Quantification of triacylglycerol regioisomers by ultra‐high‐performance liquid chromatography and ammonia negative ion atmospheric pressure chemical ionization tandem mass spectrometryLeskinen, Heidi M.; Suomela, Jukka‐Pekka; Kallio, Heikki P.
doi: 10.1002/rcm.4346pmid: 19957298
The regioisomer composition of triacylglycerols (TAGs) in various vegetable oils was determined with a new liquid chromatography/tandem mass spectrometry (LC/MS/MS method). A direct inlet ammonia negative ion chemical ionization (NICI) MS/MS method was improved by adapting it to LC negative ion (NI) atmospheric pressure chemical ionization (APCI) MS/MS system using ammonia as nebulizer gas. The method is based on the preferential formation of [M–H–RCOOH–100]− ions during collision‐induced dissociation by loss of sn‐1/3 fatty acids from [M–H]− ions. Calibration curves were created from nine reference TAGs: Ala/L/L, Gla/L/L, L/L/O, L/O/O, P/O/O, P/P/O, Po/Po/V, Po/Po/O, and C/O/O. The calibration curves were used to quantify the regioisomer compositions of selected TAGs in rapeseed oil, sunflower seed oil, palm oil, black currant seed oil, and sea buckthorn pulp oil. The method discriminates the different regioisomers and the results obtained by this method were in good agreement with previous results. This proves that this new method can be used for the determination of regiospecific distribution of fatty acids in TAGs. Copyright © 2009 John Wiley & Sons, Ltd.
The use of acetone as a substitute for acetonitrile in analysis of peptides by liquid chromatography/electrospray ionization mass spectrometryKeppel, Theodore R.; Jacques, Martin E.; Weis, David D.
doi: 10.1002/rcm.4352pmid: 19957295
The recent worldwide shortage of acetonitrile has prompted interest in alternative solvents for liquid chromatography/mass spectrometry (LC/MS). In this work, acetone was substituted for acetonitrile in the separation of a peptide mixture by reversed‐phase high‐performance liquid chromatography (RP‐HPLC) and in the positive electrospray ionization mass spectrometry (ESI‐MS) of individual peptides. On both C12 and C18 stationary phases, the substitution of acetone for acetonitrile as the organic component of the mobile phase did not alter the gradient elution order of a five‐peptide retention standard, but did increase peak width, shorten retention times, and increase peak tailing. Positive ESI mass spectra were obtained for angiotensin I, bradykinin, [Leu5]‐enkephalin, and somatostatin 14 dissolved in both acetonitrile/water/formic acid (25%/75%/0.1%) and acetone/water/formic acid (25%/75%/0.1%). Under optimized ESI‐MS conditions, the mass spectral response of [Leu5]‐enkephalin was increased two‐fold when the solvent contained acetone. The substitution of acetone for acetonitrile resulted in only slight changes in the responses of the remaining peptides. A higher capillary voltage was required for optimum response when acetone was used. Compared with acetonitrile/water/formic acid (50/50/0.1%), more interfering species below m/z = 140 were found in the ESI‐MS spectra of acetone/water/formic acid (50/50/0.1%). Copyright © 2009 John Wiley & Sons, Ltd.
Determination of relative sensitivity factors during secondary ion sputtering of silicate glasses by Au+, Au 2+ and Au 3+ ionsKing, Ashley; Henkel, Torsten; Rost, Detlef; Lyon, Ian C.
doi: 10.1002/rcm.4351pmid: 19957296
In recent years, Au‐cluster ions have been successfully used for organic analysis in secondary ion mass spectrometry. Cluster ions, such as Au 2+ and Au 3+, can produce secondary ion yield enhancements of up to a factor of 300 for high mass organic molecules with minimal sample damage. In this study, the potential for using Au+, Au 2+ and Au 3+ primary ions for the analysis of inorganic samples is investigated by analyzing a range of silicate glass standards. Practical secondary ion yields for both Au 2+ and Au 3+ ions are enhanced relative to those for Au+, consistent with their increased sputter rates. No elevation in ionization efficiency was found for the cluster primary ions. Relative sensitivity factors for major and trace elements in the standards showed no improvement in quantification with Au 2+ and Au 3+ ions over the use of Au+ ions. Higher achievable primary ion currents for Au+ ions than for Au 2+ and Au 3+ allow for more precise analyses of elemental abundances within inorganic samples, making them the preferred choice, in contrast to the choice of Au 2+ and Au 3+ for the analysis of organic samples. The use of delayed secondary ion extraction can also boost secondary ion signals, although there is a loss of overall sensitivity. Copyright © 2009 John Wiley & Sons, Ltd.
Rapid identification of additives in poly(vinyl chloride) lid gaskets by direct analysis in real time ionisation and single‐quadrupole mass spectrometryRothenbacher, Thorsten; Schwack, Wolfgang
doi: 10.1002/rcm.4350pmid: 19957297
Gaskets for lids of glass jars usually consist of poly(vinyl chloride) (PVC) containing plasticisers and additional additives, which may migrate into packed foodstuffs. To conform to legal regulations, any such migration has to be determined analytically, which is a big challenge due to the huge chemical variety of additives in use. Therefore, a rapid screening method by means of direct analysis in real time mass spectrometry (DART‐MS), using a single‐quadrupole mass spectrometer, was developed. On introducing a plastisol sample into the DART interface, protonated molecules and ammonium adducts were obtained as the typical ionisation products of any additives present, and cleavages of ester bonds as typical fragmentation processes. Generally, additives present in the 1% range could be directly and easily identified if ion suppressive effects deriving from specific molecules did not occur. These effects could be avoided by analysing toluene extracts of plastisol samples, and this also improved the sensivity. Using this method, it was possible to identify phthalates, fatty acid amides, tributyl O‐acetylcitrate, dibutyl sebacate, bis(2‐ethylhexyl) adipate, 1,2‐diisononyl 1,2‐cyclohexanedicarboxylate, and even more complex additives like acetylated mono‐ and diacylglycerides, epoxidised soybean oil, and polyadipates, with a limit of detection of ≤1% in PVC plastisols. Only in the case of epoxidised linseed oil were levels of ≥5% required for identification. The detection of azodicarbonamide, used as a foaming agent within the manufacturing process, was possible in principle, but was not highly reproducible due to the very low concentrations in plastisols. Copyright © 2009 John Wiley & Sons, Ltd.
On‐line monitoring of the dynamics of trihalomethane concentrations in a warm public swimming pool using an unsupervised membrane inlet mass spectrometry system with off‐site real‐time surveillanceKristensen, Gert H.; Klausen, Morten M.; Hansen, Vagn A.; Lauritsen, Frants R.
doi: 10.1002/rcm.4360pmid: 19957292
To study the long‐term dynamics of trihalomethanes (THMs) in a warm (31–33°C) public swimming pool, we built a robust membrane inlet mass spectrometer that could perform unsupervised, on‐site monitoring of the concentration of these compounds with off‐site, real‐time surveillance. The instrument was installed in a technical room below the pool and operated continuously for more than a year practically only interrupted for filament replacements every 6–8 weeks. One to two days after a filament replacement, the instrument stabilized and kept its calibration until shortly before the next filament burnout. The on‐line monitoring of THMs revealed a daily rhythm in the concentrations of chloroform and bromodichloromethane. They increased during the pool's closing hours and decreased during opening hours with the minimum concentration being approximately half of the maximum. Over the 1 year monitoring period, the variation in the maximum registered daily concentration was 30–100 µg/L for chloroform. The variation of bromodichloromethane was 5–10 µg/L, except during bursts of 1–2 days duration, where the concentration of bromodichloromethane could reach 100 µg/L. The burst in bromodichloromethane concentration was directly correlated with salt addition (sodium chloride) to the pool water for use in the pool's electrolytic in‐line chlorination system. A correlation between THM removal from the pool water and the operation of a strong water jet system was also found. Copyright © 2009 John Wiley & Sons, Ltd.
Diversity of non‐stoichiometric substitutions on the lipopolysaccharide of E. coli C demonstrated by electrospray ionization single quadrupole mass spectrometryKojima, Hisaki; Inagaki, Minoru; Tomita, Tsuyoshi; Watanabe, Teruko
doi: 10.1002/rcm.4355pmid: 19957294
The lipopolysaccharide (LPS) of enterobacteria frequently contains various numbers of charged non‐stoichiometric substituents such as phosphate (P) and ethanolamine (EtN) groups and a third residue of 3‐deoxy‐D‐manno‐2‐octulosonic acid (KDO) on the R‐core polysaccharide backbone. These substituents can modify the biological activities of LPS including varying the stability of the outer membrane, tolerance to cationic antibiotics, pathogenicity, and sensitivity to enterobacteria bacteriophages. These diverse substituents can be clearly detected in degraded samples of LPS from E. coli C using electrospray ionization single quadrupole mass spectrometry (ESI‐Q‐MS) from a 0.1 mg/mL solution in a 50:50 mixture of methanol and 10 mM ammonium acetate (pH 6.8). The O‐deacylated derivative showed multiple peaks of [M–3H]3− ions which corresponded to species having up to eight phosphates, two ethanolamines, and an additional KDO on the backbone of Hex5 Hep3 KDO2 GlcN2 C14:0(3‐OH)2. The major components of the O,N‐deacylated derivative were the species associated with four and five phosphates on Hex5 Hep3 KDO2 GlcN2. The polysaccharide portion of LPS also revealed species which corresponded to Hex5 Hep3 KDO associated with two to four phosphates and an ethanolamine. The present method was proved to be useful to investigate the structural diversity of enterobacterial LPS. Copyright © 2009 John Wiley & Sons, Ltd.
Study of the fragmentation pattern of ketamine‐heptafluorobutyramide by gas chromatography/electron ionization mass spectrometryPieri, Maria; Castiglia, Loredana; Miraglia, Nadia; Guadagni, Rossella; Malorni, Livia; Sannolo, Nicola; Acampora, Antonio; Casa, Elvira Della
doi: 10.1002/rcm.4357pmid: 19957293
Ketamine is an anaesthetic compound used in human and veterinary medicine with hallucinogen properties that have resulted in its increased illicit use by teenagers at rave parties. Although several gas chromatography/mass spectrometry (GC/MS) methods have been reported for the quantification of the drug both in urine and in hair, its electron ionization (EI) fragmentation after derivatization with different reagents has been not yet fully investigated. The present work reports the study of the fragmentation of ketamine, derivatized with heptafluorobutyric anhydride (HFBA‐Ket), using gas chromatography/electron ionization mass spectrometry (GC/EI‐MS). The complete characterization of the fragmentation pattern represented an intriguing exercise and required tandem mass spectrometry (MSn) experiments, high‐resolution accurate mass measurements and the use of deuterated d4‐ketamine to corroborate the proposed structures and to characterize the fragment ions carrying the unchanged aromatic moiety. Extensive fragmentation was observed, mainly located at the cyclohexanone ring followed by rearrangement of the fragment ions, as confirmed by the mass spectra obtained from the deuterated molecule. The GC/EI‐MS analysis of HFBA‐Ket will represent a useful tool in forensic science since high‐throughput analyses are enabled, preserving both the GC stationary phase and the cleanliness of the mass spectrometer ion optics. Copyright © 2009 John Wiley & Sons, Ltd.