The high mass resolution of IONICON’s PTR-TOFMS series can now be complemented by a fast gas chromatographic pre-separation step. This new fastGC add-on augments your data with another dimension of chemical information, allowing to separate isomeric compounds, while maintaining fast spectral runs.
In a gas chromatographic (GC) column, compounds are separated in retention time according to their chemical properties. In contrast to classical GC, spectral runs in less than one minute are possible with the IONICON fastGC module, providing near real-time data. The fastGC is an add-on for IONICON PTR-TOF systems and uses the same sample inlet. The fastGC mode can be activated when required while not affecting the regular PTR-TOF operation otherwise. It can also be used to eliminate the influence of high concentrations of matrix compounds, e.g. ethanol in beverages, and to study fragmentation and interferences.
The setup is depicted in the figure. The fastGC module consists of the heated column, a sample loop, several valves (1-4), and an additional flow controller. The valves can configure different operation modes: such as real-time PTR-TOF measurement, sample loop loading and injection, and subsequent fastGC measurement. For more details, refer to [Romano et al].
What makes the fastGC “fast”?
The duration of a GC analysis is limited by the last compound eluting the column. This can be sped up by heating the column following defined temperature ramps. With typical ramp speeds of 30°C/minute in conventional GC systems this results in run-times of several ten minutes. Moreover, the column and its surrounding oven need to cool down before the next run can be initiated.
IONICON’s fastGC system uses shorter columns of 3-6 m, but the key to fast spectral runs is the innovative heating system: the metallic column is resistively heated, keeping the thermal mass at a minimum. This allows for fast heating rates of 15°C/second (900°C/minute) AND cooling rates of 10°C/second allowing spectral runs in < 1 min.
Integration and Usability
The fastGC control software allows changing parameters, configuring temperature ramps, and to initiate (also repeated) fastGC runs. The software is tightly interconnected with the PTR-TOF operation software to synchronize fastGC runs and data acquisition.
Most benefits of a fastGC-PTR-TOF can nicely be demonstrated by performing a headspace analysis of a “shandy drink” - a 50:50 mixture of beer and lemonade. Selected traces are shown in the figure. More scientifically relevant examples are presented in the further below.
Separation of isomers:
The trace at m/z 137 shows a multitude of nicely separated monoterpenes that would not be distinguishable without GC pre-separation. Only one of them being limonene, which is likely to be found in lemonade.
The fastGC also allows a closer inspection of fragmentation ratios using the real sample, without the necessity to revert to analyzing pure compounds. In a fastGC spectrum, the fragment ions coincide at identical retention times, see m/z 81, a known fragment of monoterpenes. Thus, fragments and their rations can easily be determined.
Separation of matrix compounds:
The fastGC has another advantage in situations where the sample matrix contains compounds in high concentrations. For example, the high ethanol concentration in the headspace of alcoholic beverages can lead to a problematic depletion of the primary ion yield. Using the fastGC, ethanol (m/z 47) elutes shortly after sample injection and rapidly decays to background levels, making subsequent detection of VOCs unproblematic.
The figure also shows the O2+ signal (m/z 32) which is proportional to the oxygen content in the sample gas. Since oxygen elutes from the column without retention, it can be used as a reference.
Food and Flavor Research
The fastGC option is particularly useful in food and flavor science. Researchers are often faced with two problems: 1) A few compounds, e.g. ethanol in alcoholic beverages, are present in high concentrations and dilution would be required, and 2) several isomeric compounds are of interest and cannot be resolved easily.
In the figure, we demonstrate the separation of several isomeric compounds from a head-space measurement of wine. Only the fast gas-chromatographic separation reveals the distinct differences in concentration of the isomers between the samples. Moreover, the high concentration of ethanol elutes the column at an earlier time and hence, does not affect the measurement of the compounds of interest compounds [Romano et al].
Biology - Separating Monoterpenes in Conifer Samples
Monoterpenes are a group of biological VOCs emitted in high quantities by numerous plant species, particularly conifers and are associated with the typical scent in a forest. A PTR-TOF can record the combined contribution of these isomers, and – with the addition of the fastGC – the contributions of different monoterpenes can be monitored individually. Materić et al. have studies monoterpene emissions from different pine needles. The figure shows fastGC-PTR-TOF chromatograms of: a) Monoterpene standards, b) Norway spruce, c) Scots pine, and d) Black pine. More see [Materic et al.]
The separation and identification of the vast number of compounds present in biological samples poses a challenge even for high mass resolution instruments, such as PTR-TOF. The fastGC add-on can substantially improve this situation. This has been demonstrated by Ruzsanyi et al. for measurements of aldehydes emitted from skin and for compounds present in human breath. For these tests a prototype version of the fastGC using a multi-capillary column had been used.
To demonstrate the separation capability of the fastGC for breath compounds, two ketones, 3-heptanone, which is a metabolite of 2-propylpentanoic acid (valproic acid) and 3-methyl-hexanone as a potential indoor air contaminant were selected. 2-propylpentanoic acid is used as antiepileptic drug primarily in the treatment of epilepsy, and major depressive disorder.
Innovation Award 2015 Winner
"The Analytical Scienist" magazine published the 2015 Innovation Awards (TASIAs), celebrating a year of innovation in December 2015. IONICON fastGC is among the 15 winners of an Innovation Award. Independent judges have decided and we are glad to be one of the award winners for advances and innovation in analytical science. Read the story!
Golden Gas Award Winner 2015
The IONICON fastGC is the winner of the Gases & Instrumentation International Magazine's 2015 Golden Gas Award in the category Gas Chromatography. We're proud to receive this recognition, honoring the ability to solve an important challenge to the gas industry. Read the story!
On current IONICON PTR-TOF models the fastGC module is integrated inside the PTR-TOFMS instrument. To facilitate the upgrade of existing PTR-TOF instruments, an externally housed version which is mounted on-top of the PTR-TOF is available.
nonpolar, MXT-1 (Restek)
|Max. heating rate:||
|Max. column temp.:||
> 250 °C
< 2% precision, < 10% accuracy
purity > 6.0
pressure < 5 barg
flow: column - adjustable: 0 - 10 ml/min
< 400 Watt
Limit of Detection – LoD
The limits of detection in the fastGC mode are higher compared to real-time measurement with the PTR-TOF: In the latter, the signal can be integrated for a prolonged time to reduce noise and improve the LOD, whereas in fastGC mode the integration time is limited by the peak width of around one second. Especially the flow through the short GC column is lower than required for the PTR-MS drift tube and therefore is supplemented by clean N2, which is equivalent to a dilution of the sample. However, the chromatographic separation of the compounds diminishes the overlap of (isomeric) compounds and can thus greatly improve the practical LoD for real samples.
With the PTR-TOF 8000, LODs of ~ 0.6 ppb could be demonstrated.