Detection limits of electron and electron capture negative ionization-mass spectrometry for aldehydes derivatized with o-(2,3,4,5,6-pentafluorobenzyl)-hydroxylamine hydrochloride

Electron ionization induced fragmentation of fluorinated derivatives of bisphenols

RATIONALE

Fluorinated derivatization agents allow for the identification and quantification of emerging pollutants with high sensitivity, yet details of their potential applications using electron ionization are lacking. The fluorine atom itself does not effectively participate in electron ionization. Furthermore, limited information exists regarding the effect of fluorine during electron ionization-induced fragmentation. To fill this gap, this report presents the fragmentation pathways of the fluorinated derivatives of ten bisphenol analogues as exemplary emerging pollutants.

METHODS

The bisphenols were derivatized by the acetylation reagent trifluoroacetic anhydride and a new silylation reagent, namely dimethyl(3,3,3-trifluoropropyl)silyldiethylamine (DIMETRIS; previously applied for the analysis of selected pharmaceuticals in environmental samples), and analyzed using GC/MS (electron ionization, 70 eV). Deuterated bisphenol A was added to the group of analytes to confirm the proposed fragmentation pathways.

RESULTS

The specific chemical structure of bisphenols gives the possibility of several resonance hybrids of C-centered radicals. This, in turn, results in several fragmentation pathways, unique for each resonance hybrid. Sequential losses of radicals and neutral fragments were observed in both types of derivative, with final stable carbenium ions. McLafferty-type rearrangements were observed between the native structure of the analytes and the introduced substituents. The gamma-shift of F onto Si in the Si(CH₂ )₂ CF₃ substituent is proposed to explain the loss of the fragment with a mass of 78 u.

CONCLUSIONS

Both types of derivatization reagent used were found to be applicable, although the use of DIMETRIS was limited for high-mass bisphenols. The introduction of fluorine by derivatization brings benefits for the qualitative and quantitative analysis of bisphenol-type compounds using GC/MS because of the presence of characteristic ions in the mass spectra.

Development and validation of an ultra high performance liquid chromatography-electrospray tandem mass spectrometry method using selective derivatisation, for the quantification of two reactive aldehydes produced by lipid peroxidation, HNE (4-hydroxy-2(E)-nonenal) and HHE (4-hydroxy-2(E)-hexenal) in faecal water

Red or processed meat rich diets have been shown to be associated with an elevated risk of colorectal cancer (CRC). One major hypothesis involves dietary heme iron which induces lipid peroxidation. The quantification of the resulting reactive aldehydes (e.g. HNE and HHE) in the colon lumen is therefore of great concern since these compounds are known for their cytotoxic and genotoxic properties. UHPLC-ESI-MS/MS method has been developed and validated for HNE and HHE quantification in rat faeces. Samples were derivatised using a brominated reagent (BBHA) in presence of pre-synthesized deuterated internal standards (HNE-d11/HHE-d5), extracted by solid phase extraction, and then analysed by LC-positive ESI-MS/MS (MRM) on a TSQ Vantage mass spectrometer. The use of BBHA allowed the efficient stabilisation of the unstable and reactive hydroxy-alkenals HNE and HHE. The MRM method allowed selective detection of HNE and HHE on the basis of characteristic transitions monitored from both the 79 and 81 bromine isotopic peaks. This method was validated according to the European Medicines Agency (EMEA) guidelines, by determining selectivity, sensitivity, linearity, carry-over effect, recovery, matrix effect, repeatability, trueness and intermediate precision. The performance of the method enabled the quantification of HNE and HHE in concentrations 0.10-0.15 μM in faecal water. Results are presented on the application to the quantification of HNE and HHE in different faecal waters obtained from faeces of rats fed diets with various fatty acid compositions thus corresponding to different pro-oxidative features.

Identification of stable cytotoxic factors in the gas phase extract of cigarette smoke and pharmacological characterization of their cytotoxicity

Smoking is a major risk factor for atherosclerotic vascular diseases, but the mechanism for its genesis is unknown. We have recently shown that the gas phase of cigarette smoke (nicotine- and tar-free cigarette smoke extract; CSE) likely to reach the systemic circulation contains stable substances which cause cytotoxicity like plasma membrane damage and cell death in cultured cells, and also that the plasma membrane damage is caused through sequential activation of protein kinase C (PKC) and NADPH oxidase (NOX) and the resulting generation of reactive oxygen species (PKC/NOX-dependent mechanism), whereas cell death is caused through PKC/NOX-dependent and -independent mechanisms. To identify these stable substances, the CSE was prepared by passing the main-stream smoke of 10 cigarettes through a Cambridge glass fiber filter, trapping of the smoke in a vessel cooled at -80°C, and subsequent dissolution in 10ml of water. The CSE was fractionated into nine fractions using reversed-phase HPLC, and each fraction was screened for cytotoxicity in cultured cells, using propidium iodide uptake assay for cell membrane damage and MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] reduction assay for cell viability. The cytotoxicity was positive in two of the nine fractions (Fr2 and Fr5). After extraction of the active fractions into dichloromethane, GC/MS analysis identified 2-cyclopenten-1-one (CPO) in Fr5 but none in Fr2. After derivatization of the active fractions with O-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine hydrochloride, GC/MS analysis identified acrolein, acetone and propionaldehyde in Fr2, and methyl vinyl ketone (MVK) in Fr5. After 4-h incubation, authentic acrolein and MVK induced concentration-dependent cytotoxicity with EC50 values of 75.9±8.2 and 47.0±8.0μM (mean±SEM; n=3), respectively, whereas acetone, propionaldehyde and CPO were without effect. However, after 24-h incubation, CPO induced concentration-dependent cytotoxicity with an EC50 value of 264.0±16.9μM (n=3). The concentrations of acrolein, MVK and CPO in the CSE were 3368±334, 2429±123 and 392.9±31.8μM (n=4), respectively, which were higher than the cytotoxic concentrations. The cytotoxicity of acrolein and MVK consisted of plasma membrane damage and decreased cell viability: the plasma membrane damage was totally prevented by treatment with an inhibitor of PKC or NOX, whereas the decreased cell viability was only partially prevented by these inhibitors. The cytotoxicity of CPO consisted only of decreased cell viability, which was totally resistant to these inhibitors. These results show that acrolein and MVK are responsible for the acute cytotoxicity of the CSE through PKC/NOX-dependent and -independent mechanisms, whereas CPO is responsible for the delayed cytotoxicity of the CSE through a PKC/NOX-independent mechanism.

Separation of dansylated 17β-estradiol, 17α-estradiol, and estrone on a single HPLC column for simultaneous quantitation by LC-MS/MS

We show here that baseline separation of dansylated estrone, 17β-estradiol, and 17α-estradiol can be done, contrary to previous reports, within a short run time on a single RP-LC analytical column packed with particles bonded with phenyl-hexyl stationary phase. The chromatographic method coupled with isotope dilution tandem MS offers a simple assay enabling the simultaneous analysis of these analytes. The method employs (13)C-labeled estrogens as internal standards to eliminate potential matrix effects arising from the use of deuterated estrogens. The assay also offers adequate accuracy and sensitivity to be useful for biological samples. The practical applicability of the validated method is demonstrated by the quantitative analyses of in vivo samples obtained from rats treated with Premarin®.

Capture of the volatile carbonyl metabolite of flecainide on 2,4-dinitrophenylhydrazine cartridge for quantitation by stable-isotope dilution mass spectrometry coupled with chromatography

Carbonyl compounds are common byproducts of many metabolic processes. These volatile chemicals are usually derivatized before mass spectrometric analysis to enhance the sensitivity of their detections. The classically used reagent for this purpose is 2,4-dinitrophenylhydrazine (DNPH) that forms the corresponding hydrazones. When DNPH is immobilized on specific cartridges it permits solvent-free collection and simultaneous derivatization of aldehydes and ketones from gaseous samples. The utility of this approach was tested by assembling a simple apparatus for the in vitro generation of trifluoroacetaldehyde (TFAA) and its subsequent capture on the attached DNPH cartridge. TFAA was generated via cytochrome P450-catalyzed dealkylation of flecainide, an antiarrhythmic agent, in pooled human liver microsomes. Stable-isotope dilution mass spectrometry coupled with GC and LC using negative chemical ionization (NCI) and electrospray ionization (ESI) was evaluated for quantitative analyses. To eliminate isotope effects observed with the use of deuterium-labeled DNPH, we selected its (15)N(4)-labeled analog to synthesize the appropriate TFAA adduct, as internal standard. Quantitation by GC-NCI-MS using selected-ion monitoring outperformed LC-ESI-MS methods considering limits of detection and linearity of the assays. The microsomal metabolism of 1.5 μmol of flecainide for 1.5h resulted in 2.6 ± 0.5 μg TFAA-DNPH, corresponding to 9.3 ± 1.7 nmol TFAA, captured by the cartridge.

Limits of detection for the determination of mono- and dicarboxylic acids using gas and liquid chromatographic methods coupled with mass spectrometry

The chromatographic separation and instrumental limits of detection (LODs) were obtained for a broad range of C(1)-C(18) monocarboxylic (MCAs) and C(2)-C(14) dicarboxylic acids (DCAs) employing either chemical derivatization followed by gas chromatography-mass spectrometry and flame ionization detection (GC-MS/FID) or direct analysis with liquid chromatography high resolution MS and tandem MS (LC-MS). Suitability, efficiency and stability of reaction products for several derivatization agents used for esterification (BF(3)/butanol), and trimethysilylation, including trimethylsilyl-N-N-dimethylcarbamate (TMSDMC) and N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) were evaluated. The lowest limits of detection for the majority of compounds below 10 pg (with the exception of acetic acid) were obtained for derivatization with BF(3)/butanol followed by GC-MS in the total ion current (TIC) mode. Further improvements were achieved when applying either selected ion monitoring (SIM), which decreased the LODs to 1-4 pg or a combination of SIM and TIC (SITI) (2-5 pg). GC-FID provided LODs comparable to those obtained by GC-MS TIC. Both trimethylsilylation (followed by GC-MS) and direct LC-MS/MS analysis yielded LODs of 5-40 pg for most of the acids. For volatile acids the LODs were higher, e.g., 25 and 590 ng for TMSDMC and BSTFA derivatized formic acid, respectively, whereas the LC-MS methods did not allow for the analysis of formic acid at all.