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Biomedical subjects

J D Winefordner

Publications and source records attributed to J D Winefordner.

At least 19 recordsLinked to original sources
PubMed2006

Radiative model of post-breakdown laser-induced plasma expanding into ambient gas.

The dynamics of the radiative plasma expansion into an ambient gas is considered. The model describes the evolution of the plasma emission spectrum and the dynamics of the resulting shock wave. The time frame for the applicability of the model is in the tens of nanoseconds after the laser pulse is terminated, until a few microseconds later when the plasma ceases to emit. It is assumed that local thermodynamic equilibrium is established and that the plume expands with spherical symmetry. The model outputs are spatial and temporal distributions of atoms, ions, and electron number densities, evolution of atom and ion line profiles, and the shock wave. The model should be applicable to spectroscopic analysis of the initial plasma state and plasma dynamics.

Journal Article↗
PubMed2004

Microchip laser-induced breakdown spectroscopy: a preliminary feasibility investigation.

A commercial, 7 microJ/pulse, 550 ps microchip laser is used to induce plasma on Pb, Si, Cu, Fe, Ni, Ti, Zn, Ta, and Mo foils and a Si wafer. The measured plasma lifetime is comparable with the duration of the laser pulse (a few ns). The plasma continuum radiation is low, while some of the strong resonance lines (e.g., Zn 213.86 nm) show self-reversal. Quantitative analysis is possible using non-gated detectors but analytical lines should be chosen with care to avoid reduction in the linear dynamic range. The mass removed (0.5-20 ng/pulse) is sufficient to yield spectra that are detectable with portable grating spectrometers equipped with non-gated, non-intensified detector arrays. The spectrum of Cd is detected with a broadband portable spectrometer (200-950 nm). The combination of the broadband spectrometer and the microchip laser is very promising for material identification, especially in field applications.

Journal Article↗
PubMed2004

Determination of the maximum temperature at the center of an optically thick laser-induced plasma using self-reversed spectral lines.

A method of temperature measurement based on the model developed by Bartels of an optically thick inhomogeneous plasma was applied to a laser plasma induced on a target containing barium. The method involves the intensity ratio measurement of two self-reversed Ba(II) lines. The temperature thus determined corresponds to the maximum temperature in the plasma center. The plasma temperature was measured for delay times between 0.5 micros and 10 micros in two spectrometer operating modes: the scanning mode and the dual-wavelength mode, the latter resulting in better precision. A detailed analysis of experimental errors was performed. The error strongly depended on the wavelength separation of the lines used. The most accurate results were obtained for the largest line separation. Using one line in the UV and the other in the visible region, the relative error was 2-6% for temperatures between 8000 K and 20 000 K. The distribution of the plasma temperature along the plasma height was measured in the same delay time range. The temperature was found to be uniform along the plasma vertical axis, thus confirming the plasma cylindrical symmetry.

Journal Article↗
PubMed2003

Automatic correction of continuum background in laser-induced breakdown and Raman spectrometry.

The goal of this work was the development and evaluation of an algorithm for the approximation and automatic subtraction of continuum backgrounds in laser-induced breakdown and Raman spectra. The background correction algorithm was applied to simple and complex spectra and its effect on identification accuracy was studied. Linear correlation was used for the identification of plastic samples using both laser-induced breakdown and Raman spectra. For both techniques, the algorithm successfully eliminated continuum background without compromising spectral integrity. A significant improvement in the percentage of correct plastic identifications was observed for Raman spectra. The approach should be applicable to a wide range of background correction problems in atomic and molecular spectroscopy.

Algorithms↗
PubMed2003

Laser-enhanced ionization with avalanche amplification: detection of cesium at fg/mL levels.

The avalanche amplification of the laser-enhanced ionization signal of Cs atoms in a flame has been studied. Ionization of Cs atoms, enhanced by two-step excitation, was detected in hydrogen and propane flames. By employing the effect of avalanche amplification of electrons, high signal-to-noise ratio (approximately 10(4)) was obtained for a 100 ppt Cs solution. The extrapolated limit of detection was 30 fg/mL (ppq).

Cesium↗
PubMed2000

In-situ evaluation of barrier-cream performance on human skin using laser-induced breakdown spectroscopy.

Laser-induced breakdown spectroscopy (LIBS) was used to evaluate the effect of barrier creams (skin protective creams) on human skin. A Nd: YAG laser at 1,064 nm was used with a pulse energy of 100 mJ. A method was developed to measure the effectiveness of barrier creams against zinc ion absorption from aqueous zinc chloride solution and oil paste zinc oxide, which represent model hydrophilic and lipophilic metal compounds, respectively. Zinc was chosen since it posed no risk to human skin. 3 representative commercial barrier creams advertised as being effective against lipophilic and hydrophilic substances were evaluated by measuring zinc absorbed through the stratum corneum. 4 consecutive skin surface biopsies (SSB) were taken from biceps of the forearms of 6 volunteers at time periods of 0.5 h and 3 h after application of the protective cream. Results were compared with control skin where no barrier cream was used. The zinc atomic emission line at 213.9 nm was selected. Gate delay and gate width time was optimized to obtain the best signal-to-noise ratio (SNR) and precision. This method provided a facile and rapid screening of the effectiveness of skin barrier creams against zinc ion penetration. The barrier creams were shown to provide appreciable protection against the penetration of both ZnCl2 and ZnO into the skin.

Adult↗
PubMed1996

Ultratrace determination of lead in whole blood using electrothermal atomization laser-excited atomic fluorescence spectrometry.

Laser-excited atomic fluorescence has been used to detect lead that was electrothermally atomized from whole blood in a graphite furnace. A 9 kHz repetition rate copper vapor laser pumped dye laser was used to excite the lead at 283.3 nm, and the resulting atomic fluorescence was detected at 405.8 nm. No matrix modification was used other than a 1:21 dilution of the whole blood with high-purity water. Using the atomic fluorescence peak area as the analytical measure and a background correction technique based upon a simultaneous measurement of the transmitted laser intensity, excellent agreement for NIST and CDC certified whole blood reference samples was obtained with aqueous standards. A limit of detection in blood of 10 fg/mL (100 ag absolute) was achieved.

Calibration↗
PubMed1996

Microsecond-pulse glow discharge atomic emission.

A microsecond pulsed glow discharge was produced with high pulse magnitude and small duty cycle. Time resolved emission and absorption spectroscopy was applied to study the processes of atomization, excitation and ionization in the glow discharge. Experimental results show that, without overheating the sample, the emission peak intensity is several orders greater than that obtained in the conventional dc mode. This implies that a much more intense plasma is generated during pulsed "on" region.

Journal Article↗
PubMed1996

Absolute and/or relative detection limits in laser-based analysis: the end justifies the means.

The absolute limit of detection usually expresses the minimum amount of analyte detectable, while the relative limit of detection refers to the minimum concentration of analyte detectable. These concepts and their differences are obviously familiar to all analytical spectroscopists. Nevertheless, the two definitions are used liberally in the literature. For example, it is not uncommon to refer to exceptional sub-femtograms detection limits for a technique used to analyse ultratrace levels of an element in water and to a modest part per million detection limit of another technique used to characterise the microdistribution of an element in a sample mass of about one microgram. In this paper, an attempt is made to point out that the terms "ultratrace analysis" and "microanalysis" must refer to two conceptually different approaches and that there are cases in which one definition is more appropriate than the other. It is argued that, while there is no objection in reporting both detection limits when a single technique is evaluated, one has to be careful in choosing the most appropriate definition when different analytical techniques are compared.

Journal Article↗
PubMed1994

Capacitively coupled microwave plasma atomic emission spectrometer for the determination of lead in whole blood.

The determination of lead in whole blood by atomic emission spectrometry using a capacitively coupled microwave plasma and a tungsten filament electrode is presented. When the plasma-supporting electrode is also used as the sample holder, transfer of the sample to the plasma is 100%. Microwaves are used to dry the sample and, at higher powers, ignite a helium plasma which results in the atomization and excitation of Pb. Using this methodology, a detection limit of 3 pg of Pb was obtained using 5-microL aqueous samples. The precision was 9%. Whole blood samples were subjected to a drying stage similar to that of the aqueous samples. Following this drying stage, a low-power (30 W) helium plasma was ignited and used to ash the blood sample. Higher power plasmas (> 150 W) were used to atomize and excite the Pb. Recovery of Pb from the blood samples was 88%, when compared to aqueous standards.

Calibration↗
PubMed1991

Determination of chloride at picogram levels by molecular fluorescence in a graphite furnace.

Chloride was determined at nanogram levels by adding excess of indium to the sample introduced into a graphite furnace and measuring the laser induced molecular fluorescence of indium chloride. The diatomic molecules of indium chloride were excited by a pulsed dye laser at 267 nm and fluorescence was measured at 359 nm. The effects of various parameters including amount of indium added, furnace thermal conditions and presence of concomitants were also studied. A linear calibration in the range of 0.025-1.25 ng and a detection limit of 17 pg of chloride were obtained under optimum conditions. The analytical usefulness of the method was checked by determining the chloride content in National Institute of Standards and Technology, Standard Reference Materials 1571a and 1571b Orchard Leaves.

Chlorides↗
PubMed1990

Studies of chemical interferences in an inductively coupled plasma using moment analysis of space-resolved emission profiles.

Interelement effects induced by sodium, aluminum, and phosphate ion on calcium and magnesium emission were studied with a two-channel spectrometer that could record spatially resolved emission profiles of an atom line and an ion line simultaneously. The statistical moments of the digitized emission profiles were calculated and were employed for rate-constant estimation using our previously established theory. Interelement effects are results of interferences in the analyte atomization, ionization, and/or recombination steps. Characteristic changes will be induced in the emission profiles by each of these interferences. These changes can be characterized by the statistical moments of the corresponding profiles. Therefore, by investigating variations in the rate constants caused by the specific concomitant, one may better understand the analyte atomization-excitation mechanisms. Sodium enhances the atomic emission of both calcium and magnesium but has little effect on their ionic emission. Based on the trends of variation in the rate constants, the atomic signal enhancement seems to be attributed more to the facilitation of analyte atomization rather than to the shift of ionization equilibrium. Aluminum and phosphate ion appear not to induce significant interferences on either elements.

Calcium↗
PubMed1990

Solid-surface room-temperature phosphorescence detection for high-performance liquid chromatography.

In the present study, we have optimized the use of a two nebulizer system for solid-surface room-temperature phosphorescence (SSRTP) as a selective, permanent record detector for high-performance liquid chromatography (HPLC). The chromatographic parameters and the analytical figures of merit of five well known phosphorescent compounds were compared to those obtained by ultraviolet detection. Calibration curves with satisfactory linear dynamic ranges and limits of detection in the nanogram and subnanogram level showed the feasibility of the SSRTP detector for HPLC. In addition, overlapped compounds were individually identified demonstrating that the selectivity of the proposed detector can be a useful feature in case of incomplete chromatographic separations of complex mixtures.

Benzopyrenes↗
PubMed1990

Surface-enhanced Raman analysis of sulfa drugs on colloidal silver dispersion.

Surface-enhanced Raman spectrometry (SERS) of three sulfa drugs (sulfadiazine, sulfamerazine, and sulfamethazine) is reported. Silver colloidal dispersions prepared by simple borohydride reduction of silver nitrate are used as substrates. The capability of SERS for spectral fingerprinting of analytes with close structural properties using easily prepared substrates and relatively simple instrumentation is illustrated. By careful attention to the timing in the measurement, quantitative information can be obtained from silver colloids. Linearity was achieved up to 100 ng mL-1. Limits of detection range in the low nanograms per milliliter level.

Colloids↗
PubMed1990

Long path atomic/ionic absorption spectrometry in an inductively coupled plasma.

A novel approach was taken to increase the atomic/ionic absorption path length in an inductively coupled plasma (ICP) by using a water-cooled quartz "T-shaped" bonnet. Atomic and ionic absorption spectrometry was performed utilizing a continuum source and line sources. Absorption spectra of synthetic multielement solutions were collected with a photodiode array. Sample introduction into the ICP was accomplished with an ultrasonic nebulizer. To prevent the bonnet from cracking, low radio frequency powers were utilized (i.e., 400-600 W). Plasma diagnostics were performed to study the plasma temperature and electron number density within the "T-shaped" bonnet. Analytical figures of merit were found to be better than those obtained from previous work attempted with inductively coupled plasma atomic absorption spectroscopy and approaching that of flame atomic absorption spectroscopy.

Spectrophotometry, Atomic↗