Mark E. Baker

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.

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.

Fluorescence imaging of latent fingerprints with a cooled charge-coupled-device detector

Images of fluorescently tagged latent fingerprints were obtained using a low power source and a scientifically operated charge-coupled device (CCD) detector. The luminescence of the fingerprints is chemically enhanced with a fluorescent tag, orthophthalaldehyde. The orthophthalaldehyde undergoes a Schiff base reaction with phenyl ring containing amino acids to produce fluorescence emission at approximately equals 446 nm under UV illumination. An inexpensive, portable, low power UV source was constructed utilizing two 4-watt UV fluorescent lamps and appropriate filters. In the past, the use of filtered lamp sources resulted in an appreciable loss in sensitivity compared to laser sources. Preliminary investigations into the use of a low power tungsten filament lamp source for the excitation of NBD chloride tagged fingerprint on paper were also conducted. Sensitive detection by way of a CCD eliminates the need for the use of expensive, high power laser sources in field instruments and provides a wide range of additional advantages over photographic film.