Mass Spectrometric Conditions Research Articles

Formation, Oxidation, and Fate of the Breslow Intermediate in the N-Heterocyclic Carbene-Catalyzed Aerobic Oxidation of Aldehydes.

The reaction paths and intermediate structures related to the formation of the Breslow intermediate and its oxidation along the oxidative/oxygenative lanes have been studied from a mechanistic point of view, with the support of gas-phase and computational studies. The results confirm the occurrence of a single-electron transfer from the Breslow intermediate to the molecular oxygen with formation of a radical couple that recombines either as a peroxide anion 7' to afford the aldehyde-to-carboxylic acid product or as a hydroperoxy derivative 7″ that evolved into an electrophilic acyl azolium, opening to the aldehyde-to-ester conversion. Steric factors enter into determining the different reactivity. All of the intermediates of both catalytic paths have been observed and characterized under mass spectrometric conditions. In particular, for the imidazoline catalyst, the (+)ESI-MS/(MS) detection of the genuine Breslow intermediate was made possible in virtue of its limited reactivity. Mechanistic aspects of the N-heterocyclic carbenes catalyzed aerobic oxidation of aldehydes shares important similarities with that one of the recently revisited benzoin condensation.

Analysis of Translocation-Competent Secretory Proteins by HDX-MS.

Protein folding is an intricate and precise process in living cells. Most exported proteins evade cytoplasmic folding, become targeted to the membrane, and then trafficked into/across membranes. Their targeting and translocation-competent states are nonnatively folded. However, once they reach the appropriate cellular compartment, they can fold to their native states. The nonnative states of preproteins remain structurally poorly characterized since increased disorder, protein sizes, aggregation propensity, and the observation timescale are often limiting factors for typical structural approaches such as X-ray crystallography and NMR. Here, we present an alternative approach for the in vitro analysis of nonfolded translocation-competent protein states and their comparison with their native states. We make use of hydrogen/deuterium exchange coupled with mass spectrometry (HDX-MS), a method based on differentiated isotope exchange rates in structured vs unstructured protein states/regions, and highly dynamic vs more rigid regions. We present a complete structural characterization pipeline, starting from the preparation of the polypeptides to data analysis and interpretation. Proteolysis and mass spectrometric conditions for the analysis of the labeled proteins are discussed, followed by the analysis and interpretation of HDX-MS data. We highlight the suitability of HDX-MS for identifying short structured regions within otherwise highly flexible protein states, as illustrated by an exported protein example, experimentally tested in our lab. Finally, we discuss statistical analysis in comparative HDX-MS. The protocol is applicable to any protein and protein size, exhibiting slow or fast loss of translocation competence. It could be easily adapted to more complex assemblies, such as the interaction of chaperones with nonnative protein states.

Oxidative Ionization Under Certain Negative-Ion Mass Spectrometric Conditions.

1,4-Hydroquinone and several other phenolic compounds generate (M - 2) -• radical-anions, rather than deprotonated molecules, under certain negative-ion mass spectrometric conditions. In fact, spectra generated under helium-plasma ionization (HePI) conditions from 1,4-hydroquinone and 1,4-benzoquinone (by electron capture) were practically indistinguishable. Because this process involves a net loss of H• and H+, it can be termed oxidative ionization. The superoxide radical-anion (O2-•), known to be present in many atmospheric-pressure plasma ion sources operated in the negative mode, plays a critical role in the oxidative ionization process. The presence of a small peak at m/z 142 in the spectrum of 1,4-hydroquinone, but not in that of 1,4-benzoquinone, indicated that the initial step in the oxidative ionization process is the formation of an O2-• adduct. On the other hand, under bona fide electrospray ionization (ESI) conditions, 1,4-hydroquinone generates predominantly an (M - 1) - ion. It is known that at sufficiently high capillary voltages, corona discharges begin to occur even in an ESI source. At lower ESI capillary voltages, deprotonation predominates; as the capillary voltage is raised, the abundance of O2-• present in the plasma increases, and the source in turn increasingly behaves as a composite ESI/APCI source. While maintaining post-ionization ion activation to a minimum (to prevent fragmentation), and monitoring the relative intensities of the m/z 109 (due to deprotonation) and 108 (oxidative ionization) peaks recorded from 1,4-hydroquinone, a semiquantitative estimation of the APCI contribution to the overall ion-generation process can be obtained. Graphical Abstract ᅟ.

Competitive homolytic and heterolytic decomposition pathways of gas-phase negative ions generated from aminobenzoate esters.

An alkyl-radical loss and an alkene loss are two competitive fragmentation pathways that deprotonated aminobenzoate esters undergo upon activation under mass spectrometric conditions. For the meta and para isomers, the alkyl-radical loss by a homolytic cleavage of the alkyl-oxygen bond of the ester moiety is the predominant fragmentation pathway, while the contribution from the alkene elimination by a heterolytic pathway is less significant. In contrast, owing to a pronounced charge-mediated ortho effect, the alkene loss becomes the predominant pathway for the ortho isomers of ethyl and higher esters. Results from isotope-labeled compounds confirmed that the alkene loss proceeds by a specific γ-hydrogen transfer mechanism that resembles the McLafferty rearrangement for radical cations. Even for the para compounds, if the alkoxide moiety bears structural motifs required for the elimination of a more stable alkene molecule, the heterolytic pathway becomes the predominant pathway. For example, in the spectrum of deprotonated 2-phenylethyl 4-aminobenzoate, m/z 136 peak is the base peak because the alkene eliminated is styrene. Owing to the fact that all deprotonated aminobenzoate esters, irrespective of the size of the alkoxy group, upon activation fragment to form an m/z 135 ion, aminobenzoate esters in mixtures can be quantified by precursor ion discovery mass spectrometric experiments.

Competitive Deprotonation and Superoxide [O₂⁻•)] Radical-Anion Adduct Formation Reactions of Carboxamides under Negative-Ion Atmospheric-Pressure Helium-Plasma Ionization (HePI) Conditions.

Carboxamides bearing an N-H functionality are known to undergo deprotonation under negative-ion-generating mass spectrometric conditions. Herein, we report that N-H bearing carboxamides with acidities lower than that of the hydroperoxyl radical (HO-O(•)) preferentially form superoxide radical-anion (O2(-•)) adducts, rather than deprotonate, when they are exposed to the glow discharge of a helium-plasma ionization source. For example, the spectra of N-alkylacetamides show peaks for superoxide radical-anion (O2(-•)) adducts. Conversely, more acidic amides, such as N-alkyltrifluoroacetamides, preferentially undergo deprotonation under similar experimental conditions. Upon collisional activation, the O2(-•) adducts of N-alkylacetamides either lose the neutral amide or the hydroperoxyl radical (HO-O(•)) to generate the superoxide radical-anion (m/z 32) or the deprotonated amide [m/z (M - H)(-)], respectively. For somewhat acidic carboxamides, the association between the two entities is weak. Thus, upon mildest collisional activation, the adduct dissociates to eject the superoxide anion. Superoxide-adduct formation results are useful for structure determination purposes because carboxamides devoid of a N-H functionality undergo neither deprotonation nor adduct formation under HePI conditions.

Novel approach to fast determination of cholesterol oxidation products in Cypriot foodstuffs using ultra-performance liquid chromatography-tandem mass spectrometry.

This paper reports the development and validation of a new method based on ultra-performance LC coupled to MS/MS for the simultaneous determination of four cholesterol oxidation products (COPs) in foodstuffs in only 4.1 min. The COPs were detected by ESI in positive-ion mode with multiple reaction monitoring, and the mass spectrometric conditions were optimized in order to increase sensitivity. The developed method was validated in terms of linearity, precision, LODs, and LOQs. Recoveries of the extraction process ranged from 86 to 98.5% when the samples were fortified at 100, 500, and 1500 ng/mL. The applicability of the method was confirmed by analyzing different food samples. Considering the paucity of data regarding the content of COPs in Cypriot foods, particular attention was devoted, for the first time, to the determination of the profile of the main COPs in widely consumed, traditional Cypriot foodstuffs (halloumi cheese, hiromeri, snails, etc.).

Persistent organochlorine pesticides in internal organs of coypu, Myocastor coypus

A highly selective and sensitive method based on gas chromatography-tandem mass spectrometry (GC-MS/MS) to identify and quantify persistent organochlorine pesticides, (18 compounds including primary compounds and metabolites), in animal internal organs (kidneys, liver, and brain) has been developed. Tandem mass spectrometric conditions were individually optimized for each target compound in Multiple Reaction Monitoring (MRM) mode to obtain maximum sensitivity. Prior to instrumental analysis, a sample preparation method based on matrix solid phase dispersion (MSPD) followed by acidic digestion with sulfuric acid to reduce matrix co-extractives was employed. Analyses of real samples were carried out on coypus (Myocastor coypus) from the autumn slaughter of 19 animals. In the analyzed samples, three of the target compounds, namely DDE-pp′ (DDT metabolite), HCB and lindane, were detected. Their concentration levels fell in the ranges of 0.003–0.007, 0.003–0.025, and 0.003–0.021 mg kg−1 (0.005, 0.010, and 0.010 mg kg−1 on average) in the case of DDE-pp′, HCB and lindane, respectively. Although low quantities of organochlorine pesticides do not pose an immediate danger to consumers' health, they should be of public health concern considering long-term, low-dose exposure.

Functional assessment of antibody oxidation by native mass spectrometry

Oxidation of methionine (Met) residues is one of several chemical degradation pathways for recombinant IgG1 antibodies. Studies using several methodologies have indicated that Met oxidation in the constant IgG1 domains affects in vitro interaction with human neonatal Fc (huFcRn) receptor, which is important for antibody half-life. Here, a completely new approach to investigating the effect of oxidative stress conditions has been applied. Quantitative ultra-performance liquid chromatography mass spectrometry (MS) peptide mapping, classical surface plasmon resonance and the recently developed FcRn column chromatography were combined with the new fast-growing approach of native MS as a near native state protein complex analysis in solution. Optimized mass spectrometric voltage and pressure conditions were applied to stabilize antibody/huFcRn receptor complexes in the gas phase for subsequent native MS experiments with oxidized IgG1 material. This approach demonstrated a linear correlation between quantitative native MS and IgG-FcRn functional analysis.In our study, oxidation of the heavy chain Met-265 resulted in a stepwise reduction of mAb3/huFcRn receptor complex formation. Remarkably, a quantitative effect of the heavy chain Met-265 oxidation on relative binding capacity was only detected for doubly oxidized IgG1, whereas IgG1 with only one oxidized heavy chain Met-265 was not found to significantly affect IgG1 binding to huFcRn. Thus, mono-oxidized IgG1 heavy chain Met-265 most likely does not represent a critical quality attribute for pharmacokinetics.

Development of a two-step indirect method for modeling Ecom50.

A novel approach is developed for modeling situations in which the modeled property is an algebraically transformed version of the original experimental data. In many cases such a transformation results in a data set with a significantly smaller data range. Here we explore the effects of range-of-data on modeling statistics. We illustrate a twostep method using data on the mass spectrometry collision energy (CE) that is required to decompose 50% of precursor ions to fragments (CE50). Earlier we showed that a nonlinear center-of-mass transformation, yielding Ecom50, produces values less dependent on the specific mass spectrometric experimental conditions. For this data set the Ecom50 range is 13.5% of the CE50 range. We propose a two-step modeling method. First, the original experimental data, CE50, (larger range-of-data) is modeled by a standard modeling method (PLS). Second, the calculated dependent variable resulting from the modeling is algebraically transformed (not modeled) according to the center-of-mass transformation, providing the generally more useful data, Ecom50. As shown here, use of this two-step method for predicting Ecom50 (from previously published data) produces a standard error 21% smaller and correspondingly reduces the confidence interval for prediction. Some specific implications for prediction are given for a published data set. This work is part of the ongoing development of a system of models to assist in the development of human metabolites.

Determination of 14 aniline derivatives in water by liquid chromatography-tandem mass spectrometry

A new and fast method was developed for the simultaneous determination of 14 aniline derivatives ( ADs) in water by direct injection-liquid chromatography-tandem mass spectrometry (LC-MS/MS) through optimizing chromatographic and mass spectrometric conditions. The water sample was filtered through a 0.45 µm polyether sulfone (PES) microfiltration membrane. The separation was performed on a Shim-pack FC-ODS column (75 mm x 4.6 mm, 3 µm) with methanol-0.1% (v/v) formic acid aqueous solution (35:65, v/v) as mobile phases in gradient elution mode. The flow rate was 0.3 mL/min, and the column temperature was 35 °C. The analytes were detected by LC-MS/MS in multiple reaction monitoring mode. Under the optimized conditions, the analysis of the 14 aniline derivatives was completed within 12 min and the calibration curves showed good linearity with correlation coefficients not less than 0.999. The detection limits of the 14 aniline derivatives ranged from 0.03 µg/L to 4. 19 µg/L. The relative standard deviations of the 14 aniline derivatives in the spiked surface water at three levels (0. 5, 5.0, 20.0 µg/L) were 0.4%-9.4% (n = 6). The proposed method has the advantages of good anti-interference ability, rapidness and high sensitivity. It was successfully applied to the analysis of real samples, and the recoveries of the 14 aniline derivatives in the spiked real samples were 68.0%-130%.

Multi-targeted interference-free determination of ten β-blockers in human urine and plasma samples by alternating trilinear decomposition algorithm-assisted liquid chromatography–mass spectrometry in full scan mode: Comparison with multiple reaction monitoring

β-blockers are the first-line therapeutic agents for treating cardiovascular diseases and also a class of prohibited substances in athletic competitions. In this work, a smart strategy that combines three-way liquid chromatography–mass spectrometry (LC–MS) data with second-order calibration method based on alternating trilinear decomposition (ATLD) algorithm was developed for simultaneous determination of ten β-blockers in human urine and plasma samples. This flexible strategy proved to be a useful tool to solve the problems of overlapped peaks and uncalibrated interferences encountered in quantitative LC–MS, and made the multi-targeted interference-free qualitative and quantitative analysis of β-blockers in complex matrices possible. The limits of detection were in the range of 2.0×10−5–6.2×10−3μgmL−1, and the average recoveries were between 90 and 110% with standard deviations and average relative prediction errors less than 10%, indicating that the strategy could provide satisfactory prediction results for ten β-blockers in human urine and plasma samples only using liquid chromatography hyphenated single–quadrupole mass spectrometer in full scan mode. To further confirm the feasibility and reliability of the proposed method, the same batch samples were analyzed by multiple reaction monitoring (MRM) method. T-test demonstrated that there are no significant differences between the prediction results of the two methods. Considering the advantages of fast, low-cost, high sensitivity, and no need of complicated chromatographic and tandem mass spectrometric conditions optimization, the proposed strategy is expected to be extended as an attractive alternative method to quantify analyte(s) of interest in complex systems such as cells, biological fluids, food, environment, pharmaceuticals and other complex samples.

Validation of a multiclass multiresidue method and monitoring results for 210 pesticides in fruits and vegetables by gas chromatography-triple quadrupole mass spectrometry

A rapid, sensitive, accurate and reliable multiresidue method for the identification and quantification of 210 relevant pesticides in four representative fruit and vegetable commodities (tomato, potato, spring onion and orange) has been developed and validated by gas chromatography in tandem with triple quadrupole mass spectrometry. The method has been fully validated and applied to 292 samples from different countries. Prior to instrumental analysis, an extraction procedure based on a sample extraction of multiclass analytes, using the ethyl acetate method was employed. Mass spectrometric conditions were individually optimized for each compound in the selected reaction monitoring (SRM) mode to achieve maximum sensitivity. The pesticides were separated in less than 25 min. This was followed by an exhaustive control of the retention times. The Retention Time Locking Method was applied, working at a constant pressure throughout the analysis. System maintenance was reduced by using a purged capillary flow device that provided backflush capabilities by reversing column flow immediately after elution of the last compound of interest. Istotopically labelled internal standards were employed to improve the quality of the analytical results.

P18: Rapid determination of THC and THC-COOH in Oral Fluid by using LC/MS/MS technique in a “dilute & shoot” approach

Oral fluid (OF) is a new biological matrix for clinical and forensic drug testing, offering easy and non-invasive sample collection mainly accomplished with commercial disposable devices. Due to a stronger correlation than urine with blood concentrations, screening based on OF is greatly gaining value in DUID (Driving under the influence of drugs) programs worldwide (Strano-Rossi et al., 2012). Furthermore, cannabinoids are usually the most prevalent analytes in illicit drug testing and for this reason application of OF testing requires sufficient reliable data to support sensitive and specific cannabinoid detection for forensic purposes (Lee et al., 2013). Cannabinoids analysis has been historically performed using GC-MS technology, either with single quadrupole or triple quadrupole systems. However, in the last decade the role of LC-MS/MS in modern forensic toxicology laboratories has gained more relevance because of less extensive sample preparation, reliable results and versatility. The present work describes a simple fully validated method for the determination of THC and THC-COOH in oral fluid by using liquid chromatography coupled to triple quad mass detection (LC-ESI-MS/MS). Chromatographic separations were carried out with a ZORBAX Eclipse Plus C18 RRHT (2,1 mm x 100 mm x 1,8 μm) column in less than 8 minutes. Chromatography and mass spectrometric instrumental conditions were optimized in order to keep minimal sample preparation. Oral fluid samples were centrifuged and diluted prior to LC-MS analysis. The lower limit of quantifications (LLOQ), defined as the lowest concentration with an intraday and inter-day accuracy RSD < 20 %, was 0.1 ng/mL in OF (0.0625 pg on column) for THC and 0.25 ng/mL in OF (0.156 pg on column) for THC-COOH. The limit of detection (LOD) defined as signal to noise ratio equal to 3 was 0.01 ng/mL in OF for THC (0.00625 pg on column) and 0.1 ng/mL (0.0625 pg on column) in OF for THC-COOH. Results are presented in terms of selectivity, matrix effect, linearity and reproducibility.

Circumambulatory movement of negative charge ("ring walk") during gas-phase dissociation of 2,3,4-trimethoxybenzoate anion.

A dramatic "ortho effect" was observed during gas-phase dissociation of ortho-, meta-, and para-methoxybenzoate anions. Upon activation under mass spectrometric collisional activation conditions, anions generated from all three isomers undergo a CO2 loss. Of the m/z 107 ions generated in this way, only the 1-dehydro-2-methoxybenzene anion from the ortho isomer underwent an exclusive formaldehyde loss. A peak for a formaldehyde loss in the spectra of 2,4-, 2,5-, and 2,6-dimethoxybenzoates and the absence of an analogous peak from 3,4- and 3,5-dimethoxy derivatives confirmed that this is a diagnostically useful ortho-isomer-specific phenomenon. Moreover, the spectrum from 2,3-dimethoxybenzoic acid showed peaks for two consecutive formaldehyde losses. The 1-dehydro-2,3,4-trimethoxybenzene anion (m/z 167) generated from 2,3,4-trimethoxybenzoate in this way endures three consecutive eliminations of formaldehyde units. For this, the negative charge, initially located on position 1, circumambulates to position 2, then to position 3, and finally to position 4 to form the final phenyl anion. The proposed stepwise fragmentation pathway, which resembles the well-known E1cB-elimination mechanism, is supported by tandem mass spectrometric observations made with 2-[(13)C(2)H3]methoxy-3-[(13)C]methoxy-4-methoxybenzoic acid, and ab initio calculations. In addition, the spectra of ions such as 1-dehydro-3,4-dimethoxybenzene anion show peaks for consecutive methyl radical losses, a feature that establishes the 1,2-relationship between the two methoxy groups.

Review of the validated HPLC and LC‐MS/MS methods for determination of drugs used in clinical practice for Alzheimer's disease

Alzheimer's disease (AD) is a neurological disorder and is the most frequent type of dementia among elderly people. Donepezil, rivastigmine, galantamine, tacrine and memantine are the US Food and Drug Administration approved oral drugs used in the treatment of AD. Quantitation of these drugs in various biological matrices and monitoring them in long-term treatment is essential to titer the dose of these drugs and ensure patient compliance. This review provides a comprehensive account of various HPLC and LC-MS/MS assays, which have been successfully employed to measure the drug levels in various biological matrices arising from preclinical and clinical studies. In addition, this review collates various considerations such as internal standard selection, extraction schemes, matrix effect, selectivity evaluation and optimization of mass spectrometric conditions to enable the development of sound bioanalytical methods for quantitation of Alzheimer's drugs. Overall LC-MS/MS methods have proven to be the choice of bioanalytical method for the quantification of Alzheimer's drugs in both preclinical and clinical studies. In conclusion, important features of LC-MS/MS methodology for Alzheimer's drugs include shortened analysis time, increased throughput, selectivity and lower cost of analysis.

Validated method to measure yakuchinone A in plasma by LC-MS/MS and its application to a pharmacokinetic study in rats

BackgroundYakuchinone A has a plethora of beneficial biological effects. However, the pharmacokinetic (PK) data of yakuchinone A still remain unknown so far. Furthermore, the quantification of yakuchinone A in biological samples has not been reported in the literature. Therefore, in the present study we aimed to develop a new method for the fast, efficient and accurate assessment of yakuchinone A concentration in plasma, as a means for facilitating the PK evaluation of yakuchinone A.ResultsA liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) method was developed and validated for the determination of yakuchinone A in rat plasma. Mass spectrometric and chromatographic conditions were optimized. Plasma samples were pretreated by protein precipitation with methanol. LC separation was performed on a Phenomenex Luna C18 column with gradient elution using a mobile phase consisting of methanol–water containing 0.5 mM formic acid (HCOOH) at a flow rate of 0.28 mL/min. ESI-MS spectra were acquired in positive ion multiple reaction monitoring mode (MRM). The precursor-to-product ion pairs used for MRM of yakuchinone A and yakuchinone B were m/z 313.1 → 137.0 and 311.2 → 117.1, respectively. Low concentration of HCOOH reduced the ion suppression caused by matrix components and clearly improved the analytical sensitivity. Yakuchinone A showed good linearity over a wide concentration range (r > 0.99). The accuracy, precision, stability and linearity were found to be within the acceptable criteria. This new method was successfully applied to analyze the rat plasma concentration of parent yakuchinone A after a single oral administration of SuoQuan capsules. Low systemic exposure to parent yakuchinone A was observed.ConclusionThe proposed method is sensitive and reliable. It is hoped that this new method will prove useful for the future PK studies.

Устранение матричных неспектральных помех при элементном анализе биологических жидкостей на квадрупольном масс-спектрометре с индуктивно связанной плазмой

The comparison of two most frequently used sample preparation techniques of biological fluids before mass-spectrometric determination of Mn, Co, Cu, Zn, As, Se, Cd and Pb – simple (direct) dilution and acid mineralization – was carried out using quadrupole mass-spectrometer. The significant underestimation of the results in comparison with diluted samples for the elements with relatively high ionization potentials was found while analyzing digested biofluids. The key role of acid effect was proven to be the reason of such discrepancy. Moreover, the contributions of saline and organic matrix non-spectral interferences in both diluted and mineralized samples – to the underestimation of the obtained results were evaluated. It was shown that the selection of the appropriate internal standard based on matching of the standard’s and analyte’s ionization potentials not the masses can eliminate the described interferences without matrix-matched calibration. Furthermore, the working mass-spectrometer conditions that allow to use any single internal standard (irrespective of it’s mass and/or ionization potential) were found. Based on the experimental data the approach of element determination in biological fluids with the use of quadrupole ICP-MS was suggested. It provides the possibility of simultaneous determination of various elements without changing the work mass-spectrometer conditions. The satisfactory agreement between the found and certified concentration values for all the elements analyzed in the diluted and mineralized samples of whole blood and urine reference materials proved the applicability of the approach. Keywords: biological fluids, elemental analysis, inductively coupled mass-spectrometry, matrix non-spectral interferences, internal standards (Russian) DOI: http://dx.doi.org/10.15826/analitika.2014.18.2.003 K.B. Osipov 1 , I. F. Seregina 1 , M. A. Bol`shov 1,2 1 Lomonosov Moscow State University, Moscow, Russian Federation 2 Institute for Spectroscopy RAS , Troitsk, Moscow, Russian Federation

Ultra high performance liquid chromatography–tandem mass spectrometry method for the determination of soluble milk glycans in rat serum

The main objective of the present work was to develop and validate a multicompound method to measure soluble milk glycans (SMGs) in biological fluids such as serum. An ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method for the identification and quantification of the following SMGs and their precursors 2'-fucosyllactose, 3'-sialyllactose, 6'-sialyllactose, lacto-N-neotetraose, N-acetylneuraminic acid, fucose, lactose and glucose in rat serum samples was set up. These analytes were separated in an Acquity UPLC BEH Amide column using acetonitrile-water gradient with ammonia as additive, in a 10 min run, and were detected and quantified using a triple quadrupole (QqQ) mass spectrometer. The mass spectrometric conditions in negative electrospray ionization mode (ESI-) were individually optimized for each analyte to obtain maximum sensitivity in the Selected Reaction Monitoring (SRM) mode. Selection of two specific fragmentation reactions for each compound allowed simultaneous quantification and identification in one run, ensuring a high specificity of the method. The limits of detection (LODs) ranged from 5 to 70 ng mL(-1) and the limits of quantification (LOQs) from 20 to 200 ng mL(-1). The inter- and intra-day variability was lower than 15% and the recoveries ranged from 85% to 115%. A biological application of the method was also described, specifically the time-course of SMGs in rat serum after an oral challenge.

Analysis of nine nitrosamines in water by combining automated solid-phase extraction with high-performance liquid chromatography-atmospheric pressure chemical ionisation tandem mass spectrometry

In this study, a highly sensitive analysis method was developed for measuring the ng L−1 levels of nine nitrosamines in various water samples. Comparison of recoveries calculated by using four different cartridge types of solid-phase extraction (SPE) indicated that the UCT activated carbon cartridge combined with the HLB cartridge showed the highest recoveries for all target nitrosamines with over 70% recoveries except NDPhA (∼ 50%). To optimise the mass spectrometric conditions, the sensitivity of nitrosamines applying atmospheric pressure chemical ionisation (APCI) and electrospray ionisation (ESI) was tested, and the APCI mode showed 2–20 times higher sensitivity. The method developed in this study was evaluated with certified reference material (CRM), and the result showed good accuracies of 83.3–98.4%. Using the optimised method, nine nitrosamines were analysed in the wastewater of the sewage treatment plants and rivers. The influents showed the highest total concentrations (3061–28,268 ng L−1), followed by the effluents (32.3–339 ng L−1) and river water (106–300 ng L−1).

Pharmacokinetics study of hemin in rats by applying 58Fe-extrinsically labeling techniques in combination with ICP-MS method

Iron is a challenging element due to its high background in various matrixes including blood, tissues even in the air and it is urgent to develop a method for the accurate determination of iron in bio-samples. After optimization of mass spectrometric conditions using collision cell technology and compensating for interference using a mathematical correction equation, an inductively coupled plasma mass spectrometry (ICP-MS) method for the quantitative determination of 58Fe originating from hemin extrinsically labeled avoiding endogenous interference was developed. After a single step of dilution, analysis of each sample was completed within 1.5min. The assay was linear in the concentration range from 0.005 to 1.0μg/ml. The precisions and accuracies determined within three consecutive days were in acceptable limits and there was no significant matrix effect. The optimized method was successfully applied to a pharmacokinetic study of 58Fe originating from hemin extrinsically labeled and iron absorption measured in rats was 1.07%. Those indicated that extrinsically label techniques in combination with ICP-MS will become a new tool for the analysis of iron preparations and other endogenous substances.