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1.
ACS Sens ; 5(3): 650-654, 2020 03 27.
Artigo em Inglês | MEDLINE | ID: mdl-32106675

RESUMO

Potentiometric pH probes remain the gold standard for the detection of pH but are not sufficiently sensitive to reliably detect ocean acidification at adequate frequency. Here, potentiometric probes are made dramatically more sensitive by placing a capacitive electronic component in series to the pH probe while imposing a constant potential over the measurement circuit. Each sample change now triggers a capacitive current transient that is easily identified between the two equilibrium states, and is integrated to reveal the accumulated charge. This affords dramatically higher precision than with traditional potentiometric probes. pH changes down to 0.001 pH units are easily distinguished in buffer and seawater samples, at a precision (standard deviation) of 28 µpH and 67 µpH, respectively, orders of magnitude better than what is possible with potentiometric pH probes.

2.
Anal Chem ; 91(7): 4889-4895, 2019 04 02.
Artigo em Inglês | MEDLINE | ID: mdl-30835441

RESUMO

We introduce here a general strategy to read out chronopotentiometric sensors by electrogenerated chemiluminescence (ECL). The potentials generated in chronopotentiometry in a sample compartment are used to control the ECL in a separate detection compartment. A three-electrode cell is used to monitor the concentration changes of the analyte, while the luminol-H2O2 system is responsible for ECL. The principle was shown to be feasible by theoretical simulations, indicating that the sampled times at a chosen potential, rather than traditional transition times, similarly give linear behavior between concentration and the square root of sampled time. With the help of a voltage adapter, the experimental combination between chronopotentiometry and ECL was successfully implemented. As an initial proof of concept, the ferro/ferricyanide redox couple was investigated. The square root of time giving maximum light output changed linearly with ferrocyanide concentration in the range from 0.70 to 4.81 mM. The method was successfully applied to the visual detection of carbonate alkalinity from 0.06 to 0.62 mM using chronopotentiometry at an ionophore-based hydrogen ion-selective membrane electrode. The measurements of carbonate in real samples including river water and commercial mineral water were successfully demonstrated.

3.
Environ Sci Process Impacts ; 17(5): 906-14, 2015 May.
Artigo em Inglês | MEDLINE | ID: mdl-25850652

RESUMO

Since aquatic environments are highly heterogeneous and dynamic, there is the need in aquatic ecosystem monitoring to replace traditional approaches based on periodical sampling followed by laboratory analysis with new automated techniques that allow one to obtain monitoring data with high spatial and temporal resolution. We report here on a potentiometric sensing array based on polymeric membrane materials for the continuous monitoring of nutrients and chemical species relevant for the carbon cycle in freshwater ecosystems. The proposed setup operates autonomously, with measurement, calibration, fluidic control and acquisition triggers all integrated into a self-contained instrument. Experimental validation was performed on an automated monitoring platform on lake Greifensee (Switzerland) using potentiometric sensors selective for hydrogen ions, carbonate, calcium, nitrate and ammonium. Results from the field tests were compared with those obtained by traditional laboratory analysis. A linear correlation between calcium and nitrate activities measured with ISEs and relevant concentrations measured in the laboratory was found, with the slopes corresponding to apparent single ion activity coefficients γ(*)(Ca(2+)) = 0.55(SD = 0.1mM) and γ(*)(NO(3)(-)) = 0.75(SD = 4.7µm). Good correlation between pH values measured with ISE and CTD probes (SD = 0.2 pH) suggests adequate reliability of the methodology.


Assuntos
Monitoramento Ambiental/instrumentação , Água Doce/química , Potenciometria , Poluentes Químicos da Água/análise , Compostos de Amônio/análise , Cálcio/análise , Calibragem , Carbonatos/análise , Ecossistema , Monitoramento Ambiental/métodos , Nitratos/análise , Reprodutibilidade dos Testes
4.
Chimia (Aarau) ; 68(11): 772-7, 2014 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-26508483

RESUMO

Aquatic environments are complex living systems where biological and chemical constituents change rapidly with time and space and may exhibit synergistic interactions. To understand these processes, the traditional approach based on a typically monthly collection of samples followed by laboratory analysis is not adequate. It must be replaced by high-resolution autonomous in situ detection approaches. In our group at the University of Geneva, we aim to develop and deploy chemical sensor probes to understand complex aquatic systems. Most research centers around electrochemical sensing approaches, which involves: stripping voltammetry at gel-coated microelectrode arrays for direct measurements of bioavailable essential or toxic trace metals; direct potentiometry for the measurement of nutrients and other species involved in the nitrogen and carbon cycles; online desalination for oceanic measurements; the development of robust measurement principles such as thin layer coulometry, and speciation analysis by tandem electrochemical detection with potentiometry and dynamic electrochemistry. These fundamental developments are combined with instrument design, both in-house and with external partners, and result in field deployments in partnership with environmental researchers in Switzerland and the European Union.


Assuntos
Monitoramento Ambiental , Suíça , Poluentes Químicos da Água/análise
5.
J Colloid Interface Sci ; 303(2): 460-71, 2006 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-16978638

RESUMO

Deposition of positively charged nanosized latex particles onto planar silica and cellulose substrates was studied in monovalent electrolyte solutions at pH 9.5. The deposition was probed in situ with optical reflectometry in a stagnation point flow cell. The surface coverage can be estimated reliably with island film theory as well as with a homogeneous film model, as confirmed with atomic force microscopy (AFM). The deposition kinetics on the bare surface was of first order with respect to the particle concentration, whereby the deposition rate was close to the value expected for a perfect collector. The efficiency coefficient, which was defined as the ratio of the experimental and theoretical deposition rate constants, was in the range from 0.3 to 0.7. Subsequently, the surface saturated and a limiting maximum coverage was attained (i.e., blocking). These trends were in qualitative agreement with predictions of the random sequential absorption (RSA) model, where electrostatic interactions between the particles were included. It was observed, however, that the substrate strongly influenced the maximum coverage, which was substantially higher for silica than for cellulose. The major conclusion of this work was that the nature of the substrate played an important role in a saturated layer of deposited colloidal particles.


Assuntos
Celulose/química , Látex/química , Nanopartículas/química , Óptica e Fotônica , Dióxido de Silício/química , Concentração de Íons de Hidrogênio , Microscopia de Força Atômica , Modelos Químicos , Propriedades de Superfície
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