Performance Verification Statement for the HACH FP 360 sc UV Fluorometer.

Abstract

Instrument performance verification is necessary so that effective existing technologies can be recognized, and so that promising new technologies can 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 Hach FP 360 sc UV fluorometers. 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 FP 360 sc 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 and the data logger was configured to provide output with units of ppb Oil concentration. 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 FP 360 sc exhibited concentration dependent linear responses to several of the challenge compounds with response sensitivity ranked as carbazole >> quinine sulfate > #2 Diesel Fuel > naphthalene disulfonic acid and was insensitive to basic blue. Trials in the COOGER wave test tank at the Bedford Institute of Oceanography revealed linear responses up to 1 ppm total added crude oil with a dynamic range similar to the laboratory based #2 Diesel fuel challenge. Instrument response did vary with crude oil type and dispersion state. 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 at or below the limit of detection for total petroleum hydrocarbons (≤ 25 ppb), yet for Baltimore Harbor the FP 360 sc output was above the baseline response in deionized water and somewhat consistent 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, however 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. One hundred percent of the data was recovered from the instrument and no outlier values were observed for any of the laboratory tests, field deployment tests, or tank exposure tests. In general, results indicate that for all types of test application 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.