Laser spectroscopy in analytical chemistry:light on the next millennium

To date, lasers are widely accepted tools in analytical spectroscopy, involved in various stand-alone and hyphenated techniques. Furthermore, significant progress can be noted in this field. In this paper, first of all some laser characteristics are discussed. Subsequently, five selected topics are outlined to illustrate recent achievements and future developments:

1. Laser-induced fluorescence for detection in capillary electrophoresis, including the use of ultraviolet, continuous-wave lasers in combination with wavelength-resolved emission detection; the use of diode laser-induced fluorescence in the red region of the electromagnetic spectrum and the use of Ti:sapphire lasers for multiphoton-excited fluorescence detection.

2. Degenerate four-wave mixing for detection in liquid microseparation systems (based on the coherence of laser light).

3. Fluorescence line-narrowing spectroscopy for identification purposes, a cryogenic high-resolution molecular fluorescence technique with a high potential in environmental analysis.

4. Recent developments in Raman spectroscopy (including ultraviolet-Resonance Raman and hyphenation of liquid chromatography and Raman spectroscopy).

5. Use of lasers for sample introduction in inorganic analysis based on controlled material ablation.

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.

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.     

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.     

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.     

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.     

Time-resolved spectroscopy of long-path fluorescence and scattering for measuring total absorption of fluids

Optical methods are appropriate tools to detect organic micro-pollutants in fluids. A new technique is introduced which uses the decay of interaction processes like fluorescence and elastically scattered radiation by a fluid. Principally two different parameters are determined:

1. (i) the decay-time of the conventional interaction τ_C, which occurs at relatively short path-lengths of the incidence beam in the fluid, and

2. (ii) the decay-time τ_MP of the multi-path-saturation interaction originating at long path-lengths, e.g. in multi-path-reflection cuvettes, where the incidence beam is fully absorbed by the fluid.

A relation between the decay-time and the absorption coefficient of a fluid is theoretically derived. A simple preliminary experiment is performed considering distilled water polluted with non-fluorescent azobenzene and fluorescent quinine-sulphate. A nitrogen laser has been used to generate the fluorescence and scattering signals. The reciprocal value of the difference between the decay-time of the multi-path and conventional signals, 1/(τ_MP − τ_C), yields the total absorption coefficient directly. In comparison to the conventional absorption technique the decay-time method is characterized by a higher sensitivity.     

Adsorption of complexes formed by cationic starch and anionic surfactants on quartz studied by QCM-D

The adsorption of complexes of cationic starch, (CS) and a series of homologous sodium alkanoates on silica was studied with the quartz crystal microbalance with dissipation (QCM-D) instrument. The systems were chosen so as to represent CS/surfactant ratios below and above the critical association concentrations of the surfactants but below their critical micelle concentrations. It was found that

– surfactants did not adsorb on cationic polymers that were very tightly bound to the surface;

– surfactants did adsorb on polyelectrolytes forming layers with loops and tails extending into the solution, provided the concentration of surfactant was at least around the critical association concentration (cac) of the surfactant/polymer system;

– adsorption of surfactant was promoted by increasing the surfactant chain length and by adding simple electrolyte that weakened the electrostatic polymer/surface interaction and

– multilayers were formed when the surfactant concentration in solution was well above the cac; their formation was promoted by increasing hydrophobic interactions, e.g. by increasing the surfactant chain length.

XIIth international meeting on radiation processing Avignon 25–30 March 2001 (Polymer irradiation: past–present and future)

Radiations are used efficiently and economically for the production of new or modified polymers. The following processes are considered:

1. Radiation curing;

2. Radiation cross-linking;

3. Radiation grafting.

These processes are commonly used today in industry and provide a broad range of new potential applications in various fields. The history of their development is briefly reported. The chemical reactions underlying these processes are described.

(1) Radiation curing is used commercially on a large scale for the production of improved coatings, lacquers and inks. The process can be conducted at very high speeds. Curing of magnetic formulations leads to particularly stable products, which compete favourably with more conventional materials.

(2) Radiation cross-linking is an established technology in the wire and cable industry. It emparts to the modified insulators improved resistance to solvents, to ageing and to elevated temperatures. The resulting cross-linked network also reduces the migration of fillers and thereby stabilizes in time any message imprinted with magnetic or colored pigments dispersed in a polymer.

(3) Radiation grafting is a powerful method for modifying more profoundly the properties of a polymer and for creating numerous, entirely new materials. The chemical modification can be applied at will into the bulk of the material or limited to a surface zone of any desired depth. This method can be used for instance, for introducing polar groups in the bulk or on the surface of non-polar polymers, for increasing or reducing the wettability of a polymer, for imparting a better compatibility of a polymer to a specific coating and the like.

The irradiation of water-soluble polymers in aqueous solutions, with or without the addition of another monomer gives rise to a variety of cross-linked gels which find useful applications in the biomedical field. Other promising applications will be considered.     

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.

Fluorine-19 NMR spectroscopy of polyhalonaphthalenes. Part II polychloropolyfluoronaphthalenes via nucleophilic fluoride dechlorination

Six new polychloropolyfluoronaphthalenes have been identified by F-19 NMR whose empirical formulae are C₁₀ Cl_8−n F_n where n is 5 and 6 two trichloropentafluoronaphthalenes and four dichlorohexafluoronaphthalenes:-

• 1,3,8-trichloro-2,4,5,6,7-pentafluoronaphthalene,

• 1,3,6-trichloro-2,4,5,7,8-pentafluoronaphthalene,

• 1,3-dichloro-2,4,5,6,7,8-hexafluoronaphthalene,

• 1,8-dichloro-2,3,4,5,6,7-hexafluoronaphthalene,

• 1,6-dichloro-2,3,4,5,7,8-hexafluoronaphthalene and

• 2,7-dichloro-1,3,4,5,6,8-hexafluoronaphthalene.

In the partly fluorinated compounds such as 1,3,6,8-tetrachloro- 2,4,5,7-tetrafluoronaphthalene, nucleophilic fluoride dechlorination occurs at both and β positions. Initial substitution in octachloronaphthalene is more selective and occurs predominantly at the -position; both subsequent exchanges occur at sites two carbons away from the initial site. The results support the idea that the transition state is stabilised by chlorine at the sites of electron density, ortho and para to the site of nucleophilic attack.     

Two methods for the speciation analysis of mercury in fish involving microwave-assisted digestion and gas chromatography-atomic emission spectrometry

In this paper a novel approach for the speciation analysis of mercury (methyl mercury and mercury II) in fish tissue using gas chromatography-microwave induced plasma atomic emission spectromertry is described. Focused microwave-assisted digestion which has been used previously in speciation analysis only for the determination of organotin and organoselenium compounds, was applied for sample preparation, a technique which enables mild, quick and complete dissolution of the sample. The important parameters for the digestion of fish tissues were optimised for the given analytical problem. Since no experience was available for the further treatment of the produced sample solution two different derivatisation/injection procedures were examined:

1. (1) ethylation with sodium tetraethylborate, extraction into hexane and injection with a cooled injection system and

2. (2) hydride generation with sodium tetrahydroborate together with purge-and-trap injection. The latter reaction has not been used previously for the determination of mercury species in fish samples.

The optimum parameters for both procedures were evaluated and the methods were validated by analysis of a standard reference material (CRM 464). The 3σ detection limits were (1) 3.0 pg g⁻¹ and (2) 12.5 pg g⁻¹.     

Membrane introduction mass spectrometry

An overview of membrane introduction mass spectrometry (MIMS) is presented and comparisons are made with other direct sample introduction techniques. Special attention is given to the unique advantages and the limitations of newer variants on the MIMS technique, including affinity MIMS, reverse-phase and trap MIMS. The salient features of the interfaces used in MIMS are summarized and the various membrane materials commonly used are delineated. The applicability of MIMS is illustrated via discussion of

1. (i) bioreactor monitoring (represented by yeast fermentation),

2. (ii) environmental monitoring (illustrated by analysis of contaminated ground water samples) and

3. (iii) on-line chemical reaction monitoring (exemplified by the photolysis of aryl esters).

The applicability of MIMS to the analysis of environmental samples, including complex mixtures in water, air and soil, is noted.     

An improved method to predict second cross virial coefficients

A previous method of the author to calculate the second cross virial coefficients is re-considered to improve the reliability of the predictions and to reduce the number of empirical rules. The method is based on the reduced second cross coefficient at the normal boiling temperature, , whose value is always assumed equal to unity. This value is then extrapolated to the experimental temperatures using only two empirical constants: K₁, a corrective multiplying factor of and K, in an exponential term as a multiplying factor of temperature. To improve the reliability of the method, literature experimental data are grouped in three binary classes:

- non-polar or slightly polar fluids;

- at least one strongly polar fluid;

- strong interactions of the acid–base type.

Only the critical constants and the normal boiling temperature are required as input parameters.

Deviations of calculated results from experimental one are in the range 25–40 cm³ mol⁻¹ for the first and the second class and below 300 cm³ mol⁻¹ for the third class.     

Human exposure to endocrine-disrupting chemicals: assessing the total estrogenic xenobiotic burden

A relationship has been hypothesized between adverse effects on human and wildlife reproductive health and a number of chemical substances capable of altering hormonal homeostasis. A testing system to screen for endocrine activities and the development of appropriate biomarkers of cumulative exposure are required. This article reports the work of our group in the following areas

1. (i) the identification of chemical agents with estrogenic hormonal activity,

2. (ii) existing evidence on forms and sources of human exposure, and

3. (iii) developing a methodology to assess the total estrogenic burden, defined as the estrogenic activity in a bioassay of human samples from which ovarian estrogens have been previously eliminated.

     

The oxidation of sulphide minerals

The literature associated with the thermal behaviour of mineral sulphides has been selectively and critically reviewed. Particular attention has been paid to:

• • the importance of characterising the starting material, as well as intermediate products

• • the effect of experimental variables on the thermal analysis results

The various reactions that sulphides can undergo in inert and oxidising atmospheres are presented. Under mild oxidising conditions, such as an air atmosphere and heating rates of 10–20°C min⁻¹, the oxidation occurs as a sequence of reactions usually controlled by oxygen diffusion, although in some situations decomposition of the sulphide with evolution of sulphur can occur. Besides the formation of oxides and sulphates, and the subsequent decomposition of the latter, solid-solid reactions can occur between sulphates and unreacted sulphides. In ternary systems, such as the iron-nickel sulphides, considerable ion diffusion can take place.

Under more vigorous oxidising conditions, such as an oxygen atmosphere with a heating rate in excess of 40°C min⁻¹, some sulphides can be ignited. Under these conditions the relative ignition temperatures of sulphides can be measured, and the effects of variables such as particle size and stoichiometry on the ignition temperature examined.

The oxidation of pyrite is presented as a case study of the effects of experimental variables on the results of thermal analysis. The application of the results of studies to the industrial processing of sulphides of economic importance has been discussed.     

Spline and polynomial models of the efficiency function for Ge gamma-ray detectors in a wide energy range

Summary In one of our recent papers, the applicability of linear parameter functions for fitting the full-energy peak efficiency of n-type Ge gamma-ray detectors has been examined over a wide energy range of 50-8500 keV. In that paper we compared six different analytical functions and showed that higher-order polynomial functions on a log-log scale gave the best performance. However, there is a drawback to using the log-log scale when an additive function of efficiency at different energies or of the inverse efficiency has to be used in a fitting procedure. In the present study, the applicability of higher-order polynomial and spline functions to linear and inverse efficiency, but logarithmic energy scales, is examined.     

Anwendung von mathematischen statistischen methoden für einige probleme der quantitativen emissionsspektralanalyse

The standard deviation of the ΔY-values of an analytical line pair is discussed in function of the correlation and orthogonal regression coefficients as well as of the standard deviations of Y_x and Y_r.

It was stated that the orthogonal regression coefficient depends on the ratio s_x/s_r.

A criterium is set up for choosing the right analytical line pair. The optimal field for the values ^sδy is given in function of the ratio s_x/s_r as well as of the correlation coefficient.     

Ratio control variate method for efficiently determining high-dimensional model representations

The High-Dimensional Model Representation (HDMR) technique is a family of approaches to efficiently interpolate high-dimensional functions. RS(Random Sampling)-HDMR is a practical form of HDMR based on randomly sampling the overall function, and utilizing orthonormal polynomial expansions to approximate the RS-HDMR component functions. The determination of the expansion coefficients for the component functions employs Monte Carlo integration, which controls the accuracy of the RS-HDMR interpolation. The control variate method is an established approach to improve the accuracy of Monte Carlo integration. However, this method is often not practical for an arbitrary function f(x) because there is no general way to find the analytical control variate function h(x), which needs to be very similar to f(x). In this article, we show that truncated RS-HDMR expansions can be used as h(x) for arbitrary f(x), and a more stable iterative ratio control variate method was developed for the determination of the expansion coefficients for the RS-HDMR component functions. As the asymptotic error (standard deviation) of the estimator given by the ratio control variate method is proportional to 1/N(sample size), it is more efficient than the direct Monte Carlo integration, whose error is proportional to 1/square root(N). In an illustration of a four-dimensional atmospheric model a few hundred random samples are sufficient to construct an RS-HDMR expansion by the ratio control variate method with an accuracy comparable to that obtained by direct Monte Carlo integration with thousands of samples.     

有限圆盘电极上计时电流方程式

本文报道一个形式简单、结果准确、适用于任何时间的有限圆盘电极上计时电流方程式,结果为i_t=4nFD_RT₀[θ/(1+θ)]C_R^*,f(τ)[式中 ,τ=4D_Rt/r₀²,r₀为电极半径,t为时间,0=expnF(E-E⁰)/RT]。