Alain Berthod

Surface Enhanced Raman Spectrometry on Silver Hydrosols Studied by Flow Injection Analysis

Surface enhanced Raman scattering (SERS) corresponds to the increase of the Raman scattering cross section of organic molecules (five to six orders of magnitude) when molecules are adsorbed onto metal surfaces. The use of silver hydrosols, obtained by chemical reduction of silver nitrate solutions, is convenient. An important drawback is irreproducibility of hydrosol preparation procedures and the nonlinearity between the SERS response and the analyte concentration. In order that these problems could be overcome, flow injection analysis (FIA) has been used. With FIA, constant, reproducible silver hydrosol formation results. SERS signals of para-aminobenzoic acid (PABA) were measured over four orders of magnitude of concentration range and over three pH units. The precision of FIA-SERS signals for PABA was 5%, and the limit of detection of PABA was in the ppb range with the use of the Raman band at 1605 cm−1 with an Ar+ laser at 514.5 nm.

Fluorescence in microemulsions and reversed micelles: a review and new results

The use of fluorescence to study physicochemical structures of alcohol/surfactant/water systems, microemulsions and reversed micelles is reviewed, and the application of these media in analytical fluorescence spectroscopy is discussed. The sodium dodecylsulfate/1-pentanol/heptane/ water system is studied by using pseudo-ternary diagrams. Wide areas of existence of thermodynamically stable and optically clear phases (Winsor IV and two liquid crystals) were found both in the absence and presence of sodium sulfate (0.2 M). The influence of the composition of media on the fluorescence characteristics of pyrene, benzo [e]pyrene, 2-naphthol and p-amino-benzoic acid is studied.

Evaluation and optimization of experimental conditions for surface-enhanced Raman detection of analytes in flow injection analysis

Abstract Surface-enhanced Raman spectrometry (SERS) is potentially a powerful analytical tool. The present study evaluates the experimental conditions required to obtain reproducible SERS signals of two model compounds, p -aminobenzoic acid and 9-aminoacridine, introduced into a flowing stream. The critical parameters in the preparation of the silver sols and the introduction of the analyte include concentrations of reagents, time of activation of the sols, time of interaction of the aggregated particles and the analyte, and the acidity of the flowing stream. Under the controlled experimental conditions of flow injection analysis, the reproducibility for measuring a 20-μl sample of 10 μg/ml p -aminobenzoic acid is 3.2% and the detection limit is 30 ng.

Solid-surface room-temperature phosphorimetric detection of caffeine, theophylline and theobromine in liquid chromatography

Solid-surface room-temperature phosphorimetry (SSRTP) is proposed as an alternative detection technique for the liquid chromatographic determination of caffeine, theophylline and theobromine. The measurements are performed in a continuous mode with a two-nebulizer automated system for SSRTP detection. The analytical figures of merit obtained with the proposed detector are compared with those obtained by UV absorption detection. The SSRTP and LJV chromatograms of spiked urine samples are compared, and the possibility of keeping the SSRTP substrates as permanent records of analyzed samples is discussed.

Solid-surface room-temperature phosphorescence detection for high-performance liquid chromatography

In the present study, we have optimized the use of a two nebulizer system for solid-surface room-temperature phosphorescence (SSRTP) as a selective, permanent record detector for high-performance liquid chromatography (HPLC). The chromatographic parameters and the analytical figures of merit of five well known phosphorescent compounds were compared to those obtained by ultraviolet detection. Calibration curves with satisfactory linear dynamic ranges and limits of detection in the nanogram and subnanogram level showed the feasibility of the SSRTP detector for HPLC. In addition, overlapped compounds were individually identified demonstrating that the selectivity of the proposed detector can be a useful feature in case of incomplete chromatographic separations of complex mixtures.

Flow injection for continuous sample introduction in solid-substrate room-temperature phosphorescence

Abstract The feasibility of using flow injection as a continuous sample introduction method for solid-surface room-temperature phosphorescence (SSRTP) is studied. A two-nebulizer system is used to spray the heavy-atom and analyte solutions separately onto the moving filter-paper strip. The analytical figures of merit obtained for three well known phosphorescent compounds show that flow injection can be successfully employed in SSRTP methods.

Flow-injection system for determination of critical micelle concentrations of ionic and nonionic surfactants

Abstract A practical technique is presented for the rapid, accurate determination of the critical micelle concentrations (CMCs) of ionic and nonionic surfactants. The precision, speed and instrumental simplicity of a flow-injection system are combined with a gradient chamber and flow-through conductance and absorbance detection to produce a system capable of determining the CMC of surfactant solutions in less than 30 min. The exponential response gradients from the resulting system are monitored by a chart recorder and simple manual calculations yield the CMC. The validity of the technique is verified by determination of the CMC values for both ionic (cetyltrimethylammonium bromide and chloride and sodium dodecyl sulfate) and nonionic (Brij-35, Brij-56, Brij-99, Triton X-100) surfactants. The proposed technique does not require the extensive solution preparation, repetitive measurements, complex instrumentation and data manipulation typical of other methods for determining CMCs.

Sensitive, indirect photometric detector for high-performance liquid chromatography using a light-emitting diode

A low-noise detector for indirect photometric detection has been constructed using a highly stable source--a light-emitting diode (LED). Use of the detector is demonstrated for reversed-phase liquid chromatography by adding methylene blue to the mobile phase to make a background signal. The indirect determination of alcohols by their effect on methylene blue concentration distribution is demonstrated, and an investigation is made into the conditions for high sensitivity. Because the source exhibits low noise, the detection limits for alcohols are as low as more complex and expensive detection methods, despite the lower radiant power of the LED. Detection limits for nine alcohols are below micrograms injected amounts.

A Becquerel-disc phosphoroscope for the measurement of lifetimes in room-temperature phosphorimetry☆

A Becquerel-disc phosphoroscope is constructed from a commercially available optical chopper with variable frequency and digital read-out. By use of a continuous source, phosphorescence lifetimes in the range 1-1000 msec can be measured with better than 4% relative standard deviation.