Two-step Laser Mass Spectrometry Research Articles

Analysis of water contaminants and natural water samples using two-step laser mass spectrometry

The applicability of two-step laser mass spectrometry (L2MS) to the analysis of water contaminants and environmental water samples is demonstrated. First, the ionization characteristics of a selection of naphthyl and carbamate pesticides and of phenol were determined. The ion signal of all compounds increased with ionization laser pulse energy, within the investigated range (20-200 microJ). Ion yields relative to an internal standard, benz[alanthracene, reached 30% for naphthyl pesticides ionized at 225 nm and 2-8% at 266 nm. At 266 nm, similar relative ion yields were found for phenol. Carbamate pesticides showed lower relative ion yields at all wavelengths, by a factor of approximately 10-100, but higher relative ion yields, on the order of 1%, were obtained when using short (ps) laser pulses for ionization. These data allow one to estimate the detection limits of these analytes in a variety of matrixes once they are known for one of the compounds. Second, the quantitative analysis of carbaryl, phenol, and polycyclic aromatic hydrocarbons in rainwater is demonstrated. The aqueous samples were frozen to permit direct L2MS analysis of organic pollutants without tedious sample preparation. Detection limits were in the low-microgram per liter concentration range and recoveries of phenol from spiked rainwater samples were above 90%. The specific advantages are exemplified with the investigation of dynamic washout processes of atmospheric organic pollutants with a resolution of 0.01 mm of precipitation.

Laser Mass Spectrometric Analysis of Organic Atmospheric Aerosols. 2. Elucidation of Urban Air Pollution Processes

The dynamic behavior of aerosol-bound polycyclic aromatic hydrocarbons (PAHs) and other polycyclic aromatic compounds (PACs) in urban air was studied over the course of several whole days, both next to a street with heavy traffic and in a city park. Two-step laser mass spectrometry, a highly sensitive and selective technique, allowed measurements with 15 min time resolution. Large variations in particle concentration and chemical composition were observed, reflecting the contributions from Diesel trucks and gasoline-powered cars to urban aerosols. These sources were clearly identified using specific mass spectral patterns. Photochemically induced decay of oxygenated polycyclic aromatic hydrocarbons (OPAHs) was observed to occur within only a few hours. Rapid speciation of aerosol-bound organic carbon is now possible to complement data on routinely monitored atmospheric pollutants.

Laser Mass Spectrometric Analysis of Organic Atmospheric Aerosols. 1. Characterization of Emission Sources

Carbonaceous aerosol particles stemming from combustion processes play a key role in air pollution. Major emission sources include Diesel vehicles, gasoline vehicles, residential heating, wood fires, and cigarettes. The chemical characterization of the particles is essential to the identification of their origin. This task can be accomplished using two-step laser mass spectrometry (L2MS). Only small sample quantities are necessary, and the measurements can be performed within minutes. L2MS was found to be a valuable alternative to more laborious chemical analysis techniques that often require extensive sample preparation. Tracer mass spectral patterns were identified, notably based on specific polycyclic aromatic hydrocarbons (PAHs) and other polycyclic aromatic compounds (PACs). Their specificity allows the identification of different particle emission sources at sites of exposure.

Évolution de la teneur en composés aromatiques des aérosols urbains au cours d'une journée. Étude par spectrométrie de masse à deux lasers

Laser desorption/laser photoionization mass spectrometry (two-step laser mass spectrometry, L2MS) is a powerful tool for the selective analysis of particle-bound organic compounds. After infrared laser-induced thermal desorption, the analytes are photoionized by an ultraviolet laser pulse. The ions are then mass separated and detected in a time-of-flight mass spectrometer. The main feature of this analytical method is an excellent sensitivity, allowing the direct analysis of very amail quantities of particles collected on a filter. This allowed us to follow the temporal development of selected polycyclic aromatic hydrocarbons on urban aerosol samples with only 15 minutes time resolution. Data obtained over the course of one day in February 1998 is presented. The temporal behavior was found to be quite different for different mass spectral peaks, which may be due to different emission sources.

Time-resolved analysis of particle-bound aromatic compounds in urban air using two-step laser mass spectrometry

Time-resolved analysis of particle-bound aromatic compounds in urban air using two-step laser mass spectrometry

Laser Mass Spectrometric Analysis of Polycyclic Aromatic Hydrocarbons with Wide Wavelength Range Laser Multiphoton Ionization Spectroscopy

In many analytical techniques, 1+1 resonance-enhanced multiphoton ionization (1+1 REMPI) is used because it is an efficient and optically selective soft ionization method. While 1+1 REMPI of jet-cooled molecules has been extensively studied, little has been reported so far about this mechanism as it is used in analytical techniques, that is, in the cases where the molecules are not jet-cooled and where widely varying ionization wavelengths are employed. We used two-step laser mass spectrometry (L2MS) to study the wavelength (238-310 nm) dependence and the laser pulse energy dependence of the ion yield for 17 polycyclic aromatic hydrocarbons (PAHs). We discuss how these data allow prediction of the efficiency of 1+1 REMPI for a given compound. These advances open new perspectives for better understanding the L2MS spectra obtained directly from complex mixtures such as environmental samples.

Detection of organic compounds on Mars

McKay et al. detected polycyclic aromatic hydrocarbons (PAHs) in Martian meteorite ALH 84001 by two-step laser mass spectrometry. From the presence of PAHs, together with other results, they concluded that there were past life of Mars. On the other hands, no organisms nor organic compounds were detected in Martian regolith in Viking experiments in 1976. In order to obtain solid evidence for organisms or bioorganic compounds compounds on Mars, further analyses of Martian samples are required. There may be four classes of organic compounds on Mars, which are (i) organic compounds abiotically formed from primitive Mars atmosphere, (ii) Organic compounds delivered out of Mars, (iii) Organic compounds biotically formed by Mars organisms, and (iv) Organic compounds abiotically formed from the present Mars atmosphere. Possible organic compounds on Mars and analytical methods for them are discussed.

Analysis of Polycyclic Aromatic Hydrocarbons in Kerogens Using Two-Step Laser Mass Spectrometry

Kerogen-bearing rocks from the Green River, Phosphoria, and Mowry formations were analyzed for polycyclic aromatic hydrocarbons (PAHs) using two-step laser mass spectrometry (L2MS). This method allows sensitive analyses to be carried out within minutes, and samples can be introduced into the instrument directly without pretreatment or processing. L2MS spectra were recorded from intact rocks and rock powder as well as from demineralized samples using a well-established acid digestion procedure to isolate the kerogen. The main findings were as follows: (i) Spectra from demineralized samples and from pulverized rocks look almost identical. This similarity shows that grinding is sufficient as a sample preparation method for L2MS. Conventional acid digestion does not alter the PAH compositions of these samples. (ii) For immature and marginally mature samples, demineralization and grinding induce a change in the mass spectra compared to data taken from fracture surfaces of intact rock. This preliminary study shows the potential usefulness of L2MS for direct chemical analysis of complex materials such as kerogen; it may be useful to distinguish among kerogens of different maturities.

Microprobe two-step laser mass spectrometry as an analytical tool for meteoritic samples

Microprobe two-step laser mass spectrometry (μL2MS) is a new mass spectrometric method in which the two essential steps of any mass spectrometric analysis, vaporization and ionization, are carried out using two independent laser sources. In the first step, the output of a pulsed infrared laser is focused on the sample to cause rapid heating in the spot area illuminated, which is typically 40 μm by 40 μm. In the second step, the output of a pulsed ultraviolet laser causes (1+1) resonance-enhanced multiphoton ionization (REMPI) of those desorbed neutral molecules that (1) are able to absorb this UV wavelength and (2) whose ionization potential is less than the energy of two photons of this UV wavelength. The resulting ions are then mass analyzed in a reflectron time-of-flight apparatus. Under suitable conditions fragmentation can be avoided in both the vaporization and ionization steps so that μL2MS can be applied to the analysis of a mixture of molecules. Applications of μL2MS to meteorite samples are presented as a means of detecting trace amounts of certain organic molecules present in complex materials without prior sample preparation, extraction, purification, and separation steps. Moreover, this analysis can be carried out with micrometer spatial resolution so that in favorable cases the presence or absence of certain molecules can be correlated to mineralogical features of the sample.

Spatially Resolved in-Situ Analysis of Polymer Additives by Two-Step Laser Mass Spectrometry

Two-step laser mass spectrometry has been employed for the direct in-situ analysis of a variety of additives in different polymers. Because of the high sensitivity and optical selectivity of this approach, mass spectra can be obtained directly from the polymer material. The effects of CO2 laser irradiation (λ = 10.6 μm) on samples of poly(oxymethylene) (POM), poly(vinyl chloride) (PVC), polypropylene (PP), and poly(ethylene terephthalate) (PET) and the mechanism of additive desorption have been examined. Several hydroxyphenylbenzotriazole (Tinuvin) UV stabilizers as well as a phenolic antioxidant (Santo White) were successfully detected in typical industrial polymers. The detection limit for Santo White antioxidant in POM was found to be as low as 28 ppm. Finally, depth profiling by stepwise CO2 laser ablation was carried out for a POM injection bar containing 0.1 wt % antioxidant. These spatially resolved measurements established that the near surface concentration of antioxidant was 40% lower than in th...

Chemical Analysis of Cancer Therapy Photosensitizers by Two-Step Laser Mass Spectrometry

We have applied two-step laser mass spectrometry (L2MS) to the qualitative chemical analysis of porphyrin-derived photosensitizer dyes used for detection and photodynamic therapy of cancer. The only ionization technique applied so far to these low-volatility compounds had been fast atom bombardment (FAB), which suffers from problems associated with cluster formation of the porphyrins upon FAB ionization. From FAB and chromatography data, the existence of porphyrin dimers, trimers, and oligomers in commercial photosensitizers was concluded to be crucial for tumor localization, but it is possible that clustering or preformed van der Waals aggregates gave rise to these results. L2MS indicates that commercially available hematoporphyrin derivative and Photofrin II contain no detectable amounts of covalently bound porphyrin oligomers. Synthetic porphyrin dimers and trimers could be unambiguously detected by L2MS.

Application of two-step laser mass spectrometry to the analysis of polynuclear aromatic hydrocarbons in contaminated soils

Contaminated site remediation is a multistage process that commences with an initial indication of contamination and is concluded with the long-term monitoring of remedial measures. Critical to the successful completion of the process is the informative nature of the site assessment data. This information ultimately determines the level of confidence with which risks to human health and the environment can be adequately assessed and managed. In this paper, the authors describe initial investigations into the use of laser desorption laser photoionization time-of-flight mass spectrometry for the direct determination of PAH analytes in solid waste matrices. This relatively new technique has potential as an on-site field screening tool, offering the ability to determine a wide variety of organics contained in a wide variety of matrices. It involves a two-step process in which the first laser desorbs primarily intact neutral molecules from the sample and the second laser causes [open quotes]soft ionization[close quotes] of selected classes of compounds which are identified by time-of-flight mass spectrometry. This method of mass analysis, with its advantages of rapid, multiplexed data acquisition is ideally interfaced to the pulsed lasers used for sample desorption and photoionization. 26 refs., 2 figs.

Organic compounds in the Forest Vale, H4 ordinary chondrite

We have analyzed the H4 ordinary chondrite Forest Vale for polycyclic aromatic hydrocarbons (PAHs) using two-step laser mass spectrometry (L 2MS) and for amino acids using a standard Chromatographic method. Indigenous PAHs were identified in the matrices of freshly cleaved interior faces but could not be detected in pulverized silicates and chondrules. No depth dependence of the PAHs was found in a chipped interior piece. Amino acids, taken from the entire sample, consisted of protein amino acids that were nonracemic, indicating that they are terrestrial contaminants. The presence of indigenous PAHs and absence of indigenous amino acids provides support for the contention that different processes and environments contributed to the synthesis of the organic matter in the solar system.

Microscopic organic analysis using two-step laser mass spectrometry: application to meteoritic acid residues

We have developed a mlcroanalytlcal Instrument to analyze the organk constltuonts of partlculates and Inhomogeneous samples wtth aspaUal ramlutbn ol approxlmatdy 40 pm. Om method, two-step laser desorptlon/laser lonlzatlon mass spectrometry (L2MS), uses an Infrared laser to volatlllze constttuent mokuks Intact and an ultraviolet law to lonlze desorbed molecules In a selective manner with Imle or no frcrqrwntcrtion. In partlcular, our lnrtrwnent Is currently tuned to detect polycycllc aromatic hydrocarbons (PAHs), whlch have a strong aboorptlon cross section at the lonlzatlon laser wavelength of 266 m. The detection lhnlt of our Instrmnt k approxbnately 6 hnol for the compound wonene (CUH,*). We demonstrate the use of thk Instrument to analyze acld reddues from SIX motrltw the samples cor#kt of particles that are about 200 pm In dlameter. Quantltatlve and qualltatlve trends In PAH comporltlon are IdentHled for different classes of metwrltes. SgnHIcant dMeronces are seen between the carbonaceous and ordlnary chondrftes. Moreover, wlthln a rlngk clam of ordlnary chondrltes we see an Increase h dkybtbn wtth Increasing petrographk type (thennal metamorphlsm).

Subfemtomole quantitation of molecular adsorbates by two-step laser mass spectrometry

Donnees sur l'analyse quantitative des molecules adsorbees en surface. Application au cas de l'ester de dimethyle de la protoporphyrine IX, de l'estradiol-β et de l'adenine