J. D. Winefordner

Fundamentals and Applications of Laser-Induced Breakdown Spectroscopy

Abstract Laser-induced breakdown spectroscopy is reviewed by dividing the literature into three categories according to target phase: solid, liquid, or gas. Within each category, the literature is ...

Variables Influencing the Precision of Laser-Induced Breakdown Spectroscopy Measurements

Several factors influence the precision of laser-induced breakdown spectroscopy (LIBS) measurements. This paper reports on the effect of emission signal temporal development, sample translational velocity, number of spectra accumulated, laser pulse stability, detector gate delay, surface roughness, and use of background correction on LIBS precision. The results are presented in two formats: within measurement/shot-to-shot precision (intra-measurement) and between measurement precision (inter-measurement). The data indicate that intra- and inter-measurement precision are optimized under different conditions. The best precision obtained was 0.03%.

The electronic partition functions of atoms and ions between 1500°K and 7000°K

Abstract Electronic partition functions of the atoms and first ions of 73 elements have been calculated over the temperature range of 1500–7000°K. The results are presented in the form of a fifth order polynomial expression which has been fitted to the data by a method of least squares.

Review of Multielement Atomic Spectroscopic Methods

A comparison of multielement atomic spectroscopic methods is given. The atomic spectroscopic methods, including atomic absorption flame and nonflame spectrometry, atomic fluorescence flame and nonflame spectrometry, and atomic emission spectrometry (including sources consisting of flames, inductively coupled plasmas, and microwave plasmas) are reviewed and compared especially with respect to their inherent advantages and disadvantages for multielement analysis. The types of optical detection systems, including temporal devices, spatial devices, and multiplex devices whether the spectral information is collected sequentially, simultaneously in parallel mode, or simultaneously in multiplexed mode are also compared with respect to their advantages and limitations for measuring atomic spectra and for multielement analysis. In this review, a comparison of atomic spectroscopic methods and optical detection devices is given. The comparison is given with respect to signal-to-noise ratio, experimental limits of detection, and other practical analytical figures of merit. It is hoped that this review will aid the analyst in selecting a multielement atomic method for trace analysis and especially make the analyst aware of the unavoidable tradeoffs in such a selection.

Effective normalization technique for correction of matrix effects in laser-induced breakdown spectroscopy detection of magnesium in powdered samples

The goal of this research was to investigate the influence of the matrix on the laser-induced spectroscopy of magnesium. Powdered samples were used and were presented to the measurement as thin distributions on adhesive tape. A wide range of NIST certified reference materials were used as samples. With careful sample preparation and correction for sample surface density on the tape (determined by weighing), reasonable consistency in the Mg signal intensity was obtained regardless of sample matrix. Relative error of ∼10% and a precision of 10–20% were obtained for the determination of Mg in several certified samples.

Lanthanide-sensitized luminescence for the detection of tetracyclines

Abstract Organic chelates of lanthanide ions, priviously used to enhance the detection sensitivity of the ions, are now used for the sensitive detection of the ligands. When complexed with europium(III), tetracycline displays the broad-banded absorption characteristics of an organic ligand. The excited ligand undergoes intersystem crossing to a triplet state, and then transfers its energy to a 4 f level within the europium(III) ion. the resulting narrow, line-like luminescence of the europium(III) ion has a peak intensity ten times greater than the peak intensity of the uncomplexed ligand. This lanthanide-sensitized luminescence technique is used to quantify tetracycline and two of its analogues. Detection limits are in the nanogram range. Experimental conditions are discussed.

A review and tutorial discussion of noise and signal-to-noise ratios in analytical spectrometry—II. Fundamental principles of signal-to-noise ratios

Abstract This review consists of two parts which discuss signal-to-noise in a tutorial manner. The sources of noise, the mathematical representation of noise, and the major types of noises in emission and luminescence spectrometry are discussed. An extensive treatment of noise and signal-to-noise ratios of paired readings is given using the relation between the auto-correlation function and the spectral noise power. These signal-to-noise expressions under optimized measurement conditions are given in terms of currents and count rates as well as in terms of charge and counts for the cases of d.c. and a.c. measurements; the present treatment is limited to the cases when the background shows only either shot noise or flicker noise. Finally, the consequences of the combination of these noise sources is considered. Signal expressions for optical spectrometry are also given. Tables give the expressions for signal-to-noise ratios in the various cases.

Room-temperature phosphorescence of several polyaromatic hydrocarbons☆

The room-temperature phosphorescence of several polyaromatic hydrocarbons (anthracene, coronene, phenanthrene, pyrene, benzo[a]pyrene) and carbazole on paper support has been investigated. Heavy-atom solvents such as silver nitrate and sodium iodide were found to have specific effects in inducing phosphorescence emission from these compounds.

The effect of sample environment on the room-temperature phosphorescence of several polynuclear aromatic hydrocarbons

Abstract Room-temperature phosphorescence (r.t.p.) of numerous molecules has been studied with emphasis on several polynuclear aromatic hydrocarbons (PAH). The heavy atom effect has led to a significant enhancement of r.t.p. signals for the PAH studied with the trend being Tl+ > Ag+ > Pb2+ > Hg2+. The Tl+ also resulted in enhanced spectral features of emission bands. R.t.p. could be induced from PAH on a sodium acetate sample support as well as on filter paper. A study of the effect of different gaseous environments provided anomalous results.

Physical and Analytical Aspects of a Microwave Excited Plasma

A microwave generator operated at about 100 W was used to maintain a narrow plasma (6 cm long ×0.3 mm diam) in flowing argon at atmospheric pressure. A tapered rectangular cavity was used to couple microwave power to the plasma discharge. Approximate temperature and electron density measurements of the plasma were made with and without water being nebulized; the temperature measurements indicated a lack of thermodynamic equilibrium. The plasma discharge was examined as a source of excitation in atomic emission spectrometry. An aerosol (produced by a system consisting of a pneumatic sprayer, a heated chamber, and a special condenser) was introduced into a plasma having an excitation and ionization temperature of about 5000 K and an electron density of about 1015 cm−3 at a position 0.3 mm from the center of the plasma. Limits of detection were measured for cadmium, gallium, indium, mercury, and zinc. Appreciable signals were also observed for calcium, lead, strontium, and boron, but no limits of detection were measured.