Review of express drug detection tools.

Overview of express drug detection tools.

Chemical reagent and material kits are widely used in Russia, and recently there has been a trend towards using immunochemical reagents and devices operating on these principles.

Detection and seizure of narcotic drugs and psychotropic substances from illegal circulation requires the use of special technical means that ensure the objectivity, justification and completeness of the implementation of preventive measures and influence applied by law enforcement agencies to persons from whom these drug samples are seized.

These means must satisfy a number of requirements, among which their selectivity, speed, absence of false negative results, and cost-effectiveness are not the least important.

This publication is devoted to achievements and unresolved problems, as well as possible errors in choosing a research method.

When conducting measures to detect and seize narcotic drugs from illegal circulation, their rapid detection in the studied sample of objects plays an important role.

Due to the specific characteristics of drugs, special technical means must be used to solve the problem.

The simplest of these are sets of chemical reagents, the generally accepted requirements for which are the absence of operations that require special laboratory equipment: heating, filtering, extraction with precise separation of liquid layers, centrifugation, etc.

Usually the tests consist of pre-prepared reagents that retain their properties for a long time and in a wide range of climatic conditions.

These tests can be used to conduct research by people without special chemical training and special protective equipment (protective clothing, glasses, gloves, etc.).

However, it should be borne in mind that the results obtained by the method in question are of preliminary value, given the insufficient selectivity of color reactions.

This is explained by the huge number of existing compounds and the diversity of their structure, with most organic compounds having a number of homologues, and when any group can be identified by the corresponding reaction, then the same reaction can be given by homologues that form similar reaction products.

Despite these limitations, the practical significance of drop analysis for detecting narcotic compounds is very high, since with a small expenditure of materials and time it allows choosing the right direction for further research, easily adapting to changing conditions, for example, to the emergence of new drugs or new methods of their packaging and disguise. The sensitivity of chemical analysis methods is 10-5 – 10-7 grams of substance.

Due to the limited selectivity of virtually every reagent used in drug testing, several reagents must be used, preferably according to a specific, strictly agreed upon scheme.

All currently known drug detection schemes provide for the sequential use of tests, and failure to do so will almost always lead to errors in identification.

In addition, this approach reduces the number of reactions that must be carried out to obtain a result.

For different substances, it ranges from 2 to 5.

The economic result from reducing the consumption of reagents is also important.

Domestic and foreign manufacturers distribute chemical tests of three main types: drop, ampoule and aerosol, which are based on reactions with concentrated inorganic acids in the presence of transition metal ions, condensation reactions with aldehydes, complexation reactions with various dyes in a heterogeneous environment, as well as reactions of drugs with mixed reagents of the above groups.

Drop-type kits — are designed to conduct analysis on porcelain or glass plates with depressions (plates), where samples of objects are placed, which are then treated with reagents using pipettes or droppers.

The best-known drop-type reagent kit is the kit described in the manual for national laboratories developed by the UN drug control program.

Another well-known drop-type test kit is the Folin-Vogel kit (Austria) with a set of reagents from Merck (Germany).

The peculiarity of this kit is the combination of drop analysis with special strips impregnated with colored reagents.

In some drop-type tests, strips of filter or chromatographic paper or fabric are used instead of plates.

The company “NarcoTech, Inc.” (USA) produces several kits of this type, designed for the analysis of individual drugs, such as cocaine, opiates, methamphetamine, drugs such as “ecstasy” and a number of others, as well as a complete set of reagents.

All reagents are poured into vials in quantities sufficient to conduct, depending on the type of drug, from 120 to 600 tests with a total number of tests exceeding 2800. The cost of such a complete set is less than 80 US dollars, which, when converted to 1 test, gives 3 cents.

This type of reagent kit is the simplest and cheapest to manufacture. Tests for some types of drugs can be used in a camouflaged form, ensuring a covert inspection.

However, the use of this type of kit requires the researcher to have high chemical qualifications both when conducting the test itself, given that most of them consist of extremely active reagents, such as concentrated acids, and when interpreting the results obtained.

Aerosol kits — are designed to conduct analysis on filter or chromatographic paper, on which the test objects are placed, followed by spraying with colored reagents from aerosol cans.

The most well-known aerosol tests are tests for heroin, cocaine, barbiturates and cannabinoids (HERO-, COCA-, BARBY- and CANNABISPRAY), produced by one of the Israeli companies.

These tests are highly sensitive and fairly easy to use. However, as their repeated tests conducted by the employees of the Forensic Science Center of the Ministry of Internal Affairs of Russia have shown, these tests give a large number of false positives, which significantly reduces their practical value.

In addition, when using tests, stable aerosols of toxic and aggressive reagents are formed, which negatively affect the health of people present during testing. Aerosol tests are currently practically not used in the practice of law enforcement agencies in Russia.

Ampule tests — are designed to conduct analysis by mechanically crushing glass ampoules with reagents in transparent reaction containers, polymer bags or tubes.

This is the most common type of kit in practice, including the generally accepted standard «NIK» kit from Becton-Dickinson (USA), as well as kits from other manufacturers, including Russian ones.

Table 1 provides a comparative description of domestic express tests for drug analysis.

Table 1. Comparative description of domestic express tests for drug analysis.

Currently, one of the most advanced kits for detecting narcotic drugs and psychotropic substances is the “NARKOTSVET” kit, which is designed to analyze solid and liquid objects, plant material.

The fundamental difference between the kit and well-known domestic and foreign analogues is that it is the first to implement a digital coding scheme for the coloring resulting from the processing of the object under study and the chemical reagent.

It was possible to implement this scheme after creating a number of modified chemical reagents with increased selectivity and sensitivity.

As a result, it was possible to largely eliminate errors associated with violations in the testing sequence inherent in kits from other manufacturers.

In addition, this scheme allows for a fairly simple automation of the process of reading results.

Currently, according to the information we have, the developers of the kit are working on creating an automatic test results counter.

The general scheme for conducting research using the drop chemical analysis method is shown in Figure 1. In this scheme, each column represents the color of the reaction mixture when a reagent (the number of which is indicated in the leftmost column) is applied to a specific drug.

Figure 1. Scheme for conducting research using the NARCOSPECTRE kit.

The NARCOSPECTRE kit allows for research on so-called spilled drugs, such as on the floor, on clothing, etc.

This kit turned out to be the only kit capable of correctly identifying as narcotics such objects as “brown” cocaine — a drug that has recently appeared in the illegal circulation, specially treated to make it difficult to detect by chemical tests, or phencyclidine on tobacco, marijuana or parsley grass.

The sensitivity of the kit is sufficient even to detect residues of injectable buprenorphine solutions on the walls of ampoules.

The tests included in the basic set of “NARCOSPECTRUM” are arranged as follows:

• Tests 1-4 are universal, allowing to judge the chemical properties of substances and partially, their structure. The presence of these tests is necessary when conducting screening.
• Tests 5-7 are specific, allowing to judge either the specific properties of substances or their belonging to a specific group of substances.

The selectivity of chemical reagents was tested on more than 280 medicinal substances and tablet forms. As a result, good performance of the kit for detecting narcotic drugs was demonstrated.

At the same time, a minimum number of false positive results is observed, mainly for cocaine, crack, phenylalkylamine group, cyclodol, aprofen.

Table 2 provides statistical parameters for the possibility of obtaining false positive results for a number of narcotic drugs.

The number of false positive results for individual substances was no more than 3.2%.

Table 2. False positive results when testing with the NARCOSPECTRE kit false positive results

The complete set consists of 11 tubes filled with reagents that allow you to detect more than 20 narcotic drugs and psychotropic substances. The cost of such a set does not exceed 20 US dollars.

However, the customer can significantly reduce it by completing the set with reagents directly necessary for solving their problems.

Thus, domestic developments in the field of kits for express analysis of drugs by chemical methods have high tactical and technical indicators in terms of selectivity, nomenclature of substances tested, ease of use and dimensions.

They are fully adapted to Russian conditions.

In the near future, we should expect the emergence of new devices, including automated ones, implemented on the principles discussed above.

Currently, there are express tests on sale from numerous manufacturers, including domestic ones, for detecting traces of drugs in human urine — cocaine, amphetamine, methamphetamine, metabolites of tetrahydrocannabinol, morphine, heroin, which are based on immunochromatographic analysis.

Immunochromatographic analysis (ICA) is a method for determining low concentrations of substances in biological materials. Such materials include whole blood, serum or blood plasma, saliva, urine, feces.

ICA is a relatively young method of analysis, it is often referred to in the literature as dry immunochemistry method, strip test, QuikStrip cassette, QuikStrip dipstick, express test or express analysis.

These names are related to the speed of this method of analysis. We will use the name ICA (immunochromatographic rapid tests (ICA)), since it most accurately indicates the principle of the method and its place among other methods of analysis. All immunological methods of analysis are based on the reaction «antigen — antibody».

Antigen is a substance that is recognized by our body as foreign and which can trigger an immune (protective) reaction.

Antibodies— these are proteins that are produced by the cells of our body in response to the introduction of an antigen. The most important property of antibodies is their ability to specifically bind to an antigen.

This means that each antibody (Ab) recognizes and binds only to a specific antigen (Ag).

All immunological methods of analysis, including IHA, are based on this unique feature of antibodies.

1. Positive result: The appearance of two dark bands in the test zone (T) and the control zone (K).

2. Negative result: Appearance of only one dark stripe in the control zone.

	— the antigen being tested;
	— a conjugate of an antibody specific to the antigen being tested with a dye migrating along the strip, together with physiological fluid;
	— an antibody specific to the test antigen immobilized on a test strip;
	— secondary antibody specific to antibodies with dye, immobilized on a test strip.

Figure 2. Schematic diagram of the IHA method.

IHA tests use three types of antibodies: 1) soluble monoclonal antibodies to the antigen being tested, conjugated («cross-linked») with colloidal gold — a dye that can be easily identified even in the smallest concentrations.

These antibodies are applied near the area where the test strip is immersed in physiological fluid (urine, blood); 2) polyclonal antibodies to the antigen under study, rigidly immobilized in the test zone of the strip; 3) secondary antibodies to monoclonal antibodies, rigidly immobilized in the control zone of the test strip.

When the test is immersed in physiological fluid, it begins to migrate along the strip according to the principle of thin-layer chromatography (hence the name — IHC). Antibodies with dye move along with the liquid.

If the antigen being studied is present in this fluid, it binds to both the first and second type of antibodies.

This causes the accumulation of antibodies with the dye around the antibodies rigidly immobilized in the test zone of the ICA strip, which appears as a bright dark strip. The antibodies that have not bound to the dye migrate further along the strip and inevitably interact with the secondary antibodies in the control zone, where the second dark strip is observed.

The interaction (and dark band) in the control zone should always appear (if the analysis was performed correctly), regardless of the presence of the antigen being studied in the physiological fluid.

Based on the above, the following test results exist:

1) two bands— positive result;

2) one band— negative result; 3) no bands— the analysis was performed incorrectly.

IHA tests are extremely easy to use and have high sensitivity, up to several nanograms per ml of the object.

However, it should be taken into account that these tests have low selectivity and require mandatory confirmation of a positive result by other analytical methods. In practice, they are used in clinical or forensic chemistry laboratories as a means of rapid selection among a large number of samples requiring further examination.

In this case, the interpretation of the results obtained should be entrusted only to trained, highly qualified employees.

For example, as our research has shown, a significant number of IHC tests from various manufacturers, including Russian ones, give a positive result in urine testing for opiates in individuals who have recently consumed culinary products containing poppy seeds or taken several tablets of combination drugs containing codeine, which, according to current Russian legislation, can be distributed over-the-counter, i.e. freely and without control.

This circumstance should be especially taken into account in connection with the adoption of the Administrative Code of the Russian Federation and the introduction of liability for illegal drug use.

Thus, IHC tests are designed to test biological fluids for the presence of drugs in them.

In this case, the following should be taken into account:

1) these tests function only under physiological or very close to physiological conditions, such as pH value, temperature, absence of strong oxidizing or reducing agents, a certain ionic strength of the medium, and others;

2) tests almost all IHA tests are designed to detect in biofluids not the drugs themselves, but their metabolites — breakdown products in the human body, which are excreted from the body much more slowly than the active substance.

For example, IHA tests for marijuana are designed to detect the metabolite of tetrahydrocannabinol, which is practically absent in marijuana itself, or the IHA test for cocaine is designed to determine benzoylecgonine, which is not present in all samples seized from illegal circulation.

With the appearance of IHA tests on the Russian market several years ago, attempts have been made to use them as diagnostics for express analysis of various objects with the aim of classifying them as narcotic drugs or psychotropic substances.

This completely ignores the specifics of both the tests themselves, see above, and the specifics of the objects being studied, which can and do contain active components, such as alkali («crack»).

In addition, the use of these tests in the form proposed by the manufacturer required an extremely labor-intensive procedure in non-laboratory conditions for diluting the test objects to working concentrations of the tests, approximately 1: 1000 and more.

As a result of tests conducted several years ago by basic organizations for testing tests, including the Expert-Criminalistic Center of the Ministry of Internal Affairs of Russia, produced by the Russian enterprise

Progressive Bio-Medical Technologies Ltd. (Moscow) and submitted for approval to the Standing Committee on Drug Control, these products were recognized unsuitable for the determination of narcotic substances in non-biological objects due to their low efficiency.