Data Accuracy and Predictors of High Ratings of Colon and Rectal Surgeons on an Online Physician Rating Website.

BACKGROUND: Online physician rating Web sites are used by over half of consumers to select doctors. No studies have examined physician rating Web sites for colon and rectal surgeons. OBJECTIVE: The purpose of this study was to evaluate the accuracy and rating patterns of colon and rectal surgeons on the largest physician rating Web site. DESIGN: Physician characteristics and ratings were collected from a randomly selected sample of 500 from 3043 Healthgrades "colon and rectal surgery specialists." Board certifications were verified with the American Board of Surgery and American Board of Colon and Rectal Surgery Web sites. SETTINGS: Data acquisition was completed on July 18, 2018. PATIENTS: Patients were not directly studied. MAIN OUTCOME MEASURES: The primary outcome was to assess the accuracy of Healthgrades in reporting American Board of Surgery and American Board of Colon and Rectal Surgery certification. The secondary outcome was to identify factors associated with high star ratings. RESULTS: A total of 48 (9.6%) of the 500 sampled were incorrectly identified as practicing US surgeons and excluded from subsequent analysis. Healthgrades showed 80.1% agreement with verified board certifications for American Board of Surgery and 85.4% for American Board of Colon and Rectal Surgery. The mean star rating was 4.2 of 5.0 (SD = 0.9), and 77 (21.6%) had 5-star ratings. In a multivariable logistic model (p < 0.001), 5-star rating was associated with 1 to 9 years (OR = 2.76; p = 0.04) or >40 years in practice (OR = 3.35; p = 0.04) and fewer reviews (OR = 0.88; p < 0.001). There were no significant associations with surgeon sex, age, geographic region, or board certification. LIMITATIONS: Data were limited to a single physician rating Web site. CONCLUSIONS: In the modern age of healthcare consumerism, physician rating Web sites should be used with caution given inaccuracies. More accurate online resources are needed to inform patient decisions in the selection of specialized colon and rectal surgical care. See Video Abstract at http://links.lww.com/DCR/B91. PRECISIÓN DE DATOS Y PREDICTORES DE ALTAS CALIFICACIONES DE CIRUJANOS DE COLON Y RECTO EN UN SITIO WEB DE CALIFICACIÓN MÉDICA EN LÍNEA: Más de la mitad de los consumidores utilizan los sitios web de calificación de médicos en línea para seleccionar médicos. Ningún estudio ha examinado los sitios web de calificación de médicos para cirujanos de colon y recto.Evaluar la precisión y los patrones de calificación de los cirujanos de colon y recto en el sitio web más grande de calificación de médicos.Las características y calificaciones de los médicos se obtuvieron de una muestra seleccionada al azar de 500 de 3,043 "especialistas en cirugía de colon y recto" de Healthgrades. Las certificaciones del Consejo se verificaron en los sitios web del Consejo Americano de Cirugía y del Consejo Americano de Cirugía de Colon y Recto.La adquisición de datos se completó el 18 de julio de 2018.Los pacientes no fueron estudiados directamente.El resultado primario fue evaluar la precisión de Healthgrades al informar la certificación por el Consejo Americano de Cirugía y por el Consejo Americano de Cirugía de Colon y Recto. El resultado secundario fue identificar factores asociados con altas calificaciones en estrellas.Un total de 48 (9.6%) de la muestra de 500 fueron identificados incorrectamente como cirujanos practicantes de EE. UU. y excluidos del análisis subsecuente. Healthgrades mostró un 80.1% de concordancia con las certificaciones verificadas del Consejo Americano de Cirugía y el 85.4% con el Consejo Americano de Cirugía de Colon y Recto. La calificación promedio de estrellas fue 4.2 / 5 (SD 0.9), y 77 (21.6%) tuvieron calificaciones de 5 estrellas. En un modelo logístico multivariable (p <0.001), la calificación de 5 estrellas se asoció con 1-9 años (OR 2.76, p = 0.04) o más de 40 años en la práctica (OR 3.35, p = 0.04) y menos evaluaciones (OR 0.88, p <0.001). No hubo asociaciones significativas con el género, edad, región geográfica o certificación por los Consejos del cirujano.Los datos se limitaron a un solo sitio web de calificación de médicos.En la era moderna del consumismo en atención médica, los sitios web de calificación de los médicos deben usarse con precaución debido a imprecisiones. Se necesitan recursos en línea más precisos para que las decisiones de los pacientes sean informadas en la selección de atención quirúrgica especializada de colon y recto. Consulte Video Resumen en http://links.lww.com/DCR/B91. (Traducción-Dr. Jorge Silva-Velazco).

Portfólio on-line: estratégia para melhorar o sistema de avaliação da disciplina de Atenção Integral à Saúde do curso de Medicina / Online portfolio: strategy to improve the assessment system of the Integral Health Care discipline in the medical course / Portafolio on-line: estrategia para mejorar el sistema de evaluación de la disciplina de Atención Integral de Salud del Curso de Medicina

Resumo Este estudo relata a estratégia para aprimorar o portfólio como instrumento de avaliação da aprendizagem em uma disciplina oferecida aos estudantes do quarto ano de graduação em Medicina, por meio do portfólio on-line. A disciplina é constituída de atividades práticas de atendimento integral à saúde da criança, do adolescente, do adulto e da mulher na atenção primária do município de Campinas. A utilização do portfólio permite que os estudantes reflitam sobre os atendimentos realizados em relação ao conhecimento, à habilidade clínica e ao vínculo médico-paciente na consulta. O portfólio on-line possibilitou rever os critérios de avaliação, agilizar e facilitar a gestão da correção, realizada por oitenta avaliadores de três especialidades médicas. O acesso às informações do portfólio na plataforma moodle permitiu a rápida tomada de decisão em aspectos que precisam ser adequados para a melhoria do processo ensino-aprendizagem.(AU)

Abstract This study reports on the strategy to improve the use of online portfolios as a learning assessment instrument of a discipline taught to fourth-year medical students. The discipline comprises practical activities of comprehensive care of children, teenagers, adults, and women in primary care in the Brazilian city of Campinas. Using portfolios, students are able to reflect upon the provided care as to the knowledge, clinical skills, and doctor-patient bond shown in the appointment. The online portfolio enabled to review the assessment criteria, and streamline and facilitate managing the assessment conducted by 80 evaluators from three medical specialties. Access to the portfolio's information in the Moodle platform enabled a fast decision-making process in aspects that need to be adequate to improve the teaching and learning process.(AU)

Resumen Este estudio relata la estrategia para perfeccionar el portafolio como instrumento de evaluación del aprendizaje en una disciplina ofrecida a los estudiantes del 4º. año de la graduación en medicina, por medio del portafolio online. La asignatura se compone de actividades prácticas de atención integral a la salud del niño, del adolescente, del adulto y de la mujer en la atención primaria del municipio de Campinas. La utilización del portafolio permite que los estudiantes reflexionen sobre las atenciones realizadas con relación al conocimiento, a la habilidad clínica y al vínculo médico-paciente en la consulta. El portafolio online posibilitó revisar los criterios de evaluación, agilizar y facilitar la gestión de la corrección realizada por 80 evaluadores de tres especialidades médicas. El acceso a las informaciones del portafolio en la plataforma Moodle permitió la rápida toma de decisiones en aspectos que tienen que adecuarse para la mejora del proceso enseñanza-aprendizaje.(AU)

On-line monitoring of the photocatalytic degradation of 2,4-D and dicamba using a solid-phase extraction-multisyringe flow injection system.

A fully automated on-line system for monitoring the photocatalytic degradation of herbicides was developed using multisyringe flow injection analysis (MSFIA) coupled to a solid phase extraction (SPE) unit with UV detection. The calibration curves were linear in the concentration range of 100-1000 µg L(-1) for 3,6-dichloro-2-methoxybenzoic acid (dicamba) and 500-3000 µg L(-1) for 2,4-dichlorophenoxyacetic acid (2,4-D), while the detection limits were 30 and 135 µg L(-1) for dicamba and 2,4-D, respectively. The monitoring of the photocatalytic degradation (TiO2 anatase/UV 254 nm) of these two herbicides was performed by MSFIA-SPE system using a small sample volume (2 mL) in a fully automated approach. The degradation was assessed in ultrapure and drinking water with initial concentrations of 1000 and 2000 µg L(-1) for dicamba and 2,4-D, respectively. Degradation percentages of approximately 85% were obtained for both herbicides in ultrapure water after 45 min of photocatalytic treatment. A similar degradation efficiency in drinking water was observed for 2,4-D, whereas dicamba exhibited a lower degradation percentage (75%), which could be attributed to the presence of inorganic species in this kind of water.

Analysis of free and esterified sterols in edible oils by online reversed phase liquid chromatography-gas chromatography (RPLC-GC) using the through oven transfer adsorption desorption (TOTAD) interface.

An online reversed phase liquid chromatography-gas chromatography (RPLC-GC) method is proposed to quantify free, total and esterified sterols of edible oils. To determine free sterols the diluted oils are injected into the liquid chromatograph, where free sterols are separated from triglycerides and the sterol fraction is automatically transferred to the gas chromatograph to be analysed. To determine total sterols the samples were saponified with potassium hydroxide in ethanolic solution and the unsaponifiable fraction was extracted with diethyl ether. The extract was then analysed by RPLC-GC, avoiding the laborious thin layer chromatography step used in the Official European Union (EU) Method. The relative standard deviations (RSDs) from the absolute peak area varied from 7.6% to 15.8%. Limits of detection (LODs) were less than 8.5 mg/kg. No variability in retention time was observed. The method was applied to the determination of total sterols in edible oil samples and the results were compared with those obtained with the Official EU Method. Good agreement was found between both methods, except in the case of campesterol.

Optimal conditions for the direct RP-HPLC determination of underivatized amino acids with online multiple detection.

The combined use of a dual-UV detector as well as a fluorimetric and a multielectrode electrochemical detector (equipped with a dual electrode, consisting of a conventional size 3 mm diameter glassy carbon electrode (GCE) and of a pair of 30 µm thick carbon microfibers) is proposed for the detection of the following 15 underivatized amino acids: L: -histidine (his), L: -cysteine (cys), creatine (crn), S-methyl-L: -cysteine (me-cys), DL: -homocysteine (hcy), L: -methionine (met), beta-(3,4-dihydroxyphenyl)-L: -alanine (dopa), L: -tyrosine (tyr), DL: -m-tyrosine (m-tyr), L: -a-methyl-dopa (me-dopa), L: -phenylanine (phe), DL: -alpha-methyltyrosine (me-tyr), 5-hydroxy-tryptophan (5htp), 3-nitro-L: -tyrosine (NO(2)Tyr) and L: -tryptophan (trp), as well as of two dipeptides: L: -cystathionine (cysta), L: -carnosine (car), and of creatinine (cre). A multilinear solvent (acetonitrile) gradient elution program, determined by a simple optimization algorithm, is required for the efficient reversed phase separation of the above mixture of 18 solutes within 27 min at a flow rate of 1.0 mL/min and at 25°C.

Automatic on-line monitoring of atmospheric volatile organic compounds: gas chromatography-mass spectrometry and gas chromatography-flame ionization detection as complementary systems.

Traditionally air quality networks have been carrying out the continuous, on-line measurement of volatile organic compounds (VOC) in ambient air with GC-FID. In this paper some identification and coelution problems observed while using this technique in long-term measurement campaigns are described. In order to solve these problems a GC-MS was set up and operated simultaneously with a GC-FID for C2-C11 VOCs measurement. There are few on-line, unattended, long term measurements of atmospheric VOCs performed with GC-MS. In this work such a system has been optimized for that purpose, achieving good repeatability, linearity, and detection limits of the order of the GC-FID ones, even smaller in some cases. VOC quantification has been made by using response factors, which is not frequent in on-line GC-MS. That way, the identification and coelution problems detected in the GC-FID, which may led to reporting erroneous data, could be corrected. The combination of GC-FID and GC-MS as complementary techniques for the measurement of speciated VOCs in ambient air at sub-ppbv levels is proposed. Some results of the measurements are presented, including concentration values for some compounds not found until now on public ambient air VOC databases, which were identified and quantified combining both techniques. Results may also help to correct previously published VOC data with wrongly identified compounds by reprocessing raw chromatographic data.

[Central online quality assurance in radiology: an IT solution exemplified by the German Breast Cancer Screening Program]. / Zentrale Online-Qualitätssicherung in der Radiologie:eine IT-Lösung am Beispiel des deutschenMammografie-Screening-Programms.

PURPOSE: Physical-technical quality assurance is one of the essential tasks of the National Reference Centers in the German Breast Cancer Screening Program. For this purpose the mammography units are required to transfer the measured values of the constancy tests on a daily basis and all phantom images created for this purpose on a weekly basis to the reference centers. This is a serious logistical challenge. To meet these requirements, we developed an innovative software tool. MATERIALS AND METHODS: By the end of 2005, we had already developed web-based software (MammoControl) allowing the transmission of constancy test results via entry forms. For automatic analysis and transmission of the phantom images, we then introduced an extension (MammoControl DIANA). This was based on Java, Java Web Start, the NetBeans Rich Client Platform, the Pixelmed Java DICOM Toolkit and the ImageJ library. RESULTS: MammoControl DIANA was designed to run locally in the mammography units. This allows automated on-site image analysis. Both results and compressed images can then be transmitted to the reference center. We developed analysis modules for the daily and monthly consistency tests and additionally for a homogeneity test. CONCLUSION: The software we developed facilitates the immediate availability of measurement results, phantom images, and DICOM header data in all reference centers. This allows both targeted guidance and short response time in the case of errors. We achieved a consistent IT-based evaluation with standardized tools for the entire screening program in Germany.

The Bristol Online Obesity Screening Tool: experience of using a screening tool for assessing obese children in primary care.

The incidence of childhood obesity is rising in the United Kingdom and this has far-reaching and serious consequences both for the physical and psychological well-being of the child, as well as significant financial implications for the health service. General practitioners (GPs) play a central role in identifying and assessing such children and directing them to the best services. While most cases of obesity are simply due to an imbalance in calorie intake and expenditure, children do need to be formally assessed to ensure that red flags are not missed, which might signify an important underlying aetiology, co-morbidity or complication. To date, there have not been tools available to guide a GP through this assessment. In this paper, we present and explain the thinking behind a tool, which was developed for use by GPs from Bristolas part of a trial to assess the transferability of a childhood obesity clinic into primary care. We look at the evidence base behind the guidelines and then assess the appropriateness and safety of the 152 referrals made using this tool. We believe that this screening tool would enable over 85% of obese children to seek their initial weight management in primary care. Additional evaluation is needed in different regions to ensure effectiveness, sensitivity and specificity of this new tool.

An approach to on-line electrospray mass spectrometric detection of polypeptide antibiotics of enramycin for high-speed counter-current chromatographic separation.

In the field of pharmaceutical and biomedical analysis of peptides, a rapid on-line detection and identification for a methodology have been required for the discovery of new biological active products. In this study, a high-speed counter-current chromatography with electrospray mass spectrometry (HSCCC/ESI-MS) was developed for the on-line detection and purification of polypeptide antibiotics of enramycin-A and -B. The analytes were purified on HSCCC model CCC-1000 (multi-layer coil planet centrifuge) with a volatile solvent of two-phase system composed of n-butanol/hexane/0.05% aqueous trifluoroacetic acid solution (43/7/50, V/V/V), and detected on an LCMS-2010EV quadrupole mass spectrometer fitted with an ESI source system in positive ionization following scan mode (m/z 100-2000). The HSCCC/ESI-MS peaks indicated that enramycin-A (major m/z 786 [M+3H](3+) and minor m/z 1179 [M+2H](2+)) and enramycin-B (major m/z 791 [M+3H](3+) and minor m/z 1185 [M+2H](2+)) have the peak resolution value of 2.9 from 15mg of loaded enramycin powder. The HSCCC collected amounts of the peak fractions were additionally 4.3mg (enramycin-A), and 5.9mg (enramycin-B), respectively. These purified substances were analyzed by LC/ESI-MS with scan positive mode. Based on the LC/ESI-MS chromatograms and spectra of the fractions, enramycin-A and -B were estimated to be over 95% purity. The overall results indicate that this approach of HSCCC/ESI-MS is a powerful technique for the purification and identification of bioactive peptides.

On-line solid-phase extraction of large-volume injections coupled to liquid chromatography-tandem mass spectrometry for the quantitation and confirmation of 14 selected trace organic contaminants in drinking and surface water.

We describe the development and validation of an on-line solid-phase extraction of large-volume injections coupled to liquid chromatography-tandem mass spectrometry method for the simultaneous quantitation and confirmation of 14 selected trace organic contaminants in drinking and surface water. Selected compounds were: anti-infectives (clarithromycin, sulfamethoxazole and trimethoprim), an anticonvulsant (carbamazepine) and its transformation product 10,11-dihydrocarbamazepine, an antihypertensive (enalapril), antineoplastics (cyclophosphamide and methotrexate), herbicides (atrazine, cyanazine, and simazine) and two of their transformation products (deethylatrazine and deisopropylatrazine) and an antiseptic (triclocarban). The breakthrough volume determinations showed that out of all the investigated sorbents, the Strata-X on-line solid-phase extraction column showed the best performance. The method used a load volume of 10.0 mL and was validated using the corresponding matrices, yielding for most compounds, R(2)>0.99. Extraction recoveries ranged from 60 to 109%. The intra- and inter-day precision were <14 and <16%, respectively. The method detection limits ranged from 0.6 to 6 ng L(-1). Matrix effects were in general low. The performance of the on-line method was demonstrated with the analysis of real water samples. The application of alternative techniques of confirmation was also explored using accurate mass measurements on a time-of-flight mass spectrometer and the data-dependent reverse energy ramp scan on a triple quadrupole.

Electrochemistry meets enzymes: instrumental on-line simulation of oxidative and conjugative metabolism reactions of toremifene.

The metabolism of the selective estrogen receptor modulator toremifene was simulated in an on-line electrochemistry/enzyme reactor/liquid chromatography/mass spectrometry system. To simulate the oxidative phase I metabolism, toremifene was oxidized in an electrochemical (EC) flow-through cell at 1,500 mV vs. Pd/H2 to its phase I metabolites, some of which are reactive quinoid species. In the presence of glutathione-S-transferase (GST), these quinoid compounds react with glutathione, which is also the common detoxification mechanism in the body. While reacting with glutathione, the chlorine atom is eliminated from the toremifene moiety. Due to higher conversion rates, GST supplied in continuous flow proved to be more efficient than using immobilized GST on magnetic microparticles. In the absence of GST, not all GSH adducts are formed, proving the necessity of a phase II enzyme to simulate the complete metabolic pathway of xenobiotics in an on-line EC/LC/MS system.

Early clinical experience with kilovoltage image-guided radiation therapy for interfraction motion management.

Interest in image-guided radiation therapy (IGRT) reflects the desire to minimize interfraction positioning variability. Using a kilovoltage (kV) imaging unit mounted to a traditional LINAC allows daily matching of kV images to planning digitally reconstructed radiographs (DRRs). We quantify and evaluate the significance of calculated deviation from the intended isocenter. Since September 2004, 117 patients with various malignancies were treated using the On-Board Imaging (OBI) system, with 2088 treatment sessions. Patients were positioned by the treating therapist; orthogonal images were then obtained with the OBI unit. Couch shifts were made, aligning bony anatomy to the initial simulation image. Routine port films were performed weekly (after that day's OBI session). Ninety percent of all lateral, longitudinal, and vertical shifts were less than 0.8 cm, 0.6 cm, and 0.7 cm, respectively. The median vector shift for each anatomic site was: 0.42 cm for head and neck, 0.40 cm for CNS, 0.59 cm for GU/prostate, and 0.73 cm for breast; shift magnitude did not change with successive OBI sessions. The use of OBI effectively corrects setup variability. These shifts are typically small and random. The use of OBI likely can replace weekly port films for isocenter verification; however, OBI does not provide field shape verification.

Gas chromatographic high-throughput screening techniques in catalysis.

Discovering highly efficient catalysts is of great scientific and economical interest. Advances in high-throughput assays in combination with sophisticated analytical techniques have increased the rapidity with which catalysts can be identified and optimized. Understanding how kinetics in the mechanism of catalysis is controlled by structural parameters is essential for a directed design of catalysts. To identify such rate-controlling elementary steps and to develop and refine models, comprehensive experimental kinetic data of a broad variety of substrates are necessary. In the present article concepts of high-throughput screening techniques in catalysis using gas chromatography are reviewed in a survey covering the period from 1998 to 2007. To cover also the origins of concepts and groundbreaking experiments in this research area milestones going back to 1950 are also reviewed. The first part of the review will focus on off-line gas chromatographic analysis, the second part on on-line gas chromatographic analysis covering sequential, parallelized and high-throughput multiplexing gas chromatography. The third part presents recent advances in the integration of chemical transformation and analysis in gas chromatography. The present review article describes the state-of-the-art, scope and limitations, and applications of these different high-throughput screening approaches.

A fully automated 2-D LC-MS method utilizing online continuous pH and RP gradients for global proteome analysis.

The conventional 2-D LC-MS/MS setup for global proteome analysis was based on online and offline salt gradients (step and continuous) using strong-cation-exchange chromatography in conjunction with RP chromatography and MS. The use of the online system with step salt elution had the possibility of resulting in peptide overlapping across fractions. The offline mode had the option to operate with continuous salt gradient to decrease peak overlap, but exhibited decreased robustness, lower reproducibility, and sample loss during the process. Due to the extensive washing requirement between the chromatography steps, online continuous gradient was not an option for salt elution. In this report, a fully automated, online, and continuous gradient (pH continuous online gradient, pCOG) 2-D LC-MS/MS system is introduced that provided excellent separation and identification power. The pH gradient-based elution provided more basic peptides than that of salt-based elution. Fraction overlap was significantly minimized by combining pH and continuous gradient elutions. This latter approach also increased sequence coverage and the concomitant confidence level in protein identification. The salt and pH elution-based 2-D LC-MS/MS approaches were compared by analyzing the mouse liver proteome.

Molecular weight and structure characterization of sodium hyaluronate and its gamma radiation degradation products by flow field-flow fractionation and on-line multiangle light scattering.

A combined flow field-flow fractionation (FlFFF)/multiangle light scattering (MALS)/differential refractive index (DRI) detection method has been utilized for the size fractionation and characterization of ultrahigh molecular weight (MW) sodium hyaluronate (NaHA) samples. Separation of broad MW NaHA polymers was carried out by a frit inlet asymmetrical FlFFF channel employed with a linear field programming method followed by the on-line monitoring of light scattering at multiple angles for the calculation of MW and for the study of the conformation of NaHA samples. NaHA samples examined were: (1) two different viscosity fractions of NaHA obtained by a refinement process and (2) NaHA products of gamma radiation degradation. While the NaHA samples of two different viscosity fractions exhibited clearly different MW distributions and similar conformation, the radiation degraded NaHA samples showed a clear difference in both MW distribution and polymer structure.

Automatic target localization and verification for on-line image-guided stereotactic body radiotherapy of the spine.

To facilitate image-guided stereotactic body radiotherapy (IG-SBRT) of spinal and paraspinal tumors, the authors have developed an on-line image registration system for automated target localization and patient position verification with high precision. When rotations are present in a patient's daily setup position, a setup error of a few millimeters can be introduced in localization of the isocenter by using surrounding bony structures. This setup error not only will deteriorate the dose coverage of the tumor, more importantly it will overdose the spinal cord. To resolve this issue, the image registration program developed by the authors detects translational shifts as well as rotational shifts using 3D CT image registration. Unacceptable rotations were corrected by either repositioning the patient or adjusting the treatment couch that was capable of rotational corrections when such a couch was available for clinical use. One pair of orthogonal digitally reconstructed radiographs (DRR) were generated from the daily pretreatment CT scan to compare with the corresponding DRRs generated from the planning CT scan to confirm the target shift correction. After the patient's position was corrected a pair of orthogonal portal images were taken for final verification. The accuracy of the image registration result was found to be within 0.1 mm on a head and neck phantom. Target shifts of a fraction of a millimeter were readily visible in our DRR comparison and portal image verification. The time needed to complete the image registration and DRR comparison was about 3 minutes. An integrated system that combines a high-speed CT scanner and a linear accelerator was used for imaging and treatment delivery. Application of the program in actual IG-SBRT cases demonstrated that it was accurate, fast, and reliable. It serves as a useful tool for image-guided radiotherapy where high precision of target localization is required.

On-line preconcentration strategies for analyzing pesticides in fruits and vegetables by micellar electrokinetic chromatography.

Five pesticides (fludioxonil, procymidone, pyriproxyfen, dinoseb and carbendazim) were separated in reversed migration micellar electrokinetic chromatography (RM-MEKC) using 20 mmol l(-1) phosphate buffer at pH 2.3, containing 25 mmol l(-1) sodium dodecylsulfate and 10% methanol. Three on-line concentration strategies, sweeping (SW), normal stacking with reversed migration and a water plug (SRW) and stacking with reverse migration and removal of sample matrix using polarity switching (SRMM), were compared. About 10-, 30- and 50-fold increases in detection sensitivity, compared with standard hydrodynamic injection (5 s at 0.5 psi), were observed with SW, SRW and SRMM, respectively. Limits of detection (LODs) ranged from 0.002 to 0.03 microg ml(-1) using only the on-line preconcentration procedures without any off-line concentration of the extract. A solid-phase extraction (SPE) procedure, for previous isolation and concentration of the analytes, was used in combination with any of the proposed on-line preconcentration strategies, which achieves the determination of pesticides at limits of quantification (LOQs) lower than 0.01 mg kg(-1). The recoveries obtained by SPE in samples spiked at 0.01 mg kg(-1) were between 70 and 100%, with RSDs between 10 and 18% using SRMM. Samples of fruits and vegetables were taken from the market, extracted by the proposed procedure and analyzed with RM-MEKC with the on-line strategies.