concentration of 3000 ppm in

methanol, respectively. These standards were used for the investigation of a single-

step swab extraction. The same stock solution of chlorate was also used to generate

a deposit of mixed organic/inorganic compounds on the test surface for the

evaluation of the proposed protocol.

High-purity water obtained from a Sartorius arium 611 water purification

system, HPLC grade acetone (Lab-Scan Analytical Sciences, Bangkok, Thailand),

HPLC grade acetonitrile (LiChroSolv1, Merck, Kilsyth, VIC, Australia), and HPLC

grade methanol (Chem-Supply, Gillman, SA, Australia) were used to prepare the

extraction solvents.

N. Song-im et al. / Forensic Science International 223 (2012) 136–147138

HPLC grade methanol and high purity water were used for the conditioning of the

SPE cartridges and in the preparation of the sample matrix and washing solutions.

The details of additional chemicals required for the quantitative analyses of the six

target compounds have been described elsewhere [14].

2.3. Materials

Skin cleansing alcohol wipes were purchased from two sources. Kendall

WebcolTM wipes (3.3 � 3.1 cm) were obtained from a local pharmacist and Mini Liv-

wipes (3.3 � 3.0 cm) were purchased from Livingstone International Pty. Ltd.

(Rosebery, NSW, Australia). Each wipe, supplied in individual, sealed sachets, comes

pre-saturated with isopropanol/water (7:3 v/v). For ease of understanding, the

Kendall wipe is referred to as the regenerated cellulose (RC) wipe and the Mini Liv-

wipe is referred to as the polyester (PolyEs) wipe in the remainder of this article.

Laminate sheets (7.5 � 6 cm, Laminex1 200 White with natural finish) were

supplied by The Laminex Group Pty. Ltd. (Fyshwick, ACT, Australia). The surface was

cleaned using alcohol wipes and allowed to completely dry at room temperature

before use as a test substrate.

2.4. Single-step swab extraction for the combined recovery of organic and inorganic

explosive residues

Solvent mixtures containing water and various percentages of organic solvent

(i.e., acetone, acetonitrile or methanol) were evaluated in this phase of the study. Six

different compositions of extracting solvent (0, 20, 40, 60, 80 and 100% v/v of

organic solvent with water) were used to extract the four representative explosive

compounds (PETN, TNT, RDX and TATP) from each of the selected alcohol wipes.

Aqueous mixtures containing the same organic solvents at percentages ranging

from 0 to 80% v/v were also evaluated for the extraction of the two selected anions

(chlorate and nitrate) from the polyester wipes.

For PETN, TNT and RDX, a 15 mL aliquot of stock solution (1000 mg/mL),

equivalent to 15 mg of the target explosive, was applied to each alcohol wipe (one

target compound per wipe). Each wipe was then allowed to dry in a fume cupboard

for 15 min before being transferred to a 4 mL clear glass vial.

For the TATP extraction experiments, the wipes were first dried in a fume

cupboard for 15 min and then 30 mL of stock solution (equivalent to approximately

30 mg of TATP) transferred to the wipes. Each wipe was then immediately

transferred to a 4 mL clear glass vial. It was found, from preliminary experiments,

that the persistence of this quantity of TATP on dry wipes was less than 5 min. It is

for this reason that no further air drying was undertaken after adding the TATP

solution onto the sampling medium.

To each glass vial, one millilitre of extraction solvent was added. The vials were

then sealed with Parafilm1 and the extraction carried out by sonication in an

ultrasonic bath for 10 min. There were three repeats and one negative control for

each composition of test solvent on each type of alcohol wipe, with four target

explosives (making a total of 96 samples).

After an extraction time of 10 min, the vials were allowed to cool to room

temperature. The wipes were pounded with the tip of a glass Pasteur pipette and

the extract subsequently drawn through the wipe and transferred to a 5 mL

volumetric flask. Where required, a specified volume of the internal standard

stock solution was added and the volume made up with a suitable diluent. The

amount of target compound in the final solution was determined using the

quantitative methods detailed in our previous study [14]. Five-point calibration

curves, covering the concentration range 0.2–3 ppm for PETN (r2 = 0.9907–

0.9968), TNT (r2 = 0.9956–0.9989) and RDX (r2 = 0.9915–0.9989), and 1–6 ppm for

TATP (r2 = 0.9963–0.9999), were prepared on each day that sample analyses were

conducted.

For the extraction of the inorganic compounds, 15 mL of the stock solution of

chlorate (2000 mg/mL in methanol) or 20 mL of the stock solution of nitrate

(3000 mg/mL in methanol) were deposited onto a polyester wipe (equivalent to

30 mg of chlorate or 60 mg of nitrate). The wipes were allowed to dry in a fume

cupboard for 15 min and then each wipe transferred to a 4 mL clear glass vial. One

millilitre of extracting solvent was added to each glass vial. Vials were then sealed

and subjected to sonication for 10 min. The extract was then transferred to a 5 mL

volumetric flask in the same manner as described previously. A specified volume of

internal standard was added and the volume made up with deionised water. The

amount of target anion in the final solution was quantified using the analytical

method detailed in our previous study [14].

A five-point calibration curve, covering the concentration range of 1–6 ppm for

chlorate (r2 = 0.9906–0.9957) and 1–12 ppm for nitrate (r2 = 0.9977–0.9995), was

prepared on each day that sample analyses were conducted. There were three

replicate samples and one negative control for each composition of extracting

solvent tested, with two target anions.

2.5. Assessment of the retention capacity of the selected sorbents

The general method of ascertaining the retention capacity of a SPE cartridge is to

determine its breakthrough volume by continuously loading a constant volume of

the testing solution until the compound of interest is detected in the effluent.

However, this method is unrealistic in the case of swab extracts where the loading

volume would be in the range of a couple of millilitres at most. In this study, another

approach was applied whereby a series of washing solutions with different elution

strengths was loaded to assess the retention capacity of each SPE cartridge. Three

organic explosive compounds (PETN, TNT and RDX) were used to evaluate the

retention property of the selected sorbents. Various compositions of a mixture of

water and methanol were used as washing solvents. The reason for choosing

methanol was its compatibility with the HPLC mobile phase used in the

quantification step. Also, in a reverse phase extraction system, methanol has a

lower elution strength compared to acetonitrile and acetone. By using a low elution

strength solvent, this might provide the benefit of recognising small differences in

the retention behaviour of compounds among the selected sorbents.

All selected SPE cartridges were conditioned, in the same manner, by washing

with 3 � 1 mL of methanol and then 3 � 1 mL of water before the testing solution

was added. An Alltech 16-port vacuum manifold with disposable PTFE needles

(supplied by Grace Davison Discovery Sciences, Rowville, VIC, Australia) was used

to carry out all experiments. Nexus, ENV and Oasis cartridges were processed

without the aid of a vacuum and a flow rate of approximately 0.5–0.8 mL/min was

controlled by adjusting the stopcock of the manifold. Extractions with XAD and C18

required a low vacuum of approximately minus 10 inches of mercury to achieve the

same flow rates.

Two millilitres of 10% v/v methanol/water solution, containing 10 mg of PETN,

TNT or RDX, was loaded into a conditioned SPE cartridge. The effluent was collected

into a 5 mL volumetric flask. An internal standard was added and the volume was

made up with a suitable diluent. The presence of target compounds in the final

solution was determined using the HPLC method detailed elsewhere [14]. The same

cartridge was then washed with 2 mL of a solution of 20% methanol/water. The

effluent was collected into a 5 mL volumetric flask. The internal standard was then

added, the volume made up with diluent, and the presence of target compounds

checked. The experiment was repeated on the same cartridge with a series of

washing solvents of increasing methanol concentration, in 10% v/v steps. When the

target compound was found in the effluent, the percentage of methanol in the

washing solvent for the next wash was changed to 5% higher (rather than 10%) and

the experiment was continued until no target compound was detected in the

effluent.

There were three replicate samples plus one negative control for each cartridge/

target compound combination. Five-point calibration curves were constructed in

the range 0.2–2 ppm for all the target compounds (PETN, r2 = 0.9909–0.9982; TNT,

r2 = 0.9987–0.9994; RDX r2 = 0.9974–0.9991). New curves were prepared on each

day that sample analyses were conducted.

2.6. Development and optimisation of a clean-up procedure

The development of a solid-phase extraction method generally comprises three

major steps, namely: (i) loading; (ii) washing; and (iii) elution. During the loading

step, the sorbent has to demonstrate that it can retain the compound of interest

from a solution that is as similar to a ‘‘real’’ sample matrix as possible. In this

instance, two solvent systems that could provide a single-step extraction for both

organic and inorganic compounds were used as a testing matrix. Following from the

results obtained in the first section of this study, a solution of 40% acetonitrile/water

and a solution of 60% methanol/water were chosen as solvent matrices to

investigate the adsorption of target compounds onto the resin. Four representative

organic compounds (PETN, TNT, RDX and TATP) were spiked into each testing

matrix to assess the retention capacity of the three short-listed sorbents (XAD-7,

Oasis HLB and Nexus).

The sorbent that demonstrated a high retention capacity towards all four target

compounds was selected for further study; specifically, to determine the maximum

volume of washing solution that could be used to remove any interfering

compounds without eluting the target compounds from that sorbent. The final step

was to find the type of solvent and the minimum volume that could then be used to

elute the target compounds from the sorbent.

A solution of single target compound in 60% v/v methanol/water (PETN, TNT, and

RDX at a concentration of 3 ppm; TATP at a concentration of 5 ppm) was prepared

by dilution from a certified stock solution. Two millilitres of this solution were

loaded into each conditioned SPE cartridge. (Details regarding conditioning of the

selected SPE cartridges and the procedure for the manifold extraction were

provided in the previous section.) The effluent was collected in a 5 mL volumetric

flask. The internal standard was added (not required in the case of TATP), the

volumes made up with a suitable diluent, and the quantity of target compound in

the final solution determined using the methods described elsewhere [14]. Five-

point calibration curves were constructed in the range 0.2–2 ppm for PETN, TNT and

RDX, and 0.6–3 ppm for TATP (r2 = 0.950–0.986). New curves were prepared on

each day that sample analyses were conducted.

As a positive control, another two millilitres of explosive solution were

transferred to a 5 mL volumetric flask without passing through a cartridge. The

internal standard was added (where required), the volume made up, and the

solution subjected to the relevant quantitative analysis. The results from this

solution served as a reference for 100% breakthrough.

A solution of each explosive at the same concentration was prepared in 40% v/v

acetonitrile/water (the second testing matrix) and the whole experiment repeated

in the same manner.


The optimisation of the washing step with the two short-listed sorbents (Oasis

and Nexus) was carried out utilizing a solution of 60% v/v methanol in water as a

washing solution in order to simplify the final clean-up procedure.

A solution of single explosive compound in 60% v/v methanol/water (PETN, TNT,

and RDX at a concentration of 6 ppm; TATP at a concentration of 10 ppm) was

prepared by dilution from a certified stock solution. One millilitre of this explosive

solution was loaded onto each conditioned SPE cartridge and the effluent collected

into a 5 mL volumetric flask. An internal standard was added (where required), the

volume made up, and the amount of target compound quantified. The same

cartridge was then washed with 3 � 1 mL of 60% v/v methanol/water. During each

wash, the effluent was collected and analysed using the same quantitation method.

The percentage of breakthrough was calculated and again compared with the result

from the analysis of a test solution that was not passed through a cartridge.

The final step in the development of a clean-up procedure was to ascertain the

type of eluting solvent to recover the target explosives from the SPE cartridge. That

solvent had to be able to break the interaction between the sorbent and the target

compound utilising a minimum volume (to ensure that a concentrated final extract

is obtained). Furthermore, the final extract had to be compatible with the

instrumental techniques commonly used for the identification of organic

explosives, such as gas chromatography mass spectrometry (GC/MS). It also had

to be compatible with the HPLC quantitative method utilised in this study.

A solution containing one explosive in 60% v/v methanol/water (PETN, TNT, and

RDX at concentrations of 6 ppm, TATP at a concentration of 10 ppm) was prepared

by dilution from a certified stock solution. One millilitre of the explosive solution

was loaded onto a conditioned SPE cartridge and the effluent discarded. The same

cartridge was then washed with 2 � 500 mL of the tested extraction solvent

(acetone, acetonitrile and methanol). Each time, the effluent was collected into a

5 mL volumetric flask. An internal standard was added, the volume made up, and

the amount of target compound in the final solution determined.

Another solution was prepared for use as a reference for 100% elution by

transferring the required amount from a certified stock solution of explosive (6 mL for

PETN, TNT and RDX; 10 mL for TATP) into a 5 mL volumetric flask which already

PETN

% Acetone

0 20 40 60 80 100

% R

eco

ver

y

0

20

40

60

80

100

0

20

40

60

80

100

RC wipes

PolyEs wipes

a

PETN

% Methan

0 20 40

% R

eco

ver

y

0

20

40

60

80

100 c

Fig. 1. Extraction profiles for PETN from selected alcohol wipes using various composition

error bars represent � one standard deviation (SD) for three replicate samples per experi

contained 500 mL of testing solvent. The internal standard was added (except for

TATP), the volume made up, and quantitative analysis conducted in the same manner.

2.7. Feasibility study on the proposed universal swabbing protocol

15 mL of PETN solution (equivalent to 15 mg) was firstly added onto the test

surface (laminate sheet), followed by 15 mL of TNT solution (equivalent to 15 mg)

and 15 mL of chlorate solution (equivalent to 30 mg), all at the same location to

simulate a mixed residue. The substrate was then allowed to dry in a fume cupboard

for 5 min.

A polyester wipe was then applied with a gloved hand to collect the residues. The

collection was conducted by wiping the whole surface in one direction without

repeat on the same area (to simulate the sampling of a questioned surface). The

wipe was then transferred to a 4 mL clear glass vial, 1 mL of 60% methanol/water

added, and the vial sealed with Parafilm1. The extraction was then carried out by

sonication in an ultrasonic bath for 10 min. While waiting for the extraction to be

completed, a Nexus SPE cartridge was conditioned as previously described.

When the extraction was completed, the vial was allowed to cool to room

temperature. The wipe in the vial was pounded with the tip of a glass Pasteur

pipette and the extract drawn through the wipe and transferred to the conditioned

Nexus cartridge. The effluent was collected in a 5 mL volumetric flask. A 30 mL

solution of sulphate anion (1000 ppm) was added to the volumetric flask as an

internal standard and the volume made up with deionised water. The amount of

chlorate in this final solution was quantified using capillary electrophoresis (CE) in

indirect photometric detection mode using a chromate background electrolyte as

detailed elsewhere [14]. A five-point calibration curve was constructed in the range

1–6 ppm (r2 = 0.9921–0.9956) and a new curve prepared on each day that sample

analyses were performed.

The Nexus cartridge, after collection of the inorganic fraction, was washed with

2 mL of 60% v/v methanol/water followed by 500 mL of acetonitrile. The cartridge

was then finally eluted with 500 mL of acetonitrile and the effluent collected in a

5 mL volumetric flask. 12 mL of 2-NT solution was added as an internal standard.

PETN

% Acetonitrile

0 20 40 60 80 100

% R

eco

ver

y

0

20

40

60

80

100

0

20

40

60

80

100

RC wipes

PolyEs wipes

b

ol

60 80 100

0

20

40

60

80

100

RC wipes

PolyEs wipes

s of water and organic solvents (acetone (a), acetonitrile (b) and methanol (c)). (The

ment).


The volume was made up with a 1:1 mixture of methanol and water and the amount

of TNT and PETN in this final solution determined using an Agilent 1120 high

performance liquid chromatography (HPLC) system with a diode array detector. An

isocratic run using methanol/water (60:40) as the mobile phase at a flow rate of

1 mL/min on a 4.6 � 150 mm Zorbax Eclipse XDB-C18 analytical column with

particle size of 5 mm was applied for the separation. 10 mL of sample solution was

injected into the HPLC system and the separation performed at 30 8C. The detection

of the target compounds was achieved by monitoring at a wavelength 212 nm with

a bandwidth of 4 nm and using a reference wavelength of 300 nm with a bandwidth

of 100 nm for baseline correction.

A five-point calibration curve was constructed in the range 0.2–3.2 ppm for both

TNT (r2 = 0.9976–0.9981) and PETN (r2 = 0.9931–0.9943). New analytical curves

were prepared on each day that sample analyses were performed. The whole

experiment, starting from the wiping of the test surface through to the SPE clean-up

was repeated over a period of three days. There were seven samples and one

negative control, which generated 8 solutions for inorganic analysis and another 8

solutions for organic analysis, on each of the three days.

3. Results and discussion

3.1. Single-step swab extraction for the combined recovery of organic

and inorganic explosives

In the extraction of PETN from the selected alcohol wipes, it wasfound that the percentage recovery increased as the proportion oforganic solvent in the extracting solvent increased (Fig. 1). Using amixture of acetone and water, the maximum recovery from thepolyester wipe was reached when the composition of theextracting solvent contained more than 40% v/v acetone. For the

TNT

% Acetone

0 20 40 60 80 100

% R

ecover

y

0

20

40

60

80

100

0

20

40

60

80

100

RC wipes

PolyEs wipes

a

TNT

% Metha

0 20 40

% R

ecover

y

0

20

40

60

80

100

RC wipes

PolyEs wipes

c

Fig. 2. Extraction profiles for TNT from selected wipes using various compositions of wate

represent � one standard deviation (SD) for the replicate samples per experiment. For the R

For all other data points, there were three replicates).

regenerated cellulose wipe, at least 60% v/v acetone was requiredfor good recovery. Using an extracting solvent that contained 40%v/v or more of acetonitrile in water was found to provide themaximum recovery for PETN from both wipes. However, in thecase of methanol, at least 60% v/v was required in the extractingsolvent to achieve maximum recovery.

The TNT extraction results are summarised in Fig. 2. Ananomalous extraction profile was observed for the recovery of TNTfrom the regenerated cellulose wipes using a mixture of acetoneand water. There was a slight increase in recovery when theproportion of acetone in the extracting solvent was increased up to80%. However, when the composition of the solvent was greaterthan 80% acetone, a considerable drop in recovery was observed(Fig. 2). This low recovery at high concentrations of acetone wasstill observed when the extractions were repeated on two otheroccasions. In addition, the results were consistent with theobserved low recovery of TNT from the RC wipes when 100%acetone was employed as the extracting solvent.

From these results, there is an indication of some interaction(such as selective binding) between TNT and the regeneratedcellulose in the wipes. It appears that the extracting solvent needsto have a relatively high polarity in order to break this interaction.Attempts to extract using acetone from different suppliers and alsothe use of a sequential extraction using acetone followed byacetonitrile gave inconclusive results. Further investigation isrequired to determine the nature of this phenomenon.

TNT

% Acetonitrile

0 20 40 60 80 100

% R

ecover

y

0

20

40

60

80

100

0

20

40

60

80

100

RC wipes

PolyEs wipes

b

nol

60 80 100

0

20

40

60

80

100

r and organic solvents (acetone (a), acetonitrile (b) and methanol (c)). (The error bars

C wipe, there were six and nine replicates for the 80 and 100% data points, respectively.


In the cases of the polyester wipe, there was no significantchange in the recovery of TNT across the testing range of acetone/water compositions.

A slight improvement in the recovery of TNT from both wipeswas observed when the extracting solvent contained a higherproportion of acetonitrile or methanol. The high recovery of TNT(more than 60%) using only deionised water (i.e., 100% water) as anextracting solvent should also be highlighted. This result ispossibly explained by the intermediate hydrophobicity of TNT(log Kow = 1.6 [8]).

A very good recovery of RDX from both types of alcohol wipeswas observed regardless of the composition of the extractingsolvent and the type of organic solvent used (Fig. 3). The highrecovery of RDX when extracted with deionised water could againbe explained based on its low hydrophobicity (log Kow = 0.87 [8]).

In general, an improvement in the extraction efficiency of TATPwas found to be correlated to a higher portion of organic solvent inthe extracting solvent (Fig. 4). However, the magnitude of theimprovement was found to be strongly dependant on the type ofsampling media and the organic solvent employed.

Only the polyester wipes were tested in the remainingexperiments. There were several reasons for selecting thepolyester wipes. In a comparison between the two types ofalcohol wipes, the polyester wipe was found to be more robust andnot as easily ripped as the regenerated cellulose wipe. In addition,the polyester wipes could be more readily compacted in the glass

RDX

% Acetone

0 20 40 60 80 100

% R

ecover

y

0

20

40

60

80

100

0

20

40

60

80

100

RC wipes

PolyEs wipesa

RDX

% Met

0 20 40

% R

ecover

y

0

20

40

60

80

100

c

Fig. 3. Extraction profiles for RDX from selected wipes using various compositions of wate

represent � one standard deviation (SD) for three replicate samples per experiment).

vials for the extraction process, thus occupying less volume andresulting in a higher recovery in most cases. The processing of awipe inside the glass vial was also easier due to the reduced spaceoccupied by the wipe itself. The unexplained low recovery of TNTfrom the regenerated cellulose wipes utilising acetone as theextraction solvent was also a factor that favoured the polyesterwipes.

The extraction profiles for chlorate and nitrate from thepolyester wipes are summarised in Fig. 5. In the evaluation ofthe acetone extraction of chlorate from these wipes, a slightdecrease in recovery was observed when the range of acetone inthe extracting solvent increased from zero to approximately 40% v/v. The recovery then gradually improved as the proportion ofacetone in the mixture increased from 40 to 80% v/v. There was nosignificant change in chlorate recovery when extracting withvarious compositions of methanol/water and acetonitrile/watermixtures.

There was no significant difference in the recovery of nitratefrom the polyester wipes using a mixture of water and any of thetested organic solvents over the range from zero to 80% v/v.

3.2. Assessment of the retention capacity of the selected sorbents

The quantity of target compound in each fraction collected fromeach cartridge was used to calculate the percentage breakthrough.If the entire starting amount of 10 mg was found in that fraction

RDX

% Acetonitrile

0 20 40 60 80 100

% R

ecover

y

0

20

40

60

80

100

0

20

40

60

80

100

RC wipes

PolyEs wipesb

hanol

60 80 100

0

20

40

60

80

100

RC wipes

PolyEs wipes

r and organic solvents (acetone (a), acetonitrile (b) and methanol (c)). (The error bars

TATP

% Acetone

0 20 40 60 80 100

% R

ecover

y

0

20

40

60

80

100

0

20

40

60

80

100

RC wipes

PolyEs wipes

a

TATP

% Acetonitrile

0 20 40 60 80 100

% R

ecover

y

0

20

40

60

80

100

0

20

40

60

80

100

RC wipes

PolyEs wipes

b

TATP

% Methanol

0 20 40 60 80 100

% R

ecover

y

0

20

40

60

80

100

0

20

40

60

80

100

RC wipes

PolyEs wipes

c

Fig. 4. Extraction profiles for TATP from selected wipes using various compositions of water and organic solvents (acetone (a), acetonitrile (b) and methanol (c)). (The error

bars represent � one standard deviation (SD) for three replicate samples per experiment).


then the breakthrough was determined to be 100%. The results arepresented as breakthrough profiles that display plots of thepercentage of methanol in the loading solution versus thecumulative percentage breakthrough from the first collection upto the collection from the fraction in question.

The ideal SPE cartridge for cleaning up an extract from auniversal swab would have a profile where a 100% breakthroughoccurs at a very high percentage of methanol. That would indicatethat the sorbent has a strong interaction with the analyte (i.e., theanalyte is strongly retained by the sorbent at lower concentrationsof methanol).

As demonstrated in Figs. 6 and 7, most of the sorbents retainPETN and TNT well. No breakthrough was observed when themajority of the cartridges were flushed with a solvent containingless than 60% v/v methanol for PETN and less than 55% v/vmethanol for TNT. C18 was the only sorbent that could not providesufficient retention as no PETN could be retained on the cartridgewhen the cartridge was washed with 60% v/v methanol/water.With respect to TNT on the C18 sorbent, 100% breakthrough wasobserved when washed with a lower strength of 55% v/v methanol/water.

The poor retention capacity of C18 was clearly demonstrated inthe case of RDX, where 100% of the RDX was eluted from thecartridge when washed with only 40% v/v methanol/water (Fig. 8).Bond-Elut ENV also demonstrated a limited retention capacity

towards RDX. As shown in Fig. 8, no RDX could be retained on thistype of cartridge when flushed with 55% v/v methanol in water.

Considering the profiles obtained from all three explosivecompounds, and using the criterion that a considerable break-through (more than 50%) should not occur when washing with amixture of 50% v/v methanol and water, the C18 and Bond-ElutENV sorbents were excluded from future consideration.

3.3. Development and optimisation of a clean-up procedure

When comparing the retention capacity of the three selectedsorbents (XAD-7, Oasis and Nexus) across the two testing matrices,most sorbents performed well with a solution of 60% v/v methanolin water. However, considerable breakthrough was observed whena 40% v/v acetonitrile/water solution was used as the testingmatrix, especially in the case of TATP and RDX (Table 1). Theseresults therefore precluded the use of a 40% v/v mixture ofacetonitrile/water as an extracting solvent for a universal swab asit is incompatible with the subsequent solid-phase extractionprocedure. Also, as is clearly shown in Table 1, the XAD-7 cartridgedemonstrated a limited retention capacity towards TATP in thematrix of 60% v/v methanol/water. Therefore, this sorbent was notincluded in subsequent method development.

In the optimisation of the washing step with the two short-listedsorbents (Oasis and Nexus), the results in Table 2 indicate that the

% Acetone

0 20 40 60 80

% R

ecover

y

0

20

40

60

80

100

0

20

40

60

80

100

Chlorate

Nitratea

% Acetonitrile

0 20 40 60 80

% R

ecover

y

0

20

40

60

80

100

0

20

40

60

80

100

Chlorate

Nitrateb

% Methanol

0 20 40 60 80

% R

ecover

y

0

20

40

60

80

100

0

20

40

60

80

100

Chlorate

Nitratec

Fig. 5. Extraction profiles for chlorate and nitrate from the polyester wipes using various compositions of water and organic solvents (acetone (a), acetonitrile (b) and

methanol (c)). (The error bars represent � one standard deviation (SD) for three replicate samples per experiment).


interaction between the target compounds and the Nexus cartridgewas stronger than with the Oasis sorbent. Less breakthrough wasobserved with the Nexus cartridge after the cartridge was washedthree times. Thus, Nexus was identified as the most suitable sorbentfor use in establishing a final clean-up procedure. The volume ofwashing solution was subsequently restricted to 2 mL in order tokeep the loss (breakthrough) of TATP as low as possible.

For the study of eluting solvent, most of target compounds werenot found in the first fraction (Table 3). This was a result of the first500 mL of the eluting solvent replacing the residual loading solvent(60% v/v methanol/water) held by the bed of the sorbent. Typically,before the elution step, the SPE cartridge would be dried by passinga stream of air or nitrogen gas through it. However, this step wasspecifically excluded in this study in order to minimise the loss ofTATP that would potentially occur.

Table 1Percentage breakthrough (mean � 1 SD, n = 3) of the target organic explosives from the s

loading of 2 mL of test solution (PETN, TNT, and RDX at a concentration of 3 ppm; TATP at a co

indicates that no breakthrough was detected.

Explosive 60% methanol/water

XAD-7 Oasis Nexu

PETN – – –

TNT – – –

RDX – – –

TATP 46 � 7% 8 � 4% –

The eluting power of acetone and acetonitrile were found to behigher than that of methanol. This was clearly the case for PETNand TNT, where the amount recovered by eluting with methanolwas found to be lower than the limit of quantitation of the HPLCmethod. When comparing acetone and acetonitrile as elutingsolvents, there were no significant differences in their efficiency.Nevertheless, acetonitrile was chosen as an eluting solvent for twospecific reasons. Firstly, it is more compatible with the HPLCmethod used for the quantitative analyses as acetonitrile has a farlower UV cut-off than acetone. Secondly, the final extract wouldnot be suitable for the identification of TATP by GC/MS if acetonewere used in the elution step. This is due to the ambiguity that mayarise during the interpretation of results, as the electron impactmass spectrum of TATP at trace levels has similarities with thespectrum of acetone.

elected sorbents using two different solvent mixtures. Each experiment involved the

ncentration of 5 ppm) onto the selected SPE cartridge. The endash mark (–) in the table

40% acetonitrile/water

s XAD-7 Oasis Nexus

– – –

2 � 1% – –

49 � 1% 42 � 5% 21 � 3%

47 � 8% 23 � 7% 18 � 4%

PETN

% Methanol

0 10 20 30 40 50 60 70 80 90 100

Cu

mula

tiv

e %

Rec

ov

ery

0

20

40

60

80

100

120

0

20

40

60

80

100

120

XAD-7

Isolute C-18

BondE lut ENV

Nexus

Oasis

Fig. 6. Breakthrough profiles for PETN on the selected SPE sorbents. (The error bars


TNT

% Methanol

0 20 40 60 80

Cum

ula

tive

% R

ecover

y

0

20

40

60

80

100

0

20

40

60

80

100BondElut-ENV

Nexus

Isolute C-18

XAD-7

Oasis

Fig. 7. Breakthrough profiles for TNT on the selected SPE sorbents. (The error bars


RDX

% Methanol

0 10 20 30 40 50 60 70 80

Cum

ula

tive

% B

reak

thro

ugh

0

20

40

60

80

100

0

20

40

60

80

100

XAD-7

Isolute C18

Nexus

BondElut ENV

Oasis

Fig. 8. Breakthrough profiles for RDX on the selected SPE sorbents. (The error bars

represent � one standard deviation (SD) for three replicate samples per experiement).

Day 1 Day 2 Day 3

% R

ecover

y

0

20

40

60

80

100

0

20

40

60

80

100

PETN

TNT

Chlorate

Fig. 9. Percentage recovery of the three target compounds from the laminate testing

surface utilising the proposed swabbing/clean-up protocol over a period of three

days. (The error bars represent � one standard deviation (SD) for seven replicate

samples).


By combining the best conditions from each step during theoptimisation of the solid-phase extraction technique, a clean-upprocedure for the organic compounds is proposed as follows: (i)the explosive residue extract in 60% v/v methanol/water is loadedonto a conditioned Nexus cartridge; (ii) the cartridge is washedwith 2 mL of 60% v/v methanol/water and then 500 mL ofacetonitrile added to flush residual washing solvent from thesorbent bed (with the effluent discarded); (iii) the cartridge iseluted with 500 mL of acetonitrile and the effluent collected fordirect analysis by HPLC (or dried over anhydrous sodium sulphatebefore being subjected to GC/MS analysis, for example).

Table 2Cumulative percentages of breakthrough (mean � 1 SD, n = 3) of the target organic explos

water (1 mL per wash). The endash mark (–) in the table indicates that no breakthrough w

Explosive Oasis

Load 1st wash 2nd wash 3rd wa

PETN – – – –

TNT – – – –

RDX – – 17 � 7% 72 � 8%

TATP – 7 � 1% 11 � 1% 26 � 8%

The performance of the proposed clean-up procedure needed tobe evaluated with real-world samples containing environmentalcontaminants. In order to obtain a testing solution that had amatrix as close as possible to ‘‘real’’ samples submitted forexplosive residue analysis, 185 polyester wipes were used tosample from various surfaces in high traffic areas both indoors andoutdoors (including kitchen surfaces, a computer keyboard, anATM keypad, door knobs, furniture arm rests, vehicle rims, externalwindow surfaces, and traffic signs). These polyester wipes wereextracted and the combined extract used as a ‘‘backgroundsolution’’ that was spiked with target explosive compounds at 2

ives from the selected sorbents subjected to a series of washings with 60% methanol/

as detected.

Nexus

sh Load 1st wash 2nd wash 3rd wash

– – – –

– – – –

– – – 2 � 1%

– – 6 � 1% 14 � 4%

Surface swabbed

with a polyester-

based alcohol wipe

Wipe placed in

4 mL glass vial

Add 1 mL 60% v/v

methanol/water and

seal with Parafilm®

Place in ultrasonic

bath for 10 min then

cool to RT

Pound the wipe with

the tip of a glass

pipette

Transfer extract to a

conditioned Nexus

SPE cartridge

Collect effluent (A)

Add 500 L deionised

water to cartridgeCollect effluent (B)

Combine (A + B)

and analyse for

inorganics

Wash cartridge with

2 mL 60% v/v

methanol/water

Discard effluent

Add 500 L

acetonitrile to

cartridge

Add 500 L

acetonitrile to

cartridge

Collect effluent (C)

LC analysis

Remove residual

water (e.g., anh.

sodium sulphate)

GC analysisor

Fig. 10. Flow-chart depicting the proposed universal swabbing and clean-up protocol for the combined recovery of organic and inorganic explosive residues. Commercial

polyester-based alcohol wipes are recommended as the swabbing medium.


concentrations (2 and 6 ppm for PETN, TNT and RDX; 4 and 10 ppmfor TATP). This generated a testing solution that could be used todetermine the recovery of the target compounds as well as theremoval of ‘‘typical’’ contaminants by the proposed SPE clean-upprocedure.

As indicated in Table 4, the recovery at a low startingconcentration was relatively good, with an average recovery ofat least 50% for each of the target compounds. However, theproposed clean-up procedure performed better for the recovery ofthe organic target compounds at the higher concentration, wheremore than 80% recovery was obtained except in the case of TNT(around 60% recovery). In addition, the analytical results did not

indicate any significant level of interfering compounds in the finalextracts.

3.4. Feasibility study on the universal swabbing protocol

The three target compounds in this part of the study (TNT, PETNand chlorate) were recovered from the laminate surface andprocessed utilising the proposed protocol for sampling mixturescontaining both organic and inorganic explosive compounds.Chlorate was found in the solution made up from the effluentcollected after loading the initial extract onto the SPE cartridge.TNT and PETN were found in the solution made up from the

Table 3Percentage recovery (mean � 1 SD, n = 3) of each organic explosive from the Nexus cartridge when eluted with each of three test solvents (500 mL per fraction). The endash mark (–)

in the table indicates that no target compound was detected in that fraction.

Explosive Acetone Acetonitrile Methanol

1st fraction 2nd fraction 1st fraction 2nd fraction 1st fraction 2nd fraction

PETN – 94 � 8% – 97 � 2% – <17%

TNT – 96 � 2% – 98 � 3% – <17%

RDX – 98 � 3% – 99 � 3% – 24 � 14%

TATP – 87 � 5% 6 � 2% 93 � 5% – 93 � 7%

Table 4Percentage recovery of the four target organic explosives following the proposed

clean-up procedure.

Explosive Starting amount

(mg in 1 mL of extract)

Recovery

(mean � 1 SD, n = 5)

PETN 2 80 � 9%

6 94 � 7%

TNT 2 54 � 6%

6 62 � 5%

RDX 2 53 � 3%

6 91 � 7%

TATP 4 50 � 10%

10 87 � 16%


effluent after the final acetonitrile elution of the SPE cartridge. Thisdemonstrated that the combined recovery and clean-up of organicand inorganic explosive compounds utilising one alcohol wipe wasfeasible.

A good recovery (more than 60%) of both TNT and PETN wasachieved and there was minimal variation among the samples runon the same day and on different days (Fig. 9). However, arelatively low recovery of chlorate (below 40%) was obtained overthe three days of testing. It was later determined that aconsiderable amount of chlorate was retained on the bed of resinin the SPE cartridge. This was confirmed when a higher recovery(greater than 50%) was obtained when the protocol was modifiedwith an additional step of flushing with 500 mL of deionised waterafter loading the extract. This extra step had no effect on therecovery of PETN and TNT so the final recommended protocol,summarised in Fig. 10, incorporates this step.

4. Conclusions

This study, aimed at establishing an optimised protocol for thecombined recovery of organic and inorganic explosive residues,followed from our previous work that recommended the use ofcommercially-available alcohol wipes as a sampling medium [14].Representative organic (TNT, PETN, RDX and TATP) and inorganiccompounds (chlorate and nitrate) were employed to determinesolvent extraction profiles and to test the relative efficiency of anumber of SPE adsorbents. Ultimately, 60% v/v methanol/water waschosen for the simultaneous extraction of organic and inorganicresidues from the alcohol wipes, with polyester-based wipesexhibiting a number of advantages over cellulose-based wipes.

Of the SPE adsorbents tested, the ABS ELUT Nexus cartridgesdemonstrated the most favourable properties for the processing ofthe swab extracts. These cartridges demonstrated a high retentioncapacity towards all of the target organic compounds in a matrix of60% v/v methanol/water. Good recoveries of all of the selectedorganic explosives were achieved by utilising acetonitrile as aneluting solvent. It was demonstrated that these cartridges couldnot only be used for extract clean-up, but also for the separation ofthe swab extract into organic and inorganic components forindependent analyses.

By incorporating the single-step solvent extraction with theoptimised SPE clean-up procedure, a combined organic/inorganicsampling protocol was established. For validation, the proposedprotocol, using a polyester-based alcohol wipe as a universal swab[14], was applied for the collection of an organic/inorganic testmixture deposited on a laminate surface. The results indicated thatall target compounds (both organic and inorganic) were efficientlyrecovered and could be detected in the extract from a single wipe.The initial protocol was further adjusted to improve the recovery ofthe inorganic target compounds.

The final optimised swabbing and clean-up protocol issummarised in Fig. 10. The inorganic fraction can be analyseddirectly by CE or ion chromatography (IC), for example (althoughfurther optimisation may be required for IC analysis as thiswas not specifically tested in this study). The organic fractioncan be analysed directly using LC-based techniques (e.g., LC/MS)but must be dried prior to analysis by gas chromatography(e.g., by passing the extract through anhydrous sodiumsulphate).

Given the wide range of potentially interfering compounds thatmay be encountered during the collection and analysis of explosiveresidues, more work is required to evaluate the performance of theproposed protocol (particularly the SPE clean-up phase) whensignificant levels of various contaminants are present.

Acknowledgement

The authors would like to acknowledge the strong support forthis project from Forensic and Data Centres, Australian FederalPolice.

References

[1] D. Warren, R.W. Hiley, S.A. Phillips, K. Ritchie, Novel technique for the combinedrecovery, extraction and clean-up of forensic organic and inorganic trace explo-sives samples, Sci. Justice 39 (1999) 11–18.

[2] H.E. Cullum, C. McGavigan, C.Z. Uttley, M.A.M. Stroud, D.C. Warren, A secondsurvey of high explosives traces in public places, J. Forensic Sci. 49 (2004) 684–690.

[3] S. Doyle, Quality and the trace detection and identification of organic highexplosives, in: A. Beveridge (Ed.), Forensic Investigation of Explosions, seconded., CRC Press, Boca Raton, 2011, pp. 539–583.

[4] J.M.F. Douse, Trace analysis of explosives in handswab extracts using AmberliteXAD-7 porous polymer beads, silica capillary column gas chromatography withelectron-capture detection and thin-layer chromatography, J. Chromatogr. 234(1982) 415–425.

[5] J.M.F. Douse, Trace analysis of explosives at the low nanogram level in handswabextracts using columns of Amberlite XAD-7 porous polymer beads and silicacapillary column gas chromatography with thermal energy analysis and electroncapture detection, J. Chromatogr. 328 (1985) 155–165.

[6] T. Tamiri, An improved procedure for cleaning post-explosion debris, in: Paperpresented at the 5th International Symposium on Analysis and Detection ofExplosives, Washington, D.C., USA, 4–8 December, 1995.

[7] R.Q. Thompson, D.D. Fetterolf, M.L. Miller, R.F. Mothershead, Aqueous recoveryfrom cotton swabs of organic explosives residue followed by solid phase extrac-tion, J. Forensic Sci. 44 (1999) 795–804.

[8] R. Tachon, V. Pichon, M.B. Le Borgne, J.-J. Minet, Comparison of solid-phaseextraction sorbents for sample clean-up in the analysis of organic explosives, J.Chromatogr. A 1185 (2008) 1–8.

[9] J.J. Richard, G.A. Junk, Determination of munitions in water using macroreticularresins, Anal. Chem. 58 (1986) 723–725.


[10] T.F. Jenkins, P.H. Miyares, K.F. Myers, E.F. Mccormick, A.B. Strong, Comparison ofsolid phase extraction with salting-out solvent extraction for preconcentration ofnitroaromatic and nitramine explosives from water, Anal. Chim. Acta 289 (1994)69–78.

[11] J. Liu, S.A. Severt, X. Pan, P.N. Smith, S.T. Mcmurry, G.P. Cobb, Development of anextraction and cleanup procedure for a liquid chromatographic–mass spectro-metric method to analyze octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine ineggs, Talanta 71 (2007) 627–631.

[12] R. Batlle, H. Carlsson, P. Tollback, A. Colmsjo, C. Crescenzi, Enhanced detection ofnitroaromatic explosive vapors combining solid-phase extraction-air sampling,

supercritical fluid extraction, and large-volume injection-GC, Anal. Chem. 75(2003) 3137–3144.

[13] S. Jonsson, L. Gustavsson, B. Van Bavel, Analysis of nitroaromatic compounds incomplex samples using solid-phase microextraction and isotope dilution quan-tification gas chromatography–electron-capture negative ionisation mass spec-trometry, J. Chromatogr. A 1164 (2007) 65–73.

[14] N. Song-im, S. Benson, C. Lennard, Evaluation of different sampling media for theirpotential use as a combined swab for the collection of both organic and inorganicexplosive residues, Forensic Sci. Int., http://dx.doi.org/10.1016/j.forsciint.2012.05.006.



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