Abstract
Drug overdoses in the United States of America reached over 110 000 in 2023 with a large percentage due to fentanyl and other synthetic opioids. While provisional data from the U.S. Centers for Disease Control and Prevention (CDC) shows a decrease of 26.9% in drug overdoses in the United States during 2024, these numbers are still staggering. Fentanyl is used medicinally to manage pain in dosage forms such as intravenous solutions, oral transmucosal lozenges, and transdermal patches. It has potency ∼100 times that of morphine, so these dosage forms effectively manage delivery of the small amount of fentanyl required to achieve the desired therapeutic effect. In recent years, illicit powder versions of fentanyl have become available. Small amounts are mixed with other drugs and cutting agents. These low-dose-fentanyl mixtures emerged as a threat. It is necessary to identify fentanyl in these mixtures to mitigate risk to illicit-drug users, first responders, and the public at large. Although there are several spectroscopic methods used for the reliable detection and identification of fentanyl as an unadulterated powder, these methods are unable to achieve the limits of fentanyl detection required in low-dose mixtures. The purpose of this study was to determine whether commercial off-the-shelf (COTS) ion mobility spectrometry (IMS) with a dielectric barrier discharge (DBD) non-radioactive ionization source and preprogrammed fentanyl detection algorithms could be used to detect and identify fentanyl at low concentrations in an acetaminophen matrix. Acetaminophen is commonly encountered in illicit drug samples. The use of preprogrammed detection algorithms is consistent with how field users operate, relying on methods that have been optimized by the instrument manufacturer for an established set of target threats. This research shows that COTS IMS which uses a DBD non-radioactive ionization source and preprogrammed fentanyl detection algorithms can detect fentanyl at concentrations as low as 0.1% (w/w) in acetaminophen.
This is a visual representation of the abstract.
Introduction
Fentanyl is a synthetic opioid used to manage acute and chronic pain, 1 and the story of how this opioid has become so important in the treatment of pain in modern clinical practice has been described. 2 Fentanyl was first synthesized by Paul A. Janssen as an alternative to morphine and meperidine, solving problems with morphine–oxygen anesthesia including incomplete amnesia, occasional histamine-related reactions, and marked increases in intra- and post-operative respiratory depression. 3 Fentanyl is significantly stronger (∼100 times) than morphine4,5 and is highly lipophilic, lending itself to rapid absorption by highly perfused tissues (including the brain) before redistributing from these tissues to muscle and fat. 6 It has been prescribed therapeutically since the early 1960’s and is currently available in dosage forms including intravenous solutions, oral transmucosal lozenges (fentanyl lollipops), and transdermal patches.2,7 These dosage forms effectively manage delivery to the patient of the small amount of fentanyl required to achieve the desired therapeutic effect. Although there are cases of misuse and abuse of fentanyl throughout its marketed history,8–14 it was not until the past decade or so that the number of deaths attributed to fentanyl overdose reached an epidemic level. The U.S. Centers for Disease Control and Prevention (CDC) reports that the age-adjusted rate of drug overdose deaths involving synthetic opioids other than methadone, which includes fentanyl, fentanyl analogs, and tramadol, was mostly stable from 2003 to 2013, but then increased by a factor of 21.8 between 2013 to 2021 to a rate of 21.8 per 100 000 standard population. 15 This increase in the number of overdose deaths is the result of a number of factors including the introduction of powdered versions of fentanyl, fentanyl precursors, and analogs into the United States.16–25 Illicit fentanyl tablets have also been identified as a problem.17,19–21,23–25 “Mexican oxy” is one example of illicit tablets containing fentanyl. These tablets are intentionally mislabeled or represented to be oxycodone tablets.26,27 The pills vary widely in strength, with some that contain a tiny amount fentanyl while others contain enough to cause lethal overdoses. 26 The lethal ingested dose of fentanyl in humans is reported by the U.S. Drug Enforcement Administration to be just over 2 mg. 21 The intravenous LD50 of fentanyl is reported as 3 mg/kg in rats, 1 mg/kg in cats, 14 mg/kg in dogs and 0.03 mg/kg in monkeys. 28 While provisional data from the CDC's National Center for Health Statistics indicate there were an estimated 80 391 drug overdose deaths in the United States during 2024, a decrease of 26.9% from the 110 037 deaths estimated in 2023, the National Drug Threat Assessment 2024 highlights the dangerous shift from plant-based to synthetic drugs. This shift has resulted in the most dangerous and deadly drug crisis the U.S. has ever faced. 24
Portable ion mobility spectrometry (IMS) is a useful method for analysis in the field of several types of dangerous chemicals of interest to the military, security professionals, law enforcement, and first responders. Analysis times for these instruments are seconds, and they can be quite sensitive. These systems are typically designed to be portable, with sizes ranging from small handheld devices to larger desktop models. IMS was initially developed and deployed by the military for the detection of low levels of vapor-phase chemical warfare agents (CWAs) and toxic industrial chemicals (TICs)29,30 and are still used for this purpose. They were then adapted for the aviation industry for use as explosive trace detectors (ETDs) where they are still used to detect microscopic traces of explosives.30–33 IMS systems have also been optimized and used for the detection and identification of trace amounts of illicit drugs,34–40 and commercial off-the-shelf (COTS) systems are now being used to detect and identify trace amounts of fentanyl and its analogs in the field.41–46 A method for evaluating COTS ion mobility spectrometers for trace detection of fentanyl and fentanyl-related substances has even been reported. 47
Much of the earlier published research on fentanyl using IMS was performed by researchers who used COTS systems but developed their own IMS methods to detect fentanyl. Verkouteren and Staymates developed an IMS method for the detection of controlled substances using two different commercial COTS IMS systems. 36 They determined at least one controlled substance was detected when binary mixtures of these substances were analyzed, and that over-the-counter tablet medications for cold, flu, and allergy relief could be distinguished from tablets containing controlled substances. Regarding fentanyl, they evaluated mixtures of fentanyl with heroin as this was reported to be a particularly problematic combination. The fentanyl and heroin peaks exhibited some spectral overlap, but the method could detect fentanyl at concentrations of ∼10% (weight %) in heroin; heroin was not detected in these mixtures when fentanyl concentrations were greater than ∼30%. Sisco et al. programmed a COTS IMS system with 22 opioid compounds including 16 fentanyl analogs and detected fentanyl in the presence of heroin down to 0.1% by weight fentanyl. 41 Lower instrumental resolution in the IMS caused the formation of a heroin and fentanyl combination peak which could be reliably traced to the presence of heroin and fentanyl or a fentanyl analog. These authors advised that detection of nanogram (ng) levels of fentanyl in a binary fentanyl and heroin mixture is possible but can be complicated by decreased resolution in certain commercial instrument models.
Since these previous studies were performed, some IMS manufacturers have deployed systems with methods programmed to detect fentanyl. Unlike those used in these previous studies with radioactive ionization sources such as 63Ni, many of these newer instruments use non-radioactive sources. Ionization conditions and sample matrix can have a significant impact on signal and detection capabilities. 48 Acetaminophen is one of several potential drugs expected to be encountered in sample matrices of fentanyl samples. Acetaminophen is a common ingredient present in legitimately prescribed opioid medications at relatively high amounts compared to the opioid,49–51 and is also detected in many illicit or diverted drug tablets.19,21,25,36,52 Sisco et al. showed that when using their IMS method, fentanyl signal suppression by acetaminophen was not significant. However, when using thermal deposition direct analysis in real time mass spectrometry (TD DART-MS), inhibition of the fentanyl signal increased with increasing amount of acetaminophen, though the signal was never fully quenched. At a 1000:1 acetaminophen:fentanyl ratio, the fentanyl peak maximum was 36% of the peak area relative to pure fentanyl. Competitive ionization was considered the primary reason for observed signal intensity changes in both the IMS and TD DART-MS fentanyl/acetaminophen mixture data. 41 Verkouteren and Staymates reported that while acetaminophen is not intended to generate an IMS response and was shown to have no effect on the detection of controlled substances in their work, the impact of competitive ionization on the intensity of target IMS peaks was not evaluated in their study. 36 Loss in signal intensity due to inert materials is possible and has been reported.35,53 The reason for observed losses is not clearly defined and may be because the inert materials interfere with the desorption processes. 36 There are a number of published studies using IMS systems that use non-radioactive sources to evaluate illicit drug substances including fentanyl.36,41–45 While Verkouteren et al. included some COTS systems with non-radioactive sources when they developed a method for evaluating ion mobility spectrometers for trace detection of fentanyl and fentanyl-related substances, 47 these authors are not aware of any studies that evaluate fentanyl and the impact of mixture components on the fentanyl IMS detection using a preprogrammed fentanyl detection method.
This research evaluates the impact of percent fentanyl in acetaminophen matrices on the fentanyl detection capabilities of a COTS drift-tube IMS system with a dielectric barrier discharge (DBD) non-radioactive ionization source preprogrammed to automatically detect fentanyl. DBD sources are discharge ionization sources which have an insulating (dielectric) material in between metal electrodes. DBDs are self-sustaining in electrode configurations containing an insulating material in the discharge path. This dielectric barrier is responsible for a self-pulsing plasma operation and, thus, the formation of non-thermal plasma at normal pressure. The discharge creates electrons with high average kinetic energy (1–10 eV), metastable species, and high-energy photons. The ionization profile for DBDs is similar to that of corona discharge sources, and like with the corona, an advantage of pulsing is a reduction in production of nitrogen oxide species. A primary analytical benefit of a DBD ionization source is a larger and more-controlled ionization region48,54,55 The preprogrammed detection method was provided by the manufacturer and available for purchase at the time this testing was performed. It was used without any refinement or optimization. This approach is consistent with how field users typically operate, relying on pre-programmed detection parameters that have been optimized by the instrument manufacturer for an established set of target threats. Of interest, too, is that the COTS IMS used in this study performs variable-temperature desorption.
Experimental
Materials and Methods
Physical mixtures of fentanyl citrate (fentanyl) and acetaminophen powders were prepared at concentrations (w/w) of 1% fentanyl and 0.1% fentanyl using a digital Wig-L-Bug mixer/amalgamator model MSD and then dissolved in ethanol. The fentanyl was purchased from Cayman Chemical. The acetaminophen was purchased from Sigma-Aldrich. For each analysis, the volume of solution required to deliver the target number of nanograms of fentanyl was directly deposited onto a single-use swab and allowed to dry under ambient conditions. Three replicates at each concentration for each target number of nanograms of fentanyl were prepared and analyzed. The amount of fentanyl dosed on each swab ranged in sample amount from 1–20 ng for 1% fentanyl in acetaminophen; for the 0.1% fentanyl in acetaminophen, the dosed amounts of fentanyl were 0.5 and 1 ng.
Ion Mobility Spectrometer
Analysis was performed using an IONSCAN 600 (Smiths Detection, USA) ion mobility spectrometer with the system's proprietary single-use swabs. The IONSCAN 600 uses a DBD non-radioactive ionization source. It performs a variable-temperature desorption using a flash heater, and a single-tube analysis of both positive and negative ions, although only positive mode detections are used for fentanyl identification. The method used was provided by the instrument vendor and was the deployed method for fentanyl detection at the time this analysis was performed (control parameter set N (25332-1)). Method settings and system component versions are shown in Table I. When this COTS IMS is used in the field, microscopic particle residues of the drug substance are recovered using a swab. During this swabbing, other trace residues present in the sample are also recovered on the swab. For this testing, rather than swabbing for microscopic particles, fentanyl/acetaminophen solutions of specified concentrations were deposited directly onto the swab.
IMS analysis and version settings.
During an analysis using this COTS IMS, the swab is inserted into the system inlet where the sample is thermally desorbed from the swab by flash heating. The vapors are directed into the instrument's ionization region using a flow of clean, dry air. Ionization using a DBD ionization source occurs. Dopant chemicals are introduced in the ionization region and intended to control the ionization reactions so that reproducible, stable analyte ions are formed regardless of sample matrix. Dopant and calibrant chemicals used in the IONSCAN 600 are dipropylene glycol monomethylether, hexachloroethane, nicotinamide, and nitrobenzonitrile. An electronic ion shutter is used to introduce ions formed into the drift region in bundles called ion swarms. The ions are placed in a constant electric field and accelerate through the drift region. As the ion swarms pass through the region, they collide with neutral drift-gas molecules, which are flowing in the opposite direction of the ion swarm. These collisions cause a deceleration of the ion swarms based on their size, shape, and charge. Once they reach an equilibrium, the ion will achieve a constant drift velocity. The time taken by the ion to travel the distance between the ion shutter and the ion detector is known as the ion's drift time, td, which is usually on the order of about 20 milliseconds or less. For the method used in this COTS IMS, the fentanyl ion td is ∼10 milliseconds. The measured td is then used to calculate the ion's reduced mobility, K0, which is the ion's mobility, K, corrected for temperature and pressure. K0 is characteristic of the mass, charge, and collision cross-section of the ion and used to establish analyte identity. Figure 1 shows a schematic of a drift-tube IMS system which uses clean, dry air as both the carrier gas used to introduce the sample into the system and the buffer gas used within the drift region.
Schematic of a drift-tube IMS.
Preprogrammed Automatic Detection
The instrument used was programmed to automatically alarm for fentanyl if fentanyl was detected. It uses two different sets of peak properties to calculate drift time for the fentanyl ion peak and, therefore, generates two different K0 values for the measured fentanyl ion peak. The instrument automatically alarms if the peak is detected using either method. The first method is labeled by the system as “Fentanyl”, the second is labeled “Fentanyl-T”. Details on what features of the peak are used to calculate drift time for each method were requested by the authors from the instrument manufacturer but were not provided due to their proprietary nature. The stated K0 value of the calibrant, nicotinamide, is 1.8255 cm2/Vs under the analysis conditions. The stated K0 value of fentanyl under these same conditions is 1.0575 cm2/Vs. The experimental drift times of both the calibrant and fentanyl ions are measured and reported. The measured K0 value of the fentanyl is then calculated using Eq. 1. If the observed K0 value is within the acceptable range programmed into the method using either the Fentanyl or Fentanyl-T algorithm, the system will alarm for fentanyl.
Manual Data Review
For each analysis where fentanyl was detected using the Fentanyl algorithm, each segment of the six-second analysis was reviewed, and the maximum amplitude Fentanyl value from these segments was documented. In addition, the sum of all maximum amplitude values in these segments was documented and reported as the cumulative amplitude. For both the maximum and cumulative amplitudes, the average response of the replicates at each concentration where fentanyl was detected was calculated. This same procedure was performed for the peak values that were detected using the Fentanyl-T algorithm.
Results and Discussion
Since two methods were used to calculate the drift time, two different measured K0 values and related peak information may be reported if fentanyl is detected. The expected K0 value for the fentanyl ion peak under these analysis conditions was 1.0575 ± 0.0035 cm2/Vs. The average K0 observed value determined for all analyses when peak properties were calculated using the Fentanyl method was 1.0581 cm2/Vs with a standard deviation of 0.0002. When peak properties were calculated using the Fentanyl-T method, the K0 observed average value of the fentanyl ion was 1.0587 cm2/Vs with a standard deviation of 0.0003.
For the eight samples analyzed in triplicate, the system returned an automatic identification of fentanyl for 22 of the 24 analyses. The two that did not alarm automatically were from the samples with the lowest amount of fentanyl for both the 1% and 0.1% samples. The first was replicate one of the 1% fentanyl sample (1 ng fentanyl/99 ng acetaminophen); the second was replicate three of the 0.1% fentanyl sample (0.5 ng fentanyl/499.5 ng acetaminophen). For both of these replicates, although neither the Fentanyl nor Fentanyl-T methods detected a fentanyl peak, the plasmagrams for each analysis were manually reviewed and a peak at the anticipated drift time was clearly present in at least a few of the segments for each analysis. It is also worth noting that the Fentanyl-T signal for the analyses performed on swabs with 1 ng of fentanyl was substantially larger when the amount of acetaminophen in the matrix was higher. The average Fentanyl-T maximum and cumulative amplitude signals for the two replicates of the 1% fentanyl sample (1 ng fentanyl/99 ng acetaminophen) were 231 and 1099, respectively. The average of the three replicates of the 0.1% fentanyl sample (1 ng fentanyl/999 ng acetaminophen) were 666 and 5086, respectively. The reason for this may be fentanyl signal enhancement due to either the high amount of acetaminophen present during the ionization process, or from the other calibrant and/or dopant ions present during the measurement. This observation warrants further investigation. Also, the average of the two replicates of the 0.1% fentanyl samples at 0.5 ng fentanyl/499.5 ng acetaminophen sample amount had higher maximum and cumulative amplitude signals for the Fentanyl-T signal (476 and 3539, respectively) than did the samples of 1% sample when 1 ng fentanyl/99 ng acetaminophen were analyzed.
This data also shows that the Fentanyl-T algorithm was better able to detect fentanyl than the Fentanyl algorithm. All 22 out of 24 automatic detections of fentanyl alarmed for the Fentanyl-T algorithm; only 13 of the 24 were detected with the Fentanyl algorithm. This data is summarized in Table II. Figures 2 and 3 show the Fentanyl-T cumulative amplitude plotted as a function of the amount of fentanyl and acetaminophen deposited on the swab, respectively.
Fentanyl-T cumulative amplitude average values as a function of ng of fentanyl deposted on the swab. Error bars are the standard deviation of three (20, 10, 5, 3, 2 ng fentanyl) or two (1 ng fentanyl) replicates. The zero value at 1 ng fentanyl was removed from the average and standard deviation calculations because a zero value does not mean the fentanyl peak was not present, but rather the peak did not meet the alarm threshold.
Fentanyl-T cumulative amplitude average values as a function of ng of acetaminophen deposited on the swab. Error bars are the standard deviation of three (1980, 990, 495, 297, 198 ng Acetaminophen) or two (99 ng acetaminophen) replicates. The zero value at 99 ng acetaminophen was removed from the average and standard deviation calculations because a zero value does not mean the fentanyl peak was not present, but rather the peak present did not meet the alarm threshold.
Results of automatic alarms for each analysis performed.
When analyzed using a COTS IMS with preprogrammed automatic fentanyl detection methods, fentanyl was detected in an acetaminophen matrix at single-digit-ng-and-lower fentanyl levels in concentrations as low as 0.1% fentanyl. This can be operationally significant. Figure 4 is a photo illustration of a 2 mg sample of fentanyl alongside a U.S. penny. Both powder mixtures and illicit tablets encountered in the field may contain such small amounts of fentanyl. Tablets vary in size and weight, but assuming a tablet weight of 500 mg, the fentanyl concentration of a lethal tablet would be approximately 0.4% (w/w). While these experiments do not evaluate fentanyl in tablet form, with an optimized sampling method, it is reasonable to expect that similar detection limits would be achieved from low-dose-fentanyl tablets containing large amounts of acetaminophen.
Photo illustration of 2 milligrams of fentanyl, a lethal dose in most people. ©Public domain, U.S. Drug Enforcement Administration.
There are a number of challenges to detecting low doses of fentanyl and the value of this COTS IMS capability is significant. Both infrared and Raman methods, which are routinely deployed to first responders in portable forms for analytical testing at the scene, are unable to detect an analyte when its concentration in the sample is less than a few percent because the signal of the matrices will mask the signal of the fentanyl. This can be a complicating factor and will challenge library-matching algorithms of these portable systems, especially as the concentration of the analyte decreases. Portable mass spectrometers including gas chromatography mass spectrometry (GC-MS) and high-pressure mass spectrometry are also technologies deployed to field users for the analysis of drugs. Both of these methods can detect small amounts of drug substances, even in a mixture sample. While the exact amount of drug required for detection for either of these technologies is specific for the drug substance, neither of these portable methods have been shown to detect 1 ng of fentanyl. Typically, detection limits for portable versions of these technologies require double- or triple-digit ng amounts of drug substance for detection and/or automatic identification.
The use of portable IMS is not just significant because of its ability to achieve low limits of detection for low-dose-fentanyl mixture samples at the sample site. IMS systems are size, weight, and power friendly, and operate at ambient pressure. 48 These features are especially important for systems used in the field. In addition, COTS IMS systems are programmed to work like a black box in that a red screen with an identification is the displayed result if a target threat is present, and a green screen is displayed if no target threat is detected. Methods used to detect and identify substances are typically developed by the instrument manufacturer and usually tested by third parties before deployment. Third-party test reports may or may not be available to the public. While this red-light/green-light approach removes some of the value that a scientist might gain from interpreting an IMS spectrum (sometimes referred to as a plasmagram), this approach is quite beneficial in environments where these systems are being used by non-scientist operators to provide fast, reliable, actionable information at the sample site so real-time, data-driven operational decisions can be made.
While there are significant benefits portable IMS systems offer for the detection of low doses of fentanyl in mixture samples, there are also some challenges to deploying these systems. Sample overload can be a challenge. Care should be taken to control sample amount introduced to the system to prevent overload from occurring. This can be difficult in field environments where the amount and chemical composition of the sample recovered on the swab for analysis is unknown. When overload occurs, the system may require a bakeout to remove the overloaded contaminant. Throughout this research, no overload of the system occurred from the sample amounts dosed onto swabs. In addition, in every instance, no carryover was observed in subsequent analyses after an alarm occurred. This may be due, in part, to the low-thermal-mass inlet with flash heating used in this IMS system. Contact between the swab and the desorber is minimized, likely resulting in a reduction in contamination and system overload.
Maintenance is also important for IMS systems and includes periodic bakeout and regeneration processes. Periodic bakeouts are required to clean the internal components of the system. Periodic regenerations are required to maintain performance of the air purification unit which keeps the flow of air through the system clean and dry. The manufacturer recommends routine maintenance to include an automatic bakeout and regeneration be performed on alternating days for the IMS used in the study. These processes were programmed to run on alternating days (overnight) and were sufficient to keep the system clean and the air flow clean and dry throughout the testing. No additional cleaning or bakeout of the system was required.
It is also important to consider future research. This study evaluates the detection limits of fentanyl in an acetaminophen sample matrix. This is important because acetaminophen is commonly found in narcotics-based pain medications and is encountered in illicit drug samples,19,21,25,36,52 but it is possible the drug product may contain components other than acetaminophen. In addition, environmental interferents may be present in the sample matrix. These interferents and other components have the potential to impact ion formation, analyte desorption profiles, and detection results and should be investigated. It would also be useful to investigate why there was an observed enhancement of fentanyl signal at 1 ng deposition of fentanyl when the amount of acetaminophen in the matrix was higher. Further work should also consider the evaluation of fentanyl detection limits of low-dose-fentanyl tablets rather than powder mixtures since other factors such as sample preparation and extraction efficiency are important.
Conclusion
Ion mobility spectrometry is a method that has been deployed extensively for the detection of trace amounts of dangerous chemicals such as drugs and explosives. The extension of this method to the detection and identification of single-digit-ng amounts of fentanyl in an acetaminophen matrix at 1% and 0.1% concentration has been demonstrated using a COTS IMS system with a preprogrammed fentanyl detection method. This capability is important because of the infiltration of the illicit drug market with low-dosage fentanyl drug forms, and the need for the immediate detection and identification of these substances by law-enforcement personnel at the sample site. Results at the scene provide fast, reliable, actional information so real-time, data-driven operational decisions can be made. Other portable analytical methods that are typically used in these situations to perform identifications of illicit drugs are not capable of achieving the low limits of detection in mixture samples required for this drug substance at relevant concentrations.
