Development of hybrid monoliths incorporating metal-organic frameworks for stir bar sorptive extraction coupled with liquid chromatography for determination of estrogen endocrine disruptors in water and human urine samples.

A novel coating based on hybrid monolith with metal-organic framework (MOF) onto conventional Teflon-coated magnetic stir bars was developed. For this purpose, the external surface of the Teflon stir bar was firstly vinylized in order to immobilize a glycidyl methacrylate (GMA)-based polymer onto the magnet. Then, an amino-modified MOF of type MIL-101 (NH2-MIL-101(Al)) was covalently attached to the GMA-based monolith. After the synthesis process, several parameters affecting extraction of target estrogens by stir bar sorptive extraction (SBSE) including pH, ionic strength, extraction time, stirring rate, desorption solvent, and desorption time were also investigated. The resulting hybrid monolith was evaluated as SBSE sorbent for extraction of three estrogens (estrone, 17ß-estradiol, estriol) and synthetic 17ß-ethinylestradiol from water and human urine samples followed by HPLC with fluorescence detection (excitation and emission wavelengths, 280 and 310 nm, respectively). Under the optimal experimental conditions, the analytical figures of the method were established, achieving satisfactory limits of detection in the range of 0.015-0.58 µg L-1, recovery results ranging from 70 to 95% with RSD less than 6%, and precision values (intra- and inter-extraction units) below 6%.

Influence of photo-initiators in the preparation of methacrylate monoliths into poly(ethylene-co-tetrafluoroethylene) tubing for microbore HPLC.

In this study, poly(butyl methacrylate-co-ethyleneglycol dimethacrylate) polymeric monoliths were in situ developed within 0.75 mm i.d. poly(ethylene-co-tetrafluoroethylene) (ETFE) tubing by UV polymerization via three different free-radical initiators (α,α'-azobisisobutyronitrile (AIBN), 2,2-dimethoxy-2-phenylacetophenone (DMPA) and 2-methyl-4'-(methylthio)-2-morpholinopropiophenone (MTMPP). The influence of the nature of each photo-initiator and irradiation time on the morphological features of the polymer was investigated by scanning electron microscopy, and the chromatographic properties of the resulting microbore columns were evaluated using alkyl benzenes as test substances. The beds photo-initiated with MTMPP gave the best performance (minimum plate heights of 38 µm for alkyl benzenes) and exhibited a satisfactory reproducibility in the chromatographic parameters (RSD < 11%). These monolithic columns were also successfully applied to the separation of phenylurea herbicides, proteins and a tryptic digest of ß-casein.

Photografted fluoropolymers as novel chromatographic supports for polymeric monolithic stationary phases.

In this study, porous polymer monoliths were in situ synthesized in fluoropolymers tubing to prepare microbore HPLC columns. To ensure the formation of robust homogeneous polymer monoliths in these housing supports, the inner surface of fluoropolymer tubing was modified in a two-step photografting process. Raman spectroscopy and scanning electron microscopy (SEM) confirmed the successful modification of the inner poly(ethylene-co-tetrafluoroethylene) (ETFE) wall and the subsequent attachment of a monolith onto the wall. Poly(glycidyl methacrylate-co-divinylbenzene), poly(butyl methacrylate-co-ethyleneglycol dimethacrylate) and poly(styrene-co-divinylbenzene) monoliths were in situ synthesized by thermal polymerization within the confines of surface vinylized ETFE tubes. The resulting monoliths exhibited good permeability and mechanical stability (pressure resistance up to 9 MPa). The chromatographic performance of these different monolithic columns was evaluated via the separation of alkyl benzenes and proteins in a conventional HPLC system.

Preparation of organic monolithic columns in polytetrafluoroethylene tubes for reversed-phase liquid chromatography.

In this work, a method for the preparation and anchoring of polymeric monoliths in a polytetrafluoroethylene (PTFE) tubing as a column housing for microbore HPLC is described. In order to assure a covalent attachment of the monolith to the inner wall of the PTFE tube, a two-step procedure was developed. Two surface etching reagents, a commercial sodium naphthalene solution (Fluoroetch®), or mixtures of H2O2 and H2SO4, were tried and compared. Then, the obtained hydroxyl groups on the PTFE surface were modified by methacryloylation. Attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy and scanning electron microscopy (SEM) confirmed the successful modification of the tubing wall and the stable anchorage of monolith to the wall, respectively. Special emphasis was also put on the reduction of the unwanted effects of shrinking of monolith during polymerization, by using an external proper mold and by selecting the adequate monomers in order to increase the flexibility of the polymer. Poly(glycidyl methacrylate-co-divinylbenzene) monoliths were in situ synthesized by thermal polymerization within the confines of surface-vinylized PTFE tubes. The modified PTFE tubing tightly held the monolith, and the monolithic column exhibited good pressure resistance up to 20 MPa. The column performance was also evaluated via the isocratic separation of a series of alkylbenzenes in the reversed-phase mode. The optimized monolithic columns gave plate heights ranged between 70 and 80 µm. The resulting monoliths were also satisfactorily applied to the separation of proteins.

Photoinduced chemiluminescence determination of carbamate pesticides.

A liquid chromatography method with post-column photoinduced chemiluminescence (PICL) detection is proposed for the simultaneous determination of eight carbamate pesticides, namely aldicarb, butocarboxim, ethiofencarb, methomyl, methiocarb, thiodicarb, thiofanox and thiophanate-methyl. After chromatographic separation, quinine (sensitizer) was incorporated and the flow passed through an UV lamp (67 s of irradiation time) to obtain the photoproducts, which reacted with acidic Ce(iv) and provided a CL emission. The PICL method showed great selectivity for carbamate pesticides containing sulphur in their chemical structure. A solid-phase extraction process increased sensitivity (LODs ranging from 0.06 to 0.27 ng mL(-1)) and allowed the carbamate pesticides in surface and ground water samples to be determined, with recoveries in the range 87-110% (except for thiophanate-methyl, whose recoveries were between 60 and 75%). The intra- and inter-day precision was evaluated, with RSD ranging from 1.1 to 7.5% and from 2.6 to 12.3%, respectively. A discussion about the PICL mechanism is also included.

Native vs photoinduced chemiluminescence in dimethoate determination.

The determination of dimethoate using either its native chemiluminescent (CL) properties or its photoinduced chemiluminescence obtained by irradiation with a 15 W low-pressure mercury lamp was studied. Thereby, two flow injection systems (FIA) with and without irradiation were exhaustively optimized and their analytical characteristics studied. Better sensitivity and selectivity was found in absence of irradiation, due to the enhancing effect of hexadecylpyridinium chloride (HPC), which acted as a sensitizer. In the developed FIA-CL system, the alkaline hydrolysis of dimethoate with NaOH was performed on-line in presence of HPC. The oxidation of the product of hydrolysis with Ce(IV) in hydrochloric medium induced chemiluminescence. The method provided a limit of detection of only 0.05 ng mL(-1) without any pre-treatment. However, the combination with solid phase extraction allowed the removal of some potential interferents as well as the preconcentration of the pesticide. Finally, the developed method was successfully applied to natural waters with recoveries between 95 and 108%.

Determination of diquat by flow injection-chemiluminescence.

A simple, economic, sensitive and rapid method for the determination of the pesticide diquat was described. This new method was based on the coupling of flow injection analysis methodology and direct chemiluminescent detection; to the authors' knowledge, this approach had not been used up to now with this pesticide. It was based on its oxidation with ferricyanide in alkaline medium; significant improvements in the analytical signal were achieved by using high temperatures and quinine as sensitiser. Its high throughput (144 h(-1)), together with its low limit of detection (2 ng mL(-1)), achieved without need of preconcentration steps, permitted the reliable quantification of diquat over the linear range of (0.01-0.6) microg mL(-1) in samples from different origins (river, tap, mineral and ground waters), even in the presence of a 40-fold concentration of paraquat, a pesticide commonly present in the commercial formulations of diquat.

Flow injection-photoinduced-chemiluminescence determination of ziram and zineb.

A simple, sensitive and rapid method for the determination of the pesticides ziram and zineb was described. This new method was based on the coupling of FIA methodology and direct chemiluminescent detection; this approach had not been used up to now with these pesticides. The additional use of an 'on line' photochemical reaction, which was performed by using a photoreactor consisting of a long piece of PTFE helically coiled around a 15W low-pressure lamp, increased by a factor >20 the chemiluminometric response of the pesticides. An additional 3-fold improvement in the analytical signal was also achieved by using quinine as sensitizer. The obtained throughputs were very high (121 and 101 h(-1) for ziram and zineb, respectively); this feature together with its low limit of detection (1 ng mL(-1)) makes this method particularly well suited to routine analyses of environmental samples. On the other hand, its applicability to two members of the dithiocarbamate family of pesticides, makes it promising for the determination of the rest of the members of this family. The method was demonstrated by application to spiked water samples from different origins (ground, river and irrigation).

Fluorescence determination of the pesticide asulam by flow injection analysis.

This paper presents the analytical determination of the pesticide Asulam based on its native fluorescence. The method was optimized in either a flow injection analysis (FIA) assembly or in batch. The maximum fluorescence intensity was observed for basic pH solutions and at a lamda(ex) of 258 nm and a lamda(em) of 342 nm. The influence of different empirical parameters, such as the pH, the presence of surfactants, solvent polarity or solved oxygen amount, was studied. The calibration range was fitted with a linear equation from 0.01-3 mg l(-1) Asulam and 0.005-15 mg l(-1) Asulam for batch and continuous-flow, respectively. The RSD for both procedures was 1.0%. After testing the influence of a large series of potential interferents, the method was applied to water samples from different locations.

Chemiluminescent determination of the pesticide bromoxynil by on-line photodegradation in a flow-injection system.

A new, robust and simple method is proposed for the chemiluminescent determination of the pesticide Bromoxynil. The empirical procedure is performed with the aid of a flow-injection manifold provided with an on-line photo-reactor to obtain chemiluminescent photofragments. After a period of 12 s of irradiation with an 8 W low-pressure mercury lamp, a chemiluminescent oxidation was performed with the system potassium permanganate in a polyphosphoric acid medium. The photolysis required a basic medium (KOH 0.014 mol l(-1)) with ethanol (1%) as a sensitizer. The method allowed the determination of 134 samples (h-1) of Bromoxynil in a wide interval of concentrations, over the range 5 x 10(-3) - 1 mg l(-1); the detection limit was 5 x 10(-3) mg l(-1). The RSD (n=24) at 0.25 mg l(-1) of the pesticide level was 2.3%. The method was applied to a water sample and to a formulation.

Automated simultaneous triple dissolution profiles of two drugs, sulphamethoxazole-trimethoprim and hydrochlorothiazide-captopril in solid oral dosage forms by a multicommutation flow-assembly and derivative spectrophotometry.

This article deals with the simultaneous determination of three dissolution profiles with the aid of the new and emerging continuous-flow methodology known as multicommutation. This methodology is based on a flow network of a set of solenoid valves controlled by the computer and acting as independent multicommutators to allow the easy and automated control of flowing solutions. The obtained three dissolution profiles from one dosage form are the whole formulation profile or "global profile" recommended by pharmacopoeias, and, at same time, are recorded two "individual" profiles from two drugs present in the formulation. This is the second attempt to obtain simultaneously three dissolution profiles with a single spectrophotometric detector and the first with the multicommutation methodology. The selected pharmaceutical formulations contained a couple of active principles with overlapped spectra, namely sulphamethoxazole and trimethoprim or hydrochlorothiazide and captopril. The obtained empirical plots profiles fitted with the Higuchi equation also known as the three-parameter equation.

A tandem-flow assembly for the chemiluminometric determination of hydroquinone.

A direct chemiluminescent procedure for determination of hydroquinone based on the emergent flow methodology known as multicommutation or tandem-flow is presented for first time. The manifold was based on a set of three channels and three solenoid valves; and, the determination was performed at 60 degrees C and at flow-rate of 7.5mlmin(-1). The complete cycle lasted 35s, which resulted in a sample flow trough of 103h(-1). The chemical process was the hydroquinone oxidation with the system sulphuric acid-potassium permanganate; and the light emission was clearly enhanced by the presence of quinine sulphate and benzalkonium chloride reaching a detection limit of 30mugl(-1). The dynamic interval was over the range 0.1-15.0mgl(-1) and a large list of interferents were assayed; the chemical robustness was also tested. The method was applied to different type of samples: namely, pharmaceutical formulations, a photographic solution and irrigation and residual superficial waters.

Three simultaneous dissolution profiles on a solid pharmaceutical formulation by a FIA manifold provided with a single spectrophotometric detector.

This article deals with the simultaneous determination of three dissolution profiles in the same pharmaceutical formulation. The officially proposed procedure from the pharmacopoeias is adapted to the FIA methodology to obtain the officially recommended profile or "global profile", and two "individual" profiles, corresponding to dissolution rate of two different active principles present in the formulation; both drugs have overlapped UV-vis spectra. The simultaneous determination of several profiles is based on the derivative spectra and the zero crossing mathematical procedure for the "individual" profiles of an active principle; the "global" profile of the formulation is obtained from the order zero derivative. The empirical profiles were adjusted by regression analysis using the three-parameter (Higuchi equation) plot method which was selected as the most suitable. The analytical errors when the concentration of one drug is very small or very high are also checked.

Determination of nitrite by inhibition of the chemiluminescence of acriflavine in a flow-injection assembly.

The indirect determination of nitrite was performed with a flow-injection assembly on the basis of the inhibition of the analytical output obtained in a luminometer by oxidation of acriflavine. The acriflavine solution merged with the nitrite and the resulting mixture was injected into a pure water stream. This solution merged with the oxidant solution (potassium permanganate in sulfuric acid medium) and the resulting chemiluminiscence was affected (inhibited) by the presence of nitrite after reaction with the aminoacridine. The method was applicable over the range 10-800 microg l(-1) of nitrite with a correlation coefficient of 0.9960. The relative standard deviation was 1.4% and the throughput was 76 samples h(-1). The influence of foreign substances was also tested. A solid-phase reactor, filled with Amberlite IRA-900, was inserted in the assembly for the on-line preconcentration of nitrite; the analytical output resulted in an increase of up to 11.5-fold. The method was applied to the determination of nitrites in residual waters, industrial formulations and soil samples.

o-Dianisidine: a new reagent for selective spectrophotometric, flow injection determination of chlorine.

A flow injection analysis (FIA) procedure for the determination of free chlorine in industrial formulations and water samples is proposed. The manifold is provided with a gas-diffusion unit which permits the removal of interfering species and also the preconcentration of chlorine. The determination of chlorine is performed on the basis of the oxidation by o-dianisidine as a chromogenic reagent to a coloured product which can be monitored at 445 nm. The method (for a preconcentration step of 60 s) is linear over the range 0.04-1.00 mg l(-1) of chlorine, the limit of detection is 0.04 mg l(-1), the reproducibility of the procedure (as RSD of the slope) is 3.7% for a series of four independent calibrations, the precision (as RSD of a series of 30 continuous FIA peaks of 0.56 mg l(-1) of chlorine) is 1.4% and the sample throughput is 40 h(-1). A detailed comparative study of the analytical characteristics of a single mono-channel reverse FIA assembly and the same system but provided with a Fluoropore membrane filter of 0.5 microm pore size was performed to check the advantages of the new approach in terms of sensitivity, selectivity and limit of detection.

Solid-phase reactors as high stability reagent sources in flow analysis: selective flow injection spectrophotometric determination of cysteine in pharmaceutical formulations.

The flow injection spectrophotometric determination of cysteine was carried out by reaction with cobalt(II) ions entrapped in a polymeric material and filling a packed-bed reactor; the released cobalt(II) complexed with the amino acid was monitored at 360 nm. The method worked with a high repeatability, even with independent reactors, days and solutions. Selectivity of the procedure was tested with twenty different foreign compounds found in pharmaceutical formulations containing cysteine, parent amino acids included; no serious interferences were observed. The calibration graph for cysteine was linear over the range 1-90 micrograms ml-1 with a relative standard deviation of 0.8% at 60 micrograms ml-1 (n = 158). The calculated sample throughput was 90 h-1. The method was applied to determine the content of cysteine in pharmaceutical formulations.