SRS Labs QMS 100 Series, Руководство пользователя

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Capillary Design 1-11
Technical Reference
The chromatography industry uses a large variety of capillaries, from which we can select capillaries for
the QMS. The figure below shows the conductivity for several commonly available bore diameters.
1E-08
1E-07
1E-06
1E-05
1E-04
1E-03
1E-02
1 10 100 1000
length (cm)
C (liter/s) 2
4
5
6
7
Figure 6. Conductivity of five different capillaries as a function of length. The curves are labeled with the bore
diameter in thousandths of an inch. Both axis are logarithmic.
As an example, consider a capillary for atmospheric pressure and an capillary exit pressure of 1 mbar.
From the speed curve for the diaphragm pump, the throughput,
Q , is 2.5
×
10
-2
mbar liter s
-1
( Q = P S )
and the required conductivity is 2.5
×
10
-5
liter s
-1
. The horizontal dotted line in figure 6 shows that for
each capillary diameter there is an appropriate length. The application dictates which bore diameter is
appropriate. If the system being measured was far away from the QMS, 3 meters of the 7/1000
capillary would be best. On the other hand, for something close 0.7 meters of 5/1000 would be less
expensive. The gas velocity through the capillary quickly reaches the speed of sound. Thereby, until the
capillary becomes
very long, it is not an important contributor to the response time of the QMS.