Do not install the column too low or too high within the injector.
Column efficiency is dependent on:
Basic resolution equation
Selectivity
Comparison of analyzing components using BPX1 and BPX50
Comparison of analyzing components using BP1 and BP20 (WAX)
Internal diameter (ID) can vary from 0.245 to 0.255 for a typical 0.25 mm ID column. When the inlet pressure and length are held constant, the flow rate can change by 16%.
The smaller the diameter, the greater the efficiency.
Decreasing column diameter results in:
The longer the column; the greater the efficiency.
Doubling the length increases resolution by 40%.
Retention (capacity) is dependent on:
Increasing the film thickness will increase retention and improve resolution for volatiles.
Retention (capacity) is dependent on:
Hydrogen delivers the most time efficient separation
Advantages |
Disadvantages |
|
Hydrogen |
|
|
Helium |
|
|
Nitrogen |
|
|
The lower the HETP, the better.
Turn on the carrier gas and adjust the column pressure to the desired value. If pressure for the column has not been pre-determined, adjust flow rate temporarily to that recommended as listed in the tables below.
Cut the column end and check column flow by dipping the column end into a small vial containing a solvent (e.g. pentane). A stream of bubbles should be observed. If not, check for possible leaks in the GC inlet or for any sign of damage to the column.
Column ID (mm)
|
Column length (m) |
Flow rate (mL/min)
|
|||||||
10 |
12 |
15 |
25 |
30 |
50 |
60 |
120 |
||
Approximate column head pressure (psi (kPa)) | |||||||||
0.1 |
39 (270) |
44 (300) |
50 (340) |
- |
- |
- |
- |
- |
0.7 |
0.15 |
17 (120) |
19 (130) |
- |
32 (220) |
36 (250) |
50 (340) |
- |
- |
1 |
0.22 |
- |
8 (55) |
- |
14 (100) |
16 (110) |
24 (170) |
27 (190) |
- |
1.54 |
0.25 |
- |
- |
7 (48) |
- |
12 (83) |
- |
21 (140) |
33 (230) |
1.75 |
0.32 |
- |
3 (21) |
4 (28) |
6 (41) |
7 (48) |
10 (69) |
12 (83) |
- |
2.24 |
0.53 |
- |
0.72 (5) |
0.9 (6) |
1.5 (10) |
1.8 (12) |
3 (21) |
3 (21) |
- |
3.71 |
Column ID (mm)
|
Column length (m) |
Flow rate (mL/min)
|
|||||||
10 |
12 |
15 |
25 |
30 |
50 |
60 |
120 |
||
Approximate column head pressure (psi (kPa)) | |||||||||
0.1 |
56 (390) |
63 (435) |
71 (490) |
- |
- |
- |
- |
- |
0.56 |
0.15 |
26 (180) |
29 (200) |
- |
47 (325) |
52 (360) |
71 (490) |
- |
- |
0.84 |
0.22 |
- |
13 (90) |
- |
22 (150) |
25 (170) |
35 (240) |
39 (270) |
- |
1.23 |
0.25 |
- |
- |
11 (76) |
- |
19 (130) |
- |
30 (210) |
48 (330) |
1.4 |
0.32 |
- |
5 (34) |
6 (41) |
9 (62) |
11 (76) |
16 (70) |
18 (124) |
- |
1.79 |
0.53 |
- |
1.3 (9) |
1.6 (11) |
3 (21) |
3 (21) |
5 (34) |
6 (41) |
- |
2.97 |
What is normal column bleed?
What is not normal column bleed?
Why is low bleed better?
We substitute some of the oxygen with the aromatic ‘benzene’ into the polymer backbone, known as the silphenylene unit. The aromatic ring acts as an "energy sink". As the column is heated in the GC, the vibrational and rotational energies increase. The aromatic ring helps disperse this energy, thus preventing phase breakdown.
There are three categories of column activity:
Depending on the solute analysed, the effects of air oxidation of a column is generally observed first as either an:
How air can get into your system
Effect on a 5% Phenyl polysiloxane-silphenylene column using air as a carrier gas
Effect of subjecting columns to air as a carrier gas