Page 32 - Performance Verification Statement for the Chelsea UV Aquatracka Fluorometer

Ref. No. [UMCES]CBL 2013-014

ACT VS12-01

Vertical profiling results for all six casts are presented in figures 12-14. Each panel

displays the Aquatracka response in mV along with a continuous trace of temperature and

salinity for that cast. In addition, total hydrocarbon, CDOM, Turbidity, and Chlorophyll

concentrations from the discrete reference samples are plotted on the same graph. It should be

noted that despite the presence of a visible sheen of oil on the surface of the water above the

leaking barge, all total hydrocarbon concentrations were reported as below detection for all

reference samples collected (stated method of detection limit ≤ 25 ppb). EEM characterizations

of the reference samples revealed some possible evidence of hydrocarbons in the surface sample

of site 2, cast 5 and mid-depth sample for site 2, cast 3 (Fig. 15), however, even those peaks fell

mostly outside the optical window of the Aquatracka. Only minimum levels of fluorescent

signal was observed throughout the EEM maps of the other samples.

A distinct difference in response was observed between the nearshore and offshore sites.

In Terrebonne Bay, a CDOM and chlorophyll enriched environment, instrument output was near

3100 mV similar to levels observed during the Baltimore Harbor deployment (Fig. 16).

Instrument response was approximately 600 mV lower for all of the offshore profiles (range

2800 - 2900 mV), only 100 mV above instrument baseline. Field instrument response mapped

onto to estimated EEM

QSE

intensity determined from the full set of challenge compounds

including crude oil (Fig. 17), but the narrow range of features detected and associated non-

detects in our analytical reference samples precludes assigning this signal variation to specific

hydrocarbon detections.

SUMMARY of INSTRUMENT RESPONSE ACROSS ALL TEST APPLICATIONS

The Aquatracka UV-CDOM and UV-HC in situ fluorometers exhibited the expected

logarithmic voltage response to challenge analyte concentration for those compounds whose

fluorescence properties best match the optical configuration of the instrument package. Detector

saturation was encountered above 1 ppm of optically matched analytes. The UV-HC

configuration detected a variety of crude and refined oil products to at least 1 ppm TPH. Overall

the instruments’ logarithmic voltage response corresponded to the fluorescence intensity within

the range of their optical windows, regardless of compound type, or dispersal state (Fig 17.)

Care should be taken in specific interpretation of environmental fluorescence signals in

absence of analytical reference samples.

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