OMNISEC is the premier multi-detector gel-permeation/size-exclusion chromatography (GPC/SEC) system from Malvern. It is a complete solution for the molecular characterization of synthetic polymers, natural polymers and polysaccharides, and proteins. As a system, it comprises two parts, OMNISEC REVEAL, the integrated multi-detector module, and OMNISEC RESOLVE, the integrated separations module.
OMNISEC REVEAL combines refractive index, UV/Vis absorbance, light scattering and viscometer detectors to measure concentration, molecular weight and intrinsic viscosity with unparalleled sensitivity and accuracy as part of a GPC/SEC system.
OMNISEC RESOLVE includes a fully integrated degasser, pump, autosampler, and column oven for mobile phase delivery, sample presentation and separation before measurement in OMNISEC REVEAL.
With the technical capabilities that have gone into the modules, an OMNISEC system offers numerous major advances over previous generations of systems. Table 1 provides a summary of these.
This technical note describes the features and benefits of the OMNISEC system and explains how OMNISEC sets a new standard in molecular characterization.
| Benefit | Innovation |
|---|---|
Better quality data means: a) A more accurate representation of the physical parameters of the material resulting in better control of material properties and more predictable performance b) Improved result precision (e.g. MW %RSD for PLGA down from 8% on TDA to 1% on OMNISEC) c) Better sample flexibility (Low molecular weight polymers – polyols, alkyds, additives, peptides; low dn/dc polymers – PLGA, PCL) d) Observing finer changes between samples | - 10x improved light scattering sensitivity. - 8x improved refractive index sensitivity.- More stable temperature control for better baselines. - Advanced pump design for more stable baselines. - Reduced inter-detector volumes and band-broadening. - Improved signal and data processing. |
| Minute sample amounts (as little as 100 ng of BSA or a 105 kDa polystyrene) | - 10x improved light scattering sensitivity means more signal from smaller injection masses. - 8x improved refractive index sensitivity means more signal from smaller injection masses. - Zero-waste injections increase the number of measurements per ml sample by at least 30%. |
| Measure lower molecular weights (as low as 200 Da) to open up new applications e.g. Polyols, alkyds, additives, peptides | - 10x improved light scattering sensitivity. |
| Measure samples with lower dn/dc which opens up a wider range of applications e.g. PLGA, polycaprolactone | - 10x improved light scattering sensitivity enables higher quality measurements of low dn/dc samples which only scatter a small amount of light. |
| Maximum system uptime | - Self-balancing viscometer with user-exchangeable capillaries extends the life of the capillary bridge and reduces replacement time from days to <20 minutes. - Pump with continuous seal back wash prevents wear from salt build up. |
| Reduced cost of ownership | - Reduced service requirement. - Self-balancing viscometer with user-exchangeable capillaries reduces cost of repair. |
| Versatility | - Self-priming pump, low volume degasser and delay column bypass reduce mobile phase exchange time to <1hr (vs >2-3 hr in the TDAmax). |
| No system on the market is easier to use, setup or integrate | - OMNISEC software has a workflow-based design to make setup, acquisition and analysis simple and quick to learn - USB connection for instant setup. - Plug-and-play design reduces the need to open the instrument and risk accidental damage. - Crystal clear instructional material. |
| Drastically reduced sample aggregation/degradation | - Autosampler cooling prevents sample aggregation and degradation. - Room temperature control means no need for elevated temperatures during acquisition |
| Seamless integration of advanced GPC/SEC into existing lab workflows | - Make injections from vials or 96-well plates. |
OMNISEC REVEAL is the advanced detector module. It contains all four detectors in a single integrated unit. It can be run on its own as a plug-and-play detector when combined with any existing GPC/SEC system (simply connect flow to the inlet, and an injection trigger) or as part of a complete system including OMNISEC RESOLVE. As an integrated multi-detector system, it is an incredibly powerful tool for the complete molecular characterization of synthetic polymers, natural polymers and polysaccharides, and proteins.
The integrated approach offers a number of technical advantages. By housing all the detectors together in a single compartment, the distances between them can be kept to an absolute minimum. This minimizes the level of band-broadening (dispersion) and tailing that happens between the detectors, maintaining the peak shapes throughout the run. Well-proven software corrections accurately account for any dispersion that does take place. The use of a single temperature controlled compartment allows the entire measurement to be made at an accurately controlled temperature. For polymer applications, this means the temperature can be elevated to reduce the viscosity of certain mobile phases such as DMSO (dimethyl sulphoxide). For protein applications, this means the protein sample is not undergoing the additional stress of repeated heating and cooling cycles as it is heated up in detector cells and then cooled to room-temperature repeatedly.
OMNISEC REVEAL includes the following 4 detectors in series:
The differential refractive index detector is a robust design that places it as the very first detector with the others following in series. This maximizes the sensitivity of the other detectors, in particular, the viscometer, and helps to minimize the band broadening between the detectors, again improving measurement accuracy. Precise temperature control and high quality electronics all contribute to exceptional baseline stability improving sensitivity eight times over the TDA, improving the accuracy of the concentration measurements
The UV/Vis absorbance detector is a photo-diode array capable of making measurements from 190-900 nm and therefore covers the full UV and visible range. This widens the potential applications range to include samples such as polythiophenes which may absorb light outside the UV range.
The light scattering detector in OMNISEC REVEAL is the most sensitive on the market. Its sensitivity enables measurements of molecular weights as low as 200 Da (PEO; columns 2 x A6000M, buffer: 0.2 M Na2SO4; injection: 3.927 mg/mL, 100 µL); injection masses as low as 100 ng of material (Polystyrene, column: 1 x T6000M; mobile phase: THF; injection: 0.0125 mg/mL, 10 µL) (BSA, columns 1 x PLS3030; buffer: PBS; injection 0.05 mg/mL, 2 µL), or novel polymers with low dn/dc.
The light scattering detector is a successful RALS/LALS design pioneered by Viscotek. It determines absolute molecular weight by measuring the intensity of the light scattered by the sample. A RALS (right-angle light scattering) detector measures the scattered light at 90° and has excellent sensitivity due to its simple optical design.
The LALS (low-angle light scattering) detector measures the scattered light at just 7°. A LALS detector can accurately measure the absolute molecular weight of all molecules without extrapolation or fitting of the angular data. The combination of RALS and LALS offers the sensitivity of a RALS detector with the accuracy of a LALS detector to provide excellent molecular weight measurements across the whole range addressed by GPC/SEC. The additional benefit of the RALS/LALS design is that the flow cell volume is just 18µL. This minimizes band broadening and tailing (dispersion) that occurs between detectors.
The viscometer in OMNISEC REVEAL is based on the original Wheatstone bridge design patented by Viscotek but has been re-engineered to improve its usability and performance. The new viscometer includes two major improvements over previous designs
The first is the user-exchangeable capillary bridge. In older viscometer designs, a blockage in one of the capillaries required an expensive service call or possibly even a return-to-base repair taking days to weeks and costing thousands of dollars. OMNISEC REVEAL’s viscometer now contains a user-exchangeable bridge allowing easy replacement in just 10 minutes. This dramatically reduces the cost of a failure, both financial and in downtime.
Secondly, the viscometer features fully-automated bridge balancing. This feature is software controlled – by adjusting the resistance on one side of the viscometer bridge it can balance a new bridge or re-balance an old bridge. This makes the installation of the new viscometer bridge trouble-free and can even extend the life of a partially blocked bridge. The digital viscometer’s transducers are of a 316 stainless steel piezo-resistive design to maximize the solvent compatibility and pH range. They are protected by built-in transducer over-pressure protection which opens a purge valve if the pressure is too high to protect them from damage.
The overall result is a new generation of viscometer technology and a dramatic improvement in viscometer usability.
The chromatography components of OMNISEC RESOLVE include:
The isocratic pump delivers mobile phase to the column and detectors, and has been optimized to improve separation quality and baseline stability, providing better separations and higher quality data. It includes automatic continuous back-flushing of the pump seals to reduce the chance of any salt precipitation in buffers containing high-levels of salt, subsequently reducing the likelihood of seal wear and failure. This makes the system ideal for separations in DMF with LiCl or aqueous buffers.
The degasser has an efficient low-volume design, which means that mobile phases can be rapidly exchanged for quick solvent changeover and reduced downtime. This helps reduce mobile phase exchange time to less than one hour compared with at least 2-3 hours in the TDAmax.
The autosampler can inject samples from up to two 48 vial trays or 96-well micro-titer plates. Temperature control of the sample compartment means that polymer samples can be warmed to reduce solvent viscosity for loading. Protein samples can be cooled to 4°C to protect them from any aggregation or degradation while awaiting injection. In “zero-waste mode” sample injections up to 100 µL can be made with no waste of sample, minimizing the sample requirement for precious samples such as proteins. Compared with the GPCmax, this reduces sample use by at least 30%.
The column oven can hold up to 6 analytical columns or a single GE TricornTM 300/10 (e.g. Superdex) column. Temperature control all the way up to 65°C maintains a stable separation temperature maximizing measurement sensitivity.
Summaries of the features and benefits of the OMNISEC system are given in figure 2 and table 2.
Figure 2: Summarized benefits of the components of an OMNISEC system.
| Number | Feature | Benefit |
|---|---|---|
| 1 | Light scattering sensitivity | Measure less sample (100 ng). Measure lower molecular weights (200 Da). Measure lower dn/dc samples (PLGA, PCL). |
| 2 | Self-balancing viscometer with user exchangeable bridge | Reduce service time from days to minutes. Reduce replacement cost. |
| 3 | Refractive index sensitivity | Measure less sample (100 ng). Measure lower concentrations of high molecular weight samples (hyaluronic acid). |
| 4 | Self-priming GPC pump with continuous seal back wash | Reduces the likelihood of pump failure due to wear in polar solvents or high salt buffers. Helps reduce mobile phase exchange time to <1hr (vs 2-3 hr in TDAmax). |
| 5 | Zero-waste injections | Prevents waste of precious samples. Make more measurements from less sample (at least 30% more measurements). |
| 6 | Cooled autosampler | Prevents fragile samples from aggregation or degradation (e.g. proteins). |
| 7 | Low volume degasser | Reduces mobile phase exchange time to <1 hr (vs 2-3 hr in TDAmax). |
| 8 | UV/Vis PDA | Open up application range (e.g. polythiophenes). Identify wavelength of maximum absorbance. Monitor spectral changes. |
| 9 | Plug & play connectivity | Faster out-of-the-box setup. |
| 10 | Workflow-based software | Makes setup, acquisition and analysis simple and quick to learn. |
Multi-detection means that the results that are available from the system are greater than the sum of the detectors available. The true power of multi-detection is the combination of these results. For instance, while molecular weight and intrinsic viscosity are measured alone, their combination allows the calculation of hydrodynamic radius (Rh) and the Mark-Houwink parameters which are used to assess structural changes such as branching. This is demonstrated in the multi-detection pyramid shown in figure 3.
Figure 3: The multi-detection pyramid
The sum total of the described features of OMNISEC REVEAL makes measurements using this detector the most accurate and precise available. Figure 4 shows 8 overlaid RI chromatograms of a NIST polystyrene standard, SRM1478. Measured molecular weight is shown across the top of the peak. The resulting statistics are inlaid. The overlay can be seen to be excellent, with the table showing calculated RSD values for Mn, Mw, Mz, IV and Rh to all be less than 0.5%.
Figure 4: Overlaid RI chromatograms of SRM1478
Malvern’s OMNISEC system is the ultimate in GPC/SEC multi-detection offering the most high-quality and accurate data available from an advanced GPC/SEC system.
As a detector-only module, OMNISEC REVEAL can be connected to any existing GPC/SEC system to add the power of advanced detection. In combination with OMNISEC RESOLVE it forms a complete GPC/SEC solution. This system is easier to use, requires less servicing and provides the highest quality data available.
