HighSpeed GPC/SEC
- Solutions for HighSpeed GPC/SEC
- PSS products and services for HighSpeed GPC/SEC
- Theoretical background HighSpeed GPC/SEC
Solutions for HighSpeed GPC/SEC
GPC/SEC measurements require a certain amount of time. Depending on the number of analytical columns the time requirement per sample/injection is in the range of 12 minutes to 60 minutes. To handle an ever increasing number of samples in shorter time several strategies have been implemented. However, many of these solutions have the disadvantage that information is lost (e.g. Flow Injection Polymer Analysis, FIPA - no distribution information, only averages) or that resolution is lost (shorter or less columns). There are only a few options that are information rich and fast:
- Instrument cloning
- Multiplexing: parallel analysis on a single shared instrument
- Overlaid injection
- Small particle technology
- Column dimension modifications
HighSpeed GPC/SEC with specially designed columns
PSS products and services for HighSpeed GPC/SEC
PSS offers complete turn-key systems for instrument cloning as well as dedicated GPC/SEC systems with HighSpeed columns for interaction-free aqueous and organic GPC.
The turn-key system is based on the modular SECcurity GPC System with WinGPC UniChrom GPC/SEC software. The WinGPC UniChrom overlaid injection feature allows to save 30-50% time and solvent with any injection, due to the unique WinGPC data structure with the integrated sample database. Overlaid injection works for GPC/SEC and HighSpeed GPC/SEC alike.
PSS has identified HighSpeed columns with optimized column dimensions as the best solution for fast GPC/SEC. HighSpeed columns allow efficient separation within 2 minutes analysis time per column and sample. They are operated at higher flow rates. Their column dimensions (inner diameter and length) are especially designed for these conditions.
The SECcurity GPC System is ideally equipped for the PSS HighSpeed columns and allows high flow rates with highest flow precision. The autosampler provides fast injection cycles to allow injections every minute. WinGPC Unity offers convenient automation routines incuding automatic calibration/recalibration and reporting. The WinGPC Report Designer can set automatic QC flags (e.g. passed/fail) and can be programmed to automatically caculate additional results.
PSS offers also products for clients, that only want to reduce the analysis time and sample preparation time while keeping their analytical columns. PSS ReadyCals are polymer cocktails preweighted into autosampler vials. Each of the three vials has three or four polymers of the same type with different molar masses. So a 12 (9)-point calibration curve can be constructed from only three injections. The cocktail is composed that all samples are baseline separated even when only one (linear or mixed-bed) column is used, giving also access to universal calibration curves.
Theoretical background HighSpeed GPC/SEC
Do HighSpeed Columns need more solvent than other columns?
HighSpeed columns need to be run at higher flow rate, but since the separation is over in only a few minutes, the same amount of solvent is needed than with analytical columns. An easy example shows that
|
Column/dimensions |
operating flow rate |
required analysis time |
required solvent amount per sample |
|
analytical (8x300 mm) |
1 ml/min |
12.5 minutes |
12.5 ml |
|
HighSpeed (20x50 mm) |
6.25 ml/min |
2 minutes |
12.5 ml |
So HighSpeed columns are a solution to save time, but require the same amount of solvent than analytical columns. If the amount of solvent should be reduced microbore columns are the best option.
Resolution, reproducibility, and back pressure for PSS HighSpeed columns
The resolution and the separation efficiency of a GPC/SEC column depends on the pore volume. PSS HighSpeed columns provide the same pore volume than analytical columns. Optimized column material and adapted column frits help to overcome limitations normally present when the column diameter is increased. Therefore PSS HighSpeed columns show comparable resolutions with analytical columns.
The example shows the separation of seven different Poly(styrene) molar mass standards on a conventional column and a HighSpeed column. Both columns are able to separate the mixture, but the required analysis time is significantly different.
The reproducibility can be best shown with an example:
A commercial Poly(carbonate) has been analyzed in THF on PSS HighSpeed GPC columns SDV 5µ 1 000 Å and 100 000 Å. The sample has been injected 60 times, the overall analysis time was 2.5 hours. The figure shows the overlay of 10 repeat injections.
Results Poly(carbonate):
Mw = 29 610 ± 150 g/mol,
with an RSD of 0.5 %
Nominal Mw producer: 30 000 g/mol.
Back pressure:
Due to the large inner diameter and the optimized column materials HighSpeed columns (6.25 ml/min) produce lower back pressure than analytical columns (1 ml/min). Therefore they minimize shear degradation and are ideal for stress free sample testing, especially for high molecular weight compounds.
What does overlaid injection mean?
The separation efficiency and the resolution of a GPC system depends on the number of columns used. The more columns the better are the achieved results. On the other hand the analysis time and solvent consumption increases with the number of columns. If the number of columns can not be reduced the overlaid injection feature of WinGPC allows to save time and eluent with every injection while keeping the resolution.
Every GPC/SEC column has a defined interstitial volume, where only solvent can elute while the sample is still moving through the column. Analytical columns from PSS with a length of 30 cm and a diameter of 0.8 cm have an interstitial volume of approximately 5 ml per column. For separations at a flow rate of 1 ml/min this means that during the first 5 minutes per column sample can not be eluted. Due to this fact it is not necessary to wait for complete elution of one sample before injecting the next sample.
The figure shows 2 different injects in WinGPC, each inject indicated by an injection mark (blue triangle at the bottom) and the sample name at the top right. Before the system peaks and the internal standard (light green triangle) of “PS 280 br” are eluted, the next sample “PS 1124 a” is already injected at 8.5 ml. The analysis and data evaluation
of sample “PS 280 br” is not affected by that; baseline and
integration limits can be set as required by national and
international GPC standards, e.g. ISO 13885.