Water-soluble organic compounds (WSOC) often represent a large fraction of the total organic mass found in the atmospheric aerosol. They play a very important role in determining the ability of aerosol particles to act as cloud condensation nuclei (CCN), influencing cloud and fog formation and cloud albedo. Molecular characterization of WSOC in fogwater samples was achieved using a twostage ion-trap mass spectrometer equipped with electrospray ionization (ESIMS/MS). Negative ionization conditions in the electrospray interface finalized our characterization of the acidic fraction of WSOC that comprises both monoand di-carboxylic acids and polycarboxylic acids for which a similarity was suggested with naturally occurring humic (or fulvic) acids, and which are sometimes referred to in the literature as humic-like substances (HULIS). Molecular structure elucidation was accomplished using several model compounds and exploiting mass spectral resolution for compound separation. Single compound identification was attempted by recording typical MS/MS fragmentation pathways of model substances and comparing them with actual sample pathways in order to establish specific correspondences. Besides this spectrum-matching identification process, MS/MS interpretation led to several hypothetical structures for HULIS, extending the comprehension of their chemical nature. Suwannee River fulvic acid, proposed as a suitable model for representing the complex mixtures of HULIS in cloud and water aerosol extracts, was also analyzed, and the data obtained were compared with those from WSOC.

A new LC/MS method for the determination of organophosphorus pesticides in water, based on the use of direct-electron ionization (EI) interface, is presented. Direct-EI is a new device that, in a very simple fashion, couples a nano-HPLC system with a mass spectrometer equipped with electron ionization capability. The nanoscale liquid flow allows for a direct introduction of eluate into the ion source and, after nebulization, for its ionization under typical EI conditions. Library-matchable EI spectra are generated for a choice of full scan or SIM detection of the analytes. In our case, a selection of organophosphorus pesticides, commonly distributed in local sugar beet cultivation, were considered. The new interface permits a very sensitive detection of the analytes in a wide range of linear response (0.09-9 ng). When applied to a real sample, the method allowed detecting four different pesticides at a concentration level of approximately 3 ng x L(-1).

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. They are the extremes of two different technical approaches: The first one typically employs very high pressure for the efficient separation of analytes dissolved in a sometimes complex liquid phase; the second one, a sophisticated detector for chromatography, measures the mass-to-charge ratio of the analytes and operates at a very high vacuum, a rarefied gas phase with no tolerance for extraneous substances. The characteristics of HPLC and EIMS are often seen as incompatible: The effort of achieving and maintaining the high vacuum required for mass spectrometry operation is in contrast with the intrinsic nature of HPLC, predominantly operating at high solvent flow rates. In addition, the low tolerance of mass spectrometers for non-volatile mobile phase components contrasts with a HPLC dependence on non-volatile buffers to achieve high-resolution separations. The two techniques, which in principle appear totally incompatible, may nevertheless show an impressive number of overlapping applications. Small to medium sized molecules, typically under 1000 u, that for several reasons are suitable for HPLC analysis, can generate highly informative, reproducible, library matchable EI mass spectra for an easier identification and characterization. Thousands of these compounds can be found in many different areas of environmental, biological, or pharmaceutical interest. Therefore, a single analytical tool that combines the two techniques without limiting their potential is highly desirable. Today, most of the commercially available HPLC/MS interfaces are based on the atmospheric pressure ionization technique (API), namely electrospray (ESI) and atmospheric pressure chemical ionization (APCI) [1,2,3,4] in which the ionization of the sample is obtained at atmospheric pressure in the liquid phase and only the ionic species are then admitted into the high vacuum analyzer region. This particular ionization process is considered soft in terms of internal energy, with no fragmentation normally observed. Polarity is a key factor for a satisfying response of ESI and APCI interfaces. Electron ionization, because of the higher internal energy involved, produces several neutral and ionic fragments in a peculiar combination of abundance and mass-to-charge ratio characteristic of each compound as a real chemical fingerprint. EI itself is n...

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