On-line solid-phase extraction-short-column liquid chromatography combined with various tandem mass spectrometric scanning strategies for the rapid study of transformation of pesticides in surface water.

The applicability of solid-phase extraction-short-column liquid chromatography using two short columns (i.e., 10 and 20 mm long) coupled on-line with tandem mass spectrometric detection is demonstrated for the rapid degradation study of pesticides and their transformation products in water at the low-microgram/l level. Photolysis was used as a means to transform the parent compounds into their degradation products and the experiments were carried out at environmentally relevant concentrations. The use of on-line sample enrichment/separation in photodegradation studies allows the rapid analysis of aqueous samples directly after irradiation without further transformation of the compounds of interest. The versatility of MS allows various selective screening strategies to be employed, i.e., full-scan mode, neutral loss, precursor-ion and product-ion scan modes. This allows the identification of possible degradation products and the calculation of the rates of disappearance of the parent compound and appearance of transformation products.     

Analytical techniques in the study of highly-nitrated nitrocellulose

This work presents an updated overview of the analytical techniques used to study highly-nitrated nitrocellulose, which is used in explosives and is of forensic interest. Most articles published in the past decade were designed:(1) to investigate polymeric parameters of nitrocellulose (e.g., molar mass distribution, viscosity and specific refractive index) by size-exclusion chromatography;(2) to determine the morphological and thermal characteristics of nitrocellulose using thermal and spectroscopic techniques; and,(3) to study the thermal, biological and mechanical degradation of nitrocellulose by thermal, spectroscopic, and mass spectrometric (MS) techniques, alone or coupled to gas chromatography.However, the few papers that focused on the determination of nitrocellulose used in explosives employed analytical techniques [e.g., vibrational techniques (infrared and Raman spectroscopy), MS and ion-mobility spectrometry (IMS) and liquid chromatography (LC) (high-performance LC and ion chromatography)]. Most of the information reported by these techniques has been qualitative. Only quantitative determination of nitrocellulose or its nitrogen content has been performed by measuring the nitrite and/or nitrate ions released from its basic hydrolysis.     

Analyses of macrolide antibiotic residues in eggs, raw milk, and honey using both ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry and high-performance liquid chromatography/tandem mass spectrometry

Two liquid chromatography mass spectrometric techniques, i.e. ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry (UPLC/Q-Tof MS) and high-performance liquid chromatography/tandem mass spectrometry (LC/MS/MS), were used for quantification, confirmation or identification of six macrolide antibiotic residues and/or their degradation products in eggs, raw milk, and/or honey. Macrolides were extracted from food samples by acetonitrile or phosphate buffer (0.1 M, pH 8.0), and sample extracts were further cleaned up using solid-phase extraction cartridges. UPLC/Q-Tof data were acquired in Tof MS full scan mode that allowed both quantification and confirmation of macrolides, and identification of their degradation products. LC/MS/MS data acquisition was achieved using multiple reaction monitoring (MRM), i.e. two transitions, to provide a high degree of sensitivity and repeatability. Matrix-matched standard calibration curves with the use of roxithromycin as an internal standard were utilized to achieve the best accuracy of the method. Both techniques demonstrated good quantitative performance in terms of accuracy and repeatability. LC/MS/MS had advantages over UPLC/Q-Tof MS in that its limits of detection were lower and repeatability was somewhat better. UPLC/Q-Tof provided ultimate and unequivocal confirmation of positive findings, and allowed degradation product identification based on accurate mass. The combination of the two techniques can be very beneficial or complementary in routine analysis of macrolide antibiotic residues and their degradation products in food matrices to ensure the safety of food supply.     

An integrated method for degradation products detection and characterization using hybrid ion trap/time-of-flight mass spectrometry and data processing techniques: Application to study of the degradation products of danofloxacin under stressed conditions

A new strategy using hybrid ion trap/time-of-flight mass spectrometry coupled with high-performance liquid chromatography and post-acquisition data mining techniques was developed and applied to the detection and characterization of degradation products of danofloxacin. The degradation products formed under different forced conditions were separated using an ODS-C18 column with gradient elution. Accurate full-scan MS data were acquired in the first run and processed with the combination of extracted ion chromatograms and LC-UV chromatograms. These processes were able to find accurate molecular masses of possible degradation products. Then, the accurate MS/MS data acquired through data-dependent analysis mode in another run facilitated the structural elucidations of degradation products. As a result, a total of 11 degradation products of danofloxacin were detected and characterized using the developed method. Overall, this analytical strategy enables the acquisition of accurate-mass LC/MS data, search of a variety of degradation products through the post-acquisition processes, and effective structural characterization based on elemental compositions of degradation product molecules and their product ions. The ability to measure degradation products via tandem mass spectrometry coupled with accurate mass measurement, all in only two experimental runs, is one of the most attractive features of this methodology. The results demonstrate that use of the LC/MS-IT-TOF approach appears to be rapid, efficient and reliable in structural characterization of drug degradation products.     

Novel liquid-chromatography columns for proteomics research

The enormous interest in proteomics research in recent years has inspired many developments in peptide chromatography. Different strategies have been developed to cope with the vast complexity of proteomics samples, trying to provide sufficient degree of separation to be able to exploit fully the potential of protein identification by mass spectrometry (MS). As reversed-phase liquid chromatography (RPLC) coupled to MS is still the method of choice for the analysis of protein digests, many efforts focus on the development of high-efficiency RP methods (e.g., monolithic columns and ultra-high-performance LC). This can also increase the speed and the sensitivity of the analysis of protein digests.As RPLC-MS alone is unlikely to provide sufficient resolution to unravel the composition of highly complex samples comprehensively, multidimensional methods will remain essential in proteome research. In this area, hydrophilic interaction chromatography (HILIC) seems to be a promising alternative to the traditional strong cation-exchange-based methods. Also, HILIC has found application in the analysis of post-translational modifications (e.g., phosphorylation and glycosylation).This review describes recent developments in LC methods for proteomics research, focusing on advances in column technology and the application of novel column materials. Illustrative examples show the possibilities of the new columns in proteomics research.     

Liquid chromatography-tandem mass spectrometric analysis and regulatory issues of polar pesticides in natural and treated waters

Pesticides are among the most detected contaminants in the aquatic environment. This is mainly due to their use in agriculture and their physico-chemical properties that enable transportation and a persistent or pseudo-persistent existence in the water media. Several directives and guidelines set maximum levels of pesticides in water in order to protect the human and environmental health. A brief discussion of the existing directives and guidelines concerning pesticides in water is presented, e.g., the new regulatory framework for the Registration, Evaluation and Authorisation of Chemicals (REACH), and the Directive 91/414/EEC concerning the placing of plant protection products on the market. Up-to-date analytical tools to support the REACH program are of prime importance to ensure its complete implementation. Since liquid chromatography (LC) coupled to mass spectrometry (MS) is considered the most appropriate technique for determination of most modern pesticides in environmental waters, the most recent developments and applications in this field are discussed in detail in this review.     

LC–MS/MS and NMR characterization of forced degradation products of mirabegron

A rapid, precise, and reliable liquid chromatography tandem mass spectrometry (LC–MS/MS) method has been developed for the characterization of stressed degradation products of mirabegron. It is used in the treatment of overactive bladder and administered to treat urinary symptoms such as urgency or frequency and incontinence. It also works by relaxing the muscles around bladder.

Mirabegron was subjected to hydrolysis (acidic, alkaline, and neutral) and peroxidation, as per ICH-specified conditions. The drug showed degradation under stress conditions. However, it was stable to neutral conditions. A total of seven degradation products were observed and the chromatographic separation of the drug and its degradation products was achieved on X-TerraRP-8 (250 mm × 4.6 mm, i.d., 5 µm) column using 0.01 M ammonium acetate as mobile phase-A and 60:40 ratio of acetonitrile (ACN):water as mobile phase-B. The degradation products were characterized by LC–MS/MS and its fragmentation pathways were proposed. Probable possible structures were drawn based on parent and daughter molecular ions. One peroxide degradant impurity was isolated using preparative LC and characterized using liquid chromatography–mass spectrometry and NMR data.     

Herbal medicine analysis by liquid chromatography/time-of-flight mass spectrometry

The fact that the effects of herbal medicines (HMs) are brought about by their chemical constituents has created a critical demand for powerful analytical tools performing the chemical analysis to assure their efficacy, safety and quality. Liquid chromatography coupled to mass spectrometry (LC–MS) is an excellent technique to analyze multi-components in complex herbal matrices. Due to its inherent characteristics of accurate mass measurements and high resolution, time-of-flight (TOF) MS is well-suited to this field, especially for qualitative applications. The purpose of this article is to provide an overview on the potential of TOF, including the hybrid quadrupole- and ion trap-TOF (QTOF and IT-TOF), hyphenated to LC for chemical analysis in HMs or HM-treated biological samples. The peculiarities of LC–(Q/IT)TOF-MS for the analysis of HMs are discussed first, including applied stationary phase, mobile-phase selection, accurate mass measurements, fragmentation and selectivity. The final section is devoted to describing the applicability of LC–(Q/IT)TOF-MS to routine analysis of multi-components, including target and non-target (unknown) compounds, in herbal samples, emphasizing both the advantages and limitations of this approach for qualitative and quantitative purposes. The potential and future trends of fast high-performance liquid chromatography (HPLC) (e.g. rapid resolution LC and ultra-performance LC) coupled to (Q)TOF-MS for chemical analysis of HMs are highlighted.     

V-type nerve agents phosphonylate ubiquitin at biologically relevant lysine residues and induce intramolecular cyclization by an isopeptide bond

Toxic organophosphorus compounds (e.g., pesticides and nerve agents) are known to react with nucleophilic side chains of different amino acids (phosphylation), thus forming adducts with endogenous proteins. Most often binding to serine, tyrosine, or threonine residues is described as being of relevance for toxicological effects (e.g., acetylcholinesterase and neuropathy target esterase) or as biomarkers for post-exposure analysis (verification, e.g., albumin and butyrylcholinesterase). Accordingly, identification of novel protein targets might be beneficial for a better understanding of the toxicology of these compounds, revealing new bioanalytical verification tools, and improving knowledge on chemical reactivity. In the present study, we investigated the reaction of ubiquitin (Ub) with the V-type nerve agents Chinese VX, Russian VX, and VX in vitro. Ub is a ubiquitous protein with a mass of 8564.8 Da present in the extra- and intracellular space that plays an important physiological role in several essential processes (e.g., proteasomal degradation, DNA repair, protein turnover, and endocytosis). Reaction products were analyzed by matrix-assisted laser desorption/ionization-time-of-flight- mass spectrometry (MALDI-TOF MS) and μ-high-performance liquid chromatography online coupled to UV-detection and electrospray ionization MS (μHPLC-UV/ESI MS). Our results originally document that a complex mixture of at least mono-, di, and triphosphonylated Ub adducts was produced. Surprisingly, peptide mass fingerprint analysis in combination with MALDI and ESI MS/MS revealed that phosphonylation occurred with high selectivity in at least 6 of 7 surface-exposed lysine residues that are essential for the biological function of Ub. These reaction products were found not to age. In addition, we herein report for the first time that phosphonylation induced intramolecular cyclization by formation of an isopeptide bond between the ε-amino group of a formerly phosphonylated lysine and the side chain of an adjacent acidic glutamic acid residue.

Recent and future developments of liquid chromatography in pesticide trace analysis

Until recently, the application of liquid chromatography (LC) in pesticide analysis was usually focused on groups of compounds or single compounds for which no suitable conditions were available for analysis with gas chromatography (GC). However, recent developments in both detection and column material technology show that LC significantly enlarged its scope in this field of analysis. Obviously, the most striking example is the rather abrupt transition of LC coupled to mass spectrometric detection (MS) from an experimental and scientifically fashionable technique to a robust, sensitive and selective detection mode rendering LC-MS being increasingly used in pesticide trace analysis. Other recent major developments originate from the innovation of new LC column packing materials, viz. immuno-affinity sorbents, restricted access medium materials and molecular imprinted polymers improving considerably the screening of polar pesticides by means of reversed-phase LC with UV detection. In this review the merits and perspectives of these important LC developments and their impact to current and future applications in pesticide trace analysis are presented and discussed.     

Trace mycotoxin analysis in complex biological and food matrices by liquid chromatography-atmospheric pressure ionisation mass spectrometry

Mycotoxins are toxic secondary metabolites produced by filamentous fungi that are growing on agricultural commodities. Their frequent presence in food and their severe toxic, carcinogenic and estrogenic properties have been recognised as potential threat to human health. A reliable risk assessment of mycotoxin contamination for humans and animals relies basically on their unambiguous identification and accurate quantification in food and feedstuff. While most screening methods for mycotoxins are based on immunoassays, unambiguous analyte confirmation can be easily achieved with mass spectrometric methods, like gas chromatography/mass spectrometry (GC/MS) or liquid chromatography/mass spectrometry (LC/MS). Due to the introduction of atmospheric pressure ionisation (API) techniques in the late 80s, LC/MS has become a routine technique also in food analysis, overcoming the traditional drawbacks of GC/MS regarding volatility and thermal stability. During the last few years, this technical and instrumental progress had also an increasing impact on the expanding field of mycotoxin analysis. The aim of the present review is to give an overview on the application of LC-(API)MS in the analysis of frequently occurring and highly toxic mycotoxins, such as trichothecenes, ochratoxins, zearalenone, fumonisins, aflatoxins, enniatins, moniliformin and several other mycotoxins. This includes also the investigation of some of their metabolites and degradation products. Suitable sample pre-treatment procedures, their applicability for high sample through-put and their influence on matrix effects will be discussed. The review covers literature published until July 2006.     

Hyphenation of infrared spectroscopy to liquid chromatography for qualitative and quantitative polymer analysis: degradation of poly(bisphenol A)carbonate

Hyphenation of infrared spectroscopy (IR) to liquid chromatography (LC) has been applied to study chemical changes in poly(bisphenol A)carbonate (PC) as a result of degradation. Especially coupling of LC to FTIR through solvent elimination is a sensitive approach to identify changes in functionality observed in the LC chromatograms as has been demonstrated by coupling of liquid chromatography under critical conditions (LCCC) to IR. Furthermore, an example is shown in which two-dimensional liquid chromatography, i.e. LCCCxSEC, was coupled to IR by means of a flow cell. This resulted in data sets containing most probably valuable data, but extracting relevant information from these large data sets is not straightforward at all. Therefore, multivariate data analysis (MVDA) of SEC-FTIR data was used to extract relevant data from large data sets. This approach revealed chemical differences due to degradation that could not be detected by other means. Spectral features could be identified that allowed to quantitatively predict the degradation of poly(bisphenol A)carbonate as a function of degradation conditions.     

GC-MS analytical methods for the determination of personal-care products in water matrices

This article discusses the more recent methods combining gas chromatography and mass spectrometry (GC-MS) for analysis of personal-care products (PCPs) in water matrices. We describe different procedures for sample extraction and preparation as well as different instrumental methods commonly used for these compounds. GC-MS and GC-tandem MS (GC-MS²), which are complementary to liquid chromatography combined with MS (LC-MS), allow identification and quantification of PCPs belonging to different classes with the sensitivity and the selectivity necessary for environmental monitoring. The compounds investigated include fragrances (e.g., nitro and polycyclic musks), antimicrobial compounds (e.g., triclosan), ultraviolet blockers (e.g., methylbenzylidene camphor), antioxidants and preservatives (e.g., phenols and p-hydroxybenzoic acid (parabens)) and insect repellents (e.g., N,N-diethyl-m-toluamide (DEET)). We critically review data in the literature by focusing attention on analytical methods devoted to simultaneous detection and quantification of structurally diverse pharmaceuticals and PCPs.     

Determination of antifouling pesticides and their degradation products in marine sediments by means of ultrasonic extraction and HPLC–APCI–MS

A method has been developed for the simultaneous determination of antifouling pesticides and some of their degradation products, e.g. dichlofluanid, diuron, demethyldiuron, 1-(3,4-dichlorophenyl)urea, sea-nine, Irgarol 1051 and one of its metabolites (2-methylthio-4-tert-butylamino-s-triazine) in marine sediments. The determination of these compounds in sediment samples was performed by means of methanolic ultrasonic extraction then clean-up on an Isolute ENV+ solid phase extraction (SPE) cartridge. The resulting extract was then analyzed by reversed-phase high-performance liquid chromatography coupled with atmospheric-pressure chemical-ionization mass spectrometry in negative and positive ion modes (HPLC–APCI–MS). Recovery ranged from 54–109% for the antifouling agents and their degradation products. The determination limits for the different compounds varied between 0.2 and 1.6 μg kg^–1 dry sediment. The analytical procedure was successfully applied to the determination of these pesticides and their degradation products in marine sediment samples from different marinas of the Catalan coast. The compounds detected were: diuron, dichlofluanid, demethyldiuron, sea-nine, and Irgarol 1051. The highest concentrations were those of diuron and Irgarol 1051 – 136 and 88 μg kg^–1, respectively.     

Study of Clethodim Degradation and By-Product Formation in Chlorinated Water by HPLC

Two of the most commonly used chlorinating agents for water disinfection, hypochlorite and chloramines, were employed to investigate the degradation of clethodim in conditions simulating tap water treatment. The main clethodim degradation products were identified by using liquid chromatography (LC) coupled with mass spectrometry (MS). The main degradation process was oxidation to sulfoxide and then to sulfone. Degradation half-life was calculated for both parent clethodim and the first degradation product, clethodim sulfoxide. Whereas some other different minor by-products were identified when the degradation occurs with either sodium hypochlorite or chloramines, no other chlorinated by-products were found under the conditions tested.     

Investigating the presence of omeprazole in waters by liquid chromatography coupled to low and high resolution mass spectrometry: degradation experiments

Omeprazole is one of the most consumed pharmaceuticals around the world. However, this compound is scarcely detected in urban wastewater and surface water. The absence of this pharmaceutical in the aquatic ecosystem might be due to its degradation in wastewater treatment plants, as well as in receiving water. In this work, different laboratory‐controlled degradation experiments have been carried out on surface water in order to elucidate generated omeprazole transformation products (TPs). Surface water spiked with omeprazole was subjected to hydrolysis, photo‐degradation under both sunlight and ultraviolet radiation and chlorination. Analyses by liquid chromatography coupled to quadrupole time‐of‐flight mass spectrometry (LC–QTOF MS) permitted identification of up to 17 omeprazole TPs. In a subsequent step, the TPs identified were sought in surface water and urban wastewater by LC–QTOF MS and by LC coupled to tandem mass spectrometry with triple quadrupole. The parent omeprazole was not detected in any of the samples, but four TPs were found in several water samples. The most frequently detected compound was OTP 5 (omeprazole sulfide), which might be a reasonable candidate to be included in monitoring programs rather than the parent omeprazole. Copyright © 2013 John Wiley & Sons, Ltd.     

Determination of ascorbic acid and its degradation products by high‐performance liquid chromatography‐triple quadrupole mass spectrometry

This study describes application of liquid chromatography coupled with triple quadrupole mass spectrometry (LC‐MS) for evaluation of vitamin C stability, the objective being prediction of the degradation products. Detection was performed with an UV detector (UV‐Vis) in sequence with a triple‐quad mass spectrometer in the multiple reaction mode. The negative ion mode of ESI and MS‐MRM transitions of m/z 175→115 (quantifier) and 175→89 (qualifier) for ascorbic acid was used. All the validation parameters were within the range of acceptance proposed by the Food and Drug Administration. The method was fully validated in terms of linearity, LOD, LOQ, accuracy, and interday precision. Validation experiments revealed good linearity with R² = 0.999 within the established concentration range, and excellent repeatability (9.3%). The LOD of the method was 0.1524 ng/mL whereas the LOQ was 0.4679 ng/mL. LC‐MS methodology proves to be an improved, simple, and fast approach to determining the content of vitamin C and its degradation products with high sensitivity, selectivity, and resolving power within 6 minutes of analysis.     

Combined use of liquid chromatography with mass spectrometry and nuclear magnetic resonance for the identification of degradation compounds in an erythromycin formulation

A commercial erythromycin formulation containing erythromycin A (EA) as the major compound showed the presence of an unknown degradation compound that was co-eluted with erythromycin E (EE) in the European Pharmacopoeia (Ph. Eur.) liquid chromatographic (LC) method. The amount of the degradation compound increased with respect to time. To separate this unknown (UNK1), investigation was performed with different LC methods coupled to ultraviolet detection (LC-UV). With the present Ph. Eur. method, the degradation compound could not be well separated. However, with the most selective LC-UV method (XTerra method), two more degradation products (UNK2 and UNK3) were found in the formulation which could not be observed using other methods because of their poor separation. By combining the results obtained with LC-UV, LC/MS and LC/NMR, the degradation products were identified as pseudoerythromycin A hemiketal (PsEAHK), erythromycin A enol ether carboxylic acid and erythromycin C enol ether carboxylic acid. PsEAHK is known to be a base-catalysed degradation product of EA, whereas the other two degradation products were newly identified.     

Liquid chromatography/mass spectrometric studies on atorvastatin and its stress degradation products

A comprehensive mass fragmentation pathway of atorvastatin, which has not been reported so far, was established by subjecting the drug to multi-stage mass spectrometric (MSn) studies. It was used along with liquid chromatography/mass spectrometric (LC/MS) and liquid chromatography/time-of-flight mass spectrometric (LC/TOFMS) analyses to identify the drug degradation products formed under stress conditions of hydrolysis, oxidation and photolysis. Other than lactone, which is a reported hydrolysis product, six unknown hydrolytic products could be identified, viz., dehydrated drug, dehydrated drug lactone, and diastereomers of the drug, drug lactone, dehydrated drug, and dehydrated drug lactone. Among the two products separated under oxidative conditions, one was lactone, again formed as a result of drug hydrolysis in an acidic environment of peroxide solution. The other was similar to a reported oxidative product. Under photolytic conditions in solution, one new product could be identified, while most of the others matched with those known from the literature. Hence overall a more complete degradation pathway of the drug was established than known at present, by using a stress testing approach and employing LC/MS techniques.     

Mass spectrometry applied to the analysis of estrogens in the environment

Environmental analytical chemistry has recently changed focus from analysis of non-polar, persistent contaminants (e.g. polychlorinated biphenyls and dioxins) to more polar and labile compounds that interfere with biological processes. For example, natural and synthetic estrogens and their metabolites have been detected in sewage treatment plant effluents at nanogram/liter concentrations that are similar to those at which both total sex reversal and intersex (containing both testes and ova) is induced in fish exposed to these compounds in laboratory experiments. The development of techniques for the analysis of natural and synthetic estrogens in biological fluids (i.e. serum and urine) has been a priority in the biomedical field. However, the recent recognition that estrogen hormones are contaminants in the environment that may contribute to endocrine disruption has focused attention on the need for highly sensitive and specific techniques that are applicable for trace analysis in complex environmental matrices. Three optimized mass spectrometric protocols have been developed for the determination and quantitation of steroid hormones in environmental matrices using gas chromatography/tandem mass spectrometry (GC/MS/MS), liquid chromatography/mass spectrometry selected ion monitoring, (LC/MS - SIM) and liquid chromatography/tandem mass spectrometry (LC/MS/MS). The advantages and disadvantages of each method are presented.