Column Connection and Linear Type Columns
In case of conventional columns, it is usual to connect columns with different pore sizes for covering a wide molecular weight range. However, in the calibration curve of connected columns, an inflection point will appear and a shoulder around the inflection point. Linear type columns solved this problem and linear calibration curve for a wide molecular weight range can be obtained.
In order to analyze polymer samples, whose molecular weights spread over a wide range, it is necessary to chose a SEC column, which covers a wide molecular weight range. However, since the molecular weight range covered by one column is limited, it is necessary to connect several columns together, which have different pore size.
Chromatograms (1) to (5) show the results of analysis for the same polystyrene sample using different columns. A single column is used for (1), two different columns are used for (2) (KF-805 + KF-804), (3) (KF-806 + KF-803) and (4) (KF-806 + KF-804) and three different columns are used for (5) (KF-806 + KF-805 + KF-803). One problem was found from the results that the peak patterns were different from each other in spite of the fact that the sample is the same. Another problem is that a shoulder was found in the peak pattern. In the case of (2) and (4), apparent shoulders can be found at the points shown with the arrow. These shoulders are generated when different columns are connected in series and their calibration curves are not straight. In order to solve the above problem, linear type columns were developed. Linear type columns packed with mixed gel, which is a mixture of different pore size, is recommended. Since the ratio of gels in the mixture is carefully chosen to realize a straight calibration curve for a wide molecular weight range, it is possible to obtain a same elution pattern at any time. For better separation, the use of two or three linear column types in series is recommended. Refer to chromatogram (6) (KF-806L).
Sample : PS, Polystyrene
Columns : Shodex GPC KF-800, KF-800L series (8.0mmID*300mm each) Eluent : THF Flow rate : 1.0mL/min
Calibration curves for GPC KF-800L series, linear type columns are shown.
Sample : PS, Polystyrene
Columns : Shodex GPC KF-800L series (8.0mmID*300mm each) Eluent : THF
Calibration curves for GPC K-800L series, linear type columns are shown.
Sample : PS, Polystyrene
Columns : Shodex GPC K-800L series (8.0mmID*300mm each) Eluent : CHCl3
GPC KF-806M and KF-806L are both packed with mixed type gel. However, compared with KF-806M, KF-806L which was developed recently has better linearity in the calibration curve.
Sample : PS, Polystyrene
Columns : Shodex GPC KF-806M, KF-806L (8.0mmID*300mm each) Eluent : THF
When two or three different columns (non linear type) are connected in series, it is difficult to obtain a complete linear calibration curve. On the other hand, an linear calibration curve can be obtained, when the same linear type columns are connected in series. The above table shows the mean error (%) for each combination of columns. The calibration curves were determined by the method of least squares with cubic equations. The mean error (%) was obtained by taking the average of the errors in molecular weight compared to molecular weight read from the calibration curves with actual molecular weights of the six polystyrene standards. Connection of three linear type column, GPC KF-806L gave the smallest error.
Sample : PS, Polystyrene
| Combination of Column |
Mean % Error in M |
Correlation Coefficient |
|---|---|---|
|
KF-805 + KF-804
|
14.68 | 0.9996 |
|
KF-806 + KF-803
|
6.79 | 0.9999 |
|
KF-806 + KF-804
|
11.47 | 0.9997 |
|
KF-806 + KF-805
+ KF-803 |
4.38 | 0.9999 |
|
KF-806L x 3
|
2.54 | 1.0000 |
Columns : Shodex GPC KF-806 + KF-805 + KF-803, KF-806L x 3 (8.0mmID*300mm each) Eluent : THF Flow rate : 1.0mL/min
The linear type column, GPC KF-804L, has a wide linear range in calibration curves from low to high molecular range. Compared with the conventional column, KF-804, the separation is improved around the oligomer area.
Sample : PS, Polystyrene
Columns : Shodex GPC KF-804, KF-804L (8.0mmID*300mm each) Eluent : THF
A compasion of the separation of polystyrene by three linear type columns and connection of three different columns is shown.
Sample :
1. PS, Polystyrene (MW: 9,120,000)
2. PS, Polystyrene (MW: 1,100,000)
3. PS, Polystyrene (MW: 410,000)
4. PS, Polystyrene (MW: 128,000)
5. PS, Polystyrene (MW: 33,000)
6. PS, Polystyrene (MW: 10,200)
7. PS, Polystyrene (MW: 1,350)
8. n-Propylbenzene (MW: 120)
Columns : Shodex GPC KF-806 + KF-805 + KF-803, KF-806L x 3 (8.0mmID*300mm each) Eluent : THF Flow rate : 1.0mL/min Detector : Shodex RI Column temp. : Room temp.
The linear type column, GPC KF-804L, can separate PS(MW: 580) (peak 7) better than the conventional column, KF-804.
Sample :
1. PS, Polystyrene (MW: 501,000)
2. PS, Polystyrene (MW: 156,000)
3. PS, Polystyrene (MW: 66,000)
4. PS, Polystyrene (MW: 21,900)
5. PS, Polystyrene (MW: 7,000)
6. PS, Polystyrene (MW: 2,450)
7. PS, Polystyrene (MW: 580)
8. Ethylbenzene (MW: 106)
Columns : Shodex GPC KF-804L x 2 : Shodex GPC KF-804 x 2 (8.0mmID*300mm each) Eluent : THF : THF Flow rate : 1.0mL/min : 1.0mL/min Detector : UV(254nm) : UV(254nm) Column temp. : Room temp. : Room temp.
This is a comparison of separation results obtained between two connected linear type columns (GPC KF-805L) and two connected conventional columns (KF-805 + KF-803). When different columns are connected, a shoulder appears, while no shoulder appears, when two of the same column type are connected.
Sample :
1. PS, Polystyrene (MW: 9,120,000)
2. PS, Polystyrene (MW: 1,100,000)
3. PS, Polystyrene (MW: 410,000)
4. PS, Polystyrene (MW: 128,000)
5. PS, Polystyrene (MW: 33,000)
6. PS, Polystyrene (MW: 10,200)
7. PS, Polystyrene (MW: 1,350)
8. n-Propylbenzene (MW: 120)
Columns : Shodex GPC KF-805L x 2 : Shodex GPC KF-805 + KF-803 (8.0mmID*300mm each) Eluent : THF : THF Flow rate : 1.0mL/min : 1.0mL/min Detector : Shodex RI : Shodex RI Column temp. : Room temp. : Room temp.