Drugs as evidence

The analysis of materials suspected to be or to contain controlled substances represents the largest portion of the workload in most forensic laboratories. When suspected controlled substances are submitted as physical evidence (exhibits), the forensic chemist must identify and in some cases quantify the controlled substances present. The most common forms of evidence seen can be summarized as the "five p's:" powders, plant matter, pills, precursors, and paraphernalia.

Powders run the gamut of crystalline white to resinous brown. Hashish, a concentrated form of marijuana, lies between plant and powder. Many powders are oily and odiferous, while others can only be described (unofficially and informally) as goo. Typical plant matter exhibits are marijuana, mushrooms, and cactus buttons. As biological evidence, plant matter must be stored properly to prevent rotting and degradation prior to analysis; failure to do so can create goo.

Pills such as prescription medications or clandestinely synthesized tablets are common forms of physical evidence. In cases where the evidence is or appears to be commercially manufactured drugs (OTC or prescription), tentative identifications can be made visually using references such as the Physician's Desk Reference. In other cases the pills may have other markings such as crosses or imprints. Amphetamines, methamphetamine, and LSD are often sold illicitly in pill form, although typically the pills are cruder than those produced commercially.

Precursors are compounds or materials used in the clandestine synthesis of drugs such as methamphetamine. Immediate precursors are those that require only one or two simple steps to convert the controlled substance, while distant precursors require more steps. Some precursors are controlled and listed on schedules of the CSA, while others are not. For example, 1-phenylcyclohexylamine (PC) and 1-piperidinocyclohex-anecarbonitrile (PCC) are listed on Schedule II; both are precursors used to synthesize phencyclidine (PCP), a Schedule II substance. Likewise, phenyl acetone (phenyl-2-propanone, or P2P) was once the preferred starting point for illicit methamphetamine; it is now listed on Schedule II. Lysergic acid and lysergic acid amide, precursors of LSD, are listed on Schedule III. Other precursors are not necessarily controlled but must still be identified as part of investigations of clandestine synthesis.

Drug paraphernalia are the implements and equipment used to prepare and ingest drugs. Typical items include syringes (a significant biohazard to the analyst), cookers used to prepare heroin and other drugs, pipes and bongs (water-filled vessels) used in smoking marijuana, and razor blades, mirrors, and straws used for snorting cocaine. Such items present a sampling and analytical challenge since only traces of material may remain. Typically analysts rinse the items with a solvent to extract the residues, a destructive step that significantly alters an entire evidence exhibit.

Of the five p's the most frequently submitted by numbers of cases is plant matter suspected of being or containing marijuana. Methamphet-amine, cocaine, amphetamine, and heroin are also common, although the order and numbers vary across regions and states. The last 10 years have seen increasing incidence of use of predator drugs, methamphetamine, and MDMA, while rates of cocaine and heroin appear to have stabilized. Different states and regions deal with different problems: Hawaii and West Virginia are hotspots of marijuana production; Washington State grapples with more than 1,000 clandestine laboratories; and border states, north and south, struggle to stem the flow of smuggled drugs.

Forensic chemistry being what it is, forensic chemists may unexpectedly encounter other types of evidence. For instance, although one of its street names is angel dust, phencyclidine is a controlled substance often seized in liquid form, usually a greenish solution with an overwhelming smell. Spray cans, bags, or rags soaked with inhalants can turn up in forensic laboratories. The day after Halloween can bring an interesting array of submissions, such as suspect apples and candy bars.


In addition to identifying and quantifying illicit drugs themselves, forensic chemists often must identify cutting agents added to many drug exhibits. Clandestine chemists use cutting agents to stretch the supply of a controlled substance and maximize profits. Cutting agents are often chosen based on their chemical similarity to the controlled substance being produced. Heroin has a bitter taste mimicked by quinine. Cocaine is an anesthetic used to numb the eye for eye surgery, so it should be no surprise that cocaine is often cut with a local anesthetic such as Novocain. Other common cutting agents include sugars such as mannitol and inositol and less frequently baking soda, caffeine, and table sugar. Starches such as cornstarch are also common. Identification of diluents is an important part of drug profiling, discussed in the next section.

Just like drugs, cutting agents are categorized. Diluents (thinners) are substances that are not drugs. Baking soda and sugars fall into this category. Adulterants are pharmacologically active and typically have effects that are grossly similar to the drug. Caffeine added to cocaine is an example where both the drug and the adulterant are stimulants.

Aside from cutting agents, impurities are materials that occur naturally with the drug (if a natural product) or are added to it inadvertently during processing. Consider a cup of tea, which is a natural product obtained from plant matter. It is not a pure substance, but contains many different alkaloids including caffeine and theophylline. The same is true of illicit drugs obtained directly or indirectly from plant matter such as cocaine or heroin. Finally, contaminants are substances that find their way into the sample by accident. If heroin is extracted using lime (Ca(OH)2) and the lime is contaminated with sand, the sand that ends up in the heroin is a contaminant that originated as a contaminant in the lime.

The cutting agents and other materials that are found in illicit drugs—diluents, adulterants, impurities, and contaminants—are all of interest to the forensic chemist as he or she conducts the process of drug profiling.


Profiling a drug sample means analyzing the composition beyond simple identification and quantitation of the controlled substance(s) present. It is a more detailed analysis that leads to what is sometimes called a "chemical fingerprint." The goal of profiling is to identify what processing or synthetic methods were used to make a drug. If the drug is a natural product such as cocaine or heroin, another goal is to identify the geographic region where the plant was grown. Often the information obtained through profiling is used to categorize drug samples into similar groups to provide investigative information such as common origin. The road from the fields or the clandestine lab to the street and to the forensic lab has many steps, each of which can add distinctiveness to the sample batch.

The first step in profiling starts with a description of color, appearance (sparkling powder versus oily, for example), and microscopic characterization of diluents, such as starches or sugars. The examination then becomes more complex and interesting as the analyst may test for isotope ratios, co-extracted components, impurities, adulterants and diluents, and even the DNA of plants that are part of the process.

Measurements of stable isotope ratios (SIRs) have long been used in ecological and botanical research. Isotopes of an element have the same number of protons in the nucleus of their atoms but a different number of neutrons. Most elements have stable, naturally occurring isotopes. For example, the most abundant form of carbon has six protons and six neutrons in the nucleus and is called carbon 12 or 12C. However, of all the carbon atoms on Earth, about 1 percent have an extra neutron in the nucleus, known as 13C. The common form of oxygen is 16O, but 18O also exists. These are examples of what are called "stable isotopes" because they are found in relatively stable ratios. 13C abundance is usually 1 percent of that of 12C, for example. When the ratios differ from the normal proportion, this provides important information. Any process that alters the normal ratio of stable isotopes is called fractionation, and forensic chemists can use data like this in profiling.

Isotopes of an element are chemically identical. This means that 12C and 13C behave chemically the same way. The only difference between them is their mass since 13C has an extra neutron. The same is true of isotopes of oxygen, nitrogen, and so on. Since isotopes are chemically identical, fractionation is caused by the mass differences. For example, 18O constitutes approximately 0.2 percent of all oxygen found on Earth. A water molecule that incorporates 18O is slightly heavier than a molecule containing the more common 16O isotope. The "heavier" water will

92 drugs, poisons, and chemistry need slightly more energy to evaporate from the liquid phase into the gas phase. Similarly, when rain or snow falls, gravity favors heavier isotopes over lighter ones and more of the lighter compounds will evaporate compared to the heavier ones. These are examples of abiotic (nonbio-logical) fractionation processes. Biological processes also lead to fractionation, although the basis of this fractionation is purely physical and not chemical. For example, when water evaporates from a leaf surface, water molecules incorporating lighter isotopes evaporate more quickly than molecules containing heavier isotopes. As a result the leaf becomes enriched in the heavier isotopes. Similar cycles and interactions can be identified for nitrogen, a key nutrient for plants.

Why are these processes and ratios important to a forensic chemist? If the drug involved in an investigation comes from a plant, the isotope ratios can tell the story of when, where, and how the plant grew. The isotopic ratios within a plant are the result of numerous and complex fractionation processes that are unique to a region and that depend on climate, temperature, precipitation, elevation, season, and soil. Plants from the same place will have similar isotope ratios, while those grown in different soils or even in the same soil at a different time will have different ratios. For plant-derived drugs isotopic ratio analysis can provide information on geographical region of origin, but only if trustworthy standards are available for comparison. Just like human fingerprints, one chemical fingerprint is only useful if there is a standard comparison.

Co-extracted components are another set of characteristics that forensic chemists analyze as part of profiling. With drugs derived from plants there are always alkaloids extracted along with the drug or its precursor. In the case of opium, morphine is the target compound and precursor to heroin, but other alkaloids are inevitably carried throughout processing. Codeine, thebaine, papaverine, noscapine, and other trace alkaloids will be extracted along with the morphine and will interact and react along with morphine as processing continues. These ratios of opium alkaloids and chemical derivatives are similar within a batch but variable outside that batch. Additionally, because of their chemical similarity, analytical methods such as TLC, GC-MS, or HPLC (described previously) optimized for heroin or cocaine usually will also separate and identify these impurities. As a result analysis of impurities can be performed simultaneously with the necessary evidentiary analysis.

Each stage of processing introduces impurities to a batch, much as any laboratory analysis can be contaminated by impure reagents or dirty glassware. Acids and bases can be contaminated with trace metals and ions, as can water. Solvents can carry organic contaminants or be contaminants themselves. Residual solvents and any characteristic impurities contained can be trapped within the powdered drug. Use of different solvents at different stages adds further to residuals. Because residual solvents are likely to be found in higher concentrations that trace contaminants of reagents, they have become part of profiling methodologies.

Adulterants and diluents added to a batch of an illicit drug can provide useful information regarding batches and groups. Adulterants common in heroin are acetaminophen (the active ingredient in Tylenol), caffeine, and lidocaine, all of which chromatograph well and can be detected simultaneously with the heroin. Diluents tend to be more variable, running the gamut from baking soda to sugars and quinine. Many of these are harder to identify as part of routine analysis since some are removed during sample preparation steps. Even if diluents can be isolated, identification often requires more time than can be spared in routine cases. Sometimes a quick microscopic examination of residues is sufficient to identify starches or sugars, but often more specialized testing is needed.

Finally, when the drug is a plant, there is another option for profiling. As a plant, marijuana has DNA, which allows for typing and grouping of samples as well as definitive identification of the species, something that chemical tests cannot achieve. This work is in the early stages and may become in a few years, an important profiling tool available to forensic chemists. While profiling of drugs is not routinely done in most cases, it can provide investigators with invaluable investigative information. However, the primary job of most forensic drug chemists is to identify what drug or drugs are present in physical evidence.

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