Recent Advances in On-line Mass Spectrometry Toolbox for Mechanistic Studies of Organic Electrochemical Reactions.

Electrochemical reactions are very complex and involve a variety of physicochemical processes. Accurate and systematic monitoring of intermediate process changes during the reaction is essential for understanding the mechanism of electrochemical reactions and is the basis for rational design of new electrochemical reactions. On-line electrochemical analysis based on mass spectrometry (MS) has become an important tool for studying electrochemical reactions. This technique is based on different ionization and sampling means and realizes on-line analysis of electrochemical reactions by establishing electrochemistry-MS (EC-MS) coupling devices. In particular, it provides key evidence for elucidating the reaction mechanism by capturing and identifying the reactive reaction intermediates. This review will categorize various EC-MS devices and the organic electrochemical reaction systems they study, highlighting the latest research progress in recent years. It will also analyze the properties of various devices and look forward to the future development of EC-MS.

Functionalized carbon nanotube-polyaniline composite coating for on-line microextraction on a screw coupled with high performance liquid chromatography to determine opium alkaloids.

A novel and efficient on-line microextraction on a screw coupled with high-performance liquid chromatography with an ultraviolet-visible detector was developed to extract and determine trace quantities of five opium alkaloids. All detections of the analytes were achieved at 210 nm. The surface of the screw grooves was electrochemically coated with the carbon nanotubes-COOH/polyaniline composite. The surface characterization was assessed by Fourier transform infrared spectroscopy and field emission scanning electron microscopy. The prepared screw was inserted into a cartridge of a guard column, and then the constructed microextraction on a screw device was placed in the loop of a six-port HPLC injection valve. The parameters affecting the extraction efficiency of the analytes were optimized using the one variable-at-a-time method. The effective parameters for the extraction efficiency of the analytes, including sample volume, extraction time, sampling flow rate, desorption solvent type, ionic strength, and pH were investigated and optimized. Under optimal conditions, the detection limits were 3-10 µg L-1, and the linear dynamic ranges were 10-2000 µg L-1 with a coefficient of determination greater than 0.9940. The inter-day and intra-day (n = 3) relative standard deviations were less than 7% and 5%, respectively. The proposed method was simple and reproducible, with an acceptable relative recovery (90-108%) for determining opium alkaloids in water and urine samples.

Functional Femtoliter Droplets for Ultrafast Nanoextraction and Supersensitive Online Microanalysis.

A universal femtoliter surface droplet-based platform for direct quantification of trace of hydrophobic compounds in aqueous solutions is presented. Formation and functionalization of femtoliter droplets, concentrating the analyte in the solution, are integrated into a simple fluidic chamber, taking advantage of the long-term stability, large surface-to-volume ratio, and tunable chemical composition of these droplets. In situ quantification of the extracted analytes is achieved by surface-enhanced Raman scattering (SERS) spectroscopy by nanoparticles on the functionalized droplets. Optimized extraction efficiency and SERS enhancement by tuning droplet composition enable quantitative determination of hydrophobic model compounds of rhodamine 6G, methylene blue, and malachite green with the detection limit of 10-9 to 10-11 m and a large linear range of SERS signal from 10-9 to 10-6 m of the analytes. The approach addresses the current challenges of reproducibility and the lifetime of the substrate in SERS measurements. This novel surface droplet platform combines liquid-liquid extraction and highly sensitive and reproducible SERS detection, providing a promising technique in current chemical analysis related to environment monitoring, biomedical diagnosis, and national security monitoring.

A porous organic polymer with magnetic nanoparticles on a chip array for preconcentration of platinum(IV), gold(III) and bismuth(III) prior to their on-line quantitation by ICP-MS.

A chip-based array is described for magnetic solid-phase microextraction (MSPME) of the ions of Pt, Au and Bi. Magnetic porous organic polymers (MOPs) prepared from magnetite nanoparticles and 1,3,5-tris(4-aminophenyl)benzene are introduced as a novel adsorbent. Eight solid phase extraction columns packed with MOPs were integrated in parallel on a microfluidic chip for array microextraction. After elution with a 12% (m/v) solution of cysteamine hydrochloride (pH 8.0), the eluent is introduced into an ICP-MS instrument for quantification. Under the optimized conditions, the limits of detection for Pt, Au and Bi are 8.6, 4.4 and 3.4 ng L-1, respectively. The sample throughput is 7 h-1, and the adsorption capacities are 32, 24 and 24 µg mg-1 for Pt, Au and Bi, respectively. The method was validated by the determination of Bi in a certified reference material (GSH-1A; human hair), and the values obtained coincided with the certified value. This method was also applied to the determination of Pt, Au and Bi in (spiked) urine and cell samples, and good recoveries (85.8-113%) were achieved. The method is highly sensitive and has a high throughput and a low sample/reagent consumption (with 500 HeLa cells consumed). Graphical abstract Schematic presentation of the magnetic packed column, microfluidic chip, and online chip-based MSPME-ICPMS system. Design sketch of the online system: microextraction unit (blue lines), microvalves (black lines), outlet channels (yellow lines), permanent magnets (red), urine and cell samples.

Determination of major aromatic constituents in vanilla using an on-line supercritical fluid extraction coupled with supercritical fluid chromatography.

An on-line supercritical fluid extraction coupled with supercritical fluid chromatography method was developed for the determination of four major aromatic constituents in vanilla. The parameters of supercritical fluid extraction were systematically investigated using single factor optimization experiments and response surface methodology by a Box-Behnken design. The modifier ratio, split ratio, and the extraction temperature and pressure were the major parameters which have significant effects on the extraction. While the static extraction time, dynamic extraction time, and recycle time had little influence on the compounds with low polarity. Under the optimized conditions, the relative extraction efficiencies of all the constituents reached 89.0-95.1%. The limits of quantification were in the range of 1.123-4.747 µg. The limits of detection were in the range of 0.3368-1.424 µg. The recoveries of the four analytes were in the range of 76.1-88.9%. The relative standard deviations of intra- and interday precision ranged from 4.2 to 7.6%. Compared with other off-line methods, the present method obtained higher extraction yields for all four aromatic constituents. Finally, this method has been applied to the analysis of vanilla from different sources. On the basis of the results, the on-line supercritical fluid extraction-supercritical fluid chromatography method shows great promise in the analysis of aromatic constituents in natural products.

On-line approaches for the determination of residues and contaminants in complex samples.

The determination of residues and contaminants in complex matrices such as in the case of food, environmental, and biological samples requires a combination of several steps to succeed in the aimed goal. At least three independent steps are integrated to provide the best available situation to deal with such matrices: (1) a sample preparation technique is employed to isolate the target compounds from the rest of the matrix; (2) a chromatographic (second) step further "purifies" the isolated compounds from the co-extracted matrix interferences; (3) a spectroscopy-based device acts as chromatographic detector (ideally containing a tandem high-resolution mass analyzer) for the qualitative and quantitative analysis. These techniques can be operated in different modes including the off-line and the on-line modes. The present report focus the on-line coupling techniques aiming the determination of analytes present in complex matrices. The fundamentals of these approaches as well as the most common set ups are presented and discussed, as well as a review on the recent applications of these two approaches to the fields of bioanalytical, environmental, and food analysis are critically discussed.

Recent approaches for on-line analysis of residues and contaminants in food matrices: A review.

This review highlights recent developments for on-line determination of residues and contaminants in complex matrices such as food samples. This involves the on-line coupling of a sample preparation technique (as the first "dimension") with a chromatographic system (second "dimension"), usually followed by mass spectrometry. Although frequently treated as quite distinct techniques, the role of all devices utilized as the first dimension in this approach aims to decrease the sample complexity while eliminating as much as possible the matrix contaminants to facilitate the qualitative and quantitative determination of the compounds of interest. This review will focus on the following techniques as the first dimension: (i) on-line solid-phase extraction; (ii) in-tube solid-phase microextraction; (iii) matrix solid-phase dispersion; and (iv) turbulent flow chromatography. The second dimension is usually performed using a chromatographic column to isolate the analyte(s) of interest for further mass spectrometry determination. A description of the basis of this on-line approach and its distinct set up possibilities is presented, which is followed by a critical review of the literature covering this subject in the last ten years (focusing on the last five years) with emphasis on the analysis of residue and contaminants in food samples.

Discriminative Power of Handwriting and Drawing Features in Depression.

This study contributes knowledge on the detection of depression through handwriting/drawing features, to identify quantitative and noninvasive indicators of the disorder for implementing algorithms for its automatic detection. For this purpose, an original online approach was adopted to provide a dynamic evaluation of handwriting/drawing performance of healthy participants with no history of any psychiatric disorders ([Formula: see text]), and patients with a clinical diagnosis of depression ([Formula: see text]). Both groups were asked to complete seven tasks requiring either the writing or drawing on a paper while five handwriting/drawing features' categories (i.e. pressure on the paper, time, ductus, space among characters, and pen inclination) were recorded by using a digitalized tablet. The collected records were statistically analyzed. Results showed that, except for pressure, all the considered features, successfully discriminate between depressed and nondepressed subjects. In addition, it was observed that depression affects different writing/drawing functionalities. These findings suggest the adoption of writing/drawing tasks in the clinical practice as tools to support the current depression detection methods. This would have important repercussions on reducing the diagnostic times and treatment formulation.

Pressurized liquid extraction assisted by high-intensity ultrasound to obtain hesperidin from lime waste: Integration of in-line purification and on-line chromatographic analysis.

Hesperidin is a phenolic compound usually found in citrus fruits, which is known for its anti-inflammatory and antioxidant properties. This bioactive compound has already been used to formulate medications to treat chronic venous insufficiency. In this work, through a system which allows the in-line coupling of the pressurized liquid extraction (PLE) and high-intensity ultrasound (HIUS) with solid phase extraction (SPE), and analysis by high-performance liquid chromatography with UV-Vis detector (HPLC-UV) in on-line mode, a method was developed to obtain, separate, and quantify hesperidin from the industrial waste of lime. An eco-friendly approach with water and ethanol as extraction solvents was used. Parameters such as temperature (80, 100, and 120 °C) and HIUS power (0, 200, and 400 W) were evaluated regarding hesperidin yield. In this context, the higher hesperidin yield (18.25 ± 1.52 mg/g) was achieved using water at a subcritical state (120 °C and 15 MPa). The adsorbent SepraTM C-18-E isolated hesperidin from the other extracted compounds employing 50% ethanol in the SPE elution. The possibility ofon-lineanalysis coupling a high-performance liquid chromatograph to an ultraviolet detector (HPLC-UV) system was studied and shown to be a feasible approach for developing integrated technologies. Conventional extractions and their antioxidant capacities were evaluated, highlighting the advantages of the HIUS-PLE-SPE extractive method. Furthermore, the on-linechromatographic analysis showed the potential of the HIUS-PLE-SPE- HPLC-UV system to quantify the extracted compounds in real time.

An on-line sample pretreatment technique for the HPLC analysis of plant samples.

A continuous-flow, on-line sample pretreatment technique using a silica gel microsyringe extractor has been developed. All steps including extraction, separation, clean-up, and concentration occur in the microsyringe. The overall sample pretreatment process takes <10 min per sample. Different polarity chemicals in the plant sample are successively extracted and separated, and analyzed in parallel using HPLC-UV and HPLC-UV-MS/MS. Polycyclic aromatic hydrocarbons, alkylphenols, and plant hormones were determined as model compounds for nonpolar, intermediate polarity, and polar fractions, respectively. All the parameters that influence the extraction and separation efficiency of the microsyringe extractor have been optimized and evaluated. Under the optimized conditions, recoveries of target compounds ranged from 78.4 to 101.9%, the RSD was <12.8% and the square of the correlation coefficient was >0.99. Complex plant samples of Sambucus Mandshurica Kitag have been tested using this method. Fluorene, phenanthrene, pyrene, and plant hormones were detected in all the samples, and concentrations ranged from 24.2-34.9, 43.8-67.1, 25.9-29.2, and 14.5~110.8 ng/g, respectively.

Automated quality analysis in continuous downstream processes for small-scale applications.

Development of integrated, continuous biomanufacturing (ICB) processes brings along the challenge of streamlining the acquisition of data that can be used for process monitoring, product quality testing and process control. Manually performing sample acquisition, preparation, and analysis during process and product development on ICB platforms requires time and labor that diverts attention from the development itself. It also introduces variability in terms of human error in the handling of samples. To address this, a platform for automatic sampling, sample preparation and analysis for use in small-scale biopharmaceutical downstream processes was developed. The automatic quality analysis system (QAS) consisted of an ÄKTA Explorer chromatography system for sample retrieval, storage, and preparation, as well as an Agilent 1260 Infinity II analytical HPLC system for analysis. The ÄKTA Explorer system was fitted with a superloop in which samples could be stored, conditioned, and diluted before being sent to the injection loop of the Agilent system. The Python-based software Orbit, developed at the department of chemical engineering at Lund university, was used to control and create a communication framework for the systems. To demonstrate the QAS in action, a continuous capture chromatography process utilizing periodic counter-current chromatography was set up on an ÄKTA Pure chromatography system to purify the clarified harvest from a bioreactor for monoclonal antibody production. The QAS was connected to the process to collect two types of samples: 1) the bioreactor supernatant and 2) the product pool from the capture chromatography. Once collected, the samples were conditioned and diluted in the superloop before being sent to the Agilent system, where both aggregate content and charge variant composition were determined using size-exclusion and ion-exchange chromatography, respectively. The QAS was successfully implemented during a continuous run of the capture process, enabling the acquisition of process data with consistent quality and without human intervention, clearing the path for automated process monitoring and data-based control.

Simultaneous extraction and analysis of apple pomace by gradient pressurized liquid extraction coupled in-line with solid-phase extraction and on-line with HPLC.

Due to the complex characteristics and variable composition of apple pomace, sample preparation for chromatographic analysis is a great challenge. To solve this problem, we proposed using a solvent gradient using Pressurized Liquid Extraction (PLE), where the solvent gradually changes from water to ethanol during the extraction. Different dynamic gradients, static time, and temperatures were evaluated and showed relevant effects on the yields of target analytes. It was possible to improve extraction yields of compounds with different characteristics using the extraction solvent gradient. By coupling solid-phase extraction in-line, it was possible to separate compounds into fractions, where furfural, HMF, and chlorogenic acid gradually eluted from the adsorbent. At the same time, flavonoids were retained and eluted in the later fractions. On-line analysis by HPLC provided real-time information about the process and permitted the creation of a 3D chromatogram of the sample.

On-Line Monitoring of Enzymatic Degumming of Soybean Oil Using Near-Infrared Spectroscopy.

Degumming is an oil refinement process in which the naturally occurring phospholipids in crude vegetable oils are removed. Enzymatic degumming results in higher oil yield and more cost-efficient processing compared to traditional degumming processes using only water or acid. Phospholipase C hydrolyses phospholipids into diglycerides and phosphate groups during degumming. The diglyceride content can therefore be considered a good indicator of the state of the enzymatic reaction. This study investigates the use of near-infrared (NIR) spectroscopy and chemometrics to monitor the degumming process by quantifying diglycerides in soybean oil in both off-line and on-line settings. Fifteen enzymatic degumming lab scale batches originating from a definitive screening design (with varying water, acid, and enzyme dosages) were investigated with the aim to develop a NIR spectroscopy prediction method. By applying tailored preprocessing and variable selection methods, the diglyceride content can be predicted with a root mean square error of prediction of 0.06% (w/w) for the off-line set-up and 0.07% (w/w) for the on-line set-up. The results show that the diglyceride content is a good indicator of the enzyme performance and that NIR spectroscopy is a suitable analytical technique for robust real-time diglyceride quantification.

Pressurized liquid extraction coupled in-line with SPE and on-line with HPLC (PLE-SPExHPLC) for the recovery and purification of anthocyanins from SC-CO2 semi-defatted Açaí (Euterpe oleracea).

This study aimed to extract anthocyanins from dried and semi-defatted açaí pulp using green technologies based on the coupling of pressurized liquid extraction (PLE) with in-line purification through solid-phase extraction (SPE) and on-line analysis by high-performance liquid chromatography (HPLC). Critical parameters that affect the extraction efficiency and purification were investigated and optimized by response surface methodology (RSM). PLE was performed with acidified water at different pH (2.0, 4.5, and 7.0) and temperatures (40, 80, and 120 °C) at 15 MPa, 2 mL/min, and solvent-to-feed mass ratio equal to 40. SPE was optimized in a column packed with the adsorbent PoraPak™ Rxn. Different ethanol concentrations (50, 75, and 100 %) and temperatures (30, 40, and 50 °C) were evaluated for the anthocyanin's elution. The optimal conditions of the two experimental designs were determined by the RSM, firstly for PLE: 71 °C and pH 2; then using this PLE condition, the optimization of the SPE was obtained: 30 °C and 50 % ethanol. The developed PLE method provided similar anthocyanin yield to other techniques, and the coupling with SPE in-line produced an extract 5-fold more concentrated than PLE alone. Therefore, the system (PLE-SPE × HPLC-PDA) proved to be a powerful tool for monitoring the extraction process in real-time.

Flowing on-line preparation of deglycosylation, labeling and purification for N-glycan analysis.

The current in-solution analysis of N-glycans suffers from several disadvantages including tedious de-glycosylation time and multi-step pre-treatment procedures. Here, an ultra-simple flowing on-line analysis of labeled N-glycans for high-performance liquid chromatography with fluorescence detection (HPLC-FLD) was developed for eliminating the deficiencies. This on-line analysis consisted of an immobilized enzyme reactor (IMER) of PNGase F for efficient release of N-glycans, labeling of released N-glycans and following purification of derivatives on microfluidic chip. Notably, efficient preparations for all type of N-glycans were completed within ∼30 min. To our best knowledge, this is the first time to integrated the whole preparation of N-glycan deglycosylation, labeling and purification only by a simple fluidic flow with our developed device. Good reproducibility and stability were achieved with the relative standard deviation (RSD) less than 10%. Furthermore, the glycome studies with human serum revealed a good adaptability for biological samples. Our work provides an efficient N-glycomic strategy that can be applied to further multilayered clinical analysis.

Automated method for short-chain aldehydes emission measurement by dynamic solid-phase microextraction on-fiber derivatization GC-MSD coupled with a flow-cell.

A novel automated method was developed to test short-chain aldehyde emissions using a chamber and a flow-cell coupled with a dynamic solid-phase microextraction (SPME) on-fiber derivatization technique. Calibration curves of short-chain aldehydes were developed for quantitation of target analytes, including formaldehyde, acetaldehyde, propionaldehyde, and acrolein emitted from the chamber outlet. The linearity range for the aldehydes was 0.8 to 2130.0 µg/m3. The limits of quantitation (LOQ) for various aldehydes ranged from ∼0.2 - 1.9 µg/m3. By using this method, emission rate curves are measured with an automated system. Compared with a traditional 2,4-dinitrophenyl hydrazine (DNPH)-high performance liquid chromatography (HPLC) method for aldehyde emission measurement, this method provided an automated technique to study the emission of short-chain aldehydes from multiple samples in one experiment. Furthermore, by using dynamic SPME coupled to an on-fiber derivatization technique, the repeatability and sensitivity of the method is comparable and even better than traditional techniques.

Feasibility study for simple on-line Raman spectroscopic detection of microplastic particles in water using perfluorocarbon as a particle-capturing medium.

A simple Raman spectroscopic scheme for on-line detection of microplastics (MPs) in water is demonstrated. Instead of using a conventional physical filter for MP separation, perfluorohexane (PFH, C6F14) was deployed as an MP-capturing medium in this study. When PFH was added into a water-filled L-shape tube, it formed a firm droplet at the bottom of the 90° curve due to its strong hydrophobicity and high density. When a tap water sample containing dispersed polyethylene (PE) particles was flowed through the L-tube, the contained PFH droplet effectively captured the PE particles, with an average recovery of 95.9%. Next, for reliable quantitative analysis, it was necessary to measure the entire PE particle captured PFH droplet in Raman spectral acquisition without partial spectroscopic sampling. Therefore, a wide area illumination (WAI) scheme providing a laser illumination diameter of 6 mm was adopted for sampling of the whole droplet. The intensity ratios of PE and PFH peaks in the collected spectra clearly increased with elevated quantities of dispersed PE particles. When samples of PE particles were measured in sea water, which possesses much higher ionic strength than does tap water, the shapes of PE particle-captured PFH droplets did not change, and the accuracy was maintained. Based on these results, the demonstrated analytical scheme is feasible for field analysis; further study is required to strengthen its utility.

On-line spectroscopic study of brominated flame retardant extraction in supercritical CO2.

Removal of brominated flame retardants (BFRs) from polymers before disposal or recycling will alleviate negative environmental effects and ensure safe usage of recycled products. Extraction of BFRs in supercritical CO2 is appealing but also presents challenges to industries due to limited solubility and lack of kinetic studies. For a more comprehensive evaluation of supercritical extraction potentialities, we (i) developed an on-line pressure apparatus that is compatible with both the FTIR and UV-vis spectrometers to enable kinetic and thermodynamic studies; (ii) studied kinetic extraction involving three conventional and two novel BFRs as well as three typical polymeric matrix. Solubilities were determined using the gravimetric method or X-ray fluorescence. FTIR exhibited a superior applicability compared to UV-vis in the following BFR extraction's time-dependency binary and ternary systems. We observed that faster stirring speed, higher temperature, and finer particle size can accelerate the overall extraction kinetics. In binary systems, it took less than 2 h to achieve equilibrium for each BFR at 60 °C, 25 MPa and 1000 rpm. In the presence of polymeric matrix, slower extraction kinetics were observed due to the occurrence of competitive dissolution and molecular diffusion within the matrix. Mathematical models derived from irreversible desorption and Fick's diffusion laws fitted well with the observed extraction kinetics of BFRs, thus enabling us to identify the rate-determining step. The high solubilization rate coefficients that we measured for BFRs revealed that the dynamic extraction process in up-scaling design could compensate for the low solubility with flowing supercritical CO2.

A new modified sliding window empirical mode decomposition technique for signal carrier and harmonic separation in non-stationary signals: Application to wind turbines.

Modern control applications justify the need for improved techniques capable of coping with the non-stationary nature of measured signals while being able to monitor systems in real-time. Empirical Mode Decomposition (EMD) is known for its efficiency in time domain analysis of multi-component signals through Intrinsic Mode Functions (IMFs) extraction. Recent years witnessed the introduction of Sliding Window EMD (SWEMD) capable of analyzing signals in real time applications. However, complex signals require several sifting iterations while a rather increased number of IMFs might result in impracticality for on-line applications. This paper introduces a new modified faster SWEMD capable of extracting harmonics from non-stationary signals in real-time operation. The method uses the traditional EMD properties in the first pass for a small number of sifting processes. In addition, a new section is added to the algorithm based on inflection point tracking of the residue derivative from the first pass is added, in order to track low frequency waves and render the analysis faster. The method is validated for non-stationary signals with and without added colored noise and applied on measured turbine side angular velocity for harmonic extraction in wind turbines as an application. The proposed method may well be used for fault detection and disturbance rejection in mechanical systems.

Insights into the effect of chlorine on arsenic release during MSW incineration: An on-line analysis and kinetic study.

The effect of chlorine on arsenic (As) release dynamics during municipal solid waste (MSW) incineration in a fluidized bed was studied on the basis of an on-line analysis system. This system can continuously and quantitatively measure the concentrations of trace elements in flue gas. Chlorine addition increases obviously the concentration of arsenic in flue gas, indicating a promoting effect of chlorine on arsenic release during MSW incineration. Based on the temporal concentration of arsenic in flue gas, the overall kinetic parameters of arsenic release during MSW incineration were calculated. A second-order kinetic law r(x) = 81.6e-66.9/RT (-1.05x2 - 0.01x + 1.03) was ascertained for arsenic release during MSW incineration without chlorine addition, and r(x) = 177.3e-65.3/RT (-0.68x2 - 0.43x + 1.08) for arsenic release with chlorine addition. Thermodynamic calculations were performed to predict the partitioning behavior of arsenic during MSW incineration. The addition of chlorine can not only compete with gaseous arsenic to react with mineral, but is also able to increase the volatilization of arsenic by forming volatile arsenic chlorides, thereby affecting the release kinetics of arsenic during MSW incineration.