Many High Performance Liquid Chromatography (HPLC) and Size Exclusion Chromatography (SEC) systems and detectors are compatible with each other thanks to analog and digital connections which allow them to exchange raw detector signals and injection trigger signals.
Malvern’s OmniSEC software (version 5.1) now has the added ability to communicate with Waters Empower® software, which is widely used for SEC measurements. This allows the user to copy sample sequences directly from Empower® and synchronize measurements thanks to the injection trigger signals.
This technical note describes how to connect Viscotek detectors to Waters systems, in particular the Waters Alliance® system, and how to use OmniSEC in combination with Empower® to run trouble-free separation sequences.
Fluidic connections of the HPLC tubing should be made as normal, trying to minimize dead volumes and the number of connections.
Typically, refractive index (RI) detectors are plumbed last in the flow sequence. This protects the RI flow cell, which is typically fragile, from any additional backpressure caused by subsequent tubing and detector cells.
Viscometers must also be plumbed last in line since their design splits the sample in half. As a result, if a modular RI and modular viscometer are to be used in the same system, they should be plumbed in parallel. The flow split required for this setup reduces the flow rate to each detector, which has the unfortunate effect of reducing the sensitivity of the viscometer (as the sensitivity of this detector is partially dependent on flow rate). The Triple Detector Array (TDA) has a robust RI flow cell allowing the RI and viscometer to be plumbed in series. This maintains the maximum sensitivity across all of the detectors.
In order to exchange injection trigger signals and analog signals from modular detectors supplied by different manufacturers, electrical connections must be made between the instruments. This is typically done using the connections on the back of different instruments. Most autosamplers, and even manual injection loops, offer some form of trigger event to indicate the beginning of the run. Similarly, most concentration detectors (UV and RI) have analog connections to send an analog representation of the raw signal to another device. This is usually scaled between 0–1 V and can be set to different scales in the hardware settings. Connections to the Waters Alliance® autosampler and e2414 RI detector are shown in the figure 1:
Figure 1: Diagramatic representation of the electrical connections on the Waters Alliance
® autosampler and RI detector.
The Viscotek detectors are all capable of accepting these signals and processing them in OmniSEC. The 270 Dual Detector, TDA, and Zetasizer µV (via the OmniFACE A/D board) all share a phoenix connection as shown in figure 2A, while the SEC-MALS 20 can accept analog signals through the gold RCA connectors labelled “ANALOG IN” and a trigger signal through the phoenix connector labelled “DIGITAL IN” (figure 2B).
Figure 2: A: Phoenix connection on the 270, TDA and OmniFACE. B: Connections on the rear of the SEC-MALS 20.
Analog detector signals are connected simply by joining the appropriate connections. The cable with part number CAB2966 has loose wires at either end and can be used to connect the Waters RI detector to the 270, TDA and Zetasizer µV. This should be connected to the “RI in HI” and “RI in LOW” connections. The cable with part number SEC0001 has an RCA plug and loose wires and can be used to connect the RI detector to the SEC-MALS 20 detector. In both cases, take care to ensure the polarity is correct. Simply compare the polarity of the signal on the front of the detector with that displayed when collecting data in OmniSEC or inject a standard.
Injection trigger signals are simply connected by joining the appropriate connections. Cable CAB2966 is suitable for connections from the Waters autosampler to all Viscotek detectors. Since the Waters autosampler offers a contact closure signal, it is independent of polarity.
Sample sequence setup
OmniSEC has the ability to read and import sequences created in Waters Empower® software. In Empower® these are called “sample set methods”. Create a “sample set method” in Empower® as usual. Once this is setup, open the sequence editor in OmniSEC.
Log OmniSEC into Empower® by clicking the ‘login’ button and enter the username and password of the Empower® user. The “Projects” drop-down menu allows the selection of the relevant project containing the desired sequence. Once the project is selected, the “Sequences” drop-down menu will be populated with all of the “sample set methods” contained within that Empower® project. Select a ‘sample set method’ and click the ‘load’ button (the ‘login’ button is renamed to ‘load’) to fill the sequence with the injections in the method. Delays and other non-injection events in the sequence will be ignored and only the injections will be added to the sequence. The sequence will stay synchronized thanks to the trigger signals. Figure 3 shows a summary of the process within OmniSEC.
Figure 3: The sequence editor window in OmniSEC and Empower login window.
Before starting the sequence, set the run length in the “Acquire – Configure” menu so that the runs in OmniSEC are 1 minute shorter than those in Empower®. This will allow OmniSEC to save the data, move to the next run and wait for the next injection. Doing this ensures that injections triggers are not missed during this period.
Once the sequence has been imported, click “ok” and start the sequence. OmniSEC will initialize the detectors and wait for an injection trigger. Start the sequence in Empower®. As injections are performed by the Waters system, OmniSEC will register the injection triggers and collect data as the samples are injected by the Waters system.
The Viscotek range of detectors can easily be connected to a Waters chromatography system to add advanced SEC detection such as light scattering to these systems. OmniSEC 5.1 has the ability to query Waters Empower® for sample sequences to avoid having to create duplicate sequences saving time and reducing errors. This technical note has briefly described how to connect the Viscotek detectors to a Waters system and how to initiate data collection.