Mass Spectrometry Imaging Techniques: Non-Ambient and Ambient Ionization Approaches.

Molecular information can be acquired from sample surfaces in real time using a revolutionary molecular imaging technique called mass spectrometry imaging (MSI). The technique can concurrently provide high spatial resolution information on the spatial distribution and relative proportion of many different compounds. Thus, many scientists have been drawn to the innovative capabilities of the MSI approach, leading to significant focus in various fields during the past few decades. This review describes the sampling protocol, working principle and applications of a few non-ambient and ambient ionization mass spectrometry imaging techniques. The non-ambient techniques include secondary ionization mass spectrometry and matrix-assisted laser desorption ionization, while the ambient techniques include desorption electrospray ionization, laser ablation electrospray ionization, probe electro-spray ionization, desorption atmospheric pressure photo-ionization and femtosecond laser desorption ionization. The review additionally addresses the advantages and disadvantages of ambient and non-ambient MSI techniques in relation to their suitability, particularly for biological samples used in tissue diagnostics. Last but not least, suggestions and conclusions are made regarding the challenges and future prospects of MSI.

A Facile Determination of Herbicide Residues and Its Application in On-Site Analysis.

Abuse of herbicides in food safety is a vital concern that has an influence on the sustainable development of the world. This work presents, a modified ionization method with separation of the sample and carrier gas inlets, which was utilized for efficient ionization and analyte transfer of herbicides in crops. The working parameters of voltage, injective distance, desorption temperature, and the carrier gas flow rate were optimized to achieve the high efficiency of the transfer and ionization of the analyte. When it was applied in the analysis of herbicides in laboratory, the method exhibited excellent performance in achieving the quantitative detection of herbicides in solutions and residues spiked in an actual matrix with a limit of quantification of 1-20 µg/kg and relative standard deviations of less than 15%. Although a simple QuEchERS process was used, the programmable heating platform ensured efficient gasification and transfer of the target analyte, with the advantages of high speed and selectivity, avoiding the noted matrix effect. The method exhibited a relatively acceptable performance by using air as the discharged gas (open air). It could be used to monitor herbicide residues in the growth stage via on-site non-destructive analysis, which obtained low LODs by dissociating the herbicides from the crops without any pretreatment. It showed great potential for the supervision of the food safety market by achieving non-destructive detection of crops anytime and anywhere. This finding may provide new insights into the determination of pesticide emergence and rice quality assessment.

[Rapid detection of four amphetamine-type drugs in hair by pulsed direct current electrospray mass spectrometry].

Amphetamine-type drugs are synthetic compounds with an amphetamine parent structure. These compounds cause addiction, central nervous system excitation, and hallucinations. The number of drug users worldwide has gradually increased because amphetamine-type drugs can be synthesized in a simple and artificial manner. The current methods for anti-drug screening and toxicant identification are limited by the large quantity and variety of the drug analytes and long detection times. Thus, the development of broad-spectrum, rapid, and high-throughput detection methods is an urgent necessity. In addition, conventional amphetamine-type drug test samples, such as blood and urine, are only suitable for short-term drug identification. Hair has the advantages of easy preservation, stability, and a long detection window, which can compensate for the deficiencies of body-fluid-based test materials. Hair samples can reflect long-term drug use, which is beneficial for tracing drug sources, and has become an important means of providing evidence in court. Because most laboratory instruments are unable to perform the rapid on-site detection of amphetamine-type drugs in hair, establishing a high-throughput, qualitative and quantitative rapid on-site detection method is necessary. In this study, pulsed direct current electrospray ionization (Pulsed-DC-ESI) coupled with mass spectrometry was used for the rapid detection of four amphetamine-type drugs (amphetamine, methamphetamine, 3,4-methylenedioxyamphetamine, and 3,4-methylenedioxymethamphetamine) in hair. Methanol was used as the extraction solvent, and the grinding method was used for extraction. The pretreatment process included cutting, grinding, and centrifugation. The pretreatment time for each sample was about 10 min. Multiple samples could be processed in batches, greatly improving the efficiency of analysis. Pulsed-DC-ESI is an ambient ionization technology that can be conducted via direct injection without chromatographic separation. The tip of the spray capillary tube was immersed 1 cm below the surface of the sample solution to allow absorption via the capillary effect. When the spray capillary tube contained 1 µL of the sample solution, detection was performed. Pulsed-DC-ESI generates an electrospray at the same frequency as the mass spectrum, thereby avoiding the problem of sample wastage, which often occurs in traditional ESI. The portable mass spectrometer used for analysis is a linear ion trap mass spectrometer. The parameters of Pulsed-DC-ESI, such as the inner diameter of spray capillary tip, spray voltage, and distance between electrode and solution, were optimized based on the mass spectral responses of the amphetamine-type drugs. The optimized ion source conditions included a inner diameter of spray capillary tip of 25 µm, spray voltage of 2 kV, and the distance between electrode and solution of 20 mm. The optimal sample solvent was methanol. The optimized method can achieve simultaneous detection of the four amphetamine-type drugs within 20 s. The linear ranges of amphetamine, methamphetamine, and the two other drugs were 1-25, 1-100, and 1-50 ng/mg, respectively. The limits of detection and quantification of the four drugs in hair were 0.1-0.2 and 1 ng/mg, respectively. All linear correlation coefficients were greater than 0.99, and the average spiked recoveries were 86.6%-114.7%. The intra-day precisions were 4.14%-7.34%, and the inter-day precisions were 3.71%-8.43%. The proposed method was used to screen 2000 samples provided by various testing institutions. A total of five samples were positive for methamphetamine, which is consistent with the results of conventional forensic identification methods. Thus, the developed method can be used for the rapid detection of amphetamine-type drugs.

Oriented Self-assembly of Flexible MOFs Nanocrystals into Anisotropic Superstructures with Homogeneous Hydrogels Behaviors.

Building of metal-organic frameworks (MOFs) homogeneous hydrogels made by spontaneous crystallization remains a significant challenge. Inspired by anisotropically structured materials in nature, an oriented super-assembly strategy to construct micro-scale MOFs superstructure is reported, in which the strong intermolecular interactions between zirconium-oxygen (Zr─O) cluster and glutamic acid are utilized to drive the self-assembly of flexible nanoribbons into pumpkin-like microspheres. The confined effect between water-flexible building blocks and crosslinked hydrogen networks of superstructures achieved a mismatch transformation of MOFs powders into homogeneous hydrogels. Importantly, the elastic and rigid properties of hydrogels can be simply controlled by precise modulation of coordination and self-assembly for anisotropic superstructure. Experimental results and theoretical calculations demonstrates that MOFs anisotropic superstructure exhibits dynamic double networks with a superior water harvesting capacity (119.73 g g-1 ) accompanied with heavy metal removal (1331.67 mg g-1 ) and strong mechanical strength (Young's modulus of 0.3 GPa). The study highlights the unique possibility of tailoring MOFs superstructure with homogeneous hydrogel behavior for application in diverse fields.

Toxic effects of isofenphos-methyl on zebrafish embryonic development.

Isofenphos-methyl (IFP) is widely used as an organophosphorus for controlling underground insects and nematodes. However, excessive use of IFP may pose potential risks to the environment and humans, but little information is available on its sublethal toxicity to aquatic organisms. To address this knowledge gap, the current study exposed zebrafish embryos to 2, 4, and 8 mg/L IFP within 6-96 h past fertilization (hpf) and measured mortality, hatching, developmental abnormalities, oxidative stress, gene expressions, and locomotor activity. The results showed that IFP exposure reduced the rates of heart and survival rate, hatchability, and body length of embryos and induced uninflated swim bladder and developmental malformations. Reduction in locomotive behavior and inhibition of AChE activity indicated that IFP exposure may induce behavioral defects and neurotoxicity in zebrafish larvae. IFP exposure also led to pericardial edema, longer venous sinus-arterial bulb (SV-BA) distance, and apoptosis of the heart cells. Moreover, IFP exposure increased the accumulation of reactive oxygen species (ROS) and the content of malonaldehyde (MDA), also elevated the levels of antioxidant enzymes of superoxide dismutase (SOD) and catalase (CAT), but decreased glutathione (GSH) levels in zebrafish embryos. The relative expressions of heart development-related genes (nkx2.5, nppa, gata4, and tbx2b), apoptosis-related genes (bcl2, p53, bax, and puma), and swim bladder development-related genes (foxA3, anxa5b, mnx1, and has2) were significantly altered by IFP exposure. Collectively, our results indicated that IFP induced developmental toxicity and neurotoxicity to zebrafish embryos and the mechanisms may be relevant to the activation of oxidative stress and reduction of acetylcholinesterase (AChE) content.

On-site Simultaneous Determination of Neonicotinoids, Carbamates, and Phenyl Pyrazole Insecticides in Vegetables by QuEChERS Extraction on Nitrogen and Sulfur co-doped Carbon Dots and Portable Mass Spectrometry.

In food safety monitoring, on-site and simultaneous detection of a variety of insecticides with different concentrations in the same matrix is necessary. However, the task remains challenging. In this study, a novel nitrogen and sulfur co-doped carbon dot (N, S-CD) was synthesized and used as a QuEChERS clean-up reagent to reduce matrix interferences in the determination of insecticides in vegetables. In addition, a portable mass spectrometer (µ-MS) was employed, without chromatography separation, to directly determine neonicotinoids, carbamates, and benzopyrazole insecticides (with acetamiprid, imidacloprid, thiamethoxam, fipronil, and carbofuran as models) in the pretreated samples. The N,S-CD µ-MS method exhibited effective clean-up performance with satisfactory matrix effects between -15.2% and 15.7%. The recoveries of spiked vegetable samples ranged from 82.2% to 109.7% for the five target insecticides, and the relative standard deviations (RSDs) ranged from 3.8% to 16.5%. The linear ranges were from 2.0 to 5.0 ng/g, with low detection limits (LOD) from 0.5 to 1.0 ng/g. Moreover, the total pretreatment and detection time was within 20 min. Thus, the incorporation of N,S-CD with QuEChERS extraction, together with the portable µ-MS system, could be a promising and feasible strategy for on-site, rapid, and simultaneous detection of various insecticides in vegetables.

Ambient Ionization Mass Spectrometry: Application and Prospective.

Mass spectrometry (MS) is a formidable analytical tool for the analysis of non-polar to polar compounds individually and/or from mixtures, providing information on the molecular weights and chemical structures of the analytes. During the last more than one-decade, ambient ionization mass spectrometry (AIMS) has developed quickly, producing a wide range of platforms and proving scientific improvements in a variety of domains, from biological imaging to quick quality control. These methods have made it possible to detect target analytes in real time without sample preparation in an open environment, and they can be connected to any MS system with an atmospheric pressure interface. They also have the ability to analyze explosives, illicit drugs, disease diagnostics, drugs in biological samples, adulterants in food and agricultural products, reaction progress, and environmental monitoring. The development of novel ambient ionization techniques, such as probe electrospray ionization, paper spray ionization, and fiber spray ionization, employed even at picolitre to femtolitre solution levels to provide femtogram to attogram levels of the target analytes. The special characteristic of this ambient ion source, which has been extensively used, is the noninvasive property of PESI of examination of biological real samples. The results in the current review supports the idea that AIMS has emerged as a pioneer in MS-based approaches and that methods will continue to be developed along with improvements to existing ones in the near future.

Combining portable mass spectrometer with bamboo stir bar sorptive extraction for the on-site detection of malachite green, crystal violet and their metabolites in fishes.

In this work, a disposable and inexpensive bamboo stir bar containing an organic membrane was constructed to perform stir bar sorptive extraction (SBSE), followed by portable mass spectrometry to achieve on-site detection of four residual drugs (malachite green, crystal violet and their metabolites) in fishes. The entire method uses only microliter quantities of organic solvents, enabling environmentally friendly pretreatment. The portable mass spectrometer can simultaneously detect four target analytes in a sample in approximately ten seconds. Under the optimal conditions, the proposed method was successfully applied to simultaneously detect four drugs in fish samples with detection limits of 0.16-0.59 µg/kg. The spiked recoveries for mandarin fish and lateolabrax maculatus were 74.5-96.5%, with relative standard deviations (RSD) of 4.4-16%. In addition, the matrix effects of the four analytical targets in the method were experimentally verified to range from 7.30% to 20.62%. The method can potentially be extended to the on-site detection of other veterinary drug residues in foods.

Thermal desorption bridged the gap between dielectric barrier discharge ionization and dried plasma spot samples for sensitive and rapid detection of fentanyl analogs in mass spectrometry.

The urgent threat of new psychoactive substances worldwide promotes rapid detection and identification demand for public security. Ambient ionization mass spectrometry (AIMS) has become mainstream among various detection techniques. Still, scant successful applications have been fulfilled toward dried blood spot (DBS) or plasma spot (DPS) as an easy-to-implement sampling format in AIMS. This work bridged the gap between dielectric barrier discharge ionization mass spectrometry (DBDI-MS) and DPS/DBS samples by thermal desorption (TD) assistance. It made the impossible mission of direct DBDI-MS measurement on DPS/DBS samples containing fentanyl analogs (FTNs) possible. Guided by finite element simulations and a customized three-dimensional printing interface, we constructed a semi-covered flat-TD surface for sufficient desorption and ionization of FTNs from DPS/DBS samples without any sample pretreatment or sample separation. We successfully quantified eight FTNs in DPS samples using deuterated fentanyl as internal standard by triple quadrupole tandem mass spectrometry (MS/MS) and proved its practical applicability in the fentanyl-exposed rat plasma samples. This DBDI-TD-MS method also fits well with DBS samples, and it only took 20 s to analyze each sample. Further, based on summarized fragmentation characteristics of twenty FTNs, we established a backbone alerting ion-guided screening rule for suspect screening of FTNs in DPS samples via quadrupole time-of-flight MS/MS and built a chemometric approach for convenient mutual verification of screening "unknown" artificial samples. We hope this ideal DBDI-TD-MS method finds its valuable role in national security, doping control, and public health for routine large-scale analysis or on-site detection.

[Detection of drugs in urine by ambient direct ionization mass spectrometry].

According to the Report of Drug Situation in China (2020), the growth rate of the number of drug abusers in China has decreased, but the number of drug abusers is still large. An efficient screening method is necessary for controlling drug abuse. As an important type of biological sample, urine is widely used for the rapid screening of drug addicts. However, because of the complex composition, low content, and strong interference from the body's metabolism, the detection of drugs in urine remains a challenge. Traditional rapid screening techniques such as immunocolloidal gold analysis have a high false positive rate and insufficient quantitative capability. In addition, laboratory mass spectrometry methods require complicated time-consuming sample pre-processing and strict environmental conditions, and hence, are unsuitable for on-site rapid analysis. In recent years, various direct ionization mass spectrometry techniques such as direct analysis in real time (DART), desorption electrospray ionization (DESI), and dielectric barrier discharge ionization (DBDI) have advanced rapidly. These techniques have been applied to public safety, food safety, environmental detection, etc. In contrast to traditional ionization mass spectrometry methods, these direct ionization techniques allow for the in situ analysis of samples with simple or no pretreatment; moreover, they have the advantages of high analytical efficiency and sensitivity. In particular, pulsed electrospray ionization has the characteristics of less sample demand, compact, lightweight equipment, and no carrier gas. This paper presents a rapid method based on pulsed electrospray ionization mass spectrometry for the detection of urine samples. A rapid detection platform comprising a probe electrospray ionization source, a portable linear ion trap mass spectrometer (MS), and their coupling interface is adopted. The probe electrospray ion source includes a conducting metal wire, plastic handle, and silica glass capillary, whose tip has an inner diameter of 50 µm. The guide rail at the coupling interface is used to align the probe with the sample inlet of the portable mass spectrometer and maintain a distance of 10 mm between the probe tip and the sample inlet of the MS. The spray voltage of the probe electrospray ion source and the temperature of the MS inlet capillary are optimized at 1.8 kV and 205 ℃, respectively. In addition, rapid and efficient pretreatment techniques for urine samples have been developed. Buffer salts used for pH regulation and liquid-liquid extraction based on ethyl acetate were adopted for the pretreatment process. The linearity of the detection ability and the linear ranges of various drug-spiked solutions were also investigated. The results showed that the correlation coefficients for the quantitative detection of methamphetamine, ketamine, methylenedioxymethamphetamine (MDMA), and cocaine were greater than 0.99 at concentrations ranging from 1 to 100 ng/mL. Moreover, the limits of detection (LODs) for the five conventional drug-spiked urine were 0.5-30 ng/mL. The spiked recoveries ranged from 56.1% to 103.7%, with relative standard deviations (RSDs) of 9.0%-27.8%, implying that the combination of the instruments and the pretreatment method can lead to good accuracy. To validate the performance of the rapid detection method, 40 positive and 110 negative urine samples were tested and analyzed. The overall accuracy was over 99%, and the five conventional drugs in urine samples could be detected within 20 s. The research findings of this work could promote the development of rapid detection technology, accelerate the popularization and application of ambient direct ionization mass spectrometry, and improve the services of on-site law enforcement.

Multilayer Self-Assemblies for Fabricating Graphene-Supported Single-Atomic Metal via Microwave-Assisted Emulsion Micelle.

Inspired by molecular self-assemblies in nature, this article reports a versatile strategy for confined encapsulation of single-atomic metal into high-quality rGO nanosheets by the microwave-assisted emulsion micelle method. Multilayer self-assembly of organometallics-surfactants micelles into the interlayer of nanosheets can not only promote microwave exfoliation and reduction of GO but also precisely control loading and distribution of single-metal atoms. With this synthetic strategy, the simultaneous trinity of exfoliation, reduction, and composition are achieved for 1 min. Experimental results and density functional theory calculations demonstrate that graphene-supported FeN4 O2 sites exhibit optimal binding energy toward superior selective adsorption (adsorption amount of 1975.6 mg g-1 with separation efficiency of 97.6%) and electrocatalytic oxidation (TOFs as high as 1.31 min-1 ). This work provides a simple and efficient avenue for the large-scale preparation of single-atomic metal composites in environmental and energy fields.

Hollow Cathode Discharge Ionization Mass Spectrometry: Detection, Quantification and Gas Phase Ion-Molecule Reactions of Explosives and Related Compounds.

Mass spectrometry (MS) has become an essential analytical method in every sector of science and technology. Because of its unique ability to provide direct molecular structure information on analytes, an extra method is rarely required. This review describes fabrication of a variable-pressure hollow cathode discharge (HCD) ion source for MS in detection, quantification and investigation of gas-phase ion molecule reactions of explosives and related compounds using air as a carrier gas. The HCD ion source has been designed in such a way that by altering the ion source pressures, the system can generate both HCD and conventional GD. This design enables for the selective detection and quantification of explosives at trace to ultra-trace levels. The pressure-dependent HCD ion source has also been used to investigate ion-molecule reactions in the gas phase of explosives and related compounds. The mechanism of ion formation in explosive reactions is also discussed.

Single Cell Mass Spectrometry With a Robotic Micromanipulation System for Cell Metabolite Analysis.

OBJECTIVE: The increasing demand for unraveling cellular heterogeneity has boosted single cell metabolomics studies. However, current analytical methods are usually labor-intensive and hampered by lack of accuracy and efficiency. METHODS: we developed a first-ever automated single cell mass spectrometry system (named SCMS) that facilitated the metabolic profiling of single cells. In particular, extremely small droplets of sub nano-liter were generated to extract the single cells, and the underlying mechanism was verified theoretically and experimentally. This was crucial to minimize the dilution of the trace cellular contents and enhance the analytical sensitivity. Based on the precise 3D positioning of the pipette tip, we established a visual servoing robotic micromanipulation platform on which single cells were sequentially extracted, aspirated, and ionized, followed by the mass spectrometry analyses. RESULTS: With the SCMS system, inter-operator variability was eliminated and working efficiency was improved. The performance of the SCMS system was validated by the experiments on bladder cancer cells. MS and MS2 analyses of single cells enable us to identify several cellular metabolites and the underlying inter-cell heterogeneity. CONCLUSION: In contrast to traditional methods, the SCMS system functions without human intervention and realizes a robust single cell metabolic analysis. SIGNIFICANCE: the SCMS system upgrades the way how single cell metabolites were analyzed, and has the potential to be a powerful tool for single cell metabolomics studies.

Gas phase ion-molecule reactions of nitroaromatic explosive compounds studied by hollow cathode discharge ionization-mass spectrometry.

In this study, we have developed a variable pressure operating hollow cathode discharge (HCD) ion source to investigate the gas phase ion-molecule reactions of nitroaromatic explosive compounds. The developed HCD ion source coupled MS system has also been validated as an analytical method to analyze explosives at trace levels. The ion source was designed in such a way that the plasma can be generated alternatively at high pressure (~30 Torr), medium pressure (~5 Torr) and low pressure (~1 Torr) regions. The plasma contains a sufficient amount of reactant ions, electrons and excited species, thus the gaseous analyte molecules were efficiently ionized when they passed through the plasma. In the ion-molecule reactions of the nitroaromatic explosives, the discharge products of NOx- (x = 2,3), O3 and HNO3 originating from the plasma-excited air were suggested to contribute to the formation of mostly [M - H]-, [M - NO]-, [M+NO3-HNO2]- and [M-NO+HNO3]- adduct ions at the higher ion source pressures (~5 and 28 Torr) while the electron rich plasma leads to the formation of molecular ion, M-•, at the lower ion source pressure (~1 Torr). Formation of the hydride-adduct ions of the nitroaromatic compounds reveals the surface-assisted Birch type reduction in the HCD plasma. The variety of spectral patterns in the air-assisted glow discharge would be useful for high through-put detection of TNT and TNT-related explosives. An ambient helium dielectric barrier discharge (DBD) ion source was also used and gave identical mass spectra of the nitroaromatic explosive compounds to those observed by the HCD ion source, but did not give any hydride-adduct ions of the explosive compounds. Ion formation mechanism of these ions is also discussed.

Simultaneous detection and quantification of explosives by a modified hollow cathode discharge ion source.

Detection of explosives at trace levels is crucial for security purposes because of increasing worldwide terrorist threats at public places. Previously, a hollow cathode discharge (HCD) ion source has been fabricated for detection of explosives. Recently, the HCD ion source has been modified for a dual pressures operating system and coupled to a linear ion trap MS to analyze explosives simultaneously. Here, trinitrotoluene (TNT), nitroglycerin (NG), pentaerythritol tetranitrate (PETN) and 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) were taken as model explosive compounds and the mass spectra were recorded in the negative mode ionization. At the higher ion source pressure (~28.0-30.0 Torr), NG, PETN and RDX gave adduct ions with the NO3- ion while TNT showed the [TNT + NO3-HNO2]- (m/z 242) simultaneously. However, NG and PETN did not give any ion signals at the lower ion source pressure (~0.8-1.0 Torr) while TNT exhibited its molecular ion, [TNT]-• (m/z 227), as a major ion through electron attachment and RDX showed fragment ions that followed electron capture dissociation concurrently. The modified HCD ion source exhibited better sensitivity in simultaneous detection and quantification of the explosives. The NO3- and NO2- as reagent ions in the air HCD plasma form stable adduct ions with the NG, PETN and RDX even with TNT at the higher temperature (140-200 °C). The formation of the NO3-, NO2- in the HCD plasma also causes the formation of [TNT-H]- (m/z 226) at the higher ion source pressure. The inner metallic surface of the hollow tube assists the Birch reduction type reaction that results in the formation of hydride ion of the TNT, [TNT + H]- (m/z 228). No significant difference in the spectral pattern for simultaneous and individual measurements for the explosives was observed at the higher ion source pressure. Therefore, it may conclude that the present modified HCD ion source can be used for simultaneous detection and quantification of the explosive compounds at trace and/or ultra-trace levels using air as a carrier gas.

Ultra-trace level detection of nonvolatile compounds studied by ultrasonic cutter blade coupled with dielectric barrier discharge ionization-mass spectrometry.

In analytical mass spectrometry, an efficient desorption is needed for nonvolatile compounds at ultra-trace level detection. In this paper, an ultrasonic cutter-assisted non-thermal desorption method for ultra-trace level detection of different types of nonvolatile compounds such as drugs of abuse, explosives, pharmaceuticals, spinosad, cholesterol, rhodamine B, glucose and amino acids has been described. The relevant compounds were deposited on the ultrasonic blade except pharmaceutical tablets that were used directly, and gently touched on perfluoroalkoxy (PFA) made substrate with oscillation frequency about 40 kHz in order to desorb the solid molecules. The desorbed gaseous molecules were ionized using a home-made helium dielectric barrier discharge ionization (DBDI) source and then detected by an ion trap mass spectrometer. The synergistic effect caused by gaining the oscillation and frictional/mechanical energy enhanced desorption of the solid molecules into gaseous phase, thereby, resulting in detection at ultra-trace level. PFA made substrate showed better limits of detection (LODs) compared to that of wood made substrate. The LOD values for most of the target analytes were ranging from 20.00 ± 0.91 to 200.25 ± 9.04 pg with RSD values ≤ 5% except for pharmaceutical tablets where only depletion amounts were estimated. The LOD value of cocaine in urine was 39.88 ± 1.65 pg with RDS ≤4.56% showed to be a very promising analytical tool for analysis of drugs of abuse in biological samples under ambient conditions. Drugs of abuse, pharmaceuticals, spinosad, cholesterol, rhodamine B, glucose and amino acids were detected mostly as their protonated molecular ions while RDX and HMX were detected as their molecular cluster/adduct ions as [M + NO2]- and [M + NO3]-, and AN was detected as a cluster ion of HNO3 with NO3-, [HNO3 + NO3]-, without suffering from fragmentation. An effective mechanism of the enhanced sensitivity of the tribodesorption-DBDI-MS system in analyzing the nonvolatile compounds has been discussed.

[Rapid detection of sulfonamides by heat assisted desorption-dielectric barrier discharge ionization mass spectrometry].

Sulfanilamide is a common antibacterial drug that is used in clinical practice and in the industry. However, its abuse has emerged as a serious problem in the aquaculture industry, and more predominantly in the poultry industry, where it is administered for therapeutic purposes or as a growth promoter. In this study, a novel technical platform, heat-assisted desorption-dielectric barrier discharge ionization mass spectrometry (HAD-DBDI-MS), was used to detect sulfanilamide in situ. A method for the rapid identification of five typical sulfanilamide drugs sulfamopyridine, sulfamethoxan, sulfamethoxoline, sulfamidine, and sulfamethoxazole was established after optimizing a series of parameters. Secondary mass spectrometry was used to distinguish the sulfanilamide drugs from one another and from other isomers. Our HAD-DBDI-MS method enhanced the sulfanilamide sensitivities by reducing the limits of detection by about 1-2 orders of magnitude compared to those obtained with the DBDI-MS method. As further research, the profiles of chicken feed with added sulfamopyridine standard as well those of commercial feed with added sulfamidine and sulfamethoxazole were obtained using HAD-DBDI-MS respectively. With the HAD-DBDI-MS method, sulfamopyridine could be directly detected in the complex chicken meat matrix. However, satisfactory results were not obtained when direct HAD-DBDI-MS was used for sulfamidine and sulfamethoxazole detection in the feed matrix. The identification ability was improved when methanol was introduced as the assisting solvent. In this method, chicken feed spiked with sulfamidine and sulfamethoxazole standards were pressed into tablets, and methanol was dropped on the tablet surface. The experimental data indicate that HAD-DBDI-MS is suitable for the rapid identification of sulfanilamide drugs in poultry feed and meat products, thus showing potential value as a detection tool for future application.

Challenges and Strategies of Chemical Analysis of Drugs of Abuse and Explosives by Mass Spectrometry.

In analytical science, mass spectrometry (MS) is known as a "gold analytical tool" because of its unique character of providing the direct molecular structural information of the relevant analyte molecules. Therefore, MS technique has widely been used in all branches of chemistry along with in proteomics, metabolomics, genomics, lipidomics, environmental monitoring etc. Mass spectrometry-based methods are very much needed for fast and reliable detection and quantification of drugs of abuse and explosives in order to provide fingerprint information for criminal investigation as well as for public security and safety at public places, respectively. Most of the compounds exist as their neutral form in nature except proteins, peptides, nucleic acids that are in ionic forms intrinsically. In MS, ion source is the heart of the MS that is used for ionizing the electrically neutral molecules. Performance of MS in terms of sensitivity and selectivity depends mainly on the efficiency of the ionization source. Accordingly, much attention has been paid to develop efficient ion sources for a wide range of compounds. Unfortunately, none of the commercial ion sources can be used for ionization of different types of compounds. Moreover, in MS, analyte molecules must be released into the gaseous phase and then ionize by using a suitable ion source for detection/quantification. Under these circumstances, fabrication of new ambient ion source and ultrasonic cutter blade-based non-thermal and thermal desorption methods have been taken into account. In this paper, challenges and strategies of mass spectrometry analysis of the drugs of abuse and explosives through fabrication of ambient ionization sources and new desorption methods for non-volatile compounds have been described. We will focus the literature progress mostly in the last decade and present our views for the future study.

Calculation of the overlap factor for scanning LiDAR based on the tridimensional ray-tracing method.

The overlap factor is used to evaluate the LiDAR light collection ability. Ranging LiDAR is mainly determined by the optical configuration. However, scanning LiDAR, equipped with a scanning mechanism to acquire a 3D coordinate points cloud for a specified target, is essential in considering the scanning effect at the same time. Otherwise, scanning LiDAR will reduce the light collection ability and even cannot receive any echo. From this point of view, we propose a scanning LiDAR overlap factor calculation method based on the tridimensional ray-tracing method, which can be applied to scanning LiDAR with any special laser intensity distribution, any type of telescope (reflector, refractor, or mixed), and any shape obstruction (i.e., the reflector of a coaxial optical system). A case study for our LiDAR with a scanning mirror is carried out, and a MATLAB program is written to analyze the laser emission and reception process. Sensitivity analysis is carried out as a function of scanning mirror rotation speed and detector position, and the results guide how to optimize the overlap factor for our LiDAR. The results of this research will have a guiding significance in scanning LiDAR design and assembly.

An interface for online coupling capillary electrophoresis to dielectric barrier discharge ionization mass spectrometry.

The online combination of capillary electrophoresis (CE) with mass spectrometry (MS) has long been desired for the capability of direct and simultaneous separation and detection with high efficiency, accuracy, and throughput. In this work, a novel CE-MS interface was developed, using dielectric barrier discharge ionization (DBDI). The interface employed a spray tip with a coaxial three-layer structure, into which the CE sample solution, the sheath liquid, and the nebulizing gas were introduced. The spray tip was put between the DBDI outlet and the MS inlet, thus the CE sample solution could be blended with the sheath liquid, then nebulized. The nebulized sample could be ionized by DBDI, and finally analyzed by MS. The key parameters of the interface were optimized. Then, proof-of-concept experiments separating and detecting the mixture of metronidazole and acetaminophen solutions were conducted. The results showed high separation efficiency, low time consumption, high reproducibility, and convenience in operation. In addition, the interface exhibited a high tolerance of non-volatile salts and surfactants, which would be widely used in CE analyses. All of these results demonstrated that the newly developed CE-DBDI-MS interface could be successfully used in CE-MS studies, and could be further utilized in multiple areas involving efficient separation and detection.