Synthesis and characterization of high-integrity solid-contact polymeric ion sensors

High-integrity solid-contact (SC) polymeric ion sensors have been produced by using spin casting and electropolymerization techniques in the preparation of the SC employing the conductive polymer, poly(3-octylthiophene) (POT). The physical and chemical integrity of the POT SCs have been evaluated using scanning electron microscopy (SEM), atomic force microscopy (AFM), secondary ion mass spectrometry (SIMS), and X-ray photoelectron spectroscopy (XPS). Furthermore, the electrochemical stability of SC polymeric ion sensors has been investigated using electrochemical impedance spectroscopy (EIS). The results of this study demonstrate that electropolymerization and spin casting methods also comprising annealing of the synthesized SC film are capable of producing SCs that are relatively free of imperfections such as pores and pinholes. This leads to electrochemically stable and robust polymeric ion sensors where the SC/sensor interface is resistant to the formation of a detrimental water layer that normally gives rise to spurious ion fluxes and a degradation in the sensitivity and selectivity of the SC polymeric ion sensor.     

Computer modeling of fluorescence dip spectroscopy with pulsed laser excitation

This article is an electronic publication in Spectrochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta Part B (SAB). The hard copy text is accompanied by a disk with a demonstration program, block libraries, demonstration files, and ancillary files. The article discusses the computer modeling of fluorescence dip spectroscopy, a relatively new and powerful atomic diagnostic technique. The models were found to agree essentially perfectly with previously published photostationary results and to extend those results to the more realistic laser temporal profiles encountered in actual experiments.

The fluorescence dip parameters were found to be robust so long as the system under study approached saturation conditions. Short, noisy laser pulses were found to be acceptable, for determination of the fluorescence dip parameters, provided the laser pulses were sufficiently intense to cause near saturation of the three level system. Conversely, steady state excitation was not found to be crucial to the determination of accurate fluorescence dip parameters. For a five level model of the silver atomic system, “negative fluorescence dips” were readily found in the simulations, even though some of the relevant parameters were rough estimates of the actual, unknown parameters.     

Reminiscences and lessons on the occasion of a silver jubilee

This paper, written to commemorate the publication of Walsh's classical paper on the potentialities of atomic absorption spectroscopy (AAS) 25 years ago, contains nothing new. It is a personal recollection of the work done independently at our laboratory prior to 1955 which resulted in the construction of a “negative filter” (for use in atomic emission spectroscopy) and an “absorption flame photometer.” Some lessons are drawn from the historical development of AAS about the inventing of new analytical methods in general.     

Double pulse laser ablation and plasma: Laser induced breakdown spectroscopy signal enhancement

A review of recent results of the studies of double laser pulse plasma and ablation for laser induced breakdown spectroscopy applications is presented. The double pulse laser induced breakdown spectroscopy configuration was suggested with the aim of overcoming the sensitivity shortcomings of the conventional single pulse laser induced breakdown spectroscopy technique. Several configurations have been suggested for the realization of the double pulse laser induced breakdown spectroscopy technique: collinear, orthogonal pre-spark, orthogonal pre-heating and dual pulse crossed beam modes. In addition, combinations of laser pulses with different wavelengths, different energies and durations were studied, thus providing flexibility in the choice of wavelength, pulse width, energy and pulse sequence. The double pulse laser induced breakdown spectroscopy approach provides a significant enhancement in the intensity of laser induced breakdown spectroscopy emission lines up to two orders of magnitude greater than a conventional single pulse laser induced breakdown spectroscopy. The double pulse technique leads to a better coupling of the laser beam with the plasma plume and target material, thus providing a more temporally effective energy delivery to the plasma and target. The experimental results demonstrate that the maximum effect is obtained at some optimum separation delay time between pulses. The optimum value of the interpulse delay depends on several factors, such as the target material, the energy level of excited states responsible for the emission, and the type of enhancement process considered. Depending on the specified parameter, the enhancement effects were observed on different time scales ranging from the picosecond time level (e.g., ion yield, ablation mass) up to the hundred microsecond level (e.g., increased emission intensity for laser induced breakdown spectroscopy of submerged metal target in water). Several suggestions have been proposed to explain the mechanism of double pulse enhancement.     

Influence of non-quenching collisions upon saturated resonance fluorescence

When an analyte atomic vapour is irradiated by a monochromatic laser beam with sufficient energy density, the excited atom population (and hence fluorescence intensity) may approach saturation. Non-quenching collisions that change the Doppler shift of an excited atom may decrease by one or two orders of magnitude the amount of energy density necessary to achieve a given degree of saturation. A steady state theory is developed that allows predictions to be made from collisional rate constants.     

100-femtosecond MeV electron source for ultrafast electron diffraction

A near-relativistic 100-fs MeV electron beam is developed by using a photocathode rf gun for revealing the hidden ultrafast dynamics of intricate molecular and atomic processes in materials through experimentation of ultrafast time-resolved electron diffraction (UED). The transverse and longitudinal dynamics of femtosecond electron beam in the rf gun were studied theoretically by particle simulation. The growths of the emittance, bunch length and energy spread due to the rf and space charge effects were investigated by changing the laser parameters, field gradient and electron charge. The theoretical studies indicate that a 100-fs MeV electron beam with the transverse emittance of 0.1 mm mrad and the relative energy spread of 10⁻³–10⁻⁴ at bunch charge of 0.1–2 pC (10⁶–10⁷ electrons per pulse) is achievable for UED, in which the intensity is three orders of magnitude higher than that produced by the conventional dc or pulsed guns.     

Isotope selective element analysis by diode laser atomic absorption spectrometry

The analytical figures of merit of isotope selective diode laser atomic absorption spectrometry (DLAAS) in low-pressure graphite furnaces are given for lithium and rubidium. While⁶Li and⁷Li were measured by Doppler-limited as well as by Doppler-free absorption spectroscopy of the 670.79 nm resonance line, Doppler-free saturation spectroscopy was applied for analysis of the⁸⁵Rb and⁸⁷Rb D2 resonance line at 780.03 nm. Three different modulation techniques were applied and compared: (i) intensity modulation, (ii) wavelength modulation, and (iii) a combination of intensity and wavelength modulation.     

Terpenoid Hydrazones as Biomembrane Penetration Enhancers: FT-IR Spectroscopy and Fluorescence Probe Studies

Hydrazones based on mono- and bicyclic terpenoids (verbenone, menthone and carvone) have been investigated in vitro as potential biomembrane penetration enhancers. In this regard, liposomes composed of lecithin or cardiolipin as phospholipid phase components with incorporated fluorescence probes have been prepared using the thin-film ultrasonic dispersion method. The mean particle size of the obtained liposomes, established using laser diffraction, was found to be 583 ± 0.95 nm, allowing us to categorize them as multilamellar vesicles (MLVs) according to their morphology. Pursuant to fluorescence analysis, we may assume a reduction in microviscosity and, consequently, a decrease in the packing density of lecithin and cardiolipin lipids to be the major mechanism of action for terpenoid hydrazones 1–15. In order to determine the molecular organization of the lipid matrix, lipids were isolated from rat strata cornea (SCs) and their interaction with tested compounds was studied by means of Fourier transform infrared spectroscopy. FT-IR examination suggested that these hydrazones fluidized the SC lipids via the disruption of the hydrogen-bonded network formed by polar groups of SC constituents. The relationship between the structure of terpenoid hydrazones and their ability to enhance biomembrane penetration is discussed.     

Saturation of energy levels in analytical atomic fluorescence spectrometry—II. Experimental

In Part I of this investigation, a theoretical model was proposed to describe the saturation of atomic energy levels under conditions of intense but brief irradiation by a suitable excitation source. The experimental verification of that model is presented herein. In this study, the effects of dye laser-induced saturation of analyte concentration, flame composition and atomic properties of the elements were all examined and quantitated in terms of a measurable parameter, the saturation spectral power density (SSPD). The results of those studies reveal that SSPD is relatively independent of analyte concentration and flame composition but is a strong function of the nature of each particular atomic transition employed. Moreover, because of strong quenching in most analytical flames, a simple steady-state model for saturation applies even for brief (5.6 ns) pulses from a nitrogen-laser pumped dye laser. Most importantly, it is shown that reliable values for the SSPD can be obtained only through careful experimental design; considerations important in such measurements are therefore carefully detailed.     

Two-beam linear magneto-optical spectroscopy of atomic transitions between short lived states

Two-beam, linear magneto-optical spectroscopy is a powerful tool for studying short-lived states. We present both measurements and a quantitative theoretical analysis of magneto-rotation observed in the forward scattering of a linearly polarised laser beam passing through an amplifying atomic medium placed in a longitudinal magnetic field. The probed transition connects two short-lived, excited atomic levels, the upper state (here the 7S _1/2 level of cesium) being prepared initially via another transition from ground state, excited by a linearly polarised pump beam. The probe polarisation undergoes three different magneto-optical processes: optical rotation, with separate contributions from the two transitions, and linear dichroism due to Hanle precession of the upper state alignment. Complete resolution of the hyperfine structures and ninety degree switching of the probe polarisation enable us to isolate all of these processes. To lowest order in optical thickness the relative intensities and lineshapes are well interpreted.     

Versuche mit einem tiefgekühlten Zwillingsholkathoden-Interferometer—Spektrometer—II. Das optische System

The optical arrangement consists of a double beam imaging system an interferometer spectrometer attached to it. The two cathode spots are projected by the imaging system to the flip-flop mirror in the optical axis of the interferometer. One of the two cathode spots can be projected either to the slit of a spectroscope or to that of a spectrograph, respectively, for preliminary observation. For measuring the intensity ratios, neutral wedges are built into the imaging system. The principal component of the system is a piezo-electrically controlled Fabry—Perot interferometer spectrometer. The deparallelisation of the Fabry—Perot mirrors during the scanning, caused by the “fatigue” of the piezo-electrical system, was eliminated using suitable circuits. The good performance of the interferometer was checked by measuring of the finesse and resolution of selected spectral lines of different spectral lamps and the resonance radiation of a He---Ne gas laser. The optical set-up is suitable for general spectroscopic and spectrographic observations, for measuring radial intensity distributions, for obtaining high resolution spectra and for the determination of intensity ratios in the radiation of the twin hollow cathode source in the visible spectral range.     

Bridging the gaps in analytical atomic absorption spectrometry

The techniques of analytical, valence electron, atomic spectrometry (absorption, fluorescence and emission), by themselves, are mainly for the determination of the amount of an element in a sample which has been prepared as a . For a large fraction of trace element analysis such an approach is satisfactory. However, there are some other very important requirements in trace element analysis not now adequately being addressed by analytical atomic spectrometry. A selection of these, familiar to the present writer, will be covered in this presentation. Some interesting initiatives to “bridge the gaps” are now being made. The topics to be discussed are; elemental speciation, direct analysis of solids, elemental and natural isotope analysis using plasma sources, micro analysis by laser probe and vapour generation approaches to improved detection limits. This is not intended to be an exhaustive review of these subject areas but will present material of interest together with recently published key papers. Greatest emphasis is given to the very important topic of speciation.     

Kinetic model of atomic and molecular emissions in laser-induced breakdown spectroscopy of organic compounds

A kinetic model previously developed to predict the relative intensities of atomic emission lines in laser-induced breakdown spectroscopy has been extended to include processes related to CN and C₂ molecular emissions. Simulations with this model were performed to predict the relative excited-state populations. The results from the simulations are compared with experimentally determined excited-state populations from 1,064 nm laser irradiation of organic residues on aluminum foil. The model reasonably predicts the relative intensity of the molecular emissions. Significantly, the model reproduces the vastly different temporal profiles of the atomic and molecular emissions. The latter are found to extend to much longer times after the laser pulse, and this appears to be due to the increasing concentration of the molecules versus time. From the simulations, the important processes affecting the CN and C₂ concentrations are identified.     

Effects of sample matrix on detection limits in analytical inductively coupled plasma-Fourier transform spectrometry

The feasibility of making analytical atomic spectrometry measurements by inductively coupled plasma-Fourier transform spectrometry (ICP-FTS) is demonstrated. Analytical working curves and detection limits are presented for Al, Ni, Fe and Ca. The effects of sample matrix composition on detection limits for analytical ICP-FTS are investigated. It is shown that a multiplex disadvantage may occur in the case of a spectral bandpass encompassing stroog emission lines of a matrix element. A “worse case” example of this problem is presented. Possible approaches to overcoming the multiplex disadvantage in analytical ICP-FTS and some ideal criteria for ICP-FTS instrumentation are presented.     

Large molecules in high-intensity laser fields

New research fields have opened up that are related to the interactions between molecules and high-intensity optical fields where the laser intensity ranges from 10¹²–10¹⁷ W cm⁻². A broad outline of this area will be described from the perspective of products and new techniques for beam generation. Studies of large molecules have begun and some examples are introduced herein. Parent ions with little fragmentation are found to form in the intensity region below 10¹⁶ W cm⁻². The formation of intact ions can be used in femtosecond laser mass spectrometry. In the intensity region above 10¹⁶ W cm⁻², electrons are stripped from the molecules by optical field ionization and the highly charged ions can undergo a Coulomb explosion. Coulomb explosions of benzene and C₆₀ have been demonstrated, and the mechanism can be analyzed by means of molecular dynamics simulations. A high intensity femtosecond laser beam can be converted to radiation sources of coherent VUV light, X-rays etc. and some possibilities for new chemical applications will be discussed.     

Two different types of hollow-cathode discharges used for high resolution laser spectroscopy on copper

Two different techniques, Doppler-free saturation spectroscopy on a hollow-cathode discharge and fluorescence spectroscopy on a collimated atomic beam produced from a hollow-cathode discharge, have been used for high-resolution laser-spectroscopy measurements on the 3d ¹⁰ 4p and 5p states in neutral Copper. The relative merits of the two techniques are discussed.     

An experimental study on the “sequential order” rules in generalized two-dimensional correlation spectroscopy

Following our theoretical analysis on the “sequential order” rules in generalized two-dimensional (2D) correlation spectroscopy (H. Huang, Anal. Chem. 79 (2007) 8281–8292), an experimental study was conducted to test the “sequential order” rules using the FT-NIR data of poly(3-hydroxybutyrate) (PHB)/poly(l-lactic acid) (PLA) blends under uniaxial elongation and parallel polarization. The local sequential order concept proposed for the generalized two-dimensional (2D) correlation spectroscopy is now more clearly stated; “the intensity change at ν1 occurs predominantly before ν2” means that the starting time of the intensity change at ν1 is prior to that at ν2. It is this local sequential order which reflects the real and intuitive sequential order between two events in generalized situations. It has been found that the integrated/overall sequential order results obtained from the 2D correlation analysis may be contradictory to the intuitive local sequential order. In addition, different integrated/overall sequential orders could be obtained by selection of different sampling intervals from a certain set of experimental data, or choosing different number of the contours for the same sampling interval. These new experimental findings are a perfect reinforcement to our previous theoretical study and have further demonstrated the uncertainty of applying the “sequential order” rules in generalized 2D correlation spectroscopy.     

Differential sub-Doppler,one-photon,optical absorption spectroscopy of gases,and vapors with lasers

We consider in this work a high resolution, Doppler-free, one-photon, optical absorption differential spectroscopy of a mixture of two different mutually interacting gases or vapors in order to display the effects of this interaction directly in the optical spectra. Those interactions are restricted to binary collisions and they are treated in the so-called impact approximation (hard collisions). Usually, the high resolution, Doppler-free optical spectra are observed when two counterpropagating laser beams pass through the gas cell. One beam is strong enough to saturate the optical transition to several different degrees. The other beam is a weak probe absorbed by the saturated atomic or molecular pair of energy levels (a two-energy level system with angular frequency ω₀). The laser beams are supposed to have different angular frequencies and to be linearly polarized. In order to achieve the Doppler-free differential optical absorption one-photon spectra, a convenient geometrical experimental set up is proposed.     

Fluorescent probes for monitoring the pulsed‐laser‐induced photocuring of poly(urethane acrylate)‐based adhesives

Fluorescence spectroscopy was used to study the kinetics of polymerization of acrylic adhesive formulations exposed to a 355‐nm pulsed emission from an Nd‐YAG laser. Nine fluorescent probes were used for monitoring the laser curing, showing different sensitivities. In general, the fluorescence intensity emission increased as crosslinking occurred. In addition, solvatochromic fluorescent probes showed a blueshift in their emission. A relative method was applied for the evaluation of the polymerization rates in three different acrylic systems. Special features of pulsed‐laser‐induced polymerization were treated in detail, such as the influence of the laser pulse frequency and the incident laser beam intensity. The polymerization rate slowed down as the pulse repetition rate decreased. An inhibition period due to oxygen quenching was observed, and it was highly dependent on the laser repetition rate and the nature of the photoinitiator. The effect of the laser beam intensity on the kinetics of such fast reactions was studied. In general, increasing the laser energy improved the rate of polymerization. The degree of cure improved as the polymerization rate increased as a result of faster crosslinking, rather than relaxation volume kinetics. Moreover, a saturation rate effect occurred that depended on the photoinitiator. The different behaviors of the two photoinitiators in the curing of the same acrylic formulation was explained on the basis of primary radical termination. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1227–1238, 2004     

Biological monitoring with atomic spectroscopy

Atomic spectroscopy holds a central role in biological monitoring. With this powerful and mature analytical tool, meaningful measurements can be made of a number of important elements in biological specimens. These measurements are useful in two general settings: (1) with toxic elements, by measurement of concentrations in excess of “expected” ranges; and (2) with essential elements, in which deficiencies may be observed. Several considerations are of major importance to effectively apply atomic spectroscopy to these measurements; (1) choice of an appropriate specimen; (2) selection of the most appropriate analytical method; (3) collection and preservation of the specimen; (4) analysis of the specimen; and (5) evaluation of the data generated. The usefulness of the various forms of atomic spectroscopy will be shown with two illustrative examples, and some evaluation will be provided of the future directions of research and upcoming issues in biological monitoring.