Rapid analysis of aromatic contaminants in water samples by means of laser ionization mass spectrometry

Three different approaches to laser ionization mass spectrometric analysis of aromatic compounds in water samples are described and their performances are compared. Whereas the first two methods are based on direct laser desorption and subsequent laser ionization of either frozen or adsorbed samples in a time-of-flight mass analyzer, the third performs laser ionization in a quadrupole ion-trap into which the sample is transferred from a GC injector via a short piece of capillary tubing. For the laser-desorption method a detection limit in the 100 µg L^–1 range was determined for fluorene in frozen samples. The easier to handle analysis of adsorbed samples yielded sensitivities which were lower by about two orders of magnitude. As both direct techniques do not reach the sensitivity required for ultra trace analysis in water a preconcentration step in form of solid-phase microextraction was added before measurement using the laser ionization quadrupole ion-trap mass spectrometer. Sensitivity in the desired ng L^–1 range was easily achieved.     

Collision-induced dissociation of glycero phospholipids using electrospray ion-trap mass spectrometry.

Characterisation of phospholipids was achieved using collision-induced dissociation (CID) with an ion-trap mass spectrometer. The product ions were compared with those obtained with a triple quadrupole mass spectrometer. In the negative ion mode the product ions were mainly sn-1 and sn-2 lyso-phospholipids with neutral loss of ketene in combination with neutral loss of the polar head group. Less abundant product ions were sn-1 and sn-2 carboxylate anions. CID using a triple quadrupole mass spectrometer, however, gave primarily the sn-1 and sn-2 carboxylate anions together with lyso-phosphatidic acid with neutral loss of water. For the ion trap a charge-remote-type mechanism is proposed for formation of the lyso-phospholipid product ions by loss of alpha-hydrogen on the fatty acid moiety, electron rearrangement and neutral loss of ketene. A second mechanism involves nucleophilic attack of the phosphate oxygen on the sn-1 and sn-2 glycerol backbone to form carboxylate anions with neutral loss of cyclo lyso-phospholipids. CID (MS(3) and MS(4)) of the lyso-phospholipids using the ion-trap gave the same carboxylate anions as those obtained with a triple quadrupole instrument where multiple collisions in the collision cell are expected to occur. The data demonstrate that phospholipid species determination can be performed by using LC/MS(n) with an ion-trap mass spectrometer with detection of the lyso-phospholipid anions. The ion-trap showed no loss in sensitivity in full scan MS(n) compared to multiple reaction monitoring data acquisition. In combination with on-line liquid chromatography this feature makes the ion-trap useful in the scanning modes for rapid screening of low concentrations of phospholipid species in biological samples as recently described (Uran S, Larsen A, Jacobsen PB, Skotland T. J. Chromatogr. B 2001; 758: 265).     

Studies on azaspiracid biotoxins. II. Mass spectral behavior and structural elucidation of azaspiracid analogs

In this report, the mass spectral analysis of azaspiracid biotoxins is described. Specifically, the collision-induced dissociation (CID) behavior and differences between CID spectra obtained on a triple-quadrupole, a quadrupole time-of-flight, and an ion-trap mass spectrometer are addressed here. The CID spectra obtained on the triple-quadrupole mass spectrometer allowed the classification of the major product ions of the five investigated compounds (AZA 1-5) into five distinct fragment ion groups, according to the backbone cleavage positions. Although the identification of unknown azaspiracids was difficult based on CID alone, the spectra provided sufficient structural information to allow confirmation of known azaspiracids in marine samples. Furthermore, we were able to detect two new azaspiracid analogs (AZA 1b and 6) in our samples and provide a preliminary structural analysis. The proposed dissociation pathways under tandem mass spectrometry (MS/MS) conditions were confirmed by a comparison with accurate mass data from electrospray quadrupole time-of-flight MS/MS experiments. Regular sequential MS(n) analysis on an ion-trap mass spectrometer was more restricted in comparison to the triple-quadrupole mass spectrometer, because the azaspiracids underwent multiple [M + H - nH(2)O](+) (n = 1-6) losses from the precursor ion under CID. Thus, the structural information obtained from MS(n) experiments was somewhat limited. To overcome this limitation, we developed a wide-range excitation technique using a 180-u window that provided results comparable to the triple-quadrupole instrument. To demonstrate the potential of the method, we applied it to the analysis of degraded azaspiracids from mussel tissue extracts.     

Analysis of vitamin E in food and phytopharmaceutical preparations by HPLC and HPLC-APCI-MS-MS

Summary The analysis of α, β, γ, δ-tocopherols, trienols, α-tocopheryl acetate and nicotinate (vitamin E) in complex matrices was carried out using a new liquid chromatographic (HPLC) method giving better separation efficiency, selectivity and sensitivity than that described in the literature. The use of normal-phase (NP)-HPLC on silica gel with issoctane-diisopropylether-1,4-dioxane as optimized mobilepphase yielded higher resolution than conventional reversed-phase (RP)-HPLC using methanol mobile phase. Identification of peaks was by UV-absorbance at 295 nm, diode array, or fluorescence detection (λ _ex = 295 nm,λ _ex = 330 nm). The latter was found to be more selective and ten times more sensitive than UV-absorbance detection. A quadrupole, ion-trap mass spectrometer with an atmospheric-pressure ionization (APCl) interface was used to detect vitamin E constituents in the femtomole range. With collision-induced dissociation (CID) in the ion source, which gave characteristic fragmentation, the identity of the investigated compounds could be confirmed. Plots of peak area versus amount injected allowed quantitation of α, β, γ, δ-tocopherols and-trienols, α-tocopheryl acetate and nicotinate in real samples such as peanut, almond, spinach, spelt grain bran, latex and tablets. The method described offers fast identification and quantitation of vitamin E constituents of complex biological origin. Dedicated to Professor Dr. Heinz Engelhardt on the occasion of his 65^th birthday.     

Comparison of two quantitative GC–MS methods for analysis of tomato aroma based on purge-and-trap and on solid-phase microextraction

Two analytical procedures, one based on purge-and-trap and the other on solid phase microextraction, both followed by GC–MS measurement using an ion-trap mass spectrometer in the electron impact mode, have been developed for determination and quantitation of up to 39 aroma compounds in fresh tomatoes. The method based on purge-and-trap for isolation of the volatile compounds uses Tenax as adsorbent and a hexane–diethyl ether mixture as solvent for elution. The method was validated for linearity, precision (better than 20% for most compounds), and limit of detection, which was approximately 1 ng g⁻¹. This method enabled identification of up to 30 compounds in real samples. Use of SPME was considered as an alternative, to simplify sample treatment while maintaining the information level for the samples (e.g. the number of compounds detected) and quality of quantitation. A procedure based on SPME using a Carboxen/polydimethylsiloxane fibre was developed and validated for determination of 29 aroma compounds; precision was better than 20% and limits of detection ranged from 4 to 30 ng g⁻¹.     

Evaluation of the oxidative status of virgin olive oils with different phenolic content by direct infusion atmospheric pressure chemical ionization mass spectrometry

Atmospheric pressure chemical ionization mass spectrometry was used to predict the oxidative status of virgin olive oils (VOO) during their storage. VOO samples, with and without phenolic compounds, were stored in the dark at 60 °C up to 7 weeks. The VOO samples were diluted in an alkaline propanol/methanol mixture and directly infused into an ion-trap mass spectrometer. The abundances of the [M−H]⁻ peaks of free fatty acids, oxidized fatty acids, tocopherols and phenolic compounds, jointly with their oxidized forms, were measured and used as predictors. Two linear discriminant analysis (LDA) models were constructed in order to classify samples according to their oxidative levels. The first model was constructed using both VOO samples (with and without phenols), considering as predictors only fatty acids and their oxidized products. The second LDA model was constructed with the VOO sample with phenolic compounds considering as predictors all the peaks measured. In both models, the samples divided in the eight different storage times were correctly classified (100%) by leave-one-out cross-validation with an excellent resolution among all the category pairs (for the first model Wilks’ lambda, λ _w = 0.229 and for the second λ _w = 0.928). This method is a very fast tool for on-line monitoring of VOO oxidation status.     

Evaluation of an analytical method for determining phthalate esters in wine samples by solid-phase extraction and gas chromatography coupled with ion-trap mass spectrometer detector

A solid-phase extraction (SPE) method was developed for extraction and analysis of six phthalate esters in wine samples using Carbograph 1 sorbent. The SPE procedure allowed efficient recovery of the investigated phthalates ranging between 78% and 105% with a relative standard deviation (RSD) ≤6.5 for an ethanolic phthalic acid ester (PAE) standard solution and between 73–71% and 96–99% with a RSD ≤8.4 for red wine samples spiked with 20 and 50 ng mL⁻¹ of PAE, respectively. The adsorption isotherms and breakthrough curves for Carbograph 1/water solution were reported. Gas chromatography coupled with an ion-trap mass spectrometer detector (GC/IT-MS) was used for analysis. The instrumental analytical protocol was found to yield a linear calibration in the range 0.01-10.0 μg mL⁻¹ with R ² values ≥0.9992. The limits of detection in GC/IT-MS (SIM mode) vary between 0.2 and 14 ng mL⁻¹ (RSD ≤5.6) whereas the limits of quantification range between 0.5 and 25 ng mL⁻¹ (RSD ≤5.9); the intra- and inter-day repeatabilities calculated as RSD for wine samples, were between 0.9–7.8 and 1.0–10.5, respectively. The analytical method developed was applied to several commercial wine samples. Furthermore, the investigated methods are simple, reliable, reproducible, and not expensive.     

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.     

Determination of cadmium in oyster tissue using isotope dilution inductively coupled plasma mass spectrometry: comparison of results obtained in the standard and He/H2 cell modes

An inductively coupled plasma quadrupole mass spectrometer equipped with an octopole collision/reaction cell was used for the determination of cadmium in oyster tissue samples using isotope dilution inductively coupled plasma mass spectrometry. The oyster samples in question were found to contain Mo and Zr. In our feasibility study on a Cd standard solution (10 μg L⁻¹) containing a matrix of Mo (1000 μg L⁻¹) or Zr (250 μg L⁻¹), the potentially interfering species (MoO⁺ or ZrO⁺) present at the analytical mass of cadmium concerned (m/z 111, 112 or 114) was reduced effectively through the use of a mixture of He and H₂ as cell gases. The accuracy of the method was validated by the analysis of a matrix-matched certified reference material (CRM) of NIST SRM 1566b. The CRM was analyzed under the standard and He/H₂ cell modes. Two isotopic pairs of ¹¹⁴Cd/¹¹¹Cd and ¹¹²Cd/¹¹¹Cd were selected for quantification purposes. The recoveries of cadmium obtained in the two cell modes were compared with each other. The validated method was applied successfully to the APMP.QM-P5 pilot study for international comparability purposes.     

Studies on azaspiracid biotoxins. III. Instrumental validation for rapid quantification of AZA 1 in complex biological matrices

Azaspiracids are neurotoxins produced by marine algae that have been detected in harvested mussels since 1995. They pose a significant threat to human health through the consumption of contaminated shellfish, and negatively impact the economy of areas where shellfish are harvested and processed. Regulatory agencies are beginning to advocate instrumental assays over traditional mouse bioassay methods. The development and validation of an assay method for AZA 1, the predominant azaspiracid toxin, and the production of a calibration standard and reference material will therefore be vital for quality control in monitoring laboratories worldwide. This report demonstrates a rapid and reproducible liquid chromatography/mass spectrometry (LC/MS) method for separation of all twelve known azaspiracids. Using a triple-quadrupole mass spectrometer, ultra-high sensitivity was obtained at the low-femtogram level injected on-column. At the same time, a linear response of three orders of magnitude was observed. We compared the results with those measured on an ion-trap mass spectrometer. The triple-quadrupole instrument was more sensitive, reliable and reproducible than the ion-trap instrument. The detection limit obtained on the ion-trap mass spectrometer was ten times higher than that obtained on the triple quadrupole. During the study, a new azaspiracid analog (AZA 7c) was discovered.     

LC–ESI–MS for Rapid and Sensitive Determination of Aripiprazole in Human Plasma

A rapid, sensitive, and accurate high-performance liquid-chromatographic–mass spectrometric (HPLC–MS) method, with estazolam as internal standard, has been developed and validated for determination of aripiprazole in human plasma. After liquid–liquid extraction the compound was analyzed by HPLC on a C₁₈ column, with acetonitrile—30 mm ammonium acetate containing 0.1% formic acid, 58:42 (v/v), as mobile phase, coupled with electrospray ionization mass spectrometry (ESI-MS). The protonated analyte was quantified by selected-ion recording (SIR) with a quadrupole mass spectrometer in positive-ion mode. Calibration plots were linear over the concentration range 19.9–1119.6 ng mL⁻¹. Intra-day and inter-day precision (CV%) and accuracy (RE%) for quality-control samples (37.3, 124.4, and 622.0 ng mL⁻¹) ranged between 2.5 and 9.0% and between 1.3 and 3.5%, respectively. Extraction recovery of aripiprazole from plasma was in the range 75.8–84.1%. The method enables rapid, sensitive, precise, and accurate measurement of the concentration of aripiprazole in human plasma.     

LC-ESI-MS Method for the Determination of Mizolastine in Human Plasma

A sensitive and rapid liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) method has been developed and validated for the determination of mizolastine in human plasma using dipyridamole as the internal standard (I.S.). Plasma samples were simply pretreated with methanol for deproteinization. Chromatographic separation was performed on an Agilent Zorbax C₁₈ column with a mobile phase of 10 mM ammonium acetate buffer containing 0.1% formic acid–methanol (20:80, v/v) at a flow rate of 1 mL min⁻¹. The electrospray ionization (ESI) interface was employed in a single quadrupole mass spectrometer. The analytes were protonated in the positive ESI interface and detected in single ion monitoring (SIM) mode. Chromatographic separation was achieved in less than 3.5 min. The linearity was established over the range of 0.5–600 ng mL⁻¹. The lower limited of quantification (LLOQ) of the method was 0.5 ng mL⁻¹. The intra- and inter-run standard deviations were both less than 11.2%. The method was applied to study the pharmacokinetics of the mizolastine sustained-release tablets in healthy volunteers.     

Simultaneous Quantification of Sodium Ferulate, Salicylic Acid, Cinnarizine and Vitamin B1 in Human Plasma by LC Tandem MS Detection

A rapid and simple high performance liquid chromatographic method coupled with tandem mass spectrometry (LC–MS–MS) via electrospray ionization (ESI) has been developed and validated to separate and simultaneously quantify sodium ferulate (SF), salicylic acid (SA), cinnarizine (CIN) and vitamin B1 (VB1) in human plasma. Gemfibrozil (GEM) was used as the internal standard (IS) for SF and SA, whereas lomerizine (LOM) was used as the IS for CIN and VB1. The plasma samples were prepared by one-step protein precipitation followed by an isocratic elution with 10 mM ammonium acetate buffer (pH = 5.0): acetonitrile (35:65, v/v,) on an Agilent Zorbax SB-CN column (150 mm × 2.0 mm ID, 5 μm). The precursor and product ions of these drugs were monitored on a triple quadrupole mass spectrometer, operating in the selected reaction monitoring mode (SRM) with polarity switch, in the negative-ion mode for SF, SA and GEM, in the positive-ion mode for CIN, VB1 and LOM. The method was validated over the concentration range of 1.5–1,000 ng mL⁻¹ for SF, 20–5,000 ng mL⁻¹ for SA, 2–500 ng mL⁻¹ for CIN, 1–30 ng mL⁻¹ for VB1. The intra- and inter-batch precisions were less than 15% of the relative standard deviation. The recoveries for analytes and IS achieved from spiked plasma samples were consistent and reproducible. The validated LC–MS–MS method has been successfully applied to the pharmacokinetic study of sodium ferulate and aspirin capsule in healthy volunteers.     

Development of an on-line matrix solid-phase dispersion/fast liquid chromatography/tandem mass spectrometry system for the rapid and simultaneous determination of 13 sulfonamides in grass carp tissues

A novel analytical protocol based on interfacing on-line matrix solid-phase dispersion (MSPD) with high-performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS) was developed for extraction and determination of 13 sulfonamide residues in grass carp tissues. The target analytes were separated on a fused-core C18-silica column with a period of 7 min and quantified by a triple–quadrupole linear ion-trap mass spectrometer in positive ion multiple-reaction monitoring (MRM) mode. The proposed method was optimized and validated according to Commission Decision 2002/657/EC. The matrix-matched calibration curves were performed at six concentration levels and good linear relationship (R² = 0.993–0.998) was observed within the range of 0.1–100 ng mL⁻¹. The mean values of relative standard deviation of intra- and inter-day ranging from 1.8% to 7.8% and from 2.8% to 10.3% were obtained, respectively. Moreover, satisfied recoveries (69.0–96.3%) of all studied sulfonamides were demonstrated in different spiked levels, with RSDs ≤ 13.2%. The proposed method has been applied successfully to the analysis of sulfonamides in several grass carp samples, and the results indicated that this novel instrumental coupling was fast, sensitive, reliable and environmental friendly with good prospects.     

Trapping of a tert-adamantyl peroxyl radical in the gas phase

A bridgehead adamantyl peroxyl radical has been prepared and isolated in the gas phase by the reaction of a distonic radical anion with dioxygen in a quadrupole ion-trap mass spectrometer.     

Confirmation of phenylbutazone residues in bovine kidney by liquid chromatography/mass spectrometry

A confirmatory method is described for phenylbutazone (PB) residues in bovine kidney tissue. Ground kidney tissue is diluted with water, and the mixture is made basic with 25% ammonium hydroxide in water; the lipids are extracted with ethyl and petroleum ethers. The ether layer is discarded, and the tissue is acidified with 6N HCl. PB residues are extracted with tetrahydrofuranhexane (1 + 4). The extract is passed through a silica solid-phase extraction column, and the eluate is evaporated to dryness. The residue is dissolved in acidified acetonitrile-water-acetic acid (50 + 49.4 + 0.6). A single quadrupole mass spectrometer coupled to a liquid chromatograph with an electrospray interface is used to confirm the identity of the PB residues in the kidney extract. Negative-ion detection with selected-ion monitoring of 4 ions is used. Sets of control and fortified-control kidney tissues (at 50, 100, and 200 ppb PB) and several kidney tissue field samples were analyzed for method validation. The method was tested further during the course of a survey to determine the incidence of PB residues in bovine kidney samples obtained from slaughterhouses across the country. In addition, the method was tested for use with an ion-trap mass spectrometer coupled to a liquid chromatograph, which allowed confirmation of PB at lower levels (5-10 ppb) in kidney tissue.     

Analysis of 19-norandrosterone in human urine by gas chromatography–isotope-dilution mass spectrometry: method adopted by LGC for participation in the Comité Consultatif pour la Quantité de Matière (CCQM) Pilot Study P68

The method used at LGC for analysis of “total” 19-norandrosterone (19-norandrosterone glucuronide plus “free” 19-norandrosterone) in urine for the Comité Consultatif pour la Quantité de Matière Pilot Study (CCQM-P68) is described. The analytical method used was a modified version of the method developed at the National Measurement Institute of Australia, which used a hydrolysis and derivatisation procedure first described by the German Sports University. This method is routinely used by World Anti-Doping Agency-accredited laboratories for sports drug testing. The main modifications made to the method were the use of 19-norandrosterone glucuronide as a calibration standard and 19-norandrosterone glucuronide-d4 as an isotopically labelled internal standard, and the use of a bench-top quadrupole gas chromatograph–mass spectrometer. The results produced by LGC (2.14 ± 0.15 ng g⁻¹ expanded uncertainty, coverage factor k = 2) were in excellent agreement with those from other participating national metrology institutes and thus further validates the exact-matching isotope-dilution mass spectrometric procedures used at LGC for a wide range of reference measurement applications, including measurement of ng g⁻¹ levels of steroids in a biological matrix.     

Purity testing of organometallic catalysts by micro liquid chromatography-electron ionization mass spectrometry

Summary A micro liquid chromatography-mass spectrometry system utilizing 100 μm i. d. packed capillary columns has been used for purity testing of organometallic catalysts. The total effluent, 1 μLmin⁻¹ from the column, was introduced directly into the ion source of a bench-top quadrupole mass spectrometer and electron ionization mass spectra were acquired. In full scan mode a mass limit of detection of 10–15 ng was achieved for the organometallic compounds investigated. The catalysts dimethyl pentamethylcyclopentadienyl iridium dimethylsulphoxide (Cp^*Ir(DMSO)Me₂) and di(pentamethylcyclopentadienyl dichloro iridium) ((Cp^*IrCl₂)₂) were purity tested and their electron ionization mass spectra recorded. Impurities present down to 1% of the main compound could be determined using large volume injection.     

Simultaneous extraction of polycyclic aromatic hydrocarbons and polychlorinated biphenyls in agricultural soils by pressurized liquid extraction and determination by gas chromatography coupled to tandem mass spectrometry

A simple and rapid method based on pressurized liquid extraction has been validated for the simultaneous extraction of polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) from agricultural soil samples. Effective extraction was carried out in less than 17 min for all the studied compounds, and good recoveries were obtained for PAHs and PCBs, ranging from 70% to 112%, when blank samples were spiked at 2.5 μg kg⁻¹, except for naphthalene with recoveries close to 40%. The separation and determination were performed by gas chromatography coupled to tandem mass spectrometry using a triple quadrupole mass analyzer. The target compounds were detected by electron impact with selected reaction monitoring, and mass spectrometric conditions were optimized in order to increase selectivity and sensitivity. The developed method was validated, and matrix-matched calibration was used for quantification purposes. Repeatability and interday precision ranged from 0.9% to 16.8% and from 1.6% to 22.3%, respectively. Limits of quantification ranged from 0.07 to 2.50 μg kg⁻¹. The proposed method was applied to the analysis of agricultural soil samples collected from Almeria (Spain), and PAHs and PCBs were detected in some samples at concentrations ranging from 0.1 to 210 μg kg⁻¹.     

Heterophase synthesis and standard enthalpies of formation of metal acetylacetonates

Vaporization of Mn(acac)₃ has been studied by mass spectrometry on a quadrupole mass spectrometer with direct insertion probe, which was not previously used for these purposes. The enthalpy of sublimation of Mn(acac)₃ was calculated to be 130.5 ± 4.0 kJ/mol. Heterophase interactions in the [M-Mn(acac)₃] system were studied directly during the mass spectral experiment (in situ method). The reaction products were judged from the mass spectra of the gas phase. The enthalpies of formation in the gas phase Δ _f H _gas ^T of Pb, In, and Ga acetylacetonates were estimated to be −654, −1057, and −1035 kJ/mol, respectively.