Q: Why do some columns give a stable baseline from the beginning and others show baseline drift (bleeding) for a long time?
A: This is a question of production efficiency. Column material is produced by forming tiny droplets of polymer (could also be around detergent colloids – detergent/colloids) and then cross linking. This brings the required pores Into the final column material. After this step the remaining monomers, debris, colloids etc. have to be removed by a multistep washing process. This washing process, if done thoroughly, can take more than eight weeks of constant manipulation and changing the washing medium, thus adding to the production cost. If this process is ended prematurely in order to save cost it will continue in the customers system leading to slow signal drift for an extended time.
Q: Is the price of a column directly connected to the quality? In other words: do I get a better column if I spend more money on a set of columns?
A: only to a small extent. The cost of a product depends only to some extent on the quality of the product. In addition we have influence of the amount of money spent on marketing, on application assistance, on new developments to fullfil the needs of actual new requests from GPC users with new polymers and to improve columns including applications of. We have the influence of the company structure – the relation of production to overhead costs, the cost of establishing and keeping a brand name. And finally depends on the structure of the production company – whether it is still innovation driven and customer oriented, or already has been taken over by an investment partner that first looks for profitability.
Q: When buying lower cost columns, do I have to expect only getting limited support?
A: No, not generally. There are suppliers that do not rely on high cost advertisements in media but rather on the good reputation of their products within the scientific community. This allows providing the full range of application support even when offering at low cost levels.
Q: What determines the number of columns to use?
A: That depends on the sample material – the expected range of molar masses present in the material. At the other hand it also depends on the pore distributions of the column filling material. If columns with rather narrow bore size distributions are used, it is common to use three columns with small, medium and large bore porosity.
A new alternative is to use columns filled with BPT*-gel material. BPT* stands for “Broad Pore Technology”. This material has a wide distribution range of pores. Usually it is sufficient to use just two BPT*-columns instead of three columns filled with traditional gels.
Q: What is the advantage of using BPT synthesis technology columns?
A: There are several advantages. The most obvious one is the fact that only two BPT- instead of three traditional columns are sufficient to achieve the required separation – which cuts separation column cost by around -30%. The next advantage is the straight calibration line response.
As in BPT columns separation is achieved in just two columns, this means that broadening is reduced leading to better signals, better s/n ratio. Further for the same reason solvent consumption is reduced.
Q: Why does BPT* technology lead to a better calibration line?
A: The reason for the better calibration curve response is in production details. Let’s ask the well known developer of columns, Dr. Dauwe for an explanation: “The main advantage is to be found in a very wide separation range. In most cases this is reached by producing “mixed bed columns” where different pore size products are mixed to cover a larger separation range. In many cases two to four sizes are combined to fill a column.
On first glance calibration curves, e.g. built from 12 data points look perfectly linear. In reality however we have two to four underlying calibration curves of the individual pore size populations. When analyzing broadly distributed polymers where we expect Gaussian size distributions we might find inhomogeneity always at the same position of the Gaussian distribution. This effect may not be caused by the polymer itself but rather from not optimally mixed porosity portions. Even if we try to compensate this effect by fitting with a polynomial of 5th or 7th order we only rely on mentioned 12 data points to calculate the calibration curve. This can become difficult.
The BPT* was developed to avoid this problem. From just one gel synthesis a material can be produced to cover a very large size range that allows good calibration curves even with less than 12 data points reaching very high accuracy results even with a very simple polynomial fit.”
Q: Does the BPT* influence my sample throughput?
A: Yes, because of the smaller internal system volume, not only the separation time is reduced, but also solvent consumption is reduced.
Q: Are there special columns for very low molar mass samples, e.g. oligomers available?
A: Yes, the 35A column material offers a very high window for very small molar masses such as oligomers. This is achieved by forming a high volume of very small pores, leading to very good resolution in the 100 to 1000Da range.
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