Tracking Illicit Drugs with Strontium Isotope Analysis

Tracking Illicit Drugs with Strontium Isotope Analysis

The manufacture and distribution of illicit drugs such as heroin is a primary focus of many major law enforcement organisations worldwide, including the Drug Enforcement Agency (DEA) in the United States and the National Crime Agency (NCA) in the United Kingdom. Unfortunately, as drug shipments pass hands between dealers and cross borders so rapidly, it can be difficult if not impossible to trace a batch of drugs back to an initial manufacturer. As a result of this, the chances of locating and arresting the manufacturers of illicit drugs can be slim.

To a forensic drugs analyst, a whole range of characteristics can be examined and used to classify and compare different batches of the same drug, including physical appearance, packaging, and chemical composition. To an extent, heroin chemical signatures are already beneficial in comparing different batches of the drug in attempts to establish links and possible sources of the narcotics. This may be based on agents or adulterants a product has been cut with, and the relative concentrations of those substances. The manufacturing process itself can vary in terms of chemicals and apparatus used and the skills of the manufacturer, resulting in further characteristic differences in the chemical profile. However these differences may not be distinct enough to be valuable and are certainly not able to pinpoint the country from which a batch originated. Though there is still no reliable method of tracing an illicit drug back to a particular location, ongoing research is aiming to change this.

One method of studying the history and even origin of a sample is to use isotopic composition. Isotopes are different forms of elements that are incorporated into substances in the environment in varying ratios and abundances, influenced by a number of factors that can alter these ratios. These processes can be described as isotopic fractionation. Interestingly, isotopic ratios can be characteristic to different regions of the world, enabling certain materials to be traced back to the geographic region based on the ratios of particular isotopes contained within that material. With this in mind, they have often been used to trace unidentified human remains to a particular location or study the origin of food products. Focusing on isotopes allows for heroin samples to be studied and compared based on regional characteristics as oppose to the variation caused by the production process.

For the first time, researchers at Florida International University have utilised strontium isotope ratio analysis to determine the provenance of illicit heroin samples. 186 unadulterated, undiluted heroin samples of known origin were obtained from a number of geographic regions including Southeast Asia, Southwest Asia, South America, and Mexico. Of a particularly challenging nature is South American heroin and SA-like Mexican heroin, which can be extremely difficult to differentiate based on their chemical compositions alone. Heroin samples were dissolved via a microwave-assisted acid digestion method before being subjected to a technique known as a multi-collector inductively-coupled plasma mass spectrometry (MC-ICP-MS). This instrument utilises an inductively coupled plasma ion source to ionise target analytes, which are then separated and analysed by the mass spectrometer. The use of MC-ICP-MS allows for the strontium concentration of particular samples to be determined. The strontium isotope ratio (87Sr/86Sr) value of each individual sample was then compared with the overall mean values of ratios from different regions in order to establish the likely origin of that particular heroin sample. Samples from the same geographic region would be expected to exhibit a similar isotope ratio.


Multi-collector inductively-coupled plasma mass spectrometer (MC-ICP-MS) Source:

The results demonstrated the possibility of differentiating between heroin of different geographic origin. South American and Mexican heroin samples were correctly classified 82% and 77% of the time respectively. South East and South West Asian heroin samples were somewhat more difficult to differentiate due to more of an overlap between strontium isotope ratio values. SE Asian samples were correctly classified 63% of the time and SW Asian samples only 56% of the time. It is not clear whether this elemental strontium is endogenous or the result of external contamination, but either way it is sufficiently characteristic to be associated with a particular geographic location.

The strontium isotope composition of heroin can be affected by a number of factors, including the soil in which components are grown and groundwater in the area, which can result in region-specific isotope compositions. The use of strontium isotope ratio analysis has presented promising results in the origin determination of illicit heroin. Although a larger scale study incorporating samples of a more worldwide origin would be ideal, initial results suggest that this technique could allow for an unknown illicit drug sample to be traced back to a country of origin, aiding criminal intelligence agencies in the war against drugs.


Debord, J., Pourmand, A., Jantzi, S., Panicker, S. & Almirall, J. Profiling of Heroin and Assignment of Provenance by 87Sr/86Sr Isotope Ratio Analysis. Inorg Chim Acta. In press (2017).

Keeping the Skies Safe with Analytical Chemistry

Ever since events such as 9/11, the Lockerbie bombing and the (fortunately) failed shoe bomber, the stringency of airport security has been ever increasing. Anyone who has passed through an airport has no doubt witnessed the occasional swabbing of luggage or electronic items. The staff will take a quick swab of the item, stick it into a mysterious machine and usually send the passenger on their way with little explanation of what has just occurred.

But what exactly are they testing for in this scenario, and just what is the instrument they’re using?

As one might expect, the biggest target of this security step is explosive substances as a counter-terrorism measure, in addition to illicit narcotics in an attempt to crack down on drug trafficking. In an airport setting, the analytical testing technique of choice is ion mobility spectrometry.

Ion mobility spectrometry (IMS) is an analytical technique used to identify chemical compounds based on the differences in the movement of ions under an electric field. The concept for the technique was established in the early twentieth century, however it was not until the 1970s that the instrumentation was actually properly developed. There are currently tens of thousands of IMS devices deployed around the world. Not only are they utilised in airports for drug and explosives screening, but also by the military for the detection of chemical warfare agents and in industrial settings to monitor air quality. The range of applications is potentially vast, but the principles of operation are the same.

As you may have witnessed, a small swab is rubbed over the surface to be tested, typically a piece of luggage or an electronic device such as a laptop, before being inserted into the ion mobility spectrometer. As the sample needs to be introduced in its gaseous form, the swab may be subjected to heating in order to thermally desorb analytes from the swab and allow them to be transported into the instrument for analysis. In order to manipulate the analytes entering the instrument, they must first be converted into ions, their charged form. Ionisation is typically achieved using a radioactive source, such as 63Ni (nickel-63) or 241Am (Americium-241), which first form reactant ion species from the carrier gas (usually air), which then leads to the ionisation of the sample material. These newly-formed ions will then enter a region under an electric field and drift towards a series of electrodes. The ions will pass through the drift region at different speeds depending on the shape and size of the ion clusters and strike the electrodes, the signals being amplified and detected. Depending on the instrument and needs of the analysis, either positive or negative ions will be produced (in some cases both simultaneously).


IMS schematic. Source: Smiths Detection (

The IMS utilised in airports will typically hold a database of known explosive and narcotic substances against which to compare samples. There will be a certain threshold, typically based on peak intensity, that must be reached before a positive identification will be indicated, and if there is a “match”, the operator will be alerted to a potential identification.

In comparison to other analytical tools available, ion mobility spectrometers are far from being the best. For instance mass spectrometry, an alternative technique for the analysis and identification of chemical compounds, can offer greater sensitivity, higher resolution, improved accuracy and better identification. So why use IMS? It essentially comes down to cost and ease of use. The simple design and ability to operate at atmospheric pressure means the instruments can be fairly small in size, some even being hand-held and so rendering them completely portable. They have low power consumption, so can simply be powered by a few AA batteries. The ease of use of the IMS means anyone can be trained to use the instrument, thus technical or scientific expertise is not required.

But what is perhaps most important for use in an airport setting with potentially thousands of passengers each hour, is the ability to conduct analyses quickly, and this is something that the IMS can offer. Many commercial ion mobility-based instruments can provide results in a matter of seconds. For instance, the IONSCAN by Barringer (now owned by Smiths Detection) boasts the ability to detect over 40 explosives and narcotics in just 8 seconds.

In a security setting there are three primary types of IMS that may be encountered. The smallest of the devices are handheld and sample by drawing in analytes present in the atmosphere. These may be used to analyse potential hazards relating to unattended baggage, for example. The second type, which is perhaps the most commonly encountered IMS in airports, is a benchtop instrument which requires introduction of the sample via some type of swab. And finally, some airport security units may utilise a larger, human-sized IMS portal. This setup uses airflow to dislodge particles of explosives or drugs from clothing or the passenger’s body and analyse them.

Unsurprisingly, the instruments are not infallible, and false positive or negative results are a possibility. Some ions will have the same drift time so may be indistinguishable from known explosives or drugs, triggering an alarm. In actual fact this response may simply have been caused by a cosmetic or pharmaceutical product that happens to produce a response similar to a known narcotic. On the contrary, dirt, oil and other contaminants may mask the presence of substances of interest, thus causing no alert despite the presence of a drug or explosive.

Furthermore, the IMS is somewhat limited in that it can only identify the presence of a compound contained within its database. So whereas it may be able to detect common explosives such as RDX, TNT and PETN, and frequently encountered narcotics such as cocaine, heroin and cannabis, it would not necessarily alert to the presence of an unknown compound (unless it was very similar in chemical structure to something in the database).

Fortunately research in the field of analytical chemistry is constantly ongoing, aiming to improve instrumentation and analytical techniques to resolve these issues and ultimately produce more reliable and robust security measures.



G. Ewing et al. A critical review of ion mobility spectrometry for the detection of explosive and explosive related compounds. Talanta. 54 (2001) 515-529.

Homeland Security Science & Technology. IMS-Based Trace Explosives Detectors for First Responders. [online] Available:

Smiths Detection. Ion Mobility Spectrometry (IMS). [online] Available:

Introducing the Controversial Psychoactive Substances Act

Introducing the Controversial Psychoactive Substances Act

As of this week the Psychoactive Substances Act came into effect in the UK, a long-awaited and much-disputed piece of legislation that will attempt to transform the existing drug marketplace. The act will make it an offence to supply any substance that can produce a psychoactive effect (of course with the exception of the likes of alcohol and caffeine), aiming to specifically target new psychoactive substances (NPS) or ‘legal highs’, which have thus far evaded the Misuse of Drugs Act.

But just what are New Psychoactive Substances, and why has it been so difficult to enforce laws against their supply and use?


NPS are synthetic chemical substances created to mimic the effects of existing illegal substances, such as cannabis or ecstasy. These drugs are often designed in such a way that they are sufficiently chemically similar to an illicit drug to cause the desired psychoactive effects, but adequately different to bypass the existing legislation.  The legislation currently controlling illicit substances in the UK is specific in the substances under regulation, meaning any slight changes to the chemical structure of an illicit drug can technically render the drug uncontrolled and legal to supply or use.

New psychoactive substances are typically sold as powders, pills or smoking mixtures (somewhat resembling cannabis). You may have heard these drugs referred to as “legal highs”, rather inaccurately indicating they are legal and even safe to use. But a brief internet search will pull up an array of news pieces highlighting unexpected illnesses and deaths brought on by the use of these drugs. The primary danger surrounding the use of new psychoactive substances is the lack of research involving these substances, exacerbated by the ever-changing and difficult-to-monitor composition of the drugs. In addition to this, as NPS are specifically sold as being unsuitable for human consumption, thus avoiding certain regulations, the user cannot be confident in exactly what they are buying. Although many legal highs do offer a list of ingredients on the packaging, the highly unregulated nature of this market casts doubt on the accuracy of such information. Forensic analysis of NPSs has shown that they may contain unexpected constituents and even quantities of illicit drugs.

The NPS market has boomed in recent years, with new drugs hitting the streets faster than scientists can even identify them. They have thus far been widely available online and in head shops (establishments openly selling paraphernalia for the use of cannabis and other drugs), typically advertised as bath salts or plant food. Unfortunately the ever-changing variety of ‘legal highs’ available has presented forensic scientists with a particular challenge. The analysis of more typical drugs is relatively straightforward, with the analyst armed with well-trialled presumptive tests, analytical methods and libraries for comparison. However as new psychoactive substances are developed with modified chemical structures, they may not react with presumptive tests and library matching may prove useless without a comparison.

The premise of the act has come under great scrutiny, with opponents asserting the Act will blindly ban harmless substances (not true) or that it will be utterly unenforceable (somewhat true). A similar piece of legislation has been instigated in the Republic of Ireland, but with little success, as highlighted by the extremely low number of successful prosecutions under the law. In fact, the implementation of this legislation in Ireland was actually followed by an increase in NPS use amongst teenagers from 16% to 22%. That is not to say the legislation was the cause of this increase, but it is an interesting point nonetheless.

Despite the criticism and uncertainty, the Psychoactive Substances Act will attempt to curb the supply of psychoactive substances and protect potential users of these drugs. Although it will not be an offense to possess new psychoactive substances for personal use, it will be a criminal act to supply such substances. It will be inconceivable to halt the online sale of psychoactive substances, but it will be possible to prevent head shops, of which there are hundreds around the UK, from blatantly advertising and selling these drugs. Although the Psychoactive Substances Act promises to be a difficult piece of legislation to enforce, if at the very least it prevents new psychoactive substances from being freely advertised as a normal and ‘safe’ alternative to drugs, a great improvement will be made. But only time will tell if this new piece of legislation will really reduce the use of these no longer legal highs.



Home Office.Trade in so-called ‘legal highs’ now illegal. [online] Available:

New Psychoactive Substances Act 2016 [online] Available:

Killer Cocktails: The Chemistry Behind the Lethal Injection

Killer Cocktails: The Chemistry Behind the Lethal Injection

In many countries worldwide, including the United States, lethal injection is used as a humane method of executing a death row inmate. With the lethal injection, the life of the inmate can theoretically be cleanly and swiftly ended through administering a number of drugs, with no pain and minimal trauma.

The debate over the lethal injection hit the news again last month when the U.S. Supreme Court ruled against claims that the use of a drug used in lethal injections (midazolam hydrochloride) violates the Eighth Amendment (relating to prohibiting cruel and unusual punishment). Despite this method of capital punishment largely replacing supposedly less humane forms of death such as the electric chair and hanging, there is still great debate over the ethics of certain drugs used, and whether they actually do provide a swift and pain-free death.

But what drugs are involved in this lethal cocktail, and how do these end life in an apparently ethical manner?

The procedure for lethal injection can vary across different countries and even different states. In the United States, execution by lethal injection is typically achieved through the intravenous use of three drugs in succession, each with a different purpose, though in some instances a single-drug method is used, usually involving a lethal dose of anaesthetic.

Sodium Thiopental (Source: Chemspider)

Sodium Thiopental (Source: Chemspider)

But let’s look at the three-part cocktail. The first drug to be administered is usually a barbiturate to act as an anaesthetic (painkiller), used to ensure the remaining steps in the procedure do not cause any pain. Traditionally sodium thiopental is used, a fast-onset but short-acting barbiturate. Barbiturates are compounds which can ultimately produce anaesthetic effects. They act as agonists of gamma-aminobutyric acid (GABA) receptors, which are inhibitory neurotransmitters in the central nervous system. By binding to this receptor, the activity of the central nervous system is depressed, bringing about effects ranging from mild sedation to general anaesthesia. In this instance, a sufficient dosage is administered to render the inmate unconscious, thus ensuring a painless procedure. However some have argued that the fast-acting effects of sodium thiopental can wear off before the execution procedure is complete.

Succinylcholine Chloride (Source: Chemspider)

Succinylcholine Chloride (Source: Chemspider)

Once the inmate is unconscious, a neuromuscular-blocking drug is then administered, generally succinylcholine (also known as suxamethonium chloride) or pancuronium bromide. Compounds such as succinylcholine bind to acetylcholine receptors, blocking the action of acetylcholine, a neurotransmitter essential in the proper functioning of skeletal muscle. When succinylcholine binds to this receptor, a cation channel in the receptor opens and depolarisation of the neuromuscular junction occurs. Normally when acetylcholine binds to this receptor, it soon dissociates following depolarisation and the muscle cell will be ready for the next signal. However compounds such as succinylcholine have a significantly longer duration, ultimately resulting in paralysis. In short, administering a drug such as succinylcholine prevents acetylcholine from communicating with the muscles and thus paralyses the inmate’s muscles, including those used to breathe. Other drugs such as pancuronium bromide can also be used, which have a different mechanism of action but ultimately achieve the same final result of muscle paralysis.

Finally the salt potassium chloride is administered. Within the body a variety of salts are vital for brain function, transmission of nerve signals and the beating of the heart, and these salt levels are tightly regulated by the body. In the normal functioning of the body, the majority of potassium is confined to the cells, with very little being present in the bloodstream at any one time. The introduction of a large amount of potassium chloride disrupts this electrochemical balance as the body’s cell are not able to equilibrate, rendering the cells unable to function, leading to cardiac arrest. In simpler terms, the overdose of potassium chloride brings about a condition known as hyperkalemia, in which the potassium concentration in the body is too high, causing the heart to fail. The inmate is officially declared dead when a cardiac monitor indicates the heart has stopped.

Recently, the drug used to initially render the inmate unconscious, sodium thiopental, has been difficult to obtain for a number of reasons, thus some states in the U.S. have used midazolam hydrochloride, a drug which has ultimately caused a great deal of controversy in recent years, such as in the Clayton Lockett case. This benzodiazepine is commonly used as a sedative, but when used during the lethal injection procedure, it is generally combined with an opiate. This is because midazolam itself has no analgesic (painkilling) effect, thus an additional drug is required to achieve this. Despite its recent use, claims have been made that a number of executions using this drug resulted in the prisoners showing signs of consciousness and gasping, suggesting that they were not quite as unconscious as intended. If the inmate is not unconscious when the muscle paralyser and electrolytes are administered, they may experience suffocation due to the muscle paralysing agent and burning caused by the potassium chloride.

So there we have it – some of the primary drugs administered during the lethal injection procedure and how they react within the body to bring about death. For more information on the death penalty (namely in the U.S), visit the Death Penalty Information Center.


Johnson, B. A. 2011. Addiction Medicine: Science and Practice Volume 1. New York: Springer.

Kroll, D. 2014. The Drugs Used in Execution by Lethal Injection. [online] Available from:

Kemsley, J. 2015. Sedative for Lethal Injections Affirmed. [online] Available from:

Cover Image Credit: Thomas Boyd (The Oregonian)