Pierre Giusti

Ultratrace determination of uranium and plutonium by nano-volume flow injection double-focusing sector field inductively coupled plasma mass spectrometry (nFI–ICP-SFMS)

A sensitive analytical procedure based on nano-volume flow injection (FI) and inductively coupled plasma double-focusing sector field mass spectrometry (ICP-SFMS) was developed for the ultratrace determination of uranium and plutonium. A 54-nl sample was injected by means of a nanovolume injector into a continuous flow of carrier liquid at 7 μl min−1 prior to ICP-SFMS. The absolute detection limits were 9.1 × 10−17 g (3.8 × 10−19 mol, ∼230000 238U atoms) and 1.5 × 10−17 g (6 × 10−20 mol, ∼38000 242Pu atoms) for uranium and plutonium, respectively. The method was validated for the determination of the uranium isotope ratios by the analysis of a certified isotope reference material (NIST U350). The analysis of a contaminated urine sample showed the enriched uranium to be the origin of contamination. Another application concerned the determination of plutonium at the subfemtomolar level in water with a detection limit down to the ag ml−1 range (6 × 10−18 g ml−1).

Interfacing reversed-phase nanoHPLC with ICP-MS and on-line isotope dilution analysis for the accurate quantification of selenium-containing peptides in protein tryptic digests

An interface between nanoHPLC and ICP-MS was developed. It allowed the stable introduction into an ICP of mobile phases containing up to 90% of acetonitrile at flow rates of less than 500 nL min−1. The on-line post-column addition of an isotopically enriched spike at flow rates of less than 4 μL min−1 enabled isotope dilution quantification of heteroatom containing analytes while the consumption of the labelled isotope was low. The coupled system was applied to the accurate, sensitive and specific determination of selenopeptides in nanolitre volumes (11 nL) of a tryptic digest of selenomethionyl calmodulin (17002 Da). The peptides were separated by reversed phase nanoLC (340 nL min−1 flow rate) whereas ICP collision cell MS was used for the simultaneous detection of 80Se (analyte) and 76Se (spike). The absolute detection limit was 40 fg (80Se), a factor of 2 less than ever reported for a capillary HPLC-ICP-MS coupling. The sensitivity was constant during the chromatogram, regardless of the percentage of acetonitrile in the mobile phase. The selenium recovery was 103 ± 4%. For selenopeptide analysis the sum of Se determined in each of the peaks equalled the total Se injected on the column. Since the tryptic peptides, miscleaved and/or oxidized peptides, incompletely digested protein and undigested protein could be determined in one run, the method allowed the precise evaluation of the efficiency and quality of tryptic digestion using several nanolitres of sample only.

ICP-MS-assisted nanoHPLC-electrospray Q/time-of-flight MS/MS selenopeptide mapping in Brazil nuts

A method was developed for the identification of selenium-containing peptides issued from proteins of a Se-rich (82.9 mg kg–1) foodstuff, Brazil nut (Bertholletia excelsa). A sample purification procedure was optimized to cope with the 100-fold excess of sulfur analogues and matrix interferences. It was based on the consecutive size-exclusion fractionation of proteins and tryptic peptides, and enrichment of the Se-containing fractions, prior to nanoHPLC-ES-Q/TOF MS/MS. The characteristic isotopic patterns of selenium compounds (always minor peaks) were detected in ESI mass spectra at retention times precisely indicated by the matrix interference-free, sensitive (DL 1.3 fmol) 80Se detection by ICP collision cell MS in the same separation conditions. The potential of the method was demonstrated by the identification of 15 Se-containing peptides, from which all but one were found to originate from the selenised isoforms of the 2S protein.

Selenopeptide mapping in a selenium-yeast protein digest by parallel nanoHPLC-ICP-MS and nanoHPLC-electrospray-MS/MS after on-line preconcentration

ICP collision cell MS was optimized for the detection and retention-time marking of selenium-containing peptides in nanoHPLC (75 μm column) after on-line 100-fold preconcentration on a capillary (300 μm id) precolumn. The mobile phase composition, gradient and flow rate were chosen to allow electrospray-MS/MS to be successfully run in parallel in identical separation and preconcentration conditions in order to produce two matching sets of chromatograms: an element-specific one and a molecule-specific one. Knowledge of the retention time of a Se-containing peptide of interest allowed efficient data mining in the corresponding ES-MS chromatogram and the identification of minor Se-species. A third chromatogram was run to obtain collision-induced dissociation data for the target peptides. The performance of the method was demonstrated for a comprehensive on-line characterization of a mixture of peptides in a tryptic digest of a Se-containing protein fraction isolated by size-exclusion chromatography from a selenium yeast extract. The method allowed the identification of whole series of Se/S substitutions in individual peptides and, in some cases, sequencing of isomers differing in the position of selenomethionine residues in the amino acid sequence.

Atmospheric solid analysis probe-ion mobility mass spectrometry of polypropylene.

Polyolefin, including polypropylene (PP), constitutes an important class of materials. In particular, the recent interest in recycling plastic wastes necessitates their characterization as well as their degradation mechanism being understood. PP materials characterization by mass spectrometry, including polymer and additives parts, is not direct and generally involves a pyrolysis step to produce ionizable species. In this study, we extended the use of atmospheric solid analysis probe (ASAP) in combination with traveling wave ion mobility mass spectrometry (TWIM-MS) for the characterization of PP materials, including polymer as well as additives. Different commercial PP samples, from polymer standard to plastic item, were studied. The use of ASAP allow analysis to be done without any sample preparation, while TWIM-MS permitted a clear separation of polymer ions and additive signals. Several series of polymer pyrolysis residues, similar to those produced by classic pyrolysis, were obtained. Moreover, additive characterization has been done and supported by accurate mass measurements and tandem mass spectrometry experiments. Finally, this strategy put in evidence the role of additives in polymer degradation.

μFlow-injection–ICP collision cell MS determination of molybdenum, nickel and vanadium in petroleum samples using a modified total consumption micronebulizer

An interface based on a total consumption micronebulizer was developed for the introduction of xylene solutions into ICP MS. The increase in the nebulizer capillary diameter and the elimination of the internal connections reduced the problem of clogging, pressure instability and memory effects. The xylene carrier could be introduced for several hours at a rate of 30 μl min−1. The sample (2.5 μl) was injected into the carrier flow to produce peaks of 5 s at half-height (20 s at the base) which allowed a throughput of ca. 100 h−1 for the simultaneous determination of Mo, Ni and V. Calibration curves with good linearity (R2 > 0.999) over at least three orders of magnitude and detection limits at the sub-ng ml−1 levels were obtained. The method was validated by the analysis of a sample by an independent (ICP AES) method and by the analysis of a NIST CRM 1085c lubricating oil material. The use of a helium-pressurized collision cell was essential to obtain good accuracy for Ni and V but was not required for Mo.

Identification of new selenium non-peptide species in selenised yeast by nanoHPLC electrospray Q/time-of-flight-MS/MS

A novel analytical strategy was proposed for the identification of selenium species in selenised yeast. It was based on on-line nanoHPLC electrospray hybrid quadrupole time-of-flight MS/MS analysis following a one-step fractionation of an aqueous extract by size-exclusion chromatography. The enhanced purity of the species arriving at a given moment at the detector allowed the detection of a series of compounds with the characteristic selenium isotopic pattern during a single chromatographic run. The high resolution and mass accuracy provided by the TOF analyser allowed, in combination with the double bond equivalent information and in-source fragmentation data, the determination of the empirical formulae of the detected selenium species. The identification was completed by targeted on-line fragmentation of pseudomolecular ions corresponding to the most abundant Se isotopes. Besides the identification of previously reported compounds (m/z 433, m/z 431) the data obtained confirmed the presence and allowed the structural characterization of 5 new adenine-containing selenium species (m/z 661, 613, 475, 406 and 403) along with some of their sulfur analogues. The signal-to background ratios obtained for these compounds with ES-MS detection were distinctly higher than those obtained with ICP-MS detection.

Rapid analysis of polyester and polyethylene blends by ion mobility-mass spectrometry

In this work ion mobility-mass spectrometry (IM-MS) coupled to an atmospheric solid analysis probe (ASAP) was used for the characterization of polymer blends involving biodegradable polymers (poly(lactic acid) (PLA), poly(butylene succinate) (PBS)) and poly(ethylene) (PE). Interestingly both PLA and PBS yielded by ASAP an ionization ion series corresponding to cyclic oligomers that were nearly identical to those obtained by conventional Py-GC-CI/MS. However from the drift-time vs. m/z plot of a PLA–PE blend, the ion series of both polymers can be readily identified, as the PLA ions are significantly more compact than the PE ions. From this 2D plot specific mass spectra can be extracted which are almost identical to those of each polymer alone. This work highlights the potential of ASAP–IM-MS to achieve a very fast analysis of complex polymer blends. It was demonstrated that coupling gas phase ion separations (IM) with direct and weakly discriminant ionization techniques (ASAP) significantly enhances the dynamic range of accessible concentrations and polymer polarities, opening a new avenue to carry out more complex “materiomics” studies.

Identification of ion series using ion mobility mass spectrometry: the example of alkyl-benzothiophene and alkyl-dibenzothiophene ions in diesel fuels.

Ion mobility-mass spectrometry (IMMS) has been presented as a promising method for analysis of highly complex mixtures. This coupling adds an additional postionization separation dimension to MS. The IM separation of ions is obtained in the millisecond time scale and can be particularly helpful when chromatographic separation is not possible. For obtaining relevant information about the samples, data processing is usually the bottleneck because of the high amount of data generated with IMMS. In the current work, we present a new workflow using specific comparison software dedicated to IMMS data, which allows one to compare m/z-drift time plots to highlight differences between samples. Two diesel fuels have been compared, i.e., the feed and the product of hydrodesulfurization (HDS) process, and this approach allowed us to clearly highlight the variation of intensity of several ions distributed along the plots of both samples. Accurate mass measurements and post IM collision induced dissociation experiments allowed us to identify two series of polycyclic aromatic sulfur-containing heterocycle (PASH) compounds among the matrix ions.

Petroleomics by Direct Analysis in Real Time-Mass Spectrometry

AbstractThe analysis of crude oil and its fractions by applying ambient ionization techniques remains underexplored in mass spectrometry (MS). Direct analysis in real time (DART) in the positive-ion mode was coupled to a linear quadrupole ion trap Orbitrap mass spectrometer (LTQ Orbitrap) to analyze crude oil, paraffin samples, and porphyrin standard compounds. The ionization parameters of DART-MS were optimized for crude oil analysis. DART-MS rendered the optimum conditions of the operation using paper as the substrate, T = 400°C, helium as the carrier gas, and a sample concentration ≥6 mg mL-1. In the crude oils analysis, the DART(+)-Orbitrap mass spectra detected the typical N, NO, and O-containing compounds. In the paraffin samples, oxidized hydrocarbon species (Ox classes, where x = 1–4) with double-bond equivalent of 1–4 were detected, and their structures and connectivity were confirmed by collision-induced dissociation (CID) experiments. DART(+)–MS has identified the porphyrin standard compounds as [M + H]+ ions of m/z 615.2502 and 680.1763, where M = C44H30N4 and C44H28N4OV, respectively, based on the formula assignment and by phenyl losses observed on CID experiments. Graphical Abstractᅟ