Analytical potential of a laser ablation–glow discharge–optical emission spectrometry system for the analysis of conducting and insulating materials

The analytical capabilities of a glow discharge (GD) as a secondary source for excitation/ionization of the material provided by laser ablation (LA) have been compared to conventional laser induced breakdown spectroscopy (LIBS). In LA–GD both sources can be independently adjusted to optimize the sampling process and then its subsequent excitation. This could involve a number of analytical performance advantages, such as reduced matrix dependence, greater precision and sensitivity than those encountered in LIBS. For such purpose, an ablation chamber design including two electrodes to generate the GD discharge has been built and assayed. A comparison between LIBS and LA–GD–OES has been carried out, both, under reduced argon and helium atmospheres. Different sets of samples (conducting reference materials, glass and fluorine pellets) have been used to evaluate the novel coupled technique. The LA–GD coupled system has shown to provide lower detection limits. In addition, best linear correlations between intensities and concentrations and lower matrix effects have also been found using the coupled system. Moreover, special advantages of the LA–GD–OES have also been demonstrated for the analysis of fluorine.     

Quantification of bromine in flame-retardant coatings by radiofrequency glow discharge–optical emission spectrometry

There is an increasing concern regarding the toxicity and environmental distribution and impact of brominated organic compounds employed as flame retardants. Thus, present interest in searching for new analytical techniques and methods allowing a rapid, simple and reliable detection of those compounds in materials and wastes potentially containing such flame retardants is not surprising. The feasibility of using radiofrequency glow discharge plasma spectrometry coupled with optical emission spectrometry (rf-GD-OES) as a rapid and simple tool to directly analyse bromine-containing flame-retardant polymeric layers is investigated here. Polymeric layers for calibration were made by mixing appropriate amounts of tetrabromobisphenol A, bisphenol A, phloroglucinol and diphenylmethane-4,4′-diisocyanate in tetrahydrofuran. The corresponding blanks (polymers without tetrabromobisphenol A) were also prepared. Detection of bromine was investigated both in the visible (at 470.48 nm) and in the near-infrared (at 827.24 nm) regions, using a charge-coupled device for detection. Discharge parameters affecting the emission intensity of bromine were first optimized (in argon and helium as possible plasma gases) and the analytical performance characteristics were then evaluated. The best detection limit (0.044% Br) was achieved measuring Br I 827.24 nm in a He discharge, using a forward power of 70 W and a pressure of 45 Torr. The linearity range extended up to 27% Br. Finally, the applicability of the rf-GD-OES method proposed to the quantitative analysis of bromine in solid materials coated with flame-retardant commercial paints was successfully demonstrated. Figure Flame Retardants     

Comparison of liquid chromatography-microchip/mass spectrometry to conventional liquid chromatography–mass spectrometry for the analysis of steroids

The feasibility of a microfluidic-based liquid chromatography-electrospray ionization/mass spectrometric system (HPLC-Chip/ESI/MS) was studied and compared to a conventional narrow-bore liquid chromatography-electrospray ionization/mass spectrometric (LC-ESI/MS) system for the analysis of steroids. The limits of detection (LODs) for oxime derivatized steroids, expressed as concentrations, were slightly higher with the HPLC-Chip/MS system (50–300 pM) using an injection volume of 0.5 μL than with the conventional LC-ESI/MS (10–150 pM) using an injection volume of 40 μL. However, when the LODs are expressed as injected amounts, the sensitivity of the HPLC-Chip/MS system was about 50 times higher than with the conventional LC-ESI/MS system. The results indicate that the use of HPLC-Chip/MS system is clearly advantageous only in the analysis of low-volume samples. Both methods showed good linearity and good quantitative and chromatographic repeatability. In addition to the instrument comparisons with oxime derivatized steroids, the feasibility of the HPLC-Chip/MS system in the analysis of non-derivatized and oxime derivatized steroids was compared. The HPLC-Chip/MS method developed for non-derivatized steroids was also applied to the quantitative analysis of 15 mouse plasma samples.     

Liquid sampling–atmospheric pressure glow discharge (LS-APGD) ionization source for elemental mass spectrometry: preliminary parametric evaluation and figures of merit

A new, low-power ionization source for the elemental analysis of aqueous solutions has recently been described. The liquid sampling–atmospheric pressure glow discharge (LS-APGD) source operates at relatively low currents (<20 mA) and solution flow rates (<50 μL min⁻¹), yielding a relatively simple alternative for atomic mass spectrometry applications. The LS-APGD has been interfaced to what is otherwise an organic, LC-MS mass analyzer, the Thermo Scientific Exactive Orbitrap without any modifications, other than removing the electrospray ionization source supplied with that instrument. A glow discharge is initiated between the surface of the test solution exiting a glass capillary and a metallic counter electrode mounted at a 90° angle and separated by a distance of ~5 mm. As with any plasma-based ionization source, there are key discharge operation and ion sampling parameters that affect the intensity and composition of the derived mass spectra, including signal-to-background ratios. We describe here a preliminary parametric evaluation of the roles of discharge current, solution flow rate, argon sheath gas flow rate, and ion sampling distance as they apply on this mass analyzer system. A cursive evaluation of potential matrix effects due to the presence of easily ionized elements indicate that sodium concentrations of up to 50 μg mL⁻¹ generally cause suppressions of less than 50%, dependant upon the analyte species. Based on the results of this series of studies, preliminary limits of detection (LOD) have been established through the generation of calibration functions. While solution-based concentration LOD levels of 0.02–2 μg mL⁻¹ are not impressive on the surface, the fact that they are determined via discrete 5 μL injections leads to mass-based detection limits at picogram to single-nanogram levels. The overhead costs associated with source operation (10 W d.c. power, solution flow rates of <50 μL min⁻¹, and gas flow rates <10 mL min⁻¹) are very attractive. While further optimization in the source design is suggested here, it is believed that the LS-APGD ion source may present a practical alternative to inductively coupled plasma sources typically employed in elemental mass spectrometry.     

Top-down analysis of 30–80 kDa proteins by electron transfer dissociation time-of-flight mass spectrometry

Electron transfer dissociation (ETD)-based top-down mass spectrometry (MS) is the method of choice for in-depth structure characterization of large peptides, small- and medium-sized proteins, and non-covalent protein complexes. Here, we describe the performance of this approach for structural analysis of intact proteins as large as the 80 kDa serotransferrin. Current time-of-flight (TOF) MS technologies ensure adequate resolution and mass accuracy to simultaneously analyze intact 30–80 kDa protein ions and the complex mixture of their ETD product ions. Here, we show that ETD TOF MS is efficient and may provide extensive sequence information for unfolded and highly charged (around 1 charge/kDa) proteins of ～30 kDa and structural motifs embedded in larger proteins. Sequence regions protected by disulfide bonds within intact non-reduced proteins oftentimes remain uncharacterized due to the low efficiency of their fragmentation by ETD. For serotransferrin, reduction of S–S bonds leads to significantly varied ETD fragmentation pattern with higher sequence coverage of N- and C-terminal regions, providing a complementary structural information to top-down analysis of its oxidized form.

High-resolution Orbitrap mass spectrometry for the analysis of carotenoids in tomato fruit: validation and comparative evaluation towards UV–VIS and tandem mass spectrometry

In this study, a generic extraction protocol and full-scan high-resolution Orbitrap-mass spectrometry (MS) detection method were developed, enabling the metabolomic screening for carotenoids in tomato fruit tissue. To this end, the carotenoids lutein, zeaxanthin, α-carotene, β-carotene, and lycopene (representing both xanthofylls and carotenes) were considered. The extraction procedure was optimized by means of a D-optimal design and consisted of a liquid–liquid extraction with methanol/tert-butyl methyl ether (1:1, v/v). The considered compounds were detected by a single-stage Exactive^TM mass spectrometer, operating at a mass resolution of 100,000 full width at half maximum. The validation study demonstrated excellent performance in terms of linearity (R ²?>?0.99), repeatability (CV?≤?10.6 %), within-laboratory reproducibility (CV?≤?12.2 %), and mean corrected recovery (ranging from 85 to 106 %). Additionally, a comparative evaluation towards well-established detection techniques, i.e., tandem mass spectrometry (MS/MS) and ultraviolet-visible spectroscopy (UV–VIS) photodiode array, indicated superior performance of high-resolution Orbitrap-MS with regard to specificity/selectivity and sensitivity (with limits of detection ranging from 1.0 to 3.8 pg μL^?1). As a result, it may be concluded that high-resolution Orbitrap-MS is a suited alternative for UV–VIS or MS/MS in analyzing carotenoids and may offer significant value in carotenoid research because of the metabolomic screening possibilities.

Oxidative degradation products analysis of polymer materials by pyrolysis gas chromatography–mass spectrometry

Pyrolysis gas chromatography–mass spectroscopy (PGC–MS) has been proved to be a powerful method to analyze both the volatile additives and the macromolecular structure of polymer materials. In this paper, flash evaporation technique was used to analyze the volatile degradation products of polymer materials during natural and artificial aging. In high density polyethylene (HDPE) composites, mainly n-alkanes with carbon number from 14 to 29 were detected after natural aging, while no oxidative product was found. Different composites have different n-alkane distributions. In contrast, various oxidative products including ketones, alcohols, esters and unsaturated species could be found in aged polypropylene (PP) nanocomposites. Nanoparticles accelerated the chain scission of PP and increased the formation of oxidative products significantly. During thermal oxidation of nitrile rubber (NBR) seal rubbers, heat/oxidation-induced extra crosslinking predominated and no volatile degradation products was detected. The main change happened in the volatiles is the decrease of additives, especially paraffins, antioxidant RD and hindered phenol. This resulted in the hardening of the rubber and the weakening of the protection from oxidation. Furthermore, the additive distribution along the depth was investigated, showing different migration speeds of different additives. From the additive levels remained in the NBR rubber, it is possible to predict the degradation status. In summary, PGC–MS can supply abundant information of polymer degradation and is helpful for mechanism research.     

Fast counter-electroosmotic capillary electrophoresis–time-of-flight mass spectrometry of hyaluronan oligosaccharides

Fast capillary electrophoresis–mass spectrometry measurements under counter-electroosmotic analyte migration conditions are presented. Efficient separations of a homologous series of six hyaluronan oligosaccharides (comprising 1–6 hyalobiuronic acid moieties) could be completed in 65 s. Separations were achieved in short-length fused silica capillaries under high electric field strengths of up to 1.25 kV·cm⁻¹. Capillary inner diameters ranging from 5 to 50 μm were investigated, resulting in an optimal value of 15 μm. The influence of capillary dimensions and buffer composition on separation efficiency and sensitivity are discussed. Optimal separations were achieved using a 28 cm × 15 μm capillary, a separation high voltage of 35 kV, a background electrolyte of 25 mM ammonium acetate adjusted to pH 8.5, and negative ionization mode. The optimized method was successfully applied to a bovine testicular hyaluronidase digest of hyaluronan. Only minimal sample pretreatment for protein-containing samples is required. The simple manual injection procedure and fast separations allow for a sample throughput of 35 samples per hour.     

Assessing the suitability of a green solvent for gel permeation chromatography–mass spectrometry analysis

The study presents the possibility of performing the analysis of oligomeric structures and polymer additives by gel permeation chromatography (GPC) with atmospheric pressure chemical ionization (APCI) mass spectrometry (MS) in dibuthoxymethane (DBM, butylal), a halogen-free and less hazardous solvent than typically used chloroform and tetrahydrofuran. Polystyrene oligomers and Irganox® additives were analyzed in DBM using 2.1?mm internal diameter GPC columns, allowing to decrease the flow rate down to 50?µL/min, compatible with APCI–MS interface. The ionization was controlled by adding 1% chloroform in DBM to obtain (M+Cl)^? adducts, allowing a fast optimization of method parameters.     

Application of Langmuir–Blodgett technology for the analysis of saturated fatty acids using the MALDI-TOF mass spectrometry

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Comparison of supercritical fluid chromatography–tandem mass spectrometry and liquid chromatography–tandem mass spectrometry for the stereoselective analysis of chlorfenvinphos and dimethylvinphos in tobacco

This study used reversed-phase liquid chromatography–tandem mass spectrometry and supercritical fluid chromatography–tandem mass spectrometry for determination of the stereoisomers of chlorfenvinphos and dimethylvinphos in tobacco. Tobacco samples were extracted and purified with a modified quick, easy, cheap, effective, rugged, and safe technique using spherical carbon. The performance of both methodologies was comprehensively compared in terms of methods validation parameters (separation efficiency, linearity, selectivity, recovery, repeatability, sensitivity, matrix effect, etc.). Under optimized conditions, the calibration curves of the stereoisomers of chlorfenvinphos and dimethylvinphos in the range of 10–500 ng/mL showed excellent linearity with R² ≥ 0.997 in both methods. The adequate recoveries of analytes from three different spiked tobaccos were obtained using reversed-phase liquid chromatography–tandem mass spectrometry (86.1–95.7%) as well as supercritical fluid chromatography–tandem mass spectrometry (86.5–94.0%). The relative standard deviations for spiked samples were all below 7.0%. Compared with supercritical fluid chromatography–tandem mass spectrometry, lower matrix effects and LODs can be obtained in reversed-phase liquid chromatography–tandem mass spectrometry.     

Preparation and evaluation of an immunoaffinity sorbent for the analysis of opioid peptides by on-line immunoaffinity solid-phase extraction capillary electrophoresis–mass spectrometry

In this study, we explored a procedure for the preparation of an immunoaffinity (IA) sorbent for the analysis of opioid peptides by on-line immunoaffinity solid-phase extraction capillary electrophoresis–mass spectrometry (IA-SPE-CE–MS). We followed a site-specific antibody immobilization approach based on the covalent attachment of the oxidized antibodies through their carbohydrate moieties to hydrazide silica particles, using a polyclonal antibody against Endomorphin 1 and 2 (End1 and End2). The main features of the IA sorbent were studied, such as the amount of hydrazide groups and antibodies attached onto oxidized diol silica particles. Once the procedure was optimized, standard solutions of End1 and End2 were used in order to establish the IA-SPE-CE–MS methodology. Acceptable repeatability, reproducibility and linearity range values were obtained for the proposed methodology. The limits of detection (LODs) of 1 ng mL⁻¹ were approximately 100-fold better than those obtained by CE–MS. Selectivity of the IA sorbent was good but some cross-reactivity against Dynorphin A (1–7) was observed when a mixture of several opioid peptides was analyzed. Human plasma samples spiked with End1 and End2 were also analyzed and both peptides could be detected down to 100 ng mL⁻¹.     

Gas chromatography – inductively coupled plasma – time-of-flight mass spectrometry for the speciation analysis of organolead compounds in environmental water samples

The application of inductively coupled plasma – time-of-flight mass spectrometry for the speciation analysis of organolead compounds in environmental waters is described. Construction of the transfer line was achieved by means of a relatively simple and rapid coupling procedure. Derivatization of the ionic lead species was achieved by in-situ propylation with sodium tetrapropylborate; simultaneous extraction of the derivatized compounds in hexane was followed by separation and detection by capillary gas chromatography hyphenated to inductively coupled plasma–time-of-flight mass spectrometry. Detection limits for the different organolead species ranged from 10 to 15 fg (as Pb), corresponding to procedural detection limits between 50 and 75 ng L^–1, on the basis of a 50 mL snow sample, extraction with 200 μL hexane, and subsequent injection of 1 μL of the organic extract on to the column. The accuracy of the system was confirmed by additional analysis of the water samples by capillary gas chromatography coupled with microwave-induced plasma–atomic-emission spectrometry and the analysis of a standard reference material CRM 605 (road dust) with a certified content of trimethyllead.     

Gas chromatography–mass spectrometry analysis of pheomelanin degradation products

Melanoma is most rapidly increasing in the white population and people with pheomelanin skin type are at high risk to develop melanoma. However, little is known about the pheomelanin structure and function, and further elucidation of this melanin is therefore an important task. A GC/MS method was developed based on hydriodic acid hydrolysis of pheomelanin in the urine. Derivatization was performed with ethyl chloroformate and ethanol:pyridine (4:1, v/v). N,O-Ethoxycarbonyl-ethyl esters were extracted with chloroform and analyzed by GC/MS. 4-Amino-3-hydroxyphenylalanine and 3-amino-4-hydroxyphenylalanine together with one benzothiazinone and two benzothiazole compounds were detected and identified in hydrolyzed samples of synthetic pheomelanin and melanin from the urine of a patient with melanoma. These findings strongly suggest that heterocyclic pheomelanin-type units are incorporated in the pigment structures.     

Combination of β-elimination and liquid chromatography/quadrupole time-of-flight mass spectrometry for the determination of O-glycosylation sites

Determination of O-glycosylation sites in glycopeptides was developed by using two model compounds designed from mucin2 tandem repeat motif and erythropoietin. β-Elimination/addition reaction using dimethylamine on glycosylated site through a Michael-type condensation produced efficient deglycosylation with appropriate chemical modification. The use of dimethylamine was efficient to release the O-linked glycan in a reaction time period of 2-6 h at 55 °C. Peptide sequencing was then performed using the liquid chromatography/quadrupole time-of-flight mass spectrometry and MS-MS experiments. Interpretation of fragmentation pathways of the β-elimination/addition products enabled straightforward recognition of glycosylation site. Compared to the fragmentation of corresponding native peptides, mass shift of −18 Da or +27 Da was clearly observed for the two kinds of β-elimination/addition products of the glycosylated threonine. Dimethylamine was found to provide higher efficiency of β-elimination/addition than methylamine and ammonia.     

Environmental PAH analysis by gas chromatography–atmospheric pressure laser ionization–time-of-flight–mass spectrometry (GC-APLI-MS)

The application of polycyclic aromatic hydrocarbon (PAH) analysis by gas chromatography coupled with atmospheric pressure laser ionization and mass spectrometry (GC-APLI-MS) to environmental samples was investigated in the study. The limit of detection for 40 PAH in a standard mixture was 5–100 fg, demonstrating GC-APLI-MS to be a highly sensitive technique and more sensitive by a factor of 100–3,500 compared to GC-MS. Acenaphthylene and cyclopenta[cd]pyrene were not detectable <2,500 fg per injection. To make use of this very high PAH sensitivity, the technique was applied to samples of environmental interest with limited available sample amounts such as particulate matter (PM), soot and a sample from a bioaccumulation test with Lumbriculus variegatus. First, special sample preparation was necessary and ultrasonic extraction proved to be suitable, if a thorough clean-up was performed and plastic materials avoided. By GC-APLI-MS and GC-MS, 224 and 28 single PAH compounds were detected in PM, about 1,000 and 15 in birch soot, and 9 and 2 in worm tissue, respectively, revealing the enormous potential of the method. The selectivity of GC-APLI-MS was shown for a crude oil where >2,200 PAH were detected without any sample preparation.     

Multiresidue analysis of 83 pesticides and 12 dioxin-like polychlorinated biphenyls in wine by gas chromatography–time-of-flight mass spectrometry

A multiresidue method is described for simultaneous estimation of 83 pesticides and 12 dioxin-like polychlorinated biphenyls (PCBs) in red and white wines. The samples (20 mL wine, acidified with 20 mL 1% HCl) were extracted with 10 mL ethyl acetate (+20 g sodium sulphate) and cleaned by dispersive solid-phase extraction (DSPE) with anhydrous calcium chloride and Florisil successively. The final extract (5 mL) was solvent exchanged to 1 mL of cyclohexane:ethyl acetate (9:1), further cleaned by DSPE with 25 mg primary secondary amine sorbent and analyzed by gas chromatography–time-of-flight mass spectrometry (GC–TOF-MS) within 31 min run time. The limits of quantification of most analytes were ≤10–20 μg/L. Acidification of wine prior to extraction prevented hydrolysis of organophosphorous pesticides as well as dicofol, whereas treatment with CaCl₂ minimized the fatty acid co-extractives significantly. Solvent exchange to cyclohexane:ethyl acetate (9:1) further minimized the co-extractives. Recoveries at 5, 10 and 20 ng/mL were >80% for most analytes except cyprodinil, buprofezin and iprodione. The expanded uncertainties at 10 ng/mL were <20% for most analytes. Intra-laboratory precision in terms of Horwitz ratio of all the analytes was below 0.5, suggesting ruggedness of the method. Effectively, the method detection limit for most analytes was as low as up to 1 ng/mL in both red and white wine, except for cyfluthrin and cypermethrin.