Search results for "Wave"
showing 10 items of 6009 documents
Excitonic energy level structure and pigment-protein interactions in the recombinant water-soluble chlorophyll protein. II. Spectral hole-burning exp…
2011
Persistent spectral hole burning at 4.5 K has been used to investigate the excitonic energy level structure and the excited state dynamics of the recombinant class-IIa water-soluble chlorophyll-binding protein (WSCP) from cauliflower. The hole-burned spectra are composed of four main features: (i) a narrow zero-phonon hole (ZPH) at the burn wavelength, (ii) a number of vibrational ZPHs, (iii) a broad low-energy hole at ~665 and ~683 nm for chlorophyll b- and chlorophyll a-WSCP, respectively, and (iv) a second satellite hole at ~658 and ~673 nm for chlorophyll b- and chlorophyll a-WSCP, respectively. The doublet of broad satellite holes is assigned to an excitonically coupled chlorophyll dim…
A complementary mobile phase approach based on the peak count concept oriented to the full resolution of complex mixtures
2011
Situations of minimal resolution are often found in liquid chromatography, when samples that contain a large number of compounds, or highly similar in terms of structure and/or polarity, are analysed. This makes full resolution with a single separation condition (e.g., mobile phase, gradient or column) unfeasible. In this work, the optimisation of the resolution of such samples in reversed-phase liquid chromatography is approached using two or more isocratic mobile phases with a complementary resolution behaviour (complementary mobile phases, CMPs). Each mobile phase is dedicated to the separation of a group of compounds. The CMPs are selected in such a way that, when the separation is cons…
Focused microwave-assisted Soxhlet extraction: An expeditive approach for the isolation of lipids from sausage products
2003
A prototype of extractor based on the conventional Soxhlet principles but assisted in the cartridge zone by focused microwaves is proposed for accelerating the extraction of lipids from sausage products. The extraction process has been optimised using a multivariate design involving the main variables influencing the performance of the prototype (namely, irradiation power P, irradiation time T and number of cycles C). Under the optimum working conditions (P=160 W, T=10 s and C=14), the extraction of lipids from different Spanish sausage products is complete in 45 min. The extracts thus obtained have been compared with those provided by conventional Soxhlet extraction for 8 h by development …
Procedures of Separation and Pre‐concentration for Molybdenum Determination Using Atomic Spectrometry—a Review
2004
Abstract The literature concerning the improvement of atomic and ionic procedures for molybdenum determination through separation and pre‐concentration were updated. Analytical procedures based on flame atomic absorption spectrometry (AAAS), electrothermal or graphite furnace atomic absorption spectrometry (GFAAS), inductively coupled plasma optical emission spectrometry (ICP‐OES), and inductively coupled plasma mass spectrometry were reviewed taking into consideration the preliminary steps, which can enhance the selectivity and sensitivity based on co‐precipitation, solvent extraction, and solid‐phase extraction. Both in‐batch and on‐line procedures were considered.
ICP-MS multielement determination in fly ash after microwave-assisted digestion of samples.
2001
A microwave assisted digestion procedure has been developed for dissolution of fly ash samples prior to the inductively coupled plasma-mass spectrometric determination of their elemental composition. The developed methodology was validated by carrying out the analysis of two high-silicate containing reference materials (CRM 134R sewage amended soil and NIES JR 1 rock) and by means of the comparison between results found by microwave-assisted digestion and ICP-MS of fly ash samples with those found by neutron activation analysis (NAA) for Sb, Cs, Cr, Co, Fe, U and Zn determination. The method developed can be recommended for routine multielement analysis of fly ash.
A clean analytical method for the spectrophotometric determination of formetanate incorporating an on-line microwave assisted hydrolysis step
1999
Abstract A fast and completely automated procedure is proposed for the spectrophotometric determination of formetanate in waters by means of its reaction with p-aminophenol (PAP). The method involves the on-line alkaline hydrolysis of formetanate to m-aminophenol (MAP) and its reaction, in the presence of KIO 4 as oxidant agent, with the quinoneimine form of PAP, to form a blue indophenol dye which absorbs at 576 nm. The on-line hydrolysis can be carried out in a 6 m reaction coil located inside the cavity of a domestic microwave oven operated at 650 W, or in a 4 m reaction coil located inside the cavity of a Microdigest 301 microwave system operated at 60 W and allows us, in both cases, a …
An ultrasound-assisted digestion method for the determination of toxic element concentrations in ash samples by inductively coupled plasma optical em…
2007
Abstract A method of ultrasound-assisted digestion followed by inductively coupled plasma optical emission spectrometry (ICP-OES) used for the determination of toxic element concentrations (arsenic, barium, cobalt, copper, lead, nickel, strontium, vanadium and zinc) in ash samples was developed. All the measurements were performed in robust plasma conditions which were tested by measuring the Mg(II) 280.270 nm/Mg(I) 285.213 nm line intensity ratios. The highest line intensity ratios were observed when a nebulizer gas flow of 0.6 L min−1, auxiliary gas flow of 0.2 L min−1 and plasma power of 1400 W were used for radially viewed plasma. The analysis of SRM 1633b showed that the ultrasound-ass…
Net analyte signal as a deconvolution-oriented resolution criterion in the optimisation of chromatographic techniques
2003
The performance of two multivariate calibration measurements, multivariate selectivity (SEL(s)) and scalar net analyte signal (scalar NAS), as chromatographic objective functions (COFs), was investigated. Since both assessments are straightforwardly related to the quantification of analytes in the presence of interferents, they were expected to confer new features in the optimisation of compound resolution, not present in conventional assessments. These capabilities are especially interesting in situations of low resolution, where peak deconvolution becomes an attractive alternative. For comparison purposes, chromatographic resolution (R(s)) and peak purity (p(s)) were used as reference COF…
Pressurized liquid extraction of organic contaminants in environmental and food samples
2015
Pressurized liquid extraction (PLE) is an automated technique that uses elevated temperature and pressure to achieve exhaustive extraction from solid matrices, so reducing solvent consumption and enhancing sample throughput when compared with traditional procedures. Hence, it can be considered an environment-friendly technique, generating small volumes of waste and reducing costs and time. This review focuses on application of this green technique to the analysis of organic contaminants in food and environmental matrices for monitoring purposes. We examine fundamentals and key aspects of the development of a PLE method, including pressurized hot-water extraction, together with some relevant…
H-point standard additions method for resolution of overlapped chromatographic peaks with a conventional fluorescence detector. Determination of phen…
1996
The H-Point Standard Additions Method (HPSAM) is proposed in order to resolve overlapping peaks in liquid chromatography by using a conventional fluorescence detector. The method uses as analytical signals the heights or the areas obtained at two previously selected emission wavelengths, and good results are obtained for highly overlapping peaks with highly overlapping fluorescence spectra. The principal benefits of the method are the ease of finding the required wavelengths, its insensitivity to changes in the retention time of the peak from one injection to another, and the possibility of using it in highly or only partially overlapping peaks. We have applied the method to the determinati…