Table 2.

Benefits and constraints of TD-GC×GC-FID/qMS analytical instrumentation.

Instrumentation	Benefits	Constraints	Considerations
Sorbent tubes and thermal desorption autosampler	High analytical capacity Low storage requirements High storage stability under adequate conditions (brass caps, dry purged, cooled) Low background artefacts	Maximum carrier pressure 60 psi Minimum trap flow 2 mL/min Retention of water on sorbent Sorbent selectivity and volatility range	Max pressure limits 1D and 2D flow rate combinations Reduced sensitivity due to necessary low 1D rates creating increased split Incorporate dry purge step
Flow modulator	Inexpensive, low consumables cost Easy to use, few connections Suitable for volatile analysis	Requires high 2D flow rate Broader modulated peak widths	Compatibility of detector(s) with high column flow rates Acquisition rate of detector(s) to capture modulated peaks
Fast scanning qMS	Cost effective Fast scanning (20,000 amu/s) Suitable for targeted analysis after biomarker identification	Compatible with < 1.5 mL/min flow rates Max acquisition rate <40 Hz Mass spectral skewing	Need to split 2D flow to avoid over-pressurising detector Setup to either accommodate quantitative or qualitative analysis Sensitivity changes with acquisition rate and split column flow
FID	Cost effective Compatible with flow modulator High acquisition rate Broad dynamic range	No mass spectral assignment	Setup to either accommodate quantitative or qualitative analysis Need supporting mass spectrometer for identification of unknowns
Splitter plate	Enables multiple detectors Easy to use Offers control of split ratio between detectors	Provides constant flow to one detector Requires a constant positive pressure from auxiliary EPC	Change in sensitivity due to split Sensitivity of the secondary detector(s) without constant flow control Alignment of results requires balanced restrictor lengths