Chapter:
Topic:
PURGE-AND-TRAP
10 Station Purge-and-Trap Autosampler (continued)
Gas injection
port
=--1;4@}1
16mm
x
250mm ./
disposable /'
sample spargiDg
tube
Sparge head and
disposable
glass
sample
tube
Insulated
heated
transfer
linejacket
.>
--_~
Sparge
gas
inlet
"""-.. (from
sparge
gas
outlet
on
SRI 8610C GC)
wide-bore
fused silica-lined
mota!
capillary
transfer
line
to
8610CGC
purge--8Dd-tr.lp
inlet
(replaces
GC
_go
bead)
<,
SRI 10 STATION PURGE-AND-TRAP AUTOSAMPLER FRONT VIEW
allows the analyst
to
have access to each sample sparging head and injection port, and tomove the
autosampler around on the lab bench as needed, while maintaining
all
connections and operahility. As
the autosampler is a stand-alone
unit,
it
does not require ahard attachment orbracket for GC
mounting. A3' length of 1/16" stainless steel tubing carries the sparge gas from the GC's EPA-Style
Purge-and-Trap Sampler sparge gas outlet (previously supplying gas
to
the single sparge head),
and
an insulated, electrically-heated capillary transfer line returns the sample-laden gas to the
purge-and-trap system's dual adsorbent traps
via
the GC-mounted purge-and-trap plumbing and
sampling valve hardware. The glass sample tubes are low-cost disposable 16mm x 250mm (2Occ)
straight-mouthed test tubes available in bulk packs from SRI or any laboratory supplier. The sparge
head assemblies arestainless steel hardware
that
is heated
by
the valve oven
that
they are mounted
to,
eliminating cold metal condensation of sparged analytes.
The
bilateral configuration of sparge heads
with
respect
to
the stream selection valve, located inside the heated, insulated valve oven,
permits
the
use of the minimum amount of valve plumbing. This
ensures
efficient and complete transfer of
sample-laden gas through the autosampler system, for delivery to the GC and purge-and-trap
concentrator. The headspace
gas
injection ports use the same 1/8" molded silicon
septa
that are used
in
the
Ge's
direct
on-column
injector,
minimizing
the need
to
maintain
a variety of consumable
replacement
parts.
Unlike the
on-column
injector, the headspace injection
ports
accept needle sizes
larger
than
26 gauge, such as those commonly found on large volume gas sampling syringes.
