Examinando por Autor "de Jong, Gerhardus J."
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Ítem Fully Compatible and Ultra-Sensitive Micellar Electrokinetic Chromatography-Tandem Mass Spectrometry Using Sheathless Porous-Tip Interfacing(Elsevier, 2017-11-17) Moreno-González, David; Haselberg, Rob; Gámiz-Gracia, Laura; García-Campaña, Ana M.; de Jong, Gerhardus J.; Somsen, Govert W.The on-line coupling of micellar electrokinetic chromatography and mass spectrometry (MEKC-MS) is often hampered by incompatibility problems leading to reduced separation performance and unfavorable limits of detection (LODs). Here we propose a new selective and highly sensitive MEKC-MS/MS method employing a sheathless porous-tip interface in combination with a micellar phase comprised of semi-volatile surfactant molecules. Carbamate pesticides (CRBs) were selected as representative model compounds being neutral toxic pollutants potentially present at trace levels in environmental water samples. A background electrolyte of 75 mM perfluorooctanoic acid adjusted to pH 9.0 with ammonium hydroxide allowed efficient separation of 15 CRBs and appeared fully compatible with electrospray ionization (ESI)-MS. Interfacing parameters, such as the distance between the capillary tip and mass-spectrometer inlet, ESI voltage, and dry gas temperature and flow were optimized in order to attain good spray stability and high analyte signal-to-noise ratios. For CRBs the LODs ranged from 0.2 to 3.9 ng L−1 (13 nL injected, i.e., 2% of capillary volume), representing an improvement for certain CRBs of more than 300-fold when compared with conventional sheath-liquid interfacing. Good linearity (R2 > 0.99) and satisfactory reproducibility were obtained for all CRBs with interday RSD values for peak area and migration time of 4.0–11.3% and below 1.5%, respectively. Analysis of spiked mineral water showed that the new MEKC-MS/MS method allows selective and quantitative determination of CRB concentrations below the maximum residue limit of 100 ng L−1 without the need for sample preconcentration.Ítem Micellar electrokinetic chromatography–electrospray ionization mass spectrometry employing a volatile surfactant for the analysis of amino acids in human urine(Wiley, 2013-09) Moreno-González, David; Sastre Toraño, Javier; Gámiz-Gracia, Laura; García-Campaña, Ana M.; de Jong, Gerhardus J.; Somsen, Govert W.A new MEKC-ESI-MS method for the analysis of amino acids (AAs) in human urine was developed employing ammonium perfluorooctanoate (APFO) as volatile surfactant. The influence of APFO on the MS signal of AAs was evaluated by infusion experiments, which showed that APFO hardly affects analyte responses and presents significantly less ion suppression than equal concentrations of ammonium acetate. In order to obtain efficient separation of AAs, MEKC parameters such as the pH and APFO concentration of the BGE, were optimized. Optimum AA resolution, including baseline separation of leucine and isoleucine, was obtained using 150 mM APFO (pH 9.0) as BGE, representing a considerable selectivity improvement over CE using 50 mM ammonium acetate (pH 9.0). Optimization of CE-MS parameters, such as sheath liquid composition and flow rate, and ESI and MS settings, led to LODs ranging from 9 to 26 ng/mL for the 20 tested AAs, which is highly favorable for an MEKC-MS method. Good linearity (r2 > 0.99) and repeatability were obtained for all AAs tested with RSD values of 3.0–6.7% for peak area and <1.5% for migration time. The applicability of the MEKC-MS method was demonstrated by the quantitative determination of AAs in urine employing only a 1:1 dilution with BGE as sample pretreatment. All AAs could selectively be detected and quantified obtaining relevant concentration values for normal human urine.Ítem MICELLAR ELECTROKINETIC CHROMATOGRAPHY–ELECTROSPRAY IONIZATION MASS SPECTROMETRY EMPLOYING A VOLATILE SURFACTANT FOR THE ANALYSIS OF AMINO ACIDS IN HUMAN URINE(Wiley, 2013-09) Moreno-González, David; Sastre Toraño, Javier; Gámiz-Gracia, Laura; García-Campaña, Ana M.; de Jong, Gerhardus J.; Somsen, Govert W.A new MEKC-ESI-MS method for the analysis of amino acids (AAs) in human urine was developed employing ammonium perfluorooctanoate (APFO) as volatile surfactant. The influence of APFO on the MS signal of AAs was evaluated by infusion experiments, which showed that APFO hardly affects analyte responses and presents significantly less ion suppression than equal concentrations of ammonium acetate. In order to obtain efficient separation of AAs, MEKC parameters such as the pH and APFO concentration of the BGE, were optimized. Optimum AA resolution, including baseline separation of leucine and isoleucine, was obtained using 150 mM APFO (pH 9.0) as BGE, representing a considerable selectivity improvement over CE using 50 mM ammonium acetate (pH 9.0). Optimization of CE-MS parameters, such as sheath liquid composition and flow rate, and ESI and MS settings, led to LODs ranging from 9 to 26 ng/mL for the 20 tested AAs, which is highly favorable for an MEKC-MS method. Good linearity (r2 > 0.99) and repeatability were obtained for all AAs tested with RSD values of 3.0–6.7% for peak area and <1.5% for migration time. The applicability of the MEKC-MS method was demonstrated by the quantitative determination of AAs in urine employing only a 1:1 dilution with BGE as sample pretreatment. All AAs could selectively be detected and quantified obtaining relevant concentration values for normal human urine.