Supercritical Fluid Chromatography Mass Spectrometry Research Articles

Identification of diflubenzuron by packed-capillary supercritical fluid chromatography-mass spectrometry with electron-capture negative ionization

The thermolabile insecticide diflubenzuron [1-(4-chlorophenyl)-3-(2,6-difluorobenzoyl)urea] was successfully chromatographed by supercritical fluid chromatography on a 320 μm I.D. Inertsil C 8 column using neat carbon dioxide as mobile phase. Detection and electron-capture negative ionization (ECNI) mass spectrometric characterization were accomplished using a double focusing mass spectrometer with a modified ion source and coaxial direct fluid introduction. Detection limits of 1.0 μg/ml and 0.03 μg/ml were obtained in full-scan and selected-ion monitoring (SIM) mode, respectively. The restrictor heater temperatyre was found to have a major influence on the signal intensity and fragmentation pattern, as thermal degradation was believed to take place or be initiated on the hot restrictor wall. The reactive abundance of the molecular ion amounted to 100% using restrictor temperatures of 160°C and 170°C, while it was completely absent at 190°C. At the lower temperatures, [M - HF] −• was the most significant fragment ion.

Packed column supercritical fluid chromatography-mass spectrometry with particle beam interface aided with particle forming solvent

The particle beam interface aided with particle forming solvent was evaluated for packed column supercritical fluid chromatography-mass spectrometric coupling. Fundamental studies on the effects of various operational parameters were undertaken. Factors influencing aerosol formation (nebulizing capillary I.D., particle solvent type and flow-rate) were evaluated. Pure CO 2 and methanol-modified CO 2 were utilized with equal success. The sensitivity of the system was evaluated in terms of limit of detection (LOD). The electron impact scan and single ion monitoring modes were determined to be 10 and 1 ng for caffeine, respectively. These LODs are 10 to 100 times better than previous reported estimates. Separations of carbamate pesticides and polyaromatic hydrocarbons are shown as examples of the system's utility. Electron impact spectra were artifact-free and comparable to on-line library spectra.

Supercritical Fluid Extraction-Supercritical Fluid Chromatography-Mass Spectrometry for the Analysis of Additives in Polyurethanes

The analysis of biocompatible polyurethanes is used to illustrate the feasibility of supercritical fluid extraction-supercritical fluid chromatography-mass spectrometry using a simple supercritical fluid chromatographic-mass spectrometric interface for the study of polymer additives. Consistent and, for the most part, representative mass spectra can be obtained in an analysis that takes less than an hour to complete. Off-line supercritical fluid extraction-gas chromatography-mass spectrometry and supercritical fluid extraction-supercritical fluid chromatography-flame ionization detection were used to characterize the extracted material.

Evaluation of the particle beam interface for packed-column supercritical fluid chromatography-mass spectrometry with pure and modified CO 2

The particle beam interface was evaluated for microbore packed-column supercritical fluid chromatography-mass spectrometry coupling. The experiments were conducted with mobile phase of pure CO 2 and methanol-modified CO 2 under flow injection and chromatographic conditions. The effects of various operational parameters were characterized. The electron impact limits of detection (LODs) of the system for single ion monitoring and scan modes were determined to be 5 and 40 ng for caffeine, respectively. These LODs are 2.5 to 25 times better than previous reported estimates. Sensitivity was found to be highly dependent on the modifier percentage with 4% methanol-modified C0 2 Yielding optimal results. Separations of phenylurea pesticides and steroids are shown as demonstrations of system utility. Background subtracted electron impact spectra were artifact-free and comparable with on-line library spectra.

Simple determination of relative hydrogen atom affinities by supercritical fluid chromatography/atmospheric pressure chemical ionization mass spectrometry

AbstractCoupled supercritical fluid chromatography and atmospheric pressure chemical ionization mass spectrometry was applied to estimate hydrogen atom affinities. The intensities of the M+ and MH+ peaks in the mass spectra were measured at various drift voltages (collision energies). The ratios of the two peaks were plotted against the drift voltages to obtain threshold drift voltages. The threshold drift voltages of polycyclic aromatic hydrocarbons were plotted and found to be proportional to the values of reported hydrogen atom affinities. The value for acenaphthylene was estimated to be 292.9 kJ mol−1 from this relationship.

Supercritical Fluid Chromatography of Garlic (Allium sativum) Extracts with Mass Spectrometric Identification of Allicin

Supercritical fluid chromatography-mass spectrometry has been used successfully to identify allicin (2-propene-1-sulfinothioic acid S-2-propenyl ester), the predominant thiosulfinate in freshly cut garlic (Allium sativum). A low oven temperature (50 degrees C) and low restrictor tip temperature (115 degrees C) were needed in order to obtain a chemical ionization (CI) mass spectrum of allicin with the protonated molecular ion, m/z 163, as the major ion. The effects of tip temperature on the CI mass spectrum of allicin are presented.

The direct combination of HPLC solute focusing with supercritical fluid chromatography and mass spectrometry to enhance sensitivity and improve identification of trace components in polar solvent extracts

AbstractA system for combining normal and reversed phase high‐performance liquid chromatography solute focusing with packed column supercritical fluid chromatography and supercritical fluid chromatography–mass spectrometry has been developed. The technique has been used to identify paracetamol and stanozolol in spiked plasma extracts and its utility for the analysis of a sample from a process waste stream is illustrated.

Capillary column supercritical fluid chromatography/mass spectrometry of polycyclic aromatic compounds using atmospheric pressure chemical ionization

AbstractCapillary column supercritical fluid chromatography (SCF) was combined with atmospheric pressure chemical ionization (APCI) mass spectrometry through a heated pneumatic‐nebulizer interface, originally developed for liquid chromatography/mass spectrometry (LC/MS), and subsequently modified for use with supercritical fluid chromatography/mass spectrometry (SFC/MS). A high pressure syringe pump was used to pass SFC‐grade carbon dioxide, used as the mobile phase, through a capillary SFC column which was contained in an oven, maintained at 100°C. The eluent passed through the heated pneumatic‐nebulizer interface into the ionization region of the mass spectrometer with the aid of the flow of nebulizing gas. The system was optimized using benz[a]anthracene, and then applied to analyze a standard mixture of polycyclic aromatic compounds (PACs) as well as complex mixtures of PACs obtained by the fractionation of a pond sediment contaminated by coke‐oven residues. A detection limit of 40 pg was established for chrysene.

Packed-column supercritical fluid chromatography coupled with electrospray ionization mass spectrometry

A new approach to combined supercritical fluid chromatography—mass spectrometry (SFC-MS) was explored using a two-pump supercritical fluid chromatograph, and a packed column with the outlet directly interfaced to an electrospray (ES) ion source attached to a single quadrupole mass spectrometer. The experimental set-up is described and preliminary results are reported for mobile phase flow-rates in the range 0.15–1 ml/min, using CO 2 modified by the addition of 1–30% (v/v) of a polar organic solvent. The combined system has a greater potential for the analysis of polar molecules by MS than earlier SFC-MS instruments that utilized capillary column SFC directly coupled to the ion source of a chemical ionization mass spectrometer. A liquid-phase ionization process was utilized for solute ion formation, and it could be applied to the determination of high-mass and polar molecules separated by packed column SFC; however, the MS response is dependent on the mobile phase composition and the SFC-ES-MS instrument is still limited to the determination of low-mass samples owing to cold trapping on some critical surfaces.

Determination of chlorinated pesticides by capillary supercritical fluid chromatography—mass spectrometry with positive- and negative-ion detection

An interface between a capillary supercritical fluid chromatograph and a double-focusing mass spectrometer was developed. Modification of the standard electron ionization (EI)-chemical ionization (CI) combination ion source was necessary to obtain useful mass spectra with negative-ion detection. A detection limit in the lower nanogram range of the chlorinated pesticides (DDT and dieldrin) was found irrespective of the mode of detection. Positive-ion methane CI resulted in a relatively abundant [M+ H] + ion, whereas positive-ion isobutane and ammonia CI appeared not to be amenable to the detection of chlorinated pesticides. The EI-charge exchange mass spectra of the investigated pesticides generally did not match the library mass spectra. In the negative-ion mode, CO 2 was an efficient moderating gas giving relatively large amounts of M −·, in addition to some fragment ions. More fragmentation was observed when N 2O replaced CO 2 as the mobile phase. No major effects on the mass spectra, obtained by using pure mobile phase, were observed on adding methane, isobutane or ammonia.

Characterization of fuels by multi-dimensional supercritical fluid chromatography and supercritical fluid chromatography—mass spectrometry

A multi-dimensional supercritical fluid chromatographic (SFC) system was evaluated for the determination of saturated compounds, alkenes, mono-, di- and triaromatics and polar compounds in diesel fuel distillates. The system consisted of three packed microcolumns, which were packed with cyano-modified silica, silica and in situ silver ion-impregnated cation exchanger. Further, an interface for SFC—electron impact MS was constructed. The application of direct fluid introduction was possible when packed microcolumns of 50 μm I.D. were employed. The different groups of organic compounds were readily separated, with the exception of alkanes/alkenes and monoaromatics. This separation became increasingly incomplete as the boiling range of the distillates was increased. Using SFC-MS, it was found that the lack of baseline separation depended solely on the tailing of the alkane/alkene peak. However, for most diesel distillates, only a minor part of the alkane/alkene peak co-eluted with the monoaromatics. In addition, examination by SFC-MS provided data for the proper selection of integration limits. The determination of aromatics was in good agreement with the results obtained using the HPLC method IP 391/90.

Supercritical fluid chromatography/mass spectrometry using a quadrupole mass filter/quadrupole ion trap hybrid mass spectrometer with external ion source

The combination of capillary supercritical fluid chromatography (SFC) and ion trap mass spectrometry using an external, differentially-pumped ion source is described. This was accomplished using a capillary SFC instrument with direct, on-column injection, and a custom-built, direct-introduction interface to a quadrupole mass filter/ion trap (Q/trap). The hybrid mass spectrometer was equipped with a standard EI/CI ion source and operated with conventional ion trap detector (ITD) electrodes and electronics

Off-line supercritical fluid chromatography/plasma desorption mass spectrometry for simple mixture characterization

Supercritical fluid chromatography/mass spectrometry (SFC/MS) is a powerful tool for the characterization of less volatile, complex mixtures. Unfortunately, on-line SFC/MS instrumentation is relatively expensive, and instrument time is limited. Here we describe an investigation of off-line SFC/plasma desorption mass spectrometry (PDMS) for the characterization of relatively simple mixtures. As an example of the potential of this approach, PD mass spectra of individual oligomers from a mixture of propoxylated dimethylpyrazoles are presented. The mixture was separated by capillary SFC with ultraviolet (UV) absorbance detection, individual peaks were collected on PDMS foils, and the foils were subjected to PDMS analysis. A variety of PDMS foils were compared, and NaI-pretreated, nitrocellulose-coated, aluminized-mylar foils provided the best results for the mixtures investigated in this work. Thirteen nanograms of an ethoxylated standard provided a signal-to-noise ratio of 3. The reproducibility of the overall method, as implemented here with manual collection, was relatively poor. The relative standard deviation of the PDMS response for an alkyl-phenol ethoxylate standard was 26%. Off-line PDMS characterization of a non-UV-absorbing compound, sucrose octamyristate, is also demonstrated. The retention time of the compound of interest is determined during an SFC separation using flame ionization detection. During a second separation, the detector flame is extinguished and the PDMS foil is held above the detector at the appropriate retention time. While limited in its ability to resolve closely eluting components, the off-line approach does provide greater flexibility and potentially greater mass range than conventional on-line SFC/MS. This approach also has the potential to provide the majority of SFC users, who do not have on-line SFC/MS capabilities, with a relatively straightforward method for obtaining mass spectral information on important peaks in an SFC separation.

Characterization of N-linked glycans by supercritical fluid chromatography—mass spectrometry

N-Linked glycans have been characterized by supercritical fluid chromatography (SFC) and SFC-MS using positive- and negative-ion chemical ionization. Four common oligosaccharide derivatives have been prepared and their chromatographic properties assessed on three SFC columns of varying polarity. Carbon dioxide has been used as the SFC mobile phase, with ammonia or CO 2 added to the ion source for positive-and negative-ion chemical ionization, respectively. Direct SFC-MS interfacing allows the analytical manipulations of single-ion monitoring, total-ion plots, background subtraction, library searches, and spectral reconstruction algorithms. Positive ammonia chemical ionization yields abundant molecular-weight information, (MH) +, and (MNH 4) + with little or no fragmentation. To capitalize on sensitivity, samples were prepared with the pentafluorobenzyl aminobenzoate reagent, acetylated, and analyzed by SFC-NICI-MS. This modification improves column efficiency and resolution and greatly enhances detecting sensitivity. These “soft” ionization conditions provide abundant molecular-weight-related anions for collision-induced dissociation and subpicogram detection.

Characterization of glycosphingolipids by supercritical fluid chromatography-mass spectrometry

Gangliosides have been characterized by supercritical fluid chromatography—chemical ionization mass spectrometry (SFC-CIMS) as permethyl and pertrimethylsilyl derivatives, using carbon dioxide as the SFC mobile phase and CI reagent gas. Ganglioside classes and ceramide heterogeneity within each class are well resolved by SFC. Direct SFC-interfacing allows the analytical manipulations of single-ion monitoring, total-ion plots, background subtraction, library searches, and spectral reconstruction algorithms. Addition of ammonia to the CI ion chamber (NH 3 as a CI reagent gas) yields abundant molecular-weight-related ions, (MH) + and (MNH 4) + from analyte derivatives. Substitution of methanol for ammonia yields considerable parent-ion fragmentation, providing structural information on carbohydrate sequence, fatty acid, and sphingoid components. Under these latter conditions a unique α-cleavage fragment is observed which differentiates fatty acid from sphingosine heterogeneity. For ganglioside samples, the carboxyl group of neuraminyl residue(s) have been esterified with pentafluorobenzyl bromide and the products analyzed by negative ion chemical ionization MS. This modification improves chemical selectivity and greatly enhances detecting sensitivity. These “soft” ionization conditions provide abundant molecular-weight-related anions for collision-induced dissociation and subpicogram detection.

Analysis of veterinary drugs using supercritical fluid chromatography and supercritical fluid chromatography—mass spectrometry

Packed-column supercritical fluid chromatography has been used for the separation of four veterinary antibiotics (levamisole, furazolidone, chloramphenicol and lincomycin) on an amino-bonded stationary phase utilizing carbon dioxide with methanol modifier as the mobile phase. The effect of change of modifier identity was also studied. Packed-column supercritical fluid chromatography—mass spectrometry employing both moving belt and modified thermospray was also studied using these compounds.

Analysis of sulphonamides using supercritical fluid chromatography and supercritical fluid chromatography—mass spectrometry

Packed-column supercritical fluid chromatography has been used for the separation of mixtures of sulphonamides on silica and amino-bonded stationary phases utilizing carbon dioxide with methanol modifier as the mobile phase. The effect of modifier concentration, column pressure and modifier identity on retention was also studied. Packed-column supercritical fluid chromatography—mass spectrometry (SFC—MS) of these mixtures utilizing both moving-belt and modified thermospray interfaces was also studied. The identification of sulphamethazine in a spiked porcine kidney extract was performed by SFC—MS using the moving-belt interface.

Characterization of low molecular weight poly(acrylic acid) samples by capillary supercritical fluid chromatography and capillary supercritical fluid chromatography-mass spectrometry

Low molecular weight poly(acrylic acid) (PAA) samples were derivatized to increase their solubilities in the supercritical mobile phase, CO2. tert-Butyldimethylsilyl ester derivatives provided better chromatographic performance and molecular weight range than did trimethylsilyl or methyl esters. Individual oligomers were resolved through approximately n = 28. Higher oligomers, up to approximately n = 45 (corresponding to an underivatized molecular weight of more than 3300), were eluted from the column but were not resolved. Ammonia chemical ionization and electron ionization supercritical fluid chromatography–mass spectrometry data revealed that the PAA terminal groups of the samples studied were sulfonate and hydrogen.

Separation of oligosaccharides by capillary supercritical fluid chromatography and analysis by direct coupling to high-resolution mass spectrometer: Application to analysis of oligomannosidic N-glycans

Supercritical fluid chromatography separations and supercritical fluid chromatography chemical ionization mass spectrometry analysis of permethylated and pertrimethylsilylated oligosaccharides are reported. Supercritical fluid chromatography was carried out using a DB-5 coated capillary column with carbon dioxide as a mobile phase. Peralkylated oligosaccharides were detected by flame ionization and by chemical ionization mass spectrometry using the GC interface. Analysis of permethylated malto-oligosaccharides, as well as oligomannosides from mannosidosis, was achieved by chemical ionization mass spectrometry with ammonia and provided the pseudo-molecular ions (M+H) + and (M+NH 4) +, in addition to some other fragments which allow interpretations of the structure of different oligosaccharides. The good resolution and sensitivity obtained emphasize the potential of supercritical fluid chromatography mass spectrometry for rapid separations and analysis of complex glycan mixtures.

Separation of malto-oligosaccharide derivatives by capillary supercritical fluid chromatography and supercritical fluid chromatography-mass spectrometry

Pressure-programmed, capillary supercritical fluid chromatography (SFC) can be used to separate silylated malto-oligosaccharides of degree of polymerization (d.p.) 1 to beyond 20 in a single analysis