Liquid phase IR-MALDI and differential mobility analysis of nano- and sub-micron particles.

Infrared matrix-assisted desorption and ionization (IR-MALDI) enables the transfer of sub-micron particles (sMP) directly from suspensions into the gas phase and their characterization with differential mobility (DM) analysis. A nanosecond laser pulse at 2940 nm induces a phase explosion of the aqueous phase, dispersing the sample into nano- and microdroplets. The particles are ejected from the aqueous phase and become charged. Using IR-MALDI on sMP of up to 500 nm in diameter made it possible to surpass the 100 nm size barrier often encountered when using nano-electrospray for ionizing supramolecular structures. Thus, the charge distribution produced by IR-MALDI could be characterized systematically in the 50-500 nm size range. Well-resolved signals for up to octuply charged particles were obtained in both polarities for different particle sizes, materials, and surface modifications spanning over four orders of magnitude in concentrations. The physicochemical characterization of the IR-MALDI process was done via a detailed analysis of the charge distribution of the emerging particles, qualitatively as well as quantitatively. The Wiedensohler charge distribution, which describes the evolution of particle charging events in the gas phase, and a Poisson-derived charge distribution, which describes the evolution of charging events in the liquid phase, were compared with one another with respect to how well they describe the experimental data. Although deviations were found in both models, the IR-MALDI charging process seems to resemble a Poisson-like charge distribution mechanism, rather than a bipolar gas phase charging one.

Detection of volatile organic compounds in the headspace above mold fungi by GC-soft X-radiation-based APCI-MS.

Mold fungi on malting barley grains cause major economic loss in malting and brewery facilities. Possible proxies for their detection are volatile and semivolatile metabolites. Among those substances, characteristic marker compounds have to be identified for a confident detection of mold fungi in varying surroundings. The analytical determination is usually performed through passive sampling with solid phase microextraction, gas chromatographic separation, and detection by electron ionization mass spectrometry (EI-MS), which often does not allow a confident determination due to the absence of molecular ions. An alternative is GC-APCI-MS, generally, allowing the determination of protonated molecular ions. Commercial atmospheric pressure chemical ionization (APCI) sources are based on corona discharges, which are often unspecific due to the occurrence of several side reactions and produce complex product ion spectra. To overcome this issue, an APCI source based on soft X-radiation is used here. This source facilitates a more specific ionization by proton transfer reactions only. In the first part, the APCI source is characterized with representative volatile fungus metabolites. Depending on the proton affinity of the metabolites, the limits of detection are up to 2 orders of magnitude below those of EI-MS. In the second part, the volatile metabolites of the mold fungus species Aspergillus, Alternaria, Fusarium, and Penicillium are investigated. In total, 86 compounds were found with GC-EI/APCI-MS. The metabolites identified belong to the substance classes of alcohols, aldehydes, ketones, carboxylic acids, esters, substituted aromatic compounds, terpenes, and sesquiterpenes. In addition to substances unspecific for the individual fungus species, characteristic patterns of metabolites, allowing their confident discrimination, were found for each of the 4 fungus species. Sixty-seven of the 86 metabolites are detected by X-ray-based APCI-MS alone. The discrimination of the fungus species based on these metabolites alone was possible. Therefore, APCI-MS in combination with collision induced dissociation alone could be used as a supervision method for the detection of mold fungi.

Spot variation fluorescence correlation spectroscopy by data post-processing.

Spot variation fluorescence correlation spectroscopy (SV-FCS) is a variant of the FCS techniques which may give useful information about the structural organisation of the medium in which the diffusion takes place. We show that the same results can be obtained by post-processing the photon count data from ordinary FCS measurements. By using this method, one obtains the fluorescence autocorrelation functions for sizes of confocal volume, which are effectively smaller than that of the initial FCS measurement. The photon counts of the initial experiment are first transformed into smooth intensity trace using kernel smoothing method or to a piecewise-continuous intensity trace using binning and then a non-linear transformation is applied to this trace. The result of this transformation mimics the photon count rate in an experiment performed with a smaller confocal volume. The applicability of the method is established in extensive numerical simulations and directly supported in in-vitro experiments. The procedure is then applied to the diffusion of AlexaFluor647-labeled streptavidin in living cells.

What information is contained in the fluorescence correlation spectroscopy curves, and where.

We discuss the application of fluorescence correlation spectroscopy (FCS) for characterization of anomalous diffusion of tracer particles in crowded environments. While the fact of anomaly may be detected by the standard fitting procedure, the value of the exponent α of anomalous diffusion may be not reproduced correctly for non-Gaussian anomalous diffusion processes. The important information is however contained in the asymptotic behavior of the fluorescence autocorrelation function at long and at short times. Thus, analysis of the short-time behavior gives reliable values of α and of lower moments of the distribution of particles' displacement, which allows us to confirm or reject its Gaussian nature. The method proposed was tested on the FCS data obtained in artificial crowded fluids and in living cells.

Investigation of neuroleptics and other aromatic compounds by laser-based ion mobility mass spectrometry.

Laser-based ion mobility (IM) spectrometry was used for the detection of neuroleptics and PAH. A gas chromatograph was connected to the IM spectrometer in order to investigate compounds with low vapour pressure. The substances were ionized by resonant two-photon ionization at the wavelengths λ = 213 and 266 nm and pulse energies between 50 and 300 µJ. Ion mobilities, linear ranges, limits of detection and response factors are reported. Limits of detection for the substances are in the range of 1-50 fmol. Additionally, the mechanism of laser ionization at atmospheric pressure was investigated. First, the primary product ions were determined by a laser-based time-of-flight mass spectrometer with effusive sample introduction. Then, a combination of a laser-based IM spectrometer and an ion trap mass spectrometer was developed and characterized to elucidate secondary ion-molecule reactions that can occur at atmospheric pressure. Some substances, namely naphthalene, anthracene, promazine and thioridazine, could be detected as primary ions (radical cations), while other substances, in particular acridine, phenothiazine and chlorprothixene, are detected as secondary ions (protonated molecules). The results are interpreted on the basis of quantum chemical calculations, and an ionization mechanism is proposed.

A complex multi-notch astronomical filter to suppress the bright infrared sky.

A long-standing and profound problem in astronomy is the difficulty in obtaining deep near-infrared observations due to the extreme brightness and variability of the night sky at these wavelengths. A solution to this problem is crucial if we are to obtain the deepest possible observations of the early Universe, as redshifted starlight from distant galaxies appears at these wavelengths. The atmospheric emission between 1,000 and 1,800 nm arises almost entirely from a forest of extremely bright, very narrow hydroxyl emission lines that varies on timescales of minutes. The astronomical community has long envisaged the prospect of selectively removing these lines, while retaining high throughput between them. Here we demonstrate such a filter for the first time, presenting results from the first on-sky tests. Its use on current 8 m telescopes and future 30 m telescopes will open up many new research avenues in the years to come.

Application of laser-based ion mobility (IM) spectrometry for the analysis of polycyclic aromatic compounds (PAC) and petroleum products in soils.

The capability of laser-based IM spectrometry to detect PAC and petroleum products (oils) in model matrices, laboratory reference (LR) materials and in real-world contaminated soil samples was demonstrated. Quantitative IM investigations of PAC-doped PVC films yielded detection limits in the ppm range for single PAC. The potential of IM spectrometry for in situ analysis was demonstrated by the analysis of PAC-containing certified reference (CR) material, and of petroleum product-containing LR materials and real-world soil samples. The calibration of IM signals obtained from oil-doped LR materials was also possible, and detection of oils with concentrations below 100 mg kg(-1) was achieved. The in situ analysis of real-world contaminated soils with the IM and LIF techniques was in good accordance with ex situ reference investigations.

In situ laser-induced fluorescence (LIF) analysis of petroleum product-contaminated soil samples.

General considerations of the calibrations of in situ measurements are presented and the concept of using an "average oil" with average analysability for calibration purposes is introduced. The in situ analysis of 30 petroleum product-contaminated soil samples with laser-induced fluorescence (LIF) spectroscopy was performed. Compared to an uncontaminated laboratory reference (LR) soil, 23 soil samples exhibited significantly higher LIF signals, so that these soil samples were classified as contaminated. The repeatability and reproducibility of the in situ LIF analysis were investigated. For the calibration of the LIF data, two LR oils (a fuel oil and a crude oil) were employed. The degree of soil contamination with petroleum products ranged from the limit of detection (LOD) for LIF analysis (ca. 100 ppm), or below, to more than 10,000 ppm. The petroleum product concentrations determined with in situ LIF analysis reveal a reasonable correlation with the results of standard IR analysis after extraction of the contaminated soils.

In vivo laser-induced fluorescence detection of pyrene in nematodes and determination of pyrene binding constants for humic substances by fluorescence quenching and bioconcentration experiments.

The bioconcentration of pyrene by bacterivorous thread worms (nematodes) of the species Caenorhabditis elegans was studied with laser-induced fluorescence (LIF) spectroscopy, fluorescence imaging and a radiotracer method. The vibronic band intensities of the LIF spectra indicated that the microenvironment of pyrene in the nematodes was similar to a low-polarity solvent, and thus provided direct evidence that pyrene was accumulated in lipid-rich areas inside the nematodes. The concentration of pyrene in the nematodes was estimated from the monomer/excimer fluorescence intensity ratio. Results from this method were in fair agreement with results using 14C labeled pyrene for measuring pyrene bioconcentration. Preliminary results indicated that LIF measurements of pyrene may be possible even in single nematodes. Fluorescence microscopic observations revealed that pyrene was not adsorbed on the outside of the organisms, but was strongly concentrated in restricted areas inside the worms. In the second part of the study, the effects of six different humic substances (HS) on the bioconcentration of pyrene were investigated and sorption coefficients (KDOC) calculated from reductions in bioconcentration (KDOC(biol)) were compared with sorption coefficients measured with a fluorescence quenching technique (KDOC(flu)). The results of these two different experimental methods agreed well (with KDOC(biol) being slightly lower than KDOC(flu), indicating that the fraction of pyrene that was determined as freely dissolved by the fluorescence quenching method was comparable to the bioavailable fraction.

Determination of optical parameters for light penetration in particulate materials and soils with diffuse reflectance (DR) spectroscopy.

The results of our investigations of particulate materials (aluminium oxide, quartz sand) and "real world" soils (a brown sand and a dark brown soil) using diffuse reflectance (DR) spectroscopy are presented. The findings are discussed within the framework of Kubelka-Munk (KM) theory as a simplified description of light propagation in highly turbid media. The relation between the KM and the Lambert-Beer (LB) treatment is outlined. The KM parameters determined were the scattering and absorption coefficients (S and K, respectively), and the light penetration depths, dp(KM). It was found that in the UV/VIS spectral range the scattering coefficients of the materials investigated vary by ca. one order of magnitude (S = 6-> 100 cm-1), whereas the absorption coefficients change by more than three orders of magnitude (K = < 1-> 1500 cm-1). The different absorption and scattering properties of the materials lead to strong variations in light penetration depths from the micron into the mm regime [dp(KM) = < 20-> 3500 microns].

Fluorescence quenching of polycyclic aromatic compounds by humic substances. Part 1. Methodology for the determination of sorption coefficients.

An introduction to the methodology of fluorescence quenching measurements as an experimental tool for investigating the sorption of hydrophobic organic substances by dissolved organic matter (OM) is given. Special attention is paid to the implications of inner-filter effects (IFEs) on the determination of sorption coefficients. The essential aspects of the theoretical description of IFEs are outlined and various procedures for the IFE correction of fluorescence quenching measurements in the presence of dissolved OM are presented. Geometric parameters relevant for the quantitative description of IFE applying a 90 degrees arrangement between fluorescence excitation and detection are determined by different methods, newly developed or adapted from the literature, for the fluorescence spectrometer used in this work. Moreover, an experimental validation of the applicability of different IFE correction procedures is performed. In order to evaluate the variations of sorption coefficients that result from the use of different IFE correction procedures, the quenching of the fluorescence of the well-known polycyclic aromatic compound pyrene by a commercially available humic substance in aqueous solution is investigated. Compared to the apparent sorption coefficient, which is obtained without any IFE correction, the sorption coefficients determined with the correction of primary IFE or with the correction of primary and secondary IFE are on average ca. 40 or 60% lower. The application of different IFE correction procedures allows the determination of sorption coefficients with appropriate precision of +/- 15%.

Combination of laser-induced fluorescence and diffuse-reflectance spectroscopy for the in situ analysis of diesel-fuel-contaminated soils.

Results of our laser-induced fluorescence (LIF) and diffuse-reflectance investigations of quartz sand and different soils spiked with Diesel fuel are reported. The LIF calibration functions, which were found to be significantly different for the various matrices, and the limits of detection were determined. For excitation at lambda(ex) = 266 nm, the limits of detection obtained ranged from 7 parts in 10(6) for quartz sand to approximately 200 parts in 10(6) for dark sand with organic matter and for dark peat. Furthermore, the diffuse-reflectance spectra of the matrices in the ultraviolet-near-IR range were determined. An attempt to correlate the slopes of the LIF calibration functions with the reflectances of the matrices is presented. The obtained normalized calibration functions are well suited to take into account relevant optical soil parameters and to reduce the variability of the LIF calibration behavior significantly.

Fluorescence spectroscopy of polynuclear aromatic compounds in environmental monitoring.

The occurrence of polynuclear aromatic compounds (PAC) in the environment and experimental techniques suitable for the detection of PAC in environmental compartments are briefly reviewed. The specific requirements for on-site andin situ environmental analysis are outlined. Particular emphasis is given to fluorescence spectroscopic techniques for the investigation of humic acid- and soil-containing samples. Some examples of studies in the literature on Shpol'skii and jet spectroscopy and on laser-induced fluorescence (OF) measurements of PAC and mineral oils are highlighted. Contaminants in the environment are usually encountered as multicomponent mixtures in very complex matrices. Total fluorescence analysis in combination with the chemometrical technique of rank annihilation factor analysis (RAFA) was employed for the evaluation of a six-component PAC mixture in toluene. It was shown that even in the presence of strong spectral overlap the qualitative identification of all compounds and the reliable quantification of five substances was possible. Results are presented from our stationary and time-resolved fluorescence investigations of the interactions between pyrene and humic acid in water. The Stern-Volmer analysis showed a significant effect of pH on the static quenching efficiency which can be explained by the pH-dependent macromolecular structure of humic acids. Preliminary results from studies of the deactivation of triplet PAC and quenching of delayed fluorescence by humic acid are reported. LIF measurements of mineral oils directly from soil surfaces and of a model oil in a soil column were performed with a fiber-optic coupled multichannel spectrometer. The fluorescence intensity/ concentration relationships were established for a crude and a fuel oil; the corresponding lower limits of detection (LOD) were determined to be 0.025 and 0.125% m/m (mass/mass percentages). These detection limits are compared with realistic oil contaminations of soils. In a soil column designed to mimic fixed-bed bioreactors the distributions of fluorescence signal intensities from a perylene-doped model oil before and after water flooding were determined. These results fromin situ measurements can provide a quantitative basis for the modelling of temporal and spatial contaminants' distributions in reactor design.