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HIGH-PERFORMANCE GC NEEDS HIGH-PERFORMANCE SOFTWARE
How to Get the Most from Your GC System
Gas chromatograph (GC) performance depends on both hardware and software capabilities. You may never
realize the potential of your high-performance GC if your data system does not let you take full advantage
of all its features.
Matching Software and Hardware Performance
High-performance GCs need high-performance software. Some data handling systems, for example, are unable to
acquire full dynamic range data in a single run. When performing fast GC, software limitations can also
sacrifice the accuracy of results.
One Example: Complete, Accurate Results in One Run
Data from a high-performance GC may span ten orders of magnitude and 35 bits. Some GC data systems, such as
Perkin-Elmer, Varian, and Shimadzu, limit the collection range to only six orders of magnitude. Unless you
happen to know the concentration of sample components of interest and they happen to fall within the dynamic
range of the software, you may have to perform two or three runs to obtain complete, accurate results.
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Figure 1. Setting the data range too low truncates large peaks, causing inaccurate quantitation. Small
peaks are not detected or integrated when the data rate is set too high (lower chromatogram).
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Even if these conditions are met, multiple runs will be required when samples contain both high-concentration
components (large peaks) and trace impurities (small peaks) that extend beyond the dynamic range of the
data system. Figure 1 shows how a data system may cut off the top of a large peak, causing incorrect area
percent calculations if the range is set too low. If the range is set too high, as in the lower chromatogram,
the data system cannot collect data from very small peaks and therefore leaves them unreported. Either way,
the quantitative results are inaccurate.
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Figure 2. Fast GC requires fast data acquisition rates to maintain acceptable peak shape and
quantitation accuracy.
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Data collection rates must increase to maintain quantitative accuracy and repeatability as peak
widths decrease and analysis speed increases.
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This problem simply does not exist with the multitechnique Agilent Technologies ChemStation and ChemStation
Plus. Because they match the full capabilities of Agilent high-performance GCs, you can quantitate all data
accurately in a single run (Figure 2).
Another Example: Reduced Run Times
Agilent ChemStation and ChemStation Plus software also complement the fast-GC capabilities of the Agilent
6890 Plus and Agilent 6850 Series GCs. Fast GC lets you reduce run times by a factor of ten or more, which
means increased sample throughput and reduced turnaround time. For example, you can perform a detailed
hydrocarbon analysis (DHA) that has a typical run time of 120 minutes in only 30 minutes with the same
elution order and resolution. Agilent Technologies provides free method translation software (available
on our Web site at www.agilent.com/chem) that can help you convert current methods to faster methods
quickly and effortlessly.
To achieve shorter run times, GC detectors must collect data at higher sampling rates—typically 50 to
200 Hz. Yet some data systems cannot process data at these rates, which are necessary to maintain the
accuracy of fast GC results.
Proper peak quantitation requires a minimum of 10 data points per peak. At a data-sampling rate of
10 Hz, or 10 data points per second, peaks less than one second wide will have less than 10 data points
and therefore may not be quantitated accurately. At 200 Hz, there are 200 data points per second, which
means that peaks as narrow as 50 msec can be handled reliably (see table). One word of caution: data
collection rates higher than 200 Hz can cause such unwanted results as high noise and large data files.
Taking Full Advantage of Fast GC
Data systems that require an analog-to-digital converter (A/D) or instrument interface box to control
the GC may limit the data collection rate. Perkin-Elmer, for example, can control four dual-channel
GCs per interface box, but restricts the data collection rate to 10 Hz per channel. If the chromatography
data system cannot keep up with the speed of the signal from the GC detector, the peak shape and,
therefore, quantitation accuracy are sacrificed.
The multitechnique Agilent ChemStation and Agilent ChemStation Plus let you take full advantage of fast
GC; they can collect signals from multiple dual-channel instruments simultaneously at rates of up to
200 Hz per channel.
GC hardware is being enhanced continuously to provide faster, more sensitive, and more accurate answers.
Data handling systems need to reflect commensurate advancements, managing GC data easily and accurately
at any speed and without extra work. Otherwise, software may limit your laboratory's productivity regardless
of the performance capabilities of your hardware.
Click for information on matching GC hardware and software performance.
Click for information on fast GC.
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