Biomedical subjects

Isabel C S F Jardim

Publications and source records attributed to Isabel C S F Jardim.

13 recordsLinked to original sources

PubMed2006

Use of near infrared emission spectroscopy in the study of supporting materials and stationary phases for liquid chromatography.

Near infrared emission spectroscopy (NIRES) has been investigated in the study of different materials employed in liquid chromatography. The samples were heated in a nitrogen atmosphere and the emission spectra were obtained using a lab-made NIRES instrument. Through principal component analysis (PCA) using the raw emission spectra, it was possible to distinguish different materials according to their physical and/or chemical characteristics. Linear relationships between emissivity spectra and the contents of the coating material or the specific surface areas was observed for stationary phases or bare silicas, respectively. Furthermore, the thermal stability of stationary phases could be followed in real time.

Algorithms↗

PubMed2006

Poly(methyloctylsiloxane) immobilized on silica as a sorbent for solid-phase extraction of some pesticides.

A laboratory-made sorbent for solid-phase extraction (SPE) was obtained by thermal immobilization of poly(methyloctylsiloxane) (PMOS) onto silica. Cartridges packed with the new sorbent were used for the simultaneous determination of imazethapyr, nicosulfuron, diuron, linuron and chlorimuron-ethyl in water. These pesticides were separated and quantified using high-performance liquid chromatography with diode array detection (HPLC-DAD). The recoveries achieved with the laboratory-made PMOS cartridges were compared with those of some commercially available silica-based and polymer-based cartridges having C18, C8 and NH(2) pendant groups. Method validation using the laboratory-made sorbent was performed for the five pesticides at three fortifications levels (1x, 2x and 10x the limit of quantification of each pesticide). The laboratory-made PMOS cartridge has low cost preparation and showed good recoveries (72-111%) for all pesticides. Repeatability and intermediate precision were lower than 15%. Its performance was similar or even better, in some cases, than those of the commercial cartridges.

Chemical Fractionation↗

PubMed2006

Immobilized polymeric stationary phases using metalized silica supports.

Immobilized presynthesized polymers on porous metalized (zirconized or titanized) silica particles as new stationary phases with improved chemical stability for RP-HPLC are reviewed. The preparations using different polymers, such as poly(methyloctylsiloxane), poly(methyltetradecylsiloxane), and poly(butadiene), different immobilization steps (gamma radiation, thermal treatment, and microwave radiation), and the chromatographic performances of these phases for polar, apolar, acidic, and basic compounds are discussed. The stability of some of these stationary phases using alkaline mobile phases is also presented.

Journal Article↗

PubMed2005

High-performance liquid chromatographic determination of pesticides in tomatoes using laboratory-made NH2 and C18 solid-phase extraction materials.

A method for high-performance liquid chromatographic (HPLC) multiresidue determination of six pesticides in tomatoes was developed and validated. Silica-based C18 (octadecyl) and NH2 (aminopropyl) solid-phase extraction (SPE) sorbents, made in our laboratory, were used for sample preparation. The SPE materials were obtained by thermal immobilization of appropriate polysiloxanes onto 40 microm silica surfaces and were used in sample preparation for multiresidue analysis of the following pesticides: tebuthiuron and diuron (urea herbicides), simazine, atrazine and ametryn (triazines herbicides) and benomyl (benzimidazol fungicide). The results were compared with similar commercial materials. Reversed-phase high-performance liquid chromatography (RP-HPLC) using a Purospher RP-18 5 microm column and ACN: 0.01% aqueous NH4OH, pH 8.4 (35:65, v/v) as mobile phase, at 0.7 mlmin(-1), with 235 nm UV detection, was used for separation and quantification of the pesticides. Method validation was performed at three fortification levels (100, 200, 1000 microg l(-1)). Limits of detection and quantification show that the methods developed can be used to detect the pesticides in concentrations below the maximum residue levels (MRL) established by the Codex Alimentarius, USA, European Union and Brazilian legislations. The results showed that aminopropyl materials have a better performance than the octadecyl sorbents. Laboratory-made materials give results similar to commercial sorbents, with recoveries and precisions in agreement with directives for method validation in residue analysis.

Chromatography, High Pressure Liquid↗

PubMed2005

Characterization of a new stationary phase based on microwave immobilized polybutadiene on titanium oxide-modified silica.

Titanium oxide-modified silica was prepared by reaction of silica with titanium tetrabutoxide and then was used as support in the preparation of stationary phases with self-immobilized polybutadiene (PBD) and PBD immobilized through microwave radiation. Chromatographic performance of the stationary phases was evaluated in terms of the efficiency (plates/m), asymmetry (A(s)), retention factor (k) and resolution (R(s)) of two standard sample mixtures, one of then containing the basic compound N,N-dimethylaniline. A microwave irradiation of 30 min at 520 W gave the best efficiency (86,500 N m(-1)), greater than that of a 6-day self immobilized phase (69,500 N m(-1)). Self-immobilized stationary phases prepared with bare silica were also studied for comparison. These resulted in lower chromatographic performance, 43,800 N m(-1), when compared to the self-immobilized phase prepared with titanized silica.

Butadienes↗

PubMed2004

New materials for solid-phase extraction and multiclass high-performance liquid chromatographic analysis of pesticides in grapes.

Sample preparation procedures which included the use of new aminopropyl (NH2) and octadecyl (C18) solid-phase extraction (SPE) sorbents are proposed for the simultaneous multiclass determination of the fungicide benomyl and of the herbicides tebuthiuron, diuron, simazine, atrazine, and ametryn in grapes, using single wavelength high-performance liquid chromatography. Sorbent preparation uses a fast, easy, and effective procedure to obtain silica-based materials, made by depositing polysiloxanes on a silica support followed by thermal immobilization. Recovery results of the compounds, after elution from the SPE cartridges, indicate that the most efficient system employed silica loaded with 40% of an aminofunctional polydimethylsiloxane as sorbent, using dichloromethane:methanol (95:5, v/v) as eluent. Method validation, carried out in agreement with International Conference on Harmonization directives, was performed at three fortification levels (100, 200, and 1000 microg kg(-1)). Limits of detection and quantification show that the method developed can be used to detect the pesticides at concentrations below the maximum residue levels established by Codex Alimentarius, the US Environmental Protection Agency, the European Union, and Brazilian legislation.

Chromatography, High Pressure Liquid↗

PubMed2004

Microwave-immobilized polybutadiene stationary phase for reversed-phase high-performance liquid chromatography.

Polybutadiene (PBD) has been immobilized on high-performance liquid chromatography (HPLC) silica by microwave radiation at various power levels (52-663 W) and actuation times (3-60 min). Columns prepared from these reversed-phase HPLC materials, as well as from similar non-irradiated materials, were tested with standard sample mixtures and characterized by elemental analysis (%C) and infrared spectroscopy. A microwave irradiation of 20 min at 663 W gives a layer of immobilized PBD that presented good performance. Longer irradiation times give thicker immobilized layers having less favorable chromatographic properties.

Butadienes↗

PubMed2004

Influence of air on polybutadiene used in the preparation of stationary phases for high-performance liquid chromatography.

A 100 ml bottle of polybutadiene, PBD, was repeatedly exposed to air over a period of 6 months. Samples were taken at time zero (PBD-0), after 3 months (PBD-3) and 6 months (PBD-6). These samples were sorbed onto HPLC silica by an open-air solution-evaporation procedure, which involved exposure to the atmosphere for 6 days. Portions of the three sets of samples were used to compare self-immobilization and the effects of 100 degrees C thermal treatments in air or nitrogen on HPLC performance of the resulting phases. It is concluded that self-immobilization is enhanced by prior exposure of sorbed PBD to air and subsequent heating at 100 degrees C further enhances column performance. The best performance (10(5) plates m(-1)) resulted from 4 h heating of PBD-6 material in nitrogen.

Air↗

PubMed2003

Application of new high-performance liquid chromatography and solid-phase extraction materials to the analysis of pesticides in human urine.

A method for the simultaneous determination of diuron and linuron pesticides in human urine was developed, using both solid-phase extraction (SPE) and high-performance liquid chromatography (HPLC) phases made in our own laboratory. These materials were prepared by sorption of polysiloxanes onto a silica surface, followed by immobilization. The HPLC columns were prepared from poly(methyloctylsiloxane), PMOS, immobilized onto silica with microwave radiation while the SPE cartridges where made with poly(methyloctadecylsiloxane), immobilized thermally. Method validation was performed for diuron and linuron for three fortification levels. The recoveries obtained were 85-103%, the inter- and intra-assay precisions were less than 1.6 and 1.8%, respectively. The limits of quantitation and detection for diuron were 2.4 and 8.0 microg/l and for linuron were 5.0 and 12 microg/l, respectively.

Chromatography, High Pressure Liquid↗

PubMed2003

Preparation of a polybutadiene stationary phase immobilized by gamma radiation for reversed-phase high-performance liquid chromatography.

Polybutadiene (PBD) has been immobilized on HPLC silica by gamma radiation doses in the range from 5 to 180 kGy. Columns prepared from these reversed-phase materials, as well as from similar non-irradiated materials, were tested with standard sample mixtures and characterized by elemental analysis (% C) and infrared spectroscopy. A low dose of 5 kGy is sufficient to produce a layer of immobilized PBD which functions as an efficient and stable stationary phase. Higher doses give thicker immobilized layers having less favorable chromatographic properties.

Butadienes↗

PubMed2003

Determination of herbicides and a metabolite in human urine by liquid chromatography-electrospray ionization mass spectrometry.

A method was developed to determine simazine, atrazine and their metabolite, 2-chloro-4,6-diamino-1,3,5-triazine, in urine. The presence of these herbicides in urine may reflect possible exposure to pesticides. Sample preparation involved protein precipitation and solid-phase extraction. The samples were analyzed by high-performance liquid chromatography-mass spectrometry. The detection limits were 0.4 microg/l and the analytes have a linear response in the interval 6-800 microg/l. The precision of the method was reflected in the RSD of < 2.4% for the herbicides studied. Based on the detectable herbicide levels from spiked urine samples collected from unexposed volunteers, this method can be used to determine the low levels necessary for establishing reference values of the selected herbicides and the metabolite.

Chromatography, Liquid↗

PubMed2002

Poly(methyloctadecylsiloxane) immobilized on silica by gamma radiation for use in solid-phase extraction.

This work presents a fast, easy and effective procedure to obtain silica-based C18 type sorbents for use in solid-phase extraction (SPE). The solid-phase was made by depositing a polymer, poly(methyloctadecylsiloxane) (PMODS), on the silica support followed by immobilization using gamma irradiation. The method presents an application of green chemistry in the analytical laboratory, since there are no toxic residues after the synthesis. Water samples spiked with a mixture of pesticides (benomyl, tebuthiuron, diuron, simazine, atrazine and ametryn) were extracted in the off-line mode in order to evaluate the performance of this sorbent.

Absorption↗

PubMed2002

High-performance liquid chromatographic stationary phases based on poly(methyloctylsiloxane) immobilized on silica. I. Physical and chemical characterizations.

Five different reversed-phase materials for high-performance liquid chromatography were obtained by deposition of poly(methyloctylsiloxane) in HPLC silica particles, followed by immobilization using different processes: thermal treatment (120 or 220 degrees C for 4 h), irradiation with microwaves (495 W for 15 min), gamma radiation (dose of 80 kGy) and self-immobilization. These phases were characterized by gel permeation chromatography, percent carbon, 13C and 29Si solid-state nuclear magnetic resonance spectroscopy, infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy. The results show that the different immobilization processes produce different physical characteristics in the prepared phases.

Carbon Isotopes↗