Laser-based non-fluorescence detection techniques for liquid separation systems

Over the last two decades, the possibility to use lasers for detection purposes in column liquid chromatography (LC) and capillary electrophoresis (CE) received much attention in the analytical chemistry literature. Most attention has been devoted to laser-induced fluorescence. The present review covers developments on non-fluorescence techniques for LC and CE. The techniques considered are thermal lens spectrometry, photoacoustic detection, refractive index detection including refractive index backscattering, Raman spectroscopy and degenerate four-wave mixing (a special mode of transientholographic spectroscopy). The paper starts with an outline of the characteristics of lasers; it ends with an overall evaluation and a discussion of the perspectives of the techniques dealt with.     

A computer program for searching the best model for describing different experimental systems

An algorithm for searching the best polynomial analytical function for describing different experimental systems is presented. It is based

1. (1)on the generation of all possible analytical functions of a given order, with a given number of terms and with a given number of independent variables, and

2. (2)on the calculation of the parameters of all selected functions using the linear regression method.

To show the ability of the program two different examples are given:

1. (1) searching the best univariate polynomial model, and

2. (2) modelling of the stability of a two-component mixture as a function of three factors.

Fourier transform infrared spectroscopy and the analytical study of works of art for purposes of diagnosis and conservation

This paper is a study of the analytical capacity of Fourier transform infrared spectroscopy (FT-IR) for any type of samples from works of art. The analytical information obtained with this technique on organic and inorganic compounds is extremely useful in the preliminary studies necessary for diagnosis and to decide on the conservation process. This paper reports the analysis and study with FT-IR on samples extracted from the microlayers in several works of art from different periods (16th to 18th century) comprising wall paintings and canvas. The most outstanding of these being the frescoes by A. Palomino from two ceilings in the Santos Juanes church. The analytical procedures for the different components of the works studied such as

1. (a) varnish applied to wood panels and canvas paintings,

2. (b) binding media and pigments used by the artists,

3. (c) inerts, mortars, stuccos and grounds have been optimized. The FT-IR technique offers a quick analysis of microsamples (less than 0.5 mg) and is able to characterise the different molecular groups which provide information on the nature of the different materials of organic and inorganic origin used by the artist and thus permits the diagnosis of pathologies requiring conservation treatment.

Concerning the interconnections of some parameters of self-organizing oxyhydrate gels and their experimental determination

The appearance of a pulsating current in the elongated cell filled with the zirconium oxyhydrate gel under short-circuited electrodes and constant mixing was shown. The pulsating character of the current is expressed in the form of current splashes. The reason for the appearance of current splashes is the self-organization of the gel with time; to be more exact, the reason is the constant conformational reorganization of the oxyhydrate matrix. When magnetic field acts on the zirconium oxyhydrate gel, increases in both the current values and the current splashes are observed. The increase of the gel particle sizes in a magnetic field is detected. Thus, it is of interest to consider the connection between the period of appearance of current splashes, splashes amplitudes and the sizes of gel aggregate regions.

In this regard, it is important to find out the connection between the parameters of the self-organizing gel cell. We suppose that:

1. In the process of self-organizing, the concentration of monomers forming the matrix in a gel area may change with time.

2. Solution of the task is independent of time. Generally speaking, it is possible to find a time-dependant solution of the task, but it is hardly worth doing.

Different level of fluorescence in Raman spectra of montmorillonites

The paper presents the study of selected montmorillonite standards by Raman spectroscopy and microscopy supported by elemental analysis, X-ray powder diffraction analysis and thermal analysis. Dispersive Raman spectroscopy with excitation lasers of 532 nm and 780 nm, dispersive Raman microscopy with excitation laser of 532 nm and 100× magnifying lens, and Fourier Transform-Raman spectroscopy with excitation laser of 1064 nm were used for the analysis of four montmorillonites (Kunipia-F, SWy-2, STx-1b and SAz-2). These mineral standards differed mainly in the type of interlayer cation and substitution of octahedral aluminium by magnesium or iron. A comparison of measured Raman spectra of montmorillonite with regard to their level of fluorescence and the presence of characteristic spectral bands was carried out. Almost all measured spectra of montmorillonites were significantly affected by fluorescence and only one sample was influenced by fluorescence slightly or not at all. In the spectra of tested montmorillonites, several characteristic Raman bands were found. The most intensive band at 96 cm⁻¹ belongs to deformation vibrations of interlayer cations. The band at 200 cm⁻¹ corresponds to deformation vibrations of the AlO₆ octahedron and at 710 cm⁻¹ can be assigned to deformation vibrations of the SiO₄ tetrahedron. The band at 3620 cm⁻¹ corresponds to the stretching vibration of structural OH groups in montmorillonites.     

Accredited dose measurements for validation of radiation sterilized products

The activities and services of the accredited Risø High Dose Reference Laboratory are described. The laboratory operates according to the European standard EN 45001 regarding Operation of Testing Laboratories, and it fulfills the requirements of being able to deliver traceable dose measurements for control of radiation sterilization. The accredited services include:

1. 1. Irradiation of dosimeters and test samples with cobalt-60 gamma rays.

2. 2. Irradiation of dosimeters and test samples with 10 MeV electrons.

3. 3. Issue of and measurement with calibrated dosimeters.

4. 4. Measurement of the dosimetric parameters of an irradiation facility.

5. 5. Measurement of absorbed dose distribution in irradiated products.

The paper describes these services and the procedures necessary for their execution.     

Laser-induced population depletion effects in double resonance excitation with Hg vapors

By monitoring the green fluorescence transition of mercury vapor 7 ³S₁→6 ³P⁰₂ (546.074 nm) excited by two pulsed dye lasers tuned at two connected atomic resonant frequencies, i.e. 6 ¹S₀→6 ³P⁰₁ (253.652 nm) and 6 ³P⁰₁→ 7 ³S₁ (435.835 nm), a decrease in the green fluorescence yield is experimentally observed when the intensity of the 435.835-nm excitation transition exceeds 5 kW/cm². A similar result is obtained at the yellow fluorescence transition 6 ³D₁→6 ¹P⁰₁ (578.967 nm) when the second step is tuned to the 6 ³P⁰₁→6 ³D₁ transition (313.159 nm). At the same time, an increase in the transmittance of the ground state transition (253.652 nm) is observed. It is speculated that this effect, which occurs only when both laser pulses are temporally coincident, and is therefore not due to photoionization, can be ascribed to the existence of laser induced effects, such as a.c. Stark splitting of levels and possibly electromagnetically-induced transparency (EIT). Our experiment does not allow us to distinguish between these two effects, nor their quantitative evaluation. However, it is stressed that one cannot overlook them in those atomic multi-step excitation experiments in low collisional environments where a depletion of an intermediate level is involved, as for example in the case of atomic fluorescence dip spectroscopy or atomic multistep and multiphoton resonance ionization spectroscopy.     

From ephemers to monomers, oligomers and polymers. New methods for the generation and transformation of silanones

New efficient routes to the generation of silanones at relatively low temperatures are based on the following reactions:

1. (1) reaction of linear and branched perhydrocarbyldisiloxanes and oligosiloxanes, and of some of their C-functional derivatives, with gallium or indium iodides or bromides;

2. (2) reaction of hydrocarbylchlorosilanes R_4−nSiCl_n (n = 2–4) and SiCl₄ with dimethylsulphoxide (with or without Mg or Zn);

3. (3) Autodecomposition of organosilicon compounds containing and groups;

4. (4) reaction of R_4−nSiCl_n with metal oxides of high redox potential (with or without the presence of CH₃CN).

Insertions of dialkylsilanones into Si---O---Si and Si---O---C linkages as well as into the Si---Cl bond have been studied.     

A fluorescence toolbox: A review of investigation of electrophoretic separations,process, and interfaces

This review focuses on fluorescence spectroscopy techniques for the investigation of electrophoretic separations. Fluorescence has been used as a sensitive detector for capillary, gel, and microchip electrophoresis for decades. However, advanced fluorescence methods can be used to study transport, interfacial phenomena, intermolecular and affinity interactions, and other processes that occur during separation. This so‐called spectroscopic toolkit can be implemented to understand fundamental behavior in electrophoresis and electrokinetic chromatography. Techniques such as fluorescence recovery after photobleaching, fluorescence correlation spectroscopy, and fluorescence anisotropy are discussed in relation to electrophoretic separations. Newer methods such as super‐resolution microscope are also introduced.     

激光波长对拉曼光谱检测地质成分的影响

随着激光技术的不断发展,以激光为光源的拉曼光谱检测技术由于其快速、无损、无接触探测等优势,已成为地质样品成分鉴别的一种重要途径。由于激光波长是样品拉曼效应的重要决定因素之一,进一步明确其在地质样品成分检测中的影响,能够为开展行星矿物成分研究提供重要参考依据。本工作基于自主建立的532nm/785nm双色光源激光拉曼光谱探测系统,开展了不同激光波长对地质样品成分拉曼光谱的影响研究,获得了包括硝酸根、碳酸根、磷酸根、硅酸根等分子基团以及硫化物、氧化物等多种地质样品主要成分的拉曼特征光谱。通过对比表明,532nm激发光具有更高的光子能量,能够检测更多的样品成分,但荧光效应较强,785nm激发光存在拉曼信号强度较低问题,但是具有很好的荧光抑制效果,可根据实际样品种类进行最佳激发光波长的选择。     

Semiempirical molecular orbital theory in carcinogenesis research

It is generally believed that most chemical carcinogens exert their effects through covalent modification of the nucleic acid base sites. Significant clarification of the underlying chemistry involved in these early and critical events is available through the techniques of computational chemistry. The role of semiempirical molecular orbital theory in this area is reviewed using examples focusing on

1. (i) the conversion of precarcinogens to reactive electrophiles,

2. (ii) the regiochemistry of nucleic acid adduct formation,

3. (iii) the chemical and physical consequences of nucleic acid base modification, and

4. (iv) empirical structure activity relationships.

The symbiotic relationship that can exist between the semiempirical and ab initio molecular orbital procedures is emphasized, as is the continuing niche for the semiempirical methodology in the study of systems that are too large, or in situations that are insufficiently cost effective, for the application of ab initio methods.     

Review on recent advances in the analysis of isolated organelles

The analysis of isolated organelles is one of the pillars of modern bioanalytical chemistry. This review describes recent developments on the isolation and characterization of isolated organelles both from living organisms and cell cultures. Salient reports on methods to release organelles focused on reproducibility and yield, membrane isolation, and integrated devices for organelle release. New developments on organelle fractionation after their isolation were on the topics of centrifugation, immunocapture, free flow electrophoresis, flow field-flow fractionation, fluorescence activated organelle sorting, laser capture microdissection, and dielectrophoresis. New concepts on characterization of isolated organelles included atomic force microscopy, optical tweezers combined with Raman spectroscopy, organelle sensors, flow cytometry, capillary electrophoresis, and microfluidic devices.     

The degradation of poly(vinyl acetate) as a material for design objects: A multi-analytical study of the Cocoon lamps. Part 2

After the systematic study of poly(vinyl acetate) degradation presented in part 1, this work reports results from the analysis of polymeric materials from five Italian design lamps from the 1960s made of the material known as cocoon. Micro- and non-destructive molecular spectroscopic techniques have been applied directly on the object surfaces using an optical fibre probe and through examination of micro-samples: the combined use of Fourier-transform infrared spectroscopy (FTIR), pyrolysis gas-chromatography/mass-spectrometry (py-GC/MS) and Fluorescence spectroscopy allowed the assessment of the material composition and the chemical modifications of the polymers related to on-going deterioration processes. Fluorescence spectroscopy proved particularly sensitive for the detection of variations in composition among lamps and between areas on the same object, and was used to classify objects in different groups using principal component analysis of excitation emission spectra. Specific degradation products have been mapped using FTIR on micro-samples. Moreover, the interpretation of the emission spectra of the studied polymeric lamps suggests that fluorescence spectroscopy can be used for non-destructive monitoring of the degradation of historical polymeric objects.     

Analysis of a fluorescence depletion process of Rhodamine 6G in a PMMA matrix induced by nano- and picosecond lasers

The two-color fluorescence depletion process of Rhodamine 6G in PMMA matrixes was investigated using nano- and picosecond lasers. Erase-lasers of 1064 and 599 nm depleted the fluorescence from the S₁ state. Fluorescence depletion with 1064 nm was analyzed by the up-conversion from state S₁ to S₂, while that with 599 nm was simulated based on both the up-conversion and the stimulated emission. A three-state model describes this process due to a nanosecond laser well, while it could not reproduce that by picosecond lasers. Significant contributions of vibrational relaxation in S₁ and re-absorption from S₀ are suggested in the picosecond region.     

Excitation emission and time-resolved fluorescence spectroscopy of selected varnishes used in historical musical instruments

The analysis of various varnishes from different origins, which are commonly found on historical musical instruments was carried out for the first time with both fluorescence excitation emission spectroscopy and laser-induced time-resolved fluorescence spectroscopy. Samples studied include varnishes prepared using shellac, and selected diterpenoid and triterpenoid resins from plants, and mixtures of these materials. Fluorescence excitation emission spectra have been collected from films of naturally aged varnishes. In parallel, time-resolved fluorescence spectroscopy of varnishes provides means for discriminating between short- (less than 2.0 ns) and long-lived (greater than 7.5 ns) fluorescence emissions in each of these complex materials. Results suggest that complementary use of the two non destructive techniques allows a better understanding of the main fluorophores responsible for the emission in shellac, and further provides means for distinguishing the main classes of other varnishes based on differences in fluorescence lifetime behaviour. Spectrofluorimetric data and time resolved spectra presented here may form the basis for the interpretation of results from future in situ fluorescence examination and time resolved fluorescence imaging of varnished musical instruments.     

Theoretical considerations of laser induced fluorescence and ionization spectrometry: how close to single atom detection

The potential capability of detecting single atoms and/or of approaching the intrinsic detection limit, i.e. the limit where all external causes of noise in the system are eliminated, is discussed with respect to laser induced fluorescence and ionization spectrometry. These approaches have been chosen because of their widespread use in laboratories involved in analytical laser spectroscopy. Among the lasers, tunable dye lasers pumped by N₂, Nd-YAG, Excimer, Cu vapor lasers and flashlamps are considered, and flames, graphite furnaces, plasmas and low pressure glow discharges are considered as atom reservoirs. From practical considerations, it is shown that none of the conventional analytical approaches used can satisfy the requirement of a true single atom detection technique, the only exception being provided by the ionization method coupled with atomization under vacuum.     

Monte Carlo simulation of catalytic CO oxidation

A simple Monte Carlo model of the CO oxidation on a single-crystal catalyst surface is presented. The simulation model considers the following elementary reaction steps:

1. (1) chemisorption of a CO molecule, its surface migration and possible desorption

2. (2) physisorption of an O₂ molecule to a precursor state and its subsequent dissociative chemisorption

3. (3) activated reaction of adsorbed O and CO (the Langmuir - Hinshelwood reaction mechanism), formation of CO₂ and its rapid desorption.

The changes in the activation energy of reaction and in the adsorption energy of CO resulting from the interactions between adsorbed species are also considered. The model makes possible to monitor temperature programmed reaction spectra or reaction spectra obtained during changes of the ratio of the partial pressures of CO and O₂. The results of simulations for a Pd(111) single-crystal plane are compared with experiment.     

Coherent anti-Stokes Raman scattering: Spectroscopy and microscopy

In this review the basis, recent developments and applications of coherent anti-Stokes Raman scattering (CARS) in the fields of spectroscopy and microscopy are dialed with. The nonlinear susceptibility of the investigated molecule induced by pump and Stokes laser beams employed in the CARS technique is discussed. The relation between the nonlinear susceptibility, the different CARS laser intensities and the phase matching condition between them is also presented. The structure of CARS spectrum is analyzed as a function of the physical characteristics of the different employed lasers. This includes laser half widths, interference effects, cross-coherence and saturation of the resultant CARS signal by stimulated Raman scatter process (SRS). The different broadening mechanisms for CARS spectral line such as pressure and Doppler broadening are demonstrated. The recent progress in CARS for the in situ reaction flame diagnosis due to its suitability for detection of vibrational-rotational excited gas molecules present in the electronic ground state is discussed. CARS diagnosis for liquid- and solid-phases including the progress in polymeric materials is considered. The applications of CARS microscopy are reviewed in the view of its recent advances to study chemical and biological systems.     

Coupling of narrow-bore liquid chromatography to thin-layer chromatography : Part 2. Application of fluorescence-based spectroscopic techniques for off-line detection

The effluent from a narrow-bore liquid chromatographic (l.c.) separation can be immobilized on thin-layer chromatographic (t.l.c.) plates with little loss of resolution. The deposited compounds are then available for further inspection. For off-line detection, direct fluorescence emission, fluorescence excitation emission spectra, and fluorescence line-narrowing spectroscopy are investigated with tetracene and benz[k] fluoranthene as model compounds. Detection based on direct emission measurements and on measurements for which complete spectra are obtained for the separated compounds, is suitable for identification and determination. Detection limits are of the same order of magnitude as those for on-line detection in narrow-bore l.c. The fluorescence spectra of immobilized compounds can be obtained with a conventional fluorescence spectrometer equipped with a solid-sample accessory. No other special apparatus is needed. The immobilized chromatogram is also suitable for techniques incompatible with flow systems, e.g., fluorescence line-narrowing spectroscopy, which yields fluorescence spectra via laser excitation of low-temperature solid samples. Very selective narrow-line fluorescence spectra were obtained for tetracene deposited on t.l.c. plates in amounts down to the low picogram level.     

Time-resolved fluorescence spectroscopy for illuminating complex systems

Over the years, the emissive characteristics (spectral, temporal, and polarization) of fluorophores have been widely used to probe a wide variety of systems. Fluorescence lifetime and rotational reorientation time measurements, in particular, offer a means to elucidate key details about complex systems. Further, because fluorescence occurs on the nanosecond (10⁻⁹ s) timescale, competing or perturbing kinetic processes like collisional quenching, solvent relaxation, energy transfer, and rotational reorientation can affect the fluorescence and hence be quantified. Thus, a carefully chosen and “placed” fluorophore can serve as an reporter on a wide range of nanosecond or faster events. This contribution is divided into three sections. The Theory section discusses time-resolved anisotropy and intensity decay kinetics (time and frequency domains), pump–probe spectroscopy, and up-conversion. The second section describes time-correlated single photon counting (TCSPC) and multifrequency phase-modulation fluorescence instruments. The final section is divided into subsections on the use of time-resolved fluorescence: (1) to study solvation dynamics, biochemical systems, polymer photophysics, and organized media; (2) as a tool in the separation sciences, microscopy, and sensing; and (3) coupled with multiphoton excitation strategies.