Encarnación Moyano

Analysis of bisphenols in soft drinks by on-line solid phase extraction fast liquid chromatography-tandem mass spectrometry

In this study, an automated on-line solid-phase extraction coupled to fast liquid chromatography-tandem mass spectrometry (on-line SPE fast LC-MS/MS) method was developed for the simultaneous analysis of bisphenol A (BPA), bisphenol F (BPF), bisphenol E (BPE), bisphenol B (BPB) and bisphenol S (BPS) in canned soft drinks without any previous sample treatment. A C18 (12 μm particle size) loading column was used for the SPE on-line preconcentration before the liquid chromatography baseline separation of bisphenol compounds using a C18 Fused-Core™ (50 mm × 2.1 mm i.d.) column, which took less than 3 min. Gradient elution and heated electrospray were used to reduce matrix effect and improve ionization efficiency. To select the most intense and selective transitions, fragmentation studies were performed by multiple-stage mass spectrometry in an ion trap mass analyzer and tandem mass spectrometry in a triple quadrupole instrument, this latter instrument being used for quantitation in SRM mode. Quality parameters of the method were established and we obtained a simple, fast, reproducible (RSD values lower than 10%) and accurate (precision higher than 93%) method for the analysis of bisphenols in canned soft drinks at the ng L(-1) level using matrix-matched calibration.

Accelerated bimolecular reactions in microdroplets studied by desorption electrospray ionization mass spectrometry

Functional group derivatization reactions occur in the course of microdroplet/surface collisions in the ambient ionization process of desorption electrospray ionization (DESI). The unique environment in the microdroplet causes rate enhancements of as much as several orders of magnitude in typical bimolecular reactions that proceed through either cationic or anionic intermediates. The environment in the evaporating charged microdroplet differs from that of the bulk: (i) the pH of the solution moves towards the extremes, (ii) the concentrations of the reagents increase, (iii) the relative surface area increases and (iv) collision frequencies increase. The rates of acid-catalyzed reactions, such as the reaction of Girard T reagent with ketosteroids, increase with decreasing pH in positively-charged microdroplets compared to the bulk solution rates. Similarly, the increased pH in evaporating negatively-charged microdroplets contributes to an increase in the rates of base-catalyzed Michael reactions over those recorded under bulk solution conditions. The amount of product formed depends on the reaction time and the droplet size. Nanoelectrospray ionization generates larger droplets than the secondary droplets of DESI so it does not show significant product formation in the analysis period and can be used to analyze products of the DESI experiments. When secondary microdroplets (ca. 1 micron diameter) are generated either by spraying a homogeneous solution of both reagents against an inert surface (reactive DESI) or when a solution of Girard T reagent is sprayed against a solid surface bearing the ketosteroid significant amounts of product are generated. In the case of the Michael reaction with cinnamic acid an alternative dehydrogenated reaction product is formed under microdroplet conditions. Some parallels between the phenomenon reported here and the rate acceleration seen in sonochemistry are noted. The potential value of mass spectrometry in establishing conditions that enhance reaction rates is also indicated. It is possible that these observations will assist in the selection of reaction conditions involving the use of charged microdroplets to enhance the rates of ordinary bulk chemical reactions, especially those involving strong steric hindrance.

Determination of quaternary ammonium pesticides by liquid chromatography-electrospray tandem mass spectrometry.

A method for the direct determination of paraquat, diquat, chlormequat and difenzoquat in water samples, using an on-line solid-phase extraction-liquid chromatography-tandem mass spectrometry system was developed. No sample preparation was required and the detection limits were below the European Union maximum residue levels. The chromatographic separation was performed using an XTera MS C8 column. The concentration of the ion pair reagent, the pH and the gradient elution were optimized to give high recoveries and good chromatographic resolution between quats. The detection was carried out using an ion trap as mass analyzer. Parameters such as the magnitude and duration of the resonant excitation voltage and the magnitude of the trapping RF voltage for full scan tandem mass spectrometry (MS-MS) experiments were studied to establish the optimal experimental conditions. Moreover, the accurate optimization of these parameters allowed MS-MS experiments of low mass ions, below m/z 200, providing unambiguous peak identification. Finally, the reproducibility of the proposed method was shown by good run-to-run and day-to-day precision values and its applicability to the determination of quats in drinking water was evaluated using spiked samples.

Analysis of the herbicides paraquat, diquat and difenzoquat in drinking water by micellar electrokinetic chromatography using sweeping and cation selective exhaustive injection.

Optimum conditions for the determination of the herbicides paraquat, diquat and difenzoquat by micellar electrokinetic chromatography (MEKC) using sweeping and cation-selective exhaustive injection (CSEI) as on-line concentration methods were developed. Sodium dodecyl sulfate (80 mM) in 50 mM phosphate buffer (pH 2.5) with 20% acetonitrile was used as a background electrolyte for the methods studied. The limits of detection, based on a signal-to-noise ratio of 3:1, were about 2.6-5.1 mg 1(-1) in purified water when MEKC was applied for the standards. By using an on-line preconcentration method known as sweeping-MEKC, up to a 500-fold increase in detection sensitivity was obtained whereas up to a 50 000-fold increase for CSEI-sweeping-MEKC was achieved. The limits of detection using optimum CSEI-sweeping-MEKC were lower than 1 microg 1(-1) and the method was validated obtaining good reproducibility (relative standard deviation lower than 22%) and linearity. CSEI-sweeping-MEKC was successfully applied to the determination of the three herbicides in spiked tap water below the levels established by the US Environmental Protection Agency.

Ion-pair liquid chromatography–atmospheric pressure ionization mass spectrometry for the determination of quaternary ammonium herbicides

High-performance liquid chromatography coupled with atmospheric pressure ionization mass spectrometry (electrospray and atmospheric pressure chemical ionization) has been used to characterize some quaternary ammonium herbicides (quats). The separation of these compounds was carried out using ion-pair chromatography with heptafluorobutyric acid (15 mM, pH 3.3) and acetonitrile gradient elution for successful coupling to mass spectrometry. Detection limits down to 0.1-4 micrograms l-1 were obtained for spiked tap water following a preconcentration step. Good reproducibilities (day-to-day and run-to-run) were also obtained.

Capillary electrophoresis-mass spectrometry for the analysis of quaternary ammonium herbicides.

Conditions for the simultaneous determination of the three herbicides paraquat, diquat and difenzoquat and the two plant growth regulators chlormequat and mepiquat by pressure-assisted capillary electrophoresis coupled to mass spectrometry (ion-trap) using electrospray as ionisation source have been established. A 200 mM formic acid-ammonium formate buffer solution at pH 3.0 with 50% of methanol was used as carrier electrolyte. Some capillary electrophoresis-mass spectrometry parameters such as sheath liquid and sheath gas flow-rates, sheath liquid composition, electrospray voltage andthe CE capillary position were optimised. The MS and MS-MS spectra of positive ions were studied in order to obtain structural information for the confirmation of the identity. The use of labelled standards allowed to confirm fragment ions assignation. The detection limits, based on a signal-to-noise ratio of 3:1, were between 0.5 and 2.5 mg l(-1) with hydrodynamic injection (10 s) and between 1 and 10 microg l(-1) with elecrokinetic injection (20 s, 10 kV) using standards in ultrapure water. Quality parameters such as linearity and run-to-run precision (n=6) were established. Quantitation was carried out using labelled standards. The method has been applied to the analysis of contaminated irrigation water and spiked mineral water samples.

Liquid chromatography-atmospheric pressure ionization mass spectrometry for the determination of chloro- and nitrophenolic compounds in tap water and sea water

Liquid chromatography coupled to atmospheric-pressure ionization mass spectrometry (LC-API-MS) with negative ion detection was studied for the determination of a variety of phenolic compounds in environmental waters. An isocratic mobile phase of 0.05% acetic acid-acetonitrile (50:50, v/v) was used. The influence of post-column addition of different bases on the sensitivity of the detection in electrospray (ES) was studied. The [M-H]-ion was the base peak for all the compounds using both ES and atmospheric-pressure chemical-ionization (APCI) ion sources. Moreover, abundant structural information was obtained by increasing the extraction voltage. Detection limits for standard solutions ranging from 2 to 13 ng injected for LC-ES-MS and from 0.02 to 20 ng for LC-APCI-MS were obtained. Good reproducibilities (day-to-day and run-to-run) were observed. The optimum LC-ES-MS and LC-APCI-MS conditions thus determined were used for a quantitative analysis of some phenolic compounds in spiked tap water and sea water samples.

On-line solid phase extraction fast liquid chromatography–tandem mass spectrometry for the analysis of bisphenol A and its chlorinated derivatives in water samples

In this study an on-line column-switching fast LC-MS/MS method was developed to analyze bisphenol A (BPA) and its chlorinated derivatives in water. Fast liquid chromatographic separation was performed on a C18 reversed phase column based on fused-core particle technology (2.7 microm particle size) providing analysis times shorter than 3 min and high peak efficiencies. The main benefit of this LC system is that it can easily be hyphenated to a conventional on-line preconcentration device allowing the direct analysis of water samples without any pretreatment at concentrations levels down to 60 ng L(-1) and preventing contaminations frequently reported in the analysis of BPA. This on-line SPE fast LC system was coupled to a triple quadrupole mass spectrometer operating in enhanced mass resolution mode (Q1 FWHM=0.7 Th, Q3 FWHM=0.1 Th) in order to minimize interferences and chemical noise. This highly sensitive and selective method was successfully employed to analyze BPA and its chlorinated derivatives in water samples.

Solid-phase extraction and sample stacking–capillary electrophoresis for the determination of quaternary ammonium herbicides in drinking water☆

Conditions for the simultaneous determination of paraquat, diquat and difenzoquat by capillary zone electrophoresis were established by combining two preconcentration procedures. Off-line solid-phase extraction was used for the isolation and preconcentration of quats in drinking water. Quats were then analysed by capillary electrophoresis using sample stacking with matrix removal as on-column preconcentration procedure. Two different porous graphitic carbon cartridges were compared. The breakthrough volumes of the three herbicides were calculated and the loading capacity of the sorbents was compared. Recoveries higher than 80% for difenzoquat and around 40% for paraquat and diquat were obtained when a sample volume of 250 ml was percolated. For the stacking-capillary electrophoresis analysis of quats, 50 mM acetic acid-ammonium acetate (pH 4.0), 0.8 mM cetyltrimethylammonium bromide with 5% (v/v) methanol as carrier electrolyte was used. Detection limits, based on a signal-to-noise ratio of 3:1, were lower than 0.3 microg l(-1) for standards in Milli-Q water, and lower than 2.2 microg l(-1) for drinking water samples. Run-to-run and day-to-day precision of the method were established. The two preconcentration procedures used together was successfully applied to the analysis of the three herbicides in spiked drinking water at concentrations below the maximum admissible US Environmental Protection Agency levels.

Sample stacking with matrix removal for the determination of paraquat, diquat and difenzoquat in water by capillary electrophoresis

Conditions for the simultaneous determination of paraquat, diquat and difenzoquat by capillary zone electrophoresis using a stacking technique in a chemically modified capillary have been established. To apply the stacking method with sample matrix removal for the analysis of cations, an anodic electroosmotic flow is mandatory. For quats, 50 mM acetic acid-ammonium acetate (pH 4.0) with 5% (v/v) methanol as electrophoretic buffer and the addition of 0.8 mM cetyltrimethylammonium bromide as wall capillary organic modifier was proposed. Field polarity reversal time was optimised for several sample matrices. Detection was carried out at 220 and 255 nm. Detection limits, based on a signal-to-noise ratio of 3:1, were lower than 15 microg l(-1) for standards in Milli-Q water and two to ten times higher for drinking water samples. Run-to-run and day-to-day reproducibility have been established. The method was successfully applied to the determination of the three herbicides in spiked drinking water.