FL24 Tracer Fluorometer

Overview

The FL24 Tracer Fluorometer is a field-deployable, submersible optical sensor system engineered for quantitative detection and time-series monitoring of fluorescent tracers in hydrogeological investigations. Designed and manufactured in Switzerland, the instrument operates on the principle of dual-wavelength excitation and synchronous multi-channel fluorescence detection—enabling selective quantification of sodium fluorescein and other common hydrological tracers (e.g., rhodamine WT, eosin Y) while simultaneously compensating for turbidity-induced signal attenuation. Its robust stainless-steel probe (EN 1.4404) supports immersion up to 70 m depth in boreholes, wells, springs, and surface water bodies with minimum aperture ≥5 cm. The integrated 24-bit analog-to-digital conversion, high-stability LED excitation sources, and thermally compensated photodiode array ensure measurement reproducibility across wide ambient temperature gradients (–10 to +40 °C operational range). Unlike benchtop fluorometers, the FL24 is purpose-built for unattended, long-term tracer breakthrough curve acquisition under variable hydraulic conditions—making it a critical tool for groundwater residence time estimation, inter-aquifer connectivity mapping, and contaminant transport modeling.

Key Features

• Four independent excitation–detection optical channels enabling concurrent measurement of turbidity and up to three distinct fluorescent tracers
• Submersible probe rated for 70 m static water pressure; stainless-steel housing compliant with ISO 9223 C5-M corrosion class
• High-sensitivity fluorescence detection: LOD of 2 × 10⁻¹¹ g/mL for sodium fluorescein (equivalent to ~50 pM), validated per ASTM D5847 guidelines for tracer assay validation
• Turbidity compensation algorithm embedded in firmware—corrects fluorescence quenching effects across 0.2–1000 NTU range using dual-wavelength backscatter geometry
• Integrated high-precision NIST-traceable Pt1000 temperature sensor (±0.01 °C accuracy) co-located with optical path for thermal drift correction
• Configurable sampling intervals (2 s to 20 min, nine discrete settings) supporting both rapid pulse-response studies and multi-month baseline monitoring
• Detachable, waterproof data logger with 2 GB SD card storage—capable of logging 240,000 timestamped records (4 parameters × 60,000 entries)

Sample Compatibility & Compliance

The FL24 is optimized for aqueous environmental matrices including groundwater, spring discharge, river water, and treated effluent. It demonstrates linear response (R² > 0.999) for sodium fluorescein across 1 × 10⁻¹⁰ to 1 × 10⁻⁶ g/mL and maintains calibration stability over 30-day deployments without recalibration. The system complies with ISO 7027 for turbidity measurement methodology and adheres to EPA Method 418.1 principles for fluorescent tracer quantification. All firmware and data handling protocols support audit-ready operation: timestamping follows ISO 8601, metadata embedding conforms to ISO 19115-2, and raw binary logs include CRC-32 checksums. The data logger meets IEC 60529 IP68 requirements and is compatible with GLP-compliant field workflows—including electronic signature-capable configuration files and tamper-evident storage.

Software & Data Management

Data retrieval is performed via RS232 or USB interface using the proprietary GeoTracer Logger Utility (Windows/macOS/Linux), which imports binary logs into CSV or HDF5 format with full metadata preservation. The software enables batch calibration curve generation (quadratic or cubic fit), automatic turbidity-corrected fluorescence concentration calculation, and export of time-series plots aligned to UTC timestamps. Raw sensor outputs (voltage counts per channel, temperature, battery voltage, and internal diagnostics) are retained in native format for traceability. Audit trails—including user login history, parameter change logs, and firmware version stamps—are stored internally and exportable as XML. The system supports 21 CFR Part 11–compliant deployment when paired with validated laboratory information management systems (LIMS).

Applications

• Groundwater flow path delineation and inter-aquifer leakage assessment in karst and fractured-rock aquifers
• Residence time distribution (RTD) analysis for managed aquifer recharge (MAR) facilities
• Validation of numerical groundwater models (e.g., MODFLOW–MT3DMS) using observed tracer breakthrough curves
• Sanitary sewer infiltration/inflow (I/I) studies via fluorescent dye tracing in combined sewer overflows
• Wetland hydrology research—quantifying surface–groundwater exchange fluxes in riparian zones
• Regulatory compliance monitoring for tracer-based wellhead protection zone (WHPZ) verification per US EPA Guidance Manual (EPA/600/R-12/603)

FAQ

What is the maximum cable length supported for reliable signal transmission?
The standard armored cable is supplied in 30 m increments, but custom lengths up to 100 m are available with impedance-matched drivers and noise-suppressed shielding—maintaining SNR > 72 dB at full scale.
Can the FL24 be deployed in saline or brackish water?
Yes—the stainless-steel probe and epoxy-sealed optical windows meet ISO 12944-6 C5-M specifications for marine environments; however, calibration must be performed in matrix-matched standards due to ionic strength effects on quantum yield.
Is remote telemetry integration possible?
The RS232 output can be interfaced with third-party cellular or LoRaWAN telemetry modules; configuration files and firmware updates require local USB connection for security and integrity verification.
How often does the instrument require factory recalibration?
Annual recalibration is recommended for regulatory applications; field verification using certified reference standards (NIST SRM 2943 for fluorescein) is advised before each major campaign.
Does the system support real-time data streaming during deployment?
No—real-time streaming is intentionally omitted to maximize battery life and data integrity; all measurements are stored locally on the SD card with microsecond-level timestamp precision.