Chapter:
Topic:
mJEcroRSANDGASVAL~
Manual Direct Injection Technique
Aslow
injection
will
result
in
broad,
tailing
peaks
that
may
coelute.
A
quick.
properly
performed
iqjectice
will
result
in
sharper
peaks.
Jl
When perfornting analyses usingmanual direct injection, the
methodor technique
used
toprepare the syringe and perform the injection
canmean the difference between
obtaining
chromatograms
that
areeither
poorly resolved or cleanand sharp. Reproducibility can also be affected if
the amount injected varies from injection
to
injection. This is whyit is
imperative that a consistent, reproducible method or technique ofmanual
injection be
used
when perfornting direct injection.
Sample volume affects the quality of data produced
by
the gas
chromatograph.
If
too
much sample is injected, the column becomes
overloaded
and
the
peaksproduced
will
be broad and tailing. Insufficient
sample
will
likely result inquantitation inaccuracies.
If
thesyringe is not
properlyprimed and loaded' (or thesample slug contains
air
bubbles)
when injecting liquid samples, or thesyringe
has
not beenproperly
evacuated, purged and loadedwhen injecting
gas
samples, the sample
amount aetually injected
will
vary,
as
will
the results obtained.
The
procedure indicated below is just oneofmany in use today by
chromatographers perfornting direct injection of liquid samples. The
syringeandplunger arecleaned. Theplunger should not be bent, Then
the syringe is flushed thoroughly, primed, and loadedwithprecision.
t®
t@
'"""
...
oyri...
-'"
~.wming
the
phqer.
Th<a'_
~ein.
"""""
,""",
""'"
-,
vial,
and
cjc<:1
MrqlJe
CI.lUidc
ofvial
wipe
needle,
and
............
~
coprime:
oyri....
I
t
Follow
the
..
mictoIilef
•
"'_k
,
with
one
Dnw~
i
"""
l
microliter
•
-~
•
micrclitcr
of
air,
-
microliter
,
of
air
iIm
•
"""'""'"'<
•
o(~lc
_
.
...
•
I
tbe~le
,
i1&O the
qringe.
......,""
-
lIIup
otair.
"'"
...
""''''
..
,
""'"
""
syrinre
i.
1oelIed.
illKlt
!he
rlllOdIe imo
tbeiajection
port
quickly.
.......
..-,
quiel::lyand
"""""
""
,""",
immediaIely.
.q=on
"""'"
......
lea
!han
2
........
Properlyprepared, the syringeneedle is inserted completely into the injection
port
in one
smooth, quick
motion. Then
theplunger is driven home
immediately.
As soonas the plunger tiphits
theendof the sample chamber, the syringe needle iswithdrawn from the injection
port
in a quick,
smooth motion. This will prevent any sample remaining
in
the needle from having time
to
vaporize
into the injection
port
before or duringwithdrawal
(if
this
wereallowed tooccur, it would result in
peak
broadening and
tailing).
You may currently beusing adifferent technique fordirect injection.
As long as the method beingusedis consistent and reproducible, you
will
obtain reliable, consistent
reproducibility from your direct injection analyses of gasesand/or liquids.
REV. 0-17-94
