Chapter 20c

Drug detectors

Sue M. Ford

20c.1 DRUG DETECTION IN THE FIELD

20c.1.1 Background considerations

Drug detection technologies are used in various law enforcement sce-narios that present challenges for instrumentation development. Notonly do the drugs which must be detected vary, but the amounts to bedetected range from microgram quantities left as incidental contami-nation from drug activity to kilogram amounts being transported inhidden caches. The locations of hidden drugs create difficulties in de-tection as well. Customs and border agents need drug detection techno-logy to intercept drugs smuggled into the country in bulk cargo con-tainers or carried by individuals. Correctional facility personnel searchfor drugs being smuggled into the prison by mail (e.g. small amountsunder stamps) or by visitors, and furthermore need to monitor drugpossession inside the prison. Law enforcement representatives may usedetectors in schools to find the caches of student dealers. Other cus-tomers for drug detection technology include aviation and marine car-riers, postal and courier services, private industry, and the military. Inall these cases, the problem is to reveal the relatively rare presence ofdrugs in a population of individuals or items, most of which will benegative. Consequently, for drug detection purposes the ability to findillicit contraband is of greater importance than accurate quantitation.

20c.1.2 Desirable characteristics of field detectors

Drug detectors are used on-site to screen items in transit, such as cargo,pieces of mail, or personal belongings of individuals. The units must bemobile or portable. Inasmuch as innumerable objects need to be scru-tinized rapidly in order to minimize delays and inconvenience, the

Comprehensive Analytical Chemistry 47S. Ahuja and N. Jespersen (Eds)Volume 47 ISSN: 0166-526X DOI: 10.1016/S0166-526X(06)47031-8r 2006 Elsevier B.V. All rights reserved. 789

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process of screening should ideally be non-invasive, non-destructive,and rapid, and should display results within seconds. Instrumentationfor drug detection in the field must be simple enough to be used bytrained non-scientific personnel and the output should be easily inter-preted. Sample acquisition should be simple with little requirement ofsample preparation. With the exception of the X-ray and CT scanners,which weigh 0.5–3 tons [1], instrumentation for drug detection in thefield is easily transported, and includes mobile desktop units as well ashand-held instruments. On-site drug detection necessitates all phasesof analysis to be completed in the field, including sample collection,processing for presentation to the analytical module, identification, andquantitation.

20c.1.3 Sampling

The ability to successfully discover trace amounts of contrabanddepends on the sampling methodology as well as the detector. Drugresidue detection on individuals, luggage and personal effects, mail,currency, and other items such as newspaper may be assessed by parti-culate detection. The surfaces are swiped with a swab, pad, or paperdisk (sample trap), or the particles are collected on a filter by moving avacuum over the surface. For screening of multiple items, it may besufficient to swipe several times at a time with individual analysisneeded only if a positive result is obtained. The swab or trap may beextracted with solvent and the sample then introduced into the instru-ment. In some cases, samples collected on a TeflonTM pad are heated inthe instrument in order to volatilize the analyte. Most instrumentsoperate either as vapor detectors or particle analyzers, although thereare a few that can operate in both modes. Newer sampling devices, suchas those employed by the US Transportation Security Administration(produced by Smiths Detection (London, England and Pine Brook, NJ)for explosives detection, blow puffs of air at passengers from head tofoot. Particles which subsequently fall to the ground are collected bybeing sucked into vents for chemical analysis.

20c.1.4 Background contamination

Detection of drug residues that contaminate surfaces and vapors seep-ing from caches requires that the sensitivity of such methods is gene-rally in the sub-microgram range. Individuals who have handled drugsmay have residues on their hands in the range of 1–10 mg [2], which can

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remain at least 90min after handling and handwashing [3]. Anotherapplication of trace detection is in screening currency, suspected ofbeing used in illicit drug activity. Although the instrument should pickup the low quantities expected from handling in such situations, insome metropolitan areas most currency is contaminated with drugs andan instrument with the threshold set too low will generate many falsepositives.

20c.2 INSTRUMENTATION

20c.2.1 Bulk detection

Instrumentation for revealing the presence of bulk quantities of con-cealed drugs will differ from those developed to find evidence of minutequantities on surfaces. Bulk detection is concerned with amounts rang-ing from grams to kilograms [4]. Bulk detection is done by manualinspection, X-ray, CT scans, and acoustic inspection. X-ray or CT scan-ners used as bulk detectors have sensitivity of 2–10 g, and suspect itemsare subsequently confirmed by chemical analysis. Hand-held acousticinspection instruments such as the Acoustic Inspection Device (AID)and the Ultrasonic Pulse Echo (UPE) developed by Pacific NorthwestNational Laboratories/Battelle, can be used for analysis of cargo liquidsin sealed containers of various sizes within seconds [5]. The acousticalvelocity and attenuation of multiple echoes returned to the instru-ment is evaluated by software which compares the data to the shippingmanifest.

20c.2.2 Trace detection

20c.2.2.1 Wipe and sprayFor evaluating a small number of samples, non-instrument-basedkits are available which are rapid and do not require sample cleanup.Wipe and spray detection kits such as those from the Mistral Group(Bethesda, MD) can be purchased for single drugs, multiple drugs, andexplosives. The surfaces to be tested are swiped with paper sampletraps, which are then sprayed with a reagent which turns the colordepending on the compound(s) present. The reagents have been modi-fied to be stable in the kit, for example, a modified Fast Blue BB reagentfor cannabinoids and a modified cobalt thiocyanate (Scott) reagent forcocaine. The sensitivity of these kits is in the 1–10 mg range.

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20c.2.2.2 Vapor detectionSome contraband drugs have sufficient vapor pressure to be detected byvapor detectors (‘‘sniffers,’’ electronic noses), which draw in air aroundthe test area and introduce the sample directly into the instrument.With the ZNoseTM (Electronic Sensor Technology, LP, Newbury Park,CA), the components of the vapor are separated by a fast (10 s) gaschromatography system. The detector contains molecular recognitionsensor arrays based on surface acoustic wave (SAW) technology. Theindividual sensors each contain a chemoselective polymer sorbent ap-plied to the surface of acoustic wave transducers [6]. As each vaporcomponent interacts with a particular polymer, the properties of thepolymer change (mass, viscoelasticity, swelling), which in turn perturbsthe velocity of the SAW. The resulting shift in resonance frequencies ofmultiple sensors contributes to the pattern of output. Electronic nosesprovide a distinctive visual output, similar to an inkblot, which can beused to identify complex vapors by the shape of the ‘‘blot’’ or print.

Detection of vapors seeping from closed containers may be suffi-ciently sensitive that opening the container may not be necessary.Vapor detectors work for drugs such as heroin and marijuana whichhave volatile components with sufficient vapor pressure for detection,whereas particle detection and swiping are more appropriate for otherdrugs. However, drugs without appreciable vapor pressure may be de-tectable in warmer temperatures or may have components that aredistinctive enough to comprise an odor signature. For example, methylbenzoate is the component of street cocaine that dogs recognizeand represents a signature molecule that can be detected with instru-mentation.

20c.2.2.3 BiosensorsBiosensors represent another technique for simple and rapid analysesin the field (see Chapter 20a). Biosensors utilize proteins, includingantibodies, enzymes, or receptors, which have affinities for specificchemicals. The proteins are incorporated into devices which produce adetectable response (e.g. color change) proportional to the amount ofbinding of analyte to the protein. Figure 20c.1 shows the general pro-cedure for an enzyme-linked immunosorbant assay (ELISA). The pro-teins are chosen to bind specific compounds, such as the use ofantibodies to detect cocaine or the enzyme acetylcholinesterase to de-tect organophosphate pesticides [7]. However, there is some degree ofcross-reactivity. In some cases this may be advantageous in detectingstructurally related derivatives such as metabolites [8]. Biosensors may

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Fig. 20c.1. ELISA assay. (a) Antibodies to the drug of interest are secured to asolid substratum such as a test tube or micro-well plate. The sample contain-ing the analyte antigen is added to the reaction surface. (b) After the analytehas bound to the antibody, the vessel is rinsed to remove unbound antibody. Asecond antibody to the analyte is added. This antibody has a bound enzymewhich has been chosen because its reaction produces a colored product whichcan be detected spectrophotometrically. (c) After this second antibody hasbound to the first antibody–antigen complex, the surface is again rinsed toremove unbound-antibody enzyme. The enzyme substrate is added in suffi-cient excess such that the rate of product formed is proportional to the amountof enzyme present. The enzyme-linked assays are very sensitive, since eachenzyme can rapidly catalyze thousands of substrate to product reactions.

Drug detectors

be incorporated into electronic equipment using piezoelectric trans-duction [7,9], in which case the binding event of antigen to antibodycauses a change in the frequency of the signal from a piezoelectrictransducer. A simpler, yet effective, use of immunoassay is illustratedby the single-use disposable devices such as the Drugwipes. The Drug-wipes (Securetec Detektions-Systeme AG, Germany) is an immunoas-say-based biosensor device that is available for opiates, cocaine,cannabis, and amphetamines. It can be used to assay surfaces as well

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as bodily fluids such as sweat, saliva, and urine. Limited testing sug-gests that the low sensitivity of such biosensors in biological fluids re-sults in a high incidence of false negatives [10]. The method is about anorder of magnitude more sensitive for surface detection [11]. The de-tection limits for cocaine are in the range of 34ng/l (in water) for apiezoelectric immunosensor [7,9] to 50ng/ml (in sweat, saliva) [11] forDrugwipes.

20c.2.2.4 Ion mobility spectrometryIon mobility spectrometry (IMS) [3,12] is the most widely used instru-ment for drug detection. The sample is heated to vaporize the analyte,which is then ionized by atmospheric (ambient) pressure chemical ioni-zation (APCI) [3]. The resulting gas-phase ions travel through a drifttube and are separated by their distinct velocities (mobilities) in a weakelectrostatic field. IMS instruments use ambient air or nitrogen as thecarrier gas, making it particularly adaptable to field applications.

The ionization process for IMS is relatively mild, such that little orno fragmentation of the analyte occurs. A common ionization sourcefor APCI is 63Ni, which is coated on a foil of gold or nickel [3]. Theb-particle emitted reacts with nitrogen to produce a cascade of positiveand negative ions, and secondary electrons. Collisions and subsequentreactions can result in proton transfer reactions and formation of clus-ters, dimers, and adducts. The drift gas for drug detection containstrace amounts of nicotinamide, which becomes protonated and cantransfer the proton to the sample molecules [13]. 63Ni as an ionizationsource does limit the linear range and selectivity; however, it is advan-tageous for field equipment because it does not require an externalpower supply, it is not prone to malfunction, and it has good specificityfor its intended analytes. Other ionization methods, including photo-ionization, corona discharge, flame ionization, laser ionization, surfaceionization, and electrospray ionization provide opportunities for ex-tending the range and selectivity of IMS [3,14].

The linearity of IMS is not sufficient for accurate quantitation ofanalytes. However, detection of contraband essentially requires a posi-tive/negative response, so that for this purpose linearity is not critical.The method is sensitive (sub-nanogram range) and has sufficient re-solution ability [15,16]. The instrument can be adjusted to provide evenbetter resolution for specific analytes of interest (e.g. drugs vs. explo-sives). These features, along with the reliability of the instrument, havemade it the method of choice for field operations. IMS instrumenta-tion has undergone numerous modifications that are promising for field

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detection technology, including miniaturization to palm-sized units,redesign of drift tubes to increase resolution [17–19], inclusion of a GCcolumn or GS/MS as a pre-separator to reduce matrix effects [3,20], andimprovements in sampling techniques [3,14]. Smiths Detection has re-cently introduced the Ionscan 500DT, which contains two IMS detec-tors and allows for simultaneous detection of narcotics and explosivesin a single analysis.

20c.2.2.5 Mass spectrometryMass spectrometry (MS) is a reliable laboratory method for identifica-tion and analysis of organic compounds (see Chapter 11). Successivegenerations of instruments have increased the power of analysis byinterfacing MS with separation techniques such as gas chromato-graphy. The advantages of MS methodologies over IMS include versa-tility in sample analysis, improved linearity, and accurate quantitationwhen necessary. The size of mass spectrometers has been reduced suchthat it is now feasible to transport the instruments for analysis inthe field [21,22]. Although the performance is generally inferior to labo-ratory-sited instruments, software can help minimize problems relatedto resolution. The limitations of MS compared to IMS are the bulkand complexity of instrumentation (e.g. vacuum, heating/cooling of GCcolumn, power consumption) and more involved sample preparation.Additionally, the sampling and analysis times are longer, in the range of15min, compared to less than 20 s for IMS. MS technology is parti-cularly valuable when specific identification of compounds is mandatory.The instrumentation size and the length of analysis preclude the use ofMS for rapid screening of mail, luggage, and other high-throughputtasks.

20c.2.2.6 Raman spectroscopyRaman spectroscopy is used to identify substances based on the ine-lastic scattering of light. When light is applied to a molecule, the en-ergy change between incident and scattered light depends on thestructure of the molecule. Drugs and other complex molecules havemany possibilities for interaction with light, and the spectrum of scat-tered light contains a characteristic pattern of peaks (‘‘fingerprint’’)that can be used to identify substances of interest [2]. The process israpid, non-destructive, and requires minimal sample preparation [23].The instruments can be configured with fiber optic sample probes todetect chemicals on the ground and other surfaces. One application isto detect drugs in fingerprints while preserving the prints for other

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analyses [24,25]. It will also work through certain closed containerssuch as dark glass, plastic bags, and thin plastic containers. This, inparticular, makes it more useful for field applications than other spec-troscopic methods such as FT-IR. A database of spectra is neededto determine whether compounds of interest are present or absent.FT-Raman spectra libraries are commercially available, including forillicit drugs [23]. Portable instruments suitable for field use are avail-able by InPhotonics (InPhototeTM), GE StreetLabTM (GE Ion Trak,Plainville, CT), RSL-1 Raman (Spectrolab, Berkshire, England), andRA series (Renishaw plc, Gloucestershire, UK). Software is available todissect the spectra of interfering materials which may be mixed withthe target substances.

REFERENCES

1 D. Blackburn, Counterdrug technology development program. Identifica-tion, demonstration, and assessment of drug detection technology, 2003.

2 J.E. Parmeter, D.W. Murray and D.W. Hannum, Guide for the selection ofdrug detectors for law enforcement applications, NIJ Guide, 601-00(2000) 1–53.

3 G.A. Eiceman and Z. Karpas., Ion Mobility Spectrometry, CRC Press, BocaRaton, 1994.

4 S. Wright and R.F. Butler, Technology takes on drug smugglers. Can drugdetection technology stop drugs from entering prisons?, CorrectionsToday, 63 (2001) 66–68.

5 A. Diaz, Acoustic inspection and analysis of liquids in sealed containers,Sensors, 20 (2003) 14.

6 E.J. Houser, T.E. Mlsna, V.K. Nguyen, R. Chung, R.L. Mowery andA. McGill, Rational materials design of sorbent coatings for explosives:applications with chemical sensors, Talanta, 54 (2001) 469–485.

7 J. Halamek, A. Makower, K. Knosche, P. Skladal and F.W. Scheller,Piezoelectric affinity sensors for cocaine and cholinesterase inhibitors,Talanta, 65 (2005) 337–342.

8 P.J. Devine, N.A. Anis, J. Wright, S. Kim, A.T. Eldefrawi and M.E.Eldefrawi, A fiber-optic cocaine biosensor, Anal. Biochem., 227 (1995)216–224.

9 J. Halamek, A. Makower, P. Skladal and F.W. Scheller, Highly sensitivedetection of cocaine using a piezoelectric immunosensor, Biosens. Bio-electron., 17 (2002) 1045–1050.

10 P. Kintz, V. Cirimele and B. Ludes, Codeine testing in sweat and salivawith the Drugwipe, Int. J. Legal Med., 111 (1998) 82–84.

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11 R. McCullough, The use of the Drugwipe in a drug court setting. NationalLaw Enforcement and Corrections Technology Center Rocky MountainRegional Center, 5th Annual Innovative Technologies for CommunityCorrections Conference, Boston, MA, June 14–16, 2004.

12 T. Keller, A. Schneider, E. Tutsch-Bauer, J. Jaspers, R. Aderjan andG. Skopp, Ion mobility spectrometry for the detection of drugs in cases offorensic and criminalistic relevance, Int. J. Ion Mobility Spectrom., 2(1999) 22–34.

13 T. Keller, A. Miki, P. Regenscheit, R. Dirnhofer, A. Schneider andH. Tsuchihashi, Detection of designer drugs in human hair by ion mobi-lity spectrometry (IMS), Forensic Sci. Int., 94 (1998) 55–63.

14 F. Li, Z. Xie, H. Schmidt, S. Sielemann and J.I. Baumbach, Ion mobilityspectrometer for online monitoring of trace compounds, Spectrochim.Acta-B, 57 (2002) 1563–1574.

15 L.M. Matz and H.H. Hill Jr., Separation of benzodiazepines by electro-spray ionization ion mobility spectrometry-mass spectroscopy, Anal.Chim. Acta, 457 (2002) 235–245.

16 J.A. McLean, B.T. Ruotolo, K.J. Gillig and D.H. Russell, Ion mobility-mass spectrometry: a new paradigm for proteomics, Int. J. Mass Spec-trom., 240 (2005) 301–315.

17 I.A. Buryakov, Qualitative analysis of trace constituents by ion mobilityincrement spectrometer, Talanta, 61 (2003) 369–375.

18 I.A. Buryakov, Express analysis of explosives, chemical warfare agentsand drugs with multicapillary column gas chromatography and ion mobi-lity increment spectrometry, J. Chromatogr. B, 800 (2004) 75–82.

19 R.R. Kunz, W.F. Dinatale and P. Becotte-Haigh, Comparison of detectionselectivity in ion mobility spectrometry: proton-attachment versus elec-tron exchange ionization, Int. J. Mass Spectrom., 226 (2003) 379–395.

20 A.M. DeTulleo, P.B. Galat and M.E. Gay, Detecting heroin in the presenceof cocaine using ion mobility spectrometry, Int. J. Ion Mobility Spectrom.,1 (2000) 38–42.

21 P.A. Smith, M.T. Sng, B.A. Eckenrode, S.Y. Leow, D. Koch, R.P. Erickson,C.R.J. Lepage and G.L. Hook, Towards smaller and faster gas chroma-tography–mass spectrometry systems for field chemical detection,J. Chromatogr. A, 1067 (2005) 285–294.

22 A.L. Makas and M.L. Troshkov, Field gas chromatography–mass spectro-metry for fast analysis, J. Chromatogr. B, 800 (2004) 55–61.

23 H. Tsuchihashi, M. Katagi, M. Nishikawa, M. Tatsuno, A. Nishioka, A.Nara, E. Nishio and C. Petty, Determination of methamphetamine and itsrelated compounds using Fourier Transform Raman spectroscopy, Appl.Spectrosc., 51 (1997) 1796–1799.

24 J.S. Day, H.G.M. Edwards, S.A. Dobrowski and A.M. Voice, The detec-tion of drugs of abuse in fingerprints using Raman spectroscopy II:

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cyanoacrylate-fumed fingerprints, Spectrochim. Acta Part A: Mol. Biomol.Spectrosc., 60 (2004) 1725–1730.

25 J.S. Day, H.G.M. Edwards, S.A. Dobrowski and A.M. Voice, The detectionof drugs of abuse in fingerprints using Raman spectroscopy I: latent fin-gerprints, Spectrochim. Acta Part A: Mol. Biomol. Spectros., 60 (2004)563–568.

REVIEW QUESTIONS

1.

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Describe some of the desirable characteristics of field detectors.

2. Describe briefly operation of biosensors.