A rapid detection method for policy-sensitive amines real-time supervision

Boosting the sensitivity of single photon ionization time-of-flight mass spectrometry using a segmented focus quadrupole-ion guide

Single photon ionization time-of-flight mass spectrometry (SPI-TOF-MS) is a powerful analytical technique for real-time detection of trace VOCs. However, efficient ion transmission within the ionization chamber has always been a challenging issue in SPI-TOF-MS. In this study, a novel ion guide termed the Segmented Focus Quadrupole Ion Guide (SFQ-IG) was introduced for SPI-TOF-MS. The SFQ-IG device consists of 12 printed circuit boards (PCB), each containing four quarter-ring electrodes with inner diameters progressively decreasing from 26 to 4 mm. The simulation results demonstrated that SFQ-IG exhibited superior ion transmission efficiency than both ion funnel (IF) field and direct current-only (DC-only) field. By integrating into a SPI-TOF-MS, this ion guide was optimized in terms of the ionization source pressure, direct current gradient, and radio frequency amplitude. Further comparative experiments demonstrated that the SPI-TOF-MS with the SFQ-IG exhibited higher sensitivity than both the IF field (1.3-7.4 times) and DC-only field (3.5-8.8 times) for the test VOCs. The improvements in limit of detection (LOD) with the SFQ-IG ranged from 1.6 to 5.3 times compared to the DC-only field for the test VOCs. Fabricated using PCB technology, the SFQ-IG is characterized by its cost-effectiveness, compact size, and high transmission efficiency, facilitating its integration into other mass spectrometers.

Direct detection of acetonitrile at the pptv level with photoinduced associative ionization time-of-flight mass spectrometry

Photoionization mass spectrometry (PI-MS) has become a versatile tool in the real-time analysis of volatile organic compounds (VOCs) from the atmosphere or exhaled breath. However, some key species, e.g., acetonitrile, are hard to measure due to their higher ionization energies than photon energy. In this study, the direct and sensitive detection of gaseous acetonitrile based on a photoinduced associative ionization (PAI) reaction was investigated with a laboratory-built PAI time-of-flight mass spectrometer (PAI-TOFMS). By doping CH₂Cl₂ in the photoionization ion source, the mass signal of acetonitrile that cannot be effectively obtained by photoionization appeared with an extremely high intensity through the PAI reaction between acetonitrile, CH₂Cl₂, and residual H₂O in the system. Though the moisture in the sample gas has an evident impact on the detection efficiency of acetonitrile, with a relative signal intensity decreasing from 100% under dry conditions to 60% at saturated relative humidity, excellent detection sensitivity was still obtained for gaseous acetonitrile in different matrixes. The sensitivity calibration experiment showed that the detection sensitivities of acetonitrile in N₂ buffer gas, exhaled gas, and outdoor air were 682.4 ± 5.2, 17.0 ± 0.7, and 23.9 ± 0.2 counts pptv^-1, respectively, with an analysis time of 10 s. The corresponding 3σ LODs reached 0.22, 8.82, and 6.28 pptv, which are equivalent to 0.40, 16.0, and 11.4 ng m^-3. The performance of the PAI-TOFMS was first demonstrated by analyzing exhaled acetonitrile from healthy non-smokers and smokers and continuous monitoring of acetonitrile in outdoor air. In summary, this study provides a new and highly sensitive method for the real-time detection of acetonitrile through mass spectrometry.

Hydrogen-bond activated ESIPT in naphthalimide-based fluorescent probe for sensing volatile amines

Amines levels present important indicative value in food safety and human health. Although they are involved in some normal physiological responses of the organism, their overproduction or intake may cause pathological responses. Herein, we report a recyclable visual packaging bag for volatile amines detections based on the naphthylamide derivative N-S and its positive PL characteristics. Specifically, handmade test strips based on compound N-S have been applied to fish freshness labeling, and the cyclic fumigation experiment shows its restorable PL effect and efficiency. The possible PL transfer mechanism of naphthylamide derivative N-S is uncovered by the density functional theory (DFT) calculation and titration mass spectrometer and ¹H NMR. This work expands a conjugation in a molecule by hydrogen-bond activated ESIPT (H-ESIPT) and provides a portable detection method for volatile amines detection.

Ultrasensitive detection of trace chemical warfare agent-related compounds by thermal desorption associative ionization time-of-flight mass spectrometry

A thermal desorption associative ionization time-of-flight mass spectrometer was developed for ultrasensitive detection of semi-volatile chemical warfare agents (CWAs). The excited-state CH₂Cl₂-induced associative ionization method presented a soft ionization characterization and an excellent sensitivity towards CWAs. The detection sensitivities of the investigated nine CWA-related substances were 2.56 × 10⁵-5.01 × 10⁶ counts ng^-1 in a detection cycle (30 s or 100 s). The corresponding 3σ limits of detection (LODs) were 0.08-3.90 pg. Compared with the best-documented LODs via the dielectric barrier discharge ionization (DBDI) and secondary electrospray ionization (SESI), the obtained LODs of the investigated compounds were improved by 2-76 times. Additionally, the measured sensitivity of 2-Chloroethyl ethyl, a proxy for mustard gas, is 550 counts pptv^-1, which exceeds the DBDI and SESI's corresponding values (4.4 counts pptv^-1 and 6.5 counts pptv^-1) nearly by two orders of magnitude. A field application simulation was conducted by putting a strip of PTFE film contaminated with the CWA-related agent into the thermal desorption unit. The simulation showed that the sensitivities of the instrument via swipe surveying could achieve 2.19 × 10⁵ to 5.23 × 10⁶ counts ng^-1. The experimental results demonstrate that the excited-state CH₂Cl₂-induced associative ionization is an ultrasensitive ionization method for CWAs and reveal a prospect for improving the detection of CWA species future.

Interpol review of controlled substances 2016-2019

This review paper covers the forensic-relevant literature in controlled substances from 2016 to 2019 as a part of the 19th Interpol International Forensic Science Managers Symposium. The review papers are also available at the Interpol website at: https://www.interpol.int/content/download/14458/file/Interpol%20Review%20Papers%202019.pdf.

Identification of specific markers for amphetamines synthesized from glycidic acid pre-precursors and retrospective search in German profiling database

The pre-precursor market and the clandestine production of amphetamine-type stimulants (ATS) has become more diverse in recent years. Besides α-phenylacetoacetonitrile (APAAN) and α-phenylacetoacetamide (APAA), glycidic acid derivatives and methyl α-phenylacetoacetate (MAPA) are gaining importance. This conclusion is based on seizure data of police and customs. However, analytical data are needed to confirm and quantify the actual prevalence of new pre-precursors by elucidating the percentage of seized ATS that have been produced from them. A recent study showed that APAAN use is currently declining, which supports the view that new pre-precursors are being used. In this study, several conversion procedures using different batches of glycidic acid derivatives and a complete Leuckart reaction to produce amphetamine were carried out. The resulting organic phases were analyzed using gas chromatography - mass spectrometry to identify possible marker compounds. Three marker compounds were discovered and characterized using mass spectra and nuclear magnetic resonance spectroscopy. They were identified as phenyl-1-propanone, N-(1-phenylpropyl)formamide and 1-phenylpropan-1-amine. Their prevalence was investigated by searching the markers in an amphetamine impurity profiling database to determine to what extent they occurred in amphetamine samples from recent years. Data from the central German amphetamine profiling database of more than 250 cases were used for this purpose. The yearly occurrence of the three glycidate marker compounds was determined going back as far as 2009, revealing an increasing trend from 2016 on. This article presents experimental proof that APAAN is currently being replaced by other pre-precursors, such as glycidic acid derivatives.

Kinetic Understanding of the Ultrahigh Ionization Efficiencies (up to 28%) of Excited-State CH2Cl2-Induced Associative Ionization: A Case Study with Nitro Compounds

Excited-state CH₂Cl₂-induced associative ionization (AI) is a newly developed ionization method that is very effective for oxygenated organics. However, this method is not widely known. In this study, an unprecedented ionization efficiency and ultrafast reaction rate of AI toward nitro compounds were observed. The ionization efficiencies of o-nitrotoluene (o-NT), m-nitrotoluene (m-NT), and nitrobenzene (NB) were as high as (28 ± 3)%, (27 ± 2)%, and (13 ± 1)%, respectively (∼1-3 ions for every 10 molecules). The measured reaction rate coefficients of these nitroaromatics were (0.5-1.3) × 10^-7 molecule^-1 cm³ s^-1 (∼300 K). These unusual rate coefficients indicated strong long-range interactions between the two neutral reactants, which was regarded as a key factor leading to the ultrahigh ionization efficiency. The detection sensitivities of the nitroaromatics, (1.01-2.16) × 10⁴ counts pptv^-1 in 10 s acquisition time, were obtained by an AI time-of-flight mass spectrometer (AI-TOFMS). These experimental results not only provide new insight into the AI reaction but also reveal an excellent ionization method that can improve the detection sensitivity of nitroaromatics to an unprecedented degree.

Ultrasensitive detection of volatile aldehydes with chemi-ionization-coupled time-of-flight mass spectrometry

The chemi-ionization reaction is a high-efficiency pathway to produce molecular ions in plasma, however, it has rarely been applied in mass spectrometry to directly produce analyte ions. In this study, a novel chemi-ionization technique for mass spectrometry was applied for the direct and ultrasensitive detection of gaseous aldehydes. The ionization technique was enacted by a recently observed chemi-ionization reaction: the efficient proton transfer from H₂O to oxygenated compounds was stimulated by vacuum ultraviolet (VUV)-excited CH₂Cl₂. By analyzing a series of aliphatic aldehydes (C2-C5) and benzaldehyde with different proton affinities (PAs) and polarities, the ionization features of the new ionization method were investigated for the first time. The chemi-ionization of aldehydes presented soft ionization characteristics with fragmentation patterns analogous to that of VUV photoionization. The method showed ultrahigh sensitivities toward aldehydes (up to 1108 ± 6 counts pptv^-1 for benzaldehyde in 10 s acquisition time). The corresponding 3σ limits of detection (LODs) achieved 0.30-0.69 pptv, which are equivalent of 1.35-1.92 ng m^-3, for the compounds investigated. The humidity experiments revealed that the moisture in the sample gas had an evident impact on the detection efficiency of the analyte and the influence was PA dependent. In addition, the applicability of this ionization mode was further tested by analysis of aldehydes in cigarette smoke. This study provides a promising ionization method for greatly improving the current on-line detection sensitivity of volatile aldehydes.

Rapid detection of taste and odor compounds in water using the newly invented chemi-ionization technique coupled with time-of-flight mass spectrometry

Taste and odor (T&O) compounds are widespread in water environments and have attracted considerable public attention. Nowadays, the standard detections of these chemicals rely mainly on off-line methods such as GC-MS or evaluation by trained analysts' senses. In this study, we report a method for the rapid detection of T&O compounds in water by exploiting a newly invented chemi-ionization source, in combination with headspace vapor measurement at room temperature. The calibrated limits of detection (LODs) of 2-methylbutyraldehyde, methyl tert-butyl ether (MTBE), methyl methacrylate (MMA), 2-isobutyl-3-methyoxypyrazine (IBMP), and 2-isopropyl-3-methoxypyrazine (IPMP) are in the range of 3.5-50.2 ng L^-1, and the estimated LODs of 2-methylisoborneol (2-MIB) and geosmin (GSM) are 0.25 and 0.77 ng L^-1, respectively. The calibration results reveal that the instrumental LODs for 2-methylbutyraldehyde, MTBE, MMA, β-cyclocitral, 2-MIB, and GSM are 1-2 orders of magnitude better than the odor thresholds of humans. The accuracy, precision, recovery, and linearity (R²) of the method are tested. Water samples from city tap water and three rivers in Beijing are assessed using this technique, and the typical T&O compositions are observed with concentrations ranging from 0.2 to 297 ng L^-1. The new ultra-sensitive rapid detection method shows comparable sensitivities to the existing off-line technique and displays great potential for real-time detection of T&O pollution in water environments.

Development of surface-enhanced Raman spectroscopy application for determination of illicit drugs: Towards a practical sensor

Surface-enhanced Raman spectroscopy (SERS) has been widely applied to identify or detect illicit drugs, because of the ability for highly specific molecular fingerprint and independence of aqueous solutions impact. We summarize the progress in determination of illicit drugs using SERS, including trace illicit drugs, suspicious objects and drugs or their metabolites in real biological system (urine, saliva and so on). Even though SERS detection of illicit drugs in real samples still remains a huge challenge because of the complex unknown environment, the efficient sample separation and the improved hand-held Raman analyzer will provide the possibility to make SERS a practically analytical technique. Moreover, we put forward a prospective overview for future perspectives of SERS as a practical sensor for illicit drugs determination. Perhaps the review is not exhaustive, we expect to help researchers to understand the evolution and challenges in this field and further interest in promoting Raman and SERS as a practical analyzer for convenient and automated illicit drugs identification.