DETector Engineering & Technology, inc.
486 N. Wiget Lane,Walnut Creek, CA 94598 USA
telephone: (925) 937-4203
fax: (925) 937-7581
DET
e-mail:
innovations in chemical detection
NPD ION SOURCES (BEADS) USED INAGILENT NPDS
COMPARISONOF CERAMICVERSUSGLASSCONSTRUCTION
ceramicsurfacecoating
0.060 In. dla.
detennines ionization activity
metal post
0.008 In. dia.
supportwire
~~~~I
Insulator
rigid ceramic subcoatlng
I
protectswire core
I
stainless steel
stainless steel
mounUng flange
mounting flange
Bios Bead forAgilent NPD
DEl Ion Source Construction
(fits
Agilent &DEl structures)
CERAMIC
GLASS
1.) 1/16 inch diameter ceramic materials coated over an 1.) Approximately 0.040 inch diameter glass bead
internal wire core.
deposited on the loop end of o.ooa inch diameter
2.) Ceramic ion sources remain a rigid solid surface at supportwire.
the 600 - aoo°c temperatures required for NP detection. 2.) Glass bead is in a softened stateat the temperatures
3.) Additives in the ceramicswithstand temperatures In required for NP detection. Microscopic examinat ion of
excess of 1000°C so ion sources can be used w ith a used beads often reveals internal bubbles and/or
wide variety of operating conditions without danger of particulategrowthson the surface. Somevolatilization
melting.
of bead material is also likely with vaporized material
depositing on colder surfaces downstream.
4.)Ceramic sublayercoatingcompletelycovers thewire
core of the ion source and protects it from corrosion 3.) Detector operating conditions must be carefully
from additives in the surface coating or from corrosive controlled to avoidmelt ing the glass.
sample matrices. Sublayer additives are chosen to 4.) Thin supportwire iseasily bent out of shape by the
enhancethehardnessandelectrical conductanceofthat slightest touch.
ceramic coating.
5.) Thin support wire is exposed to corrosion from
5.) Additives in the ceramic surface layer determine the additives in the glass aswell as from corrosive sample
ionizing and catalytic activity of the ion source. Many matrices.
different surface coatings are possible to optimize NP 6.)Exposed supportwirecontributessome ionization in
responsecharacteristicsaswell asprovideothermodes addition to theglass bead.Tailing of Phosphoruspeaks
ofthermionic ionizationdetectionsuchasselectivityfor isa characteristicof theNP responses.
Oxygenates and Halogenates.
7.) In operat ion, electrical resistanceof the ionsource is
6.) In operation, electri cal resistance of the ion source 0.19 Ohms which means that ion source heating power
wire core is 1.2Ohmswhich ensures that heating power heats lead wires and connectors in addition to the ion
is mainlydissipated in the ion source rather than in the source, and the temperature of the ion source is
electrical lead wires and connectors.
extremely sensitive to the stabilityof the heating power
7.} Physical size of the ion sourceminimizes sensit ivity supply.
to gas flow changes in the
detector,
8.)Small physical sizeoftheglassbeadmeansthebead
is very sensitive to fluctuations in gas flows, and
positioning the bead relative to the incoming sample
orifice is critical.
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