GPC/SEC tips (Part III) – Early detection of column media compression

Relying on ‘soft’ polymeric particles to separate samples - GPC/SEC Columns are commonly prone to pressure instability. Each sample injection creates a pressure “shock” to the columns. A sudden change in flow rate when the injector valve switches from one position to the other (and for a fraction of a second when the passage of eluent is fully blocked) is the true reason for the pressure shock. While many believe GPC/SEC columns to be capable of absorbing this without experiencing any permanent damage, over time the accumulated effect of this affect risks compressing the separation media thereby creating a void volume at the head of the column. Continuous monitoring of flow in your GPC/SEC system, to ensure exact flowrate is rapidly reached after every switch of the injector valve, provides you with early detection of column compression and elimination of the consequent inaccurate results.

November 20th 2025

GPC/SEC tips (Part II) – Early detection of baseline instability.

Baseline stability is an absolute necessity in GPC/SEC. It is widely accepted that Refractive Index detectors are sensitive to the presence of dissolved gas in the eluent. Using a vacuum degasser in GPC/SEC has therefore become standard practice. However, although robust and reliable, even degassers vary in performance over time. This phenomenon is however not a “all or nothing” thing, it is more a slowly drifting into inaccurate results scenario. Over time it is not uncommon to see a slow degradation of baseline stability resulting in increased flow fluctuation and pump pulsation. As with most slow processes, early detection of the problem is highly challenging. The risk is that the problem passes undetected for a long period introducing uncertainty into the validity and comparability of your GPC/SEC measurements. To eliminate this uncertainty, we recommend continuous monitoring of the effective flow rate using a non-invasive flowmeter. This provides early detection of increased gas load in the eluent thereby minimising the risk of inaccurate results.

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GPC/SEC tips (Part I) - How to avoid problems with hydrophilic solvents.

GPC/SEC separations typically run for considerably longer periods of time than HPLC / UHPLC applications. Consequently, particular care must be taken with GPC/SEC protocols to ensure repeatable and reliable results.
When operating with hydrophilic organic solvents like THF or DMF, air moisture will slowly affect the eluent resulting in shifts of elution volume influencing the peak shape of measured polymers or even resulting in pump malfunctions. While using small reservoir volume helps, it prevents unattended 24/7 operation. Reservoir bottles with appropriate aeration filters will reduce these problems, however they must be serviced and may introduce other pollutants. A great solution to this is to continuously monitor the effective flow rate thereby providing early detection of any change in eluent quality and eliminating the risk of faulty results.

Can I rely on GPC/SEC flow markers?

GPC/SEC flow markers are substances, typically low molar mass compounds, added to or used with a GPC/SEC system to correct for variations in retention times between runs and improve data reproducibility. Unfortunately, problems with use of GPC/SEC flow markers can arise from an unstable or inconsistent flow rate, causing errors in elution volume and significantly impacting molar mass calculations. Common issues that cause problems with GPC/SEC flow markers include fluctuations in pump performance, pressure changes from polymeric columns, changes to the mobile phase, and column equilibration problems after flow interruptions. Is monitoring of the flow a necessity in GPC/SEC? Absolutely yes, however it must be done the right way. Modern flow monitoring systems such as those offered by TESTA Analytical are simple to use, non-invasive, accurate, deliver real-time information and allow real correction of the flow rate by monitoring the current flowrate at a relevant frequency. Do not stick with surpassed methods, be an expert, use a flow monitoring system.