The Experts below are selected from a list of 2058 Experts worldwide ranked by ideXlab platform
Felix Hernandez - One of the best experts on this subject based on the ideXlab platform.
-
advantages of atmospheric pressure chemical ionization in gas chromatography tandem Mass spectrometry pyrethroid insecticides as a case study
Analytical Chemistry, 2012Co-Authors: Tania Portoles, Johannes G J Mol, Juan V Sancho, Felix HernandezAbstract:Gas chromatography coupled to Mass spectrometry (GC/MS) has been extensively applied for determination of volatile, nonpolar, compounds in many applied fields like food safety, environment, or toxicology. The wide majority of methods reported use electron ionization (EI), which may result in extensive fragmentation of analytes compromising selectivity and sensitivity. This might also complicate the application of tandem MS due to lack of specific/abundant precursor ions. Pyrethroids are examples of compounds with this behavior. In this work, the potential of atmospheric pressure chemical ionization (APCI), a softer form of ionization, combined with GC and a triple Quadrupole Mass Analyzer was investigated, taking pyrethroids as a case study and their determination in fruit and vegetables as example application. Ionization and fragmentation behavior of eight pyrethroids (bifenthrin, cyfluthrin, cypermethrin, permethrin, λ-cyhalothrin, fluvalinate, fenvalerate, and deltamethrin) by APCI were studied. The fo...
-
simultaneous ultra high pressure liquid chromatography tandem Mass spectrometry determination of amphetamine and amphetamine like stimulants cocaine and its metabolites and a cannabis metabolite in surface water and urban wastewater
Journal of Chromatography A, 2009Co-Authors: Lubertus Bijlsma, Juan V Sancho, E Pitarch, Maria Ibanez, Felix HernandezAbstract:Abstract An ultra-high-pressure liquid chromatography–tandem Mass spectrometry (UHPLC–MS/MS) method has been developed for the simultaneous quantification and confirmation of 11 basic/acidic illicit drugs and relevant metabolites in surface and urban wastewater at ng/L levels. The sample pre-treatment consisted of a solid-phase extraction using Oasis MCX cartridges. Analyte deuterated compounds were used as surrogate internal standards (except for norbenzoylecgonine and norcocaine) to compensate for possible errors resulting from matrix effects and those associated to the sample preparation procedure. After SPE enrichment, the selected drugs were separated within 6 min under UHPLC optimized conditions. To efficiently combine UHPLC with MS/MS, a fast-acquisition triple Quadrupole Mass Analyzer (TQD from Waters) in positive-ion mode (ESI+) was used. The excellent selectivity and sensitivity of the TQD Analyzer in selected reaction monitoring mode allowed quantification and reliable identification at the LOQ levels. Satisfactory recoveries (70–120%) and precision (RSD 99%) for low levels of illicit drugs in water, but some difficulties were observed when high drug levels were present in wastewaters.
-
application of ultra high pressure liquid chromatography tandem Mass spectrometry to the determination of multi class pesticides in environmental and wastewater samples study of matrix effects
Journal of Chromatography A, 2009Co-Authors: Jose M Marin, Juan V Sancho, Emma Gracialor, Francisco J Lopez, Felix HernandezAbstract:An ultra-high-pressure liquid chromatography-tandem Mass spectrometry (UHPLC-MS/MS) method for the determination of 37 pesticides (herbicides, insecticides and fungicides) in environmental and wastewater has been developed. To efficiently combine UHPLC with MS/MS, a fast-acquisition triple Quadrupole Mass Analyzer was used. This Analyzer (minimum dwell time, 5 ms) allows acquiring up to three simultaneous transitions in the selected reaction monitoring mode for each compound assuring a reliable identification without resolution or sensitivity losses. A pre-concentration step based on solid-phase extraction using Waters Oasis HLB cartridges (0.2 g) was applied with a 100-fold pre-concentration factor along the whole analytical procedure. The method was validated based on European SANCO guidelines using surface, ground, drinking and treated water (from an urban solid residues treatment plant) spiked at two concentration levels (0.025 and 0.1 microg/L), the lowest having been established as the limit of quantification objective. The method showed excellent sensitivity, with instrumental limits of detection ranging from 0.1 to 7 pg. It was applied to environmental water samples (ground and surface water) as well as to samples of urban solid waste leachates (raw leachate and treated leachate after applying reversed osmosis) collected from a municipal treatment plant. Matrix effects have been studied in the different types of water samples analyzed, and several isotope-labelled internal standards have been evaluated as a way to compensate the signal suppression observed for most of the compounds studied, especially in wastewater samples. As a general remark, only those pesticides which response was corrected using their own isotope-labelled molecule, could be satisfactorily corrected in all type of samples, assuring in this way the accurate quantification in all matrix samples.
Juan V Sancho - One of the best experts on this subject based on the ideXlab platform.
-
advantages of atmospheric pressure chemical ionization in gas chromatography tandem Mass spectrometry pyrethroid insecticides as a case study
Analytical Chemistry, 2012Co-Authors: Tania Portoles, Johannes G J Mol, Juan V Sancho, Felix HernandezAbstract:Gas chromatography coupled to Mass spectrometry (GC/MS) has been extensively applied for determination of volatile, nonpolar, compounds in many applied fields like food safety, environment, or toxicology. The wide majority of methods reported use electron ionization (EI), which may result in extensive fragmentation of analytes compromising selectivity and sensitivity. This might also complicate the application of tandem MS due to lack of specific/abundant precursor ions. Pyrethroids are examples of compounds with this behavior. In this work, the potential of atmospheric pressure chemical ionization (APCI), a softer form of ionization, combined with GC and a triple Quadrupole Mass Analyzer was investigated, taking pyrethroids as a case study and their determination in fruit and vegetables as example application. Ionization and fragmentation behavior of eight pyrethroids (bifenthrin, cyfluthrin, cypermethrin, permethrin, λ-cyhalothrin, fluvalinate, fenvalerate, and deltamethrin) by APCI were studied. The fo...
-
simultaneous ultra high pressure liquid chromatography tandem Mass spectrometry determination of amphetamine and amphetamine like stimulants cocaine and its metabolites and a cannabis metabolite in surface water and urban wastewater
Journal of Chromatography A, 2009Co-Authors: Lubertus Bijlsma, Juan V Sancho, E Pitarch, Maria Ibanez, Felix HernandezAbstract:Abstract An ultra-high-pressure liquid chromatography–tandem Mass spectrometry (UHPLC–MS/MS) method has been developed for the simultaneous quantification and confirmation of 11 basic/acidic illicit drugs and relevant metabolites in surface and urban wastewater at ng/L levels. The sample pre-treatment consisted of a solid-phase extraction using Oasis MCX cartridges. Analyte deuterated compounds were used as surrogate internal standards (except for norbenzoylecgonine and norcocaine) to compensate for possible errors resulting from matrix effects and those associated to the sample preparation procedure. After SPE enrichment, the selected drugs were separated within 6 min under UHPLC optimized conditions. To efficiently combine UHPLC with MS/MS, a fast-acquisition triple Quadrupole Mass Analyzer (TQD from Waters) in positive-ion mode (ESI+) was used. The excellent selectivity and sensitivity of the TQD Analyzer in selected reaction monitoring mode allowed quantification and reliable identification at the LOQ levels. Satisfactory recoveries (70–120%) and precision (RSD 99%) for low levels of illicit drugs in water, but some difficulties were observed when high drug levels were present in wastewaters.
-
application of ultra high pressure liquid chromatography tandem Mass spectrometry to the determination of multi class pesticides in environmental and wastewater samples study of matrix effects
Journal of Chromatography A, 2009Co-Authors: Jose M Marin, Juan V Sancho, Emma Gracialor, Francisco J Lopez, Felix HernandezAbstract:An ultra-high-pressure liquid chromatography-tandem Mass spectrometry (UHPLC-MS/MS) method for the determination of 37 pesticides (herbicides, insecticides and fungicides) in environmental and wastewater has been developed. To efficiently combine UHPLC with MS/MS, a fast-acquisition triple Quadrupole Mass Analyzer was used. This Analyzer (minimum dwell time, 5 ms) allows acquiring up to three simultaneous transitions in the selected reaction monitoring mode for each compound assuring a reliable identification without resolution or sensitivity losses. A pre-concentration step based on solid-phase extraction using Waters Oasis HLB cartridges (0.2 g) was applied with a 100-fold pre-concentration factor along the whole analytical procedure. The method was validated based on European SANCO guidelines using surface, ground, drinking and treated water (from an urban solid residues treatment plant) spiked at two concentration levels (0.025 and 0.1 microg/L), the lowest having been established as the limit of quantification objective. The method showed excellent sensitivity, with instrumental limits of detection ranging from 0.1 to 7 pg. It was applied to environmental water samples (ground and surface water) as well as to samples of urban solid waste leachates (raw leachate and treated leachate after applying reversed osmosis) collected from a municipal treatment plant. Matrix effects have been studied in the different types of water samples analyzed, and several isotope-labelled internal standards have been evaluated as a way to compensate the signal suppression observed for most of the compounds studied, especially in wastewater samples. As a general remark, only those pesticides which response was corrected using their own isotope-labelled molecule, could be satisfactorily corrected in all type of samples, assuring in this way the accurate quantification in all matrix samples.
R S Houk - One of the best experts on this subject based on the ideXlab platform.
-
Mass resolution of 11 000 to 22 000 with a multiple pass Quadrupole Mass Analyzer
Journal of the American Society for Mass Spectrometry, 2000Co-Authors: Maan H Amad, R S HoukAbstract:CO+ and N2+ are separated with resolution of 11,000 [full width half maximum (FWHM)] using a conventional Quadrupole Mass spectrometer by applying square wave voltages to the entrance and exit lenses to trap or reflect the ions for multiple passes. A resolution of 22,000 (FWHM) with 63% of the total signal remaining is attained using multiple passes when ions are stored between injection pulses. Gated ion extraction also reduces the Mass shift and number and intensity of artifact peaks and permits better resolution compared to the performance obtained when the ions are injected continuously.
-
high resolution Mass spectrometry with a multiple pass Quadrupole Mass Analyzer
Analytical Chemistry, 1998Co-Authors: Maan H Amad, R S HoukAbstract:The peak shape narrows and the resolution improves if the ions are simply reflected back and forth through a conventional Quadrupole Mass Analyzer. CO+ and N2+ at m/z = 28 are separated to 50% valley with half of the original signal remaining. These two ions can be resolved to baseline (m/Δm) = 5000 with 1% of the original signal remaining.
Vladimir V. Titov - One of the best experts on this subject based on the ideXlab platform.
-
Detailed study of the Quadrupole Mass Analyzer operating within the first, second, and third (intermediate) stability regions. I. Analytical approach
Journal of the American Society for Mass Spectrometry, 1998Co-Authors: Vladimir V. TitovAbstract:The theoretical aspects of ion separation in imperfect fields of the Quadrupole Mass Analyzer operating within the first, second, and third stability regions are discussed by analysis of the beam dynamics in phase-space. The analytical approach uses an approximate solution of the Hill equation with a small heterogeneous part. These calculations indicate that the trap mechanism of ion separation is conditioned by the properties of characteristic solutions. These solutions are reduced to an approximate solution in the form of a general solution of a homogeneous Mathieu equation with combined factors taking into account a small heterogeneous part that defines the region of beam capture (acceptance) in phase-space. The infringement of independence principle of ion oscillations about each of the positional axes caused by distortions increases the cross-sectional area of the beam. The beam is cut out by the Mass Analyzer aperture. This causes transmission losses that depend on phase. Therefore, the ion current at the Mass Analyzer exit is amplitude modulated by the frequency of the radiofrequency (rf) component of the field. The maximum current is at zero phase. The modulation depth is proportional to the relative value of the distortions.
-
detailed study of the Quadrupole Mass Analyzer operating within the first second and third intermediate stability regions ii transmission and resolution
Journal of the American Society for Mass Spectrometry, 1998Co-Authors: Vladimir V. TitovAbstract:Theoretical aspects of ion separation in imperfect fields of the Quadrupole Mass Analyzer operating within the first, second, and third stability regions are applied to simulate transmission and resolution by using an analytical approach. A mathematical simulation based on statistical mechanics reveals in analytical form that the region of beam capture, i.e., the transmission, is inversely proportional to the relative values of the Mass Analyzer distortions to the 1.18th power in log scale. Otherwise, taking into account tails of peaks from unstable ion trajectories shows that the maximum attainable resolution is directly proportional to the number of cycles the ions spend in the field to the 1.33rd power. Because the ion current is amplitude modulated by the frequency of the alternating component of the field, transmission losses because of a parasitic modulation increase more than tenfold as the resolution and distortion increase. These losses are reduced to a minimum by applying a heterogeneous standing wave voltage to the Mass Analyzer with a linear distribution of amplitude along the ion transit axis. This additional standing wave increases the transmission tenfold. This procedure has the additional advantage of ion injection at zero phase in each cycle of the radiofrequency (rf) field. Experimental verification of the techniques used to avoid transmission losses caused by field distortions indicates the validity of the simulation results. The coarse approximation by means of the operating surface of electrodes in the form of rings instead of a solenoid to create a heterogeneous standing wave voltage applied to the Mass Analyzer with a linear distribution of amplitude along the drift axis increases the transmission by a factor of 5 compared with a traditional coupling Mass filter with pre- and post-filters. Such a comparison proves the advantages of ion injection into the Mass Analyzer at zero phase in each cycle of an rf field. This reduces the mechanical tolerances of the Mass Analyzer by an order of magnitude and creates prospects for an increase in attainable resolution by using electrodes of circular profile.
-
Ion separation in imperfect fields of the Quadrupole Mass Analyzer Part I. Ion beam dynamics in the phase-space
International Journal of Mass Spectrometry and Ion Processes, 1995Co-Authors: Vladimir V. TitovAbstract:Abstract The theoretical aspects of ion separation in imperfect fields of the Quadrupole Mass Analyzer are discussed by applying analysis of the beam dynamics in a phase-space. The analytical method which uses an approximate solution of the Hill equation with a small heterogeneous part which indicates that the trap mechanism of ion separation is conditioned by the properties of characteristic solutions is improved. These solutions are reduced to an approximate solution in the form of a general solution of a homogeneous Mathieu equation with combined factors taking into account a small heterogeneous part which defines the region of beam capture (acceptance) in a phase-space. The estimation criterion of simulation accuracy is the relative deviation of an operating point on the Mathieu diagram from the top of a stability triangle. The infringement of independence principle of ion oscillations about each of the positional axes caused by distortions increases the cross-sectional area of the beam. The beam is cut out by the Mass Analyzer aperture. This causes transmission losses which depend on phase. Therefore, the ion current at the Mass Analyzer exit is amplitude modulated by the frequency of the alternate component of field. The maximum current is at zero phase. The modulation depth is proportional to the relative value of the distortions.
-
Ion separation in imperfect fields of the Quadrupole Mass Analyzer Part II. Ion beam dynamics in the phase-space of the fringing field
International Journal of Mass Spectrometry and Ion Processes, 1995Co-Authors: Vladimir V. TitovAbstract:Abstract The theoretical aspects of ion separation taking account of fringing fields in the Quadrupole Mass Analyzer are analyzed by applying beam dynamics in phase-space. The mathematical simulation of fringing fields is developed by the principles of statistical mechanics. Numerical solutions of differential equations (the Hill equation) for ion motion in the fringing field are considered using matrix conversions with Galerkin-Slezkin's integral averaging in the iteration procedure. Analysis of beam dynamics in the phase-space where the law of phase volume conservation (Liouville's theorem) is valid indicates that, for stable ion motion, beam boundaries are described by a family of ellipses. The parameters of the ellipses are determined by the elements of the state transition matrix for an arbitrary set of initial conditions. Theoretical analysis indicates that beam divergence has a major influence on transmission. Transmission is an exponential function of relative transit time. The optimum time of transit through the fringing field has exponential dependences on the initial values of radial and angular envelopes of a beam with an asymptotic value of 1.77π.
Aviv Amirav - One of the best experts on this subject based on the ideXlab platform.
-
gc ms with photoionization of cold molecules in supersonic molecular beams approaching the softest ionization method
Journal of Mass Spectrometry, 2020Co-Authors: Alexander B Fialkov, Elias Ikonen, Tiina Laaksonen, Aviv AmiravAbstract:A new type of photoionization ion source was developed for the ionization of cold molecules in supersonic molecular beams (named Cold PI). The system was based on a GC-MS with supersonic molecular beams and its fly-through EI of cold molecules ion source (Cold EI) plus Quadrupole Mass Analyzer. A continuously operated deuterium VUV photoionization lamp was added and placed above and between the supersonic nozzle and skimmer whereas the Cold EI ion source served only as a portion of the ion transfer ion optics. The supersonic nozzle and skimmer were voltage biased and the VUV light crossed the supersonic expansion about 10 mm from the nozzle. We obtained over three orders of magnitude enhancement in the relative abundance of the molecular ion of squalane in Cold PI versus in photoionization of this compound as a thermal compound. Accordingly, we also proved that standard photoionization is not as soft ionization method as previously perceived for large compounds. We found that Cold PI is as soft as and possibly softer than field ionization; thus, it could be the softest known ionization method. The ionization yield was about 200-300 times weaker than with Cold EI yet our limit of detection was about 200 femtogram in SIM mode for cholesterol and pyrene which is reasonable. Practically, all hydrocarbons gave only molecular ions with rather uniform response whereas alcohols gave some molecular ions plus major fragment ions particularly with a loss of water (similarly to field ionization). We tested Cold PI in the GC-MS analysis of diesel fuels and analyzed the time averaged data for group type information. We also found that we can analyze the diesel fuels by fast under 20-s flow injection analysis in which the generated averaged Mass spectrum of molecular ions only could serve for the characterization of fuels.
-
Electron impact Mass spectrometry of alkanes in supersonic molecular beams
Journal of the American Society for Mass Spectrometry, 1995Co-Authors: Shai Dagan, Aviv AmiravAbstract:The electron impact Mass spectrometry of straight chain alkanes C_8H_18-C_40H_82, squalane, methylstearate, 1-chlorohexadecane, 1-bromohexadecane, and dioctylphthalate was studied by sampling them with supersonic molecular beams. A fly-through Brink-type electron impact ion source was used, utilizing a vacuum background ion filtration technique based on differences between the kinetic energy of the supersonic beam species and that of thermal molecules. The 70-eV electron impact Mass spectra of all the alkanes were characterized by a pronounced or dominant molecular weight peak together with all the fragment ions normally exhibited by the standard thermal 70-eV EI Mass spectra. In contrast, the NIST library of most of these molecules did not show any molecular weight peak. By eliminating tile intramolecular thermal vibrational energy we gained control over the degree of molecular ion fragmentation by the electron energy. At an electron energy of 18 eV the molecular ion dissociation was further reduced considerably, with only a small absolute reduction in the peak height by less than a factor of 2. The effect of vibrational cooling increased with the molecular size and number of atoms. Pronounced differences were observed between the Mass spectra of the straight chain triacontane and its branched isomer squalane. Similar Mass spectra of octacosane (C_28H_58) achieved with 70-eV EI in a supersonic molecular beam were obtained with a magnetic sector Mass spectrometer by using an electron energy of 14 eV and an ion source temperature of 150 °C. However, this ion source temperature precluded the gas chromatography-Mass spectrometry (GC-MS) of octacosane. The GC-MS of alkanes was studied with an ion trap gas chromatograph-Mass spectrometer at an ion source temperature of 230 °C. Thermal peak tailing was observed for C_20H_42 and heavier alkanes, whereas for C_28H_58 and heavier alkanes the severe peak tailing made quantitative GC-MS impractical. In contrast, no peak tailing existed even with C_40H_82 for GC-MS in supersonic molecular beams. The minimum detected amount of eicosane (C_20, H_42) was shown to be 60 fg. This was demonstrated by using single ion monitoring with the Quadrupole Mass Analyzer tuned to the molecular weight peak of 282 u. The coupling of electron impact Mass spectrometry in supersonic molecular beams with hyperthermal surface ionization and a fast GC-MS inlet is briefly discussed.
