LC/MS and the Cone Wash
Flow Splitting ___________________________________________________________________________
3-10
__________________________ MSQ Hardware Manual ____________________________
To achieve a rough estimate of the flow rate into the source:
1.
2.
3.
4.
5.
6.
Remove the probe from the source enclosure.
Connect the probe directly to the column outlet and set the flow rate of
the LC pump to the desired flow rate into the source; for example,
0.2 mL/min.
Count the drops that fall off the end of the insert in one minute. Make a
note of this figure.
Connect the split as shown in Figure 3-7.
Now set the LC pump to the flow rate that is required through the
column, for example, 1.0 mL/min.
Count the drops that fall off the end of the insert in one minute.
If the split is set up correctly (in this case, to give a split ratio of 4:1), then
the number of drops recorded in Step 6 will be the same as that in Step 3. If
the number of drops is greater in Step 6, shorten the length of the tubing
connected to the waste (or UV detector) stream. If there are fewer drops in
Step 6, then a longer length of tubing is required. Continue this until the
number of drops in Step 6 is the same as that recorded in Step 3.
Note.
There is no need to measure the split ratio accurately. Even
significant changes in split ratio have only a minimal effect on
chromatographic peak shape.
To accurately measure the split and therefore know the exact flow rate into
the source, use the following method:
1.
2.
3.
4.
5.
6.
Remove the probe from the source enclosure.
Connect the split to the probe and LC pump as shown in Figure 3-7.
Set the flow rate of the pump to the flow required through the column;
for example, 1.0 mL/min.
Collect and weigh the liquid that emerges from the insert in one minute.
Follow the same procedure with the liquid that emerges from the waste
(or UV detector) stream.
Calculate the ratio of the two masses of the liquid to give the split ratio,
and hence calculate the exact flow rate into the source.
For example, if 200 mg emerges from the insert and 800 mg from the waste
stream in one minute, then the split ratio is 4:1 and the flow rate into the
source can be calculated as 0.2 mL/min.
