NPS detection in prison: A systematic literature review of use, drug form, and analytical approaches

Abstract This paper presents a systematic literature review on the detection of new psychoactive substances (NPS) in prison settings. It includes the most frequently reported NPS classes, the routes and forms used for smuggling, and the methods employed to analyse biological and non‐biological samples. The search was carried out using MEDLINE (EBSCO), Scopus (ELSEVIER), PubMed (NCBI), and Web of Science (Clarivate) databases, along with reports from the grey literature in line with the PRISMA‐S guidelines. A total of 2708 records were identified, of which 50 met the inclusion criteria. Findings showed the most prevalent NPS class reported in prison was synthetic cannabinoids (SCs). The most frequently reported SCs in non‐biological samples were 4F‐MDMB‐BINACA, MDMB‐4en‐PINACA, and 5F‐ADB. These were smuggled mainly through the postal services deposited on paper or herbal matrices. Concentrations of SCs detected on seized paper ranged between 0.05 and 1.17 mg/cm2. The SCs most frequently reported in biological specimens (i.e., urine, blood, saliva, and wastewater) were 5F‐MDMB‐PICA, 4F‐MDMB‐BINACA, and MDMB‐4en‐PINACA. Concentrations of SCs reported in femoral blood and serum were 0.12–0.48 ng/ml and 34–17 ng/ml, respectively. Hyphenated techniques were predominantly employed and generally successful for the detection of NPS in biological (i.e., LC‐HRMS/MS) and non‐biological samples (i.e., LC‐HRMS/MS and GC–MS). The onsite technique IMS showed promise for detecting SCs in various forms; however, immunoassays were not recommended. Future work should focus on accurate in‐field detection of SCs deposited on paper and in urine and saliva to improve real‐time decision‐making, as well as wastewater and air monitoring for overall drug use trends.


| INTRODUCTION
In recent years, the use of new psychoactive substances (NPS) in prison settings has become a cause of concern internationally. 1-9 The situation reported by 24 countries including the United Kingdom, Germany, Sweden, Hungary, Latvia, Australia, and the United States 9-11 has proven particularly challenging. It has been reported that the use of NPS in prisons has led to increased levels of violence, organized crime, bullying, aggression, and debt. [8][9][10]12 Although initial measures including training modules for staff, implementation of mandatory drug testing (MDT), infrastructural changes, and/or legislative restrictions, 9 NPS use in prison remains an issue of major concern. 13 Whilst there is evidence suggesting that the use of NPS worldwide may be declining, this trend is not observed in marginalized groups, including prison populations. 14  but which may pose a public health threat." 1,16 In addition, NPS have been associated with public health risks similar to traditional drugs of abuse (TdA), and they have also been shown to induce unpredictable health risks. The World Drug Report 2020 further specifies that "the term 'new' does not necessarily refer to new inventions, but to substances that have recently become available." 16 Due to the structural diversity of NPS, they are largely classified according to their substance groups, for example, aminoindanes, phencyclidine-type substances, phenethylamines, piperazines, plant-based substances, synthetic cannabinoids (SCs), synthetic cathinones, tryptamines, and "other" substances such as designer opioids and benzodiazepines. 16 The use of NPS in prisons was first reported in the United Kingdom around 2013 17 and in the years to follow in other European and non-European countries. 9 These compounds represented a valid alternative to TdA because of their low price, ease of availability, and undetectability. 2,3,[7][8][9][10] In addition, high potency NPS, for example, SCs, are popular amongst prisoners as the desired effect can be achieved with a lesser amount of substance and hence for a cheaper price. 1,8,18 In particular, SCs are used in this environment to aid in coping with imprisonment, sustaining existing habits, and for self-medication or pleasure. 6 Until a few years ago NPS in the United Kingdom were not normally screened in routine MDT, 10 making them an attractive alternative to TdA. Despite that some NPS are now included in MDT, their structures are continuously being altered by producers to avoid detection. 19 The market availability of specific NPS is strictly connected to countries' respective legislation in place at the time of production and/or consumption. 20,21 This results in a constantly evolving market of NPS which presents the main analytical challenge for in-field instruments and laboratories in charge to detect and quantify these substances. The large number of structurally diverse NPS available ($950 registered by UNODC 22 and >4200 on the web 23 ), and the pace at which these appear on the market (one new NPS per week 24 ) are also contributing factors challenging detection, due to a lag in certified reference standard (RS) availability. 2,3 Low concentrations of potent NPS, for example, SCs or opioids, combined with inhomogeneous distribution on new matrices or formulations, employed to facilitate smuggling in prisons, are also factors making difficult their detection and identification. 25 Currently, there are no universal globally agreed standard operating procedures (SOP) in place to identify TdA as well as NPS in prison.
Drugs of abuse are often confiscated in this setting via cell, inmate, or visitor searches performed by prison officers. 26 In some countries, such as the United Kingdom, the United States, and Canada, the use of sniffer dogs has also been reported for detection of TdA 26 as well as SCs. 25,27 However, due to the ever-changing nature of the NPS market, it is difficult to maintain the long-term effectiveness of sniffer dogs with these substances. 9 Once samples suspected to contain drugs are identified, these are screened using in-field analytical techniques such as ion mobility spectrometry (IMS) 28 and/or sent to external forensic laboratories for confirmatory analysis. External forensic laboratories employ traditional analytical techniques such as gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS), and nuclear magnetic resonance (NMR), which are costly and time consuming, 29 but can give meaningful information even in the absence of RS. In addition, drug use can be identified by analysis of prisoners' biological specimens, 26 which are also commonly sent to external forensic laboratories for analysis.  topic.
An overview of the types of NPS reported in prisons is shown in SCs. In January 2019 in Germany, the γ-carbolines derived 5F-cumyl-PEGACLONE was found for the first time in the post-mortem blood and urine of a prisoner. 32 The same SC was later found also in urine from German prisons along with cumyl-CBMEGACLONE and cumyl-PEGACLONE, also belonging to the γ-carbolines. 21 Other newly emerging SCs belonging to the subgroup 7-azaindole carboxamides were 5F-MDMB-P7AICA and cumyl-4CN-B7AICA, also detected for the first time by urinalysis in German prisons in 2021. 21 SCs were also often reported in general studies but referred to by their street name "Spice"; these studies are collated under the "nonspecific" subgroup in (n = 1376) reported that only 10% had used "Spice" during their current sentence. 8 The discrepancies in the results of the self-reported studies might be confounded by the differing level of trust prisoners exhibit towards the organizations conducting the studies. 6 Synthetic cathinones, synthetic opioids, new benzodiazepines, and stimulants were also found. In 2017, 10 European countries reported synthetic cathinones being used in their prisons according to the EMCDDA. 9 Additionally, two subsequent studies reported the detection of mephedrone 31,63,64 and 4-methylethcathinone (4-MEC) 31 in English prisons. Synthetic cathinones were also reported in an Australian wastewater analysis (WWA) study, which identified methylone and mephedrone in a small prison facility. 63 Synthetic opioids were less reported in European prisons in comparison with SCs and cathinones. Studies reporting opioid usage were confined mainly to the North-Eastern area of Europe and in Italy. 9 Specifically, a total of 10 seizures of synthetic opioids were reported from prisons in Latvia, including acryloylfentanyl, carfentanil, and cyclopropylfentanyl. [65][66][67] In England, etizolam was identified sprayed onto letters that were seized and analysed in 2015, 27 where up to three SCs, stimulant NPS such as ethylphenidate, methoxphenidine, methiopropramine, and adulterants were also detected. It is not well understood why low potency NPS and adulterants were found in conjunction with SCs in this matrix, and it was not possible to ascertain whether these were intentionally added to achieve enhanced desirable effects 27  prison reflects, to some extent, the use in the general population. 8 Generally, in both prison and the general population, drugs with a depressant effect on the CNS are preferred over their stimulant counterparts. 71 Yet, higher use of stimulants in the general population is suggested by Bonds and Hudson (2015) where the results of urinalysis showed a 3.5-fold increase in stimulant detection for prisoner admission ("on reception" samples) versus incarcerated residents ("pre-release," MDT and VDT samples). 31

| NPS smuggling routes and forms
Knowledge of potential smuggling routes and forms, which may differ from that of TdA, 9,72 could help inform and support the prison security system in tackling detection and identification of NPS. A total of 26 studies related to NPS smuggling routes and forms, employed to illegally introduce NPS in prisons, were retrieved from the literature. The postal service was highlighted as the most prevalent smuggling route (n = 14) for bringing NPS into prisons through parcels or mail. [8][9][10]19,25,27,33,45,46,49,64,68,73 Due to the trend of spraying NPS on paper, some UK prisons photocopied prisoners' correspondence, which reduced smuggling but was time-consuming. However, in some circumstances (e.g., English and Welsh prison "Rule 39" 74 and Scotland "Legal Mail" 75 ) legal, confidential correspondence can only be opened and inspected by prison staff in specific situations, which makes photocopying and routine checks more complicated. 76 The second most reported NPS smuggling routes, each described in five articles, were concealment inside the body and transportation over prison walls.
Concealment in body orifices, 6,9, found to be concealed also in unusual items, such as carcasses of birds 6,9 or oranges. 9 To overcome this issue, some prisons installed nets around the perimeters or used radar systems to intercept drones.
Twenty-five studies applied to the forms in which NPS are smuggled into prison. The forms reported for NPS in prison ( Figure S3) were via paper matrices, herbal mixtures, food and drinks, solid materials, clothes, cosmetics, and e-liquids. Paper matrices (n = 19), commonly delivered by postal services or during social visits, were the main form reported that was used to smuggle NPS 6,9,10,12,47,[59][60][61]77 as confirmed by analytical studies performed on seized samples. 5,20,21,25,27,28,34,38,41 The term "paper matrices" is used to encompass letters, children's drawings, blank paper sheets, greeting cards, photographs, books, documents, poems, blotters, paper snippets, Bible pages, online printed catalogues, rice paper, crosswords, and sudoku puzzles. 5,6,9,10,12,20,21,25,27,28,34,38,41,47,[59][60][61]77,78 Prisoners are believed to take NPS, specifically SCs, by licking, chewing, swallowing, smoking, 27 or placing in eyes 21 the paper, which is usually cut into 1 cm 2 or smaller pieces. 28 When in this formulation and size, such samples are easily concealed, carried, and traded between inmates. 38 SCs are commonly produced in solid form, then dissolved in an organic solvent such as acetone, and easily sprayed onto paper matrices 10 or herbal material. 31 Recently, other general reports also highlight paper matrices as the most popular form to smuggle NPS in prison across Europe, especially in Finland, Germany, Hungary, Lithuania, Poland, and Sweden 5,9 because of the challenges in detection. 8 The second most prevalent form reported was herbal mix-  (2018), NPS were found infused in paper inserted between the heating constituent and the cartridge of e-cigarettes. 21 The increased risk of fatal and non-fatal overdoses, related to the consumption of SCs in the forms discussed, could also be due to their heterogeneous distribution on the matrices. 41 Areas with a high drug concentration on paper are known as "hot-spots," 9 while those on herbal mixtures are known as "hot-pockets." 79 Moreover, this has implications for chemical detection, making representative sampling by the analyst challenging. 31  legislation in countries producing NPS and international control. However, differences are seen as well; for instance, γ-carbolinone SCs were often found in Germany, yet rarely seen in UK and US prisons.

| Analysis and sample preparation of NPS in non-biological matrices
Seized NPS were mainly found impregnated into paper or herbal material in the prison setting ( coupled with mass spectrometry (MS), which are regarded as highly discriminatory techniques for forensic analysis of drugs. 73 Table 2 shows a prevalence for the use of high-resolution mass spectrometry (HRMS) such as QToF 20,21,27,34,38,41,64 and quadrupole-orbitrap. 25 In seven studies, GC-MS was employed either as stand-alone 5,31 or alongside other techniques. 21,28,34,38,41 The in-field technique IMS was evaluated in two studies screening for SCs in prison. 28,34 Bonds and Hudson developed an analytical workflow for general seized material in prison. 31 First, unknown powders were analysed by colorimetric tests while tablets were compared against the TICTAC database, then in some cases further analysed either by IR or GC-MS. "general screen" (>1300 drugs and metabolites). It was more common to see samples containing only one SC 21,28,31,64 ; however, some samples contained multiple SCs. Up to eight SCs were found in one samples by Bonds and Hudson. 31 The majority of studies found in Table 2 characterized NPS on paper seized in prison. Ford 38 in order to cover compounds with different polarities. To extract substances from paper, one extraction was used in most studies. 5,20,25,27,28,38,41 McKenzie and co-workers 38  The in-field technique IMS was evaluated in two studies screening for SCs in prison. 28,34 Generally, laboratory-based hyphenated techniques are regarded as confirmatory techniques, while in-field techniques are employed as a preliminary test. Quick, minimal, and non-destructive sample preparation makes IMS well-suited for in-field analysis by non-expert users; for example, the analytes were collected by rubbing a Teflon sample trap on the sample's surface. 28,34 Metternich et al. evaluated both simulated and prison casework samples using the IMS IONSCAN600 ® . 28 The simulated samples Reduced selectivity can occur as substances that exhibit a difference <0.025 cm 2 V À1 s À1 in their K 0 values cannot be discriminated unambiguously, 80 for example, 5F-PB-22 and AB-CHMINACA with K 0 values of 0.9995 and 0.9975 cm 2 V À1 s À1 , respectively. 28 On the other hand, newly emerging SCs with structural similarity to the compounds already in the library can potentially be identified, 34 based on the overlapping K 0 values. 80 Nonetheless, IMS has difficulty when detecting more than one analyte in a mixture, where only the analyte with higher peak intensity is detected by the instrument. For example, in a sample containing a mixture of AB-CHMINACA, APINACA, 5F-ADB, MMB-2201, and caffeine, only 5F-ADB was detected. 28 Additionally, the low LOD, in the ng range, 28,34 could lead to false positives due to cross-contamination, arising from papers collected and stored in the same evidence bag. 34

| Analysis and sample preparation of NPS in biological matrices
In this section, articles including post-mortem analysis of specimen, 4,32,40,48 case studies of prisoners admitted to hospital following NPS intake, 35,43,46 as well urine, 21,31,68 saliva 49 or wastewater 63 analysis carried out on prison samples are presented (Table 3). In general, biological samples were pretreated, before NPS extraction, by the addition of buffers (i.e., acetate, 31  inmate, which were then quantified and found to be 0.14 and 0.48 ng/ml, respectively. In addition, Krotulski

| FUTURE WORK
Based on the outcomes of this review, specific areas are suggested for future work. As SCs were smuggled principally via paper and herbal matrices, rapid and accurate in-field analysis of these sample forms would improve real-time decision-making. Due to the evolving market, focus should be given to monitoring effectiveness of current in-field techniques for identifying new emerging SCs. For instance when IMS fails to identify SCs in suspected samples which produce peaks in the typical SC detection range, it should be used in conjunction with a laboratory-based prison drugs monitoring program. 34 As a result of the reduced selectivity and inability of IMS to detect more than one substance in a mixture, future research should also focus on other in-field technologies. It should be noted that spectroscopic techniques such as Raman and FTIR, are powerful analytical techniques, 29 that can discriminate between NPS in tablet and powder forms, and between NPS isomers. These are also non-destructive and available in handheld technology; however, they struggle with interfering matrices especially if containing a low amount of NPS, such as herbal material, 31 paper matrices or tobacco. 28 The use of approaches such as surface enhanced Raman spectroscopy (SERS) using minimally invasive sampling methods could be investigated to promote practical application of SCs detection on paper and herbal matrices. Of particular interest is the application of SERS swabs and colloids, embedded with metal nanoparticles to enhance the Raman signal, already employed for the screening of TdA and NPS. 82 A methcathinone spectrum was obtained in the study performed by Lee et al. where 23 μg of the analyte was deposited into SERS active films made of hydroxyethylcellulose polymer and aggregated silver nanoparticles. The samples were wiped with a cotton bud wetted then pressed onto a pre-swelled SERS substrate. Conveniently, the film when dry is similar to paper and can be stored for a year and cut to size when needed. 83 While Yu et al. designed paper-based inkjetprinted SERS swabs able to collect trace amounts of analyte from large surface areas, which can be concentrated into a small-volume SERS-active region by lateral-flow concentration. The swabs were validated for the detection of 5 μg of heroin and 5 μg of cocaine on glass slides. The measurements show that the technique is quantitative and repeatable across multiple swabs. 84 The easy sampling approach similar to IMS could allow rapid yet selective identification of NPS in herbal and paper matrices.
As immunoassays lacked accuracy, there is still a need to develop sensitive, real-time and non-invasive POC testing to screen for SCs in biological samples (i.e., urine and oral fluids) for use in a decisionmaking context during on-site intoxication and emergencies. The IMS (IONSCAN LS ® ) with a high pressure injection system 85 was proven effective for detecting TdA gamma-hydroxybutyrate (GHB) and gamma hydroxyvalerate (GHV) in synthetic urine at approximately 3 μg/ml, which suggests the method could potentially work for saliva samples. More recently the same instrument was employed for the detection of cocaine in saliva. 86 However, their field collection device, based on a cotton swab with an indicator and a molecularly imprinted polymer (MIP) sorbent, was designed to selectively retain cocaine.
Therefore, adaptation of such device to retain SCs would be needed.
Moreover, fluorescence spectral fingerprinting combined with numerical modelling could be used to identify the likely presence of SCs, as well as provide more specific information on structural class and concentration ($1 μg/ml). This approach can detect both parent and combusted material, and it is practical for detecting SCs in oral fluids. 87 All the procedures mentioned in the above studies 85