In-depth performance investigation of a nano-LC gradient generator.

An innovative approach for nano-liquid chromatography (LC) gradient generation is presented. This system represents an optimized and refined version of a prototype proposed by the authors a few years ago: the current version is characterized by a new configuration that guarantees complete automation and easier operation. The core of the system is an electronically controlled, multiposition valve that hosts six loops, filled with different mobile phase compositions of increasing strength. A conventional flow rate of water is reduced at nano-scale through a split device to push the content of the on-line loop into the column. No mixing occurs between solvents inside the loops, due to the low flow rate and the reduced loop diameter. Valve actuation allows the selection of the on-line loop to obtain the solvent gradient. The evaluation of the system performance takes into account gradient accuracy, precision, delay time, shape (linear, convex, or concave), and organic solvent consumption. Results highlight the reliability and the competitiveness of the system, especially in terms of accuracy and precision. A comparison between the described system and a conventional split-based one demonstrates that the new approach reduces the solvent consumption by about 40 times, improving green chromatography and cutting laboratory costs.

Determination of endocrine disrupting compounds in marine water by nanoliquid chromatography/direct-electron ionization mass spectrometry.

We present a new method for the determination of 29 endocrine-disrupting compounds in marine water. This method is based on a solid-phase extraction preconcentration technique, followed by a nanoscale liquid chromatography/direct-electron ionization (EI) mass spectrometric analysis. Direct-EI is a novel technique for the rapid conversion of a GC/MS into an efficient and reliable LC/MS for EI detection. The capability to acquire EI mass spectra of the analytes, and to operate in selected ion monitoring mode during real sample analyses, allows certain identification and precise quantification. In addition, this method is not influenced by the polarity of the analytes and does not require different detection modes (positive and negative) for identification with API techniques. Limits of detection of the method span from 0.4 to 118.7 ng.L(-1), corresponding to an instrumental detection limit of 0.005-1.260 ng. Linear regression and recovery experiment data, together with their standard deviations, are also presented. Marine water samples were collected along the middle-western Adriatic Coast (Italy), near the shore and at the mouth of rivers and canals.

Liquid chromatography-electron ionization mass spectrometry: fields of application and evaluation of the performance of a Direct-EI interface.

A comprehensive evaluation and a thorough discussion of the fields of possible applications of the Direct-EI interface are described in this review. Direct-EI allows the direct introduction of the effluent from a capillary HPLC column into the electron ionization (EI) ion source of a mass spectrometer. Thanks to the reduced liquid intake and an in-source nebulizer, the interfacing process occurs smoothly and entirely into the ion source. No intermediate interfacing mechanisms of any sort are interposed between the column and the mass spectrometer, thus circumventing any undesired sample loss and minimizing the effort for instrument modification. Theoretically, any GC-MS system can be converted into an LC-MS for EI amenable compounds. Several parameters, crucial for a successful integration of liquid chromatography and mass spectrometry, have been considered in the evaluation of the functioning of such an interface: limit of detection, linearity of response, reproducibility, and chromatographic compatibility. Different mobile phases, also containing non-volatile buffers, were taken into account, demonstrating an outstanding separation flexibility. The entire set of experiments was carried out at different flow rates and temperatures of the ion source. The interface behavior was also tested in real world applications, with mixtures of pesticides, hormones, nitro-PAH, and endocrine-disrupting compounds, allowing picogram level detection and the possibility to record library-matchable, readily interpretable electron ionization mass spectra, for prompt compound characterization and confirmation.

Variable-gradient generator for micro- and nano-HPLC.

A new, simple device generates accurate nano- and microflow rate gradients from any conventional HPLC system. The core of the new device is represented by an electric-actuated, computer-controlled, multiposition HPLC valve. The valve hosts six reservoirs for as many different mobile-phase compositions of increasing strength. A low flow rate stream pushes the weakest solvent through the column as long as required and at the desired flow rate, until the chromatographic run is started. From this time on, the electric actuation allows one to select which reservoir will be on-line with the column and for how long, thus generating a specific solvent gradient, through a sequence of controlled segments of precise mobile-phase composition. This permits one not only to exactly reproduce the programmed slope but also to achieve different gradient shapes (i.e., linear, convex, concave) for different separation needs. The new device has proven to be reliable and reproducible even at the lowest flow rate tested (250 nL x min(-1)) and in different chromatographic conditions.