To implement the automation strategy for concentration and diafiltration, the following equipment reconfigurations were performed:
1) the air sensor was moved from transfer inlet 1 to the common transfer valve block outlet
2) a fraction collector was added to retentate outlet 3 to allow for multiple sample processing
3) the inlet ports on the ÄKTAcrossflow system were reassigned in the method.
Transfer inlet configuration. The system air sensor controlled sample volumes processed across all inlets. Water from a hydro purification system was used
for rinsing, water flux test, flush, and diafiltration steps. Water was used to condition the filter. The modified inlet configuration
is shown in Figure 2.
Figure 2: ÄKTAcrossflow modified transfer inlet configuration enabling automated multiple sample processing.
Fraction collector configuration. The Frac-920 fraction collector was programmed to collect five fractions for each sample processed. The collection sequence
was programmed as shown below:
Tube 1: Reservoir volume at product end
Tube 2: Product chase
Tube 3: Reservoir volume at buffer flush end
Tube 4: Flush chase
Tube 5: Fraction collector tubing clean via 25 mL buffer flush.
Merck reported that there were no cross contamination issues with their samples using the 25 mL buffer flush as determined
by HPLC analysis.
Method configuration. The ÄKTAcross-flow method wizard in the UNICORN software was used to create the initial method framework, including the pre-
and postproduct steps (see Figure 3). Scouting was enabled to vary the sample inlet used for each run. The ÄKTAcrossflow method was modified to prevent the loading
of the subsequent sample onto a fouled filter. This was achieved with inclusion of the flux drop calculation mode, combined
with conditional programming on the percent flux drop. Pre- and postwater flux test results were compared within the same
run. If the percent flux drop, as set by the user, was outside the threshold, a message would appear on screen for the user
to take action while the system entered into a hold state with the permeate outlet in recycle mode. The goal of the method
was two-fold—firstly, to concentrate the product to the minimum working volume, and secondly, to remove as much salt as possible.
Table I: The product step endpoints.
Starting volumes were typically 0.6–2 L [5–20 OD/mL]. The system holdup volume (recirculation loop including filter) was 45
mL. The molecular weight cut-off for the membrane filters was 1 KD and the membrane surface area was 1 ft2. The product step endpoints were as shown in Table I.
Figure 3: Flow scheme of ÄKTAcrossflow system. The air sensor is moved from transfer inlet 1 to the common transfer outlet.
The fraction collector is connected at the retentate valve block 3 outlet for product recovery.
An example of the method scouting setup in the UNICORN software is shown in Figure 4. User configured options are available each time a set of samples is processed with the same method. Parameters such as sample
inlet and sample volume are updated as needed for each sample set. Parameters that are identical for each sample, such as
diafiltration endpoint and flux drop percent, can also be shown for verification of status.
Figure 4: UNICORN scouting method setup. Sample names have been removed to protect proprietary information.