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10 February / March 2018


Improving Workflow in Group-Type GC×GC Analysis of Petrochemicals


by Dr Laura McGregor & Dr David Barden


SepSolve Analytical Ltd, 22 Commerce Road, Lynch Wood, Peterborough PE2 6LR UK Tel: +44 (0)1733 669222 Email: hello@sepsolve.com Web: www.sepsolve.com


Group-type GC×GC analysis has great potential to improve the speed with which chemical compositions of petrochemicals can be assessed. This article illustrates how software tools can streamline the process of achieving robust and reliable quantitation in an acceptable time frame.


Precise characterisation of petroleum- derived fuels is important for both the oil industry and for environmental monitoring, for fuel classification and liability claims respectively, but individually identifying the thousands of components present in these complex samples is so impractical as to be impossible [1,2]. Group-type analysis using comprehensive two-dimensional gas chromatography (GC×GC) offers a practical approach to such samples, with its vastly expanded separation space compared to conventional chromatography, and the added benefit of highly structured groupings of compounds for simple classification of hydrocarbons.


This article briefly describes how data- mining tools available in modern GC×GC software packages can streamline this process for the case of two petrochemical samples. The examples shown were carried out using GC×GC–TOF MS/FID with flow modulation for affordable, consumable-free GC×GC.


Experimental


Samples: 1 µL injections of naphtha (in DCM) and a heavy alkylate (in hexene) with a split ratio of 200:1.


GC×GC: INSIGHT™ flow modulator (SepSolve Analytical, Peterborough, UK). For the heavy alkylate, a splitter was used to direct the flow to the TOF MS and FID detectors in the ratio 1:4.5.


TOF MS: Instrument: BenchTOF-Select™; Mass range: m/z 35–550, Ionisation: Tandem Ionisation® mode at 70 eV and 14 eV.


FID: H2 flow: 40 mL/min; Airflow: 400 mL/ min; Temperature: 300°C. Simple Templating for FID


In relatively simple samples, stencils can be created in the software for particular sample types, and then applied to new samples for rapid group-type speciation of the components, as well as reporting of summed peak integrals. The stencil regions are easily drawn around the target class and altered to the desired shape. Stencil regions can even be connected in contiguous meshes to ensure no areas of the chromatograms are overlooked. This is illustrated in Figure 1 for the case of a sample of naphtha, with


Figure 1. GC×GC–FID colour plot of naphtha, showing the pre-defined stencil regions and integrated peaks (denoted by ‘×’ symbols). This information is translated into an area percent table (inset) that provides a fast overview of sample composition – in this case, >99.9% of the total sample composition is classified using the stencil regions.


Software: ChromSpace® GC×GC software (Markes International, Llantrisant, UK) for full instrument control and data processing.


Full experimental details are available from SepSolve.


integration carried out by summing the areas of peaks that fall within each region (even if they have tails that extend outside that region).


Parallel Detection by TOF MS/FID


For more complex samples, parallel detection with TOF MS/FID provides improved confidence in results, because the TOF MS data can be used to precisely define the stencil boundaries, prior to quantitation using FID. For example, heavy alkylates may contain extensive overlap between chemical classes, making it impossible to accurately define regions based solely on FID data. This can be resolved by using extracted ion chromatograms (EICs) on the MS data to


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