Characteristics of dissolved organic matter (DOM) in Chinese farmland soils under different climate zone types: A molecular perspective.

Interactions between dissolved organic matter (DOM) and surrounding environments are highly complex. Understanding DOM at the molecular level can contribute to the management of soil pollution and safeguarding agricultural fields. Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) has enabled a molecular-level understanding of DOM. Accordingly, in this study, we investigated soil samples from 27 different regions of mainland China with various soil types and climatic characteristics. Based on the geographical features of the four typical climatic zones in mainland China (temperate monsoon, temperate continental, subtropical monsoon, and Qinghai-Tibet Plateau climates), we employed high-resolution mass spectrometry to determine the molecular diversity of DOM under different climatic conditions. The results indicated that lignin and tannin-like substances were the most active categories of DOM in the soils. Collectively, the composition and unsaturation of DOM molecules are influenced by sunlight, precipitation, temperature, and human activity. All climatic regions contained a substantial number of characteristic molecules, with CHO and CHON constituting over 80%, and DOM containing nitrogen and sulfur was relatively more abundant in the monsoon regions. The complex composition of DOM incorporates various active functional groups, such as -NO2 and -ONO2. Furthermore, soil DOM in the monsoon regions showed higher unsaturation and facilitated various (bio) biochemical reactions in the soil.

Analysis of extracellular and intracellular antibiotic resistance genes in commercial organic fertilizers reveals a non-negligible risk posed by extracellular genes.

Livestock manure is known to be a significant reservoir of antibiotic resistance genes (ARGs), posing a major threat to human health and animal safety. ARGs are found in both intracellular and extracellular DNA fractions. However, there has been no comprehensive analysis of these fractions in commercial organic fertilizers (COFs). The present study conducted a systematic survey of the profiles of intracellular ARGs (iARGs) and extracellular ARGs (eARGs) and their contributing factor in COFs in Northern China. Results showed that the ARG diversity in COFs (i.e., 57 iARGs and 53 eARGs) was significantly lower than that in cow dung (i.e., 68 iARGs and 69 eARGs). The total abundance of iARGs and eARGs decreased by 85.7% and 75.8%, respectively, after compost processing, and there were no significant differences between iARGs and eARGs in COFs (P > 0.05). Notably, the relative abundance of Campilobacterota decreased significantly (99.1-100.0%) after composting, while that of Actinobacteriota and Firmicutes increased by 21.1% and 29.7%, respectively, becoming the dominant bacteria in COFs. Co-occurrence analysis showed that microorganisms and mobile genetic elements (MGEs) were more closely related to eARGs than iARGs in COFs. And structural equation models (SEMs) further verified that microbial community was an essential factor regulating iARGs and eARGs variation in COFs, with a direct influence (λ = 0.74 and 0.62, P < 0.01), following by similar effects of MGEs (λ = 0.59 and 0.43, P < 0.05). These findings indicate the need to separate eARGs and iARGs when assessing the risk of dissemination and during removal management in the environment.

Vermicompost: In situ retardant of antibiotic resistome accumulation in cropland soils.

The dissemination of antibiotic resistance genes (ARGs) in soil has become a global environmental issue. Vermicomposting is gaining prominence in agricultural practices as a soil amendment to improve soil quality. However, its impact on soil ARGs remains unclear when it occurs in farmland. We comprehensively explored the evolution and fate of ARGs and their hosts in the field soil profiles under vermicompost application for more than 3 years. Vermicompost application increased several ARG loads in soil environment but decreased the high-risk bla-ARGs (blaampC, blaNDM, and blaGES-1) by log(0.04 - 0.43). ARGs in soil amended with vermicompost primarily occurred in topsoil (approximately 1.04-fold of unfertilized soil), but it is worth noting that their levels in the 40-60 cm soil layer were the same or even less than in the unfertilized soil. The microbial community structure changed in soil profiles after vermicompost application. Vermicompost application altered the microbial community structure in soil profiles, showing that the dominant bacteria (i.e., Proteobacteria, Actinobacteriota, Firmicutes) were decreased 2.62%-5.48% with the increase of soil depth. A network analysis further revealed that most of ARG dominant host bacteria did not migrate from surface soil to deep soil. In particular, those host bacteria harboring high-risk bla-ARGs were primarily concentrated in the surface soil. This study highlights a lower risk of the propagation of ARGs caused by vermicompost application and provides a novel approach to reduce and relieve the dissemination of ARGs derived from animals in agricultural production.

Revisiting the Surface Energy Parameters of Standard Test Liquids with a Corrected Contact Angle Method over Rough Surfaces.

Interfacial free energy is a quantitative basis for explaining and predicting interfacial behavior that is ubiquitous in nature. The contact angle (CA) method can determine the surface free energy (γ) as well as Lifshitz-van der Waals (γLW) and Lewis acid/base (γ+/γ-) components of a solid material from its CAs with a set of known test liquids according to the extended Young-Dupré equation. However, the reliability of the "known" parameters of the test liquids is questioned due to the long-neglected surface roughness effect during calibration of the liquids. This study proposed a simple and practicable two-step approach to correct the energy parameters of several test liquids by incorporating Wenzel's surface roughness relationship into CA measurement. Step 1: water and two apolar liquids (diiodomethane and α-bromonaphthalene) were used as benchmarks to calibrate the surface roughness and energy parameters of two reference solids [apolar poly(tetrafluoroethylene) and monopolar poly(methyl methacrylate)], and step 2: the reference solids were used to calibrate any other test liquids by solving the energy parameters from their CAs in the extended Young-Dupré-Wenzel model. Monte Carlo simulation was used to evaluate error transmission and robustness of the model solutions. The obtained energy parameters (γLW/γ+/γ-) of four test liquids (dimethyl sulfoxide, formamide, ethylene glycol, and glycerol) are 28.01/13.68/4.67, 34.95/3.53/37.62, 26.26/7.51/15.74, and 32.99/9.24/26.02 mJ/m2, respectively, and different from the literature values. The liquids were applied to characterize an example solid surface with true γLW/γ+/γ- values of 28.00/1.00/8.00 mJ/m2 and a roughness index (r) of 1.60. Without correction of the liquid parameters, the calculated surface energy, hydration energy, and hydrophobic attraction energy of the solid sample can deviate by 50, 13, and 27%, respectively. This proves the necessity of correcting parameters of the test liquids before they can be used in CA and interfacial energy studies in the presence of surface roughness.

Spatial Distributions, Compositional Profiles, Potential Sources, and Intfluencing Factors of Microplastics in Soils from Different Agricultural Farmlands in China: A National Perspective.

More attention has been paid to ubiquitous microplastics (MPs). As a major food producer, the situation of MPs in China's farmland is of even greater concern. Spatial distributions, characteristics, and compositions of MPs in five types of agricultural lands with representative crops were investigated by collecting 477 soil samples from 109 cities in 31 administrative regions of mainland China. To better control MPs in farmland, nearly 400 field questionnaires were obtained, and meteorological conditions, soil properties, and other statistics were collected to quantify potential sources and determine influencing factors. The average abundances of MPs was 2462 ± 3767 items/kg in the agricultural soils, and MP abundance in the greenhouses, farmlands with film mulching, and blank farmlands from four integrated physical geographic regions were determined. The contributions of agricultural films, livestock and poultry manures, irrigation water, and air deposition to MPs in farmlands have been calculated. Influencing factors, such as recovery method, plowing frequency, meteorological conditions, and part of soil properties, were significantly correlated with the abundances of MPs in the agricultural soils (p < 0.05), while mulching age mainly affected MPs in the greenhouses (p < 0.05). This study provides basic scientific data for decision-making and further analysis.

Manure application: A trigger for vertical accumulation of antibiotic resistance genes in cropland soils.

The application of livestock manure increases the dissemination risk of antibiotic resistance genes (ARGs) in farmland soil environment. However, the vertical migration behavior and driving factor of ARGs in manured soil under swine manure application remains undefined. Here, the dynamics of ARGs, mobile genetic elements (MGEs) and bacterial communities in different soil depths (0 - 80 cm) with long-term swine manure application were tracked and conducted using real-time qPCR. Results showed that long-term application of swine manure remarkably facilitated the vertical accumulation of ARGs and MGEs, in particular that the relative abundance of blaampC showed significant enrichment with increasing depth. ARGs abundance was similar in the three fields with long-term application of swine manure. (p＞0.05). Procrustes analysis indicated that microbial communities were the dominant drivers of ARGs variation in topsoil, and the changes of environmental factors played a vital role in vertical migration ARGs in cropland soils. Additionally, the variation patterns of high-risk ARGs (i.e., blaampC, blaTEM-1) were influenced by the dominant bacteria (Actinomycetes) and pH. This study illustrated that the swine manure application promoted the vertical migration of ARGs, including multidrug resistance determinants, highlighting the ecological risk caused by long-term manure application.

Deciphering discriminative antibiotic resistance genes and pathogens in agricultural soil following chemical and organic fertilizer.

Fertilizers containing rich nutrients can change the profiles of antibiotic resistant pathogens (ARPs) and antibiotic resistance genes (ARGs) in receiving soils; however, the discriminative ARGs and ARPs in agricultural soil following different fertilizer applications remain unknown. Using metagenomic sequencing combined with binning approach, the present study investigated the discriminative ARGs and ARPs under various fertilizer applications (chemical and organic fertilizer) in a 8-year field experiment. VanR, multidrug ARG transporter, vanS, ermA, and arnA were the discriminative ARGs in the chemical fertilizer group, whereas rosB, multidrug transporter, mexW, and aac(3)-I were enhanced in the organic fertilizer group. The metagenomic binning approach revealed that both fertilizer applications caused pathogen proliferation. Chemical fertilizer caused the increase in the pathogenic genus Luteimonas, and organic fertilizer facilitated the proliferation of the pathogenic genera Dokdonella and Pseudomonas. The pathogenic species Pseudomonas_H sp014836765, carrying mexW and multidrug transporter, was enriched only in the organic fertilizer group, indicating that it was a discriminative ARP in the organic fertilizer group. Our results demonstrated that fertilizer application, particularly organic fertilizer application, can facilitate the proliferation of ARGs and ARPs in the receiving soil, posing the risk of the development and spread of soil-borne ARPs.

Study on the Distribution of Low Molecular Weight Metabolites in Mango Fruit by Air Flow-Assisted Ionization Mass Spectrometry Imaging.

Mass spectrometry imaging is a novel molecular imaging technique that has been developing rapidly in recent years. Air flow-assisted ionization mass spectrometry imaging (AFAI-MSI) has received wide attention in the biomedical field because of its features such as not needing a pretreatment sample, having high sensitivity, and wide coverage of metabolite detection. In this study, we set up a mass spectrometry imaging method for analyzing low molecular metabolites in mango fruits by the AFAI-MSI method. Compounds such as organic acids, vitamin C, and phenols were detected from mango tissue by mass spectrometry under the negative ion scanning mode, and their spatial distribution was analyzed. As a result, all the target compounds showed different distributions. Citric acid was mainly distributed in the pulp. Malic acid, quinic acid, and vitamin C universally existed in the pulp and peel. However, galloylglucose isomer and 5-galloylquinic acid were predominantly found in the peel. These results show that AFAI-MSI can be used for the analysis of mango fruit endogenous metabolites conveniently and directly, which will facilitate the rapid identification and in situ characterization of plant endogenous substances.

Risk Assessment of Triflumezopyrim and Imidacloprid in Rice through an Evaluation of Residual Data.

Triflumezopyrim, a novel mesoionic insecticide used to control planthoppers, is a potential substitute for imidacloprid. In this study, triflumezopyrim and imidacloprid residues in rice were determined using a quick, easy, cheap, effective, rugged, and safe procedure combined with ultra-high-performance liquid chromatography-tandem mass spectrometry. The limit of quantification of both triflumezopyrim and imidacloprid was 0.01 mg kg-1, and the average recovery values were 94-104% and 91-106%, with relative standard deviations (RSDs) of 1.1-1.4% and 2.1-3.4% (n = 5), respectively. The consumer protection level was assessed by calculating the theoretical maximum daily intake using the reported maximum residue limits of triflumezopyrim and imidacloprid. The established method was successfully applied to 200 commercial rice samples collected from four provinces in China, and their potential public health risks were assessed using triflumezopyrim and imidacloprid residues. The risk associated with triflumezopyrim and imidacloprid dietary intake was assessed by calculating the national estimated short-term intake and the acute reference dose percentage (%ARfD). The results show that the theoretical maximum daily intake (NEDI) values of triflumezopyrim and imidacloprid in different age and gender groups were 0.219-0.543 and 0.377-0.935 µg kg-1 d-1 bw, and the risk quotient (RQ) values were 0.188-0.467% and 0.365-0.906%, respectively. The acute reference dose (%ARfD) of triflumezopyrim and imidaclopridin ranged from 0.615 to 0.998% and from 0.481 to 0.780%, respectively.

Tracking antibiotic resistance genes (ARGs) during earthworm conversion of cow dung in northern China.

Using cow dung to breed earthworms poses a risk of environmental transmission of antibiotic resistance genes (ARGs). The purpose of this study was to address the occurrence, persistence and environmental fate of ARGs during earthworm conversion of cow dung. The results showed that ARGs persisted through the whole process. Notably, earthworm conversion effectively reduced some ARGs in cow dung, but a definite concentration of ARGs still remained in earthworms and vermicompost (up to 10-1 and 10-2 copies/16S copies, respectively). We found that tet-ARGs were the most abundant in 15 earthworm farms (10-6~10-1 copies/16S copies) and some high-risk ARGs (i.e., blaampC, blaOXA-1 and blaTEM-1) were even prevalent in these farms. Interestingly, although ARGs differ widely in cow dung (10-10~10-1 copies/16S copies), the ARGs levels were comparable in vermicompost samples from different farms (10-8~10-2 copies/16S copies). Notably, earthworm conversion effectively reduced some ARGs in cow dung, but significant level of ARGs still remained in earthworms and vermicompost (up to 10-1 and 10-2 copies/16S copies, respectively). Nevertheless, the concentrations of some heavy metals (Cu, Zn and Ni), the abundance of mobile genetic elements (MGEs) and total nitrogen content were confirmed to be correlated to the enrichment of some ARGs. Overall, this study demonstrated the high prevalence of ARGs contamination in earthworm farms, and also highlighted the dissemination risk of ARGs during the earthworm conversion of cow dung.

Tracking antibiotic resistance gene transfer at all seasons from swine waste to receiving environments.

Antibiotic resistance genes (ARGs) in livestock farms have attracted a growing attention with potential effects on human health. As one of the most important organic fertilizer, swine waste provided an ideal environment for understanding the dissemination and accumulation of ARGs in agricultural ecosystems. Here we conducted a year-round follow-up trace from swine waste to receiving environments, with the purpose of revealing the contamination profiles and ecological risks of ARGs at different seasons. Results indicated that a variety of common ARGs and even high-risk ARGs (i.e., blaampC, blaOXA-1, blaTEM-1 and mcr-1) were prevalent from swine waste to farmland soil, with changing in various degrees from season to season. Regarding the occurrence pattern of ARGs, tetracycline resistance genes (tet-ARGs) were predominant genes at four seasons in all fresh pig feces, swine manure, manured soil and wastewater. The levels of most ARGs in solid waste were reduced at a different degree via natural composting, and the removal effect was best in summer, while ARGs decreased poorly after wastewater treatment, especially in winter (up to 10-1 copies/16S copies in the residual level), which increased the possibility of propagation to receiving environment. This concern was also validated by the investigation on farmland environment with long-term application of manure, where causing an increase in ARG abundances in soils (approximately 0.9-32.7 times). To our knowledge, this study is the first to demonstrate the distribution pattern of ARGs from swine waste to its receiving farmland environment at all seasons on this integrity chain.

Family livestock waste: An ignored pollutant resource of antibiotic resistance genes.

The random discharge of livestock waste from family farms without utilization and treatment has caused great pressure on the rural ecological environment and gravely increased the environmental pollution. In this study, we targeted 26 family livestock farms to assess the occurrence characteristics of antibiotic resistance genes (ARGs) in livestock waste and its receiving farmland environment in Erhai Lake basin of China by real-time fluorescence quantitative PCR. The results showed that various common ARGs and some high-risk ARGs (i.e., blaampC, blaOXA-1 and blaTEM-1) were prevalent in family livestock waste, and the pollution of tetracycline resistance genes was the most serious in these family livestock farms. Meanwhile, we also found that the ARG levels were higher in family chicken farms than that in pig and cattle farms, and ARGs pollution in layer waste and sow waste was more severe than that in broiler waste and piglet/fattening pig waste, respectively. Troublesomely, significant ARGs levels could be discharged via manure application, further causing the increase of ARGs abundance in soil environment (approximately 11-36 times). This study demonstrated the high prevalence and severity of ARGs contamination in family livestock farms, also emphasizing that family livestock waste was a non-ignored important pollutant resource of ARGs in the environment.

Determination of Surface Energy Parameters of Hydrophilic Porous Membranes via a Corrected Contact Angle Approach.

While the contact angle is a well-applied indicator of membrane hydrophobicity and surface energy, the interference of surface roughness and porosity in contact angle measurement and surface energy calculation has been long neglected in the field of porous membrane study. We propose an improved method to straightforwardly derive the surface energy of the porous membrane from contact angles with the interference effect corrected. A linearized model was established combining the Young-Dupré and Cassie-Baxter equations, from which the surface energy (Lifshitz-van der Waals and Lewis acid/base components) and roughness index (surface area difference) can be solved simultaneously at a given porosity using contact angles measured with a set of standard polar/nonpolar test liquids. The model solution was examined using hydrophilic microfiltration membranes with different pore morphologies (including perforated plate-like PCTE, irregular particulate bed-like PVDF, and fibrous mesh-like PTFE membranes), with the robustness of the results evaluated via Monte Carlo simulation. In comparison with the verified results of the model solution, it was found that the Lifshitz-van der Waals Lewis acid/base energy values for the tested membranes would deviate by 50-87, 30-160, and 52-97%, respectively, if surface roughness and porosity were neglected in the calculation. The profound effect of roughness and porosity on surface energy determination was further confirmed via theoretical analysis of the Young-Dupré and Cassie-Baxter relationships. This improved approach may apply to the surface energy characterization of hydrophilic rough porous membranes (e.g., hydrophilic microfiltration membranes).

Stokes Shift and Specific Fluorescence as Potential Indicators of Organic Matter Hydrophobicity and Molecular Weight in Membrane Bioreactors.

Hydrophobicity and molecular weight (MW) are two fundamental properties of dissolved organic matter (DOM) in wastewater treatment systems. This study proposes fluorescence Stokes shift and specific fluorescence intensity (SFI) as novel indicators of hydrophobicity and MW. These indicators originate from the energy gap and photon efficiency of the fluorescence process and can be readily extracted from a fluorescence excitation-emission matrix (EEM). The statistical linkages between these indicators and hydrophobicity/MW were explored through investigation of DOM across 10 full-scale membrane bioreactors treating municipal wastewater. Stokes shift was found to exhibit a general rule among the hydrophobicity components in the order of hydrophilic substances (HIS) < hydrophobic acids (HOA) < hydrophobic bases (HOB). The Stokes shift of 1.2 µm-1 is a critical border, above which the relative fluorescence correlated significantly with the HOA-related content (Pearson's r = 0.8). With regard to MW distribution (<1, 1-10, 10-100, and >100 kDa), SFI was found to be the most sensitive to the change of MW of <1 kDa proportion, especially at the excitation/emission wavelengths of 200-320/310-550 nm (r > 0.9). Hydrophobicity-related π conjugation and MW-dependent light exposure might be responsible for the correlations. These fluorescence indicators may be useful for convenient monitoring of DOM in wastewater treatment systems.

Integrative Assessment of Mixture Toxicity of Three Ionic Liquids on Acetylcholinesterase Using a Progressive Approach from 1D Point, 2D Curve, to 3D Surface.

The joint toxicities of [BMIM]BF4, [BMIM]PF6, and [HMIM]BF4 on acetylcholinesterase (AChE) were systematically investigated by using a progressive approach from 1D single effect point, 2D concentration-response curve (CRC), to 3D equivalent-surface (ES) level. The equipartition equivalent-surface design (EESD) method was used to design 10 ternary mixtures, and the direct equipartition ray (EquRay) design was used to design 15 binary mixtures. The toxicities of ionic liquids (ILs) and their mixtures were determined using the microplate toxicity analysis (MTA) method. The concentration addition (CA), independent action (IA), and co-toxicity coefficient (CTC) were used as the additive reference model to analyze the toxic interaction of these mixtures. The results showed that the Weibull function fitted well the CRCs of the three ILs and their mixtures with the coefficient of determination (R2) greater than 0.99 and root-mean-square error (RMSE) less than 0.04. According to the CTC integrated with confidence interval (CI) method (CTCICI) developed in this study, the 25 mixtures were almost all additive action at 20% and 80% effect point levels. At 50% effect, at least half of the 25 mixtures were slightly synergistic action, and the remaining mixtures were additive action. Furthermore, the ESs and CRCs predicted by CA and IA were all within the CIs of mixture observed ESs and CRCs, respectively. Therefore, the toxic interactions of these 25 mixtures were actually additive action. The joint toxicity of the three ILs can be effectively evaluated by the ES method. We also studied the relationship between the mixture toxicities and component concentration proportions. This study can provide reference data for IL risk assessment of combined pollution.

A novel liquid chromatography detector based on a dielectric barrier discharge molecular emission spectrometer with online microwave-assisted hydrolysis for determination of dithiocarbamates.

A novel detector for liquid chromatography (LC) for the determination of dithiocarbamate (DTC) fungicides is presented with a miniaturized dielectric barrier discharge-microplasma molecular emission spectrometer and an online microwave-assisted hydrolysis reactor. DTCs in the sample/standard solutions together with SnCl2 were pumped to the reactor to be converted to CS2 with high efficiency, which was then separated from the liquid phase and transformed for the detection of the specific molecular emission at 257.49 nm by the spectrometer. Under optimized conditions, the performance of this new detector was evaluated by its determination of different types of DTC including mancozeb, thiram, zineb, propineb, and metiram, and the limit of detection (LOD) values were found to be in the range 0.1-1.0 µg mL-1. The results from 20 test vegetable and fruit samples determined with the proposed method agreed well with those obtained using the standard headspace gas chromatography-electron capture detector (GC-ECD) method. Preliminary experimental results showed that the proposed method provided slightly higher LOD values than those obtained using GC-ECD. Most importantly, the new LC detector could detect each DTC chemical, whereas the traditional method could not distinguish between analytes of different subclasses of DTC.

Assessment of heavy metals in loose deposits in drinking water distribution system.

Heavy metal accumulation and potential releases from loose deposits in drinking water distribution system (DWDS) can have critical impacts on drinking water safety, but the associated risks have not been sufficiently evaluated. In this work, the potential biological toxicity of heavy metals in loose deposits was calculated based on consensus-based sediment quality guidelines, and the effects of some of the main water quality parameters, such as the pH and bicarbonate and phosphate content, on the release behaviors of pre-accumulated heavy metals were investigated. The results showed that heavy metals (Cu, As, Cr, Pb, and Cd) significantly accumulated in all the samples, but the contents of the heavy metals were multiple magnitudes lower than the Fe and Mn contents. The potential biotoxicity of As and Cu was relatively high, but the biotoxicity of Cd was negligible. The water quality can significantly influence the release of heavy metals from loose deposits. As the pH increased from 7.0 to 9.0, the release of As and Cr obviously increased. The release of As, Cu, Pb, and Cr also accelerated with the addition of phosphate (from 1 to 5 mg/L). In contrast to the trends for the pH and phosphate, variations in the bicarbonate content did not have a significant influence on the release of As and Cr. The release ratios of heavy metals in the samples were very low, and there was not a correlation between the release rate of the heavy metals in the loose deposits and their potential biotoxicity.

Dielectric barrier discharge carbon atomic emission spectrometer: universal GC detector for volatile carbon-containing compounds.

It was found that carbon atomic emission can be excited in low temperature dielectric barrier discharge (DBD), and an atmospheric pressure, low power consumption, and compact microplasma carbon atomic emission spectrometer (AES) was constructed and used as a universal and sensitive gas chromatographic (GC) detector for detection of volatile carbon-containing compounds. A concentric DBD device was housed in a heating box to increase the plasma operation temperature to 300 °C to intensify carbon atomic emission at 193.0 nm. Carbon-containing compounds directly injected or eluted from GC can be decomposed, atomized, and excited in this heated DBD for carbon atomic emission. The performance of this new optical detector was first evaluated by determination of a series of volatile carbon-containing compounds including formaldehyde, ethyl acetate, methanol, ethanol, 1-propanol, 1-butanol, and 1-pentanol, and absolute limits of detection (LODs) were found at a range of 0.12-0.28 ng under the optimized conditions. Preliminary experimental results showed that it provided slightly higher LODs than those obtained by GC with a flame ionization detector (FID). Furthermore, it is a new universal GC detector for volatile carbon-containing compounds that even includes those compounds which are difficult to detect by FID, such as HCHO, CO, and CO2. Meanwhile, hydrogen gas used in conventional techniques was eliminated; and molecular optical emission detection can also be performed with this GC detector for multichannel analysis to improve resolution of overlapped chromatographic peaks of complex mixtures.

Miniaturized dielectric barrier discharge carbon atomic emission spectrometry with online microwave-assisted oxidation for determination of total organic carbon.

A simple, rapid, and portable system consisted of a laboratory-built miniaturized dielectric barrier discharge atomic emission spectrometer and a microwave-assisted persulfate oxidation reactor was developed for sensitive flow injection analysis or continuous monitoring of total organic carbon (TOC) in environmental water samples. The standard/sample solution together with persulfate was pumped to the reactor to convert organic compounds to CO2, which was separated from liquid phase and transported to the spectrometer for detection of the elemental specific carbon atomic emission at 193.0 nm. The experimental parameters were systematically investigated. A limit of detection of 0.01 mg L(-1) (as C) was obtained based on a 10 mL sample injection volume, and the precision was better than 6.5% (relative standard deviation, RSD) at 0.1 mg L(-1). The system was successfully applied for TOC analysis of real environmental water samples. The obtained TOC value of 30 test samples agreed well with those by the standard high-temperature combustion coupled nondispersive infrared absorption method. Most importantly, the system showed good capability of in situ continuous monitoring of total organic carbon in environmental water.

Development of a highly sensitive aptamer-based electrochemical sensor for detecting saxitoxin based on K3Fe(CN)6 regulated silver nanoparticles.

BACKGROUND: Saxitoxin (STX) is the most toxic marine toxin, which can pose several adverse effects on human health. High sensitivity, fast response, and low-cost detection of STX contamination are of significance to reducing the fishery and seafood industries' loss. Among the various types of biosensors, the electrochemical biosensors have been extensively studied in the detection of STX, but the electrode surface modification material is easy to fall off, resulting in unstable electrochemical signals and poor reproducibility. It is imperative to have a ratiometric electrochemical biosensor for STX. RESULTS: In this study, we developed a novel aptamer-based electrochemical sensor (AECs) for the sensitive detection of STX based on a K3Fe(CN)6 regulated silver nanoparticles (Ag NPs) modified with aptamer. The AECs was constructed by immobilizing aptamer on Ag NPs surfaces. Under optimized conditions, the AECs showed a linear response towards STX in the range from 0.04 to 0.15 µM with the regression equation of Y = -8.0 + 233.7 X (R2 = 0.9956). The limit of detection (LOD) was calculated to be 1 nM (based on 3 N/S), which is significantly lower than the regulatory limits for STX in seafood. Moreover, the AECs showed excellent sensitivity, reproducibility and stability, as well as the detection in samples with acceptable recovery ranged from 71.2 % to 93.8 %, demonstrating its broad application prospects in detection of STX in seafood samples. SIGNIFICANCE: This work proposed an AECs to achieve sensitive detection of STX. A reaction system of K3Fe(CN)6 etched Ag NPs was introduced and used as the signal source to avoid the instability of the electrochemical signal, which can produce a ratiometric electrochemical signal output mode, improving the stability and sensitivity of electrochemical detection of STX.