Air monitoring for synthetic cannabinoids in a UK prison: Application of personal air sampling and fixed sequential sampling with thermal desorption two-dimensional gas chromatography coupled to time-of-flight mass spectrometry

In recent years, there have been increasing complaints from staff working in UK prisons of secondary exposure to psychoactive drug fumes, often believed to be synthetic cannabinoids. Our pilot study aimed to provide an initial evidence base for this issue and reveal compounds of interest within indoor prison air. Here, we present a new method for the detection of synthetic cannabinoids in air and demonstrate its application in a UK prison. Air sampling was conducted using a fixed sequential sampler, alongside personal air sampling units worn by prison officers within an English prison. Air samples were collected onto thermal desorption (TD) tubes and analysed via comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC (cid:1) GC-TOF MS). This study is the first of its kind in a prison setting, and the approach is of importance to analytical scientists, policy makers and public health employees tasked with the health and safety of prison staff. GC (cid:1) GC-TOF MS analysis was able to separate and identify a range of compounds present in the prison air samples. Analysis of the TD tubes did not reveal any synthetic cannabinoids from the fixed pump air samples or the personal pump samples worn by prison officers. Air monitoring in prisons presents a challenge of logistics and science. Fixed sequential air sampling combined with personal air monitoring devices allowed air from multiple locations


| INTRODUCTION
For several years now, prison staff working in the United Kingdom has consistently expressed concern about the prevalence of psychoactive substance abuse by prisoners. 1 There have been reports (in the media and first-hand from prison officers) of staff illness ranging from symptoms such as headaches and disorientation, to more serious symptoms, which it is claimed arise from secondary exposure to drug fumes whilst working at prisons. The drugs in question are often reported as new psychoactive substances (NPS). The Psychoactive Substances Act 2016 2 defines a psychoactive substance as something that produces a psychoactive effect in a person by stimulating or depressing the central nervous system and affecting mental functioning or emotional state. To date there is no evidence to support the claims from UK prison staff concerning secondary exposure to these compounds. Here, we report a new method for the detection of synthetic cannabinoids in air and demonstrate its application in a UK prison.
Research to date has largely focused on the sampling of psychoactive substances that are present in particulate matter (PM), typically with the common grain sizes of 2.5 and 10 μm (so-called PM2.5 and PM10, respectively) as these sizes may be inhaled. [3][4][5] Such particulates may be sampled from air using various volume samplers, low, medium or high volume. Low volume samplers have been used in this manner to collect airborne particulates in a small establishment to minimise microenvironment perturbation, which can occur with larger volume samplers. 6 Polytetrafluoroethylene (PTFE) membrane filters or quartz filters are used for the collection of PM, and such membranes may then be subjected to solvent extraction or similar prior to analysis. Analytical systems require significant separation capabilities to effectively resolve the high number of airborne components that are often present in such samples. Gas or liquid chromatography coupled to mass spectrometry (GCMS or LCMS) have been used in several air sampling studies. 4,[7][8][9][10][11][12][13][14] Solid phase microextraction (SPME) with ion mobility spectrometry (IMS) have also been applied in this field. Lai et al. 14 applied SPME and IMS for the headspace sampling and analysis of airborne cocaine, MDMA and marijuana.
To ascertain broad drug trends in prison populations, drug monitoring research in prisons has more often been accomplished using wastewater analysis, 15,16 as opposed to other matrices. There has been greater success in the detection of volatiles in high-risk areas that face relatively constant exposure to psychoactive substances due to the nature of how they are used. [17][18][19] Lai et al. 14 screened commercial cargo air for illicit substances using SPME and IMS. Doran et al. 20 used both SPME and charcoal cartridge sampling to determine air quality in police drug safes and storage areas, that is, high-risk drug exposure areas. Various analytical approaches have been used to investigate other high-risk areas. Madireddy et al. 21 investigated the presence of eight drugs on countertop surfaces in a selected drug household; they compared the target recoveries of the SPME fibre to the containers they were in to determine the ageing process of the volatiles on the surface. Variability was low for some of the recoveries after a certain number of hours (15 h), comparing them to van Dyke et al. 22 indicates that wipe sampling is a viable and reproducible method of surface analysis for certain illicit compounds (methamphetamine and related compounds). Fent et al. 23 (2011) conducted similar research to assess the ventilation and exposure in a Kentucky police station drug vault and adjacent areas. The employees were experiencing relevant health symptoms, and there were concerns it was due to the drug exposure in these areas. Concentrations (nanograms per cubic meter of methamphetamine, oxycodone and THC in the air) were found to be relatively low; however, cocaine ranged from no detection to up to 12,000 ng/m 3 (which is relatively low compared to actual recreational doses). Surface sampling revealed quantifiable levels of all the target drugs except for methamphetamines (cocaine was the highest). These combined methods, further information from employees, ventilation assessments, temperature and humidity data revealed that this workplace needs to improve its health and safety regulations to avoid it becoming a high-risk drug exposure area.
Investigating the issue of secondary exposure to NPS specifically in prisons is a complicated undertaking. Possible approaches include wide-scale investigations to determine which specific NPS and traditional drugs are being abused in prisons, and mandatory drug testing of prisoners assists with gathering this intelligence. In addition, wastewater sampling at prison sites has been shown to provide useful intelligence on drug trends within prisons over specific time periods. 15 Smoke-free policies in prisons certainly have improved the level of potential harm due to second-hand exposure to cigarettes. However, second-hand exposure to drug fumes in prisons remains a serious issue requiring investigation. Our study is the first of its kind, and we present here the instrumentation, methodology and data from this first prison trial.

| TD and sorbent tubes
TD is a proven 'front-end' technology for GC and GC-MS that is applicable to the analysis of volatile and semivolatile organic compounds (VOCs and SVOCs) in a wide range of samples-gases, liquids and solids. It combines pre-concentration, desorption/extraction and GC injection. Sorbent tubes, used to trap target analytes emitted from the samples, are thermally desorbed by heating in a flow of inert gas. The released components are then transferred to an electrically cooled, narrower 'focusing' trap within the TD system. After completion of the primary (tube) desorption stage, the focusing trap is desorbed by rapidly heating in a reverse flow of carrier gas ('backflush' operation). This transfers the organic compounds into the capillary GC column for separation.
This maximises concentration enhancement and produces narrow chromatographic peaks optimising sensitivity across a broad volatility range.
The use of TD sorbent tubes offers some advantages over alternative sampling techniques such as SPME. SPME typically contains a very small amount of phase and is a competitive equilibration technique. With TD sorbent tubes as you pass the gas through multiple beds of sorbent material the material adsorbs volatiles from the gas so enriching the sample rather than simply reaching an equilibration level with the exposed atmosphere. The TD technique is simple to employ as a dynamic technique (pumped air) rather than passive, so many litres of air sample can be drawn over the sorbent material in the TD tube, vastly enhancing the contact area of the sorbent with the surrounding air.
TD tubes may utilise a multi sorbent bed tube containing sorbents of different service area and strength. The first bed that the air sample is exposed to is often a weaker sorbent such as Tenax; this has been shown to have high retention for compounds in the range C6+ enabling it to be used to retain compounds from many litres of sampled air. The Tenax is then backed with a carbon base sorbent with a much higher surface area; this is good for enriching compounds in the range C3+. The reason for placing a weaker sorbent in front of the stronger sorbent is not due to the sampling stage but the TD stage. Tenax will readily release compounds in the range C6-C35 if heated to around 220-280 C with a reverse flow, however if semivolatiles reached the stronger sorbent, in the case a dual bed sorbent was not used, then some of the semi volatile compounds could become irreversibly retained. Hence, using tubes with multiple beds is common practice. In comparison, SPME uses an equilibration approach, and there is competitive sorption from components in the sample and because the phase is very small in comparison to TD sorbent tubes, it can easily become saturated with one chemical at the expense of reduced enrichment of other chemicals.   When designing air sampling experiments of this nature using TD tubes, it is important to consider breakthrough volumes. If very volatile analytes are expected then the use of serially coupled TD tubes may be employed. For this application, serial coupling of tubes was not employed; instead, a multibed sorbent packed in the tubes was utilised, because the expected target components were not very volatile then it was deemed the likelihood of breakthrough of the trap for these particular components would be highly unlikely.

| Prison officer volunteers
Seven TD tubes were inserted into the tube manifold block of the MTS-32, the first two tubes were trial tubes and the remaining five collected air for analysis during the sampling period. Each TD tube sampled air for 4.8 h at a flow rate of 50 ml/min for a total of five tubes over 24 h (excluding the initial trial tubes).
A checklist was prepared for the static sampler and was completed at the end of the allocated sampling time. Following the sampling period TD tubes were removed from the unit, capped and stored in a refrigerator.

| ACTI-VOC air sampling protocol
Two ACTI-VOC portable air pumps were provided to the 15 staff volunteers to be used during a 8-or 12-h shift during the study period.
They are designed to use one TD tube at a time, at a set flow rate, whilst recording the sampling time. Figure 1  Following the static and personal air sampling protocols, the TD tubes were transported to the laboratory to be analysed using the TD-GC Â GC-TOF MS analytical system.

| TD parameters
The TD instrument was a UNITY-xr, utilising a materials emissions (U-T12ME-2S) cold trap. Pre-purge was set for 1 min at 50 ml/min. Tube desorption ran for 10 min at 280 C, 50 ml/min. Trap puge was 1 min at 50 ml/min with a low temperature of 30 C and high of 300 C set to maximum heating rate. Trap hold time was 2 min, with outlet split at 4 ml/min and flow path temperature of 180 C.

| GC Â GC method and TOF conditions
The GC was an Agilent 7890B GC using helium carrier gas. Oven ramp was set to 40 C for 2 min, ramped at 5.5 C/min to 250 C and held     Table 1.

| Spectral libraries and chromatographic searching
F I G U R E 2 Column set configuration employed for GC Â GC. Primary column: Rx1-5ms. Secondary column: Bpx50

| Prison study results overview
On average the GC Â GC-TOF-MS system resolved 1000 to 2000 peaks in each sample of air sampled within the prison (fixed or personal pumps). Chromatography was searched against the three libraries as discussed in Section 3.7. Any peak reported as matching a compound of interest (psychoactive substance or thermal degradation product) was manually examined to compare the mass spectrum.
There was no evidence of synthetic cannabinoids detected in the MTS-32 air samples or ACTI-VOC personal pump air samples.
A possible explanation for the negative finding could be that no synthetic cannabinoids were being used during the study period or that the level of substance use was very low. The increased restrictions on prison visitation and prisoner movement during the study period as a result of Covid-19 may have contributed to this. It is also a possibility that synthetic cannabinoids were present in the air, but at levels too low to detect. Whilst our study did not reveal detectable drug concentrations in the prison air, there may be alternative explanations to attempt to explain the serious symptoms experienced by prison officers in the past. Drug residues may be transferred to work surfaces and handles in a variety of settings 19 and such contamination could pose a risk. In our opinion though, a contaminated surface mechanism of secondary drug exposure seems unlikely as a cause of prison officer symptoms. Some UK prisons have described quite high numbers of officers claiming exposure to psychoactive substances within short periods of time, which does not tally well with a surface transfer mechanism.
Doran et al. 20 investigated air quality inside police drug safes and storage areas and also found no evidence of drug residues in air samples. Surface drug residues were found on handles and shelving units; however, no residues (22 illicit compounds and 2 metabolites) were detected using carbon traps and analysis via LC-MS-MS. The authors reported that chemical odours emanating from drug safes may not be a result of the drugs themselves but are likely due to VOCs arising from chemicals used in drug manufacture amongst other potential sources. The preparation of synthetic cannabinoids by drugs users may involve bulk drug powders, dissolved in organic solvents, which are sprayed onto herbs; residual solvents may cause toxic effects. 26 We have demonstrated in our volatilisation studies for the four synthetic cannabinoids that they are detectable in air samples following volatilisation. Volatility of the synthetic cannabinoids will vary due to chemical class and structure, though it has been demonstrated in other studies that synthetic cannabinoids are also detectable in air following smoking experiments. Naqi et al. 27

| MTS-32 results
The chromatography revealed a wide range of compounds present in the prison air, and these fall into several categories: flavours, fragrances, pharmaceutical preparation, chemical reagents/intermediates, industrial manufacturing or refining of commercial products and pollutant/contaminants. These categories overlap one another for several compounds as they are multi-functional for their compound class; for example, several alcohol-based compounds serve different potential functions, so determining their origin in the current context is not possible.
There was a range of compounds found in the MTS-32 samples.
The largest proportion of the compounds detected were alkenes (13.45%), alkanes (11.21%), alcohols (10.31%), benzene derivatives (9.87%) and aldehydes (9.87%). The remaining types range from toluenes, ketones, to furans, terpenes and others in smaller proportions (0.45%-6.8%). Our analysis of the data has suggested that many of these compounds would routinely be expected in indoor air samples, particularly in sites with heavy human activity or close to vehicular traffic.   Table S1 in the supporting information.

| Trip blank TD tube
One TD tube was designated as a 'trip blank' and set aside to be kept with the other TD tubes during transportation and storage at the prison site to compare with the analytical tubes used for the ambient air via the MTS-32 and ACTI-VOC sampling devices. The purpose of this tube is to act as a control for potential contamination events occurring during storage of tubes on site or transportation to and from site.
Analysis of the trip blank revealed a small number of compounds at very low levels (in most cases approximately 1000 times lower than levels found in the real samples). These compounds present at such levels do not suggest any contamination.

| CONCLUSION
This study represents the first trial of the combination of fixed location sequential air sampling with portable, body-worn active air sampling devices for the purpose of air monitoring for synthetic cannabinoids in a public sector prison. The methodology for air sampling using this combined approach allowed a significant range within the prison to be sampled over the study period, collecting air from a prison wing (MTS-32) and from all areas patrolled by participating prison officers (ACTI-VOC). An effective methodology for GC Â GC-TOF-MS analysis of the TD tubes was created, which enabled a wide range of compounds to be detected, with excellent resolution.
Air sampling at the prison did not reveal any synthetic cannabinoids from either sampling method. It is possible that no synthetic cannabinoids were being used during the study period, or that the level of substance use was very low. The increased restrictions on prison visitation and prisoner movement during the study period as a result of Covid-19 may have contributed to this. It is also a possibility that synthetic cannabinoids were present in the air but at levels too low to detect. Laboratory trials were however successful and the approach for deployment in a prison setting including staff training, MTS-32 and ACTI-VOC sampling protocols has been piloted for the first time in this novel study.

ACKNOWLEDGEMENT
This work was funded by The Professional Trades Union for Prison, Correctional & Secure Psychiatric Workers (Grant ID 11700).

CONFLICT OF INTERESTS
There are no conflicts of interest to disclose.

ETHICAL APPROVAL
Ethical permission was granted for the study by Bournemouth University, Faculty of Science and Technology Ethics Committee (ID 27716).

CONSENT STATEMENT
All prison staff volunteers provided consent through approved ethical procedures as approved by Bournemouth University, Faculty of Science and Technology Ethics Committee (ID 27716). Permission to reproduce material from other sources: not applicable.