Online Monitoring Of Chemical Reactions Research Articles

Reaction Analysis and Process Optimization with Online Infrared Data Based on Kinetic Modeling and Partial Least Squares Quantitation.

In-situ Fourier transform infrared (FT-IR) spectroscopy has been recognized as an important technology for online monitoring of chemical reactions. However, analysis of the real-time IR data for identification and quantification of uncertain reactants or intermediates is often ambiguous and difficult. Here, we propose an analysis algorithm based on reaction kinetic modeling and the chemometric method of partial least squares (PLS) to comprehensively and quantitatively study reaction processes. Concentration profiles and apparent kinetic parameters can be simultaneously calculated from the spectral data, without the demand of complicated analysis on characteristic absorbance peaks or tedious sampling efforts for multivariate modeling. Paal-Knorr reactions and glyoxylic acid synthesis reactions were selected as typical reactions to validate the algorithm. A lack of fit of the Paal-Knorr reaction spectra was less than 2.5% at various conditions, and the absolute errors between the predicted values and HPLC measurement of glyoxylic acid synthesis were less than 6% during the reaction process. Moreover, the reaction kinetic models extracted from FT-IR data were used to simulate reaction processes and optimize the conditions in order to maximize product yields, which proved that this analysis method could be used for process optimization.

Real-time benchtop NMR spectroscopy for the online monitoring of sucrose hydrolysis

The online monitoring of chemical reactions by using benchtop Nuclear Magnetic Resonance (NMR) spectroscopy has become increasingly attractive for the past few years. The use of quantitative online NMR spectroscopy is a promising alternative to traditional analytical methods with its rapid, quantitative and non-invasive nature that makes it applicable to complex and diverse biochemical mixtures like food systems. In this study, sucrose hydrolysis by invertase was chosen as a model reaction for online monitoring. Rather than conventional NMR spectroscopy experiments that rely on the use of deuterated water, the benchtop setting allows working in protonated solvents, and tailored water suppression techniques were used to make quantification more accurate. For the hydrolysis reaction, a 10% sucrose solution was hydrolyzed. The kinetic constants determined by the fractional conversion model were comparable to the results obtained in other studies. Quantitative online NMR spectroscopy can be considered as a promising tool for monitoring food processes in a continuous mode.

Online monitoring of chemical reactions by polarization-induced electrospray ionization

Polarization-induced electrospray ionization (PI-ESI) is a simple technique for instant generation of gas-phase ions directly from a microliter-sized droplet for mass spectrometric analysis. A sample droplet was placed over a dielectric substrate and in proximity (2–3 mm) to the inlet of a mass spectrometer. Owing to the polarization effect induced by the high electric field provided by the mass spectrometer, the droplet was polarized and the electrospray was generated from the apex of the droplet. The polarization-induced electrospray could last for tens of seconds, which was sufficiently long to monitor fast reactions occurring within few seconds. Thus, we demonstrated the feasibility of using the droplet-based PI-ESI MS for the online monitoring of fast reactions by simply mixing two droplets (5–10 μL) containing reactants on a dielectric substrate placed in front of a mass spectrometer applied with a high voltage (−4500 V). Schiff base reactions and oxidation reactions that can generate intermediates/products within a few seconds were selected as the model reactions. The ionic reaction species generated from intermediates and products can be simultaneously monitored by PI-ESI MS in real time. We also used this approach to selectively detect acetone from a urine sample, in which acetone was derivatized in situ. In addition, the possibility of using this approach for quantitative analysis of acetone from urine samples was examined.

On-line Monitoring of Continuous Flow Chemical Synthesis Using a Portable, Small Footprint Mass Spectrometer

For on-line monitoring of chemical reactions (batch or continuous flow), mass spectrometry (MS) can provide data to (1) determine the fate of starting materials and reagents, (2) confirm the presence of the desired product, (3) identify intermediates and impurities, (4) determine steady state conditions and point of completion, and (5) speed up process optimization. Recent developments in small footprint atmospheric pressure ionization portable mass spectrometers further enable this coupling, as the mass spectrometer can be easily positioned with the reaction system to be studied. A major issue for this combination is the transfer of a sample that is representative of the reaction and also compatible with the mass spectrometer. This is particularly challenging as high concentrations of reagents and products can be encountered in organic synthesis. The application of a portable mass spectrometer for on-line characterization of flow chemical synthesis has been evaluated by coupling a Microsaic 4000 MiD to the Future Chemistry Flow Start EVO chemistry system. Specifically, the Hofmann rearrangement has been studied using the on-line mass spectrometry approach. Sample transfer from the flow reactor is achieved using a mass rate attenuator (MRA) and a sampling make-up flow from a high pressure pump. This enables the appropriate sample dilution, transfer, and preparation for electrospray ionization. The capability of this approach to provide process understanding is described using an industrial pharmaceutical process that is currently under development. The effect of a number of key experimental parameters, such as the composition of the sampling make-up flow and the dilution factor on the mass spectrometry data, is also discussed.

On-line monitoring of chemical reactions by using bench-top nuclear magnetic resonance spectroscopy.

Real-time nuclear magnetic resonance (NMR) spectroscopy measurements carried out with a bench-top system installed next to the reactor inside the fume hood of the chemistry laboratory are presented. To test the system for on-line monitoring, a transfer hydrogenation reaction was studied by continuously pumping the reaction mixture from the reactor to the magnet and back in a closed loop. In addition to improving the time resolution provided by standard sampling methods, the use of such a flow setup eliminates the need for sample preparation. Owing to the progress in terms of field homogeneity and sensitivity now available with compact NMR spectrometers, small molecules dissolved at concentrations on the order of 1 mmol L(-1) can be characterized in single-scan measurements with 1 Hz resolution. Owing to the reduced field strength of compact low-field systems compared to that of conventional high-field magnets, the overlap in the spectrum of different NMR signals is a typical situation. The data processing required to obtain concentrations in the presence of signal overlap are discussed in detail, methods such as plain integration and line-fitting approaches are compared, and the accuracy of each method is determined. The kinetic rates measured for different catalytic concentrations show good agreement with those obtained with gas chromatography as a reference analytical method. Finally, as the measurements are performed under continuous flow conditions, the experimental setup and the flow parameters are optimized to maximize time resolution and signal-to-noise ratio.

Online monitoring of chemical reactions by contactless atmospheric pressure ionization mass spectrometry

Journal of Mass SpectrometryVolume 47, Issue 5 p. 586-590 JMS Letters Online monitoring of chemical reactions by contactless atmospheric pressure ionization mass spectrometry Cheng-Huan Hsieh, Cheng-Huan Hsieh Department of Applied Chemistry, National Chiao Tung University, Hsinchu, 300 TaiwanSearch for more papers by this authorChin-Sheng Chao, Chin-Sheng Chao Department of Applied Chemistry, National Chiao Tung University, Hsinchu, 300 TaiwanSearch for more papers by this authorKwok-Kong Tony Mong, Kwok-Kong Tony Mong Department of Applied Chemistry, National Chiao Tung University, Hsinchu, 300 TaiwanSearch for more papers by this authorYu-Chie Chen, Corresponding Author Yu-Chie Chen yuchie@mail.nctu.edu.tw +886-3-5131527 | Fax: +886-3-5723764 Department of Applied Chemistry, National Chiao Tung University, Hsinchu, 300 TaiwanYu-Chie Chen, Department of Applied Chemistry, National Chiao Tung University, Hsinchu 300, Taiwan. E-mail: yuchie@mail.nctu.edu.twSearch for more papers by this author Cheng-Huan Hsieh, Cheng-Huan Hsieh Department of Applied Chemistry, National Chiao Tung University, Hsinchu, 300 TaiwanSearch for more papers by this authorChin-Sheng Chao, Chin-Sheng Chao Department of Applied Chemistry, National Chiao Tung University, Hsinchu, 300 TaiwanSearch for more papers by this authorKwok-Kong Tony Mong, Kwok-Kong Tony Mong Department of Applied Chemistry, National Chiao Tung University, Hsinchu, 300 TaiwanSearch for more papers by this authorYu-Chie Chen, Corresponding Author Yu-Chie Chen yuchie@mail.nctu.edu.tw +886-3-5131527 | Fax: +886-3-5723764 Department of Applied Chemistry, National Chiao Tung University, Hsinchu, 300 TaiwanYu-Chie Chen, Department of Applied Chemistry, National Chiao Tung University, Hsinchu 300, Taiwan. E-mail: yuchie@mail.nctu.edu.twSearch for more papers by this author First published: 10 May 2012 https://doi.org/10.1002/jms.2983Citations: 27Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume47, Issue5May 2012Pages 586-590 RelatedInformation

Acoustic On-Line Monitoring of Chemical Reactions in Liquids with Integrated Temperature Compensation

Acoustic On-Line Monitoring of Chemical Reactions in Liquids with Integrated Temperature Compensation

On-line monitoring of airborne chemistry in levitated nanodroplets: in situ synthesis and application of SERS-active Ag-Sols for trace analysis by FT-Raman spectroscopy.

We report a new strategy for on-line monitoring of chemical reactions in ultrasonically levitated, nanoliter-sized droplets by Raman spectroscopy. A flow-through microdispenser connected to an automated flow injection system was used to dose picoliter droplets into the node of an ultrasonic trap. Taking advantage of the flow-through characteristics of the microdispenser and the versatility of the automated flow system, a well-defined sequence of reagents could be injected via the microdispenser into the levitated droplet placed in the focus of the collection optics of the Fourier transform Raman spectrometer. In that way, chemical reactions could be carried out and monitored on-line. The developed system was used for fast, reproducible, in situ synthesis of a highly active surface enhanced Raman scattering (SERS) sol resulting from the reduction of silver nitrate with hydroxylamine hydrochloride in basic conditions. With this chemical system, SERS substrate preparation could be achieved at room temperature and in short time. The in situ prepared silver sol was used for trace analysis of several organic test molecules that were injected into the levitated SERS-active droplet again using the microdispenser. The concentration dependence of the SERS spectra was studied using 9-aminoacridine, revealing that down to the femtogram region high-quality SERS spectra could be obtained. Additionally, SERS spectra of 6-mercaptopurine, thiamine, and acridine were recorded in the levitated drop as well.

Use of System Peaks in Liquid Chromatography for Continuous Online Monitoring of Chemical Reactions

System peaks, which occur in chromatophy with multicomponent mobile phases, car be used for the continuous on-line monitoring of chemical reactions. The mobile phase reservoir is the chemical reactor, and the mobile phase, which contains the reaction mixture, is recycled continuously through the column. At predetermined times, a neat solvent, normally the solvent of the reaction, is injected. The system peaks that result reflect the status of the reaction. We describe here the use of system peaks to follow the progress of two reactions: titration of aniline and hydrolysis of aspirin. In the case of aniline titration, we obtained a titration curve by plotting the capacity ratio of the aniline system peak versus the acid volume added during the titration. The experimental endpoint agreed very well with the theoretical equivalence point. A plot of the capacity factor as a function of mobile phase pH behaves similarly to such plots in conventional chromatography. In the hydrolysis of aspirin, we followed the progress of the reaction by monitoring the formation of salicylic acid via its system peak. The data allowed us to calculate the apparent hydrolysis rate constant. The value obtained is in excellent agreement with literature values