Polychlorinated dibenzo-<Emphasis Type="Italic">p</Emphasis>-dioxins,dibenzofurans and biphenyls in fish from the Netherlands: concentrations,profiles and comparison with DR CALUX® bioassay results

A liquid chromatography–particle-beam mass spectrometer (LC–PB/MS) with interchangeable electron-impact (EI) and glow-discharge (GD) ion sources was evaluated for future application in analysis of botanical extracts. In this work a green tea tincture was characterized for a series of catechin components (catechin, epicatechin, epigallocatechin, and epigallocatechin gallate (EGCG)) and caffeine. Special emphasis was given to EGCG and caffeine, because they are important in determining the possible health effects of the green tea. The effects of instrument operating conditions were evaluated for the EI and GD ionization sources to determine their effect on analyte intensities and fragmentation patterns. These studies furnished information about the effects of these conditions in determining possible ionization pathways in the two ion sources. The mass spectra of these compounds obtained with the GD ion source are EI-like in appearance, with clearly identified molecular ions and fragmentation patterns that are easily rationalized. The absolute limits of detection for EGCG and caffeine were, respectively, 11 ng and 0.77 ng for the EI source and 3.2 ng and 0.61 ng for the GD source. The PB/EIMS and PB/GDMS combinations can be operated in a flow-injection mode, wherein the analyte is injected directly into the mobile phase, or coupled to high-performance liquid chromatography (HPLC), enabling LC–MS analysis of complex mixtures. A reversed-phase chromatographic separation of the green tea tincture was performed on a commercial C₁₈ column using a gradient of water (containing 0.1% TFA) and ACN. Quantification of EGCG and caffeine was performed by the standard addition method. The amounts of EGCG and caffeine in the tested green tea tincture were each ∼14 mg mL⁻¹.     

Comparison of electron ionization mass spectra of some organic compounds (MW < 200 Da) recorded on mass spectrometers of various types

Low-resolution electron ionization mass spectra recorded on various types of mass spectrometers (time-of-flight, quadrupole, and three-dimensional ion trap) were compared. A model mixture of 10 organic compounds (MW < 200 Da) was analyzed by gas chromatography-mass spectrometry. Pure mass spectra of analytes were extracted using the AMDIS software. The best repeatability was achieved for the time-of-flight mass spectrometer. The mass spectra recorded by a quadrupole and a time-of-flight mass spectrometer were quite similar. In the case of these instruments, library search using a commercial mass spectral data base (NIST’05) gave satisfactory result for each analyte (rank 1 or 2 in the “hit list”; Match > 900). In some cases, the mass spectra of model compounds recorded by the ion trap mass spectrometer differed in intensity of certain mass spectral peaks (but not in the set of peaks) from the mass spectra presented in the library and from the experimental mass spectra recorded by the time-of-flight and quadrupole instruments.     

Evaluation of a differential mobility spectrometer/miniature mass spectrometer system

A planar differential mobility spectrometer (DMS) was coupled to a Mini 10 handheld rectilinear ion trap (RIT) mass spectrometer (MS) (total weight 10 kg), and the performance of the instrument was evaluated using illicit drug analysis. Coupling of DMS (which requires a continuous flow of drift gas) with a miniature MS (which operates best using sample introduction via a discontinuous atmospheric pressure interface, DAPI), was achieved with auxiliary pumping using a 5 L/min miniature diaphragm sample pump placed between the two devices. On-line ion mobility filtering showed to be advantageous in reducing the background chemical noise in the analysis of the psychotropic drug diazepam in urine using nanoelectrospray ionization. The combination of a miniature mass spectrometer with simple and rapid gas-phase ion separation by DMS allowed the characteristic fragmentation pattern of diazepam to be distinguished in a simple urine extract at lower limits of detection (50 ng/mL) than that achieved without DMS (200 ng/mL). The additional separation power of DMS facilitated the identification of two drugs of similar molecular weight, morphine (average MW = 285.34) and diazepam (average MW = 284.70), using a miniature mass spectrometer capable of unit resolution. The similarity in the proton affinities of these two compounds resulted in some cross-interference in the MS data due to facile ionization of the neutral form of the compound even when the ionic form had been separated by DMS.     

A pulsed triple ionization source for sequential ion/ion reactions in an electrodynamic ion trap

A pulsed triple ionization source, using a common atmosphere/vacuum interface and ion path, has been developed to generate different types of ions for sequential ion/ion reaction experiments in a linear ion trap-based tandem mass spectrometer. The triple ionization source typically consists of a nano-electrospray emitter for analyte formation and two other emitters, an electrospray emitter and an atmospheric pressure chemical ionization emitter or a second nano-electrospray emitter for formation of the two different reagent ions. The three emitters are positioned in a parallel fashion close to the sampling orifice of the tandem mass spectrometer. The potentials applied to each emitter are sequentially pulsed so that desired ions are generated separately in time and space. Sequential ion/ion reactions take place after analyte ions of interest and different set of reagent ions are sequentially injected into a linear ion trap, where axial trapping is effected by applying an auxiliary radio frequency voltage to the end lenses. The pulsed triple ionization source allows independent optimization of each emitter and can be readily coupled to any atmospheric pressure ionization interface with no need for instrument modifications, provided the potentials required to transmit the ion polarity of interest can be synchronized with the emitter potentials. Several sequential ion/ion reactions examples are demonstrated to illustrate the analytical usefulness of the triple ionization source in the study of gas-phase ion/ion chemistry.     

Atmospheric pressure laser desorption/chemical ionization mass spectrometry: a new ionization method based on existing themes

We have designed and constructed an atmospheric pressure laser desorption/chemical ionization (AP-LD/CI) source that utilizes a laser pulse to desorb intact neutral molecules, followed by chemical ionization via reagent ions produced by a corona discharge. This source employs a heated capillary atmospheric pressure inlet coupled to a quadrupole ion trap mass spectrometer and allows sampling under normal ambient air conditions. Preliminary results demonstrate that this technique provides approximately 150-fold increase in analyte ions compared to the ion population generated by atmospheric pressure infrared matrix-assisted laser desorption/ionization (AP-IR-MALDI).     

Ratiometric analysis of the ferrocene boronate esters of 2- and 4-hydroxyestradiol by tandem electrospray mass spectrometry

A method has been developed for the semiquantitative analysis of the catechol estrogens, 2- and 4-hydroxyestradiol, using tandem electrospray mass spectrometry in a quadrupole ion trap mass analyzer. The implication of catechol estrogens in the biogenesis of breast and prostate cancer makes these labile lipophilic compounds important analytical targets. Ferrocene boronic acid is reacted with 2- and 4-hydroxyestradiol to form their cyclic boronate esters. Sample ionization is accomplished during the electrospray process by a one-electron oxidation of the ferrocene functionality to form the radical cation. The analysis depends on a non-aqueous solvent system consisting of 90% acetonitrile and 10% dichloromethane with 100 microM lithium triflate as the supporting electrolyte. The sensitivity of the analysis is greatly increased by the use of a novel electrospray interface with a large surface area stainless steel electrode coupled to a pulled fused-silica needle. Collision-induced dissociation of the selected molecular ion within the ion trap produces fragment ion spectra that can be used to distinguish between the two isobaric isomers and ultimately determine the relative amounts in mixtures containing both components. The method is sensitive to analyte concentrations in the low nM range.     

Atmospheric pressure matrix-assisted laser desorption/ionisation ion trap mass spectrometry of synthetic polymers: a comparison with vacuum matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry

Atmospheric pressure matrix-assisted laser desorption/ionisation quadrupole ion trap (AP-MALDI/QIT) mass spectrometry has been investigated for the analysis of polyethylene glycol (PEG 1500) and a hyperbranched polymer (polyglycidol) in the presence of alkali-metal salts. Mass spectra of PEG 1500 obtained at atmospheric pressure showed dimetallated matrix/analyte adducts, in addition to the expected alkali-metal/PEG ions, for all matrix/alkali-metal salt combinations. The relative intensities of the desorbed ions were dependent on the matrix, the alkali-metal salt added to aid cationisation and the ion trap interface conditions [capillary temperature, in-source collisionally-induced dissociation (CID)]. These data indicate that the adducts are rapidly stabilised by collisional cooling enabling them to be transferred into the ion trap. Experiments using identical sample preparation conditions were carried out on a vacuum MALDI time-of-flight (ToF) mass spectrometer. In all cases, vacuum MALDI-ToF spectra showed only alkali-metal/PEG ions and no matrix/analyte adducts. The tandem mass spectrometry (MS/MS) capability of the ion trap has been demonstrated for a lithiated polyglycol yielding a rich fragment-ion spectrum. Analysis of the hyperbranched polymer polyglycidol by AP-MALDI/QIT reveals the characteristic ion series for these polymers as also observed under vacuum MALDI-ToF conditions.     

Remote mass spectrometric sampling of electrospray- and desorption electrospray-generated ions using an air ejector

A commercial air ejector was coupled to an electrospray ionization linear ion trap mass spectrometer (LTQ) to transport remotely generated ions from both electrospray (ESI) and desorption electrospray ionization (DESI) sources. We demonstrate the remote analysis of a series of analyte ions that range from small molecules and polymers to polypeptides using the AE-LTQ interface. The details of the ESI-AE-LTQ and DESI-AE-LTQ experimental configurations are described and preliminary mass spectrometric data are presented.     

Combining capillary with radio-frequency-only quadrupole as an interface for a home-made time-of-flight mass spectrometer

A heated capillary tube combined with a radio-frequency-only quadrupole has been coupled with a home- made, high-resolution orthogonal-injection, time-of-flight mass spectrometer to improve ion transmission from the atmospheric pressure to the low--pressure regions. With an electrospray ion source, the performance of the interface on the intensity of spectra was investigated. For electrospray ionization, the ion intensity detected on the time-of- flight mass spectrometer was seen to increase three-fold compared with an orifice interface. It has been shown that the enhanced ion inlet designs can not only increase the ion translation efficiency, but also improve the detection limits of the mass spectrometer. Coupling atmospheric pressure matrix-assisted laser desorption/ionization with the improved interface resulted in an instrument detection limit as low as 2.5 fmol.     

Reaction of analyte ions with neutral chemical ionization gas

Analytical Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA Ion-molecule reactions of neutral methane with analyte ions under normal methane chemical ionization conditions are discussed. Reactant ions can be generated by direct electron ionization (EI) fragmentation, chemical ionization (CI) fragmentation, or collision-induced dissociation (CID). Examples in which products of such reactions appear in mass spectra in both conventional CI sources in “beam” instruments and low pressure CI in a quadrupole ion trap are presented. Also shown is an example in which MS/MS product ions react with neutral methane used for CI in an ion trap. It is shown that it is relatively straightforward to recognize such reactions in a quadrupole ion trap and in certain cases to minimize or preclude them. Effects of various operating parameters have been investigated and are discussed.     

Reduction of chemical noise in electrospray ionization mass spectrometry by supplemental IR activation

Supplemental infrared (IR) activation was applied to reduce background chemical noise and increase analyte ion signal in a linear ion trap mass spectrometer. Peptides, proteins, and small molecules were all introduced by electrospray ionization, and when regions of chemical noise were isolated and subjected to IR irradiation, protonated analyte molecules were observed in the product ion mass spectra. By isolating the entire mass range (e.g., m/z 400–2000) and then irradiating all ions in the trap, supplemental IR activation increased the signal of singly protonated peptides by almost 70% and by 40%–55% for the lower charge states of cytochrome c. This increase in analyte ion signal was less dramatic for the higher charge states of peptides and proteins. The chemical noise present in the mass spectra is attributed to incomplete desolvation of the electrospray, as the abundance of the protonated peptides observed upon supplemental IR activation of the chemical noise decreased with higher inlet capillary temperatures. Collision activation was not as effective for desolvating the ions present in the chemical noise.     

Electrospray ionization ion trap mass spectrometry of a tetrahedral supramolecular Ti4L4 cluster

The analysis of self-assembled supramolecular clusters held together by metal-ligand interactions is a relatively new area in mass spectrometry. These complexes may have molecular weights exceeding several kDa, are often highly charged and their composition is most sensitive to their chemical environment. Electrospray ionization appears to be the ionization technique of choice for their mass spectral characterization. The analysis (positive and negative ion detection mode) of the prototype compound [Ti₄L₄]^8? (L = a catechol-based tris-bidentate ligand; MW of cluster = 2293 u) using a Paul trap mass analyzer is reported. The combination of electrospray ionization and high resolution ion trap technology is a powerful tool which provides the unambiguous solution state characterization of this supramolecular cluster. The results are correlated with the known solid state structure of the cluster and reactions previously reported for mononuclear Ti(IV) catecholates.     

Fragmentation pathways of selectively labeled uropranolol using electrospray ionization on an ion trap mass spectrometer and comparison with ions formed by electron impact

Propranolol, deuterium- and 18O-labeled propranolol and related compounds were analyzed using an ion trap mass spectrometer equipped with a modified Finnigan API electrospray interface. Sequential product ion (MSn) experiments were used to elucidate fragmentation pathways for these compounds. The observed ions were compared to those observed under electron impact (EI) conditions. The electrospray ionization (ESI) ion trap spectra, as well as the EI spectra, afford useful information to allow assignments of most product ions, many of which retain portions of the aliphatic three-carbon side chain.     

Nano-liquid chromatography-direct electron ionization mass spectrometry: improving performance by a new ion source adapter

A novel interface adapter has been designed to provide a new way of directly coupling a nano-liquid chromatograph to an electron ionization mass spectrometer. It connects the transfer capillary coming from the liquid chromatograph to the ionization chamber and can be easily screwed into the ion source. Liquid coming from the column passes through the heated adapter flow path and is vaporized. A continuous flow of new liquid pushes the vapor into the ionization chamber where it is ionized and continues on to the mass analyzer. The advantages of the new adapter are reduced ice formation inside the ion source and less clogging of the transfer capillary. Improvements achieved are demonstrated on the basis of caffeine and steroid analysis. The limits of detection of selected steroids are compared with and without the adapter. The adapter improves the detection limit of the system by a factor of 2 and precision from ≤15% to ≤9% relative standard deviation. No derivatization procedure is necessary before the analysis of small polar compounds. The resulting spectra are reproducible, easily interpretable, and database searchable. The new method is robust, delivers reproducible results, and provides a highly efficient alternative to existing methods in the field of pharmaceutical analysis.     

A segmented ring,cylindrical ion trap source for time-of-flight mass spectrometry

An ion trap source has been designed for use with time-of-flight (TOF) mass analysis. Two thin diaphragms make up a segmented ring electrode; the end cap electrodes are planar wire mesh. The potential field produced by the rf voltage applied between the ring and end cap electrodes resembles that of the cylindrical ion trap. The trapped ion population for ions created by electron impact exhibits linear growth against a first-order loss that has a time constant of about 50 µs; no ion loss occurs when the electron beam is off. The observed value of q _z at low-mass cutoff for rf ion storage is ?0.84. Pulsed extraction of all ions is accomplished by switching the trap electrodes from rf to voltages required to provide a linear dc extraction field. The TOF flight path includes a wide energy range reflectron. Better than unit mass resolution is achieved through m/z 500 without collisional ion cooling. With an extraction rate of 1 kHz and a recording rate of 4 spectra per second, a linear working curve is obtained between 36 pg and 18 ng of chlorobenzene delivered chromatographically. The system has demonstrated the potential to achieve a very high sample utilization efficiency at high spectral generation rates.     

Optimization of electrospray interface and quadrupole ion trap mass spectrometer parameters in pesticide liquid chromatography/electrospray ionization mass spectrometry analysis

Optimization of both the ionization process and ion transportation in the mass spectrometer is of crucial importance in order to achieve high sensitivity and low detection limits and acceptable accuracy in liquid chromatography/electrospray ionization mass spectrometry (LC/ESI‐MS) analysis. In this paper four optimization procedures of electrospray interface and quadrupole ion‐trap mass spectrometer parameters (ESI‐MS) (nebulizer gas and drying gas flow rate, end plate voltage, capillary voltage, skimmer voltage, octopoles direct current and radio frequency, trap drive and lens voltages) were studied on three pesticides – thiabendazole, aldicarb and imazalil. The results demonstrate that the methodology of optimization strongly influences the effectiveness of finding true optima of the operating parameters. Both eluent flow rate and composition during optimization have to mimic the situation during real analysis as closely as possible in order to achieve parameters giving the highest sensitivity. Therefore, post‐column addition of analyte to the mobile phase identical in composition to the one in which analyte elutes during real analysis combined with software‐based optimization was found to be the most effective and fastest method for achieving intensity maxima. The parameters most strongly affecting ion formation and transportation, hence sensitivity, were capillary voltage, direct current of the first octopole, trap drive and the second lens for all pesticides under study. In addition to sensitivity and detection limit matrix effect was considered in the optimization process. It was found that the matrix effect can be reduced but not eliminated by adjusting the ESI and MS parameters. The optimal parameters from the point of view of the matrix effect can only be found with factorial design. Parameters giving higher sensitivity tended to be more affected by matrix effect causing higher ionization suppression by co‐eluting compounds. Copyright © 2010 John Wiley & Sons, Ltd.     

Desorption electrospray ionization of aerosol particles

We have applied desorption electrospray ionization to aerosol particles. Ions were formed from aerosols by merging suspended dry particles with an electrospray of solvent in a modified ion trap mass spectrometer. Dry aerosol particles were generated using a fluidized bed powder disperser and directed toward the inlet of the mass spectrometer. A nanospray source was used to create a spray of solvent droplets directed at the inlet and at a right angle with respect to the aerosol. Ions generated by the interaction of the particles and electrospray were transferred into the ion trap mass spectrometer. Using this method, pure samples of caffeine and erythromycin A were analyzed. In addition, commonly available food and drug powders including instant cocoa powder, artificial sweetener and ibuprofen were analyzed.     

An improved thin-layer chromatography/mass spectrometry coupling using a surface sampling probe electrospray ion trap system

A combined surface sampling probe/electrospray emitter coupled with an ion trap mass spectrometer was used for the direct read out of unmodified reversed-phase C18 thin-layer chromatography (TLC) plates. The operation of the surface sampling electrospray ionization interface in positive and negative ionization modes was demonstrated through the direct analysis of TLC plates on which a commercial test mix comprised of four dye compounds viz., rhodamine B, fluorescein, naphthol blue black, and fast green FCF, and an extract of the caffeine-containing plant Ilex vomitoria, were spotted and developed. Acquisition of full-scan mass spectra and automated collection of MS/MS product ion spectra while scanning a development lane along the surface of a TLC plate demonstrated the advantages of using an ion trap in this combination. Details of the sampling system, benefits of analyzing a developed lane in both positive ion and negative ion modes, levels of detection while surface scanning, surface scan speed effects, and the utility of three-dimensional data display, are also discussed.     

Fast quantitative detection of cocaine in beverages using nanoextractive electrospray ionization tandem mass spectrometry

Without any sample pretreatment, effervescent beverage fluids were manually sprayed into the primary ion plume created by using a nanoelectrospray ionization source for direct ionization, and the analyte ions of interest were guided into an ion trap mass spectrometer for tandem mass analysis. Functional ingredients (e.g., vitamins, taurine, and caffeine, etc.) and spiked impurity (e.g., cocaine) in various beverages, such as Red Bull energy drink, Coco-cola, and Pepsi samples were rapidly identified within 1.5 s. The limit of detection was found to be 7 ∼ 15 fg (S/N = 3) for cocaine in different samples using the characteristic fragment (m/z 150) observed in the MS³ experiments. Typical relative standard deviation and recovery of this method were 6.9% ∼ 8.6% and 104% ∼ 108% for direct analysis of three actual samples, showing that nanoextractive electrospray ionization tandem mass spectrometry is a useful technique for fast screening cocaine presence in beverages.     

Evidence for thermal decomposition contributions to the mass spectra of chlorinated phenoxyacid herbicides obtained by particle beam liquid chromatography mass spectrometry

The spectral quality of a group of chlorinated phenoxyacid herbicides has been shown to degrade under certain conditions upon introduction into the mass spectrometer by a particle beam interface. Experiments were performed to investigate these changes in spectra. Normalized ion chromatograms were generated for the herbicides, and the results showed a broadening of the profiles of some ions, indicating a longer residence time in the ion source. These ions were postulated as coming from the ionization of thermal degradation products from the herbicides. The generation of these ions was dependent on ion source temperature, analyte concentration, and, by implication, ion source cleanliness. Tandem mass spectrometry experiments were performed on these ions from the herbicides and ions from the corresonding phenols. The tandem mass spectra of the ions from the herbicides were similar to the tandem mass spectra of the ions from the phenols. Therefore, it appears that the particle beam mass spectra of the chlorinated phenoxyacid herbicides are composite spectra with contributions from the gas phase ionization of the parent herbidides and thermal decomposition products.