Monitoring an enzyme purification process using on-line and in-line NIR measurements

• Full scale ultrafiltration of an intermediate enzyme product is examined.
• Near infrared (NIR) spectroscopy is employed for monitoring of enzyme activity.
• Several parameters for enzyme activity are unified into one global parameter.
• Two parallel real-time NIR probe setups (on-line v. in-line) are evaluated.
• The in-line flow cell surpasses the on-line sampling system during operation.

The key parameter during purification of enzymes is the strength of the intermediates and products. Employing near infrared spectroscopy, enzyme activity of the concentrate can be obtained much faster than by traditional off-line analysis in a central laboratory. This paper describes the development of a monitoring system for the enzyme activity in a recovery plant and provides a comparison between two real-time probe setups (on-line v. in-line) in a full scale application. The focus in the paper will be on the chemometric calibration development plus validation and the application of the models for monitoring purposes. For this investigation, four different types of industrial enzymes have been sampled over a period of ten months. Real-time output of the partial least squares regression models was used along with conventional process data generated to evaluate the pros and cons of the in-line and on-line setup. Both implementations deliver good results in monitoring the ultrafiltration process, but problems (precipitation/phase transition) were occasionally encountered for the on-line arrangement.