Monitorización de la glucemia en el paciente crítico adulto: tipo de muestra y método de análisis. Revisión sistemática y metanálisis / Blood glucose monitoring in critically ill adult patients: Type of sample and method of analysis. Systematic review and meta-analysis

IntroducciónLa guía clínica para el manejo de la sepsis recomienda usar muestras de sangre arterial para el control glucémico. Un estudio multicéntrico en 86 unidades de cuidados intensivos españolas reveló que el 85,4% de estas utilizaban punción capilar.ObjetivoAnalizar la fiabilidad de la glucemia comparando diferentes muestras sanguíneas (arterial, venosa, capilar) e instrumentos (glucómetros, gasómetros, laboratorio central). Secundariamente, estimar el efecto de variables confusoras y el rendimiento de los instrumentos de medición determinados por las diferentes normas de calidad.MetodologíaRevisión sistemática y metanálisis con búsqueda en las bases de datos PubMed, CINAHL y Embase en septiembre-2021 y septiembre-2022, sin límites temporales ni idiomáticos. Fuentes de literatura gris: DART-Europe, OpenGrey y Google Académico. Resultados resumidos mediante síntesis cualitativa (descripción de resultados, características de los estudios) y cuantitativa (metanálisis para evaluar la diferencia de medias estandarizadas). Calidad metodológica de artículos evaluada con Quality Assessment of Diagnostic Accuracy Studies-2. Protocolo: https://osf.io/ DOI 10.17605/OSF.IO/T8KYP.ResultadosSe incluyeron un total de 32 artículos y 5.451 pacientes. No se obtuvieron discrepancias entre muestras arteriales con glucómetro vs. laboratorio (sesgo [IC95%]: 0,01 [−0,12 a 0,14] mg/dL). En cambio, muestras arteriales con gasómetro sí sobreestimaron de forma significativa (sesgo [IC95%]: 0,12 [0,01 a 0,24] mg/dL). La misma tendencia presentan capilares con glucómetro, aunque no de forma significativa (sesgo [IC95%]: 0,07 [−0,02 a 0,15] mg/dL). Hay discrepancia entre los estudios sobre el efecto del hematocrito y el equilibrio ácido-base. El mayor consenso se da en la poca concordancia del glucómetro con muestras capilares vs. laboratorio en presencia de shock y soporte vasopresor, situación de fallo renal o durante el tratamiento con vitamina C.Conclusiones... (AU)

IntroductionThe clinical guideline for the management of sepsis recommends using arterial blood samples for glycaemic control. A multicentre study in 86 Spanish intensive care units revealed that 85.4% of these used capillary puncture.ObjectiveTo analyse the reliability of glycaemia by comparing different blood samples (arterial, venous, capillary) and instruments (glucometers, gasometers, central laboratory). Secondarily, to estimate the effect of confounding variables and the performance of measuring instruments as determined by different quality standards.MethodologySystematic review and meta-analysis with search in PubMed, CINAHL and Embase databases in September-2021 and September-2022, with no time or language limits. Grey literature sources: DART-Europe, OpenGrey and Google Scholar. Results summarised by qualitative (description of results, study characteristics) and quantitative (meta-analysis to assess standardised mean difference) synthesis. Methodological quality of articles assessed with Quality Assessment of Diagnostic Accuracy Studies-2. Protocol: https://osf.io/ DOI 10.17605/OSF.IO/T8KYP.ResultsA total of 32 articles and 5451 patients were included. No discrepancies were obtained between arterial glucometer vs. laboratory samples (bias [95%CI]: 0.01 [−0.12 to 0.14] mg/dL). In contrast, arterial samples with a gasometer did significantly overestimate (bias [95%CI]: 0.12 [0.01 to 0.24] mg/dL). The same trend is seen in capillaries with a glucometer, although not significantly (bias [95%CI]: 0.07 [−0.02 to 0.15] mg/dL). There is discrepancy between studies on the effect of haematocrit and acid-base balance. The greatest consensus is on the poor agreement of glucometer with capillary vs. laboratory samples in the presence of shock and vasopressor support, renal failure or during vitamin C treatment.Conclusions... (AU)

Monitorización de la glucemia en el paciente crítico adulto: tipo de muestra y método de análisis. Revisión sistemática y metanálisis / Blood glucose monitoring in critically ill adult patients: Type of sample and method of analysis. Systematic review and meta-analysis

IntroducciónLa guía clínica para el manejo de la sepsis recomienda usar muestras de sangre arterial para el control glucémico. Un estudio multicéntrico en 86 unidades de cuidados intensivos españolas reveló que el 85,4% de estas utilizaban punción capilar.ObjetivoAnalizar la fiabilidad de la glucemia comparando diferentes muestras sanguíneas (arterial, venosa, capilar) e instrumentos (glucómetros, gasómetros, laboratorio central). Secundariamente, estimar el efecto de variables confusoras y el rendimiento de los instrumentos de medición determinados por las diferentes normas de calidad.MetodologíaRevisión sistemática y metanálisis con búsqueda en las bases de datos PubMed, CINAHL y Embase en septiembre-2021 y septiembre-2022, sin límites temporales ni idiomáticos. Fuentes de literatura gris: DART-Europe, OpenGrey y Google Académico. Resultados resumidos mediante síntesis cualitativa (descripción de resultados, características de los estudios) y cuantitativa (metanálisis para evaluar la diferencia de medias estandarizadas). Calidad metodológica de artículos evaluada con Quality Assessment of Diagnostic Accuracy Studies-2. Protocolo: https://osf.io/ DOI 10.17605/OSF.IO/T8KYP.ResultadosSe incluyeron un total de 32 artículos y 5.451 pacientes. No se obtuvieron discrepancias entre muestras arteriales con glucómetro vs. laboratorio (sesgo [IC95%]: 0,01 [−0,12 a 0,14] mg/dL). En cambio, muestras arteriales con gasómetro sí sobreestimaron de forma significativa (sesgo [IC95%]: 0,12 [0,01 a 0,24] mg/dL). La misma tendencia presentan capilares con glucómetro, aunque no de forma significativa (sesgo [IC95%]: 0,07 [−0,02 a 0,15] mg/dL). Hay discrepancia entre los estudios sobre el efecto del hematocrito y el equilibrio ácido-base. El mayor consenso se da en la poca concordancia del glucómetro con muestras capilares vs. laboratorio en presencia de shock y soporte vasopresor, situación de fallo renal o durante el tratamiento con vitamina C.Conclusiones... (AU)

IntroductionThe clinical guideline for the management of sepsis recommends using arterial blood samples for glycaemic control. A multicentre study in 86 Spanish intensive care units revealed that 85.4% of these used capillary puncture.ObjectiveTo analyse the reliability of glycaemia by comparing different blood samples (arterial, venous, capillary) and instruments (glucometers, gasometers, central laboratory). Secondarily, to estimate the effect of confounding variables and the performance of measuring instruments as determined by different quality standards.MethodologySystematic review and meta-analysis with search in PubMed, CINAHL and Embase databases in September-2021 and September-2022, with no time or language limits. Grey literature sources: DART-Europe, OpenGrey and Google Scholar. Results summarised by qualitative (description of results, study characteristics) and quantitative (meta-analysis to assess standardised mean difference) synthesis. Methodological quality of articles assessed with Quality Assessment of Diagnostic Accuracy Studies-2. Protocol: https://osf.io/ DOI 10.17605/OSF.IO/T8KYP.ResultsA total of 32 articles and 5451 patients were included. No discrepancies were obtained between arterial glucometer vs. laboratory samples (bias [95%CI]: 0.01 [−0.12 to 0.14] mg/dL). In contrast, arterial samples with a gasometer did significantly overestimate (bias [95%CI]: 0.12 [0.01 to 0.24] mg/dL). The same trend is seen in capillaries with a glucometer, although not significantly (bias [95%CI]: 0.07 [−0.02 to 0.15] mg/dL). There is discrepancy between studies on the effect of haematocrit and acid-base balance. The greatest consensus is on the poor agreement of glucometer with capillary vs. laboratory samples in the presence of shock and vasopressor support, renal failure or during vitamin C treatment.Conclusions... (AU)

Blood glucose monitoring in critically ill adult patients: type of sample and method of analysis. Systematic review and meta-analysis.

INTRODUCTION: The clinical guideline for the management of sepsis, recommends using arterial blood samples for glycaemic control. A multicentre study in 86 Spanish intensive care units (ICU) revealed that 85.4% of ICUs used capillary puncture. OBJECTIVE: To analyse the reliability of glycaemia by comparing different blood samples (arterial, venous, capillary) and instruments (glucometers, gasometers, central laboratory). Secondarily, to estimate the effect of confounding variables and the performance of measuring instruments as determined by different quality standards. METHODOLOGY: Systematic review and meta-analysis with search in PubMed, CINAHL and Embase databases in September-2021 and September-2022, with no time or language limits. Grey literature sources: DART-Europe, OpenGrey and Google Scholar. Results summarised by qualitative (description of results, study characteristics) and quantitative (meta-analysis to assess standardised mean difference) synthesis. Methodological quality of articles assessed with Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2). PROTOCOL: https://osf.io/ DOI 10.17605/OSF.IO/T8KYP. RESULTS: A total of 32 articles and 5451 patients were included. No discrepancies were obtained between arterial glucometer vs laboratory samples [bias (95%CI): 0.01 (-0.12 to 0.14) mg/dL]. In contrast, arterial samples with a gasometer did significantly overestimate [bias (95%CI): 0.12 (0.01 to 0.24) mg/dL]. The same trend is seen in capillaries with a glucometer, although not significantly [bias (95%CI): 0.07 (--0.02 to 0.15) mg/dL]. There is discrepancy between studies on the effect of haematocrit and acid-base balance. The greatest consensus is on the poor agreement of glucometer with capillary vs laboratory samples in the presence of shock and vasopressor support, renal failure or during vitamin C treatment. CONCLUSIONS: The evidence to date recommends the use of arterial blood with a blood glucose meter for better reliability of glycaemic analysis and less effect of possible confounding variables, frequently present in the critically ill adult patient.

Diseño de un modelo de ronda de seguridad para unidades de cuidados intensivos / Design of a safety round model for intensive care units

Introducción: Las rondas de seguridad (RS) son una herramienta operativa que permite conocer la adherencia a las buenas prácticas, ayuda a identificar riesgos e incidentes en seguridad del paciente (SP), permitiendo implementar acciones de mejora. El objetivo de este trabajo fue el diseño de un procedimiento para realizar RS en una unidad de cuidados intensivos (UCI). Métodos: Elaboración de un listado de verificación para el desarrollo de RS en una UCI mediante técnica de grupo nominal, con la participación de directivos, mandos intermedios y profesionales de diferentes disciplinas y categorías. En primer lugar, un grupo de expertos consensuó, atendiendo a las recomendaciones en buenas prácticas en SP, la definición de ítems, su codificación, los criterios de cumplimiento y el impacto de su incumplimiento. Posteriormente, determinó su viabilidad mediante un estudio transversal a través del pilotaje de 2 RS para ajustar los ítems en condiciones de práctica clínica real. Resultados: Se ha obtenido un modelo de RS específico para UCI mediante un listado de verificación. El grupo de expertos elaboró un primer listado compuesto por 39 ítems de 6 dimensiones esenciales y definió el modo de realización. El tiempo medio de realización de las 2 RS fue de 85minutos, incluyendo el briefing y debriefing posterior. Tras el pilotaje de validación se redujo las dimensiones a 5, se suprimió 3 ítems, se trasladó 2 ítems a otra dimensión y se modificó 3 ítems relativos a infecciones nosocomiales y consentimiento informado. Además, se redefinieron las fuentes de datos, los criterios de cumplimiento y su peso relativo. El listado definitivo fue considerado útil y relevante para mejorar la práctica. Conclusiones: Mediante una metodología de consenso se ha construido un listado de verificación para ser usado en las RS de una UCI. Este modelo puede servir de base para su empleo en servicios asistenciales de similares características.(AU)

Introduction: Safety Rounds (SR) are an operational tool that allow knowing adherence to good practices, help identify risks and incidents in patient safety (PS), allowing improvement actions to be implemented. The objective of this work was the design of a procedure to perform SR in an Intensive Care Unit (ICU). Methods: Preparation of a checklist for the development of SR in the ICU through the nominal group technique, with the participation of managers, middle managers and professionals from different disciplines and categories. In the first place, a group of experts agreed, based on the recommendations on good practices in PS, the definition of items, their coding, the criteria for compliance and the impact of non-compliance. Subsequently, its viability was determined through a cross-sectional study through the piloting of two SRs to adjust the items in real clinical practice conditions. Results: A specific SR model for ICUs has been obtained through a checklist. The group of experts prepared a first list made up of 39 items of 6 essential dimensions and defined the method of implementation. Mean time to complete the two SRs was 85minutes, including the briefing and subsequent debriefing. After the validation pilot, the dimensions were reduced to 5, 3 items were deleted, 2 items were transferred to another dimension and 3 items related to nosocomial infections and informed consent were modified. In addition, the data sources, the compliance criteria and their relative weight were redefined. The final list was considered useful and relevant to improve practice. Conclusions: Through a consensus methodology, a checklist has been built to be used in the RS of an ICU. This model can serve as a basis for its use in healthcare services with similar characteristics.(AU)

Effectiveness of closed blood sampling systems in intensive care patients: a scoping review.

BACKGROUND: Anemia associated with blood extraction for diagnostic purposes is a highly prevalent entity in intensive care units (ICU) for adults. The evidence recommends its prevention through different strategies, among which we can find the use of closed blood sampling systems (CBSS). Different experimental studies support the use of these devices. OBJECTIVE: To identify knowledge gaps regarding the effectiveness of CBSS in ICU patients. METHODS: Scoping review with search in PubMed, CINAHL, Embase, Cochrane Library and Joanna Briggs Institute databases, between September-2021 and September-2022. No time, language, or other limits were applied to ensure the recovery of all relevant studies. Gray literature sources: DART-Europe, OpenGrey and Google Scholar. Two researchers independently reviewed titles and abstracts and assessed full texts against the inclusion criteria. The following data was extracted for each study: design and sample, inclusion and exclusion criteria, variables, type of CBSS, results and conclusions. RESULTS: 18 articles were included in the final review, 11 clinical trials (RCTs) published between 1992 and 2014. Three systematic reviews were found, but they only analyzed the effect of CBSS in reducing blood loss, hemoglobin stabilization, and the need for transfusion. Five of the RCTs analyzed the risk of infection, one catheter complications, and two alterations in blood pressure readings. CONCLUSIONS: The use of CBSS is recommended to reduce blood loss in ICUs. However, there are discrepancies about their ability to prevent anemia and/or the need for blood transfusion. Its use does not increase catheter-related infection rates or alter the measurement of mean arterial pressure.

Design of a safety round model for intensive care units.

INTRODUCTION: Safety Rounds (SR) are an operational tool that allow knowing adherence to good practices, help identify risks and incidents in patient safety (PS), allowing improvement actions to be implemented. The objective of this work was the design of a procedure to perform SR in an Intensive Care Unit (ICU). METHODS: Preparation of a checklist for the development of SR in the ICU through the nominal group technique, with the participation of managers, middle managers and professionals from different disciplines and categories. In the first place, a group of experts agreed, based on the recommendations on good practices in PS, the definition of items, their coding, the criteria for compliance and the impact of non-compliance. Subsequently, its viability was determined through a cross-sectional study through the piloting of two SRs to adjust the items in real clinical practice conditions. RESULTS: A specific SR model for ICUs has been obtained through a checklist. The group of experts prepared a first list made up of 39 items of 6 essential dimensions and defined the method of implementation. Mean time to complete the two SRs was 85 min, including the briefing and subsequent debriefing. After the validation pilot, the dimensions were reduced to 5, 3 items were deleted, 2 items were transferred to another dimension and 3 items related to nosocomial infections and informed consent were modified. In addition, the data sources, the compliance criteria and their relative weight were redefined. The final list was considered useful and relevant to improve practice. CONCLUSIONS: Through a consensus methodology, a checklist has been built to be used in the RS of an ICU. This model can serve as a basis for its use in healthcare services with similar characteristics.

Clindamycin but not Intravenous Immunoglobulins reduces mortality in a retrospective cohort of critically ill patients with bacteremic Group A Streptococcal infections.

OBJECTIVE: Mortality of patients requiring Intensive Care Unit (ICU) admission for an invasive group A streptococcal (GAS) infection continues being high. In critically ill patients with bacteremic GAS infection we aimed at determining risk factors for mortality. METHODS: Retrospective multicentre study carried out in nine ICU in Southern Spain. All adult patients admitted to the participant ICUs from January 2014 to June 2019 with one positive blood culture for S. pyogenes were included in this study. Patient characteristics, infection-related variables, therapeutic interventions, failure of organs, and outcomes were registered. Risk factors independently associated with ICU and in-hospital mortalities were determined by multivariate regression analyses. RESULTS: Fifty-seven patients were included: median age was 63 (45-73) years, median SOFA score at admission was 11 (7-13). The most frequent source was skin and soft tissue infection (n=32) followed by unknown origin of bacteremia (n=12). In the multivariate analysis, age (OR 1.079; 95% CI 1.016-1.145), SOFA score (OR 2.129; 95% CI 1.339-3.383) were the risk factors for ICU mortality and the use of clindamycin was identified as a protective factor (OR 0.049; 95% CI 0.003-0.737). Age and SOFA were the independent factors associated with hospital mortality however the use of clindamycin showed a strong trend but without reaching statistical significance (OR 0.085; 95% CI 0.007-1.095). CONCLUSIONS: In this cohort of critically ill patients the use of intravenous immunoglobulin was not identified as a protective factor for ICU or hospital mortality treatment with clindamycin significantly reduced mortality after controlling for confounders.

Biotransformation of Endocrine-Disrupting Compounds in Groundwater: Bisphenol A, Nonylphenol, Ethynylestradiol and Triclosan by a Laccase Cocktail from Pycnoporus sanguineus CS43.

The biodegradation of organic compounds present in water at trace concentration has become a critical environmental problem. In particular, enzymatic oxidation by fungal laccases offers a promising alternative for efficient and sustainable removal of organic pollutants in water. In this work, the biocatalytic ability of laccases from the Pycnoporus sanguineus CS43 fungus was evaluated. A filtered culture supernatant (laccase cocktail) evidenced an enhanced biotransformation capability to remove common endocrine-disruptor compounds (EDCs), such as bisphenol A, 4-nonylphenol, 17-α-ethynylestradiol and triclosan. A biodegradation of around 89-100 % was achieved for all EDCs using synthetic samples (10 mg L-1) and after the enzymatic treatment with 100 U L-1 (50.3 U mg -1). The biodegradation rates obtained were fitted to a first order reaction. Furthermore, enzymatic biocatalytic activity was also evaluated in groundwater samples coming from northwestern Mexico, reaching biotransformation percentages between 55 and 93 % for all tested compounds. As far as we know this is the first study on real groundwater samples in which the enzymatic degradation of target EDCs by a laccase cocktail from any strain of Pycnoporus sanguineus was evaluated. In comparison with purified laccases, the use of cocktail offers operational advantages since additional purification steps can be avoided.

Determination of pesticides and their metabolites in processed cereal samples.

Fifteen pesticides including some of their metabolites (disulfoton sulfoxide, ethoprophos, cadusafos, dimethoate, terbufos, disulfoton, chlorpyrifos-methyl, malaoxon, fenitrothion, pirimiphos-methyl, malathion, chlorpyrifos, terbufos sulfone, disulfoton sulfone and fensulfothion) were analysed in milled toasted wheat and maize as well as in wheat flour and baby cereals. The QuEChERS (quick, easy, cheap, effective, rugged and safe) methodology was used and its dispersive solid-phase extraction procedure was optimised by means of an experimental design with the aim of reducing the amount of co-extracted lipids and obtaining a clean extract. Gas chromatography with nitrogen phosphorus detection were used as the separation and detection techniques, respectively. The method was validated in terms of selectivity, recoveries, calibration, precision and accuracy as well as matrix effects. Limits of detection were between 0.07 and 34.8 µg kg(-1) with recoveries in the range of 71-110% (relative standard deviations were below 9%). A total of 40 samples of different origin were analysed. Residues of pirimiphos-methyl were found in six of the samples at concentrations in the range 0.08-0.47 mg kg(-1), which were below the MRLs established for this pesticide in cereal grains. Tandem mass spectrometry confirmation was also carried out in order to identify unequivocally the presence of this pesticide.

Evaluation of a modified QuEChERS method for the extraction of pesticides from agricultural, ornamental and forestal soils.

A modified version of the QuEChERS method has been developed for the determination of a group of ten organophosphorus pesticides (i.e. ethoprofos, dimethoate, diazinon, malaoxon, chlorpyrifos-methyl, fenitrothion, malathion, chlorpyrifos, fenamiphos and phosmet) and one thiadiazine pesticide (buprofezin) in three different types of soils (forestal, ornamental and agricultural). The method was validated through linearity, recovery, precision and accuracy studies, and also by carrying out a matrix-matched calibration for the three soils owing to the existence of a strong matrix effect. Acceptable recovery values were obtained (between 45 and 96%) for all the pesticides and soils, except for malathion and malaoxon in forestal and ornamental soils, from which they could not be quantitatively extracted. Limits of detection of the whole method ranged between 0.48 and 7.78 ng/g. The method was finally applied to the determination of chlorpyrifos concentration in a treated soil for cultivation of potatoes.

Evaluation of multi-walled carbon nanotubes as solid-phase extraction adsorbents of pesticides from agricultural, ornamental and forestal soils.

A new, simple and cost-effective method based on the use of multi-walled carbon nanotubes (MWCNTs) as solid-phase extraction stationary phases is proposed for the determination of a group of seven organophosphorus pesticides (i.e. ethoprophos, diazinon, chlorpyriphos-methyl, fenitrothion, malathion, chlorpyriphos and phosmet) and one thiadiazine (buprofezin) in different kinds of soil samples (forestal, ornamental and agricultural) using gas chromatography with nitrogen phosphorus detection. Soils were first ultrasound extracted with 10 mL 1:1 methanol/acetonitrile (v/v) and the evaporated extract redissolved in 20 mL water (pH 6.0) was passed through 100 mg of MWCNTs of 10-15 nm o.d., 2-6 nm i.d. and 0.1-10 microm length. Elution was carried out with 20 mL dichloromethane. The method was validated in terms of linearity, precision, recovery, accuracy and selectivity. Matrix-matched calibration was carried out for each type of soil since statistical differences between the calibration curves constructed in pure solvent and in the reconstituted soil extract were found for most of the pesticides under study. Recovery values of spiked samples ranged between 54 and 91% for the three types of soils (limits of detection (LODs) between 2.97 and 9.49 ngg(-1)), except for chlorpyrifos, chlorpyrifos-methyl and buprofezin which ranged between 12 and 54% (LODs between 3.14 and 72.4 ngg(-1)), which are the pesticides with the highest soil organic carbon sorption coefficient (K(OC)) values. Using a one-sample test (Student's t-test) with fortified samples at two concentration levels in each type of soil, no significant differences were observed between the real and the experimental values (accuracy percentages ranged between 87 and 117%). It is the first time that the adsorptive potential of MWCNTs for the extraction of organophosphorus pesticides from soils is investigated.

Carbon monoxide adsorption on low-silica zeolites: from single to dual and to multiple cation sites.

Infrared spectra of CO adsorbed on the Al-rich Na-A zeolite were analysed by using a combined theoretical and experimental approach, showing that such spectra cannot be interpreted by assigning each IR band to CO interacting with a specific type of single cation site. This concept, which usually works well for high-silica zeolites, should not be uncritically extended to Al-rich zeolites that are crowded with cations in configurations which lead to preferential formation of CO adsorption complexes involving more than one cation site.

Thermodynamics of reversible gas adsorption on alkali-metal exchanged zeolites--the interplay of infrared spectroscopy and theoretical calculations.

Detailed understanding of weak solid-gas interactions giving rise to reversible gas adsorption on zeolites and related materials is relevant to both, fundamental studies on gas adsorption and potential improvement on a number of (adsorption based) technological processes. Combination of variable-temperature infrared spectroscopy with theoretical calculations constitutes a fruitful approach towards both of these aims. Such an approach is demonstrated here (mainly) by reviewing recent studies on hydrogen and carbon monoxide adsorption (at a low temperature) on alkali-metal exchanged ferrierite. However, the methodology discussed, which involves the interplay of experimental measurements and theoretical calculations at the periodic DFT level, should be equally valid for many other gas-solid systems. Specific aspects considered are the identification of gas adsorption complexes and thermodynamic studies related to standard adsorption enthalpy and entropy.

Single and dual cation sites in zeolites: theoretical calculations and FTIR spectroscopic studies on CO adsorption on K-FER.

Interaction of CO with K-FER zeolite was investigated by a combination of variable-temperature IR spectroscopy and computational study. Calculations were performed using omega(CO)/r(CO) correlation method in combination with a periodic density functional theory model. On the basis of agreement between experimental and calculated results, the following carbonyl complexes were identified: (i) mono- and dicarbonyl C-down complexes on single K(+) sites characterized by IR absorption bands at 2163 and 2161 cm(-1), respectively; (ii) complexes formed by CO bridging two K(+) ions separated by about 7-8 A (dual sites) characterized by a band at 2148 cm(-1); and (iii) isocarbonyl (O-down) complexes characterized by a band at 2116 cm(-1). The bridged carbonyl complexes on dual K(+) sites are about 5 kJ/mol more stable than monodentate (monocarbonyl) CO complexes. The C-O stretching frequency of monocarbonyl species in K-FER depends on K(+) location in the zeolite, and not on K(+) coordination to the framework. A combination of theoretical calculations using a periodic density functional model and experimental results showed formation of two types of monocarbonyls. The most abundant type appears at 2163 cm(-1), and the less abundant one at 2172 cm(-1). These experimentally determined wavenumber values coincide, within +/-2 cm(-1), with those derived from theoretical calculations.

Ferreting out gas adsorption heats: the pseudo-isobaric method.

A new method is demonstrated for calculating gas adsorption heats from variable-temperature infrared spectra of adsorbed molecules. By focusing on the low coverage regime, where (at equilibrium) there is only a very small fraction of molecules adsorbed, the procedure devised yields the corresponding value of adsorption enthalpy without needing to know the equilibrium pressure. Experimental measurements can thus be highly simplified, which constitutes one of the merits of the new method. Versatility for dealing with adsorption processes occurring at a low temperature, and having a small energy balance, is another favourable feature.

Infrared spectroscopic study on the surface properties of gamma-gallium oxide as compared to those of gamma-alumina.

By hydrolysis of an ethanolic gallium nitrate solution, gamma-Ga2O3 was prepared as a single-phase polymorph having a specific surface area of 160 m2 g(-1). Surface acidity and basicity of this material was studied by IR spectroscopy, using pyridine, 2,6-dimethylpyridine, acetonitrile, and carbon dioxide as spectroscopic probe molecules. For comparison, a gamma-Al2O3 sample having a surface area of 290 m2 g(-1) was also studied. On partially hydroxylated gamma-Ga2O3, the main O-H stretching bands were found at 3693 (sharp) and at 3660-3630 cm(-1) (broad), and the material proved (by adsorbed dimethylpyridine) to have a weak Brønsted acidity. Surface Lewis acidity of gamma-Ga2O3 was revealed (mainly) by adsorbed pyridine, which gave the characteristic IR absorption bands of Lewis-type adducts at 1612, 1579, 1488, and 1449 cm(-1) (values noted under an equilibrium pressure of 1 Torr at room temperature); the corresponding Lewis acid centers (coordinatively unsaturated Ga3+ ions) were found to be weaker, although more abundant, than those present on the surface of gamma-Al2O3 (unsaturated Al3+ ions). Another significant difference between gamma-Ga2O3 and gamma-Al2O3 is the smaller thermal stability of pyridine and 2,6-dimethylpyridine Lewis adducts formed on the gallium oxide. The surface basicity of gamma-Ga2O3 was studied by using carbon dioxide and deuterated acetonitrile as IR probe molecules. Adsorbed CO2 gave carbonate and hydrogen-carbonate surface species similar to those formed by gamma-Al2O3. Adsorbed acetonitrile gave rise to acetamide species, which revealed the basic character of surface O2- ions. These acetamide species were found to be more abundant on gamma-Ga2O3 than on gamma-Al2O3.

Pesticide analysis by capillary electrophoresis.

In this work, a critical and updated revision of the current situation of the analysis of pesticides by Capillary Electrophoresis (CE) is presented. The review has been written in two main sections. The first one presents a thorough revision of the various offline and on-line sample preconcentration procedures that have been used in conjunction with CE to analyze these compounds. The second part reviews the various detection strategies (i.e., UV, LIF, MS, and electrochemical) and CE modes that have been applied to the analysis of pesticides. Future trends that can be expected from this hot research area are also discussed.

Content of aliphatic hydrocarbons in limpets as a new way for classification of species using artificial neural networks.

It is demonstrated that biological species like limpets can be classified according to their level of n-alkanes when artificial neural networks are applied. Marine intertidal and subtidal limpets of the Canary Islands (Spain), Patella piperata, Patella candei crenata and Patella ulyssiponensis aspera were selected as bioindicator organisms. Samples were collected at four stations on the coasts of Fuerteventura. Concentration of n-alkanes in the soft tissues of the limpets has been determined by gas chromatography. Data were treated with artificial neural networks (ANNs) and it was found that using suitable architecture of a supervised artificial neural network, the limpets can be successfully distinguished (classified) up to 98%.

Determination of esters in dry and sweet white wines by headspace solid-phase microextraction and gas chromatography.

Headspace solid-phase microextraction (HS-SPME) was studied for the high-resolution gas chromatographic (HRGC) analysis of esters in wines. Five different SPME fibers were tested and the influence of different factors such as temperature and time of desorption, extraction time, extraction technique, stirring, sample and vial volume, sugar and ethanol content were studied and optimised using model solutions. The proposed HS-SPME-GC method is an appropriate technique for the quantitative analysis of esters in dry and sweet white wines.

Comparison of different coatings in solid-phase microextraction for the determination of organochlorine pesticides in ground water.

A solid-phase microextraction (SPME) procedure using three commercialised fibers (Carbowax-divinylbenzene, Carboxen-polydimethylsiloxane and divinylbenzene-Carboxen-polydimethylsiloxane) is presented for the determination of a selected group of organochlorine compounds in water samples. The extraction performances of these compounds were compared using fibers with two and three coatings. The optimal experimental procedures for the adsorption and desorption of pesticides were determined. The limits of detection with the divinylbenzene-Carboxen-polydimethylsiloxane fiber at levels below ng l(-1) were similar or lower than values presented in the literature for several of these compounds using polydimethylsiloxane fiber. The advantages of using this fiber, such as no salt addition, are discussed. Finally, the optimised procedures were applied successfully for the determination of these compounds in polluted ground water samples.