Atmospheric pressure laser ionization (APLI) coupled with Fourier transform ion cyclotron resonance mass spectrometry applied to petroleum samples analysis: comparison with electrospray ionization and atmospheric pressure photoionization methods

The analysis of crude oil samples remains a tough challenge due to the complexity of the matrix and the broad range of physical and chemical properties of the various individual compounds present. In this work, atmospheric pressure laser ionization (APLI) is utilized as a complementary tool to other ionization techniques for crude oil analysis. Mass spectra obtained with electrospray ionization (ESI) and atmospheric pressure photoionization (APPI) are compared. APLI is primarily sensitive towards non‐polar aromatic hydrocarbons, which are generally present in high amounts especially in heavy crude oil samples. The ionization mechanisms of APLI vs. APPI are further investigated. The results indicate the advantages of APLI over established methods like ESI and APPI. The application of APLI in combination with Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR MS) is thus demonstrated to be a powerful tool for the analysis of aromatic species in complex crude oil fractions. Copyright © 2011 John Wiley & Sons, Ltd.     

Atmospheric pressure ion focusing with a vortex stream

For successful operation of ionization analysis techniques an efficient sampling and sample ion transportation into an analytical path are required. This is of particular importance for atmospheric pressure ionization sources like corona discharge, electrospray, MALDI, ionization with radioactive isotopes (³H, ⁶³Ni) that produce nonuniform spatial distribution of sample ions. The available methods of sample ion focusing with electric fields are either efficient at reduced pressure (to 1 Torr) or feature high sample losses. In this paper we suggest to use a highly whirled gas stream for atmospheric pressure ion focusing. We use a ⁶³Ni radioactive source to produce an ionized bipolar sample at atmospheric pressure. It is shown by experiments that compared to an aspiration method a forced highly whirled vortex stream allows one to enhance the efficiency of remote ionized sample collection at distances equal to the vortex sampler diameter by an order of magnitude. With a vortex stream, a sixfold increase in the efficiency of the radial ionized sample collection has been obtained. It may be deduced that with the vortex stream remote sampling obtains a new feature which is characterized by a considerable enhancement of the efficiency of the ionized sample collection and can be called as a “gas-dynamic” ionized sample focusing. Considered is the effect of recombination losses of the ionized sample during the remote sampling thereof with the vortex sampler. Prospects for a practical implementation of the vortex sampler for solving the problems of the customs control over the smuggling of radioactive α and β sources are made based on the research results.     

Cleavage reactions of the complex ions derived from self-complementary deoxydinucleotides and alkali-metal ions using positive ion electrospray ionization with tandem mass spectrometry

The dissociation reactions of the adduct ions derived from the four self-complementary deoxydinucleotides, d(ApT), d(TpA), d(CpG), d(GpC), and alkali-metal ions were studied in detail by positive ion electrospray ionization multiple-stage mass spectrometry (ESI-MS(n)). For the [M + H](+) ions of the four deoxydinucleotides, elimination of 5'-terminus base or loss of both of 5'-terminus base and a deoxyribose were the major dissociation pathway. The ESI-MS(n) spectra showed that Li(+), Na(+), and Cs(+) bind to deoxydinucleotides mainly by substituting the H(+) of phosphate group, and these alkali-metal ions preferred to bind to pyrimidine bases rather than purine bases. For a given deoxydinucleotide, the dissociation pathway of [M + K](+) ions differed clearly from that of [M + Li](+), [M + Na](+), and [M + Cs](+) ions. Some interesting and characteristic cleavage reactions were observed in the product-ion spectra of [M + K](+) ions, including direct elimination of deoxyribose and HPO(3) from molecular ions. The fragmentation behavior of the [M + K](+) and [M + W](+) (W = Li, Na, Cs) adduct ions depend upon the sequence of bases, the interaction between alkali-metal ions and nucleobases, and the steric hindrance caused by bases.     

Positive ion electrospray ionization tandem mass spectrometry coupled to ion-pairing high-performance liquid chromatography with a phosphate buffer for the quantitative analysis of intracellular nucleotides

A novel analytical procedure has been developed for the analysis of intracellular nucleotide triphosphates. Positive ion electrospray ionization tandem mass spectrometry (MS/MS) was interfaced to ion-pairing high-performance liquid chromatography (HPLC) utilizing a mobile phase containing 10 mM ammonium phosphate, pH 6.4, with 2 mM tetrabutylammonium hydroxide and 15% acetonitrile. The methodology was developed to support the analysis of the 5'-triphosphate anabolite of the antiviral agent (-)-FTC ((2R, 5S)-5-fluoro-1-[2-(hydroxymethyl-1,3-oxathiolan-5-yl]cytosine) in human peripheral blood mononuclear cells (PBMCs). In this procedure, all nucleotides were extracted from PBMCs with aqueous methanol, isolated with high recovery using a novel ion-pairing solid phase extraction procedure, and then analyzed directly with LC/MS/MS with a 10-min analysis time. A calibration curve was generated representing (-)-FTC 5'-triphosphate ((-)-FTCTP) concentration over the range of 0.083 to 83 picomol/10(6) cells (approximately 0.08 to 80 picomoles on-column). Linear regression analysis with 1/x(2) weighting yielded a coefficient of determination (r(2)) of greater than 0.999. The back-calculated concentrations of all calibration standards had relative errors within the range of +5 to -3%. A preliminary assessment of intra-assay precision and accuracy, analyte stability, and LC/MS system stability indicated a robust method capable of being validated with a limit of quantitation estimated conservatively at 0.08 picomol/10(6) cells (approximately 0.08 picomoles on-column; signal-to-noise (S/N) = 5). The general method developed here should be adaptable to all purine- and pyrimidine-based nucleotide applications. This report provides a detailed discussion on the key HPLC, MS, and sample preparation procedures that hold the potential for even greater nucleotide sensitivity.     

Trapping and detection of ions generated in a high magnetic field electrospray ionization fourier transform ion cyclotron resonance mass spectrometer

The trapping and detection parameters employed with a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer that is interfaced to a high magnetic field electrospray ionization (ES11 source are presented. ES1 occurs at atmospheric pressure in a 1.5-T field, and FTICR detection occurs 25 cm away at 3.0 T in either one of two cells separated by a conductance limit and maintained at pressure differentials of 5 × 10⁵ and 2 × 10⁷ torr, respectively. The continuous electrospray ion current traversing the high- and low-pressure cells is 350 and 100 pA, respectively. Retarding grid studies at the high-pressure cell indicate electrospray ion kinetic energies are controllable from less than an electronvolt to more than 10 eV. These kinetic energies are a function of desolvating capillary-skimmer assembly distance and the skimmer potential. Efficient accumulation of injected ions is accomplished only when the trap-plate potential matches the ion kinetic energy. If this condition is satisfied, the trapped ion cell fills to the ion space charge limit within a few hundred milliseconds. It is concluded that even at the high pressures used, the primary trapping mechanism cannot be solely collision dependent because the rate of ion accumulation is independent of background pressure. However, optimized FTICR excitation conditions for peptides and proteins in the mass range from 10³ to more than 10⁶ kDa are found to vary strongly with pressure; this is attributed to large mass- and charge-dependent differences in ion-molecule collision frequency.     

Determination of endothelin-1 in rats using a high-performance liquid chromatography coupled to electrospray tandem mass spectrometry

A sensitive and specific liquid chromatography tandem mass spectrometry method with electrospray ionization for the determination of endothelin-1 in rat plasma and lung effluents has been developed and validated. Detection was achieved by an Applied Biosystems MDS Sciex API 2000 triple quadrupole mass spectrometer coupled to an Agilent 1100 LC system. The limit of detection and the limit of the quantification of ET-1 in matrix buffer was estimated at 40 pM and 1 nM, respectively. The precision and accuracy for both intra- and inter-day determination of the analyte ranged from 2.5% to 14.7% and from 104.2% to 113.3%, respectively. No significant relative matrix effect was observed. Stability of ET-1 established in a bench-top, autosampler, long-term storage stability as well as freeze/thaw cycles shown no significant degradation products in the samples. The results of the method validation indicated that this method is applicable for the determination of the ET-1 concentration in an effluent from the isolated lung preparation as well as in vivo in plasma samples to evaluate ET-1 as a potential biomarker of the progression of pulmonary endothelial dysfunction and pulmonary hypertension in rats induced by a monocrotaline injection.     

Hydration of gas-phase gramicidin S (M + 2H)2+ ions formed by electrospray: The transition from solution to gas-phase structure

The hydration of doubly protonated gas-phase ions of gramicidin S formed by electrospray ionization was investigated. Under “gentle” electrospray conditions, a near Gaussian distribution of (M + 2H + nH₂O)²⁺ ions with n up to 50 can be readily formed. These extensively hydrated gas-phase ions should have structures similar to those in solution. For intermediate extents of hydration, the “naked” or unsolvated ion is present in unusually high abundance. This is attributed to a competition between solvation of the charges by water vs intramolecular self-solvation via hydrogen bonding. In addition, “magic” numbers of attached water molecules are observed for n = 8, 11, and 14. These magic numbers are attributed to favorable arrangements of water molecules surrounding the charge and surface of the peptide in the gas phase. These results are indicative of a gentle stepwise transformation from the solution-phase structure of the ion to the preferred gas-phase structure as solvent evaporates from the hydrated ions.     

Comprehensive quality evaluation of Fructus Schisandrae using electrospray ionization ion trap multiple-stage tandem mass spectrometry coupled with chemical pattern recognition techniques

Electrospray ionization ion trap multiple-stage tandem mass spectrometry (ESI-MS(n)) was used to evaluate Fructus Schisandrae of similar species (Schisandra chinensis (Turcz.) Baill. fruits and Schisandra sphenanthera Rehd. et Wils. fruits) and different growth characteristics (color, shape, etc.). The application of chemical pattern recognition in the ESI-MS(n) data analysis was carried out by principal component analysis (PCA), hierarchical cluster analysis (HCA) and linear discriminant analysis (LDA). Then the antioxidant activity of different Fructus Schisandrae samples were determined by an LC-ESI-MS method and ferric reducing antioxidant power (FRAP) assay. Using the ESI-MS(n) method coupled with chemical pattern recognition analysis and correlated with the antioxidant activity evaluation, the two similar species were successfully distinguished, thus improving the therapeutic safety and effectiveness. The superior characteristics of Schisandra chinensis (Turcz.) Baill. fruits were obtained and made the selection and breeding of Chinese medicine materials more scientific. This study indicates that ESI-MS(n) is a valuable tool for the authentication of botanical origin and can also be useful for the quality control of Chinese medicinal herbs.     

Quantification of granisetron in human plasma by liquid chromatography coupled to electrospray tandem mass spectrometry

A simple, sensitive and rapid high-performance liquid chromatography/electrospray ionization tandem mass spectrometry method was developed and validated for the assay of granisetron in human plasma. Following liquid-liquid extraction, the analytes were separated using an isocratic mobile phase on a reversed-phase C18 column and analyzed by MS in the multiple reaction monitoring mode using the respective [M+H]+ ions, m/z 313/138 for granisetron and m/z 409/228 for the IS. The assay exhibited a linear dynamic range of 0.1-20 ng/mL for granisetron in human plasma. The lower limit of quantification was 100 pg/mL with a relative standard deviation of less than 5%. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. A run time of 2.0 min for each sample made it possible to analyze more than 400 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability or bioequivalence studies.     

Re-evaluation of glyphosate determination in water by liquid chromatography coupled to electrospray tandem mass spectrometry

An analytical method based on on-line solid-phase extraction-liquid chromatography coupled to electrospray tandem mass spectrometry (SPE-LC-ESI-MS/MS) for the determination of glyphosate and aminomethylphosphonic acid (AMPA) residues has been applied to the analysis of water samples within a Round Robin Study. The method had been previously validated in a variety of water samples and it fulfilled all the parameters of precision, accuracy, sensitivity and unequivocal confirmation. The results within the study that we participated were highly satisfactory in all cases with the only exception of glyphosate in groundwater samples, where surprisingly recoveries around 15% were obtained despite the use of isotope-labeled glyphosate as internal standard (I.S.). A slight modification has been introduced in the method, simply consisting of the acidification of sample with hydrochloric acid (HCl) to pH 1. Then, the sample is neutralized and immediately derivatized with 9-fluorenylmethylchloroformate (FMOC) before LC-MS/MS determination. Round Robin Study samples were reanalyzed using this approach, and the recoveries increased up to 98%. A possible explanation might be the slow kinetic interaction between glyphosate and some components of the matrix. These components might act as chelating agents, making glyphosate unavailable for derivatization and therefore for analysis. Several water samples collected at the Mediterranean area of Spain, and previously analyzed and being found to contain glyphosate, were also reanalyzed using this approach, obtaining higher concentrations (between 2 and 14 times) in most of cases.     

Fragmentation of ions in a low pressure linear ion trap

The efficiency of in-trap fragmentation in a low-pressure linear ion trap (LIT), using dipolar excitation, is dependent upon the choice of both the excitation q and the drive frequency of the quadrupole. In the work presented here, fragmentation efficiencies have been measured as a function of excitation q for drive frequencies of 816 kHz and 1.228 MHz. The experiments were carried out by fragmenting reserpine (609.23-->448.20 Th and 397.21-->365.19 Th transitions) and caffeine (195-->138 Th and 138-->110 Th transitions). The data showed that the onset of efficient fragmentation occurred at a lower Mathieu q for the LIT operated at 1.228 MHz when compared with the LIT operated at 816 kHz. A comparison of the fragmentation efficiency curves as a function of pseudo-potential well depth showed that the onset of fragmentation is independent of the drive frequency. In addition, a comparison of the fragmentation efficiency curves showed that all four of the precursor ions fragmented within a range of four V of pseudo-potential well depth. The choice of an appropriate excitation q can then be determined based upon a minimum pseudo-potential well depth, quadrupole field radius, drive frequency, and the mass of interest. Fragmentation efficiencies were also found to be significantly greater when using the higher drive frequency.     

Clonazepam quantification in human plasma by high-performance liquid chromatography coupled with electrospray tandem mass spectrometry in a bioequivalence study

A rapid, sensitive and specific method for quantifying clonazepam in human plasma using diazepam as the internal standard (IS) is described. The analyte and the IS were extracted from plasma by liquid-liquid extraction using a hexane/diethylether (20 : 80, v/v) solution. The extracts were analysed by high-performance liquid chromatography coupled with electrospray tandem mass spectrometry (HPLC-MS-MS). Chromatography was performed on a Jones Genesis C8 4 microm analytical column (100 x 2.1 mm i.d.). The method had a chromatographic run time of 3.0 min and a linear calibration curve over the range 0.5-50 ng/ml (r2 > 0.9965). The limit of quantification was 0.5 ng/ml. This HPLC/MS/MS procedure was used to assess the bioequivalence of two clonazepam 2 mg tablet formulations (clonazepam test formulation from Ranbaxy Laboratories Ltd and Rivotril from Roche Laboratórios Ltda as standard reference formulation).     

Determination of B-group vitamins in Turkish honey using ultra-performance liquid chromatography with electrospray ionization coupled to tandem mass spectrometry

A rapid and sensitive ultra-performance liquid chromatography–tandem mass spectrometry method with electrospray ionization (UPLC–ESI–MS/MS) for analysis of B-group vitamins in honey has been presented. Aim of this study is the characterization of different types of Turkish honeys according to B-group vitamins. Vitamins were determined in 17 different types of Turkish honey samples by UPLC–ESI–MS/MS. Heather honey samples were distinguished among the studied honeys with the richest vitamin content with 286.10?mg/kg, and it is followed by sunflower honey and thyme honey with the total vitamin contents of 206.01 and 163.27?mg/kg, respectively. The presence of vitamin B₁ (thiamine), vitamin B₂ (riboflavin), vitamin B₃ (nicotinamide, B₃N and nicotinic acid, B₃H), vitamin B₆ (pyridoxine), and vitamin B₉ (folic acid) was detected in all the honey samples analyzed. Moreover, vitamin B₅ (pantothenic acid) was observed in most of them. Vitamin B₁₂ (cyanocobalamin) and vitamin B₇ (biotine) were not detected in the studied honey samples. Turkish honey samples showed efficacious vitamin content for the consumers.     

Quantification of cyproheptadine in human plasma by high-performance liquid chromatography coupled to electrospray tandem mass spectrometry in a bioequivalence study

A rapid, sensitive and specific method to quantify cyproheptadine in human plasma using amitriptyline as the internal standard (IS) is described. The analyte and the IS were extracted from plasma by liquid‐liquid extraction using a diethyl‐ether/dichloromethane (70/30; v/v) solvent. After removing and drying the organic phase, the extracts were reconstituted with a fixed volume of acetonitrile/water (50/50 v/v) + 0.1% of acetic acid. The extracts were analyzed by high performance liquid chromatography coupled to electrospray tandem mass spectrometry (LC‐MS/MS). Chromatography was performed isocratically using an Alltech Prevail C18 5 µm analytical column, (150 mm x 4.6 mm I.D.). The method had a chromatographic run time of 4 min and a linear calibration curve ranging from 0.05 to 10 ng/mL (r2 > 0.99). The limit of quantification was 0.05 ng/mL. This HPLC/MS/MS procedure was used to assess the bioequivalence of cyproheptadine in two cyproheptadine + cobamamide (4 mg + 1 mg) tablet formulations (Cobactin® [cyproheptadine + cobamamide] test formulation supplied from Zambon Laboratórios Farmacêuticos Ltda. and Cobavital® from Solvay Farma (standard reference formulation)). A single 4 mg + 1 mg [cyproheptadine + cobamamide] dose of each formulation was administered to healthy volunteers. The study was conducted using an open, randomized, two‐period crossover design with a 1‐week washout interval. Since the 90% CI for Cmax and AUCs ratios were all within the 80‐125% bioequivalence limit proposed by the US Food and Drug Administration, it was concluded that the cyproheptadine test formulation (Cobactin®) is bioequivalent to the Cobavital® formulation for both the rate and the extent of absorption of cyproheptadine. Copyright © 2011 John Wiley & Sons, Ltd.     

Characterization and determination of chlorophacinone in plasma by ion chromatography coupled with ion trap electrospray ionization mass spectrometry

Plasmatic chlorophacinone is commonly measured with liquid chromatographic assay, which convenient but lacks sensitivity and selectivity and usually requires ion pair reagents to reduce the chromatographic tailed peak. In this paper, a novel method using eluent generator reagent‐free ion chromatography coupled with electrospray ionization ion trap mass spectrometric detection for the determination of chlorophacinone in plasma has been developed. After samples were extracted with 10% (v/v) methanol in acetonitrile and cleaned by solid‐phase extraction, chromatographic separation was performed on an IonPac^® AS11 analytical column (250 × 4.0 mm) using 40.0 mmol/L KOH containing 10% (v/v) methanol as organic modifier. Quantification was performed by negative electrospray ionization in multiple reaction monitoring mode. The transition m/z 373 → 201 was for the quantification ion; the transitions m/z 373 → 172 and m/z 373 → 145, as well as the isotope ions m/z 375 and m/z 203, were for the qualitative ions. All the method parameters were validated. It was confirmed that this method can be used in clinical diagnosis and forensic toxicology. Copyright © 2008 John Wiley & Sons, Ltd.     

Analysis of acrylamide in food by isotope-dilution liquid chromatography coupled with electrospray ionization tandem mass spectrometry

A confirmatory method for the determination of low levels of acrylamide in different food products is presented. The method entails extraction of acrylamide with water, precipitation of matrix constituents with acetonitrile, and two clean-up steps consecutively over Isolute Multimode and cation-exchange cartridges. The final extract is analyzed by liquid chromatography (LC) coupled to positive electrospray ionization tandem mass spectrometry employing [13C3]-acrylamide as internal standard. For the chromatographic step, a LC column based on a polymethacrylate gel is employed which shows good retention of acrylamide under isocratic flow conditions (k' = 1.2). Mass spectral acquisition is done by selected reaction monitoring, choosing the characteristic transitions m/z 72-->55, 72-->54 and 72-->27. In-house validation data for breakfast cereals and crackers show good precision of the method, with intra- and interassay variation below 10%. The limits of detection for crackers and breakfast cereals, respectively are estimated at 15 and 20 microg/kg, and recoveries of fortified samples ranged between 58 and 76%. Furthermore, the method is applicable to a number of different food products, including biscuits, crisp bread, wafers, confectionery cocoa liquor, and nuts. Finally, the good results obtained in several small-scale interlaboratory tests provided additional confidence in the performance of the method.     

Determination of stavudine in human serum by on-line solid-phase extraction coupled to high-performance liquid chromatography with electrospray ionization tandem mass spectrometry: application to a bioequivalence study

A method based on solid-phase extraction (SPE) coupled to high-performance liquid chromatography (HPLC) with positive ion electrospray ionization tandem mass spectrometry (ESI-MS/MS) detection was developed for the determination of stavudine in human serum, using didanosine as internal standard. The acquisition was performed in multiple reaction monitoring (MRM) mode. The method was linear over the studied range (10-2000 ng/mL), with r(2) > 0.99, and the run time was 4 min. The intra- and inter-assay precisions (%) were in the ranges 0.1-13.6 and 2.6-9.9, respectively, and the intra- and inter-assay accuracies were >92%. The absolute recoveries were approximately 100% (10 ng/mL), 98% (30 ng/mL), 105% (750 ng/mL) and 105% (1500 ng/mL). The limits of detection and quantitation were 4 and 10 ng/mL, respectively. The analytical method was applied to a bioequivalence study, in which 24 healthy adult volunteers (12 men) received single oral doses (40 mg) of reference and two test stavudine formulations, in an open, three-period, randomized, crossover protocol. The 90% confidence interval of the individual ratios (test formulation/reference formulation) for C(max) (peak serum concentration), AUC(0-10) and AUC(0-inf) (areas under the serum concentration vs. time curve from time zero to 10 h and to infinity, respectively), were in the range 80-125%, which supports the conclusion that the two test formulations are bioequivalent to the reference formulation with respect to the rate and extent of stavudine absorption.     

Atmospheric pressure infrared (10.6 µm) laser desorption electrospray ionization (IR‐LDESI) coupled to a LTQ Fourier transform ion cyclotron resonance mass spectrometer

We present the implementation of a CO₂ laser emitting infrared laser irradiation at 10.6 µm onto the versatile atmospheric pressure ionization platform. Infrared laser desorption electrospray ionization (IR‐LDESI) is demonstrated from liquid‐state samples at atmospheric pressure with and without ESI postionization. Multiply charged proteins ranging in molecular mass from 8.6 to 17 kDa were detected from liquid‐state samples without the addition of matrix. Copyright © 2009 John Wiley & Sons, Ltd.     

Determination of perchlorate in river by ion-pair hollow-fiber liquid-phase microextraction coupled with electrospray ionization tandem mass spectrometry

This paper describes the analysis of perchlorate (ClO₄⁻) in surface water samples by a rapid and reliable ion-pair hollow-fiber liquid-phase microextraction (HF-LPME) method coupled with flow-injection electrospray ionization tandem mass spectrometry (ESI-MS-MS) technique. The effects of the type and concentration of ion-pairing reagents, extraction time, temperature and pH value on the quantitative extraction of perchlorate by ion-pair HF-LPME were investigated and optimized. Di-n-hexyl ammonium acetate (DHAA) was employed to form an extractable ion-pair complex with aqueous perchlorate. The characteristic ions [ClO₄-ClO₄-DHA]⁻ at m/z 384.6 and 386.7 were observed in the ESI negative-ionization mode. The predominant product ions [ClO₄]⁻ at m/z 99 and 101 were used for quantitation and to maximize the detection selectivity and sensitivity. The limit of detection (LOD) was 0.5 μg/L. The reliability and precision of the standard addition method of ion-pair HF-LPME for the determination of trace levels of perchlorate in surface water were demonstrated.