Stanley J. Bajic

SINGLE-KERNEL MAIZE ANALYSIS BY NEAR-INFRARED HYPERSPECTRAL IMAGING

The objectives of this research were: (1) to develop a technique for creating calibrations to predict the constituent concentrations of single maize kernels from near-infrared (NIR) hyperspectral image data, and (2) to evaluate the feasibility of an NIR hyperspectral imaging spectrometer as a tool for the quality analysis of single maize kernels. Single kernels of maize were analyzed by hyperspectral transmittance in the range of 750 to 1090 nm. The transmittance data were standardized using an opal glass transmission standard and converted to optical absorbance units. Partial least squares (PLS) regression and principal components regression (PCR) were used to develop predictive calibrations for moisture and oil content using the standardized absorbance spectra. Standard normal variate, detrending, multiplicative scatter correction, wavelength selection by genetic algorithm, and no preprocessing were compared for their effect on model predictive performance. The moisture calibration achieved a best standard error of cross-validation (SECV) of 1.20%, with relative performance determinant (RPD) of 2.74. The best oil calibration achieved an SECV of 1.38%, with an RPD of only 1.45. The performance and subsequent analysis of the oil calibration reveal the need for improved methods of single-seed reference analysis.

High-speed digital photographic study of an inductively coupled plasma during laser ablation: comparison of dried solution aerosols from a microconcentric nebulizer and solid particles from laser ablation

High-speed photographs and videos of an ICP are used to examine the fates of solid particles produced by laser ablation (LA) in an inductively coupled plasma (ICP). The trajectories, lifetimes, and emission behavior of particles traversing the plasma are studied under a variety of conditions. Desolvated particles from a nebulized yttrium solution and particles ablated from a Y2O3 pellet are mixed and introduced simultaneously into an ICP. High-resolution digital photographs and video sequences are captured using shutter speeds of approximately 65 µs. The plasma behavior of particles generated by a quadrupled Nd:YAG laser (266 nm) and an ArF excimer laser (193 nm) are compared, and either argon or helium is used as the transport gas through the ablation cell. No red emission clouds from YO are visible in the ICP when a 20 µL min−1 nebulizer is used to spray a 2000 ppm aqueous Y solution, suggesting that the wet droplets from this nebulizer desolvate almost completely before entering the ICP. These desolvated particles from the nebulized solution atomize and ionize like the small dry particulates from laser ablation. However, many large ablated particulates are observed to fly through the plasma intact, possibly contributing to signal noise, deposition on the sampler and skimmer cones, and elemental fractionation.

Time-resolved studies of particle effects in laser ablation inductively coupled plasma-mass spectrometry : Part 1. Investigation of nanosecond and femtosecond pulse width lasers and devices for particle size selection

Transient signal responses for ablated samples as a function of particle size and laser parameters are characterized. Data are acquired with time resolution of 5 or 6 ms per data point. Large positive spikes in signal are observed and increase in both amplitude and frequency with increasing particle size. Particle sizes are selected using a differential mobility analyzer. Spikes in the signal also increase with decreasing laser rastering rates. A comparison of lasers with pulse widths of 370 fs and 5 ns shows that shortening the pulse width significantly reduces the frequency and amplitude of positive spikes in signal. These large positive spikes are attributed to the vaporization, atomization, and ionization of individual large intact particles, which are considered to be a major cause of fractionation in laser ablation ICP-MS.

Spatially-resolved analysis of solids by laser ablation-inductively coupled plasma-mass spectrometry: trace elemental quantification without matrix-matched solid standards

A two-point calibration method for laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is assessed. Desolvated particles from a Teflon microconcentric nebulizer and particles ablated from a localized position on a solid sample are mixed and introduced simultaneously into an ICP magnetic sector mass spectrometer. Analyte signals from the solution are compared with those from the ablated solid for calibration. Matrix-matched or pelletized solid standards and prior knowledge of sample composition are not required for calibration. The transport of sample particulates from the ablation cell is measured online with a piezoelectric microbalance to provide signal normalization. The relative accuracy of the quantitative analysis of NIST SRM 612 glass and NIST SRM 1264a steel is 3% to 12%, respectively, except for the elements Pb and Bi in steel. These two elements are distributed heterogeneously and are probably subject to fractionation. The use of helium instead of argon as transport gas reduced fractionation but did not eliminate it. The analyte concentrations were approximately 15–51 ppm in NIST SRM 612 glass and 9–2500 ppm in NIST SRM 1264a steel.

Analysis of glass fragments by laser ablation-inductively coupled plasma-mass spectrometry and principal component analysis.

Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is used to differentiate glass samples with similar optical and physical properties based on trace elemental composition. Laser ablation increases the number of elements that can be used for differentiation by eliminating problems commonly associated with dissolution and contamination. In this study, standard residential window and tempered glass samples that could not be differentiated by refractive index or density were successfully differentiated by LA-ICP-MS. The primary analysis approach used is Principal Component Analysis (PCA) of the complete mass spectrum. PCA, a multivariate analysis technique, provides rapid analysis of samples without time-consuming pair-wise comparison of calibrated analyses or prior knowledge of the elements present in the samples. Probabilities for positive association of the individual samples are derived from PCA. Utilization of the Q-statistic with PCA allowed us to distinguish all samples within the set to a certainty greater than the 99% confidence interval.

Influence of particle size on fractionation with nanosecond and femtosecond laser ablation in brass by online differential mobility analysis and inductively coupled plasma mass spectrometry

A differential mobility analyzer (DMA) passes laser ablation (LA) particles and agglomerates within a narrow range of electrical mobilities to the inductively coupled plasma mass spectrometer (ICP-MS). No particle collection or offline particle analysis is required. Fractionation is assessed with the Cu+/Zn+ signal ratio. Results presented in this paper support previous findings that ns LA provides many small Zn-rich particles and some much larger Cu-rich particles and that fs LA produces large agglomerates of small particles. The composition of the aerosol produced by fs LA falls between the relatively Zn-rich and Cu-rich extremes of ns LA. Femtosecond LA provides elemental ratio measurements that remain more stable with respect to time, which allows a greater degree of confidence in LA results. Even though some parameters besides pulse length differ between the lasers compared in this study, the suppression of particle size related fractionation with fs LA can be attributed to pulse length.

Time-resolved studies of particle effects in laser ablation inductively coupled plasma-mass spectrometry

Time resolved signals in laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) are studied to determine the influence of experimental parameters on ICP-induced fractionation effects. Differences in sample composition and morphology, i.e., ablating brass, glass, or dust pellets, have a profound effect on the time resolved signal. Helium transport gas significantly decreases large positive signal spikes arising from large particles in the ICP. A binder for pellets also reduces the abundance and amplitude of spikes in the signal. MO+ ions also yield signal spikes, but these MO+ spikes generally occur at different times from their atomic ion counterparts.

In situ determination of uranium in soil by laser ablation-inductively coupled plasma atomic emission spectrometry

The concentration of uranium in soil has been determined for 80 sites in an area suspected to have uranium contamination by in situ laser ablation - inductively coupled plasma atomic emission spectrometry (LA-ICPAES), utilizing a field-deployable mobile analytical laboratory. For 15 of the 80 sites analyzed, soil samples are collected so that the field LA-ICPAES results could be compared to laboratory-determined values. Uranium concentrations determined in the field by LA-ICPAES for these 15 sites range from <20 parts per million (ppm) by weight to 285 ppm. The uncertainty in the values determined, however, is large relative to the uranium concentrations encountered at this site. The 95% confidence interval (CI) values are approximately 85 ppm. The uranium concentrations determined by laboratory LA-ICPAES analysis range from <20 to 102 ppm (95% CI of approximately 50 ppm); microwave dissolution and subsequent standard addition determination of uranium by solution nebulization ICPAES using an ultrasonic nebulizer yields 19-124 ppm uranium (95% CI of approximately 10 ppm). For 11 of the 15 samples, the field- and laboratory-determined uranium concentrations agree, within the uncertainty of the determined values. 19 refs., 5 figs., 3 tabs.

Real-time atomic absorption mercury continuous emission monitor

A continuous emission monitor (CEM) for mercury (Hg) in combustor flue gas streams has been designed and tested for the detection of Hg by optical absorption. A sampling system that allows continuous introduction of stack gas is incorporated into the CEM, for the sequential analysis of elemental and total Hg. A heated pyrolysis tube is used in the system to convert oxidized Hg compounds to elemental Hg for analysis of total Hg; the pyrolysis tube is bypassed to determine the elemental Hg concentration in the gas stream. A key component of the CEM is a laboratory-designed and -assembled echelle spectrometer that provides simultaneous detection of all of the emission lines from a Hg pen lamp, which is used as the light source for the optical absorption measurement. This feature allows for on-line spectroscopic correction for interferent gases such as sulfur dioxide and nitrogen dioxide, typically present in combustion stack gas streams, that also absorb at the Hg detection wavelength (253.65 nm). This artic...

ANALYSIS OF UNDERGROUND STORAGE TANK WASTE SIMULANTS BY FOURIER TRANSFORM INFRARED PHOTOACOUSTIC SPECTROSCOPY

Underground storage tank waste sludge from nuclear fuel processes is difficult to analyze because of the extreme heterogeneity, chemical reactivity, and radioactivity of the waste. Conventional methods of analysis typically require extensive sample handling procedures either to thin the sample or to separate components prior to analysis. These procedures are time consuming, require radiation containment cells, and increase the risk of radiation exposure to lab personnel as a result of the extensive handling. In this paper a method utilizing Fourier transform infrared photoacoustic spectroscopy to analyze hazardous underground storage tank waste with a minimal amount of sample and sample handling is discussed. The method was developed with the use of waste tank simulants that were obtained from the Westinghouse Hanford Company. Emphasis was placed on the determination of disodium nickel ferrocyanide, sodium nitrate, and sodium nitrite because of the concern for the potential of exothermic reactions occurring between oxidizers and ferrocyanide-containing compounds. This method also allows for the analysis of other ions of interest in waste processes such as sodium sulfate. A simple sample preparation method is also discussed which uses freeze drying to remove water from the simulants while maintaining a uniform sample for analysis.