The classic spectroscopic methods FTIR, Raman, UV/Vis, NIR, NMR and MS have all evolved to accommodate real-time analysis.16-23 This evolution is a result of spectrometer miniaturization, enhanced reliability, development of dedicated probe, sensors and sample interfaces and intuitive software. These online technologies provide extensive data streams that can be analyzed with advanced analysis and modeling tools. Frequently, multiple in-situ techniques are used in combination to provide data that fully characterize a reaction or process.
There are three general methods to interface with reaction mixtures:
Online analysis is performed directly on a reaction stream, often through an apparatus circulating a reaction sample via a slip-stream through a flow cell.
Inline analysis implies that the analytical sensor is integral with the reaction apparatus, typically as part of a pipe or tube, providing a continual data stream as part of the overall workflow.
In-situ analysis has proven exceedingly useful for providing reaction progress, kinetics and mechanistic information since it measures under actual reaction conditions. When a sensor or probe is placed directly inside a reaction to track changes occurring as a function of time, the analysis is considered in-situ
There are three general methods to interface with reaction mixtures:
Online analysis is performed directly on a reaction stream, often through an apparatus circulating a reaction sample via a slip-stream through a flow cell.
Inline analysis implies that the analytical sensor is integral with the reaction apparatus, typically as part of a pipe or tube, providing a continual data stream as part of the overall workflow.
In-situ analysis has proven exceedingly useful for providing reaction progress, kinetics and mechanistic information since it measures under actual reaction conditions. When a sensor or probe is placed directly inside a reaction to track changes occurring as a function of time, the analysis is considered in-situ
- Common Advantages of Real-Time Techniques over Manual Sampling for Offline Analysis:
- Provides most accurate data about chemistry occurring under actual reaction conditions
- Supports Reaction Progress Kinetics Analysis (RPKA), Dynamic Response Surface Methods (DRSM), Design of Experiment (DoE), Density Function Theory (DFT) and other advanced modeling and digitalization as Data-Rich Experiments (DRE)
- Provides PAT support for Quality by Design (QbD) manufacturing strategies
- Supports the development of sustainable chemistry
- Minimizes user exposure to hazardous chemistry or chemicals
- Eliminates time delays associated with offline analysis at remote labs
- Enables actionable decision-making about chemistry based on real-time data
Online, Inline, In-Situ
The data-rich measurements from in-situ and online FTIR spectroscopy are frequently used to develop kinetic parameters, provide evidence for proposed mechanisms and determine the effect of reaction variables on process performance, in support of optimization and scale-up efforts. Adaptable to batch and continuous flow reactors, real-time FTIR spectroscopy analyzes chemistry under actual reaction conditions, capturing data at the most critical points in a reaction. Using internal reflection (ATR) diamond and silicon sensors as the interface to the reaction mixture, the technology can measure a very broad array of chemistries over a wide range of temperature and pressure variables, and in the presence of aggressive reagents.
There are numerous examples of the application of in-situ infrared analysis for real-time analysis of chemical syntheses, catalytic reactions, polymerizations, crystallizations, organometallic synthesis, etc. These investigations typically focus on the use of the technology for tracking changes in the concentration of key reaction species and the relationship of these changes to varying reaction conditions and parameters.
Key Advantages:
Measures fundamental vibrations - highly useful for molecule identification
Provides continuous, data-rich tracking and measurement of key reaction species, including transient intermediates
Monitors reaction progress including detection of key events, initiation, stalling, end-point, etc.
Captures copious amounts of data during periods of significant change in a reaction for more accurate calculation of kinetic parameters
The data-rich measurements from in-situ and online FTIR spectroscopy are frequently used to develop kinetic parameters, provide evidence for proposed mechanisms and determine the effect of reaction variables on process performance, in support of optimization and scale-up efforts. Adaptable to batch and continuous flow reactors, real-time FTIR spectroscopy analyzes chemistry under actual reaction conditions, capturing data at the most critical points in a reaction. Using internal reflection (ATR) diamond and silicon sensors as the interface to the reaction mixture, the technology can measure a very broad array of chemistries over a wide range of temperature and pressure variables, and in the presence of aggressive reagents.
There are numerous examples of the application of in-situ infrared analysis for real-time analysis of chemical syntheses, catalytic reactions, polymerizations, crystallizations, organometallic synthesis, etc. These investigations typically focus on the use of the technology for tracking changes in the concentration of key reaction species and the relationship of these changes to varying reaction conditions and parameters.
Key Advantages:
Measures fundamental vibrations - highly useful for molecule identification
Provides continuous, data-rich tracking and measurement of key reaction species, including transient intermediates
Monitors reaction progress including detection of key events, initiation, stalling, end-point, etc.
Captures copious amounts of data during periods of significant change in a reaction for more accurate calculation of kinetic parameters
Raman Spectroscopy
Online, Inline, In-Situ
By the nature of the physics that defines them, Raman and IR spectroscopy are complementary methods for reaction analysis. In-situ and online Raman spectroscopy provide continuous, data-rich tracking of key reaction species, under actual reaction conditions and kinetic information in batch and continuous flow applications. Since water is highly absorbing of mid-IR radiation but does not interfere with Raman scattering, Raman has advantages when it comes to reactions performed in aqueous media, such as bioreactions. Also, since Raman scattering provides information on particles in a solution, it is quite useful for investigating morphology
in crystallizations.
Key Advantages:
- Measures fundamental vibrations that are useful for molecule identification
- Provides sharp bands and reduced interference by overlapping vs IR
- Evaluates low frequency bonds such as metal-oxygen
- Monitors reactions in aqueous media
- Determines spectra through glass vessels and tubing
- Uses fiber optics that allows remote operation
- Tracks reactions safely ex-situ through a reactor window (e.g., high pressure catalytic reactions, polymerizations)
- Records spectra of solid particles in a solution
NIR Spectroscopy
Online, Inline, In-Situ
The applications of NIR spectroscopy cover a remarkably broad area of academic and industrial applications. NIR measures overtone or combination bands that are weaker in intensity than the fundamental vibrations. Thus there is less absorption, eliminating the need for sample dilution and enabling measurements in aqueous media. While in-situ FTIR/Raman spectroscopy is useful for identifying and tracking reaction species by molecular structure, NIR has significant advantages in rapid monitoring of optically dense mixtures or materials. Applying multivariate analysis methods, NIR is widely used for quantitative measurements and process control in chemical, pharmaceutical, polymer and bioreaction applications.
Key Advantages:
- Measures overtone or combination bands that are weaker in intensity than the fundamental vibrations, thus there is less absorption, eliminating the need for sample dilution and also enabling measurements in aqueous media
- Measures thick samples and turbid liquids or scattering solvents due to low absorption coefficient
- Operates remotely using fiber optics
- Transfers calibration through scales
- Applies to many applications
Online, Inline, In-Situ
With respect to real-time UV/Vis spectroscopy, there are numerous inline, online and in-situ areas of application. Since UV/Vis spectroscopy is based on electronic transitions, it tends to be a very sensitive technique for molecules containing double bonds, i.e. bonds that transition from the ground state to an excited state and molecules containing chromophores. The combination of exceptional sensitivity, a great number of compounds that absorb in the UV/Vis, facile sampling methods including ATR for deeply absorbing reactions and applications in aqueous media make UV/Vis a widely applied absorption spectroscopy technology for in-situ, online and ex-situ applications.
Key Advantages:
With respect to real-time UV/Vis spectroscopy, there are numerous inline, online and in-situ areas of application. Since UV/Vis spectroscopy is based on electronic transitions, it tends to be a very sensitive technique for molecules containing double bonds, i.e. bonds that transition from the ground state to an excited state and molecules containing chromophores. The combination of exceptional sensitivity, a great number of compounds that absorb in the UV/Vis, facile sampling methods including ATR for deeply absorbing reactions and applications in aqueous media make UV/Vis a widely applied absorption spectroscopy technology for in-situ, online and ex-situ applications.
Key Advantages:
- Measures electronic absorption bands; highly sensitive for quantitative measurements
- Absorbs wide range of compounds in the UV/Vis for broad applicability
- Measures chemistry occurring under actual reaction conditions
- Prevents water from interfering with UV/Vis measurements
- Allows remote operation using fiber optics
NMR
Online For decades, reaction chemistries have been investigated using the classic NMR tube. Substantial progress in hardware and software now enables NMR to be used as an online, real-time reaction analysis method with the capability to track multiple species found in reaction mixtures. Low-field, compact NMR systems and flow probes that can fit into a fume hood have accelerated the use of
the technique in real-time monitoring of both batch and continuous flow chemistry. NMR has significant advantages in its ability to determine reaction kinetics and to track the progress of reactions. The inherent sensitivity of NMR, ability to determine structural information, sharpness of peaks with minimal peak overlap and quantitative capability enable the technique to be quite useful for online applications.
Key Advantages:
- Provides highly detailed, structural information on molecules
- Gives highly sensitive data by identifying and monitoring key reaction species including reactive intermediates
- Provides kinetic and mechanistic information
- Determines product yield, endpoint, impurities; optimize reactions
- Provides quantitative data such as reaction rate information, insight into the effect of variables on reaction performance and impurity detection and identification
- Applies well to continuous flow chemistry
- Allows easy access to the process with compact bench-top system
Mass Spectroscopy
OnlineMass spectroscopy using a front-end separation method such as HPLC is well proven for observing and identifying individual reaction species and impurities, as well as giving insight into reaction mechanisms. More recently, MS has been used in online applications. This has accelerated the development of more compact, less expensive spectrometers and the expansion to methods that introduce samples by electrospray ionization and other techniques. The rapidly increasing adoption of flow chemistry in pharmaceutical synthesis and other chemistry offers an excellent opportunity for online MS application due to its ability to detect and resolve the structure of complex molecules.
Key Advantages:
- Measures mass-to-charge ratios for a broad range of condensed and gas-phase compounds
- Analyzes pure samples and complex mixtures
- Provides highly sensitive data by tracking reaction species including by-products
- Presents quantitative data such as reaction rate information, the effect of variables on reaction performance and impurity detection and identification
- Adapts to continuous flow chemistry
- Increases the breadth of applications by using novel sample introduction methods
- Allows easy access to the process with compact bench-top system
- Utilizes various sample pre-treatment and introduction methods available depending on the chemistry
Online, Inline, In-Situ
FBRM is used for analyzing particles in solution in applications as diverse as pharmaceutical crystallization, emulsion polymerization, mineral processing, etc. For crystals, particles or droplets in opaque or translucent slurries, emulsions and other heterogeneous mixtures, the in-situ technique provides chord length distribution that is related to particle size, count, shape and size distribution. In-situ FBRM measurements are used in research to understand particle/crystallization processes. They are also used in development and optimization efforts to study the effect of variables on particle or crystallization shape, size and count. Lastly, in-situ FBRM measurements are used in production to ensure that the particle process is under control to deliver critical product attributes. Particle imaging uses in-situ video microscopy probes to visualize particles and particle mechanisms in real-time as they occur in process.
Key Advantages:
- Measures reflected signal from particles to reveal particle size and particle size distribution
- Investigates, monitors and controls complex particle systems such as crystallization, flocculation and aggregation
- Determines the impact of process parameters on particle size and shape enabling precise control and predictability
- Investigates specific regions of the particle population for a greater understanding of the process
- Investigates or determines nucleation, supersaturation, metastable zone, aggregation etc.
- Enables an understanding of transient events that may affect particle structures and polymorph transitions
- Visualizes shape evolution of particles in real-time; unexpected variations can be discovered and corrected
- Improves downstream operations such as filtration via particle size optimization
Chromatography
OnlineThe separation capability of chromatography has wide applicability to reaction analysis providing detailed quantitative information about complex mixtures. Various chromatographic methods are applied to online reaction monitoring, especially with the increased transitioning of chemistry from batch to continuous flow. There are representative examples of HPLC, SFC, and GC that have been used in association with continuous flow reactors as well as in combination with MS. Additionally, for batch reaction analysis, technologies are available that automatically remove a sample from the reaction mixture at pre-determined periods, then quench and dilute the sample for injection in a chromatography system.
Key Advantages:
- Applies to many applications
- Determines product yield and endpoint with low level impurity profiling
- Provides near real-time chemistry monitoring (UPLC)
- Provides quantitative data such as reaction rate and mechanism information
- Tracks the effect of variables on reaction performance for optimization studies
- Combines chromatography with MS for better differentiation (use for batch or continuous flow chemistry)