Soft ionization mechanisms in flexible µ-tube plasma-from FµTP to closed µ-tube plasma.

In order to find an explanation for the mechanism in a plasma operated with an alternating voltage, or rather a square wave voltage, such a plasma was investigated. It was found that Penning ionization, charge transfer, and photoionization played a minor or even no role in the soft ionization mechanism of a FµTP. If the collision of plasma gases with air does not contribute to soft ionization, it should also be possible to use a separated plasma for soft ionization. Preliminary investigations show that it is possible to ignite a diagnosis gas with a plasma gas even when there is a barrier such as glass between those gases. A temporally and locally limited potential must be produced at the outer surface to achieve this. This potential should be sufficient to ionize the environment softly and to be able to use this so-called closed µ-tube plasma as a new ionization source.

Characterizing a nitrogen microwave inductively coupled atmospheric-pressure plasma ion source for element mass spectrometry.

A high-power nitrogen-based microwave inductively coupled atmospheric-pressure plasma was coupled to a quadrupole mass spectrometer to investigate its characteristics as an ion source for element mass spectrometry. The influence of operating conditions on analyte sensitivity, plasma background, and polyatomic ion formation was investigated for conventional solution-based analysis. By varying the forward power and the nebulizer gas flow rate, the plasma background ions were found to decrease with increasing gas flow rates and decreasing operating power. Analyte ions showed different trends, which could be related to the physical-chemical properties of the elements. We could identify three groups based on the location of maximum intensity in the power vs. flow rate contour plot. Atomic ions of elements with low first ionization energy and low oxygen bond strength were found to maximize at a high nebulizer gas flow rate and lower microwave power. Elements with intermediate ionization energy and higher oxygen bond strength required higher power settings for optimum sensitivity, while elements with the highest ionization energies required the highest power and lowest gas flow rates for their optimization. The latter group showed a substantial suppression in sensitivity compared to elements of similar mass, which is considered to result from the high abundance of NO in the plasma source, whose ionization energy is close to that of these elements. Metal oxide ions were found at similar or higher abundances than in the conventional argon-based ICP and could be minimized only by using a low gas flow rate and high power settings. These general trends were also observed when the vacuum interface was modified. To change the dynamics of the supersonic expansion, different sampler cone orifice sizes and sampler-skimmer distances were investigated and the interface pressure was lowered through an additional pump. These modifications did not yield significant differences in ion transmission but lowering the interface pressure reduced the relative abundance of metal oxide ions. The limits of detection were evaluated for optimized plasma conditions and found comparable to those of an argon ICP source with the same mass spectrometer.

Increased lncRNA AFAP1-AS1 expression predicts poor prognosis in gastric cancer: Evidence from published studies and followed up verification.

AIM: The purpose of this study was to clarify the influence of long non-coding RNA actin fiber-associated protein-1 antisense RNA 1 (lncRNA AFAP1-AS1) on the prognosis of gastric cancer (GC). METHODS: Based on meta-analysis, the association between the expression of AFAP1-AS1 and the prognosis of GC was estimated. GC tissue and non-cancer tissues from 136 patients were determined by quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) and verified by Gene Expression Profiling Interactive Analysis (GEPIA). Kaplan-Meier and Cox proportional hazards models were conducted to analyze the correlation between AFAP1-AS1 expression and GC prognosis. RESULTS: The pooled analysis from five studies revealed that the AFAP1-AS1 expression was significantly associated with GC overall survival (hazard ratio (HR) = 2.49 and 95% confidence interval (95% CI): 2.02-3.08, p < 0.001). Compared with non-cancer tissues, AFAP1-AS1 expression level of GC tissues were significantly upregulated (p < 0.001), which was confirmed by the results of GEPIA. The area under the receiver-operating characteristic (ROC) curve was 0.893, and the high expression of AFAP1-AS1 was correlated with poor prognosis in patients with GC (p = 0.005). Clinical grade (HR = 1.912, 95% CI: 1.246-2.934, p = 0.003), pathologic tumor node metastasis (pTNM) (HR = 2.393, 95% CI: 1.431-4.033, p = 0.001), log odds of positive lymph nodes (LODDS) (HR = 2.910, 95% CI: 1.787-4.793, p < 0.001) and AFAP1-AS1 expression (HR = 2.393, 95% CI: 1.869-3.064, p < 0.001) were independent prognostic factors for GC revealed by multivariate Cox-regression analysis. CONCLUSION: This study demonstrated that the AFAP1-AS1 may be a novel biomarker for the diagnosis and prognosis of GC.

Clinicopathological and prognostic value of lncRNAs expression in gastric cancer: A field synopsis of observational studies and databases validation.

BACKGROUND: The purpose of this study was to evaluate existing evidence in the field of long non-coding RNAs (lncRNAs) and prognosis of gastric cancer. METHODS: A comprehensive literature search was performed through the electronic database. The combined hazard ratios (HRs) and corresponding 95% confidence intervals (CIs) of overall survival (OS), disease-free survival (DFS), or progression free survival (PFS) were calculated to assess the strength of the association. Kaplan-Meier (KM) plotter was used to verify lncRNA HOX transcript antisense RNA (HOTAIR) expression and OS. RESULTS: Overall, a significant correlation between high lncRNAs expression and poor OS was explored in patients with gastric cancer (HR = 1.78, P < .001). Subgroup analysis based on statistical methods indicated the high expression of lncRNAs in log-rank (HR = 1.87, P < .001) and multivariate analysis (HR = 1.71, P < .001) were all significantly correlated with the poor OS. Clinicopathological parameters analysis showed the lncRNA expression were significantly associated prognosis, including TNM stage, tumor size, pathological differentiation, lymph nodes metastasis, distance metastasis, invasion depth and Lauren's classification. It was consistent with the verification results of bioinformatics database for lncRNA HOTAIR (P < .001). CONCLUSION: Our study confirmed the expression of lncRNAs and clinicopathological features may serve as effective indicators of prognosis in patients with gastric cancer.

Ionization of semi-fluorinated n-alkanes in controlled atmosphere using flexible micro-tube plasma (FµTP) ionization source with square- and sine-wave voltage.

Non-thermal plasma-based ionization sources have been widely used and shown excellent soft ionization performance in mass spectrometry. Despite their extensive application, the ionization mechanisms of these sources are of great interest for further exploring their full potential. A controlled atmosphere can provide a clean and controllable ionization environment and is beneficial for studying the ionization mechanism. The plasma source itself also has a significant impact on the ionization mechanism of the analyte, and the voltage waveform is one of the key parameters for controlling the plasma source. In this paper, a miniature flexible micro-tube plasma (FµTP) ionization source was sustained using both square and sine-wave voltage. The ionization processes of typical semi-fluorinated n-alkanes (SFAs) were investigated in the controlled atmosphere filled with 80% N2 and 20% O2. The main mass peaks using both square and sine-wave voltages are found to be [M-mH]+ and [M-mH+nO]+ (m = 1, 3; n = 0, 1, 2). However, for the square-wave voltage, the [M-H+O]+ species are the most abundant while [M-H]+ species are dominant for the sine-wave voltage, showing that the plasma generated with sine-wave voltage is somewhat "softer" than the one with square-wave voltage for SFAs. With the assistance of optical spectroscopy, the plasma developments in one discharge cycle for both voltage waveforms were obtained. Only one discharge can be found in each half cycle for square-wave voltage while several for the sine-wave voltage. These would be responsible for the different ionization behaviors in these two cases. This work provides more insight into the ionization mechanism of SFAs and more understanding of plasma-based soft ionization. In addition, the analytical performance was evaluated to be comparable when using these two voltage generators with a big difference in cost, which will benefit the instrumental development.

Evaluation of a novel controlled-atmosphere flexible microtube plasma soft ionization source for the determination of BTEX in olive oil by headspace-gas chromatography/mass spectrometry.

Although electron impact ionization (EI) remains the standard ionization source for GC-MS, it presents extensive fragmentation as its main limitation. The potential of a novel plasma-based soft ionization source named controlled-atmosphere flexible microtube plasma (CA-FµTP) has been evaluated in this work for the determination of monoaromatic volatile BTEX group (namely benzene, toluene, ethylbenzene, and o-, m- and p-xylenes) in olive oil, based on headspace technique. The obtained results show an attractive advantage over EI due to no fragmentation was observed. A nitrosated ion [M + NO]+ is obtained as the most abundant species. Thus, the BTEX mass spectrum identification can be carried out without major effort. In general, the sensitivity for CA-FµTP was comparable to those obtained by EI, achieving LODs ranged from 0.6 to 1.0 µg kg-1. The potential usefulness of GC-CA-FµTP-MS for the detection of BTEX was demonstrated by analyzing olive oil samples and identifying traces of these compounds in one sample. Therefore, the proposed plasma-based soft ionization is suitable for BTEX analysis in fatty complex matrixes as olive oil.

Ultrasensitive and Simultaneous Detection of Multielements in Aqueous Samples Based on Biomimetic Array Combined with Laser-Induced Breakdown Spectroscopy.

Ultrasensitive detection of metallic elements in liquids has attracted considerable attention in fields such as environmental pollution monitoring and drinking water quality control. Hence, it is of great significance to develop a sensitive and simultaneous detection strategy for multiple metal elements in liquid. Laser-induced breakdown spectroscopy (LIBS) technology shows unique advantages because of its simple, rapid, and real-time in situ detection, but the laser energy will be greatly attenuated in the liquids; thus, the sensitivity of LIBS for direct detection of metal elements in liquid samples will decrease sharply. In this study, inspired by the structure of Stenocara beetle's back, a superhydrophobic biomimetic interface with hydrophilic array was prepared for enriching low-concentration targets into detection regions, and the biomimetic array LIBS (BA-LIBS) was successfully established. The ultrasensitive and simultaneous detection of nine metal elements in drinking water was realized based on the effective enrichment method. The limits of detection of the nine metal elements in mixed solution ranged from 8.3 ppt to 13.49 ppb. With these excellent properties, this facile and ultrasensitive BA-LIBS strategy might provide a new idea for the prevention and control of metal hazards in the liquid environment.

Review: Miniature dielectric barrier discharge (DBD) in analytical atomic spectrometry.

The development of miniature, sensitive, high throughput, and in-situ analytical instruments has been becoming developing field of modern analytical chemistry. Due to its unique advantages such as easy operation, simple configuration, ambient working temperature and pressure, low power consumption, and miniature dimension, dielectric barrier discharge (DBD) has always been a hot topic in analytical chemistry. This review gives an overview of miniature DBD application in analytical atomic spectrometry, starting with an introduction to its geometrical configuration and ionization mechanisms. Then, its applications such as excitation or atomization sources in atomic emission spectrometry (AES), atomic absorption spectrometry (AAS) and atomic fluorescence spectrometry (AFS) are reviewed. Also, its application as vapor generation system in atomic spectrometry is discussed.

Direct Oxidative Nitrogen Fixation from Air and H2 O by a Water Falling Film Dielectric Barrier Discharge Reactor at Ambient Pressure and Temperature.

Current industrial production of HNO3 relies on the Ostwald process via catalytic oxidation of NH3 , which is responsible for the vast bulk of CO2 emission. An attractive alternative route to HNO3 is direct N2 oxidation to aqueous HNO3 , which avoids the NH3 intermediate. Herein, we for the first time report a non-thermal plasma-assisted nitrogen fixation process characteristic of a large gas-liquid contact based on the water falling film dielectric barrier discharge, wherein HNO3 is produced directly from ambient air and H2 O at atmospheric pressure and room temperature without the presence of any catalytic material. By optimizing the plasma reaction conditions, a relatively high synthesis rate and low energy consumption was achieved at the same time with good product selectivity.

Stepwise optimization of a Flexible Microtube Plasma (FµTP) as an ionization source for Ion Mobility Spectrometry.

The ionization source is the central system of analytical devices such as mass spectrometers or ion mobility spectrometers. In this study, a recently developed flexible microtube plasma (FµTP) is applied as an ionization source for a custom-made drift tube ion mobility spectrometer (IMS) for the first time. The FµTP is based on a highly miniaturized, robust and a small-footprint dielectric barrier discharge design with an outstanding ionization efficiency. In this study, the experimental setup of the FµTP was further improved upon to achieve optimal coupling conditions in terms of the ion mobility spectrometry sensitivity and the plasma gas consumption. One major focus of this study was the adjustment of the electrical operation parameters, in particular, the high voltage amplitude, frequency and duty cycle, in order to minimize the electric field disturbances and yield higher signals. Additionally, the consumption of helium plasma gas was reduced by refining the FµTP. It was found that the ionization efficiency could be significantly enhanced by increasing the plasma high voltage and through application of a duty cycle up to 90:10. Plasma gas flows could be reduced down to 3 mL min-1 by increasing the plasma high voltage amplitude. Furthermore, a smaller wire electrode design enables the operation of the FµTP with nitrogen and clean air. Moreover, detection limits of a homologous series of ketones in the range of 330 pptv (N2-FµTP, 2-decanone) down to 20 pptv (He-FµTP, 2-octanone) could be reached in the optimized setup. To sum up, this feasibility study demonstrates the potential of the optimized FµTP as a powerful ionization source for ion mobility spectrometry especially with regard to ionization efficiency.

Development of microwave plasma proton transfer reaction mass spectrometry (MWP-PTR-MS) for on-line monitoring of volatile organic compounds: Design, characterization and performance evaluation.

Proton transfer reaction mass spectrometry (PTR-MS) is a revolutionary on-line VOCs monitoring method. In this study, a new microwave plasma-based proton transfer reaction mass spectrometry (MWP-PTR-MS) is developed. The MWP consists of a surfatron type resonator and a cooperative ion extraction device to achieve high efficiency production of hydronium ions. Non-local thermodynamic equilibrium water plasma is generated in a quartz tube at 200 Pa with 2.45 GHz microwave. Characters of MWP, such as emission spectroscopy, input power, dirty ion suppressing and ion extraction, are explored systematically. With the same test platform, MWP has a 7-fold increment of hydronium ion production rate than glow discharge source. The counts rate of hydronium ion is 8 × 106 cps with abundance of NO+ and O2+ is less than 0.4% and 5% respectively. The performance of MWP-PTR-MS is validated by analysis of several chemicals and demonstration application is conducted. The instrument showed good linearity above 99% in the range of 4.5 × 10-11 to 4.5 × 10-9 mol/L. Benefited from the character of surface wave and 2.45 GHz microwave, MWP has high potential in improving the performance and reliability of current PTR-MS.

Emission enhancement of laser-induced breakdown spectroscopy for aqueous sample analysis based on Au nanoparticles and solid-phase substrate.

In this paper, porous electrospun ultrafine fiber with a nanoparticle coating was proposed as an effective approach to enhance the laser-induced breakdown spectroscopy (LIBS) signal for metal ions in aqueous systems. It is known that the LIBS technique is very limited when used for liquid sample analysis. On the other hand, in practical applications, many LIBS measurements have been accomplished in a liquid environment. A signal enhancement method for aqueous sample LIBS analysis was presented in this work, where Au nanoparticles and a solid-phase support were combined for the first time for aqueous sample analysis with LIBS. The system operation was relatively simple, which only required Au nanoparticles being dropped onto the surface of porous electrospun ultrafine fibers before LIBS analysis. Significant signal enhancement was achieved due to the integration of the merits of the Au nanoparticles and the ultrafine fibers. Nanoparticles possess significant LIBS signal enhancement effects by providing several plasma ignition points and then causing more efficient emissions. In addition, Au nanoparticles could also help to decrease the breakdown threshold of target elements for LIBS analysis. The electrospun ultrafine fibers as solid-phase support can accommodate a larger volume of aqueous sample. Meanwhile, the aqueous solution on the fiber surface was easy to evaporate. The experimental results showed that the limits of detection (LODs) with this method were significantly improved, 0.5 µg/mL for Cr, 0.5 µg/mL for Pb, and 1.1 µg/mL for Cu, respectively, compared with 2.0 µg/mL for Cr and 3.3 µg/mL for Cu in the previous research. In the proposed method, signal enhancement could be achieved without any extra equipment, which makes the LIBS technique feasible for direct measurement of an aqueous sample.

Characterization of local thermodynamic equilibrium in a laser-induced aluminum alloy plasma.

The electron temperature was evaluated using the line-to-continuum ratio method, and whether the plasma was close to the local thermodynamic equilibrium (LTE) state was investigated in detail. The results showed that approximately 5 µs after the plasma formed, the changes in the electron and excitation temperatures, which were determined using a Boltzmann plot, overlapped in the 15% error range, which indicated that the LTE state was reached. The recombination of electrons and ions and the free electron expansion process led to the deviation from the LTE state. The plasma's expansion rate slowed over time, and when the expansion time was close to the ionization equilibrium time, the LTE state was almost reached. The McWhirter criterion was adopted to calculate the threshold electron density for different species, and the results showed that experimental electron density was greater than the threshold electron density, which meant that the LTE state may have existed. However, for the nonmetal element N, the threshold electron density was greater than the value experimental value approximately 0.8 µs after the plasma formed, which meant that LTE state did not exist for N.

Dehydrated Carbon Coupled with Laser-Induced Breakdown Spectrometry (LIBS) for the Determination of Heavy Metals in Solutions.

In this article, a novel and alternative method of laser-induced breakdown spectroscopy (LIBS) analysis for liquid sample is proposed, which involves the removal of metal ions from a liquid to a solid substrate using a cost-efficient adsorbent, dehydrated carbon, obtained using a dehydration reaction. Using this new technique, researchers can detect trace metal ions in solutions qualitatively and quantitatively, and the drawbacks of performing liquid analysis using LIBS can be avoided because the analysis is performed on a solid surface. To achieve better performance using this technique, we considered parameters potentially influencing both adsorption performance and LIBS analysis. The calibration curves were evaluated, and the limits of detection obtained for Cu(2+), Pb(2+), and Cr(3+) were 0.77, 0.065, and 0.46 mg/L, respectively, which are better than those in the previous studies. In addition, compared to other absorbents, the adsorbent used in this technique is much cheaper in cost, easier to obtain, and has fewer or no other elements other than C, H, and O that could result in spectral interference during analysis. We also used the recommended method to analyze spiked samples, obtaining satisfactory results. Thus, this new technique is helpful and promising for use in wastewater analysis and management.

Laser-induced breakdown spectroscopy technique for quantitative analysis of aqueous solution using matrix conversion based on plant fiber spunlaced nonwovens.

In the present work, laser-induced breakdown spectroscopy (LIBS) was applied to detect concentrations of chromium and nickel in aqueous solution in the form of matrix conversion using plant fiber spunlaced nonwovens as a solid-phase support, which can effectively avoid the inherent difficulties such as splashing, a quenching effect, and a shorter plasma lifetime during the liquid LIBS analysis. Drops of the sample solution were transferred to the plant fiber spunlaced nonwovens surface and uniformly diffused from the center to the whole area of the substrate. Owing to good hydrophilicity, the plant fiber spunlaced nonwovens can hold more of the liquid sample, and the surface of this material never wrinkles after being dried in a drying oven, which can effectively reduce the deviation during the LIBS analysis. In addition, the plant fiber spunlaced nonwovens used in the present work are relatively convenient and low cost. Also, the procedure of analysis was simple and fast, which are the unique features of LIBS technology. Therefore, this method has potential applications for practical and in situ analyses. To achieve sensitive elemental detection, the optimal delay time in this experiment was investigated. Under the optimized condition, the limits of detection for Cr and Ni are 0.7 and 5.7 µg·mL(-1), respectively. The results obtained in the present study show that the matrix conversion method is a feasible option for analyzing heavy metals in aqueous solutions by LIBS technology.