Thermionic Surface Ionization
(expanding the detection of GCNPD equipment)
HEATING
CURRENT
THERMIONIC IONIZATION DETECTORDESIGN
(CONCENTRIC CYLINDERGEOMETRY)
cylindrical
shaped
ion source located
on axis of collector
cylinder provides
streamlined gas
flow and optimum
electric field for ion
collection
OptimumGeometry
(used on Agilent 6890/7890
NPDand all DEThardware)
.
__IonCollector
Cylinder
• •
r
!
f}-h:
Sample Inlet
:
L
Gas
2
I
I
I
L
Sample
&
Gas
1
&
Makeup (Gas
3)
(H 2• N 2•
Air)
•
I
I
I
I
I
I
Gas 2.J
(Air, N
2 )
Ceramic
Ion Source
(1/16
in. dia.)
Key Sensitivity and Selectivity Parameters:
1. ionsourceworkfunction (surfacecomposition);
2. ionsourcetemperature (set byheatingcurrent);
3. composition of gases around the ion source;
4. polarization between ion source and collector.
Multiplemodes of detection are achieved by
easy permutations of these 4 parameters.
DETector
Engineering
&
Technology, inc.
