Chantal Grivet

Single Hair Cocaine Consumption Monitoring by Mass Spectrometric Imaging

Matrix-assisted laser desorption/ionization mass spectrometric imaging (MALDI-MSI) was used to image the distribution of cocaine and its metabolites in intact single hair samples from chronic users down to a concentration of 5 ng/mg. Acquisitions were performed in rastering mode, at a speed of 1 mm/s and in the selected reaction monitoring (SRM) mode on a MALDI triple quadrupole linear ion trap fitted with a high repetition rate laser (1 kHz). Compared to traditional methods based on LC-MS/MS or GC-MS(/MS) which require to segment the hair to obtain spatial resolution, MALDI-MSI, with a straightforward sample preparation beforehand, allowed obtaining a spatial resolution of 1 mm and thus the chronological information about cocaine consumption contained in a single intact hair over several months could be monitored. The analysis time of an intact single hair sample of 6 cm is approximately of 6 min. Cocaine and its metabolites benzoylecgonine, ethylcocaine, and norcocaine were investigated in nine sets of hair samples for forensic purposes. The analyses were accomplished by spraying α-cyano-4-hydroxycinnamic acid (CHCA), 4-chloro-α-cyano-cinnamic acid (Cl-CCA), or (E)-2-cyano-3-(naphthalen-2-yl)acrylic acid (NpCCA) as MALDI matrices. We also propose a rapid strategy for sensitive confirmatory analyses with both MS/MS and MS(3) experiments performed directly on intact hair samples. Since only part of the hair strand is analyzed, additional analyses are possible at any time on the remaining hair from the strand.

Alternative CHCA-based matrices for the analysis of low molecular weight compounds by UV-MALDI-tandem mass spectrometry

Analysis of low molecular weight compounds (LMWC) in complex matrices by vacuum matrix-assisted laser desorption/ionization (MALDI) often suffers from matrix interferences, which can severely degrade limits of quantitation. It is, therefore, useful to have available a range of suitable matrices, which exhibit complementary regions of interference. Two newly synthesized α-cyanocinnamic acid derivatives are reported here; (E)-2-cyano-3-(naphthalen-2-yl)acrylic acid (NpCCA) and (2E)-3-(anthracen-9-yl)-2-cyanoprop-2enoic acid (AnCCA). Along with the commonly used α-cyano-4-hydroxycinnamic acid (CHCA), and the recently developed 4-chloro-α-cyanocinnamic acid (Cl-CCA) matrices, these constitute a chemically similar series of matrices covering a range of molecular weights, and with correspondingly differing ranges of spectral interference. Their performance was compared by measuring the signal-to-noise ratios (S/N) of 47 analytes, mostly pharmaceuticals, with the different matrices using the selected reaction monitoring (SRM) mode on a triple quadrupole instrument equipped with a vacuum MALDI source. AnCCA, NpCCA and Cl-CCA were found to offer better signal-to-noise ratios in SRM mode than CHCA, but Cl-CCA yielded the best results for 60% of the compounds tested. To better understand the relative performance of this matrix series, the proton affinities (PAs) were measured using the kinetic method. Their relative values were: AnCCA > CHCA > NpCCA > Cl-CCA. This ordering is consistent with the performance data. The synthesis of the new matrices is straightforward and they provide (1) tunability of matrix background interfering ions and (2) enhanced analyte response for certain classes of compounds.

Loss of Phylloquinone in Chlamydomonas Affects Plastoquinone Pool Size and Photosystem II Synthesis

Phylloquinone functions as the electron transfer cofactor at the A1 site of photosystem I. We have isolated and characterized a mutant of Chlamydomonas reinhardtii, menD1, that is deficient in MenD, which encodes 2-succinyl-6-hydroxy-2,4-cyclohexadiene-1-carboxylate synthase, an enzyme that catalyzes the first specific step of the phylloquinone biosynthetic pathway. The mutant is photosynthetically active but light-sensitive. Analysis of total pigments by mass spectrometry reveals that phylloquinone is absent in menD1, but plastoquinone levels are not affected. This is further confirmed by the rescue of menD1 by addition of phylloquinone to the growth medium. Analysis of electron transfer by absorption spectroscopy indicates that plastoquinone replaces phylloquinone in photosystem I and that electron transfer from A1 to the iron-sulfur centers is slowed down at least 40-fold. Consistent with a replacement of phylloquinone by plastoquinone, the size of the free plastoquinone pool of menD1 is reduced by 20–30%. In contrast to cyanobacterial MenD-deficient mutants, photosystem I accumulates normally in menD1, whereas the level of photosystem II declines. This decrease is because of reduced synthesis of the photosystem II core subunits. The relationship between plastoquinone occupancy of the A1 site in photosystem I and the reduced accumulation of photosystem II is discussed.

Indanetricarbonylchromium: the effects of 1-syn- and 1-anti substituents on the regioselectivity of nucleophilic addition. Crystal structures of 1-syn- and 1-anti- methoxyindanetricarbonylchromium

A series of diastereomeric syn and anti Cr(CO)3 complexes of 1-substituted indanes have been prepared by thermolysis of Cr(CO)6 or by arene exchange with naphthalene-Cr(CO)3 (3). The regioselectivity of nucleophilic addition of a-nitrile carbon nucleophiles to syn and anti 1-R-indane Cr(CO)3 complexes (R = OMe 4, Me 10) has been investigated and compared with that of analogous reactions with indaneCr(CO)3 (1). The results of an X-ray study of syn- and anti-4 are presented. Nucleophilic additions are shown to be sensitive to the steric and electronic effects of the benzylic substituent and the nucleophile. When the reaction mixtures are warmed to 0°C, equilibration of the regioisomeric cyclohexadienyl intermediates takes place.

Generic on-line solid phase extraction sample preparation strategies for the analysis of drugs in biological matrices by LC–MS/MS

In the present work we investigate the integration of a single hardware platform (Prospekt-2) allowing on-line SPE with pre-/post-trapping dilution and direct injection of plasma extracts, and also compare the benefits and challenges of the different approaches for pharmaceutical drugs with heterogeneous physicochemical properties. In the first part, the generic use of on-line SPE with direct plasma injection or after protein precipitation was investigated for the quantitative analysis of talinolol. In the second part, pre-trapping and post-trapping dilution for on-line SPE is discussed for generic method development on an oxadiazole and its major metabolite. Finally, the difference of performance between direct plasma injection vs. off-line liquid-liquid extraction is also described for the quantification of buprenorphine and naltrexone down to 50 and 100 pg/ml using a 0.25 ml plasma aliquot. All assays were in human plasma and detection was performed by mass spectrometry detection either on simple or triple stage quadrupoles. Regardless of the tested strategy, assays were found linear, with precision and accuracy with <15% for all quality controls samples and <20% for lower limit of quantitation.

Reversibility of the lithiation of η6-naphthalenetricarbonylchromium

Abstract The lithiation of naphthalenetricarbonylchromium with n-BuLi or tetramethylpiperidyllithium is under kinetic control, and with the latter reagent is highly regioselective in the 2-position. Addition of isopropylamine renders the process reversible, and an approximately 1 1 equilibrium mixture of 1- and 2-substitution product is formed.