Final Report: Portable Spectrofluorometer with Unique UV Source

EPA Contract Number: 68D98122
Title: Portable Spectrofluorometer with Unique UV Source
Investigators: Goldstein, Jack M.
Small Business: Moduspec Company
EPA Contact:
Phase: I
Project Period: September 1, 1998 through March 1, 1999
Project Amount: $69,982
RFA: Small Business Innovation Research (SBIR) - Phase I (1998) RFA Text |  Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , SBIR - Monitoring , Small Business Innovation Research (SBIR)

Summary/Accomplishments (Outputs/Outcomes):

In its Phase I project, Moduspec has developed a MINIATURIZED PORTABLE SPECTROFLUOROMETER WITH A UNIQUE UV EXCITATION SOURCE. This analyzer is capable of spectrally analyzing fluorescent compounds similar to laboratory units, but in addition possesses the capability of field in-situ analysis of untreated water, treated and recycled water, solid surface materials, and other matter suspected of contamination. In this latter role, it provides a field-screening unit that can lighten the burden of transporting large number of samples to a laboratory facility for analysis. The latter process requires careful identification of the location of the sample, its transportation with associated delays, expensive laboratory analysis of each transported sample, and finally documentation of each sample. If benign conditions can be determined in the field, much time and expense can be avoided, since then only potential hazardous materials would be sent for laboratory analysis.

Fluorescence analysis is widely employed in environmental monitoring. Oil, polyaromatic hydrocarbons (PAHS), microbial populations and other contaminants in water and on solid surfaces have spectral luminescence useful for identification and measurement. Chemicals that contaminate soil and ground water pose serious health hazards. They enter water supplies as agricultural runoff of pesticides and herbicides. Contamination also results from industrial discharge into lakes and rivers, as well as ground water from landfills, storage lagoons, waste piles, etc. Carcinogen linked ground contaminants likely cause birth defects, and must be expeditiously dealt with.

The developed PORTABLE analyzer uses conventional cuvettes for sample analysis, a flow-through cell for continuous liquid analysis, and a fiber-optic (FO) probe accessory for surface measurements. Innovative features of the analyzer include a new type of UV excitation light source, which is smaller and more power efficient than those previously used, an excitation monochromator mirror bypass system, photon counting detection, ease of calibration, and small size.

The computerized analyzer has two principle modes of operation. In the MONITOR MODE, fluorescent substances are measured by having their optimum emission and excitation wavelengths set in fixed position and the concentration of a single compound is measured vs. time while being sampled through a flow through cuvette. In the SPECTRAL SEARCH MODE compounds have their emission and excitation spectral characteristics recorded as the appropriate monochromators are used in the scanning mode, resulting in emission and extinction spectral displays that are viewed on an externally connected notebook computer. The resulting spectral displays are stored as Microsoft Excel charts and are imported into a commercial search program called "Spectral ID". There, they can be compared against a stored library of fluorescent compounds and a variety of correlation techniques can be utilized to find a suitable spectral match to aid in their identification.

During the Phase I research effort, Moduspec Company achieved basically all of the work plan objectives cited in its Phase I proposal. These include:

  1. The successful development of a UNIQUE EXCITATION SOURCE compact in size and using very little current.
  2. The design and implementation of very HIGH THROUGHPUT COMPACT MONOCHROMATORS.
  3. The design and implementation of both a PUMPED SAMPLE FLOW THROUGH CELL as well as an accessory FIBER-OPTIC SAMPLING PROBE for water sampling.
  4. Extensive computerization, via an attached Notebook Computer, permitting SEARCH AND IDENTITY OF FLUORESCENT SPECIES by use of a commercial search engine "Spectral ID".
  5. The design and implementation of an excitation grating mirror bypass system permitting the excitation monochromator allow FULL EXCITATION SOURCE RADIATION TO EXCITE FLUORESCENCE. This confers enhanced sensitivity and allows for automated spectral searches.
  6. The development and implementation of a convenient insertable solid CALIBRATION device to standardize both wavelength and sensitivity.
  7. An extremely HIGH SENSITIVITY ELECTRONIC DETECTION SYSTEM using PHOTON COUNTING techniques to enhance the signal-to-noise-ratio (SNR).
  8. The design and construction of a FIBER-OPTIC PROBE ACCESSORY for making surface fluorescence measurements on solid surfaces.

RESULTS OF THE PHASE I PROJECT

Essentially all the goals and milestones outlined in our original work plan have been successfully met. Some efforts such as the completion of the total microprocessor operating system and additional field screening studies are considered appropriate to a continuation into a Phase II project.

Our most significant success is the development of a low power UV light source that will allow fluorescent spectral studies to be made on a portable spectrofluorometer. This will for the first time make it practical to commercially produce portable spectrofluorometers. Our confidence in this is based on our development of a fully operational experimental model that is very portable and can be taken out to perform field screening of hazardous materials.

In addition, we have demonstrated that our developmental unit can perform routine laboratory analysis equivalent to a medium class commercial spectrofluorometer (Aminco SPF 125).

We have incorporated into our developmental unit sophisticated techniques only found in expensive sophisticated and expensive analyzers such as Photon Counting. Mirror Excitation Grating Bypassing, Spectral Searching and Identification. These state-of-the-art techniques could be provided in an analyzer that would sell for less than one third the price of high end units AND BE PORTABLE AS WELL!

Finally we have demonstrated that the completed analyzer is of beneficial use in the analysis of hazardous chemical substances in water and soil and this can be done in-situ in field studies.

COMMERCIAL APPLICATIONS

The research has resulted in a practical portable spectrofluorometer that would be useful as a field-screening device for hazardous materials in water and soil. The materials that can be spotted include PAHs, PCBs, Petroleum Products, Herbicides and other materials that exhibit fluorescence when excited by UV light. In many cases potential identity of the contaminant could be made by comparison against a spectral search program that would be accessible by means of a connected Notebook Computer. The performance of the unit approached that of a commercial laboratory spectrofluorometer. The sensitivity was found to be about a factor of ten less than the lab units. However, this is not considered to be a limitation on its use, since background fluorescence is generally the limitation on the practical sensitivity that is achievable. Liquid samples can be characterized using a flow-through cuvette, and solid samples are intended to be analyzed using a Fiber Optic probe. The latter application of the probe was the only area where total success was not achieved. The probe suffered from back-scattered incident UV light. This aspect is expected to be corrected to a degree by incorporation of optical devices, but is believed to be a significant limitation of the probe which is also an expensive device.

At this time there are no commercial field portable spectrofluorometers being manufactured, although a number of designs have been researched and are described in the literature. We believe this to be due to a lack of a low current, simple UV continuum source. This research project has succeeded in providing one, and we intend to patent its design. Fluorescence is a well-established technique used extensively in environmental analysis. At this time Portable Filter Fluorometers are being used, but they have severe limitations since they operate at fixed wavelengths, lack tunability and cannot perform spectral emission, excitation and synchronous scans which give a complete characterization of a fluorescent species. An ASTM method (4763-88) for water analysis includes ninety compounds that can exist in water and can be analyzed by a spectrofluorometer.

Several companies that now manufacture portable filter fluorometers have expressed interest in the commercialization of the portable spectrofluorometer. There are meetings planed to discuss our project with these companies at the upcoming Pittcon convention in March. This convention is the largest international convention on chemical analytical instrumentation. All of the research done on this Phase I project can be released to the public with the exception of detailed information on the unique UV excitation source, which is proprietary to MODUSPEC Co.

Supplemental Keywords:

Scientific Discipline, Water, Ecosystem Protection/Environmental Exposure & Risk, Chemistry, Monitoring/Modeling, Analytical Chemistry, Engineering, Engineering, Chemistry, & Physics, environmental monitoring, monitoring, portable spectrometers, continuous measurement, environmental measurement, field monitoring, fiber optics, optical sensor, analyzer, optical detectors, PAH, environmental contaminants, PAHs, measurement, water contaminants, in situ chemical profiles