Arnaldo Berloni

Large volume injection of acidic pesticides by reversed-phase micro high-performance liquid chromatography

Modern liquid chromatography-mass spectrometry interfaces often require a limited intake of mobile phase to work properly. Packed capillary columns combine high chromatographic efficiency, reduced flow-rate and an appreciable reliability and can be successfully employed in such applications. Acidic pesticides, a group of important compounds widely used in agriculture and often encountered as environmental pollutants, are positively analyzed by reversed-phase HPLC. The combination of micro-HPLC and particle beam mass spectrometry offer a powerful tool for their determination at very low concentrations. However, any detection limit obtained by this instrumentation is impaired by the constraint of a very small injection volume compatible with a narrow-bore column. In this paper, a procedure based on large volume injection is presented. This procedure is capable of increasing up to 800 times the volume of sample that can be injected into a packed capillary column. Seventeen acidic pesticides were selected for this study representing most of the compound classes commonly found in several environmental matrices. This method differs from previous attempts because of the acidic dissociation in water which may interfere with a correct solute focusing. The larger sample availability consistently improved the method sensitivity based on a LC-MS technique.

Cold solid-phase microextraction method for the determination of volatile halocarbons present in the atmosphere at ultra-trace levels.

Anthropogenic volatile halocarbons are compounds of great enviromnental concern because of their involvement in global change phenomena. They are present in the atmosphere at concentration levels in the order of parts per trillion by volume. The chosen analytical method for their determination is capillary gas chromatography coupled to mass spectrometry, preceded by an enrichment step on suitable adsorbent resins. The method here presented makes use of the solid-phase microextraction as a pre-analytical technique, using sub-ambient temperature in order to enhance the retention capability of the fiber coating. The proposed method was evaluated in terms of extraction efficiency, linearity, reproducibility, andlimits of detection. Results obtained showed that trace atmospheric halocarbons are detectable even when enriching very small air sample volumes. A good chromatographic resolution is obtained as a consequence of the extremely low injection volume. Finally a standard GC-MS instrumentation equipped with a simple split-splitless injector was employed, thus avoiding the use of expensive dedicated apparatus. The method was also applied to the analysis of actual samples collected both in remote, and in semi-remote sites.

New Approach for the Analysis of Acidic Pesticides in Water by LC/MS with a Particle Beam Interface.

A new method for the determination of 18 acidic pesticides in water by liquid chromatography/mass spectrometry is presented. A liquid-solid extraction procedure for the isolation of the pesticides from the aqueous samples was employed. The method, which avails of a micro-flow rate particle beam interface, offers improved performance for the analysis of heat-sensitive compounds such as phenoxy acid herbicides. The new technique combines the benefits of a reduced mobile-phase flow rate (1-5 μL/min) with a modified vaporization surface inside the ion source of the mass spectrometer. The electron impact ion source was covered with a Teflon layer, which has been proven to minimize compounds decomposition and adsorption. The improved vaporization of thermally unstable substances, accomplished by the modified surface, allows a higher signal response and an accurate reproduction of the original chromatographic profile. Electron impact ionization allows almost unambiguous identification of the analytes. The liquid chromatography, carried out with a C18 packed capillary column, was optimized to allow the injection of larger sample volumes, thus improving method sensitivity for trace level pollutants. The detection limits were in the range of 0.1-1 ppb, which is a considerable improvement in the analysis of these compounds with mass spectrometric detectors.

Generation of split-flow micro-gradients for capillary HPLC

SummaryThe generation of a micro-gradient for micro HPLC capillary columns is described. The system used is a modified and improved version of a split flow gradient elution device. Gradient tests have been performed and have shown good reproducibility under all conditions. The system has been successfully coupled with a particle beam LC-MS interface and the analysis of a mixture of twenty seven basic or neutral pesticides is reported.

Determination of acidic chlorinated pesticides in water : Comparison of official EPA method 515.1 and liquid-solid extraction HPLC/UV and HPLC/PBMS analyses

SummaryA comparison of the official EPA method 515.1 for determination of chlorinated acidic pesticides and a modification of it is illustrated. Extraction of the analytes from water and their determination and quantitation is by gas chromatography-electron capture detection (GC-ECD), liquid chromatography-UV detection and liquid chromatography-particle beam mass spectrometry. Although HPLC-PBMS was found to be less sensitive than the GC-ECD method, it was, nevertheless, more sensitive than HPLC-UV. The modified method is simpler, quicker and allows more accurate determination of pesticides in aqueous samples.

ANALYSIS OF VOLATILE AROMATIC COMPOUNDS IN HEAVY FUEL OILS USING PURGE AND TRAP EXTRACTION AND A GAS CHROMATOGRAPHIC–MASS SPECTROMETRIC TECHNIQUE

The volatile fraction of heavy fuel oils used in thermal power plants is characterized by the presence of trace amounts of potentially carcinogenic compounds, i.e. benzene and toluene, ethylbenzene and the xylenes (BTEX). In this paper, an original methodology for the determination of these compounds in such a complex matrix is presented. It consists of a capillary gas chromatographic-quadrupole mass spectrometric method preceded by the extraction and enrichment of the substituted benzenes by using a “purge and trap” technique. Results obtained analyzing heavy fuel oil actual samples are reported as well.