GPC/SEC & HPLC & UHPLC, oh my!
There are a lot of acronyms in science, especially when it comes to analytical instrumentation. Some of those acronyms can be easily confused for others, and not only because they share common letters. When the analytical techniques themselves are similar and the differences subtle, things can get even more complex.
In this post, I want to clarify the differences between three liquid chromatography (LC) techniques: GPC/SEC, HPLC, and UHPLC. I’ll provide a brief overview of each and discuss what differentiates them from the others. And last, I’ll highlight what exactly Malvern Panalytical can offer as a solution to your analytical needs!
GPC/SEC
Gel permeation chromatography or size exclusion chromatography is mainly used to measure the molecular weight and size of macromolecules. These samples can be synthetic polymers, natural polymers, proteins, or even a combination of the three.
The separation is based on molecular size, with the largest molecules eluting first and smallest molecules eluting last. The samples dissolved in the liquid mobile phase (an organic solvent or aqueous solution) and carried through the stationary phase consisting of porous gel particles. The smaller molecules can diffuse into these pores more readily than the larger molecules, and thus spend more time in the pores, generating a longer flow path through the column.
Columns for GPC/SEC are designed and chosen to eliminate interactions between the sample and stationary phase so the separation can occur based solely on size. This is different than with HPLC, as I’ll discuss next.
HPLC
High performance liquid chromatography is an analytical technique used to separate, quantify, and potentially identify components of a sample, regardless of molecular weight. While the hardware for HPLC is similar to that required for GPC/SEC (a pump, autosampler/injector, column set, detector(s)), the two differ in their mechanisms of sample separation.
In HPLC, the separation is based on chemical properties of the sample components, such as polarity and charge. The column chosen for an HPLC analysis is selected specifically for the type of interaction that will occur between the sample and column. As the sample is carried through the column by the mobile phase, the goal is that the column will interact more strongly with one sample component than another, providing the basis for separation. Careful choice of column and mobile phase can produce impressive separations – HPLC can even separate enantiomers!
While I mentioned that the hardware for GPC/SEC is similar to that of HPLC, there are key differences. The first is the pump, or pumps. HPLC will often employ a gradient mobile phase, created by mixing in a new solvent or buffer during the analysis to selectively move components along the column at different rates. With GPC/SEC, there is only a single isocratic pump, which is used to keep the flow rate and mobile phase composition as consistent as possible.
The other difference is the detectors. Concentration detectors such as refractive index (RI) and UV detectors are used with both techniques to quantify compounds based on their peak shape; however consideration must be given to the method. A gradient mobile phase has a changing refractive index, which can ultimately send the RI signal off-scale, which is why UV detectors (or fluorescence detectors) are more common with HPLC.
UHPLC
Ultra high performance liquid chromatography utilizes higher pressures, which allows for faster separations than HPLC. Columns are packed with special gel with smaller particles which increases the surface area to improve resolution and helps them withstand the higher pressure.
A version of UHPLC coupled with specialized SEC columns and detectors offers GPC/SEC analyses at reduced run times and with minimal mobile phase consumption.
Solutions offered by Malvern Panalytical
Malvern Panalytical’s OMNISEC system is a complete, multi-detector GPC/SEC system designed specifically for GPC/SEC. Which means it has a single isocratic pump along with detectors and software ideally suited for the comprehensive characterization of macromolecules.
The OMNISEC REVEAL ULTRA multi-detector unit is a UHPLC-compatible detector unit that can be paired with any UHPLC front end (pump, autosampler, column compartment). This combination offers the best of both worlds, the fast run times and minimal mobile phase consumption from UHPLC with the complete macromolecular characterization achievable with multi-detection GPC/SEC.
Final thoughts
I hope this post has increased your understanding of GPC/SEC, HPLC, and UHPLC, as well as the distinctions between each technique. If you have any questions, please don’t hesitate to contact us or email me directly at kyle.williams@malvernpanalytical.com.
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