Applications of desorption electrospray ionisation mass spectrometry and ion mobility spectrometry to petroleomic and lubricant analysis

The use of mass spectrometry for the analysis of petrochemical products and crude oils enables the generation of detailed molecular data essential for chemical characterisation and product development. However, the need for multistage sample preparation techniques can be time consuming and may result in the loss of information. Ambient ionisation in combination with mass spectrometry enables the direct analysis of compounds present on a surface with minimal or no sample preparation. The work presented in this thesis evaluates the application of mass spectrometry (MS) hyphenated with ambient ionisation and ion mobility for the analysis of chemical additives used in lubricant and petrochemical products and also crude oil. A technique called desorption electrospray ionisation (DESI) pioneered the ambient ionisation field. An in-house designed and constructed DESI source has been developed to enable hyphenation of DESI with MS and ion-mobility mass spectrometry (IM-MS) for the interrogation of chemical additives used in lubricant and petrochemical oils directly from multiple surface substrates. The approach has been successfully applied to the analysis of a range of chemical additives as standards and when present in a lubricating oil matrix. Data has also shown that DESI-MS can be used to map additive deposition on a surface. The quantitative capabilities of DESI-MS have been assessed using a lubricant antioxidant additive present in a lubricant oil matrix and deposited on a surface. The DESI-MS method showed good linearity with a limit of detection (LOD) for the antioxidant additive below that used in typical commercial formulations. The use of a suitable internal standard in the DESI-MS analysis has been shown to significantly improve the repeatability of the approach. Hyphenation of DESI with post ionisation separation methods, such as high field asymmetric waveform ion mobility spectrometry (FAIMS), can improve mass spectral response for targeted analytes through selective transmission. The analysis of a series of corrosion inhibitor additives in a base oil matrix has been carried out using electrospray (ESI) and DESI hyphenated with FAIMS-MS. FAIMS selection of target ions improved the sensitivity of ESI and DESI through enhanced analyte transmission and a reduction in the chemical noise resulting from the oil matrix. DESI-FAIMS-MS was shown to improve target analyte response compared to DESI-MS alone using the corrosion inhibitors as model compounds, showing how the combined technique can be used for the rapid analysis of analytes directly from surfaces with no sample preparation or pre concentration. Direct analysis in real time (DART) is an alternative ambient ionisation approach to DESI. The use of DART-MS for the direct analysis of lubricant and oil additives has been evaluated. All selected additives were successfully detected by DART-MS as standards and in an oil matrix. The surface material, DART helium gas temperature and the presence of an oil matrix were all shown to effect the desorption and ionisation of target analytes. The quantitative capabilities of DART-MS were assessed using the antioxidant additive in a lubricant oil matrix and in the presence of an internal standard. The technique showed good linearity and repeatability. The untargeted analysis of chemical additives present in a fully formulated lubricant oil has been carried out by DESI and DART ionisation techniques. The effect of DESI electrospray solvent and DART helium temperature were both shown to impact the observed mass spectral response for the sample. The analysis of crude oil is particularly problematic due to the high complexity of the sample. A crude oil sample has been analysed using ESI combined with high resolution MS, ESI-FAIMS-MS and DESI-MS. High resolution mass spectrometry enabled the identification of molecular ions that could be characterised using specialist software. The use of FAIMS resulted in shift in the observed chemical profile for the crude oil sample showing selective transmission of molecular species based upon the differential mobility of ions rather than factors such as polarity or solubility that are typically used for sample fractionation. Molecular species from within the crude oil sample were successfully desorbed and ionised by DESI-MS using a DESI solvent composition of 6:4 toluene:methanol

The quantitative surface analysis of an antioxidant additive in a lubricant oil matrix by desorption electrospray ionization mass spectrometry

Rationale Chemical additives are incorporated into commercial lubricant oils to modify the physical and chemical properties of the lubricant. The quantitative analysis of additives in oil-based lubricants deposited on a surface without extraction of the sample from the surface presents a challenge. The potential of desorption electrospray ionization mass spectrometry (DESI-MS) for the quantitative surface analysis of an oil additive in a complex oil lubricant matrix without sample extraction has been evaluated. Methods The quantitative surface analysis of the antioxidant additive octyl (4-hydroxy-3,5-di-tert-butylphenyl)propionate in an oil lubricant matrix was carried out by DESI-MS in the presence of 2-(pentyloxy)ethyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate as an internal standard. A quadrupole/time-of-flight mass spectrometer fitted with an in-house modified ion source enabling non-proximal DESI-MS was used for the analyses. RESULTS An eight-point calibration curve ranging from 1 to 80 μg/spot of octyl (4-hydroxy-3,5-di-tert-butylphenyl)propionate in an oil lubricant matrix and in the presence of the internal standard was used to determine the quantitative response of the DESI-MS method. The sensitivity and repeatability of the technique were assessed by conducting replicate analyses at each concentration. The limit of detection was determined to be 11 ng/mm additive on spot with relative standard deviations in the range 3-14%. CONCLUSIONS The application of DESI-MS to the direct, quantitative surface analysis of a commercial lubricant additive in a native oil lubricant matrix is demonstrated

Direct analysis of oil additives by high-field asymmetric waveform ion mobility spectrometry-mass spectrometry combined with electrospray ionization and desorption electrospray ionization

© 2016 American Chemical Society. The analysis of corrosion inhibitors in the presence and absence of an oil matrix is reported using electrospray ionization (ESI) and desorption electrospray ionization (DESI), hyphenated with miniaturized high-field asymmetric waveform ion mobility spectrometry (FAIMS) and mass spectrometry (MS). The target analytes were successfully ionized in solution by ESI and directly from steel surfaces using DESI ambient ionization at levels ≥0.0004% w/w (4 ppm) in oil. Differences in the mass spectral profiles observed for the additive/oil mixture are attributed to differences between the ESI and DESI ionization processes. The use of FAIMS improved selectivity for ESI generated analyte ions through reduction in the chemical noise resulting from the oil matrix. DESI enabled the direct, rapid, native state interrogation of oil samples on steel surfaces without sample pretreatment, and the hyphenation of DESI with the miniaturized FAIMS enhanced the relative analyte responses of the surface-active corrosion inhibitors

The qualitative and quantitative analysis of lubricant oil additives by direct analysis in real time-mass spectrometry

The application of direct analysis in real time combined with mass spectrometry (DART-MS) to the qualitative analysis of lubricant and oil additives, and the quantitative analysis of a lubricant antioxidant additive is reported. The additives were analysed alone and in the presence of a base oil, from filter paper, glass and steel surfaces, showing the potential of the DART-MS technique for the direct, rapid analysis of lubricant oil additives. The quantitative capabilities of the technique were evaluated for the antioxidant in an oil matrix at concentrations in the range 0.1-8mg/mL in oil (1-80μg antioxidant on spot), using a structural analogue of the antioxidant as an internal standard. The linearity (R2 =0.997), precision (% RSD=2.6%) and LOD (0.04mg/mL in oil) of the method demonstrates that DART-MS is capable of the rapid determination of additives in oil without pre-extraction