Barrier Discharge Ionization-mass Spectrometry Research Articles

Pesticide uptake and translocation in plants monitored in situ via laser ablation dielectric barrier discharge ionization mass spectrometry imaging

For reducing pesticide usage and enhancing the effectiveness of pest control, it is necessary to elucidate the mechanisms of pesticide uptake and translocation in plants. Here, atmospheric pressure laser ablation dielectric barrier discharge ionization mass spectrometry imaging (LA-DBDI-MSI) was used to for in-situ monitoring of pesticide uptake and translocation in plants with a spatial resolution of 25 μm, and only requiring minimal or no sample preparation. Roots and leaves of tomato plants that had been exposed to a systemic pesticide, difenoconazole, were studied. From MSI data of tomato leaves, we found that difenoconazole was mainly distributed in the leaf veins after 6 days of pesticide exposure, but distributed throughout the leaf after 10 days of pesticide exposure. Endogenous substances are mainly distributed in the mesophyll, but are not present in the veins. This study clarifies the uptake and translocation mechanism of pesticides in plants, which is of great significance for reducing the dosage of pesticides and improving the effect of plant disease control.

Rapid detection of aflatoxin B1, zearalenone and ochratoxin A in grains by thermal desorption dielectric barrier discharge ionization mass spectrometry.

Dielectric barrier discharge ionization is increasingly used for rapid detection in ambient mass spectrometry, although more often for gaseous and highly volatile samples than for solids and liquids. In this project, we present a rapid and sensitive method for detecting mycotoxins and demonstrate its capability for the detection of aflatoxin B1, zearalenone, and ochratoxin A in food samples. Our method is based on thermal desorption coupled to dielectric barrier discharge ionization mass spectrometry (TD-DBDI-MS), which we show generates minimal interferences and produces almost exclusively molecular ions. We detected mycotoxins in various food samples, including corn, peanuts, millet, and rice. Our method has a linear dynamic range of 1 μg kg-1 to 100 μg kg-1 for all three mycotoxins and a limit of detection (LOD) of 0.31 μg kg-1, 0.28 μg kg-1 and 0.43 μg kg-1, respectively. It is simple, rapid, reduces the pretreatment steps and has significant potential for practical applications.

Spatio-Temporal Analysis of Anesthetics in Mice by Solid-Phase Microextraction: Dielectric Barrier Discharge Ionization Mass Spectrometry.

Local anesthetics, drugs that only affect a restricted area of the body, are widely used in daily clinical practice. Less studied but equally important is the distribution of local anesthetics inside organisms. Here, we present a rapid in situ testing method of drug distribution in various organs. The temporal and spatial distribution of anesthetics in mice was measured by solid-phase microextraction (SPME), thermal desorption (TD), and dielectric barrier discharge ionization (DBDI) atmospheric pressure mass spectrometry. A coated SPME probe using a tungsten wire as the support covered with a carbonaceous material was prepared by a simple, low-cost flame method. An in-line structure of the inlet allows TD and DBDI to share the same capillary tube, which greatly improves the transmission efficiency. Nine kinds of anesthetics, such as lidocaine and dyclonine, were detected, and the limit of detection was determined to be as low as 13 pg/mL. In addition, the time-dependent distribution of drugs in mice organs was studied. We also found that macromolecules in organisms do not noticeably interfere with the detection. This method is convenient and efficient because it does not require tissue homogenates and allows direct in situ detection. Compared with the conventional analytical methods, this method is simple and rapid, works in situ, and allows microscale analysis of trace analytes in biological organisms with high sensitivity.

Recent Advances in Single-Cell Metabolomics Based on Mass Spectrometry

Recent Advances in Single-Cell Metabolomics Based on Mass Spectrometry

High-Throughput Single-Cell Mass Spectrometry Reveals Abnormal Lipid Metabolism in Pancreatic Ductal Adenocarcinoma.

Even populations of clonal cells are heterogeneous, which requires high‐throughput analysis methods with single‐cell sensitivity. Here, we propose a rapid, label‐free single‐cell analytical method based on active capillary dielectric barrier discharge ionization mass spectrometry, which can analyze multiple metabolites in single cells at a rate of 38 cells/minute. Multiple cell types (HEK‐293T, PANC‐1, CFPAC‐1, H6c7, HeLa and iBAs) were discriminated successfully. We found evidence for abnormal lipid metabolism in pancreatic cancer cells. We also analyzed gene expression in a cancer genome atlas dataset and found that the mRNA level of a critical enzyme of lipid synthesis (ATP citrate lyase, ACLY) was upregulated in human pancreatic ductal adenocarcinoma (PDAC). Moreover, both an ACLY chemical inhibitor and a siRNA approach targeting ACLY could suppress the viability of PDAC cells. A significant reduction in lipid content in treated cells indicates that ACLY could be a potential target for treating pancreatic cancer.

High‐Throughput Single‐Cell Mass Spectrometry Reveals Abnormal Lipid Metabolism in Pancreatic Ductal Adenocarcinoma

AbstractEven populations of clonal cells are heterogeneous, which requires high‐throughput analysis methods with single‐cell sensitivity. Here, we propose a rapid, label‐free single‐cell analytical method based on active capillary dielectric barrier discharge ionization mass spectrometry, which can analyze multiple metabolites in single cells at a rate of 38 cells/minute. Multiple cell types (HEK‐293T, PANC‐1, CFPAC‐1, H6c7, HeLa and iBAs) were discriminated successfully. We found evidence for abnormal lipid metabolism in pancreatic cancer cells. We also analyzed gene expression in a cancer genome atlas dataset and found that the mRNA level of a critical enzyme of lipid synthesis (ATP citrate lyase, ACLY) was upregulated in human pancreatic ductal adenocarcinoma (PDAC). Moreover, both an ACLY chemical inhibitor and a siRNA approach targeting ACLY could suppress the viability of PDAC cells. A significant reduction in lipid content in treated cells indicates that ACLY could be a potential target for treating pancreatic cancer.

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.

Metal Probe Microextraction Coupled to Dielectric Barrier Discharge Ionization-Mass Spectrometry for Detecting Drug Residues in Organisms.

In this study, a novel method for the direct coupling of metal probe microextraction (MPME) and a dielectric barrier discharge ionization (DBDI) source with mass spectrometry (MS) is reported. Analytes adsorbed on a tungsten needle were directly transferred to the DBDI source via rapid thermal desorption, which resulted in a limit of detection as low as 8 pg/mL. This is in part due to the "active capillary" configuration of the plasma ion source, where the efficiency of ion transfer to the MS is ∼100%. Specialty gases to maintain the plasma and carry analytes to the MS are not required. In contrast to direct one-step ionization of molecular adsorbates, the complete separation of the analyte desorption from the probe and the ionization event in our experimental setup greatly enhanced the sensitivity and detection reproducibility (RSD of 8.3%). We show detection of pyrimethamine, a first-line drug for the treatment and prevention of Plasmodium falciparum malaria all over the world, by this MPME/DBDI/MS method. The detection of drug residues in live fish and paramecium was achieved without the need for any sample pretreatment. The relative concentration of the drug in different organs of the fish was determined. This simple and convenient method has the potential for the analysis of chemicals even in single-cell organisms.

Rapid analysis of perfluorinated carboxylic acids in textiles by dielectric barrier discharge ionization-mass spectrometry

In this study, a rapid analytical method has been developed for the identification of nine representative perfluorinated carboxylic acids (PFCAs) in textiles using dielectric barrier discharge ionization (DBDI) coupled with a benchtop ion trap mass spectrometer. Key parameters affecting DBDI efficiency, including ion source temperature, gas flow rate, and horizontal distance between the DBDI outlet and ceramic tube inlet, were systematically optimized based on both single factor test and response surface methodology. The developed method allowed direct analysis of textiles bypassing conventional sample preparation and chromatographic separation. The applicability of the protocol was demonstrated through the analysis of 15 real textile samples of different fabrics.

Detection of multiclass explosives and related compounds in soil and water by liquid chromatography-dielectric barrier discharge ionization-mass spectrometry.

In this work, the multiclass detection of explosives and related compounds has been studied by liquid chromatography-high-resolution mass spectrometry by means of a time-of-flight mass spectrometer (TOFMS) operated in the negative ion mode, using dielectric barrier discharge ionization (DBDI). Reversed-phase high-performance liquid chromatography (HPLC) separation was performed using water-methanol mobile phase without any modifier, although the effect of ammonium acetate was studied. DBD plasma was generated by applying a square wave voltage of 2.5kV to a 100-mLmin-1 He flow. The DBDI probe was adjusted to fit the commercial API source housing so that the HPLC eluent was nebulized and vaporized in the same manner as for atmospheric-pressure chemical ionization (APCI). The ionization process was affected by the temperature of the two nitrogen streams used to vaporize the solvent and the analytes, particularly for RDX and HMX, which are thermolabile compounds. The best approach in terms of sensitivity for all the studied compounds was the use of a gradient of temperatures in the ionization source, starting at 225/200°C (vaporizer/drying gas temp) for nitramines and ending at 350/325°C for nitroaromatic compounds. High-resolution full-scan spectra of individual selected compounds were recorded by LC-DBDI-TOFMS, and the results were compared to LC-APCI-TOFMS. A better sensitivity (slope of calibration curve) was obtained by DBDI for more than 70% of the studied compounds in both wastewater and soil extracts. Graphical abstract ᅟ.

Fast screening of illicit drugs in beverages and biological fluids by direct coupling of thin film microextraction to dielectric barrier discharge ionization-mass spectrometry.

A direct and fast method for screening and quantification of illicit drugs in beverages and biological fluids was developed by using dielectric barrier discharge (DBD) as ionization technique, in combination with high-resolution mass spectrometry. Extraction of the targeted analytes was carried out with thin film microextraction (TFME) using ultrasound as agitation method. The targeted analytes were then thermally desorbed and introduced into the source without the need for any cryofocusing apparatus. The performance of this new analytical set up were compared to conventional TFME-TDU-GC/MS, showing enhanced linear dynamic range and lower limits of quantitation (low pg ml-1) achievable at the same extraction conditions (5 min extraction time). The performance of the method was tested in different beverages and body fluids, confirming its applicability for quantitative analysis of the targeted drugs in complex samples.

Screening of semifluorinated n‐alkanes by gas chromatography coupled to dielectric barrier discharge ionization mass spectrometry

The potential of an atmospheric pressure ionization source based on a dielectric barrier discharge in helium for the hyphenation of gas chromatography and mass spectrometry (GC/DBDI-MS) has been demonstrated only recently and for a limited range of compounds. Due to its 'soft' ionization properties and the possibility to choose from a variety of atmospheric pressure ionization MS instruments, GC/DBDI-MS has the potential to be an interesting alternative to 'classic' GC/MS techniques. The hyphenation of GC with DBDI-MS at atmospheric pressure is used for the determination of semifluorinated n-alkanes in ski wax samples. Different to perfluorinated n-alkanes, which are typically detected as [M-F+O]- and [M-F]- , semifluorinated n-alkanes can be detected both in positive mode as [M-3H+nO]+ and [M-H+nO]+ (n=0, 1, 2, and 3) ions, as well as in negative mode as a fragment ion representing the fluorinated part of the respective semifluorinated n-alkane. The method allowed the sensitive detection of semifluorinated n-alkanes with achievable limits of detection (LODs) in the single digit pg range injected on column. To examine the applicability of the GC/DBDI-MS method, semifluorinated n-alkanes were determined in fluorinated ski waxes. Results were confirmed by complimentary GC/electron ionization MS measurements. The unique SFA ionization patterns serve for complementary unambiguous identification of semifluorinated n-alkane species in positive mode and screening of contained n-alkanes fluorinated chain lengths in negative mode.

Analysis of amphetaminic drug compounds in urine by headspace-dielectric barrier discharge ionization-mass spectrometry

Rapid detection of trace level amphetaminic drug compounds in urine is essential to monitor consumption of these abuse drugs by athletes. In this work, the amphetaminic drug compounds were spiked in human urine and analyzed using headspace – dielectric barrier discharge (DBD) ionization-mass spectrometry method. In the headspace method, the urine spiked drug compound was treated with alkali solution, thus the free base amphetaminic molecules were released into the gas phase. The gaseous molecules were then ionized by the DBD ion source placed in front of the mass spectrometer inlet under ambient condition. This method provided comparable sensitivity with the solid-phase microextraction (SPME) in analysis of the amphetaminic compounds where no derivatization or adduct formation was required. The present method also facilitated the sensitivity enhancement with about one order of magnitude in urine compared to standard solution. Carbonate alkali solution showed the highest sensitivity for detection of the drug compounds in urine and the sensitivity was enhanced by using NH3. The limits of detection (LODs) of the various amphetaminic molecules were found to be in the range of 0.10–0.80 ng/mL for standard solutions while those for urine were in the range of 0.04–0.40 ng/mL. The analytical figures of merit of this method were evaluated under ambient condition using suitable internal standard. Results suggested the suitability of this method for analytical routine work in detection of amine-based drugs in doping test and/or in forensic laboratories. A mechanism of enhanced sensitivity by the ammoniated carbonate alkali solution in urine is also discussed.

Mechanistic Understanding Leads to Increased Ionization Efficiency and Selectivity in Dielectric Barrier Discharge Ionization Mass Spectrometry: A Case Study with Perfluorinated Compounds.

Perfluorinated compounds have unique properties and many practical applications, but are difficult to ionize efficiently with soft ionization methods. An active capillary plasma ionization source based on dielectric barrier discharge ionization (DBDI) coupled with mass spectrometry was used to study the ionization pathway of perfluorinated compounds (PFCs), with the aim of both increasing the ionization efficiency and influencing the selectivity for generating product ions in negative ion mode. Cyclic and linear perfluorinated alkanes were found to mainly form [M - F]- and [M - F + O]- ions, respectively; the [M]-• ion was only obtained at low discharge voltage. Additionally, fluorine attachment [M + F]- was observed mostly for perfluorinated alkenes. An isotope labeling experiment with 18O2 showed that the primary source of oxygen in the substitution reaction is molecular oxygen, reacting with the analyte in the form of O-• ions. The abundance of [M - F + O]- ions can thus be enhanced by increasing the plasma voltage to produce a higher O-• ion density. The loss of the fluorine (without substitution by oxygen) was mainly observed at high frequency, a fact which can be exploited for tuning the ionization toward specific product ions. Overall, the mechanistic understanding of the ionization of PFCs allowed to increase the selectivity of the product ions, resulting in increased ionization efficiency.

A quantitative approach for pesticide analysis in grape juice by direct interfacing of a matrix compatible SPME phase to dielectric barrier discharge ionization-mass spectrometry.

We evaluated the performance of a dielectric barrier discharge ionization (DBDI) source for pesticide analysis in grape juice, a fairly complex matrix due to the high content of sugars (≈20% w/w) and pigments. A fast sample preparation method based on direct immersion solid-phase microextraction (SPME) was developed, and novel matrix compatible SPME fibers were used to reduce in-source matrix suppression effects. A high resolution LTQ Orbitrap mass spectrometer allowed for rapid quantification in full scan mode. This direct SPME-DBDI-MS approach was proven to be effective for the rapid and direct analysis of complex sample matrices, with limits of detection in the parts-per-trillion (ppt) range and inter- and intra-day precision below 30% relative standard deviation (RSD) for samples spiked at 1, 10 and 10 ng ml-1, with overall performance comparable or even superior to existing chromatographic approaches.

Determination of Peroxide Explosive TATP and Related Compounds by Dielectric Barrier Discharge Ionization-Mass Spectrometry (DBDI-MS).

Dielectric barrier discharge ionization-mass spectrometry (DBDI-MS), which is based on the use of a low temperature helium plasma as ionization source, is used for the determination of trace amounts of triacetone triperoxide (TATP) and its homologue diacetone diperoxide (DADP) from surfaces. TATP is observed as [M+NH4]+ adduct, whereas DADP is observed as [M+O+NH4]+. Measurement of DADP with varying deuteration degrees (DADP, DADP-d6, and DADP-d12) indicates that DADP undergoes oxidation when ionized by DBDI. If acetonitrile is used as deposition solvent, TATP tends to show fragmentation and is not only detected as [M+NH4]+ but as [M-CH4+NH4]+ and [M-C2H4+NH4]+ as well. Quantification of TATP solutions from glass surfaces by DBDI-MS, using TATP-3,6,9-13C as internal standard, was done and validated using an LC/APCI-MS method. Achievable limits of detection (LOD) for TATP are equivalent to the deposition of 15 ng TATP and are comparable with other ambient desorption/ionization mass spectrometric techniques like desorption electrospray ionization (DESI).

Effects of Different Waveforms on the Performance of Active Capillary Dielectric Barrier Discharge Ionization Mass Spectrometry.

Active capillary dielectric barrier discharge ionization (DBDI) is emerging as a compact, low-cost, and robust method to form intact ions of small molecules for detection in near real time by portable mass spectrometers. Here, we demonstrate that by using a 10kHz, ~2.5 kVp-p high-voltage square-wave alternating current plasma, active capillary DBDI can consume less than 1μW of power. In contrast, the power consumed using a sine and triangle alternating current waveform is more than two orders of magnitude higher than that for the square waveform to obtain a similar voltage for plasma generation. Moreover, the plasma obtained using a square waveform can be significantly more homogenous than that obtained using sine and triangle waveforms. Protonated dimethyl methylphosphonate (DMMP) and deprotonated perfluorooctanoic acid (PFOA) can be detected at about the same or higher abundances using square-wave DBDI mass spectrometry compared with the use of sine and triangle waveforms. By use of benzylammonium thermometer ions, the extent of internal energy deposition using square, sine, or triangle waveform excited plasmas are essentially the same at the optimum voltages for ion detection. Using an H-bridge circuit driving a transformer optimized to reduce losses, square-wave active capillary DBDI can be continuously powered for ~50h by common 9V-battery (PP3). Graphical Abstract ᅟ.

Heat assisted sample introduction and determination of cannabinoids by dielectric barrier discharge ionization mass spectrometry

DBDI-MS equipped with an appropriate sample heater was employed to analyze directly 8 seized synthetic cannabinoids in botanical matrices. The heater allowed for a pronounced increase of the quality of acquired spectra, allowing for much easier identification of cannabinoids, as compared to standard DBDI source without heating device. A few hundred micrograms of herbal material was sufficient for easy detection of cannabinoids content in the samples. These designer drugs are difficult to identify in a conventional way due to their association with complex plant matrices during manufacturing (to mask active and illicit ingredients) and so requires time consuming extraction and sample preparation before analysis. The ability for fast and direct analysis of the so-called “legal highs” can be a useful supporting tool for an initial and rapid identification of compounds present in this type of species, and can partially replace GC/MS technique for fast screening.

Coupling neutral desorption sampling to dielectric barrier discharge ionization mass spectrometry for direct oil analysis

A new, powerful, rapid analytical method based on neutral desorption sampling in conjunction with dielectric barrier discharge ionization mass spectrometry was developed for identification of hogwash oil and edible oil samples.