The Characterisation of Oilfield Chemicals by Electrospray Ionization Multi-Stage Mass Spectrometry (ESI-MSn)

Paul J. McCormack

PhD – April 2003

Department of Environmental Sciences, University of Plymouth, Plymouth, U.K.

in collaboration with

AstraZeneca, Brixham Environmental Laboratory

A diverse range of polar organic chemicals used during the offshore production of crude oils is routinely discharged from oil production platforms in so-called Produced Water. The environmental fate of these chemicals is largely unknown. since few methods exist for their detection. In the present study, the use of multistage electrospray ionisation ion trap mass spectrometry (ESI-MSn) was investigated for the detection, identification, characterisation and quantification of compounds in both specialty oilfield chemicals (corrosion inhibitors, scale inhibitors, biocides and demulsifiers) and in Produced Water.

Both positive and negative ion collision induced dissociation (CID) multi-stage mass spectrometry (MSn) was shown to allow high specificity detection and characterization of alkylbenzenesulfonates, di-[alkyldimethylammonium-ethyl]ethers, alkylbenzyl-dimethylammonium and imidazoline compounds. CID MSn fragmentation pathways were determined for di-[alkyldimethylammonium-ethyl]ethers (up to MS5) and imidazoline compounds (up to MS3). CID MSn fragmentation pathways (up to MS3) were determined for alkylbenzenesulfonates and alkylbenzyl-dimethylammonium cations and the MS3 product ions (m/z 119 and m/z 58 respectively) were identified.

Imidazolines, which are widely used in speciality oilfield corrosion inhibitor products and which were shown to be amenable to ESI-MS detection and MSn characterisation, were investigated further by high performance liquid chromatography (HPLC) coupled with ESI-MS. A HPLC analytical separation method with ESI-MS detection was devised for synthetic palmitic and oleic acid-derived 2:1-imidazolines (2:1-PI/OI), 1:1-imidazolines (1:1-PI/OI), monoamide and diamide compounds.. The HPLC/ESI-MS responses of 2:1-PI and 2:1-OI were investigated and detection limits of 0.01g mL-1 2:1-PI and 2:1-OI (signal/noise ≥ 3) were determined in the full scan range m/z 100 – 1000.

A solid phase extraction (SPE) method for the separation of synthetic 2:1-PI and 2:1-OI compounds from crude oils was developed. when followed by HPLC/ESI-MS detection, this allowed the semi-quantitative but sensitive and specific determination of individual imidazolines at low (<10) parts per million concentrations in crude oils. Whilst non-optimised at present, the method is a significant advance and may prove useful for monitoring downhole and topside oilfield operations.

Although the synthesis of 2-methyl-2-imidazoline was reported over 100 years ago, the existence of reaction intermediates, 1:1-imidazoline products and the reaction pathways for the synthesis of 1:1/2:1-imidazolines by thermal reactions of diethylenetriamine (DETA) with fatty acids has been subject to debate ever since and is still not fully understood. It was shown herein that the thermal synthesis of 2:1-palmitic imidazoline proceeds via two different pathways depending on whether the reaction is carried out in the solid phase or in refluxing xylene solvent. Reaction intermediates and final products (1:1- and 2:1-palmitic imidazolines and mono and diamides) were identified and characterised by HPLC/ESI-MS and by MSn. CID MSn fragmentation pathways were determined for 1:1- and 2:1-palmitic imidazolines and 1,2- and 1,3-palmitic and oleic diamides.

The SPE and HPLC/ESI-MS techniques developed in this study should allow the environmental effects and fates of some of these polar compounds to be studied even more fully and a better understanding of the consequences of offshore discharges to be reached. In addition, it is clear that HPLC/ESI-MSn should also allow yet more detailed studies of the reaction mechanisms, of the industrialsyntheses of some of the commercial products. This too may have consequences for the environment, since improvements in synthesis may lead to higher product purities.

Parts of this research have been published: McCormack, P., Jones, P., Hetheridge, M.J. and Rowland, S.J. (2001) Water Research 35, 3567-3578 [doi: 10.1016/S0043-1354(01)00070-7]; McCormack, P., Jones, P. and Rowland, S.J. (2002) Rapid Communications in Mass Spectrometry 16, 705-712 [doi: 10.1002/rcm.625].

2003 by P.J. McCormack. All Rights Reserved

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