Downstream Processing (DSP): Chromatography, TFF/UF/DF & Viral Filtration Integration Guide

Connecting Cytiva ÄKTA™ (UNICORN™ 7), Sartorius Sartoflow® / Resolute®, and MilliporeSigma Mobius® / Cogent® Skids to GxPHistorian GxP Industrial Historian

1. Overview of Downstream Purification Skids

Downstream Processing (DSP)—Protein A affinity capture, ion-exchange polishing, viral inactivation, ultrafiltration/diafiltration (UF/DF / TFF), and nanofiltration—requires high-frequency, lossless signal capture (0.5 s to 1 s scan rates) with LTTB peak preservation. Unlike slow upstream temperature trends, a chromatography UV 280 nm elution peak or transmembrane pressure (TMP) spike occurs over seconds, and peak height/area (AUC) directly governs pooling gates and yield calculations.

GxPHistorian GxP Industrial Historian is pre-seeded with a chromatography UV 280 nm tag (Tag 401: CHROM_UV280_PV in init-postgres/01_control_plane_part11.sql) and includes a production Windows localhost OPC DA forwarder (edge-collector/scripts/opcda_windows_forwarder.py) specifically designed for chromatography skid workstations.

Downstream Purification Equipment Product Photo Gallery: Cytiva ÄKTA Chromatography System & Tangential Flow Filtration (TFF) Skid

Downstream Chromatography, TFF Filtration & LTTB UV280 Peak Preservation Visual Wiring Guide

1.5 Non-Technical Step-by-Step Physical & Software Connection Walkthrough

Downstream purification skids (Cytiva ÄKTA™, Sartorius Sartoflow®, MilliporeSigma Mobius® / Cogent®) use a dual-network design to protect internal real-time pump/UV control. Follow this exact checklist to plug in safely:

Downstream Skid	CRITICAL Physical Connection Rule (Where to Plug In)	Software Menu / Service to Enable	Sampling & Peak Rule
1. Cytiva ÄKTA™ avant, ÄKTA™ pilot, ÄKTA™ ready & readyflux (UNICORN™ 7)	WARNING: Never unplug the Ethernet cable going to the CU-950 Control Box (`192.168.0.x` private instrument link) or the ÄKTA will immediately fault! Instead, plug your Cat6 cable into NIC 2 (Plant Network) on the UNICORN™ 7 Windows Workstation PC (or connect to the central UNICORN™ Database Server).	Install the UNICORN™ OPC Server option (`UNICORN.OPCServer.1` for OPC DA or `UNICORN 7.6+ OPC UA Server`). Run `edge-collector/scripts/opcda_windows_forwarder.py` locally on the UNICORN PC so zero Windows DCOM firewall ports need to be opened!	Poll `UV1_280`, `Cond`, `P901`, `Flow` every `0.5 s` – `1.0 s` (`is_step_tag = false`) so ClickHouse LTTB preserves exact elution peak height ( $\text{mAU}$ ) and area ( $\text{AUC}$ ).
2. Cytiva ÄKTA™ process (Figurate™ Automation)	Open the stainless Figurate™ PLC Cabinet on the ÄKTA process skid. Plug a Cat6A Shielded cable into the Northbound Plant LAN (`X2`) port on the Emerson DeltaV™ PK Controller or Rockwell ControlLogix `1756-EN2T`.	Enable the onboard OPC UA Server (`Port 4840`) on the secondary interface (`10.20.60.15:4840`) with `Basic256Sha256` security.	Poll every `500 ms` (`0.5 s`) during `ELUTION` and `VIRAL_INACTIVATION` phases.
3. Sartorius Sartoflow® Advanced / Modular & Resolute® AutoPak	Locate the Siemens S7-1500 (`Biobrain`) inside the skid control cabinet (or the external M12 D-coded washdown bulkhead). Plug a Cat6A cable into Port `X2` (Plant Network).	On the Biobrain / BioPAT® MFCS 4 screen, enable OPC UA Server (`Port 4840`) (or enable `Permit PUT/GET` for `S7comm` on `Port 102`).	Tracks Feed Pressure ( $P_{\text{feed}}$ ), Retentate ( $P_{\text{ret}}$ ), Permeate ( $P_{\text{perm}}$ ), $\text{TMP} = \frac{P_{\text{feed}}+P_{\text{ret}}}{2} - P_{\text{perm}}$ , and Retentate Scale Weight (`kg`).
4. MilliporeSigma Mobius® Chrom 20 / FlexReady & Cogent® Process Scale TFF	Open the Rockwell CompactLogix / ControlLogix enclosure on the rear of the Mobius or Cogent skid. Plug a Cat6A cable into Port 2 (`Plant LAN`) of the dual-IP processor/switch.	On the skid HMI (or FactoryTalk Linx Gateway), enable OPC UA Server (`Port 4840`) and assign Read-Only historian permissions.	Automatically triggers an ISA-88 Event Frame when Low-pH Viral Inactivation (`pH <= 3.60`) hold timer starts and ends.

2. Downstream Integration Architecture

flowchart LR
  subgraph DSP["Downstream Processing (DSP) Skids"]
    AKTA["Cytiva ÄKTA™ process / ÄKTA™ ready / readyflux\n(UNICORN™ 7 OPC DA / OPC UA / Figurate™)"]
    SART["Sartorius Sartoflow® Advanced / Resolute®\n(BioPAT® MFCS / Siemens S7-1500)"]
    MERCK["MilliporeSigma Mobius® Chrom 20 / Cogent® TFF\n(Rockwell ControlLogix / PlantPAx®)"]
  end

  subgraph Edge["Pillar 1: Edge Collector (edge-collector)"]
    OPCDA["Windows Localhost OPC DA Forwarder\n(opcda_windows_forwarder.py + LocalSpoolBuffer)"]
    OPCUA["Telegraf [[inputs.opcua]]\n(500ms–1s High-Speed Scan)"]
    ING["HTTP Ingest (:8080/ingest)"]
    WAL["Telegraf Disk WAL Buffer\n(/var/lib/telegraf/buffer)"]
    OPCDA -->|"JSON Batch"| ING --> WAL
    OPCUA --> WAL
  end

  subgraph Core["GxPHistorian GxP Historian"]
    CH["ClickHouse 24.8 Archive\n(Gorilla Float64 + LTTB Peak Preservation)"]
    PG["PostgreSQL 16 Control Plane\n(Elution Peak & Viral Inactivation Event Frames)"]
  end

  AKTA -->|"Local COM OPC DA 2.05a"| OPCDA
  AKTA -->|"OPC UA (:4840)"| OPCUA
  SART -->|"OPC UA (:4840)"| OPCUA
  MERCK -->|"PlantPAx OPC UA (:4840)"| OPCUA
  WAL -->|"JSONEachRow"| CH
  PG <--> CH

3. Platform-Specific Integration Guides

3.1 Cytiva ÄKTA™ process, ÄKTA™ ready, ÄKTA™ readyflux & UNICORN™ 7

Cytiva’s ÄKTA™ chromatography and tangential flow filtration (TFF) family is controlled either by UNICORN™ 7 workstation/client-server software or by Figurate™ (Emerson DeltaV™ / Rockwell PlantPAx®) on larger ÄKTA™ process skids.

Pathway 1: UNICORN™ OPC Server on Windows (`opcda_windows_forwarder.py`)

Many GMP UNICORN™ installations run the licensed UNICORN OPC Server (UNICORN.OPCServer.1) on the local Windows control PC or UNICORN Server. Opening Windows DCOM ports (TCP 135 + dynamic RPC range) across cleanroom firewalls is a major cybersecurity and GAMP 5 validation liability.

Instead, deploy edge-collector/scripts/opcda_windows_forwarder.py directly on the UNICORN Windows workstation:

It connects to UNICORN.OPCServer.1 over localhost COM (OpenOPC).
Polls UV absorbance (UV 1_280), conductivity (Cond), system/pre-column/delta-column pressure (P901, DeltaP), pH, flow velocity (Flow), gradient concentration (Conc B), and RunLog phase strings at 1.0 s intervals.
Applies Stage 1 exc_dev / exc_max deadband filtering (WindowsOpcDaForwarder.poll_once) so baseline equilibration noise is compressed while steep UV elution peaks are captured at full 1-second resolution.
Buffers to LocalSpoolBuffer (opcda_spool.jsonl) during any network interruption and posts JSON batches to http://<edge-collector>:8080/ingest.

Example opcda_windows_forwarder.py Configuration for Cytiva ÄKTA™ ready / UNICORN™:

forwarder = WindowsOpcDaForwarder(
    prog_id="UNICORN.OPCServer.1",
    ingest_url="http://10.20.10.50:8080/ingest",
    tags=[
        OpcDaTagSpec(tag_id=401, item_id="AKTA_Ready_01.UV1_280.Value",     exc_dev=0.05, exc_max=5.0),
        OpcDaTagSpec(tag_id=402, item_id="AKTA_Ready_01.UV2_254.Value",     exc_dev=0.05, exc_max=5.0),
        OpcDaTagSpec(tag_id=403, item_id="AKTA_Ready_01.Cond.Value",        exc_dev=0.02, exc_max=5.0),
        OpcDaTagSpec(tag_id=404, item_id="AKTA_Ready_01.pH.Value",          exc_dev=0.01, exc_max=5.0),
        OpcDaTagSpec(tag_id=405, item_id="AKTA_Ready_01.SystemFlow.Value",  exc_dev=0.05, exc_max=5.0),
        OpcDaTagSpec(tag_id=406, item_id="AKTA_Ready_01.DeltaColumnP.Value",exc_dev=0.01, exc_max=5.0),
        OpcDaTagSpec(tag_id=407, item_id="AKTA_Ready_01.ConcB.Value",       exc_dev=0.10, exc_max=10.0),
        OpcDaTagSpec(tag_id=408, item_id="AKTA_Ready_01.OutletValve.Pos",   exc_dev=0.00, exc_max=30.0),
    ],
)

Pathway 2: Modern OPC UA (UNICORN™ OPC UA Wrapper or Figurate™ ÄKTA™ process)

For ÄKTA™ process skids running Figurate™ (DeltaV / PlantPAx) or UNICORN™ 7 with an OPC UA Server/Gateway, configure [[inputs.opcua]] in edge-collector/telegraf-clickhouse.conf with a 500ms or 1s scan interval.

3.2 Sartorius Sartoflow® Advanced / Modular TFF & Resolute® Chromatography

Sartorius Sartoflow® crossflow (UF/DF) systems and Resolute® chromatography skids run on Siemens SIMATIC S7-1500 PLCs and BioPAT® MFCS with native OPC UA:

Critical TFF/UF/DF Parameters to Archive:
- Feed Pressure ( $P_{\text{feed}}$ ), Retentate Pressure ( $P_{\text{ret}}$ ), Permeate Pressure ( $P_{\text{perm}}$ ): bar or psig (is_step_tag = false, exc_dev = 0.01)
- Transmembrane Pressure ( $\text{TMP} = \frac{P_{\text{feed}} + P_{\text{ret}}}{2} - P_{\text{perm}}$ ): bar (low_limit = 0.2, high_limit = 2.0 bar)
- Permeate Flux ( $J$ ): LMH ( $\text{L/m}^2\text{/h}$ , is_step_tag = false, exc_dev = 0.2)
- Retentate Vessel Weight & Diafiltration Volumes (DV): kg and dimensionless DV (is_step_tag = false)
- Permeate Conductivity & UV 280 nm Breakthrough: mS/cm and mAU (is_step_tag = false)

3.3 MilliporeSigma (Merck) Mobius® Chrom 20 / FlexReady & Cogent® TFF

MilliporeSigma’s Mobius® single-use chromatography systems and Cogent® process-scale TFF skids use Rockwell Automation ControlLogix PLCs with FactoryTalk® / PlantPAx®:

Connect edge-collector via OPC UA to the skid’s FactoryTalk Linx OPC UA server (opc.tcp://<skid-ip>:4840).
Map ISA-88 recipe step numbers (Recipe_Step_ID, is_step_tag = true) alongside continuous pressure, flow, conductivity, and UV tags.

4. Standard DSP Chromatography & TFF Tag Catalog

Tag ID	Tag Name	Skid / Unit Operation	Parameter	Eng Units	`is_step_tag`	`exc_dev`	Typical DSP Limits (`Low` / `High`)
`401`	`CHROM_UV280_PV`	Protein A / IEX Chrom Skid	UV 280 nm Absorbance	`mAU`	`false` (`LINEAR`)	`0.05`	`0.0` / `2000.0`
`402`	`CHROM_UV254_PV`	Protein A / IEX Chrom Skid	UV 254 nm Nucleic Acid	`mAU`	`false` (`LINEAR`)	`0.05`	`0.0` / `1500.0`
`403`	`CHROM_COND_PV`	Protein A / IEX Chrom Skid	Eluate Conductivity	`mS/cm`	`false` (`LINEAR`)	`0.02`	`0.5` / `150.0`
`404`	`CHROM_PH_PV`	Viral Inactivation / Chrom	Eluate / Hold Vessel pH	`pH`	`false` (`LINEAR`)	`0.01`	`3.50` / `3.70` (Low-pH VI)
`405`	`CHROM_FLOW_PV`	Protein A / IEX Chrom Skid	Linear Flow Velocity	`cm/h`	`false` (`LINEAR`)	`0.50`	`50.0` / `300.0`
`406`	`CHROM_DELTAP_PV`	Protein A / IEX Chrom Skid	Delta-Column Pressure ( $\Delta P$ )	`bar`	`false` (`LINEAR`)	`0.01`	`0.0` / `3.0`
`408`	`CHROM_OUT_VALVE`	Protein A / IEX Chrom Skid	Fraction/Outlet Valve Position (`0=Waste, 1=Pool`)	`pos`	`true` (`LOCF`)	`0.00`	`0.0` / `5.0`
`411`	`TFF01_TMP_PV`	UF/DF TFF Skid 01	Transmembrane Pressure (TMP)	`bar`	`false` (`LINEAR`)	`0.01`	`0.2` / `2.0`
`412`	`TFF01_FLUX_PV`	UF/DF TFF Skid 01	Permeate Flux	`LMH`	`false` (`LINEAR`)	`0.20`	`10.0` / `120.0`
`413`	`TFF01_DV_COUNT`	UF/DF TFF Skid 01	Diafiltration Volumes Exchanged	`DV`	`false` (`LINEAR`)	`0.01`	`0.0` / `10.0`

5. Why ClickHouse LTTB Downsampling (`URS-014`) is Essential for Chromatography

Standard time-bucket averaging (GROUP BY toStartOfMinute(ts)) flattens sharp chromatography UV 280 nm elution peaks and hides transient column over-pressure spikes.

GxPHistorian GxP Historian’s /api/v1/trends/plot-values endpoint (app/main.py) uses ClickHouse’s native largestTriangleThreeBuckets(N) (LTTB) algorithm over raw quality >= 192 samples:

Whether an operator views a 6-hour chromatography run across 200 screen pixels in Grafana (gxphistorian_bioreactor_hmi.json) or exports plot values for batch review, LTTB mathematically preserves the exact maximum apex (mAU) and inflection shoulders of every elution peak (verified by automated qualification test test_oq_09_lttb_peak_preservation in gxp-validation-package/tests/test_03_oq_historian_core.py).