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.     

Gas chromatography/mass spectrometric assay of endogenous cellular lipid peroxidation products: quantitative analysis of 9- and 10-hydroxystearic acids

A sensitive, specific, accurate and reproducible gas chromatography/mass spectrometry method was developed for the assay of 9- and 10-hydroxystearic acids in samples obtained as cell extracts. The preparation of the samples required specific procedures to allow the analysis of both the free and the conjugated hydroxy acids as the corresponding methyl esters. The quantification used propyl-paraben as the internal standard and monitoring of a specific fragment of each isomeric hydroxy acid methyl ester, and allowed quantification of the conjugate and the free fractions of both 9- and 10-hydroxystearic acids. This method is suitable for identification and quantification (LOQ 1.8 and 4.4 ng, respectively) of these important metabolites of lipid peroxidation. In particular the development of an assay for the free 9-hydroxystearic acid methyl ester makes the method a reliable analytical tool for investigations of the role of this metabolite in the mechanisms of tumour cell proliferation.     

Gas chromatography/mass spectrometry and pyrolysis-gas chromatography/mass spectrometry for the chemical characterisation of modern and archaeological figs (Ficus carica)

Gas chromatography/mass spectrometry (GC/MS) after alkaline hydrolysis, solvent extraction and trimethylsilylation, and analytical pyrolysis using hexamethyldisilazane (HMDS) for in situ derivatisation followed by gas chromatographic/mass spectrometric analysis (Pyrolysis-silylation-GC/MS) were used to investigate the hydrolysable and soluble constituents, and the polymerised macromolecules of an archaeological fig (Ficus carica) recovered in Zaragoza (Spain), as well as of modern figs. The main aim was to study the compositional alterations undergone by the fig tissues in a particular archaeological environment: the fig was in a vessel and covered by a layer of a mixture of orpiment and gypsum. A comparison between the GC/MS results from modern and archaeological figs revealed that degradative reactions took place, leading to the disappearance/depletion of reactive (unsaturated fatty acids) and sensitive compounds (phytosterols and triterpenes). Py-silylation-GC/MS data provided evidence of a significant degradation of the saccharide and lipid components of the fig tissue, which left a residue enriched in polyphenols and polyesters.     

Gas Chromatographic/mass spectrometric analysis of azines

Chromatographia - We have studied the gas chromatographic behaviour of several 3-methyl-2-benzothiazolone-azines. In HPLC analysis all the unsymmetrical azines show double peaks, whereas in HRGC...     

Ultrafast liquid chromatography/ultraviolet and liquid chromatography/tandem mass spectrometric analysis

Optimal liquid chromatography/mass spectrometric [LC/MS(/MS)] analysis depends on both the LC selectivity and the electrospray efficiency. Here, we outline a simple and comprehensive LC/MS/MS strategy for the rapid analysis of a wide range of pharmaceutical compounds. To achieve ultrafast LC separation with little sacrifice in peak capacity, one needs to start with a column that provides a good peak capacity at short gradient run times; secondly, it is important to use high flow rates to achieve a good gradient peak capacity. Following this strategy, it was possible to baseline-resolve a mixture (containing acidic, neutral, and basic pharmaceutical analytes) in seconds. By coupling the selectivity provided by fast LC separation with the specificity of MS/MS detection, it is possible to separate and identify a wide range of analytes in 1-min gradient analyses. Also, the impact of mobile phase pH on both the chromatographic selectivity and the MS/MS sensitivity is demonstrated.     

Analysis of thermo-oxidation products of polypropylene and polyethylene by Gas chromatography/mass spectrometry

Thermal and thermo-oxidative degradation of polyethylene and polypropylene is discussed. The products of thermal and thermo-oxidative degradation are analysed using a GC-MS after previous adsorption in a column containing a sorbent of styrene divinyl benzene copolymer type. Aldehydes are the products mostly resulting from the thermo-oxidation of polyethylene and methyl ketones are those resulting from the thermo-oxidation of polypropylene.     

Gas chromatography/combustion/isotope ratio mass spectrometric analysis of the stable carbon composition of tetrols

The stable carbon isotope compositions of tetrols, erythritol and threitol were determined by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). Using four tetrols with various δ¹³C values derivatized by methylboronic acid, the carbon isotope analysis method achieved excellent reproducibility and high accuracy. There was no carbon isotopic fractionation during the derivatization processes. The differences in the carbon isotopic compositions of methylboronates between the measured and calculated ranged from ?0.20 to 0.12‰, within the specification of the GC/C/IRMS system. It was demonstrated that δ¹³C values of tetrols could be calculated by a simple mass balance equation between tetrols, methylboronic acid, and methylboronates. The analogous 2‐methyltetrols, marker compounds of photooxidation products of atmospheric isoprene, should have similar behavior using the same derivatization reagent. This method may provide insight on sources and sinks of atmospheric isoprene. Copyright © 2009 John Wiley & Sons, Ltd.     

Study of the mechanism of polysulfone decomposition by pyrolysis/gas chromatography and pyrolysis/gas chromatography/mass spectrometry

Both co- and terpolysulfones have been flash-pyrolyzed at high temperature followed by separation and identification of the products by gas chromatography and/or gas chromatography/mass spectrometry. As expected, most of the products were the corresponding olefin and SO₂. Additionally, higher molecular weight products, including aromatics, and olefin isomerization products, were produced. Mechanisms for initiation and formation of the higher molecular weight products are presented which include the back reaction of intermediate free radicals to abstract hydrogen or to form C? C bonds followed by expulsion of SO₂. The free-radical intermediates formed by the SO₂ expulsion undergo transformations to give the aromatic products. No breakdown products were found with either O or S present, nor was SO₂H found.     

Gas chromatography/mass spectrometric identification of dopaminergic metabolites in striata of rats treated with L-DOPA

The ex vivo identification of dopaminergic metabolites present in rat striata after (L-DOPA + benserazide) treatment is reported. The different metabolites have been identified as the trimethylsilyl derivatives in the striatal extracts by gas chromatography/mass spectrometry.     

Gas chromatography/mass spectrometric study of non-commercial C-4-substituted 1,4-dihydropyridines and their oxidized derivatives

A gas chromatography/mass spectrometry (GC/MS) method for the qualitative and quantitative determination of the calcium-channel antagonists C-4-substituted 1,4-dihydropyridines, and their corresponding N-ethyl derivatives, is presented. Also, the electrochemical oxidation and the reactivity of the compounds with alkyl radicals derived from 2,2'-azobis-(2-amidinopropane) were monitored by GC/MS. Mass spectral fragmentation patterns for the C-4-substituted 1,4-dihydropy-ridine parent drugs were significantly different from those of their oxidation products, generated either by electrochemical oxidation or by reaction with alkyl radicals. However, for N-ethyl-1,4-dihydropyridine compounds it was not possible to detect the final products (pyridinium salts) using these experimental conditions.     

Gas chromatography with inductively coupled plasma mass spectrometric detection in speciation analysis

The state-of-the-art of gas chromatography coupled with inductively coupled plasma mass spectrometry (GC-ICP MS) is comprehensively reviewed. Particular attention is given to the recent advances in ICP MS detection including: GC-ICP interface designs; low power plasmas; and alternative mass analyzers (time-of-flight, double-focussing single collector, double-focussing and collision cell single-focussing multicollectors). On the level of sample preparation for speciation analysis by GC-ICP MS, new derivatization reagents and advances in extraction techniques, such as capillary purge-and-trap, solid phase microextraction and stirbar solid phase extraction are discussed. The increasing role of organometallic species labeled with stable isotopes for the detection of sources of errors during sample preparation and for isotope dilution quantification is highlighted. Applications of GC-ICP MS to the analysis of real-world samples are summarized with a focus on the areas which particularly benefit from the high ICP MS detection sensitivity and tolerance to sample matrix.     

Gas chromatography/mass spectrometry analysis of triacetone triperoxide (TATP) degradation products

Interest in the analysis and detection of triacetone triperoxide (TATP) and other organic peroxides has increased in recent years. Also of interest is the degradation and decomposition of the peroxides, not only to gain more detailed chemical information from organic peroxide samples, but also to investigate possible new procedures or mechanisms for chemical neutralisation. This report investigates the chemical degradation products of TATP after it has been treated with different acids within a sealed system over a period of 14 days. The samples were collected and analysed by solid-phase microextraction (SPME) and direct liquid injection gas chromatography/mass spectrometry (GC/MS). The results of the experiments indicate that the rate of chemical degradation of TATP and the products formed are dependent on the type of acid. The observed differences enables the type of acid used in the degradation process to be determined, provide complementary information to identify the presence of TATP, and possibly indicate new pathways that may be used to chemically neutralise TATP.     

High-temperature pyrolysis of poly(vinyl chloride): Gas chromatographic-mass spectrometric analysis of the pyrolysis products from PVC resin and plastisols

A pyrolysis–gas chromatographic–mass spectrometric technique for analyzing the pyrolysis products from polymers in an inert atmosphere is described. Initial studies encompassing the pyrolysis of poly(vinyl chloride) homopolymer and a series of PVC plastisols (based on o-phthalate esters) have provided a complete qualitative and semi-quantitative analysis of the pyrolysis products from these materials. PVC resin yields a series of aliphatic and aromatic hydrocarbons when pyrolyzed at 600°C; the amount of aromatic products is greater than the amount of aliphatic products. Benzene is the major organic degradation product. A typical PVC plastisol [PVC/o-dioctyl phthalate (100/60)] yields, upon pyrolysis, products that are characteristic of both the PVC matrix and the phthalate plasticizer. The pyrolysis products from the plasticizer dilute those from the PVC portion of the plastisol and are, in turn, the major degradation products. There are no degradation products resulting from an interaction of the PVC with the plastisol. The pyrograms resulting from pyrolysis of the various plastisols of PVC can be used for purposes of “fingerprinting.” Identification of the major peaks in a typical plastisol pyrogram provides information leading to a precise identification of the plasticizer. The pyrolysis data from this study were related to a special case of flammability and toxicity.     

Influence of pyrolysis temperature and time on the cellulose fast pyrolysis products: Analytical Py-GC/MS study

Analytical pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) was employed to achieve fast pyrolysis of cellulose and on-line analysis of the pyrolysis vapors. Experiments were performed to reveal the effects of pyrolysis temperature and time on the distribution of the pyrolytic products, especially the formation characteristics of eighteen important products. During the fast pyrolysis process, the cellulose started decomposition to form organic volatile products at the set pyrolysis temperature of 400 °C. The pyrolytic products included various anhydrosugars (dominated by the levoglucosan (LG)), anhydrosugar derivatives (mainly the levoglucosenone (LGO), 1,4:3,6-dianhydro-α-d-glucopyranose (DGP), 1,5-anhydro-4-deoxy-d-glycero-hex-1-en-3-ulose (APP) and 1-hydroxy-3,6-dioxabicyclo[3.2.1]octan-2-one (LAC)), furan compounds (typically the 5-hydroxymethyl-furfural (HMF), furfural (FF) and furan (F)), as well as light linear carbonyls (mainly the hydroxyacetaldehyde (HAA) and 1-hydroxy-2-propanone (HA)). These products were generated with different characteristics. The LG was the most important product, it was thermally stable, and its formation was favored at elevated pyrolysis temperature and time. Most of the other products were also enhanced at elevated pyrolytic conditions. However, some products, such as the LGO, were favorable to be produced at low temperatures. Based on these characteristics, discussion was performed on the possible pyrolytic pathways for the formation of the important products.     

Study of ageing of ketone resins used as picture varnishes by pyrolysis–silylation–gas chromatography–mass spectrometry

This contribution presents a research aimed at the study of the commercial products Laropal K80, Keton N and MS2A, ascribed to ketone resins prepared as thin films, in an attempt to reproduce the pictorial layers and protective finishes that are commonplace in contemporary paintings. For this purpose, a new method based on “online” silylation–pyrolysis using hexamethyldisilazane as a derivatisation reagent in pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) has been proposed. This procedure leads to the unambiguous identification of such varnishes and improves direct Py–GC–MS. Chemical changes due to the degradation effect of environmental agents have been especially considered. To that end, three different accelerated ageing processes were applied to a series of specimens prepared from the studied commercial products: thermal, UV light and ageing in an SO₂-polluted chamber. Chemical changes due to UV light ageing of Keton N resin are in good agreement with those previously reported in the literature.     

Use of activated graphitized carbon chips for liquid chromatography/mass spectrometric and tandem mass spectrometric analysis of tryptic glycopeptides

Protein glycosylation has a significant medical importance as changes in glycosylation patterns have been associated with a number of diseases. Therefore, monitoring potential changes in glycan profiles, and the microheterogeneities associated with glycosylation sites, are becoming increasingly important in the search for disease biomarkers. Highly efficient separations and sensitive methods must be developed to effectively monitor changes in the glycoproteome. These methods must not discriminate against hydrophobic or hydrophilic analytes. The use of activated graphitized carbon as a desalting media and a stationary phase for the purification and the separation of glycans, and as a stationary phase for the separation of small glycopeptides, has previously been reported. Here, we describe the use of activated graphitized carbon as a stationary phase for the separation of hydrophilic tryptic glycopeptides, employing a chip‐based liquid chromatographic (LC) system. The capabilities of both activated graphitized carbon and C₁₈ LC chips for the characterization of the glycopeptides appeared to be comparable. Adequate retention time reproducibility was achieved for both packing types in the chip format. However, hydrophilic glycopeptides were preferentially retained on the activated graphitized carbon chip, thus allowing the identification of hydrophilic glycopeptides which were not effectively retained on C₁₈ chips. On the other hand, hydrophobic glycopeptides were better retained on C₁₈ chips. Characterization of the glycosylation sites of glycoproteins possessing both hydrophilic and hydrophobic glycopeptides is comprehensively achieved using both media. This is feasible considering the limited amount of sample required per analysis (<1 pmol). The performance of both media also appeared comparable when analyzing a four‐protein mixture. Similar sequence coverage and MASCOT ion scores were observed for all proteins when using either stationary phase. Copyright © 2009 John Wiley & Sons, Ltd.     

High-temperature pyrolysis/gas chromatography/isotope ratio mass spectrometry: simultaneous measurement of the stable isotopes of oxygen and carbon in cellulose

Stable isotope analysis of cellulose is an increasingly important aspect of ecological and palaeoenvironmental research. Since these techniques are very costly, any methodological development which can provide simultaneous measurement of stable carbon and oxygen isotope ratios in cellulose deserves further exploration. A large number (3074) of tree-ring α-cellulose samples are used to compare the stable carbon isotope ratios (δ(13)C) produced by high-temperature (1400°C) pyrolysis/gas chromatography (GC)/isotope ratio mass spectrometry (IRMS) with those produced by combustion GC/IRMS. Although the two data sets are very strongly correlated, the pyrolysis results display reduced variance and are strongly biased towards the mean. The low carbon isotope ratios of tree-ring cellulose during the last century, reflecting anthropogenic disturbance of atmospheric carbon dioxide, are thus overestimated. The likely explanation is that a proportion of the oxygen atoms are bonding with residual carbon in the reaction chamber to form carbon monoxide. The 'pyrolysis adjustment', proposed here, is based on combusting a stratified sub-sample of the pyrolysis results, across the full range of carbon isotope ratios, and using the paired results to define a regression equation that can be used to adjust all the pyrolysis measurements. In this study, subsamples of 30 combustion measurements produced adjusted chronologies statistically indistinguishable from those produced by combusting every sample. This methodology allows simultaneous measurement of the stable isotopes of carbon and oxygen using high-temperature pyrolysis, reducing the amount of sample required and the analytical costs of measuring them separately.     

Gas chromatographic/mass spectrometric and microbiological analyses on irradiated chicken

Ionizing radiation is widely used as treatment technique for food preservation. It involves among others reduction of microbial contamination, disinfestations, sprout inhibition and extension of shelf life of food. However, the commercialization of irradiated food requires the availability of reliable methods to identify irradiated foodstuffs. In this paper, we present results on the application to irradiated chicken of this method, based on the detection, in muscle and skin samples, of the peaks of ions 98 Da and 112 Da, in a ratio approximately 4:1, typical of radiation induced 2-dodecylcyclobutanones (2-DCB). Aim of the work was also to study the time stability of the measured parameters in samples irradiated at 3 and 5 kGy, and to verify the efficacy of the treatment from a microbiological point of view. Our results show that, one month after irradiation at 3 kGy, the method is suitable using the skin but not the muscle, while the measured parameters are detectable in both samples irradiated at 5 kGy. The microbial population was substantially reduced even at 3 kGy.