A Closer Look at Automated In-Line Dilution

Automated in-line dilution can help solve capacity, financial, and quality concerns that biopharmaceutical manufacturing plants may be facing.
Oct 01, 2009
Volume 22, Issue 10


Automated in-line dilution is an increasingly popular technology in the biopharmaceutical industry. In-line dilution is a process that can help solve capacity, financial, and quality concerns that biopharmaceutical manufacturing plants may be facing regarding process solution preparation and delivery. This technology has several applications in biopharmaceutical manufacturing, such as purification processes, chromatography systems, solvent adjustment, pH adjustment, and cleaning systems. The fundamental aspects of automated in-process dilution systems are discussed, including engineering considerations, equipment components, process materials, operation, maintenance, and quality considerations.

Automated in-line dilution is a process in which two liquid streams are brought together in a controlled fashion to meet a target diluted solution concentration. A dilution ratio of 10:1 or more often can be achieved using current equipment designs. This typically allows for concentrates of up to 10x concentration to be used as starting material. The maximum dilution ratio is limited by both equipment constraints and the properties of the concentrated solution. Much larger dilutions can be obtained by placing multiple in-line dilution processes in series.

Figure 1
The equipment used for an in-line dilution process is compact and usually portable. The most basic equipment would include only one module and only perform one process step at a time, meaning that only two inlet streams are combined to make an intermediate or final product. If a second process step such as addition of another solution or adjustment of another parameter (e.g., pH) is desired, additional modules can be added to the equipment train. Multiple skids also can be placed in series to accomplish this task. An intermediate is the output of any individual in-line dilution module or skid. The intermediate is then directed to the inlet of the subsequent module to perform the next processing step. Figure 1 illustrates a process in which multiple dilutions or processing steps can be performed.

Figure 2
Automation of the process allows for the final product solution to be manufactured "just in time." The small portable equipment is capable of delivering the final product at the point of use. Figure 2 shows an in-line dilution skid.


The use of automated in-line dilution systems provides very significant advantages to biopharmaceutical manufacturing. One of the many concerns in biopharmaceutical facilities is capacity; biopharmaceutical companies are now obtaining much higher fermentation and cell culture yields than in the past, leading to capacity shortages in downstream processing equipment. Another challenge is manufacturing at large scale. Manufacturing 10,000-L batches of process solutions in large tanks is inherently difficult. Making a 1-L solution in a laboratory can be done very precisely using analytical instruments that are calibrated at milligram sensitivity. In contrast, making a 10,000-L solution requires load cells or level probe technology with much less precision. Mixing at large scale necessitates mixing studies and process validation to ensure that the mixing process is reliable and repeatable.

In-line dilution technology provides significant advantages compared to traditional large-scale processes because the mixing and preparation was actually being done at a small scale; compare the holdup volume of the in-line dilution skid versus a 10,000-L buffer prep tank. In addition, in-line dilution processes can incorporate feedback control with mixing to achieve highly accurate solution concentrations.

Figure 3
As stated previously, a process that was originally designed for a 10,000-L batch of process solution may now require twice as much solution because of increased yields. The manufacturing process now needs to make two 10,000-L batches in the preparation vessel and transfer each batch to a 20,000-L storage vessel. Is there a 20,000-L vessel available? Is there room to install a tank this size? Figure 3 illustrates how in-line dilution can solve this large-scale problem by using a small 2,000-L tank of concentrate compared to the large 10,000-L and 20,000-L tanks needed in the previous example.

It is not uncommon for organizations to hesitate or be uncertain about implementing new technologies. There is comfort with traditional processes where there are known failures and a general knowledge of how they are addressed. In addition to addressing new process methods, biopharmaceutical manufacturers must consider recent US Food and Drug Administration and International Conference on Harmonization (ICH) guidelines.1–3 These guidances urge companies to use process analytical technologies (PAT) in support of quality by design (QbD) and continuous improvement initiatives. The thought of incorporating PAT adds another level of complexity to adopting new process methodologies.

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