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www.restekcorp.com800-356-1688
by Greg France, HPLC Product Marketing Manager
Trace-Level Analysis of
Explosives by HPLC
Pinnacle
II
™
C18 & Cyano Columns
✔
Strictly controlled silica manufacturing ensures reproducible
chromatography.
✔
Sharp peak shape and excellent efficiency for explosives.
✔
Economically priced.
Pinnacle II
™
high performance liquid chromatogra-
phy (HPLC) stationary phases were designed to
function well under the difficult matrices encoun-
tered in environmental samples. The original
Pinnacle
™
columns served as benchmarks for the
selectivity and efficiency of these new Pinnacle II
™
columns. While striving to create columns with
characteristics similar to Pinnacle
™
columns,
Restek designed them using Restek silica. Now, we
can go a step further in providing consistent quality
and reproducibility by controlling the manufactur-
ing process back to the raw material stage.
The new Pinnacle II
™
C18 and Cyano columns func-
tion as primary and confirmation columns (respec-
tively) to efficiently separate explosives according to
US Environmental Protection Agency (EPA) Method
8330A. Environmental methods frequently employ a
confirmation column for two reasons. First, many
environmental methods require scanning for a
large number of related compounds. Because of
their similarities, analysts often will encounter
coelutions when using a single type of stationary
phase. Second, the matrices encountered in many
environmental samples can contain components
that may interfere or obscure the analytes of inter-
est. By using two columns with different selectivi-
ties, analysts can more accurately identify the ana-
lytes of interest.
Selectivity for the 14 explosives of interest listed in
Method 8330A are similar on the original
Pinnacle
™
and the new Pinnacle II
™
C18 columns
(Figure 1). On these C18 columns, there are close-
ly eluting peaks or coelutions for the following
compounds: tetryl/nitrobenzene; 2-amino-4,6-dini-
trotoluene/4-amino-2,6-dinitrotoluene; and 2,6-
dinitrotoluene/2,4-dinitrotoluene. Closer examina-
tion shows that the new Pinnacle II
™
C18 column
achieves better resolution for two of these pairs.
This may be caused by the slightly higher surface
area and carbon load, and the smaller pore size on
the Pinnacle II
™
column (110Å) as compared to
the Pinnacle
™
column (120Å). The higher carbon
load of 13% for the Pinnacle II
™
column, versus
11% for the Pinnacle
™
column, translates into
longer compound retention, and better resolution
and column lifetime.
According to Method 8330A, these 14 compounds
also need to be analyzed on a Cyano column for
confirmation (Figure 2). Changing from a reversed
phase C18 column to a normal phase Cyano col-
umn is fairly easy. The method recommends using
the same mobile phase for both columns, which
allows a quick changeover from the primary analy-
sis to the confirmation analysis. Because the mobile
phase is a simple mixture of water and methanol,
the process of switching from the C18 to the Cyano
column is only a matter of removing the primary
column and installing the confirmation column on
the same HPLC system. There is relatively little
downtime, only that required for the system to re-
equilibrate.
Figure 1
The new Pinnacle
II
™
C18 column achieves better resolution for difficult-to-analyze
pairs of explosive compounds.
Peak List for Figure 1
1. HMX
2. RDX
3. 1,3,5-trinitrobenzene
4. 1,3-dinitrobenzene
5. tetryl
6. nitrobenzene
7. 2,4,6-trinitrotoluene
8. 2-amino-4,6-dinitrotoluene
9. 4-amino-2,6-dinitrotoluene
10. 2,6-dinitrotoluene
11. 2,4-dinitrotoluene
12. 2-nitrotoluene
13. 4-nitrotoluene
14. 3-nitrotoluene
Column:
Pinnacle
™
C18
Dimensions:
250 x 4.6mm
Particle size:
5µm
Pore size:
120Å
LC_0194
Column:
Pinnacle
II
™
C18
Catalog #:
9214575
Dimensions:
250 x 4.6mm
Particle size:
5µm
Pore size:
110Å
LC_0189
min.
Conditions:
Mobile phase:
water:methanol
(50:50, v/v)
Flow:
1.5 mL/min
Temp.:
27°C
Det.:
UV @ 254nm
Sample:
Inj.:
3µL
Conc.:
500µg/mL each component
Solvent:
acetonitrile
Restek 8330 Calibration mix #1 (cat. # 31450)
Restek 8330 Calibration Mix #2: (cat. # 31451)
original
Pinnacle
™
C18
New
Pinnacle
™
II
C18