On-line Fluorescence Detection Research Articles

Study of humic-like substances of dissolved organic matter using size exclusion chromatography and chemometrics

The study of dissolved organic matter (DOM) presents a significant challenge for environmental analyses and the monitoring of wastewater treatment plants (WWTPs). This is particularly true for the tracking of recalcitrant to biodegradation dissolved organic matter (rDOM) compounds, which is generated during the thermal pretreatment of sludge. This study aims to develop analytical and chemometric methods to differentiate melanoidins from humic acids (HAs), two components of rDOM that require monitoring at various stages of wastewater treatment processes due to their distinct biological effects. The developed method implements the separation of macromolecules through ultra-high-performance liquid chromatography size-exclusion chromatography (U-HPLC SEC) followed by online UV and fluorescence detection. UV detection was performed at 210, 254, and 280 nm, and fluorescence detection at six excitation/emission pairs: 230/355 nm, 270/355 nm, 240/440 nm, 270/500 nm, 330/425 nm, and 390/500 nm. Chromatograms obtained for each sample from these nine detection modes were integrated and separated into four molecular fractions: >40 kDa, 20–40 kDa, 10–20 kDa, and <10 kDa. To enhance analytical resolution and normalize the data, ratios were calculated from the areas of chromatographic peaks obtained for each detection mode. The results demonstrate the utility of these ratios in discriminating samples composed of HAs, melanoidins, and their mixtures, through principal component analysis (PCA). Low molecular weight fractions were found to be specific to melanoidins, while high molecular weight fractions were characteristic of HAs. For the detection modes specific to melanoidins, UV absorbance at 210, 254, and 280 nm were predominantly present in the numerators, with tryptophan-like fluorescence emissions in the denominators. Conversely, fluorescence emissions largely represented both numerators and denominators for HAs. This online method also enables the discrimination of pseudo-melanoidins, compounds revealing a nitrogen deficiency in their chemical structures.

Recent advances on nanomaterial-based glutathione sensors.

Glutathione (GSH) is one of the most common thiol-containing molecules discovered in biological systems, and it plays an important role in many cellular functions, where changes in physiological glutathione levels contribute to the progress of a variety of diseases. Molecular imaging employing fluorescent probes is thought to be a sensitive technique for online fluorescence detection of GSH. Although various molecular probes for (intracellular) GSH sensing have been reported, some aspects remain unanswered, such as quantitative intracellular analysis, dynamic monitoring, and compatibility with biological environment. Some of these drawbacks can be overcome by sensors based on nanostructured materials, that have attracted considerable attention owing to their exceptional properties, including a large surface area, heightened electro-catalytic activity, and robust mechanical resilience, for which they have become integral components in the development of highly sensitive chemo- and biosensors. Additionally, engineered nanomaterials have demonstrated significant promise in enhancing the precision of disease diagnosis and refining treatment specificity. The aim of this review is to investigate recent advancements in fabricated nanomaterials tailored for detecting GSH. Specifically, it examines various material categories, encompassing carbon, polymeric, quantum dots (QDs), covalent organic frameworks (COFs), metal-organic frameworks (MOFs), metal-based, and silicon-based nanomaterials, applied in the fabrication of chemo- and biosensors. The fabrication of nano-biosensors, mechanisms, and methodologies employed for GSH detection utilizing these fabricated nanomaterials will also be elucidated. Remarkably, there is a noticeable absence of existing reviews specifically dedicated to the nanomaterials for GSH detection since they are not comprehensive in the case of nano-fabrication, mechanisms and methodologies of detection, as well as applications in various biological environments. This research gap presents an opportune moment to thoroughly assess the potential of nanomaterial-based approaches in advancing GSH detection methodologies.

QuEChERS-assisted ion pair chromatography/fluorescence detection method for determination of antimigraine combination therapy in rabbit plasma samples: Application to a pharmacokinetic study

Antimigraine combination therapy has shown significant effectiveness in relieving pain, as well as reducing the frequency, duration, and severity of migraine attacks if compared to a single migraine medication. This work represents the first analytical investigation for emphasizing the synergistic effect of combining ophthalmic beta blockers with triptans in migraine treatment. The presented study was conducted to investigate the pharmacokinetic profile of almotriptan (ALM), a serotonin (5-HT1B/1D) receptor agonist used to treat migraine, when coadministered with timolol (TIM) or verapamil (VER) which are considered as an adjuvant therapy in migraine prevention. Ion pair chromatography (IPC) with online fluorescence detection was applied to simultaneously detect and quantify the binary mixtures of ALM/TIM and ALM/VER in rabbit plasma samples. The separation was achieved using a Platinum C18 analytical column with a mobile phase composed of methanol: 35 mmol L-1 phosphate buffer solution containing 10 mmol L-1 SDS at pH = 6.8 (60:40 v/v). Several parameters were evaluated during the optimization of separation conditions including mobile phase composition, buffer concentration, buffer pH and concentration of ion pair reagent. A thorough investigation of the retention mechanism was performed, and the results showed that Coulomb forces were the main contributors to the overall retention mechanism, which may be hydrophobically assisted. QuEChERS extraction technique was utilized to extract the investigated drugs from plasma samples and a detailed study was carried out to optimize partition/extraction solvents, pH, extraction salts, sample volume and clean-up step. The method had a limit of detection and quantitation of 5.6 and 16.9 ng mL-1 for ALM in ALM/TIM mixture and 2.5 and 7.6 ng mL-1 for ALM in ALM/VER mixture, with an overall recovery not less than 95.22%. This newly proposed method offers a faster alternative to existing chromatographic methods for extraction and determination of ALM in binary mixtures with TIM or VER in rabbit plasma and provides a platform for studying pharmacokinetic parameters. The coadministration of either TIM or VER with ALM resulted in a notable rise in Cmax (maximum plasma concentration) and AUC (area under the plasma concentration-time curve) of ALM, implying possible alterations in the absorption and overall exposure of ALM.

Blue, green and yellow carbon dots derived from pyrogenic carbon: Structure and fluorescence behaviour

Fluorescence lifetimes and quantum yields featuring polycyclic aromatic hydrocarbons (PAHs) and other organics constituting pyrogenic carbon particulate matter (PM) are seldom measured. In this work, PM sampled in a fuel-rich ethylene flame was firstly separated in organic carbon (OC), soluble in dichloromethane, and refractory organic carbon (ROC), soluble in N-methyl pyrrolidinone, and then analyzed by size exclusion chromatography (SEC) coupled with online UV and fluorescence detection, and by offline fluorescence spectroscopy and mass spectrometry. It was found that three classes of differently light emitting carbon dots (CDs) could be bottom-up synthesized in the same flame system by selecting appropriately the residence time. Actually, OC presented blue fluorescence regardless the residence time, whereas ROC sampled at low and high residence time emitted fluorescence in the green (green CDs) and in the yellow (yellow CDs) region, respectively. The SEC molecular weight of all CDs presented similar trimodal distributions, centered around 300, 1000 and 10,000 u. For the first time fluorescence lifetimes and quantum yields of pyrogenic CD fractions were measured as additional parameters useful for discriminating the fluorescent components and inferring their structural properties, with the support of mass spectrometry. The different spectroscopic features of CDs could be associated to different compositional characteristics as the polydispersity of molecular components featuring blue CDs, opposed to the oligomer-like nature of green and yellow CDs. Pyrogenic CDs showed different fluorescence emission ranges, quantum yield and lifetimes, appealing for their possible applications in the fields of imaging, electronics and sensors.

High-performance size exclusion chromatography with online fluorescence and multi-wavelength absorbance detection for isolation of high-purity carbon dots fractions, free of non-fluorescent material

The carbon dots (CDs) from natural nanographite oxide mixture (NGO-MIX) and from its fraction NGO (3.5-10K) recovered after ultrafiltration and dialysis were analyzed by 3D-excitation/emission matrix and high-performance size exclusion chromatography (HPSEC) combined with online fluorescence and absorbance detections. HPSEC chromatograms obtained simultaneously with absorption within the wavelength range 200-500 nm and fluorescence detection at λexc/λem = 270/450 nm/nm showed that NGO-MIX sample is not homogeneous and consist of well resolved CDs fractions with different sizes, absorption spectra and distinct fluorescence and non-fluorescence properties. Despite the twice higher fluorescence intensity of fraction NGO (3.5-10K) compared to the NGO-MIX, some impurity of non-fluorescent components was detected by HPSEC. The absorbance spectra of chromatographic peaks, extracted from the data of multi-wavelength absorbance detector, demonstrated different combinations of absorbance maxima. It means that different chromatographic peaks correspond to sized and chemically different CDs fractions. This study demonstrated for the first time the possibility of separating oxidized nanographite into homogeneous free from non-fluorescent material CDs fractions with their simultaneous spectroscopic characterization.

A modified method of on-line solid phase extraction and fluorometric detection for underway monitoring and onboard analysis of trace ammonium in seawater

A sensitive and automated method for underway and onboard analysis of trace ammonium in seawater was established using on-line solid phase extraction and fluorescence detection. Ammonium reacted with o-phthalaldehyde and sulfite to produce isoindole derivative that was concentrated on a hydrophilic lipophilic balanced (HLB) cartridge and then rapidly eluted with ethanol and measured using a fluorescence detector. The work was modified from our previous developed method, where 30 mL of a seawater sample was introduced into a reaction bottle with a 10 mL pipette. In the modified method a 10 mL sample loop was adopted for sample introduction to reduce possible contamination caused by manual operation. More importantly, the present method makes underway monitoring much more automatic. The detection limit was 3.5 nmol L−1, and the relative standard deviation was 3.52% (n = 12) for a sample spiked with 40 nmol L−1 ammonium standard. The method was free of the effects of salinity, carry-over and dissolved organic matter, with recoveries between 94.0% and 106.1%. An equation was introduced to correct matrix effects, and pure water and seawater blank were found to be equivalent to ammonium concentration of 8.1 ± 2.2 nmol L−1 and 6.0 ± 0.8 nmol L−1, respectively. The correction method can also be introduced to determination of other trace analytes where matrix effect cannot be neglected. A technique of stopped-flow was adopted and stopped-flow time could be adjusted depending on the concentration of ammonium in the seawater samples. The sample throughput was 7–9 h−1, and the method permitted the analysis of samples over a wide range of concentrations. The modified method has been successfully applied for shipboard underway determination of ammonium in a coastal area and shipboard determination the ammonium concentration of discrete samples in three vertical profiles during a cruise in the South China Sea.

Detection and phenotyping of extracellular vesicles by size exclusion chromatography coupled with on-line fluorescence detection

New methods for quantifying extracellular vesicles (EVs) in complex biofluids are critically needed. We report the development of a new technology combining size exclusion chromatography (SEC), a commonly used EV purification technique, with fluorescence detection of specifically labelled EVs. The resulting platform, Flu-SEC, demonstrates a linear response to concentration of specific EVs and could form the basis of a system with phenotyping capability. Flu-SEC was validated using red blood cell derived EVs (REVs), which provide an ideal EV model with monodisperse size distribution and high EV concentration. Microfluidic Resistive Pulse Sensing (MRPS) was used to accurately determine the size distribution and concentration of REVs. Anti-CD235a antibody, specific to glycophorin A, and the more general wheat germ agglutinin (WGA), were selected to label REVs. The results show the quantitative power of Flu-SEC: a highly linear fluorescence response over a wide range of concentrations. Moreover, the Flu-SEC technique reports the ratio of EV-bound and free-antibody molecules, an important metric for determining optimal labelling conditions for other applications. Flu-SEC represents an orthogonal tool to single-particle fluorescent methods such as flow cytometry and fluorescent NTA, for the quantification and phenotyping of EVs.

A magneto-microfluidic platform for fluorescence immunosensing using quantum dot nanoparticles

This study reports the online fluorescent detection of carcinoembryonic antigen (CEA) and α-fetoprotein (AFP) biomarker proteins in microfluidic channels using functional nanoparticles. Functional magnetic nanoparticles labeled with two antibodies were predeposited on separated microfluidic channels. Antigens were passed through each microfluidic channel to react with the respective antibodies. Two types of fluorescent nanoparticles labeled with antibodies were then used to detect and confirm antigens in the immunocomplex. Results indicate that online fluorescent detection of proteins can provide advantages for real-time monitoring and diagnostic applications. The running time was less than 20 min for each trial. The detection limits of CEA and AFP were found to be 0.6 and 0.2 pg ml−1. These detection limits are lower than those of ELISA. The linear ranges of CEA and AFP detection were from 1.8 pg ml−1 to 1.8 ng ml−1 and from 0.68 pg ml−1 to 0.68 ng ml−1 for two deposition zones in a magnetic sandwich immunoassay. The linear ranges of this method are wider than those of ELISA and those of most other methods. The measurements of CEA and AFP in serum samples from this method differed from ELISA results by 11% and 9.4%, respectively. The detection limit of online detection has achieved the same range as those of previous offline detection. This method has a good potential for automation and multichannel analysis to increase the throughput with some modifications in the future. The proposed method can provide simple, fast, and sensitive online detection for biomarkers.

A rapid microfluidic platform with real-time fluorescence detection system for molecular diagnosis

The development of microfluidics-based quantitative real-time polymerase chain reaction for molecular diagnosis is becoming a burgeoning field of research. Here, we present a compact microfluidic real-time PCR platform integrated with a thermal cycler and an online fluorescence detection module, including a disposable microfluidic chip fabricated in polydimethylsiloxane. The fluorescence detection module is able to continuously monitor the PCR reaction in the microfluidic chip over thermal cycles, and a large amount of signal data can be rapidly analysed by a built-in computer. In order to further evaluate the performance of the developed PCR platform, we carried out a series of systemic verifications, such as precision of temperature control, sensitivity and specificity. Under the optimal conditions, the limit of detection of the target molecule reached approximately 1.0 × 102 copies/µL, with a correlation coefficient of 0.9966. In addition, hepatitis B virus could be detected quickly by this real-time PCR system in about half an hour. Furthermore, the faint target fluorescence signal emitted from the digital microfluidic chip, which contains thousands of micro-reaction chambers with a volume of 100 pL, could be easily detected on this microfluidic platform. Overall, the results indicated that the developed microfluidic PCR platform can be used for sensitive and specific detection in molecular diagnosis. More importantly, owing to adopting the pattern of modularization design, this platform is considerably compact and portable. If necessary, special custom-made chips could be cooperated with this portable platform to satisfy the needs of various molecular detection tests.

Fluorimetric detection of reserpine in mouse serum through online post-column electrochemical derivatization

A novel method combining high-performance liquid chromatography with online post-column electrochemical derivatization and fluorescence detection was established for the detection of reserpine in mouse serum. Reserpine separation was conducted using a C18 column with 5 mM H3PO4 and acetonitrile (55/45, v/v) as eluent. Reserpine was then electro-oxidized into a strongly fluorescent compound using an electrolytic cell device. Detection parameters, such as potential and fluorescence wavelength, were optimized. The linearity of the proposed method ranged from 0.01 to 5.0 mg l−1 with a correlation coefficient of 0.9997. The limit of qualification (S/N = 10) and limit of detection (S/N = 3) were 9.7 and 2.9 µg l−1, respectively. Resperine recoveries from spiked blank and drug-treated mouse serum samples ranged from 92.0 to 115%.

Simultaneous Determination of Polycyclic Aromatic Hydrocarbons and Their Nitro-derivatives in Airborne Particulates by Using Two-dimensional High-performance Liquid Chromatography with On-line Reduction and Fluorescence Detection

Simultaneous Determination of Polycyclic Aromatic Hydrocarbons and Their Nitro-derivatives in Airborne Particulates by Using Two-dimensional High-performance Liquid Chromatography with On-line Reduction and Fluorescence Detection

Oligosaccharide mapping of heparinase I-treated heparins by hydrophilic interaction liquid chromatography separation and online fluorescence detection and electrospray ionization-mass spectrometry characterization

Oligosaccharide mapping based on enzyme cleavage provides a useful molecular fingerprint of the heparin structure revealing detailed structural information regarding its sequence and the content of part of the ATIII-binding region. This approach is performed by strong-anion exchange (SAX)-HPLC separation which is incompatible with MS requiring purification of oligosaccharides for their conclusive identification. We report a novel oligosaccharide mapping strategy based on the HILIC separation of the main heparin disaccharides/oligosaccharides released by heparinase I, fluorotagged with 2-aminoacridone and on-line detected by a fluorescence detector and characterized by ESI–MS. The application of a polar solvent having a high pH with acetonitrile avoided desulfation enabling a simple and accurate structural oligosaccharide assignment. Oligosaccharide mapping, or merely complete disaccharide composition, may be performed on nanogram-scale by the fluorescence detector vs micrograms useful for classical SAX-HPLC. Additionally, only widely commercially available heparin lyase I is necessary, without the use of expensive heparinases II and III. Contrary to SAX-HPLC, this novel HILIC approach is able to separate and identify the saturated trisulfated disaccharide belonging to the non-reducing end of heparin chains. Finally, the content of 3-O-sulfo groups of the ATIII-binding region is determined.

Quantification of amyloid fibrils using size exclusion chromatography coupled with online fluorescence and ultraviolet detection

An amyloid fibrils investigation within biofilm samples requires distinguishing the amyloid β-sheet structure of these proteins and quantifying them. In this study, the property of amyloids to incorporate the fluorescent dye Thioflavin T has been exploited to propose a method of quantification. The experimental protocol includes the preparation of amyloids from commercial κ-casein (κCN) and their fractionation through size exclusion chromatography (SEC) to provide calibration curves from fluorescence and absorbance signals. Finally, a bacterial biofilm extract was injected into SEC, and the amyloid fibrils could be expressed as equivalent κCN, representing approximately 21% of the total proteins.

Combining asymmetrical flow field-flow fractionation with on- and off-line fluorescence detection to examine biodegradation of riverine dissolved and particulate organic matter

This study demonstrated that asymmetrical flow field-flow fractionation (AF4) coupled with on-line UV and fluorescence detection (FLD) and off-line excitation-emission matrix (EEM) fluorescence spectroscopy can be employed to analyze the influence of microbial metabolic activity on the consumption and production of freshwater organic matter. With the AF4 system, organic matter is on-line enriched during a focusing/relaxation period, which is an essential process prior to separation. Size-fractionated chromophoric and fluorophoric organic materials were simultaneously monitored during the 30-min AF4 separation process. Two fractions of different sizes (dissolved organic matter (DOM) and particulate organic matter (POM)) of freshwater samples from three locations (up-, mid-, and downstream) along the Han River basin of Korea were incubated with the same inoculum for 14 days to analyze fraction-specific alterations in optical properties using AF4-UV-FLD. A comparison of AF4 fractograms obtained from pre- and post-incubation samples revealed that POM-derived DOM were more susceptible to microbial metabolic activity than was DOM. Preferential microbial consumption of protein-like DOM components concurred with enhanced peaks of chromophoric and humic-like fluorescent components, presumably formed as by-products of microbial processing. AF4-UV-FLD combined with off-line identification of microbially processed components using EEM fluorescence spectroscopy provides a powerful tool to study the relationship between microbial activity and composition as well as biodegradability of DOM and POM-derived DOM from different origins, especially for the analysis of chromophoric and fluorophoric organic matter that are consumed and produced by microbial metabolic activity. The proposed AF4 system can be applied to organic matter in freshwater samples having low concentration range (0.3–2.5ppm of total organic carbon) without a pre-concentration procedure.

Determination of chemotherapeutic drugs in human urine by capillary electrophoresis with UV and fluorimetric detection using solid-supported liquid-liquid extraction for sample clean-up.

Capillary electrophoresis was used for the rapid determination of three chemotherapeutic drugs employed to treat colorectal cancer: irinotecan, tegafur, and leucovorin, and their main metabolites (7-ethyl-10-hydroxycamptothecin and 5-fluorouracil), in human urine samples. A phosphate buffer (pH 11.34; 20 mM) was selected as the background electrolyte. A hydrodynamic injection (9 s, 30 mbar) was applied and the separation was carried out using a separation temperature and voltage of 25°C and 25 kV, respectively. A capillary with two detection windows for serial online UV and fluorescence detection was satisfactorily employed. A solid-supported liquid-liquid extraction procedure was optimized for the clean-up of the urine samples and the extraction of the analytes. Matrix effects were assessed and signal suppression was observed for three of the analytes, thus, matrix-matched calibration was used for compensating residual matrix effects on these analytes. The proposed method allows the separation and quantification of the chemotherapeutics in less than 6 min. Detection limits range between 0.01 and 0.30 mg/L. The method was satisfactorily applied to the determination of the target compounds in human urine samples, with recoveries of 92.4-107.7%.

Evaluation of Suwannee River NOM electrophoretic fractions by RP-HPLC with online absorbance and fluorescence detection.

Reversed-phase high-performance liquid chromatography (RP-HPLC) with online absorbance and fluorescence detections was used for the evaluation of Suwannee River natural organic matter (SRNOM) and its fractions A, B, and C+D, obtained by conventional size exclusion chromatography-polyacrylamide gel electrophoresis (SEC-PAGE) setup, for which the electrophoretic mobility (EM) and the absorptivity varied in the order C+D > B > A, and the molecular size (MS) in the opposite order. Analysis of SRNOM and its fractions in part of their relative irreversible adsorption on C18-column and relative distribution of eluted from the column matter on hydrophobic and hydrophilic peaks showed that hydrophobicity of fractions decreased in order: A > B > C+D. The online fluorescence detection showed that SRNOM and its fractions contained at least three groups of humic substances (HS)-like fluorophores with emission maxima at 435, 455-465, and 455/420nm and two protein-like fluorophores with emission maxima at around 300 and 340nm. The HS-like fluorophore with emission maximum at 435nm was located in the hydrophilic peak in all the samples. Those with maxima at 455-465nm were detected in hydrophobic peaks of fractions A and B. SEC-PAGE setup followed by RP-HPLC allowed us to develop new approach of SRNOM separation on less heterogeneous compounds mixture for their further study and structural identification.

RP-HPLC and spectroscopic characterization of Suwannee River water NOM after concentrated urea treatment and dialysis

Suwannee River natural organic matter (SRNOM) was treated by 7M urea and then purified by dialysis on 10 kDa membrane. The untreated SRNOM and treated (USRNOM) samples were examined using UV–visible and fluorescence spectroscopies and reversed-phase high-performance liquid chromatography (RP-HPLC) with online absorbance and fluorescence detection. USRNOM was 1.5-fold more absorbing at 280nm than SRNOM and four fold less fluorescent than SRNOM upon excitation at 270 nm. RP-HPLC analyses of the two samples revealed that USRNOM was somewhat more hydrophobic than SRNOM and both samples contained at least two groups of HS-like fluorophores with different hydrophobicity and protein-like fluorophore(s). Data indicate that protein-like fluorophores were not lost during dialysis. They showed hydrophobic properties and seemed highly fluorescent. HS-like and protein-like fluorophores from water NOM could be successfully separated by RP-HPLC. This raises the prospect of their further research and identification and could be significant for future NOM chemical structure characterization.

Development of microcolumn-based one-site immunometric assays for protein biomarkers

One-site immunometric assays that utilize affinity microcolumns were developed and evaluated for the analysis of protein biomarkers. This approach used labeled antibodies that were monitored through on-line fluorescence or near-infrared (NIR) fluorescence detection. Human serum albumin (HSA) was utilized as a model target protein for this approach. In these assays, a fixed amount of labeled anti-HSA antibodies was mixed with samples or standards containing HSA, followed by the injection of this mixture onto an HSA microcolumn to remove excess antibodies and detect the non-retained labeled antibodies that were bound to HSA from the sample. The affinity microcolumns were 2.1mm i.d. ×5mm and contained 8–9nmol of immobilized HSA. These microcolumns were used from 0.10 to 1.0mL/min and gave results within 35s to 2.8min of sample injection. Limits of detection down to 0.10–0.28ng/mL (1.5–4.2pM) or 25–30pg/mL (0.38–0.45pM) were achieved when using fluorescein or a NIR fluorescent dye as the label, with an assay precision of ±0.1–4.2%. Several parameters were examined during the optimization of these assays, and general guidelines and procedures were developed for the extension of this approach for use with other types of affinity microcolumns and protein biomarkers.

Simultaneous determination of aflatoxins B₁, B₂, G₁, G₂ in Fructus Bruceae by high-performance liquid chromatography with online postcolumn photochemical derivatization.

A simple, reliable, and highly sensitive method for the simultaneous determination of aflatoxin B1 , B2 , G1 , G2 in Fructus Bruceae was developed using high-performance liquid chromatography coupled to online postcolumn photochemical derivatization and fluorescence detection. Aflatoxins were first extracted by a methanol/water mixture and then cleaned up with an AflaTest™ immunoaffinity column. Different clean-up and derivatization methods were compared and optimized. The established method was extensively validated to show satisfactory performance of linearity (R(2) ≥ 0.9997), recovery (74.3-100.8%), and precision (RSDs ≤ 2.8%) for the investigated aflatoxins. This proposed method was also applied to 11 F. Bruceae samples and the results showed that 10 out of 11 were contaminated with aflatoxins ranging from 0.26 to 27.52 μg/kg and the occurrence of aflatoxin B1 , the most toxic one, was as high as 91% in all the samples, highlighting the severe contamination and the necessity to set legal limits for aflatoxins in F. Bruceae.

Application of a fully integrated photodegradation-detection flow-batch analysis system with an on-line preconcentration step for the determination of metsulfuron methyl in water samples

This work presents the development of a fully automated flow-batch analysis (FBA) system as a new approach for on-line preconcentration, photodegradation and fluorescence detection in a lab-constructed mixing chamber that was designed to perform these processes without sample dispersion. The system positions the mixing chamber into the detection system and varies the instrumental parameters according to the required photodegradation conditions. The developed FBA system is simple and easily coupled with any sample pretreatment without altering the configuration.This FBA system was implemented to photodegrade and determine the fluorescence of the degradation products of metsulfuron methyl (MSM), a naturally non-fluorescent herbicide of the sulfonylurea׳s family. An on-line solid phase extraction (SPE) and clean up procedure using a C18 minicolumn was coupled to the photodegradation-detection mixing chamber (PDMC) that was located in the spectrofluorometer. An enrichment factor of 27 was achieved.Photodegradation conditions have been optimized by considering the influence of the elution solvent on both the formation of the photoproduct and on the fluorescence signal.Under optimal conditions, the calibration for the MSM determination was linear over the range of 1.00–7.20µgL−1. The limit of detection (LOD) was 0.28µgL−1; the relative standard deviation was 2.0% and the sample throughput for the entire process was 3h−1. The proposed method was applied to real water samples from the Bahía Blanca׳s agricultural region (Bahía Blanca, Buenos Aires, Argentina). This method obtained satisfactory recoveries with a range of 94.7–109.8%.