Elemental analysis of bead samples using a laser-induced plasma at low pressure

An Nd:YAG laser (1064 nm, 8 ns, 30 mJ) was focused on various types of fresh, fossilized white coral and giant shell samples, including samples of imitation shell and marble. Such samples are extremely important as material for preparing prayer beads that are extensively used in the Buddhist faith. The aim of this research was to develop a non-destructive method to distinguish original beads from their imitations by means of spectral measurements of the carbon, hydrogen, sodium and magnesium emission intensities and by measuring the hardness of the sample using the ratio between Ca (II) 396.8 nm and Ca (I) 422.6 nm. Based on these measurements, original fresh coral beads can be distinguished from any imitation made from hard wood. The same technique was also effective in distinguishing beads made of shell from its imitation. A spectral analysis of bead was also performed on a fossilized white coral sample and the result can be used to distinguish to some extent the fossilized white coral beads from any imitation made from marble. It was also found that the plasma plume should be generated at low ambient pressure to significantly improve the hydrogen and carbon emission intensity and also to avoid energy loss inside the crater during laser irradiation at atmospheric pressure. The results of this study confirm that operating the laser-induced plasma spectroscopy at reduced ambient pressure offers distinct advantage for bead analysis over the conventional laser-induced breakdown spectroscopy (LIBS) technique operated at atmospheric pressure.     

Determination of Riboflavin in Human Plasma by Excitation‐Emission Matrix Fluorescence and Multi‐Way Analysis

Direct determination of riboflavin (Fig. 1), a vitamin, in human plasma was accomplished based on excitation‐emission matrix (EEM) fluorescence measurements and multi‐way chemometrics method based on parallel factor analysis (PARAFAC). The PARAFAC trilinear model, without restrictions and using one factor was used in the data analysis. The excitation wavelength range was from 380 to 460 nm and the emission was recorded from 480 to 600 nm. The calibration set was constructed with sixteen standard solutions in a concentration range of 0.02–0.38 μg mL^?1 for riboflavin. The capabilities of the method for the analysis were evaluated by determination of riboflavin in synthetic and real samples with satisfactory results. The accuracy of the methods, evaluated through the root mean square error of prediction (RMSEP), was 0.0059 for riboflavin by the PARAFAC model. Also, partial least squares (PLS) model was built at one excitation wavelength and used to determine a set of synthetic and real samples. The best model was obtained with PARAFAC. This result shows that molecular fluorescence spectroscopy can be used for the development of robust analytical methods for the direct determination of riboflavin in complex backgrounds such as human plasma.     

电感耦合等离子体发射光谱(ICP-OES)在地质样品中的研究进展

电感耦合等离子体发射光谱仪在地质样品无机元素分析测试中常用,具有灵敏度高,干扰小,测定线性范围广、稳定性好等优点。本文就电感耦合等离子体发射光谱法测定地质土壤,岩石样品时,综述了酸溶法、碱熔法、烧结法三种消解体系各自特点及消解剂的特性;详细分析了样品测定时外标法、内标法、标准加入法的选择及应用;探讨了样品测试时仪器条件的优化措施,同时对电感耦合等离子体发射光谱的干扰及校正做了分析。最后,对电感耦合等离子体发射光谱测定技术在地质样品中非金属元素分析物测定的应用及未来发展进行了展望。     

Determination of Tiopronin in Pharmatceutical Preparations by Time Resolved Chemiluminescence Using the Stopped-Flow Technique

An analytical method for the determination of tiopronin in pharmaceuticals was developed. The method is based on measurements of the chemiluminescence (CL) produced by tiopronin upon reaction with sulfuric acid and potassium permanganate as the oxidant in the presence of formaldehyde as emission enhancer. This allows entire chemiluminescence intensity vs. time profiles to be recorded by using the stopped-flow technique in a continuous-flow system, which, in turn, enables the use of a new parameter (the rate of the light decay reaction) in addition to the maximum emission intensity and total emission area, which are proportional to the analyte concentration. The influence of chemical variables such as the type of acid used and its concentration, emission enhancer, and oxidant concentration on the chemiluminescence signal was examined. The calibration graph was linear from 0.05 to 3.00 mg L^?1. The limit of detection as determined according to Clayton ranged from 0.12 to 0.17 mg L^?1 and the relative standard deviation (RSD) for the analysis of 10 samples containing an analyte concentration of 1.50 mg L^?1 was 1.87%.     

THE USE OF SHORT LIVED FLUORESCENT DYES TO CORRECT FOR ARTIFACTS IN THE MEASUREMENTS OF FLUORESCENCE LIFETIMES

Abstract— The ultrafast emission for fluorophores can be used as the effective excitation pulse for prompt response measurements by photo detectors in the same spectral region as that of unknown samples. This method corrects for such artifacts as wavelength and spatial dependence of the response function of the photodetector. It is shown that the emission from triphenylmethane dyes is an excellent effective pulse with relaxation time 2 ps in the red region of the spectrum. A microchannel plate photomultiplier has only a 35 ps increase in response or lag time between excitation at 420 nm and emission at 680 nm.     

Characterization of laser induced plasmas by optical emission spectroscopy: A review of experiments and methods

Advances in characterization of laser induced plasmas by optical emission spectroscopy are reviewed in this article. The review is focused on the progress achieved in the determination of the physical parameters characteristic of the plasma, such as electron density, temperature and densities of atoms and ions. The experimental issues important for characterization by optical emission spectroscopy, as well as the different measurement methods are discussed. The main assumptions of the methods, namely the optical thin emission of spectral lines and the existence of local thermodynamic equilibrium in the plasma are evaluated. For dense and inhomogeneous sources of radiation such as laser induced plasmas, the characterization methods are classified in terms of the optical depth and the spatial resolution of the emission used for the measurements. The review deals firstly with optically thin spatially integrated measurements. Next, local measurements and characterization in not optically thin conditions are discussed. Two tables are included that provide reference to the works reporting measurements of electron density and temperature of laser induced plasmas generated with diverse samples.     

Laser ablation molecular isotopic spectrometry of water for 1D2/1H1 ratio analysis

Laser Ablation Molecular Isotopic Spectrometry (LAMIS) has been investigated for optical isotopic analysis of the deuterium to protium ratio in enriched water samples in ambient air at atmospheric pressure. Multivariate PLSR (Partial Least Squares Regression) based calibrations were carried out and validated using multiple statistical parameters. Comparisons of results are reported using two spectrometers having two orders of magnitude difference in spectral resolution. The accuracy and precision of isotopic analysis depends on the spectral resolution and the inherent isotope shift of the elements. The requirements for spectral resolution of the measurement system can be significantly relaxed when the isotopic abundance ratio is determined using chemometric processing of the spectra. Large isotopic shifts in the individual rotational branches of OH/OD molecular emission spectra were measured. Optimized temporal conditions for LAMIS measurements were established. Several sub-regions of spectra were used for PLSR calibration and the results demonstrate that both the emission intensity and degree of spectral differentiation affect the quality of the PLSR calibration. LAMIS results also were compared with traditional LIBS results obtained using PLSR and a spectral deconvolution method, demonstrating the advantages of LAMIS over LIBS with respect to isotopic composition determination.     

Determination of trace amounts of cadmium, lead, copper and zinc in natural waters by inductively coupled plasma atomic emission spectrometry with thermospray nebulisation, after enrichment on Chelex-100

Enrichment on Chelex-100, followed by evaporation when necessary, was used for the pre-concentration of Cd, Pb, Cu and Zn from natural waters. The measurements were carried out with inductively coupled plasma atomic emission spectrometry using a thermospray nebulisation system to reach the required sensitivity. The detection limits corresponding to three times the standard deviation of the blank (in 1% v/v HNO3) after a 30-fold enrichment are 0.02 microgram l-1 for Cd, 0.33 microgram l-1 for Pb and 0.03 microgram l-1 for Cu and Zn. Matrix effects, which are fairly serious with thermospray nebulisation, were taken into account by using the standard additions method. Results obtained for several river water samples were compared with those found by analysis of the non-enriched sample with inductively coupled plasma mass spectrometry or graphite furnace atomic absorption spectrometry. In all instances the agreement was satisfactory.     

Measurement of boron isotopic ratio with non-gated molecular spectroscopy of femtosecond laser-produced plasma

Laser-induced breakdown spectroscopy can be augmented by concurrent spectroscopic measurements of molecules and molecular ions resulting from recombination of laser-ablated plasmas with the ablated sample and surrounding environment. Molecular emissions can exhibit significantly greater isotopic shifts than atomic emissions, making this approach attractive for isotopic characterization of nuclear materials. We describe a measurement of boron isotopic ratios in four boron-containing samples utilizing the emission from boron monoxide radicals formed in the expanding laser-induced ablation plume. Femtosecond laser excitation is used and the emission in the 532–540 nm region of interest is studied, where a linear superposition of characteristic spectra for two boron isotopes has been applied for reconstruction of the boron isotopic ratio. It is also demonstrated that the use of non-gated measurements of emission spectra suffices for accurate isotopic characterization using this method. The application of multivariate regression to deconvolve the isotopic ratio from the measured emission spectra is discussed in detail, including the limitations and subtleties of this approach.     

Highly accurate gas chromatographic analysis of reference gases for use in vehicle emission measurements

A highly accurate gas chromatographic analytical method has been developed for the determination of the composition of gas mixtures. It was tested using a reference gas as an example consisting of 3.5% of CO, 14% of CO₂, 0.2% of propane and residual N₂ intended for the use in vehicle emission measurements. The method is based on comparison measurements with samples of a calibration gas, whose composition is iteratively adapted to that of the sample investigated using a gravimetric gas mixing method. For the gas chromatographic measurement, a molecular sieve column and a polymer column are used in parallel and in isothermal operation. All gas components can be determined by a single gas chromatographic measurement, and the relative uncertainty of measurement achievable is ?0.4%.     

The effect of alkaline pretreatment on the thermal decomposition of hemp

The goal of this study was to clarify the effect of alkaline pretreatments on the thermal decomposition and composition of industrial hemp (Cannabis sativa L.) samples. Thermogravimetric/mass spectrometric measurements (TG/MS) have been performed, on untreated, hot water washed, and alkali-treated hemp samples. The main differences between the thermal decomposition of the samples are interpreted in terms of the different alkali ion contents which have been determined using inductively coupled plasma-optical emission spectroscopy (ICP-OES) method. Principal component analysis (PCA) has been used to find statistical correlations between the data. Correlations have been obtained between the parameters of the thermal decomposition and the alkali ion content as well as the altered chemical structure of the samples. The differences in the thermal behavior of the samples are explained by the different K⁺ and Na⁺ contents and the changed structure of the hemicellulose component of the samples due to the pretreatments. The more alkali ions remain in the hemp samples after the alkali treatment, the more ash, char and lower molecular products are formed during thermal decomposition.     

Investigation of polarization effects for nanosecond laser-induced breakdown spectroscopy

The spectral and temporal polarization dependencies of nanosecond laser-induced plasmas are explored for analysis of gaseous and solid samples using various experimental configurations. Plasma emission measurements were resolved into vertical and horizontal polarization components, and the ratio of the two polarization-resolved measurements was calculated for each sample and configuration. For the solid target, measurements were recorded with the sample oriented both normal to the incident laser beam as well as at oblique angles of incidence. The results for the breakdown of a pure, nitrogen gaseous sample revealed no degree of polarization in either the continuum or atomic emission, with the ratios of the horizontally-to-vertically resolved plasma emission showing values equal to unity when resolved both temporally and spectrally. The analysis of both copper and steel solid samples also showed no polarization dependency in the spectral and temporal data when the laser was incidentally normal to the sample surface. For oblique angles of incidence, some polarization (< 10%) was observed within the first tens of nanoseconds of plasma lifetime. The polarization was manifested as a slight reduction in the horizontal component of plasma emission, but significantly, the observed polarization was found to be spectrally flat, with no difference observed between continuum and atomic emission features. The small polarization effect was found to diminish with plasma residence time, effectively vanishing by about 1 μs following breakdown. The transient polarization is hypothesized to arise from reflection effects (i.e. Fresnel reflectivity) between the plasma light and the solid target surface present with oblique angles of incidence for reflected light, with temporal effects due to the dynamic nature of the plasma development and plasma–surface interactions. Overall, no evidence was found to support any inherent anisotropy or polarization specific to the plasma continuum or the atomic emission for the transitions studied.     

Radiocarbon evaluation of natural/synthetic ratio in citric acid samples

A method is described for the evaluation of the natural/synthetic ratio in citric acid samples. The method is based on measurements of the activity of carbon-14 present in citric acid of natural origin. The parameters that affect the radiocarbon counting (background emission, scintillation quenching and relative efficiency) are discussed. Two different procedures are described which can also be applied to the evaluation of the natural/synthetic origin of other carbon-containing compounds.     

Rapid classification of alloyed steel by means of optical emission spectroscopy and a supervised learning procedure

A supervised learning procedure for classification of steel samples analyzed by means of optical emission spectroscopy was developed. The method should be applicable in simple portable spectrometers, for various groups of materials and working relatively fast. Data vectors extracted from digital spectra of unknown samples are compared with average vectors evaluated from the data vectors of repeated measurements of reference samples. The classification is carried out on the basis of the multivariate distance between the data vector of the unknown sample and the nearest average reference vector and its deviation. The supervised learning procedure was tested by 10 steel samples which could be successfully classified.     

Analysis of nitrated polycyclic aromatic hydrocarbons

Many nitrated polycyclic aromatic hydrocarbons (NPAH) that are present in low concentrations in the environment and in emission sources have been shown to be mutagenic and/or carcinogenic. This paper reviews the current methods of analysis of these compounds with the emphasis on NPAH measurements in ambient particulate matter samples.     

Synthesis and Optical Properties of Ce-doped ZnO

ZnO nanorods were synthesized using the sol-gel method, and the effects of annealing temperature and Ce doping on the morphologies and optical properties of ZnO nanostructures were investigated in detail. The XRD measurements showed that the as-synthesized ZnO nanostructures had a hexagonal wurtzite structure. SEM images showed that uniform nanorods formed at 900 °C. Photoluminescence measurements showed an ultraviolet emission peak and a relatively broad visible light emission peak for the samples sintered at different temperatures. The UV emission peak bathochromically shifted when the annealing temperature rose from 850 to 1000 °C. Ce doping decreased the synthesized temperature of the ZnO nanorods to 500 °C, and the UV peaks hypsochromically shifted.     

Diluted magnetic semiconductor properties in Zn<Subscript>1−x</Subscript>Cu<Subscript>x</Subscript>O nanoparticles synthesized by sol gel route

Nanoparticles of ZnO:Cu Diluted Magnetic Semiconductor (DMS) are prepared using sol gel method. The structural, optical and EPR properties of them are investigated. The XRD patterns of them show the formation of polycrystalline and hexagonal wurtzite structure without any secondary phase formation. The average size of particles ranges from 14 to 19 nm. In the optical absorption study of the samples, a red shit of optical band edge and a narrowing of the optical band gap are observed when Cu concentration is increased. The PL measurements illustrate 392 nm UV radiation of the near band-edge emissions of ZnO, blue emission at 450 nm and orange emission at 628 nm. The cause of decrease in intensity of these emission lines is the sincerely enhanced non-radiative transitions when Cu is doped in ZnO. EPR measurements provide substantial evidence for the presence of defect states and enhancement of exchange interaction.     

Highly accurate gas chromatographic analysis of reference gases for use in vehicle emission measurements

 A highly accurate gas chromatographic analytical method has been developed for the determination of the composition of gas mixtures. It was tested using a reference gas as an example consisting of 3.5% of CO, 14% of CO₂, 0.2% of propane and residual N₂ intended for the use in vehicle emission measurements. The method is based on comparison measurements with samples of a calibration gas, whose composition is iteratively adapted to that of the sample investigated using a gravimetric gas mixing method. For the gas chromatographic measurement, a molecular sieve column and a polymer column are used in parallel and in isothermal operation. All gas components can be determined by a single gas chromatographic measurement, and the relative uncertainty of measurement achievable is ?0.4%. Received: 6 March 1996/Revised: 30 May 1996/Accepted: 6 June 1996