where the more volatile components elute. In this segment of the analysis, a 3 second modulation period with a 500 ms hot pulse was utilised to increase trapping efficiency and resolution on the 1st dimension. Figure 5 highlights a section of the Contour Plot where the shorter modulation period provides for increased resolution on the x-axis. Figure 6 shows the portion of the Surface Plot where the less volatile components elute. In this segment of the analysis, a 5 second modulation period was utilised to accommodate the analytes that are highly retained on the 2nd dimension column. A 1000 ms hot pulse was utilised to increase desorption efficiency. The increased desorption efficiency results in improved peak shape
Figure 5: A highlighted section of the Contour Plot where the shorter modulation period (3 sec) provides for increased resolution on the x-axis.
and increased signal for the least volatile analytes in this portion of the analysis.
The Red Mousse is a weathered product created when the oil has been exposed to water and air, forming a stable emulsion. The Red Mousse sample analysed in this project was collected on the surface offshore. Figure 7 shows the Contour Plot for the Red Mousse sample. The Contour Plot with peak markers is shown in Figure 8. When data processed, 992 peaks above the s/n threshold were identified in the Red Mousse sample. The most noticeable difference from the Well Head Source Oil sample is the absence of analytes in the more volatile portion of the plot. The most volatile peak identified in the Red Mousse is 2,4,6- trimethyloctane, which has a 1st dimension tr of 1560
seconds and a 2nd dimension tr of 1.490 seconds. The most retained analyte in the 2nd dimension is 2-
methyl chrysene, which has a 1st dimension tr of 3114 seconds and a 2nd dimension tr of 3.535 seconds.
Conclusions Figure 7: A contour plot of the Red Mousse sample.
Figure 6: A surface plot of the Well Head Source Oil sample showing peak shape of the late eluting compounds.
dimension, allows for an increase in resolution on the 1st dimension in that region. The use of shorter hot pulse durations allows for increased trapping efficiency in the modulator in regions with more volatile analytes. The use of longer hot pulse durations allows for increased desorption efficiency in the modulator in regions with less volatile analytes. By varying the modulation period and hot pulse duration during the course of an analysis, it is possible to optimise the modulator’s performance to provide the best resolution on the 1st dimension column (x-axis) and improved 2nd dimension peak shape throughout the analysis. Figure 4 shows the portion of the Surface Plot
Figure 8: A contour plot of the Red Mousse sample showing peak markers for the 992 peaks with a s/n ratio of ≥ 100.
To date, the oil spill off the coast of Louisiana, in the Gulf of Mexico, is the largest oil spill in US history. The environmental and economic consequences of this event will continue well into the future. The ability to identify the chemical make-up of these incredibly complex samples, including the source oil as well as the changes in composition resulting from weathering and additional chemicals used in response to the spill will be an important tool utilised by those responding to this event. These samples contain components over a wide range of volatilities and functionalities. When analysed by GCxGC-TOFMS, the large number of individual components can be resolved and identified in a single analysis, providing an efficient means for the analyst to obtain a large amount of information about the sample with a minimum amount of effort. Leco’s Pegasus4D GCxGC-TOFMS system and ChromaTOF software are an excellent choice for the analysis of highly complex samples such as those demonstrated in this work.
Neutralised Temperature Conditions for Accurate Spectrometer Measurement
A new accessory from Ocean Optics is broadening the range of applications for its field-portable spectrometers. The SteadiQ provides a temperature controlled atmosphere, helping to stabilise temperature effects and eliminate temperature drift in inclement conditions or extreme temperatures from -20C to 50°C. The rugged, portable device assures more accurate, reliable results in field applications including solar irradiance, volcanic observation, greenhouse monitoring, and industrial environments such as cold food storage.
Available in both UV (200-1100nm) and Vis-NIR (400-2500nm) versions, the SteadiQ interfaces directly with Ocean Optics’ USB2000+, USB4000, HR2000+, HR4000, Maya2000, Maya2000 Pro, QE65000, and NIRQuest spectrometers. In extreme hot or extreme cold conditions, the unit operates independently from outside temperatures. It connects easily to the spectrometer with preconfigured plug-ins and communicates via the spectrometer’s USB port.
Circle no. 19
New Metal GC Columns Deliver Higher Reproducibility for Petrochemical Testing
Phenomenex, Inc introduces the Zebron™ ZB-1XT SimDist – a metal GC column specially designed for simulated distillation analyses in petrochemical applications. The new column features Phenomenex’s unique Glass Infusion™ technology, which ensures consistent phase coating and reproducibility. Zebron ZB-1XT SimDist are rugged and provide documented efficiency gains of up to 70% over other comparable metal columns on the market. Every column is individually tested to guarantee quality.
Simulated boiling point methods are commonly used in petrochemical analysis to determine the range of hydrocarbons in a sample. These high-temperature distillation methods require resolution greater than 2.0 of C50 and C52, posing a challenge for most columns used in this application. The new Zebron ZB-1XT SimDist column exhibits less than 3.5% loss in resolution after 90 hours at 430°C.
“Traditional metal GC columns used in these applications have exhibited uneven stationary phase bonding, which negatively affects performance and reproducibility,” explained Kory Kelly, GC Product Manager for Phenomenex. “Our proprietary bonding technology ensures consistent quality and each of our new columns is tested individually, rather than in batches.”
Circle no. 20
Chromatography Focus
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