clinical/forensic
Applications
note
RestekCorporation • (800)356-1688 • (814)353-1300 •
#59598
Dual-ColumnConfirmational GCAnalysis of BloodAlcoholsUsing the
Rtx
®
-BAC1andRtx
®
-BAC2ColumnsOptimized for thePerkin-Elmer
HS 40HeadspaceAutosampler
Figure1
Achieve baseline resolutionof all bloodalcohol components in less than3minutes using theRtx
®
-BAC1andRtx
®
-BAC2
columns andaPerkin-ElmerHS40headspace autosampler.
Dual column analysis using a two-hole ferrule.
1.0mL headspace sample of a blood alcohol mix
Oven temp.:
40°C isothermal
Inj. temp.:
200°C
Carrier gas:
He
Sample equilibration temp.:
70°C
Sample equilibration time:
15min.
Vial pressure:
30psi
Vial pressurization time:
0.15min.
Vial sampling time:
0.01min.
Transfer line:
0.32mm ID FS
Hydroguard™ tubing
Transfer line temp.:
200°C
Injection port sleeve:
2mm ID
Split flow:
20mL-per-minute.
Conc.
w/v
1. methanol
0.1%
2. acetaldehyde 0.2%
3. ethanol
0.2%
4. isopropanol
0.1%
5. acetone
0.01%
6.
n
-propanol
0.1%
30m, 0.32mm ID, 1.8µm
Rtx
®
-BAC1
(cat.# 18003)
30m, 0.32mm ID, 1.2µm
Rtx
®
-BAC2
(cat.# 18002)
Testing for thepresence and subsequent quantitationof ethanol
inblood, breath, andurine are thehighest volume tests per-
formed in forensic laboratories. In addition to ethanol, the
detectionof several other significant alcohols and theirmetabo-
lites is necessary.Gas chromatographic (GC) assays provide the
greatest amount of flexibility and specificity in analyzing for
thesevolatile compounds.Direct injectionof biological samples
intoGC columns has beenused in the past as themethodof
sample introduction. This typically leads to column contamina-
tion anddecreasedperformance. The incorporationof headspace
sampling into themethodprevents thebuildupof non-volatile
contamination at the headof the column andhelps tomaintain
consistent performance andextendcolumn lifetime.
Analysis time and resolution are two critical factorswhen
developing aGC assay for ethanol.Analysis time for each
sample shouldbe as short as possible,while stillmaintaining
baseline resolution for all analytes. Isothermal analysis is the
methodof choicebecause it eliminates the cool-downperiod
between temperatureprogrammed runs.Overall analysis time
canbe reduced in isothermal analysis by raising the temperature
of the analysis or by increasing carrier gas flow rate.However, in
attempting to shorten the analysis time, either by increasing the
flow rateor by raising the temperature,many traditional capillary
column stationaryphases fail toprovide adequate resolutionof
all of the components commonly testedduringblood alcohol
analysis.Restekhas designed twonovel capillary column
stationaryphases tomeet all of these requirements.
Our experimentation focusedonusing these twounique station-
aryphases in combinationwithheadspace sampling toprovide
dual-column confirmational analysis of blood alcohol in less than
threeminutes.The equipment used included aPerkin-Elmer
AutoSYSGCwith a split injectionport anddual-flame ioniza-
tiondetectors, and thePerkin-ElmerHS40headspace
autosampler. Instrument control anddata collectionwere
providedbyusingPerkin-ElmerNelsonTurbochrom software,
interfaced through aPerkin-ElmerNelsonLink900.
TheHS40uses abalancedpressure samplingprocedure to
transport the sample to theGC.This typeof samplingworks better
withcolumns that requirehigher headpressure. 0.32mm ID
analytical columnswere chosen for this applicationbecauseof
their higher operatingpressure.Optimal performanceof these
columnsduringheadspaceanalysisdependsonGC/headspace
system set up.Bandbroadeningcanoccur if there is excessdead
volume in the sample flowpathbetween the samplevalveand the
headof thecolumn.Lowvolume inlet linersor interfaces in the
injectionport shouldbeused to reduce theamount of excess
volumeat theexit endof the transfer line.A2mm ID sleevewas
used in this analysis to reducedeadvolume andmaintain narrow
peakwidths.Highcarrier gas flow rates through the transfer line
alsocanbeused tomaintainnarrow samplebandwidths and
speedup sample transfer to theheadof the column.Aflowof
40mL-per-minutewasused tooptimize theanalysison theHS40.
min.
2.0
1.0
6
5
4
3
2
1.2 1.4 1.6 1.8
1
2.2 2.4 2.6 2.8 3.0
min.
3.0
1.0
6
5
4
3
2
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1
