Robert S. Pomeroy

Information-Based Expert Systems for Atomic Emission Spectroscopy

The development of the direct-current plasma echelle/CID spectroscopic system for atomic emission spectroscopy (AES) provides new alternatives for automated system control and data analysis. With this system, the concept of the “intelligent” spectrometer becomes tangible. The echelle/CID system simultaneously gathers a wealth of spectral information over a wide spectral region. The mechanical stability of the system and the absence of moving parts give rise to reproducible wavelength assignment. The large amount of spectral information acquired has led to the development of information-based expert systems for AES: automated qualitative analysis, semi-quantitative analysis, and an “on the fly” matrix-dependent line selection. These algorithms are effective in situations where there is a large variability among samples. The analytical power of these routines is heavily dependent on their utilization of the large database and the use of fundamental spectroscopic principles. Examples of the use of these algorithms in environmental monitoring, in the identification of chemical waste, in the analysis of geologic materials and steels, and in HPLC-AES are presented.

Imaging applications for chemical analysis utilizing charge coupled device array detectors

Abstract Scientific charge transfer devices (CTDs) are rapidly becoming the detector of choice for optical chemical analysis. The high sensitivity and resolution of these detectors make them ideal for a wide range of chemical imaging applications. In this article we highlight some of the current trends and future research directions of CTDs as imaging detectors for chemical analysis.

A comparison of CCD and CID detection for atomic emission spectroscopy

Abstract The performances of two classes of charge transfer device detectors—the charge-coupled device and the charge injection device—are compared for atomic emission spectroscopy. For these studies, a direct current plasma source is employed with an echelle spectrograph having a spectral image size matched to the format of these array detectors. In a clean matrix, both detectors yield good detection limits. In more complex matrices, blooming, or the spilling of excess photogenerated charge from the regions of the detector which are overexposed, greatly limits the utility and sensitivity of the charge-coupled device for atomic emission spectroscopy. Several methods to improve the performance of charge-coupled device detectors are described, including preliminary work using an antiblooming charge-coupled device. The charge injection device detector is found to be highly resistant to blooming and is able to analyze complex mixtures with little to no loss in sensitivity.

Spatial and spectral imaging of plasma excitation sources

The combination of an imaging polychromator and a two-dimensional charge-coupled device (CCD) detector can provide a simple, simultaneous, efficient means of acquiring spatial and spectral maps of emission sources. Extensive theoretical and experimental studies have been carried out to obtain a more fundamental understanding of the interaction between the source and analyte. Often, spatially and spectrally resolved wavelength information has been used to generate maps of various source characteristics, such as excitation temperature, electron density, and emission intensity, to gain further insight into energy transfer, ionization, and excitation processes. The interplay of these characteristics affects the optimal analytical viewing zone of an emission source and influences the design of future sources. To compose a complete description of the processes involved in plasma excitation, one must obtain the emission information for the entire source. This requirement is commonly performed by imaging a very small portion of an excitation source and translating either the source or the spectrograph—an approach that is time consuming and relies on the source remaining stable over the course of the experiment. Ideally, a technique that simultaneously acquires two-dimensional spatial and spectral information would be the preferred method; however, this approach has not yet been successfully carried out.

Spark Spectroscopy Using Charge Transfer Devices: Analysis, Automated Systems, and Imaging

An atomic emission spectroscopic system utilizing a spark source for excitation has been developed. The instrument employs a custom echelle spectrometer and a charge injection device (CID) array detector system. This system simultaneously covers wavelengths from 200 to 450 nm with a resolution of 0.02 nm at 300 nm. Solids sample analyses of steels and aluminums were used to demonstrate this systems speed, sensitivity, and flexibility. Automated systems for rapid qualitative and semi-quantitative screening of these materials will also be discussed. Another spectroscopic system based on a commercial imaging spectrograph and a charge-coupled device (CCD) array detector has been used to obtain temporally resolved spectral images of single sparks discharges.

Charge-injection device detection for improved performance in atomic-emission spectroscopy

Studies into the use of simultaneous multiwavelength detection over a broad wavelength region (220-520 nm) demonstrate the power and flexibility offered by a charge-injection device for detection in atomic-emission spectrometry. An echelle monochromator and a charge-injection device utilizing the general electric CID17B array detector are used in conjunction with a direct current plasma source to perform multi-line analysis for Mg, Sr, Fe, Dy, Ho and Yb, increasing the sensitivity and limits of detection. By monitoring the 341-nm OH band and background Ar emission lines, changes in the nebulization and excitation conditions are easily detected. The presence of an organic matrix component not present in the standards is detected by observing the C(I) emission at 247.8 nm. These diagnostic tools can be combined with the use of an internal standard to obtain a reliability not previously available in automated AES instrumentation.

Indirect Determination of Phosphate, Silicate, and Arsenate by HPLC-AES:

The indirect determination of phosphate, silicate, and arsenate is performed by separation of their heteropoly acids by using ion-pair reverse-phase HPLC (IP-RPHPLC) and monitoring the molybdenum emission from a DCP with an echelle spectrometer and a charge-injection device (CID) detector. Limits of detection found for phosphate, silicate, and arsenate are 26, 31, and 52 ng/mL, respectively. The detection limit for arsenate is slightly degraded due to its proximity to the excess molybdate peak. These results represent an improvement in the determination for these nonmetals over results for direct aspiration into an emission source and show excellent linearity over three orders of magnitude.

Scientifically Operated CCD-Based Spectroscopic System for High-Precision Spectrometric Determinations of Seawater:

The application of an aberration-corrected imaging spectrograph with the use of fiber-optic inputs and a charge-coupled device detector to produce a sensitive, flexible, and rugged spectroscopic system capable of employment in remote sensing and field applications is presented. This investigation focuses on the optical system design, detector characteristics, and modes of operation that will result in a field instrument capable of both sensitive fluorescence and high-precision absorbance measurements. Evaluation of the optical system used the spectroscopic determination of seawater pH as the test case. Spectral measurements were made with the use of thymol blue as a pH indicator for absorbance and 7-hydroxy-coumarin as the fluorescence pH indicator. This system displayed excellent precision for both absorbance and fluorescence analyses; RSDs for absorbance and fluorescence of ±0.00065 and ±0.0015 in pH, respectively, were experimentally obtained. These findings, along with the advantages of the area array detector to provide simultaneous multiwavelength, multianalyte spectral analysis in a single, rugged optical system, make a strong case for the application of scientifically operated solid-state detector systems to remote sensing and field instrumentation.

Chapter 4 The Future of Intelligent Spectrometers in Speciation by Atomic Emission Spectrometry

Publisher Summary Future research in the area of atomic emission spectroscopic detection of chromatographic eluates employing collision induced dissociation (CID) technology should benefit from the tremendous flexibility in wavelength selection afforded by a CID/AES system, as well as the sensitivity offered by the CID. The CID is easily capable of following transient signals which require recording on sub-second time intervals, allowing the system to be applicable in all areas of chromatography. Element specific detection employing a plasma emission source offers high sensitivity regardless of the chemical origin of the detected elements and can greatly reduce the restrictions on the mobile phases which may be employed. The single largest drawback toward obtaining the detection limits for some analysis is the poor efficiency of the nebulization systems for the plasma sources. Detection limits are degraded by the inefficiency of typical nebulizers. Current research into alternate nebulizers, such as the ultrasonic nebulizer indicates that increases in detection by a factor of 10 to 20 are possible.

Analysis of microgram amounts of particulate material by simultaneous multiwavelength AES

A unique simultaneous emission spectrograph is utilized to perform qualitative and quantitative analysis on trace quantities of solid particulates. The atomic emission spectroscopic system consists of a direct current plasma source and an echelle spectrograph with a charge injection device detector, enabling the system to simultaneously measure the wavelength range from 220 nm to 520 nm with 0.02 nm resolution at 300 nm. Monitoring all wavelengths simultaneously allows the qualitative and quantitative determination of most major and minor constituent in a trace quantity of sample with little prior knowledge about the sample. The ability to perform qualitative and quantitative analysis on particulates is demonstrated by evaluating NBS certified coal fly ash, as well as a sample taken from the respirator air filter at an acute care unit in a hospital.