Application of air sampling and ion-mobility spectrometry to narcotics detection: a feasibility study

Sections

ABSTRACT
Introduction
Experiments

Details

Author: A. H. LAWRENCE and, L. ELIAS
Pages: 3 to 16
Creation Date: 1985/01/01

Application of air sampling and ion-mobility spectrometry to narcotics detection: a feasibility study *

A. H. LAWRENCE and
L. ELIAS
Unsteady Aerodynamics Laboratory, National Aeronautical Establishment, National Research Council, Ottawa, Ontatio, Canada

ABSTRACT

A feasibility study of-the application of air sampling and ion-mobility spectrometry (IMS) for detection of heroin and cocaine concealed in letter mail snowed that a unique IMS signature is associated with each type of drug and that a number of IMS peaks can be used as markers for the presence of drugs. No false reading for cocaine or heroin resulted when innocent items were monitored. Near real-time performance with sampling and analysis times of less than 30 seconds was achieved for the simultaneous detection of cocaine and heroin. The method proved to be a reliable tool for the fast screening of suspect items. Preliminary tests also showed that the method has potential for use in detecting the drugs in suitcases and on people.

Introduction

The past few years have seen a dramatic increase in the smuggling and abuse of illicit drugs. A recent study by the Royal Canadian Mounted Police revealed that sales of illicit drugs, including cocaine, heroin, cannabis and amphetamines, in Canada amounted to more than $Can 8 billion in 1981 [ 1] . The available evidence clearly shows that the growing illicit drug traffic presents a serious threat to society [ 2] .

Illicit drugs are imported into Canada in various quantities and concealed in a variety of ways. Detection of concealed drugs is made difficult by the vast volume of traffic by sea and air, the insufficient manpower available carry out searches, and often the clever means of concealment.

The sniffer dog, usually a German shepherd or a labrador, is currently the most widely used method of detecting illicit drugs. Unfortunately, a dog can only be used for a fairly short period of time before it becomes tired or bored [ 3] . The person handling the sniffer dog must be skilled in recognizing the tell-tale signs of a find. There is, therefore, a need for a technical instrument to complement the use of dogs in detecting illicit drugs. Such an instrument should be highly sensitive and specific, as well as relatively inexpensive and easy to use in order to se of practical value. An important advantage of such an instrument would obviously be its ready availability at any time.

* Manuscript received on 28 August 1984.

To meet this need, there has seen a steady growth in research and development in the field of instrumental detection and identification of illicit drugs. Numerous research and development programmes have seen initiated in Canada [ 4] and elsewhere to improve the ability of drug enforcement officials to prevent the smuggling of drugs.

Instrumental drug detection techniques may be classified into two main categories. The first category refers to air sampling followed by trace chemical analysis of ambient air to determine drug-related constituents in the form of vapours or microparticles which may be present in trace quantities. For this purpose, two types of chemical sensor have been used to date, namely the mass spectrometer [ 5, 6] and the gas-chromatograph nitrogen/phosphorus detector [ 7] . The Unsteady Aerodynamics Laboratory of the National Research Council, in conjunction with the Department of Revenue Canada, Customs and Excise, is undertaking the development of a portable narcotics detector based on the gas-chromatography nitrogen/phosphorus detector, and it is anticipated that the unit will be ready for field testing in l985.

Bulk techniques designed to detect drugs by means of their physical or chemical properties or their modes of concealment fall into the second category of detection techniques, which includes X-raying, nuclear magnetic resonance, dielectric analysis and gamma back-scattering [ 8 - 10] . In almost all bulk detection techniques, the suspected item to be examined is subjected to an electric or magnetic field. The presence of drugs is determined by the interaction of matter in the item with the probing field.

A general survey of the physical principles, the state of development and operational applications of some of the above-mentioned techniques has been described elsewhere [ 11] .

This article describes the detection of drugs through air sampling classified in the first category above. A plasma chromatography or IMS (annex I) is used as the analytical tool for this purpose. The following paragraphs summarize the method and results of a laboratory feasibility study of the potential application of IMS in the detection of cocaine and heroin. Simulated field trials were also conducted, including search scenarios involving letter-mail, suitcases and persons.

Experiments

Chemicals and standard solutions

Cocaine alkaloid (May and Baker, L64305) and heroin (T. and H. Smith, EV-9022-29) were obtained from the Department of Health and Welfare of Canada.

The stock solution (10 -6 g/µl) was prepared by dissolving 40 to 50 mg of the drugs in 50 cm 3 of acetone. The standard hexane solution was prepared by the appropriate dilution of the stock solution. The concentration of the standard solution for either cocaine or heroin was 1 x 10 -8 g/µl.

The standard solution (1 x 10 -8 g/µl in acetone) of a seized sample of either cocaine (90 per cent) or heroin (70 per cent) was similarly prepared. The samples of seized drugs were also obtained from the Department of Health and Welfare of Canada.

Instrumentation

Positive ion-mobility spectra were obtained with a Phemto-Chem 100 ion-mobility spectrometer. Ultra-high-purity nitrogen was dried by passage through molecular sieve 13X and used for both carrier and drift gases. The operating principle of the ion-mobility spectrometer detector cell (see figure I) is summarized in annex I.

Operating conditions were as follows: carrier gas flow rate, 400 cm 3 per min; drift gas flow rate, 660 cm 3 per min; drift tube and injection port temperature, 220°C ; pressure, 752 torr; electric field gradient, 3,000 V per 14 cm (214 V/cm); gate width, 0.2 milliseconds. The drift length of the Phemto-Chem 100 ion-mobility spectrometer is 8 cm.

All reported data were taken by signals averaging 24-millisecond scans in a Nicolet 535-1-04 signal averager and the averaged patterns were printed using a Hewlett Packard 7035 B X-Y recorder. The ADC resolution used with the signal averager was always 9 bits and the full-scale volt setting was kept at ±4 volts. Figures II to IX represent aggregate averages of 512 scans of 24 milliseconds each (12-second response time) after injection of the sample. Mass identification was achieved by means of a Phemto-Chem MMS-160 ion-mobility spectrometer and a mass spectrometer.

Sampling cartridge

A detachable nickel sampling cartridge was used for injection of both liquid and air samples. In a typical liquid injection, 1 µl of the standard drug solution is deposited in the cartridge and, after evaporating the solvent by passage of a carrier gas flow for a few seconds, the prose is interfaced with the inlet of the ion-mobility spectrometer [ 12] (see figure I). For air sampling, the sampling cartridge is connected to an aspirator pump operating at a set suction rate. Atmospheric chemicals are detected when ambient air is drawn through the sampling cartridge and subsequently injected into IMS as cited above.

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Results and discussion

The nature of the reactant ion spectra resulting from the carrier gas entering the ionization region was studied first. When pure nitrogen is the carrier, the negative spectrum shows no reactant ion, while the positive spectrum displays the three well-identified reactant ions shown in figure II, graph (a). These are NH 4 +, NO + and H + (H 2O) 2 [ 13] at drift times of 6.6, 7.5 and 8.4 milliseconds, respectively, and their reduced mobilities K 0 in cm 2 V -1 s -1 are 3. 12, 2.74 and 2.43, respectively. The calculation of reduced mobilities is presented in annex II. The values agree substantially with data published elsewhere [ 13] . The spectrum represented in figure II, graph (a), is usually recorded to ascertain that the instrument is free of contamination and the system functions properly.

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Ion-mobility spectra of cocaine and heroin

Positive ion-mobility spectra for pure and street samples of cocaine and heroin were obtained and are displayed in figures II to IX. Figure II, graphs (s), (c) and (d), show the change in the ion-mobility spectrum of cocaine with time. Figure II, graph (b), represents an aggregate average of 512 scans, 12 seconds after injection of the cocaine sample. The NH 4 + and NO + reactant ions at drift times of 6.6 and 7.5 milliseconds, respectively, have been depleted and the concentration of the H + (H 2O) 2 has decreased considerably by reaction with the sample. Cocaine gave a strong ion peak at a drift time of 17.6 milliseconds with a K 0 value of 1.16 cm 2 V -1 s -1. Using IMS and mass spectrometry [ 14] , it was determined that the cocaine ion-peak with a K 0 value of 1.16 cm 2 V -1 s -1 corresponds to the molecular ion peak M + of m/e = 303. Similar results were obtained by Karasek and others [ 15] . Figure II, graph (c), represents an aggregate average of 512 scans at 24 seconds after injection of the sample. The intensity of the cocaine ion peak has decreased considerably, while the concentration of the reactant ions has started to recover from depletion by reaction with the sample. Figure II, graph (d), represents an aggregate average of 512 scans at 36 seconds after injection of the sample and shows the disappearance of the cocaine ion peak.

The significance of these observations is noteworthy, since a narcotics detector based on an IMS sensor could provide near real-time analysis and would be useful where field operational constraints dictate a short response time.

Similarly, figures III and IV, graphs (b), (c) and (d), show the change in the ion-mobility spectrum of heroin with time. Under the experimental conditions described above, heroin gave two ion peaks at 17.9 and 19.6 milliseconds with K 0 values of 1.14 and 1.04 cm 2 V -1 s -1, respectively. By means of IMS and mass spectrometry, it was shown that the two principal peaks in the heroin spectrum are produced by ions with masses at 310 and 369. The ion at mass 369 corresponds to the parent ion M + and the ion at mass 310 corresponds to the ion fragment (M - CH 3CO 2) + [ 14, 15] .

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Effect of some potential interfering substances

Figure V shows the positive ion-mobility spectra from a 4-litre sample of laboratory air. The source of the ion peak at a drift time of 13 milliseconds (K 0 = 1.6 cm 2 V -1 s -1) is unknown. However, it is well separated from the cocaine and heroin molecular ion peaks. Sampling of a clean polyethylene bag and of the headspace volatiles of coffee and tea did not give any interfering peaks. In general, there is little interference for any of the ions studied. The cocaine and heroin molecular ions have long drift times, and are easily separated from common gases found in air. At present, an extensive investigation of the effect of potential interfering compounds is being carried out at the Unsteady Aerodynamics Laboratory.

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Screening of innocent and spiked letters

A set of 12 regular letters were screened, using a newly developed sampling technique [ 12] to ascertain whether or not spurious signals would occur from various letters that have been processed through the mail system. Of the 12 innocent letters examined none gave a signal response corresponding to either cocaine or heroin. Strong cocaine or heroin signals were, however, obtained from spiked letters packaged at the Unsteady Aerodynamics Laboratory (figure VI). Mail concealment methods were suggested to the authors by the Intelligence Division of the Department of Revenue Canada, Customs and Excise [ 7] .

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Examination of suitcases and personal sampling

The detection of illicit drugs in suitcases and on people was not originally part of the feasibility study, but was attempted during the test period, in a preliminary fashion, with some success. Several background readings of empty suitcases and blank subjects were taken and no response for cocaine or heroin was observed.

In the first sampling sequence, a subject planted a polyethylene bag containing one gram of cocaine street sample inside a suitcase and, subsequently, closed the zip-fastener of the suitcase. Sampling inside the suitcase, close to the package, gave a strong cocaine signal (figure VII)- Sampling very close to the zipper handle of the suitcase gave a relatively weaker but appreciable cocaine signal (figure VIII).

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In another experiment, a different subject carried one gram of heroin in a sealed polyethylene bag in his shirt pocket for a few seconds. Subsequently, he planted the package inside a suitcase and closed the zip-fastener. Direct probe sampling in the pocket, after removing the packet, gave a strong signal for heroin (figure IX). Sampling close to the zipper handle of the suitcase gave a weak but noticeable heroin signal and, finally, sampling close to the hands of the subject gave a slight positive heroin signal.

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Conclusions

The feasibility of using the air sampling technique cited in this article and the IMS sensor for detection of heroin and cocaine concealed in letter mail has been demonstrated. It has seen shown that a unique IMS signature is associated with each type of drug and that a number of IMS peaks can be used as markers for the presence of drugs. No false readings for the drugs in question resulted when innocent items were monitored. The method provides near real-time performance, and sampling-analysis times of less than 30 seconds were achieved for the simultaneous detection of cocaine and heroin.

A few preliminary tests also pointed towards a possibility of using this method for detection of illicit drugs in suitcases and on people.

Acknowledgment

The authors wish to thank Michel Asselin and Y. Boucher of the Defence Research Establishment Valcartier for their scientific and technical assistance in operating the ion-mobility spectrometer, as well as Bob Suart for his assistance and co-operation in making the facilities available to the authors for this study.

Annex I
ION-MOBILITY SPECTROMETRY

Ion-mobility spectrometry is an analytical technique that distinguishes ionic species on the basis of the differences in the drift velocity through a gas under an applied electrostatic field. It is a sensitive technique for detection of organic compounds under atmospheric pressure conditions [ 16] .

The basic components of an ion-mobility spectrometer include a small beta-ray source (Nickel-63) located in the reaction chamber region (figure I), an attached drift tube, which is maintained at an electric field gradient of approximately 200 volts per centimetre, and a collector. Molecular species present, including drug molecules, are ionized in the ion-molecule reaction chamber, and then injected into the drift tube, where the electric field causes them to flow against a countercurrent stream of drift gas. If a negative voltage is applied to create the electric field, negative ions formed in the reaction chamber region are accelerated down the drift region to the collector, which is almost at ground potential. Characteristic ions, separated in space according to their different velocities, provide an ion-mobility spectrum of the compound entering the instrument. Ion-mobility spectra may also be obtained for the positive ions formed in the reaction chamber simply by reversing the voltage supplied to create the electric field. Detection is accomplished with a fast electrometer amplifier.

Annex II
CALCULATION OF REDUCED MOBILITIES

In IMS, mobilities (cm 2 V -1 s -1) are used as the qualitative measurement of specific ions. They can be calculated directly from the drift time of the ion, the length of the drift tube, and the strength of the electric field applied. In practice, mobilities are corrected to conditions of standard temperature and pressure allowing comparisons with mobilities under different conditions. These corrected mobilities are termed reduced mobilities, K 0, and are calculated from the following equation: where d = drift length (cm), t = drift time (s), E = electric field gradient (V/cm), T = temperature (°K), and P = pressure (torr). The drift length of the Phemto-Chem 100 is 8 cm and the electric field gradient 214.2 V/cm (see section on experiments). Some reduced mobility values are given below.

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Ion(compound)

Drift time (milliseconds)

Reduced mobility (cm 2V -1s -1)

NH 4 +
6.56 3.12
NO +
7.45 2.74
H +(H 2O) 2
8.42 2.43
Cocaine (M +)
17.6 1.16
Heroin (M +)
19.6 1.04

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02

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10

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11

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12

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13

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14

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15

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