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www.restek.com2004 vol. 3
Fast Dual-Column Analysis of Pesticides or PAHs
Using an Rtx
®
-440 Capillary GC Column
Assessments for organochlorine pesticides or
polynuclear aromatic hydrocarbons (PAHs) are
critical, frequently performed GC analyses—
and they often are among the most challenging.
Issues that can arise include analyte break-
down and poor linearity, and calibration times
can be long. In addition to the problems inher-
ent to the analysis, analysts must be concerned
with column reactivity and bleed, which affect
sensitivity and reproducibility. In analyses of
PAHs, there are critical pairs to resolve and,
because the samples often include interfering
hydrocarbons, a confirmation column typically
is required. Compounding these problems is
constant pressure to process more samples in
less time.
With the new Rtx
®
-440 column, Restek makes
available an excellent choice for both of these
demanding applications.
Organochlorine Pesticides:
Sub-10-Minute Analyses
Figure 1 shows a separation of 20 commonly
analyzed organochlorine pesticides, obtained in
less than 10 minutes by using an Rtx
®
-440 col-
umn. Only
α
-chlordane and endosulfan I (peaks
10 & 11) are not separated to the baseline. The
column’s excellent thermal stability is indicated
by a virtually flat baseline between the initial
temperature and the maximum temperature of
the program, 330ºC. In a dual-column approach
to this application, an Rtx
®
-440 column can be
paired with an Rtx
®
-CLPesticides2 column. The
latter column will provide an equally fast separa-
tion (Figure 2) and near-equivalent resolution,
with a reverse in elution order for endrin alde-
hyde and 4,4'-DDT (peaks 17 & 18). By connecting
the two columns to a “Y” connector and making
the sample injection onto a 5-meter intermediate-
polarity deactivated guard column, the two analy-
ses can be conducted simultaneously.
Polynuclear Aromatic Hydrocarbons:
Baseline Resolution of Critical Pairs
In Figure 3, 16 commonly encountered PAHs
have eluted from an Rtx
®
-440 column in less
than 18 minutes. Two critical pairs, phenan-
threne/anthracene (peaks 5 and 6) and
benzo(a)anthracene/chrysene (peaks 9 and 10),
are resolved to baseline, and benzo(b)fluoran-
thene and benzo(k)fluoranthene (peaks 11 and
12) and indeno(1,2,3-cd)pyrene and
dibenzo(a,h)anthracene (peaks 14 and 15) are
almost completely separated. Also notice the
excellent thermal stability—baseline rise is
negligible even at 320ºC. Similar results can be
obtained by using an Rtx
®
-5Sil MS column or an
Rtx
®
-CLPesticides2 column and constant flow, as
shown in the Applications section of our general
catalog. An Rtx
®
-440 column can be paired with
either of these other columns, for a rapid, dual-
column/FID analysis of commonly encountered
PAHs.
•Analyze 20 organochlorine pesticides in less than 9 minutes.
•Analyze 16 PAHs in 22 minutes.
•New low-bleed, high-resolution column is ideal for dual-column analyses.
!
new
★
By Greg France, Innovations Chemist, and Gary Stidsen, Innovations Team Manager
Figure 1
Separate 20 organochlorine pesticides in 9 minutes, using an Rtx®-440 column.
Conditions for Figures 1 and 2
Sample:
Organochlorine Pesticide Mix AB #2 (cat.# 32292),
2,4,5,6-tetrachloro-
m
-xylene (ss) (cat.# 32027),
decachlorobiphenyl (ss) (cat.# 32029), diluted in
hexane, on-column amounts listed on figure
Inj.:
1.0µL splitless (hold 0.75 min.), 4mm Drilled
Uniliner
®
inlet liner (cat.# 21055)
Inj. temp.:
225°C
Carrier gas:
hydrogen, constant pressure
Linear velocity:
73cm/sec. (Rtx
®
-440) or 77cm/sec. @ 140°C
(Rtx
®
-CLPesticides2)
Oven temp.:
140°C (hold 0.5 min.) to 268°C @ 30°C/min.,
to 290°C @ 11°C/min., to 330°C @ 25°C/min.
(hold 5 min.)
Det.:
ECD @ 320°C
Compound
Conc. (ppb)
1. 2,4,5,6-tetrachloro-
m
-xylene (ss)
80
2.
α
-BHC
80
3.
γ
-BHC
80
4.
β
-BHC
80
5.
δ
-BHC
80
6. heptachlor
80
7. aldrin
80
8. heptachlor epoxide
80
9.
γ
-chlordane
80
10.
α
-chlordane
80
11. endosulfan I
80
12. 4,4'-DDE
160
13. dieldrin
160
14. endrin
160
15. 4,4'-DDD
160
16. endosulfan II
160
17. endrin aldehyde
160
18. 4,4'-DDT
160
19. endosulfan sulfate
160
20. methoxychlor
800
21. endrin ketone
160
22. decachlorobiphenyl (ss) 160
GC_EV00734
Figure 2
An Rtx®-CLPesticides2 column complements the Rtx®-440 column in
dual-column analysis of organochlorine pesticides.
GC_EV00733
Rtx
®
-CLPesticides2 30m, 0.32mm ID, 0.25µm
(cat.# 11324), intermediate-polarity deactivated
guard column, 5m x 0.32mm ID (cat.# 10044)
Rtx
®
-440 30m, 0.32mm ID, 0.50µm
(cat.# 12939), intermediate-polarity
deactivated guard column, 5m x 0.32mm ID
(cat.# 10044)