Performance Verification Statement for the WETLabs ECO FLCD(RT)D-1929 Fluorometer.

Abstract

Instrument performance verification is necessary so that effective existing technologies can be recognized, and so that promising new technologies become available to support coastal science, resource management, and ocean observing systems. The Alliance for Coastal Technologies (ACT) has therefore completed an evaluation of commercially available in situ hydrocarbon sensors. This verification included test applications for: (1) controlled laboratory tanks with additions of various organic, fluorescent compounds, (2) experimental wave tank with additions of two sources of crude oils with and without dispersants, (3) a moored deployment in Baltimore Harbor, and (4) hydrocast surveys in the Gulf of Mexico at a site near a submerged leaking oil barge. In this Verification Statement, we present the performance results of the WETLabs ECO FLCDRTD (CDOM) fluorometer. Quality assurance (QA) oversight of the verification was provided by an ACT QA specialist, who conducted technical systems audits and a data quality audit of the test data. Response specificity of the ECO FLCDRTD fluorometer to a range of organic compounds was evaluated in a series of lab tests. The instrument output was based on a linear response photodetector behind the emission optical filters with response output provided in raw counts. Instrument response with respect to challenge compound concentration varied with respect to the inherent fluorescence properties of the challenge compound as well as sensor optics. As expected, the FLCDRTD exhibited concentration dependent linear responses to several of the challenge compounds with response sensitivity ranked as quinine sulfate >> carbazole > naphthalene disulfonic acid and was insensitive to basic blue. Instrument failure, after shipping between sites, precluded assessment of sensitivity to #2 Diesel Fuel challenges. Trials in the COOGER wave test tank at the Bedford Institute of Oceanography revealed linear responses from 0.3 to 12 ppm total added crude oil in the presence of chemical dispersant. For trials where no chemical dispersant was added, the instrument response decreased slightly as oil concentrations were increased above 1.5 ppm. A greater presence of oil was noted on all downward oriented surfaces of the instruments and deployment frame after non chemically-dispersed trials, so likely this response was due to oil accumulation on the optical surfaces. Daily initial baseline signals changed with ambient water quality conditions. Instrument responses to various challenge compounds converged when compared to standardized EEMs fluorescence intensity estimated to correspond to the instruments emission optics. Field deployments in Baltimore Harbor and northern Gulf of Mexico were equivocal as all field reference samples were close to or below the reporting (50 ppb) or limit of detection for total petroleum hydrocarbons (25 ppb) for the reference analytical method. However, for Baltimore Harbor the FLCDRTD output was substantially higher than the baseline response in deionized water (50-100 counts) and was correlated with environmental background fluorescence as determined by EEMs analysis. There was no clear instrument response to EEMs intensities in the Gulf of Mexico profiling test. It is unclear if the response may have been impacted by the use of a second party data logger for this profiling application. During this evaluation, no problems were encountered with the provided software, set-up functions, or data extraction at any of the test sites. Operator error impacted one hydrocast profile and excessive instrument noise was encountered in the final laboratory trial of #2 Diesel Fuel which was conducted after all other field deployments. In general, results indicate that for all types of test applications including lab, moored and hydrocast surveys, the ambient fluorescence properties of the challenge solution need to be accounted for to make quantitative hydrocarbon estimates from these sensors. We encourage readers to review the entire document for a comprehensive understanding of instrument performance.