GCxGC-TOFMS of Riser Pipe Oil from BP Gulf Oil Spill

I recently analyzed an oil sample collected by an ROV from the riser pipe at the BP Gulf oil spill site using GCxGC-TOFMS, a powerful multidimensional technique capable of characterizing complex samples that defy one-dimensional GC-MS.

The GCxGC column setup was a 30m x 0.25mm x 0.25µm Rxi-17Sil MS in the first dimension with a 1.2m x 0.15mm x 0.15µm Rxi-1ms in the second dimension.  This arrangement puts the highly aromatic compounds (e.g. PAHs) at the bottom of the GCxGC chromatogram (contour plot; see first figure) while the aliphatics are retained by the Rxi-1ms in the second dimension, eluting away from the aromatics.  Given that PAHs, which are shown eluting in the box on the first figure, are considered the “toxic” compounds in crude oil, this is an efficient GCxGC arrangement for their interference-free determination.  Having a full mass range TOFMS allows spectral fingerprinting of the resolved components, including PAHs. 

As pointed out in literature (see below) and by experts in the field (e.g. Ed Overton, Professor Emeritus at LSU), the crude oil associated with this spill is relatively “light” in nature as regards PAHs, with mainly naphthalene, fluorene, phenanthrene, anthracene, and most importantly, their alkyl homologs (especially C1, C2, and C3 as seen in the second figure).  The reason I say most importantly is that many laboratories gearing up for seafood analysis as a result of the oil spill will focus only on the unalkylated (is that a word?) PAHs, likely because that is where most of the published toxicity information lies.  Do the alkyl PAHs, which form the bulk of the PAH contribution of this oil, have equivalent toxicity?  I don’t know, but I do wonder if they should be included in Gulf oil spill monitoring schemes, whether the analysis is for environmental or food samples.

D. J. Hallett, F.I. Onuska, and M.E. Comba, Marine Environmental Research 8 (1983) 73-85, Aliphatic and Polyaromatic Components of Weathered and Unweathered Southern Louisiana Crude Oil