Analysis of long-chain polyprenols using supercritical fluid chromatography and matrix-assisted laser desorption ionization time-of-flight mass spectrometry

The separation of long-chain polyprenols was successfully achieved using supercritical fluid chromatography (SFC). Each 100-mer greater component was separated using tetrahydrofuran as a mobile phase modifier. The molecular mass distributions derived from SFC analyses agreed with the results of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) analyses. The number-average molecular mass calculated by MALDI-TOF-MS data were also in accord with the results of quantitative 1H-NMR analysis of terminal groups. A combination of SFC and MALDI-TOF-MS analyses is a powerful tool for the elucidation of the complicated structures of natural polyprenols.     

Preserving the chromatographic integrity of high-speed supercritical fluid chromatography separations using time-of-flight mass spectrometry

The advantage of high-speed time-of-flight-mass spectrometry (TOF-MS) detection for ultrafast qualitative supercritical fluid chromatography/mass spectrometry (SFC/MS) applications allows the superior resolving power of SFC to be exploited in high-throughput analysis. A chromatographic comparison of quadrupole MS and TOF-MS shows high-speed TOF total ion current data point sampling to be more indicative of fast SFC separations and corresponding short (1-2 s) baseline peak widths. Results shown for analysis of a six-compound mixture with two peaks eluting at 0.86 and 0.89 min exhibit >50% resolution by high-speed TOF data sampling, whereas the same peaks appear to coelute using quadrupole MS data sampling. Additionally, a marked improvement in the peak baseline widths is afforded by fast TOF data acquisition of 0.1 s/spectrum, resulting in a reduction in the baseline width, 1.6 s, of sulfanilamide in a four-compound mixture that is more than 2-fold greater than that achieved at the slower data acquisition of 0.5 s/spectrum. The resulting increase in resolution and improved peak shapes allow automatic integration routines to perform more effectively. For most classes of compounds amenable to high performance liquid chromatography, including druglike species, steroids, and polymers, the union of SFC with TOF-MS provides the maximum density of chemical information per unit time available with any high-speed chromatographic/mass spectrometric method.     

Determination of molecular mass distribution of silicone oils by supercritical fluid chromatography, matrix-assisted laser desorption ionization time-of-flight mass spectrometry and their off-line combination

Silicone oil samples were characterized by supercritical fluid chromatography (SFC), matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI--TOF MS), and their off-line combination. SFC was used to separate samples of silicone oils on micropacked capillary columns. The fractions for the identification studies were obtained from SFC runs at defined time intervals, when the restrictor was pulled out from the chromatographic flame ionization detector (FID) and inserted into a glass vial with acetone. MALDI--TOF MS was used for the identification of individual oligomers in the fractions separated. The molecular mass distributions determined based on SFC and MALDI--TOF MS measurements were compared. From this comparison, it follows that the results are in good agreement. However, certain differences were observed: MALDI--TOF MS was capable of detecting somewhat larger oligomers than the SFC-FID, but the lower molecular mass oligomers were not present in the MALDI spectra. Differences in the region of lower molecular masses can be explained by evaporation of the more volatile low molecular mass oligomers resulting from heating of the sample during the MALDI--TOF MS measurements as a result of the absorption of the laser shot energy. The fact that no high mass discrimination effects of the MALDI--TOF MS measurements, compared with SFC, were observed is very promising for further applications of MALDI--TOF MS in characterizing synthetic polymers of moderate polydispersity.     

Direct coupling of capillary supercritical fluid chromatography with double-focusing high resolution mass spectrometry

An integral restrictor interface with jet separator for coupling capillary column supercritical fluid extraction – supercritical fluid chromatography with high resolution mass spectrometry (SFE-SFC-MS) has been built and used for the analysis of a fatty acid ester, and of polymer additives with a wide range of masses. The mobile phase used was supercritical carbon dioxide; a flame ionization detector (FID) was used in parallel with the mass spectrometer. Different SFC-MS interface operating conditions, e.g. temperature, restrictor position, flow rate, and sample transfer conditions were optimized to obtain good sensitivity and separation for these applications. In addition, the sensitivity of measurements performed with the direct insertion probe and by SFC-MS interface have been compared.     

Automated electrospray ionization FT-ICR mass spectrometry for petroleum analysis

Analysis of petroleum samples at the molecular level by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) typically requires a prolonged accumulation of ions and/or summing up a large number of scans. Here, a chip-based micro-ESI system (Advion NanoMate, Ithaca, NY) has been successfully automated in combination with FT-ICR MS analysis of petroleum samples. A foil-sealed 96-well glass plate prevents solvent evaporation, with no visible loss of sample after 20 h of continuous operation. Mass spectra obtained from the same sample but taken from different wells after various time delays were very similar. Data from replicate samples in different wells could be combined to enhance mass spectral signal-to-noise ratio and dynamic range. Furthermore, the automated data acquisition eliminates sample carryover, and produces heteroatom class distribution, double-bond equivalents (DBE), and carbon number very similar to those from the conventional (manual) micro-ESI experiments.     

Comparative quantitative fatty acid analysis of triacylglycerols using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and gas chromatography.

Quantitative analyses of fatty acids from five triacylglycerol products, coconut oil, palm kernel oil, palm oil, lard and cocoa butter, were carried out using two analytical methods: matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) and gas chromatography (GC), in an effort to validate the application of MALDI-TOFMS in quantitative fatty acid analysis. For the GC analysis, transmethylated products were used, whereas, for the MALDI-TOF analysis, saponified products were used. Under MALDI-TOF conditions, the acids were detected as sodiated sodium carboxylates [RCOONa + Na](+) consistent with the mode of ionization that was previously reported. Thus, the MALDI-TOF mass spectrum of saponified coconut oil showed the presence of sodiated sodium salts of caprylic acid (7.5 +/- 0.67, m/z 189), capric acid (6.9 +/- 0.83, m/z 217), lauric acid (47.8 +/- 0.67, m/z 245), myristic acid (20.4 +/- 0.51, m/z 273), palmitic acid (9.8 +/- 0.47, m/z 301), linoleic acid (0.9 +/- 0.07, m/z 325), oleic acid (4.8 +/- 0.42, m/z 327) and stearic acid (2.0 +/- 0.13, m/z 329). Saponified palm kernel oil had a fatty acid profile that included caprylic acid (3.5 +/- 0.59), capric acid (4.7 +/- 0.82), lauric acid (58.6 +/- 2.3), myristic acid (20.9 +/- 1.5), palmitic acid (7.2 +/- 1.1), oleic acid (3.8 +/- 0.62) and stearic acid (1.2 +/- 0.15). Saponified palm oil gave myristic acid (0.83 +/- 0.18), palmitic acid (55.8 +/- 1.7), linoleic acid (4.2 +/- 0.51), oleic acid (34.5 +/- 1.5), stearic acid (3.8 +/- 0.26) and arachidic acid (0.80 +/- 0.22). Saponified lard showed the presence of myristic acid (1.5 +/- 0.24), palmitic acid (28.9 +/- 1.3), linoleic acid (13.7 +/- 0.67), oleic acid (38.7 +/- 1.4), stearic acid (12.8 +/- 0.64) and arachidic acid (2.4 +/- 0.35). Finally, for saponified cocoa butter, the fatty acid distribution was: palmitic acid (32.3 +/- 1.0), linoleic acid (2.6 +/- 0.35), oleic acid (34.9 +/- 1.7) and stearic acid (30.3 +/- 1.6). Quantitative gas chromatographic analysis of the corresponding methyl esters from these triacylglycerol products yielded data that were mostly in agreement with the MALDI-TOFMS data. The MALDI-TOF experiment, however, proved to be superior to the GC experiment, particularly with regard to baseline resolution of unsaturated acids. Furthermore, the ability of MALDI-TOFMS to detect low concentrations of fatty acids rendered it more sensitive than the GC methodology.     

Qualitative and quantitative analysis of pyrolysis oil by gas chromatography with flame ionization detection and comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry

Pyrolysis oils have attracted a lot of interest, as they are liquid energy carriers and general sources of chemicals. In this work, gas chromatography with flame ionization detector (GC-FID) and two-dimensional gas chromatography with time-of-flight mass spectrometry (GC×GC-TOFMS) techniques were used to provide both qualitative and quantitative results of the analysis of three different pyrolysis oils. The chromatographic methods and parameters were optimized and solvent choice and separation restrictions are discussed. Pyrolysis oil samples were diluted in suitable organic solvent and were analyzed by GC×GC-TOFMS. An average of 300 compounds were detected and identified in all three samples using the ChromaToF (Leco) software. The deconvoluted spectra were compared with the NIST software library for correct matching. Group type classification was performed by use of the ChromaToF software. The quantification of 11 selected compounds was performed by means of a multiple-point external calibration curve. Afterwards, the pyrolysis oils were extracted with water, and the aqueous phase was analyzed both by GC-FID and, after proper change of solvent, by GC×GC-TOFMS. As previously, the selected compounds were quantified by both techniques, by means of multiple point external calibration curves. The parameters of the calibration curves were calculated by weighted linear regression analysis. The limit of detection, limit of quantitation and linearity range for each standard compound with each method are presented. The potency of GC×GC-TOFMS for an efficient mapping of the pyrolysis oil is undisputable, and the possibility of using it for quantification as well has been demonstrated. On the other hand, the GC-FID analysis provides reliable results that allow for a rapid screening of the pyrolysis oil. To the best of our knowledge, very few papers have been reported with quantification attempts on pyrolysis oil samples using GC×GC-TOFMS most of which make use of the internal standard method. This work provides the ground for further analysis of pyrolysis oils of diverse sources for a rational design of both their production and utilization process.     

Nano-flow multidimensional liquid chromatography with electrospray ionization time-of-flight mass spectrometry for proteome analysis of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the top five cancers with the highest incident of a disease worldwide. To understand the mechanisms of hepatocarcinogenesis, proteomics analysis provides a powerful tool to identify proteins that associate with HCC. We developed a two-step procedure for mapping of HCC proteomics. In the first step, in order to simplify the complexity of proteomics of HCC, the subfractionation of complex protein mixtures in HCC into “subproteomes” is presented based on the solubility of protein. While in the second step an automate comprehensive two-dimensional (2D) separation system, coupling strong cation-exchange (SCX) in the first dimension with capillary reversed-phase chromatography (cRPLC) in the second dimension is developed further to separate and analyze proteins associated with HCC. By using this system, complex sample can be injected, desalted, separated and analyzed in complete automatization. The procedure for proteomics analysis was found to be applied for proteins with great molecular mass (>100 000), small molecular mass (<20 000), highly basic (pI > 9.5) and hydrophobicity, which are not well resolved in 2D-gel electrophoresis. In total 229 proteins were identified by using the described proteomics platform. Among them, several proteins related to the process of carcinogenesis were investigated further.     

Ganglioside analysis by thin-layer chromatography matrix-assisted laser desorption/ionization orthogonal time-of-flight mass spectrometry

Metastable decomposition of ions generated in matrix-assisted laser desorption/ionization (MALDI) mass spectrometers complicates analysis of biological samples that have labile bonds. Recently, several academic laboratories and manufacturers of commercial instruments have designed instruments that introduce a cooling gas into the ion source during the MALDI event and have shown that the resulting vibrational cooling stabilizes these labile bonds. In this study, we compared stabilization and detection of desorbed gangliosides on a commercial orthogonal time-of-flight (oTOF) instrument with results we reported previously that had been obtained on a home-built Fourier transform mass spectrometer. Decoupling of the desorption/ionization from the detection steps resulted in an opportunity for desorbing thin-layer chromatography (TLC)-separated gangliosides directly from a TLC plate without compromising mass spectral accuracy and resolution of the ganglioside analysis, thus coupling TLC and oTOF mass spectrometry. The application of a declustering potential allowed control of the matrix cluster and matrix adduct formation, and, thus, enhanced the detection of the gangliosides.     

Direct coupling of capillary supercritical fluid chromatography to high resolution mass spectrometry with minimum modification

Summary The coupling of a capillary supercritical fluid chromatograph with a high resolution double focusing mass spectrometer has been accomplished without any modifications to the pumping or ion source systems. The interface utilizes a direct insertion probe (DIP), which was originally designed for the direct analysis of solid samples, together with a trit restrictor as a decompression device. The DIP is placed opposite to the SFC restrictor, and it provides sufficient heat to prevent cluster formation and cooling resulting from the expansion of the supercritical fluid into the vacuum environment. Excellent mass spectra of standard polycyclic aromatic hydrocarbons under chemical-ionization (CI) conditions using methane as the reagent gas, and under charge-exchange (CE) conditions using CO₂ as the charge exchange medium were obtained.     

Phosphopeptide analysis by directly coupling two-dimensional planar electrochromatography/thin-layer chromatography with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

A novel strategy is presented for the fractionation of complex peptide mixtures using two-dimensional planar electrochromatography/thin-layer chromatography (2D PEC/TLC). Phosphopeptides migrate more slowly in the first dimension, based upon their anionic phosphate residues, and certain predominantly acidic phosphopeptides even migrate in the opposite direction, relative to the bulk of the peptides. Phosphopeptides are further distinguished based upon hydrophilicity in the second dimension. This permits a restricted region of the plate to be directly interrogated for the presence of phosphopeptides by mass spectrometry (MS). Phosphopeptide analysis from the plates by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF)-MS and tandem MS enabled peptide sequencing and identification.     

A simple approach for coupling liquid chromatography and electron ionization mass spectrometry

A miniaturized, aerosol based interface for directly coupling a liquid chromatograph with a mass spectrometer is presented. The interface is entirely within the electron ionization (EI) source of the mass spectrometer and no additional, external devices are needed. This simple and effective approach exploits micro-flow nebulization technology providing a new interface suitable for a variety of applications of environmental and biological interest. The new interface provides necessary linearity, ruggedness, sensitivity, and reproducibility of response for trace level analysis, and readily interpretable mass spectra for unambiguous identification of unknown compounds of small to medium molecular weight.     

A supercritical fluid chromatography inlet source for secondary ion mass spectrometry

Summary The direct coupling of a supercritical fluid chromatograph with a secondary ion mass spectrometer is described. SI spectra of some polyaromatic hydrocarbons and phthalate esters show the typical fragmentation pattern [as observed in SIMS] including cationization with silver.

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SFC-Inlet-Source für die Sekundärionen-Massenspektrometrie

     

Laser desorption ionization and MALDI time-of-flight mass spectrometry for low molecular mass polyethylene analysis

Polyethylene's inert nature and difficulty to dissolve in conventional solvents at room temperature present special problems for sample preparation and ionization in mass spectrometric analysis. We present a study of ionization behavior of several polyethylene samples with molecular masses up to 4000 Da in laser desorption ionization (LDI) time-of-flight mass spectrometers equipped with a 337 nm laser beam. We demonstrate unequivocally that silver or copper ion attachment to saturated polyethylene can occur in the gas phase during the UV LDI process. In LDI spectra of polyethylene with molecular masses above approximately 1000 Da, low mass ions corresponding to metal-alkene structures are observed in addition to the principal distribution. By interrogating a well-characterized polyethylene sample and a long chain alkane, C94H190, these low mass ions are determined to be the fragmentation products of the intact metal-polyethylene adduct ions. It is further illustrated that fragmentation can be reduced by adding matrix molecules to the sample preparation.     

Investigation of chromatographic peak broadening in supercritical fluid chromatography/atmospheric pressure chemical ionization mass spectrometry

Multimode ionization source allows for switching between different ionization techniques, for example, electrospray and atmospheric pressure chemical ionization, within a single analysis. Supercritical fluid chromatography can handle a wide polarity range of substances from hydrophilic to lipophilic in a single run and can undoubtedly benefit from versatility of this ion source. Nevertheless, we observed a significant chromatographic peak broadening effect in atmospheric pressure chemical ionization mode during supercritical fluid chromatography‐mass spectrometry analysis of volatile flavor compounds with a dual ion source named ESCi (Waters). Surprisingly, this effect was not related to the separation process but was triggered solely by the ion source conditions. Neither of photodiode array detector, electrospray mode nor a dedicated atmospheric pressure chemical ionization source suffered from such a phenomenon. Chromatographic peak profiles of ten test substances obtained with the dual ion source were compared with photodiode array detector data as a reference. The broadening effect was more pronounced for volatile compounds with low polarity. Dependence of peak broadening on the ion source settings was systematically investigated. Tuning of desolvation gas flow and its temperature dramatically reduced peak distortion and increased detection sensitivity.     

Comprehensive two-dimensional gas chromatography with flame ionization and time-of-flight mass spectrometry detection: qualitative and quantitative analysis of West Australian sandalwood oil

The use of gas chromatography (GC)-mass spectrometry (MS), GC-time-of-flight MS (TOFMS), comprehensive two-dimensional GC (GCxGC)-flame ionization detection (FID), and GCxGC-TOFMS is discussed for the characterization of the eight important representative components, including Z-alpha-santalol, epi-alpha-bisabolol, Z-alpha-trans-bergamotol, epi-beta-santalol, Z-beta-santalol, E,E-farnesol, Z-nuciferol, and Z-lanceol, in the oil of west Australian sandalwood (Santalum spicatum). Single-column GC-MS lacks the resolving power to separate all of the listed components as pure peaks and allow precise analytical measurement of individual component abundances. With enhanced peak resolution capabilities in GCxGC, these components are sufficiently well resolved to be quantitated using flame ionization detection, following initial characterization of components by using GCxGC-TOFMS.     

Pyrolysis–gas chromatography mass spectrometry and field ionization mass spectrometry of polyquinones

Low- and high-molecular mass thermal decomposition products of five polyquinones with different linking aromatic structures have been analyzed by pyrolysis–gas chromatography and by direct (in-source) pyrolysis–field ionization mass spectrometry. The quantity of carboxyl groups present in the polymer is obtained by the amounts of carbon dioxide found by pyrolysis–gas chromatography. Assuming a radical thermal decomposition mechanism the distribution of ketoacidic and quinonoid segments along the macromolecular ladder could be estimated from the high-molecular mass products measured by pyrolysis–field ionization mass spectrometry. A random distribution of the two different segments was found for polyquinones with biphenylene and dibenzofuran subunits, while a structure built up of blocks of two or more identical segments was obtained for polyquinones with dibenzothiophene and diphenylmethane subunits. At the same time the anomalous structural moieties in the polyquinone ladders are also clarified with the help of the identification of the unexpected pyroysis products. Oxidated and bis-dibenzothiophene and bis-diphenylmethane subunits were found. The observed temperature dependence for the appearances of the thermal degradation products indicates that condensation and elimination reactions are taking place under the described pyrolysis conditions. Condensation in the ketoacidic segments forming new quinonoid segments proved to be important in the polymer which was a 100% poly(ketoacid), but negligible in the polyquinones containing ketoacidic segments up to 60%.