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GC Cryo-Trap
™
D24
Scientific Instrument Services, Inc.
™
Phone: 908-788-5550
www.sisweb.com/catalog/08/D24
Headspace GC Analysis
L
ow boiling point volatiles from headspace samplers can
be trapped in the GC Cryo-Trap for subsequent analysis.
This will permit the analysis of large gas volume
injections (0.5 to 100 ml or more) as well as multiple injections of
headspace volumes into capillary GC columns. After trapping
volatile organics at temperatures down to -180°C, the GC Cryo-
Trap is rapidly heated to temperatures to 400° C to release the
volatiles for separation on the capillary column. The resulting
peaks are highly resolved, even for the very light volatiles such as
butane and acetone.
In Figure #1, 0.5 µl of gasoline was dissolved in 5.0 ml of water
in a headspace vial. The sample was heated to 70°C in a CTC
Headspace Sampler and then 1.0 ml of the headspace gas was
injected over a 35 second time interval into the GC injection port
and cryo-trapped in a narrow band on a 1.5u film thickness guard
column in the GC Cryo-Trap at a temperature of -120°C. The
sample was trapped for 5.0 minutes and then rapidly heated to
200°C to release the volatiles for GC analysis. More than 100
compounds were detected and identified including the low boiling
volatiles butane and pentane. A lower trapping temperature of
-180°C was able to trap ethane and propane. Applications of this
technique could easily be expanded to the detection of low boiling
volatiles in water, soil, food products, commercial products and
other solid, liquid and gas matrix samples.
Thermal Desorption - Purge and Trap
Applications
In the thermal desorption technique, large volume gas samples
are typically purged from the sample or adsorbent resin, into the
GC injection port for analysis. Utilizing the GC Cryo-Trap, the
volatile organics from this large gas volume can be cryo-trapped or
cryo-focused in a narrow plug in the guard column in the GC Cryo-
Trap. In Figure #2, 200 milligram of black tea in water at 80°C was
purged with 450 ml of gas and the volatiles trapped on a Tenax TA
desorption trap. The volatiles on the adsorbent resin were then
thermally desorbed off the resin at a temperature of 250°C utilizing
the S.I.S. Short Path Thermal Desorption System, purged into the
GC injection port and cryo-trapped on a 5.0 u film thickness guard
column in the GC Cryo-Trap at two different temperatures (0° and -
70°C). The GC Cryo-Trap was then heated to 220°C to release the
trapped volatiles for subsequent GC/MS analysis. At a cryo-trap-
ping temperature of 0°C, volatiles down to methyl isobutyl ketone
were trapped. At a trapping temperature of -70°C, eight additional
volatiles including acetone were trapped and identified.
Direct Injection Applications
In Figure #3, a series of neat hydrocarbons from ethane
through nonane were direct injected into the GC injection port uti-
lizing the split mode and trapped on a 1.5 u film thickness guard col-
umn in the GC Cryo-Trap at a variety of temperatures. This chart
demonstrates the range of volatiles that can be trapped as a func-
tion of the GC Cryo-Trap temperature. Utilizing the Model 971 with
liquid CO
2
(minimum temperature -70°C), volatiles down to pentane
can be cryo-trapped. Utilizing the new Model 981 GC Cryo-Trap
which uses liquid nitrogen for cooling to a minimum temperature of
-180°C permits the trapping of ethane on this guard column. The
utilization of PLOT guard columns will permit the trapping of even
lower volatiles such as methane, formaldehyde and ethylene oxide.
Figure 1
Headspace analysis of gasoline in water using
GC Cryo-Trap
Figure 2
Purge and Trap of black tea, then Thermal desorb
into GC-Cryo-Trap
Figure 3
Trapping Efficiency of Hydrocarbons on .53mm DB-5
(1.5u) trapped at various GC Cryo-Trap temperatures
Applications of the GC Cryo-Trap and Micro Cryo-Trap
™
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