Process Analytical Equipment for Monitoring, Control and Cost Optimization of Inline Dilution Processes

Process Analytical Equipment for Monitoring, Control and Cost Optimization of Inline Dilution Processes Application Note #09 #01 #02 #03 #04 turning science into solutions

Automated inline dilution is a promising alternative to conventional large-scale pharmaceutical and biopharmaceutical manufacturing of diluted products. The advantages are obvious: Bulky, expensive storage vessels that require extensive maintenance, equipment administration and validation no longer need to be used and the quality of the final product is improved. However, inline monitoring and control of the dilution process is mandatory to ensure the correct product composition. State-of-the-art process analytical tools, such as near infrared spectroscopy (NIR) and refractometry, are highly valuable alternatives or supplements to conventionally employed mass or fluid flow controllers. Both these technologies offer the advantage of parametric feedback based on chemical and or physical properties of a stock solution and its diluted product. Besides monitoring the dilution process itself, process analytical equipment incorporating these technologies are capable of reliably checking and controlling the quality and composition of a stock solution and of its diluted product. The idea behind inline dilution is simple: Instead of preparing diluted products in bulky tanks, a concentrated stock solution is automatically diluted inside a processing line to obtain a target diluted product. Several dilution steps can be performed sequentially, each with a dilution ratio of typically up to 10:1. The maximal achievable dilution ratio strongly depends on the properties of the stock solution and equipment constraints. Although the basic idea is always the same, inline dilution is not limited to mixing a stock solution and a diluent, such as water or an organic solvent. Rather, inline dilution enables parallel mixing of multiple liquid streams and, furthermore, can be used to monitor and control product parameters, such as ph or conductivity.

Advantages of Inline Dilution Classical Process Ingredients Water Diluent Automated inline dilution provides significant advantages in upstream and downstream biopharmaceutical processes. Over the past decade, fermentation and cell culture yields, as well as production volumes, have been rapidly increasing, creating the need for ever-larger equipment. Processes designed for a certain volume may now require double capacities due to increased product yield. However, doubling the vessel volume is not always easy: Is there room at my manufacturing site for a bigger vessel? Are there any manufacturers who can supply such a large-size vessel? Do I have sufficient capital to set up a larger vessel? Scaling up equipment for upstream processes means that downstream process equipment needs will grow as well, e.g. for buffer preparation. In addition, when vessel-based equipment is scaled up, it becomes increasingly difficult at each scale-up level to produce a product or an initial solution with the required accuracy, homogeneity and consistent quality: Manufacturing a 10,000 l batch with high accuracy is much more challenging than is a 1 l batch because in the latter case, sophisticated, precise laboratory equipment can be used to check the parameters. Furthermore, large-sized vessels have a strong impact on procurement budgets as they entail high capital expenditure for a new production line. Mixing tank for preparation of solution with final concentration (5,000 liter) Storage tank (10,000 liter) Production tank Fermenter (10,000 liter) Inline dilution is a practical alternative to conventional preparation using large vessels as mixing and preparation can be done on a much smaller scale level. As this inline process reduces the need for quality control testing in the laboratory, feedback control using PAT tools is mandatory in order to ensure that the diluted product meets all quality requirements. Inline Dilution Process Ingredients Water Diluent Water Diluent Mixing tank to prepare concentrated solution (500 liter) Storage tank (1,000 liter) Skid for inline dilution Production tank Fermenter (10,000 liter)

PAT Monitoring and Control Tools for Inline Dilution Process refractometer Monitoring and control of binary solutions 1 Ingredients Water Diluent 2 Inline NIR spectrometer Completeness recipe control Concentration of ingredients Homogenity Process refractometer Inline NIR spectrometer Monitoring and control of the dilution process Water Diluent 1 2 Inline NIR spectrometer Product concentration Endpoint determination Process trajectories 2 Mixing tank to prepare concentrated solution (500 liter) Storage tank (1,000 liter) Skid for inline dilution Production tank Fermenter (10,000 liter) 1 Process 2 Inline NIR refractometer spectrometer Conventional monitoring and control tools for inline dilution are limited to monitoring the flow of the stock solution and the diluent. This is done by controlling the inlet stream pressure, measuring the mass flow rate or by controlling the volumetric flow. All these technologies have a major drawback in that they merely check whether the ratio of a stock solution and a diluent are correct. They do not monitor whether the concentration parameters or the product is correct or whether there are any variations in the quality of the stock and diluting solutions. Advanced PAT tools, such as process refractometry and NIR spectroscopy, provide a deeper insight into the dilution process and generate added value by optimizing processes and ensuring product quality.

Process Refractometry Process refractometer Concentration determination of binary solutions Sum parameter for complex solutions Monitoring using process refractometry enables the concentration to be determined and liquid or paste-like product streams to be identified. Typical applications for inline dilution are identification and quality assurance of stock solutions, as well as determination of the concentration of the target diluted product in binary processes. In the first case, several ideal stock solutions are employed as references to define the acceptable range of a refractive index for future stock solution batches. This involves identifying a stock solution by its refractive index to reveal its quality and or purity, without the need for any calibration. In the second case, just a few calibration samples containing different concentrations are used to reference a refractive index to the correct concentration for monitoring an inline dilution process. Unlike conventional flow control, process refractometry enables online monitoring and control of a dilution process based on information about the concentration of the target diluted product. The refractometry technique itself is based on the refraction of light when it passes from one medium into another. At a certain angle of incidence, light is no longer refracted, but is reflected instead. This so-called critical angle depends on the specific media and indicates the refractive index of a sample. In combination with the simultaneously recorded temperature of a reference sample, the concentration can be calculated using mathematical functions, called scales (e.g., Brix). Refractometry is especially suitable for simple binary dilution processes, for example, dilution of one concentrate of a medium using water, if a sum parameter is required for determining the concentration of all dissolved substances. For complex dilution processes or if several components in a stock solution or a diluted product have to be quantified, NIR spectroscopy is a valuable alternative or a supplement to process refractometry. Near Infrared Spectroscopy (NIR) Inline NIR spectrometer Quantitiative information about detailed compositions Identification Physical parameters NIR spectroscopy is a versatile technology used to determine chemical and physical sample properties. It is not limited to one single parameter; instead, it is capable of performing simultaneous multiparametric analysis. This technology is based on the absorption of light in the wavelength range of approximately 800 to 2,500 nm. The spectrum detected contains information about vibration of molecules that are present in a specific sample. In inline dilution processes, NIR spectroscopy provides quantitative information about the detailed composition of stock solutions, diluents and target diluted products. Furthermore, NIR spectroscopy permits spectral fingerprints of any solution to be recorded for precise identification and quality assurance. In addition, the stray light it detects gives insight into physical parameters, such as viscosity or particles contained. The combination of refractometry and NIR spectroscopy, in particular, enables optimal monitoring and control of inline dilution processes.

The Right Combination of Technologies for Inline Dilution Process Monitoring and Control The PAT strategy has to be adapted to the complexity of a dilution process. How many streams are combined simultaneously and or sequentially? How high are the batch-to-batch variations of my stock solution and my diluent? How homogeneous are my stock solution and my target diluted product? However, the most important question to answer is: What do I really need for optimal monitoring and control of my inline dilution process? As every process is different, no general solution can be provided. Risk analysis is often helpful to develop the optimal process control strategy: Which are the critical process steps; how often do different problems occur and what are the consequences? How is the quality of my target diluted product defined? Answering these questions will help to identify the critical quality attributes and process parameters that need to be monitored according to the PAT concept. This will help in deciding which sensors are required at which point of a dilution process. In general, NIR spectroscopy is recommended for multi-component products to monitor and control the exact composition of stock solutions and diluted products. For simple binary dilution processes or when a sum parameter for the concentration of all dissolved substances is needed, a refractometer for monitoring and control of stock solutions and target diluted products is the optimal solution. This refractometer determines whether a process in progress is within or out of specifications by comparing the actual refractive index with the predefined one. In inline dilution processes, the combined use of refractometry and NIR spectroscopy provides the double benefit of optimal process monitoring and control and of cost effectiveness: As stock solutions often consist of various components, NIR spectroscopy is required to verify their correct composition and to assure that they have the desired quality. By contrast, diluents are often pure liquids, such as water or organic solvents or simple one-component solutions. In this case, checking the refractive index permits online monitoring and control of the inlet stream, ensuring that the target diluted product has the correct dilution level. To summarize, NIR verifies the correct composition of a complex stock solution by multi-parametric analysis, while refractometry monitors the dilution process itself based on the refractive index as the sum parameter.

Sartorius Process Analyzers Integrated Solutions for Inline Dilution Processes All Sartorius process analyzers are specially designed for the continuous use under harsh process conditions, without the need for constant maintenance or vigilance. The BioPAT Reflex PMD700 process refractometer series enable online and real-time monitoring and control by determining the refractive index of samples. This series delivers the highest accuracy available worldwide. Its field-proven technology in combination with integrated process automation ensures fast response times and the highest precision. The multi-component analyzers of the BioPAT Spectro PMD500 series combine NIR and UV-VIS spectroscopy and an optional VIS camera. Each BioPAT Spectro analyzer provides not only an NIR spectral pattern of a sample, but also information on its additional properties, such as the color or the presence of contaminants. The BioPAT Spectro ensures continuous error-free performance over long operating periods as it features two redundant light sources. If one lamp fails, the system will automatically switch over to the second light source. As a result, the light bulb can be exchanged during regular, scheduled equipment maintenance without the need for interrupting a production run. Both process analyzers are optimally suited for monitoring and control of inline dilution processes and can be conveniently integrated into process systems using a choice of options: weld-in flange and cell module (BioPAT Spectro), or VariVent, APV and TriClamp connections (BioPAT Reflex). Summary Inline dilution processes can be monitored and controlled online with the BioPAT Spectro and BioPAT Reflex series, offering distinct advantages over conventional flow control tools, which are limited to monitoring and control of mixing ratios. Process refractometers and NIR spectrometers guarantee the correct composition of stock solutions, diluents and target diluted products. Furthermore, they monitor the quality of initial solutions and diluted products, thus reducing the likelihood of off-specification batches and increasing both manufacturing quality and production speed.

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