June 2013 » Chromatography Techniques
Figure 3: ASTM D5501: denatured bioethanol chromatograph in under 5 minutes.
processing delays. A typical forensics lab may
run anywhere from 50 to 1,000 samples a day,
and operate 24/7 to keep up with minimums.
Therefore, even small time savings can mean
large productivity gains in this industry.
Optimized selectivity can provide improved
resolution between drug compounds with similar structures. In Figure 2, it’s evident that the
column chemistry, Zebron ZB-Drug-1, reverses
codeine and morphine elution order compared
to a traditional 5 percent phenyl phase column.
Also apparent is that compounds that would
have formerly been troublesome to forensic scientists because of co-elutions may now resolve
on the optimized phase, leading to more accurate analysis.
Leveraging this selectivity also allows for
optimized column ID and shorter column
length for dramatically reduced analysis
times—up to 800 percent faster. This application-specific chemistry not only allows
forensic scientists to run their samples more
accurately, but also speeds up their analysis
in a way that could potentially save thousands of hours.
vides complete resolution of methanol,
ethanol and the denaturant to help increase
the efficiency and safety of bioethanol plant
production and transportation. Using an
optimized phase allows further alterations of
the dimensions to provide this resolution in
a 5-minute run (Figure 3). This is less than
half the time QC testing labs target, and it
delivers an 800 percent improvement in productivity over the traditional method.
Environmental chemists have long struggled with the analysis of semivolatile organic
compounds (SVOCs) by EPA Method 8270.
This method contains an exceptionally long
and complex compound list, which may
number over 200 if adding appendix or cli-ent-specified analytes. A varied spectrum of
chemical groups is present, from extremely
reactive acidic phenols to very basic amines,
as well as neutral compounds like polynuclear
aromatic hydrocarbons (PAHs).
General-purpose columns are not deactivated specifically for SVOC compounds, which makes analysis challenging. Manufacturers that have tried to
deactivate their columns in the past have slightly improved this; however,
columns are typically deactivated for either acidic or basic compounds and
are not well-deactivated for both. Each class of analyte is present in SVOC
methods, however, and a column that fails for one class will cause the entire
analysis to fail. The GC phase Zebron ZB-SemiVolatiles was designed to be
well-deactivated for both types of compounds.
GC columns typically used for semivolatiles testing were evaluated to
determine their performance against the stringent requirements outlined
in the Zebron ZB-SemiVolatiles QC test process. Designed to provide GC
analysts with a guarantee of performance specifically for troublesome
semivolatiles methods, this process characterizes both acidic and basic
activity and sets previously unmonitored requirements for GC column
performance that are even more stringent than required by EPA 8270D.
Minimum peak response requirements for
pyridine (0.6) and Pentachlorophenol (0.3)
serve as a metric for characterizing both basic
and acidic column activity. Columns with
higher initial peak responses can be expected
to maintain performance over time, providing
longer lifetimes for the method. Additionally,
higher responses allow runs at lower detection
levels, improving the sensitivity of the analysis.
Of the columns tested, only ZB-SemiVolatiles had high and balanced responses
for both acids and bases. Other columns had
good responses for bases but sacrificed the
response for acids, or vise versa. Excellent
separations on the ZB-SemiVolatiles column
can be achieved in less than 16 minutes, a 58
percent improvement in productivity over the
EPA Method (Figure 4). The improved results
on ZB-SemiVolatiles demonstrate the true
value of choosing an application-specific GC
column designed, deactivated and QC-tested
to deliver highly inert performance specifically
for semivolatiles methods.
Before commercialization, bioethanol plants are required to certify their
fuel using GC following ASTM Method D 5501. Ethanol in a denatured
fuel sample must be analyzed by GC and results included with the shipment. However, this method is long and inefficient, taking up to 40 minutes,
whereas the ideal run time is under 10 minutes. Many attempts have been
made to shorten the run time by altering GC column dimensions (in particular column length) while using a traditional, general purpose 100 percent
dimethylpolysiloxane stationary phase. Although short analysis times have
previously been achieved (down to 7 minutes) using a 15-meter column
length, method requirements were not met. Methanol and ethanol were not
resolved and many co-elutions with the denaturants were present.
An application-specific stationary phase, Zebron ZB-Bioethanol, pro-
Figure 4: Semivolatile organic compound scans in under 16 minutes.