A simple and economical strategy for obtaining calibration plots for relative quantification of positional isomers of YYX/YXY triglycerides using high-performance liquid chromatography/tandem mass spectrometry.

RATIONALE: Positional analysis of intact triglycerides could provide greater insights into the link between fatty acid position and lipotoxic diseases. However, this methodology has been impeded by lack of commercial availability of positionally pure triglycerides. This work reports on a strategy for defining calibration plots for YXY/YYX triglyceride systems based on the product ion intensities in the collision-induced dissociation spectra of ammoniated precursor ions. METHODS: A set of triglycerides were synthesized and analyzed by electrospray ionization tandem mass spectrometry using an ion trap mass spectrometer. The product ion spectra of the ammoniated precursor ions were collected for 42 triglyceride systems of the form YXY/YYX, where Y represents C16:0 , C18:1(c-9) and C20:4(cccc-5,8,11,14) . Three-point calibration plots were prepared by plotting the relative abundance of the YY+ product ion vs. the relative abundance of the YYX positional isomer. RESULTS: The calibration plots were shown to give relative abundances of positional isomers accurate to within ±0.02 for most systems. Using an ion trap, under a controlled set of collision parameters, the slopes of the calibration plots can be used to compare the sensitivities of the product ion intensities to fatty acid position for various triglyceride systems. The average slopes of the calibration plots for the C16:0 , C18:1(c-9) and C20:4(cccc-5,8,11,14) systems were 0.29 ± 0.05, 0.21 ± 0.05 and 0.045 ± 0.005, respectively. CONCLUSIONS: While the presence of multiple unsaturated fatty acids tends to slightly decrease the slopes of the calibration plots, the data suggest that the sensitivities are sufficient for performing positional analysis of most triglyceride systems. However, the presence of unsaturated fatty acids that contain double bonds close to the carbonyl group, such as arachidonic acid, tends to dramatically decrease positional sensitivity.

Analysis and spectral assignments of mixed actinide oxide samples using laser-induced breakdown spectroscopy (LIBS).

In this paper, we report for the first time the identification and assignments of complex atomic emission spectra of mixed actinide oxides using laser-induced plasma spectroscopy or laser-induced breakdown spectroscopy (LIBS). Preliminary results of LIBS measurements on samples of uranium dioxide (UO2)/plutonium dioxide (PuO2) and UO2/PuO2/americium dioxide (AmO2)/neptunium dioxide (NpO2) simulated fuel pellets (or mixed actinide oxide samples) are reported and discussed. We have identified and assigned >800 atomic emission lines for a UO2/PuO2/AmO2/NpO2 fuel pellet thus far. The identification and assignments of spectral emission lines for U, Pu, and Am are consistent with wavelength data from the literature. However, only a few emission lines have been assigned with a high degree of confidence for Np compared with atomic emission data from the literature. We also indicate where atomic emission lines for Cm would most likely appear in the spectral regions shown. Finally, we demonstrate that a LIBS system with a resolving power of approximately 20,000 is adequate for analyzing complex mixtures of actinide elements within the same sample.

Determination of inorganic improvised explosive device signatures using laser electrospray mass spectrometry detection with offline classification.

The mass spectral detection of low vapor pressure, inorganic-based explosive signatures including ammonium nitrate, chlorate, perchlorate, sugar, and the constituents contained within black powder are reported using laser electrospray mass spectrometry. The ambient pressure mass spectrometry technique combining nonresonant, femtosecond laser vaporization with electrospray postionization revealed primary and secondary signatures for trace quantities of inorganic explosives. A mixture of complexation agents in the electrospray solvent enabled the simultaneous detection of vaporized cations, anions, and neutrals in a single measurement. An offline classifier discriminated the inorganic-based explosives based on the mass spectral signatures resulting in high fidelity identification.

Nonresonant femtosecond laser vaporization of aqueous protein preserves folded structure.

Femtosecond laser vaporization-based mass spectrometry can be used to measure protein conformation in vitro at atmospheric pressure. Cytochrome c and lysozyme are vaporized from the condensed phase into the gas phase intact when exposed to an intense (10(13) W/cm(2)), nonresonant (800 nm), ultrafast (75 fs) laser pulse. Electrospray postionization time-of-flight mass spectrometry reveals that the vaporized protein maintains the solution-phase conformation through measurement of the charge-state distribution and the collision-induced dissociation channels.

Analysis of amphiphilic lipids and hydrophobic proteins using nonresonant femtosecond laser vaporization with electrospray post-ionization.

Amphiphilic lipids and hydrophobic proteins are vaporized at atmospheric pressure using nonresonant 70 femtosecond (fs) laser pulses followed by electrospray post-ionization prior to being transferred into a time-of-flight mass spectrometer for mass analysis. Measurements of molecules on metal and transparent dielectric surfaces indicate that vaporization occurs through a nonthermal mechanism. The molecules analyzed include the lipids 1-monooleoyl-rac-glycerol, 1,2-dihexanoyl-sn-glycero-3-phosphocholine, 1,2-dimyristoyl-sn-glycero-3-phosphocholine, and the hydrophobic proteins gramicidin A, B, and C. Vaporization of lipids from blood and milk are also presented to demonstrate that lipids in complex systems can be transferred intact into the gas phase for mass analysis.

Nonresonant femtosecond laser vaporization with electrospray postionization for ex vivo plant tissue typing using compressive linear classification.

Laser electrospray mass spectrometry (LEMS) with offline classification is used to discriminate plant tissues at atmospheric pressure using an intense (10(13) W cm(-2)), nonresonant (800 nm) femtosecond laser pulse to vaporize cellular content for subsequent mass analysis. The tissue content of the plant within the 0.05 mm(2) laser interaction region is vaporized into the electrospray plume where the molecules are ionized prior to transfer into the mass spectrometer. The measurements for a flower petal, leaf, and stem of an impatiens plant reveal mass spectral signatures that enable discrimination as performed using a compressive linear classifier. The statistical analysis of the plant tissue samples reveals reproducibility of the data for replicate tissue samples and within a single tissue sample. A similar degree of discrimination was achieved for the green and white regions of aphelandra squarrosa (zebra plant) leaves.

Mass analysis of biological macromolecules at atmospheric pressure using nonresonant femtosecond laser vaporization and electrospray ionization.

A nonresonant femtosecond laser pulse, with an intensity of 10(13) Wcm(-2), vaporizes proteins and biomolecules intact, regardless of molecular structure, size or electronic structure for subsequent electrospray ionization and transfer into a mass spectrometer. Rapid, direct analysis from dried sample, aqueous solution and cellular material is demonstrated at atmospheric pressure using laser electrospray mass spectrometry (LEMS). Measurements are presented for lysozyme (14.3 kDa), hemoglobin from human blood, ovalbumin (45 kDa) from hen egg white and phospholipids from hen egg yolk. Mass analysis of biological material is performed without dilution, extraction or sample preparation, other than placing the biological material onto the sample plate.

Identification of explosives and explosive formulations using laser electrospray mass spectrometry.

Mass analysis is demonstrated for the detection of sub-microgram quantities of explosive samples on a metallic surface at atmospheric pressure using laser electrospray mass spectrometry (LEMS). A non-resonant femtosecond duration laser pulse vaporizes native samples for subsequent electrospray ionization and transfer into a time-of-flight mass spectrometer. LEMS was used to detect 2,3-dimethyl-2,3-dinitrobutane (DMNB), 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), 3,4,8,9,12,13-hexaoxa-1,6-diazabicyclo[4.4.4]tetradecane (HMTD), and 3,3,6,6,9,9-hexamethyl-1,2,4,5,7,8-hexaoxacyclononane (TATP) deposited on a steel surface. LEMS was also used to directly analyze composite propellant materials containing an explosive to determine the molecular composition of the explosive pellets at atmospheric pressure.

Analysis of pharmaceutical compounds from glass, fabric, steel, and wood surfaces at atmospheric pressure using spatially resolved, nonresonant femtosecond laser vaporization electrospray mass spectrometry.

Laser electrospray mass spectrometry (LEMS) is demonstrated for pharmaceutical samples at atmospheric pressure. A nonresonant, femtosecond duration laser pulse vaporizes native samples at atmospheric pressure into an electrospray plume for ionization with subsequent transfer into a time-of-flight mass spectrometer. The active ingredients in pharmaceutical tablets were detected in the presence of binders and fillers in intact formulations using LEMS. Mass spectra were also obtained for microgram amounts of the pharmaceutical compounds loratadine, oxycodone, and atenolol deposited on glass, wood, steel, and polyester fabric. The neutral capture efficiency by the electrospray plume for nonresonant laser vaporization of oxycodone and atenolol desorbed from steel is 2.4% +/- 1.5% and 0.25% +/- 0.18%, respectively. LEMS imaging of the spatial distribution of an oxycodone spot on a metal slide with resolution of 250 mum is also presented.

Mass spectrometry of intact neutral macromolecules using intense non-resonant femtosecond laser vaporization with electrospray post-ionization.

Intact, nonvolatile, biological macromolecules can be transferred directly from the solid state into the gas phase, in ambient air, for subsequent mass spectral analysis using non-resonant femtosecond (fs) laser desorption combined with electrospray ionization (ESI). Mass spectral measurements for neat samples, including a dipeptide, protoporphyrin IX and vitamin B12 adsorbed on a glass insulating surface, were obtained using an 800 nm, 70 fs laser with an intensity of 10(13) W cm(-2). No appreciable signal was detected when atmospheric matrix-assisted or neat (matrix-free) fs laser desorption was performed without ESI, indicating neutral desorption.

Discrimination of composite graphite samples using remote filament-induced breakdown spectroscopy.

Remote filament-induced breakdown spectroscopy (R-FIBS) using ultrashort laser pulses was used to measure the carbon/clay ratios between three graphite composites of different hardness at a standoff distance of approximately 6 m. Measurements using R-FIBS and femtosecond laser-induced breakdown (fs-LIBS) reveal similar selectivity and ability to excite emission. Comparison of the two stand-off techniques with optical microscopy and electron microprobe point detection confirmed the qualitative analysis capability of both femtosecond remote probing techniques. The R-FIBS technique produced more accurate results compared to fs-LIBS due to the intensity clamping nature of the filament ablation source. Measurement of the plasma temperatures for the metallic emission lines (approximately 8500 K) and the C(2) Swan lines (approximately 4500 K) suggest that the plasmas from different microdomains (clay and graphite) are not in equilibrium.