processanalyticaltechnology

Process analytical technology (PAT) requires continuous monitoring of quality and this in turn requires a model able to predict product qualities that can be measured in real-time from the values of real-time process measurements. Process scale chromatography plays an important role in the purification of pharmaceutical products. Adjusting the eluent collection points allows the process to compensate for the chromatography variability rather than increased variability in the product purity. In addition to reducing product variability, using on-line HPLC also increases product yield, enables the use of increased levels of automation and reduces overall cycle time.

Determining where the product elution occurs, generally involves collecting the column eluent stream in small volumes that are sampled and analyzed in the laboratory utilizing higher resolution chromatographic techniques such as reversed-phase chromatography. This process of eluent fractionation and off-line chromatographic analysis is performed in process development area in order to generate sufficient process understanding to enable when the product elutes from the process scale chromatography column.

Fractionation of the column eluent has several negative issues associated with it including:

    * Degradation of product caused by the delays
    * Difficulty automating processing due to manual handling of fractions
    * Increased process cycle time caused by time to obtain off-line assays
    * Labor intensive
    * Error may occur
    * Reduced production capacity due to long cycle times
    * Opportunities for product contamination
    * Storage required for “Work in Process” (the column fractions)

Due to the many negative issues associated with column fractionation, companies strive to eliminate this process operation as quickly as possible. Options to eliminate fractionation include:

1. Collection of product based on column eluent volume.

In this approach, the eluent volume where the product of sufficient purity is expected to elute is determined from historical data and the start collection and stop collection set points are set. An in-line flow meter is used to measure the eluent volume to control the collection of the product of interest as it elutes from the process chromatography column.

The issue with this approach is that it is totally dependent on the reproducibility of the column elution profile which is impacted by column loading, purity of the starting material, column packing, and column gradient generation.

2. Collection of product based on column eluent volume and optical density.

In this approach, an in-line UV sensor set to 280 nm is used to measure the absorbance from the product’s peptide bonds. Since this is a non product specific measurement, the OD sensor’s output is examined in combination with the in-line flow meter to gain an additional level of resolution. That is, the product is only collected when the OD at 280 nm exceeds the OD set point and falls within the volume set point window. This imparts greater selectivity than using the eluent volume approach alone, but is still dependent on the reproducibility of the column’s elution profile.

Although the variability is less with this approach, the lack of a high level of selectivity still leads to conservative collection set points that negatively impact product yields.

3. Measurement of product purity by on-line HPLC.

The critical quality attribute of the product is its purity. Meeting a specified purity value is the criterion that determines if the process chromatography step has been successful and if the in-process material is suitable for forward processing. By transferring the specificity of HPLC to an on-line analyzer, it is possible to directly measure the critical quality attribute in near real time, thus allowing the process decision (i.e., when to start and stop collection of the product eluting from the process chromatography column) to be based on the critical quality attribute rather than being based on a surrogate measurement that is impacted by the process variability.

The increased emphasis on cost reduction and improving production efficiency needs real-time process information. Product safety methodologies result in an increased need to track product quality throughout the manufacturing process. So this on-line HPLC helps to give advanced process control and real-time product release.