Comparison of Atmospheric Pressure Chemical Ionization and Field Ionization Mass Spectrometry for the Analysis of Large Saturated Hydrocarbons.

Direct infusion atmospheric pressure chemical ionization mass spectrometry (APCI-MS) was compared to field ionization mass spectrometry (FI-MS) for the determination of hydrocarbon class distributions in lubricant base oils. When positive ion mode APCI with oxygen as the ion source gas was employed to ionize saturated hydrocarbon model compounds (M) in hexane, only stable [M - H]+ ions were produced. Ion-molecule reaction studies performed in a linear quadrupole ion trap suggested that fragment ions of ionized hexane can ionize saturated hydrocarbons via hydride abstraction with minimal fragmentation. Hence, APCI-MS shows potential as an alternative of FI-MS in lubricant base oil analysis. Indeed, the APCI-MS method gave similar average molecular weights and hydrocarbon class distributions as FI-MS for three lubricant base oils. However, the reproducibility of APCI-MS method was found to be substantially better than for FI-MS. The paraffinic content determined using the APCI-MS and FI-MS methods for the base oils was similar. The average number of carbons in paraffinic chains followed the same increasing trend from low viscosity to high viscosity base oils for the two methods.

Distinguishing Isomeric Aromatic Radical Cations by Using Energy-Resolved Ion Trap and Medium Energy Collision-Activated Dissociation Mass Spectrometry.

Different collision-activated dissociation (CAD) methods were evaluated for their effectiveness at distinguishing several ionized isomeric aromatic compounds by using a linear quadrupole ion trap/orbitrap mass spectrometer. The compounds were ionized by using atmospheric pressure chemical ionization (APCI) with carbon disulfide solvent in the positive ion mode to generate stable molecular ions with limited fragmentation. They were subjected to CAD in the linear quadrupole ion trap (ITCAD) and in an octupole collision cell (medium-energy collision-activated dissociation, MCAD; also known as HCD). Experiments conducted by attempting to vary ion activation times revealed that MCAD and ITCAD occur in the microsecond and millisecond time regimes, respectively. MCAD was found to impart substantially greater internal energies into the molecular ions compared to ITCAD. Accordingly, molecular ions subjected to MCAD favored dissociation via fast σ-bond cleavages, while molecular ions subjected to ITCAD tended to favor rearrangement reactions. MCAD used in the energy-resolved mode (ER-MCAD) enabled the distinction of six ionized isomeric compounds from each other based on modified crossing-point energies (collision energies where the molecular ions and selected fragment ions have an equal abundance). This was not true for ER-ITCAD. Overall, MCAD was superior over ITCAD at the differentiation of isomeric ions, and it provided more detailed structural information.

Sterically hindered phenols in negative ion mobility spectrometry-mass spectrometry.

Negative corona discharge atmospheric pressure chemical ionization (APCI) was used to investigate phenols with varying numbers of tert-butyl groups using ion mobility spectrometry-mass spectrometry (IMS-MS). The main characteristic ion observed for all the phenolic compounds was the deprotonated molecule [M-H](-). 2-tert-Butylphenol showed one main mobility peak in the mass-selected mobility spectrum of the [M-H](-) ion measured under nitrogen atmosphere. When air was used as a nebulizer gas an oxygen addition ion was seen in the mass spectrum and, interestingly, this new species [M-H+O](-) had a shorter drift time than the lighter [M-H](-) ion. Other phenolic compounds primarily produced two IMS peaks in the mass-selected mobility spectra measured using the [M-H](-) ion. It was also observed that two isomeric compounds, 2,4-di-tert-butylphenol and 2,6-di-tert-butylphenol, could be separated with IMS. In addition, mobilities of various characteristic ions of 2,4,6-trinitrotoluene were measured, since this compound was previously used as a mobility standard. The possibility of using phenolic compounds as mobility standards is also discussed.

An Automated Method for Chemical Composition Analysis of Lubricant Base Oils by Using Atmospheric Pressure Chemical Ionization Mass Spectrometry.

Since its invention in the 1950s, field ionization mass spectrometry (FI MS) has been, and currently is, the go-to technique employed by the petrochemical industry for the identification of the different types of nonvolatile compounds in their products. Unfortunately, FI MS has several inherent drawbacks, such as poor reproducibility. The performance of positive-ion mode atmospheric pressure chemical ionization mass spectrometry (APCI MS) with O2 gas as the sheath/auxiliary gas and a saturated hydrocarbon solvent/reagent was recently compared with that of FI MS and found to show promise as an alternative, highly reproducible method for lubricant base oil analysis. We report here on the automation of the APCI/O2/saturated hydrocarbon MS method. Isooctane was chosen as the optimal APCI solvent/reagent for base oil ionization due to the low level of fragmentation it provided for model compound mixtures. Three minutes was determined to be the shortest possible cleaning time between samples, regardless of the base oil viscosity. The total analysis time for each sample was 5 min. The reproducibility of the method was assessed by determining within-day and between-day precisions and total precision for hydrocarbon class distributions measured for three different base oils. All total precision values were found to be better than 6.2%, suggesting that the automated (+)APCI/O2/isooctane method is reproducible and robust.

Interfacing an aspiration ion mobility spectrometer to a triple quadrupole mass spectrometer.

This article presents the combination of an aspiration-type ion mobility spectrometer with a mass spectrometer. The interface between the aspiration ion mobility spectrometer and the mass spectrometer was designed to allow for quick mounting of the aspiration ion mobility spectrometer onto a Sciex API-300 triple quadrupole mass spectrometer. The developed instrumentation is used for gathering fundamental information on aspiration ion mobility spectrometry. Performance of the instrument is demonstrated using 2,6-di-tert-butyl pyridine and dimethyl methylphosphonate.

Quantification of short chain amines in aqueous matrices using liquid chromatography electrospray ionization tandem mass spectrometry.

A new liquid chromatography-electrospray ionization-tandem Mass Spectrometry (LC-ESI-MS/MS) method was developed for the determination of more than 20 C1-C6 alkyl and alkanolamines in aqueous matrices. The method employs Hydrophilic Interaction Liquid Chromatography Multiple Reaction Monitoring (HILIC-MRM) with a ZIC-pHILIC column and four stable isotope labeled amines as internal standards for signal normalization and quantification of the amines. The method was validated using a refinery process water sample that was obtained from a cooling cycle of crude oil distillation. The averaged within run precision, between run precision and accuracy were generally within 2-10%, 1-9% and 80-120%, respectively, depending on the analyte and concentration level. Selected aqueous process samples were analyzed with the method.

Determination of glycerol in oils and fats using liquid chromatography chloride attachment electrospray ionization mass spectrometry.

Existing liquid chromatography - mass spectrometry method for the analysis of short chain carboxylic acids was expanded and validated to cover also the measurement of glycerol from oils and fats. The method employs chloride anion attachment and two ions, [glycerol+35Cl]- and [glycerol+37Cl]-, as alternative quantifiers for improved selectivity of glycerol measurement. The averaged within run precision, between run precision and accuracy ranged between 0.3-7%, 0.4-6% and 94-99%, respectively, depending on the analyte ion and sample matrix. Selected renewable diesel feedstocks were analyzed with the method.

Analysis of phospholipids in bio-oils and fats by hydrophilic interaction liquid chromatography-tandem mass spectrometry.

A new, sensitive and selective liquid chromatography-electrospray ionization-tandem mass spectrometric (LC-ESI-MS/MS) method was developed for the analysis of Phospholipids (PLs) in bio-oils and fats. This analysis employs hydrophilic interaction liquid chromatography-scheduled multiple reaction monitoring (HILIC-sMRM) with a ZIC-cHILIC column. Eight PL class selective internal standards (homologs) were used for the semi-quantification of 14 PL classes for the first time. More than 400 scheduled MRMs were used for the measurement of PLs with a run time of 34min. The method's performance was evaluated for vegetable oil, animal fat and algae oil. The averaged within-run precision and between-run precision were ≤10% for all of the PL classes that had a direct homologue as an internal standard. The method accuracy was generally within 80-120% for the tested PL analytes in all three sample matrices.

Determination of short chain carboxylic acids in vegetable oils and fats using ion exclusion chromatography electrospray ionization mass spectrometry.

A new method for quantification of short chain C1-C6 carboxylic acids in vegetable oils and fats by employing Liquid Chromatography Mass Spectrometry (LC-MS) has been developed. The method requires minor sample preparation and applies non-conventional Electrospray Ionization (ESI) liquid phase chemistry. Samples are first dissolved in chloroform and then extracted using water that has been spiked with stable isotope labeled internal standards that are used for signal normalization and absolute quantification of selected acids. The analytes are separated using Ion Exclusion Chromatography (IEC) and detected with Electrospray Ionization Mass Spectrometry (ESI-MS) as deprotonated molecules. Prior to ionization the eluent that contains hydrochloric acid is modified post-column to ensure good ionization efficiency of the analytes. The averaged within run precision and between run precision were generally lower than 8%. The accuracy was between 85 and 115% for most of the analytes. The Lower Limit of Quantification (LLOQ) ranged from 0.006 to 7mg/kg. It is shown that this method offers good selectivity in cases where UV detection fails to produce reliable results.

Tetraalkylammonium halides as chemical standards for positive electrospray ionization with ion mobility spectrometry/mass spectrometry.

Chemical standards for positive ion mode electrospray ionization ion mobility spectrometry/mass spectrometry (ESI(+)-IMS/MS) are suggested. The low clustering tendency of tetraalkylammonium halides makes them ideal chemical standards for ESI(+)-IMS/MS. A homologous series of these compounds forms a useful external standard for instrument testing and resolution calibration of an IMS instrument. Selected homologues or a mixture of tetraalkylammonium halides can be used as mobility standards in the analytical runs. Absolute and relative reduced mobilities were calculated for C2--C8, C10 and C12 tetraalkylammonium halides. Absolute reduced mobilities in nitrogen were 1.88, 1.56, 1.33, 1.15, 1.02, 0.92, 0.84, 0.73, and 0.67 cm2 V(-1) s(-1), for C2--C8, C10 and C12 tetraalkylammonium halides, respectively. Relative reduced mobilities (relative to 2,6-di-tert-butylpyridine) for the same compounds were 1.20, 1.00, 0.855, 0.743, 0.658, 0.59, 0.54, 0.47, and 0.43, respectively.

Atmospheric chemistry of C3-C6 cycloalkanecarbaldehydes.

The rate coefficients for the gas phase reaction of NO3 and OH radicals with a series of cycloalkanecarbaldehydes have been measured in purified air at 298 +/- 2 K and 760 +/- 10 Torr by the relative rate method using a static reactor equipped with long-path Fourier transform infrared (FT-IR) detection. The values obtained for the OH radical reactions (in units of 10(-11) cm3 molecule(-1) s(-1)) were the following: cyclopropanecarbaldehyde, 2.13 +/- 0.05; cyclobutanecarbaldehyde, 2.66 +/- 0.06; cyclopentanecarbaldehyde, 3.27 +/- 0.07; cyclohexanecarbaldehyde, 3.75 +/- 0.05. The values obtained for the NO3 radical reactions (in units of 10(-14) cm3 molecule(-1) s(-1)) were the following: cyclopropanecarbaldehyde, 0.61 +/- 0.04; cyclobutanecarbaldehyde, 1.99 +/- 0.06; cyclopentanecarbaldehyde, 2.55 +/- 0.10; cyclohexanecarbaldehyde, 3.19 +/- 0.12. Furthermore, the reaction products with OH radicals have been investigated using long-path FT-IR spectroscopy and proton-transfer-reaction mass spectrometry (PTR-MS). The measured carbon balances were in the range 89-97%, and the identified products cover a wide spectrum of compounds including nitroperoxycarbonyl cycloalkanes, cycloketones, cycloalkyl nitrates, multifunctional compounds containing carbonyl, hydroxy, and nitrooxy functional groups, HCOOH, HCHO, CO, and CO2.

Development of an ion mobility spectrometer for use in an atmospheric pressure ionization ion mobility spectrometer/mass spectrometer instrument for fast screening analysis.

An ion mobility spectrometer that can easily be installed as an intermediate component between a commercial triple-quadrupole mass spectrometer and its original atmospheric pressure ionization (API) sources was developed. The curtain gas from the mass spectrometer is also used as the ion mobility spectrometer drift gas. The design of the ion mobility spectrometer allows reasonably fast installation (about 1 h), and thus the ion mobility spectrometer can be considered as an accessory of the mass spectrometer. The ion mobility spectrometer module can also be used as an independently operated device when equipped with a Faraday cup detector. The drift tube of the ion mobility spectrometer module consists of inlet, desolvation, drift, and extraction regions. The desolvation, drift and extraction regions are separated by ion gates. The inlet region has the shape of a stainless steel cup equipped with a small orifice. Ion mobility spectrometer drift gas is introduced through a curtain gas line from an original flange of the mass spectrometer. After passing through the drift tube, the drift gas serves as a curtain gas for the ion-sampling orifice of the ion mobility spectrometer before entering the ion source. Counterflow of the drift gas improves evaporation of the solvent from the electrosprayed sample. Drift gas is pumped away from the ion source through the original exhaust orifice of the ion source. Initial characterization of the ion mobility spectrometer device includes determination of resolving power values for a selected set of test compounds, separation of a simple mixture, and comparison of the sensitivity of the electrospray ionization ion mobility spectrometry/mass spectrometry (ESI-IMS/MS) mode with that of the ESI-MS mode. A resolving power of 80 was measured for 2,6-di-tert-butylpyridine in a 333 V/cm drift field at room temperature and with a 0.2 ms ion gate opening time. The resolving power was shown to be dependent on drift gas flow rate for all studied ion gate opening times. Resolving power improved as the drift gas flow increased, e.g. at a 0.5 ms gate opening time, a resolving power of 31 was obtained with a 0.65 L/min flow rate and 47 with a 1.3 L/min flow rate for tetrabutylammonium iodide. The measured limits of detection with ESI-MS and with ESI-IMS/MS modes were similar, demonstrating that signal losses in the IMS device are minimal when it is operated in a continuous flow mode. Based on these preliminary results, the IMS/MS instrument is anticipated to have potential for fast screening analysis that can be applied, for example, in environmental and drug analysis.