Submersible Probe Research Articles

Differential bleaching of quartz and feldspar luminescence signals under high-turbidity conditions

Abstract. Sediment burial dating using optically stimulated luminescence (OSL) is a well-established tool in geochronology. An important but often inapplicable requirement for its successful use is that the OSL signal is sufficiently reset prior to deposition. However, subaqueous bleaching conditions during fluvial transport are vastly understudied; for example the effect of turbidity and sediment mixing on luminescence bleaching rates is only poorly established. The possibility that slow bleaching rates may dominate under certain transport conditions led to the concept that OSL could be used to derive sediment transport histories. The feasibility of this concept is still to be demonstrated, and experimental set-ups are still to be tested. Our contribution to this scientific challenge involves subaquatic bleaching experiments, in which we suspend saturated coastal sand of Miocene age in a circular flume and illuminate it for discrete time intervals with natural light. We record the in situ energy flux density received by the suspended grains in the UV-NIR frequency range by using a broadband spectrometer with a submersible probe. Our analysis includes pre-profiling of each sample following a polymineral multiple signal (PMS) protocol. Using the PMS, the quartz-dominated, blue-stimulated luminescence signal at 125 ∘C (BSL-125) decays slower than the K-feldspar-dominated, infrared-stimulated luminescence signal at 25 ∘C (IR-25) even under subaerial conditions. The BSL-125 from purified quartz shows the opposite behaviour, which renders the PMS unreliable in our case. We find a negative correlation between suspended-sediment concentration and bleaching rate for all the measured signals. For outdoor bleaching experiments we propose to relate the measured luminescence dose to the cumulative received irradiance rather than to the bleaching time. Increases in the sediment concentration lead to a stronger attenuation of the UV–blue compared to the red–NIR wavelength. This attenuation thereby follows an exponential decay that is controlled by the sediment concentration and a wavelength-dependent decay constant, λ. As such λ could potentially be used in numerical models of luminescence signal resetting in turbid suspensions.

On-field high-resolution quantification of the cobalt fraction available for bio-uptake in natural waters using antifouling gel-integrated microelectrode arrays

We report the optimization, characterization, and validation of Adsorptive Square Wave Cathodic Stripping Voltammetry on antifouling gel-integrated microelectrode arrays for autonomous, direct monitoring of cobalt(II) metal species. Detection is accomplished by complexation with an added nioxime ligand. The limit of detection established for a 90 s accumulation time was 0.29 ± 0.01 nM in freshwater and 0.27 ± 0.06 nM in seawater. The microelectrode array was integrated in a submersible probe to automatically dose the complexing agent nioxime and realize an integrated sensing system. For the first time ever, the potentially bioavailable Co(II) fraction was determined in La Leyre River-Arcachon Bay continuum, enabling to evaluate the potential ecotoxicological impact of freshwater-carried Co(II) in the Arcachon Bay. The measured potentially bioavailable Co(II) concentrations were hazardous for aquatic biota along the continuum. The electrochemical Co(II) data were compared to ICP-MS data in various fractions to determine spatial Co(II) speciation.

On-Chip Antifouling Gel-Integrated Microelectrode Arrays for In Situ High-Resolution Quantification of the Nickel Fraction Available for Bio-Uptake in Natural Waters.

We aimed to monitor in situ nickel (Ni(II)) concentrations in aquatic systems in the nanomolar range. To achieve this, we investigated whether an analytical protocol for the direct quantification of cobalt (Co(II)) using adsorptive cathodic sweep voltammetry (Ad-CSV) on antifouling gel-integrated microelectrode arrays (GIME) we recently developed is also suitable for direct Ni(II) quantification. The proposed protocol consists of the reduction of the complex formed between Ni(II) (or Ni(II) and Co(II)) and nioxime adsorbed on the surface of the GIME-sensing element. The GIME enables to (i) avoid fouling, (ii) control the metal complex mass transport and, when interrogated by Ad-CSV, (iii) selectively determine the dynamic (kinetically labile Ni-nioxime) fraction that is potentially bioavailable. The nioxime concentration and pH were optimized. A temperature correction factor was determined. The limit of detection established for 90 s of accumulation time was 0.43 ± 0.06 in freshwater and 0.34 ± 0.02 nM in seawater. The sensor was integrated in a submersible probe in which the nioxime-containing buffer and the sample were mixed automatically. In situ field measurements at high resolution were successfully achieved in Lake Geneva during a diurnal cycle. The determination of the kinetically labile Ni-nioxime fraction allows one to estimate the potential ecotoxicological impact of Ni(II) in Lake Geneva. Additional Ni fractions were measured by ICP-MS and coupled to the in situ Ad-CSV data to determine the temporal Ni(II) speciation.

A submersible probe with in-line calibration and a symmetrical reference element for continuous direct nitrate concentration measurements.

Current methods to monitor nitrate levels in freshwater systems are outdated because they require expensive equipment and manpower. Punctual sampling on the field or at a fixed measuring station is still the accepted monitoring procedure and fails to provide real-time estimation of nitrate levels. Continuous information is of crucial importance to evaluate the health of natural aquatic systems, which can strongly suffer from a nitrogen imbalance. We present here a nitrate-selective potentiometric probe to measure the analyte continuously without requiring maintenance or high-power consumption. Owing to a simple design where the sensors are located directly in contact with the sample, the need for constant pump usage is eliminated, requiring just 0.7 mW power per day instead of 184 mW per day and per pump. It is estimated that with this power consumption, the setup can easily run for more than 97 h on four simple Li-ion batteries. A simple in-line one-point calibration step was implemented to allow for drift correction. At the same time, a symmetrical design was used involving a second nitrate probe as a reference electrode placed in the calibrant compartment. This, combined with an in situ calibration step, allows one to quantify nitrate ion concentrations directly, instead of yielding activities. The dependence on ion activity was removed by using the analysed sample spiked with nitrate as the calibrant. This results in essentially the same activity coefficients and additionally reduces junction potentials to a fraction of a millivolt. In addition, a symmetrical reference element served to compensate for fluctuations caused by environmental factors (temperature, convection, etc.) to achieve improved stability and signal reproducibility compared to a traditional Ag/AgCl based reference electrode. The final prototype was deployed in the Arve River in Geneva for 75 h without requiring any intervention. The nitrate levels measured using the symmetrical reference element over this period were estimated at 44.0 ± 3.5 M and agreed well with the values obtained with ion chromatography (38.2 ± 2.1 μM) used as the reference method. Thanks to a modular sensing head the potentiometric sensors can be easily exchanged, making it possible to quantify other types of analytes and leading the way to a new monitoring strategy.

COMPARATIVE CHARACTERISTICS OF SOME PLANTS FAMILY HEATHER EXTRACTS AND THE EFFECTIVENESS OF METHODS FOR THEIR PRODUCTION

The paper presents new data related to the comparative study of water-alcohol leaf extracts of the heather plants family (highbush blueberry, lingonberry, heather). Leaf extracts were obtained by three methods, two of which were using ultrasonic emitters (an ultrasound bath and a submersible ultrasonic probe), the third method, thermal (traditional), was chosen as a comparison. The extracts are characterized by parameters as the total content of extractive substances, the sum of phenolic compounds, flavonoids, the dispersed phase size particles distribution determined by the method of dynamic light scattering, and a quantitative assessment of the integral antioxidant activity is given. It has been established that ultrasonic probing has a highest activity in extracting phenolic compounds and flavonoids from lingonberry leaves and heather grass, and at the same time the level of their antioxidant activity is inferior to the extracts obtained by the traditional method at which the plant raw materials is boiled with the extractant. The traditional thermal method is characterized by the highest values of the sum of extractives for all types of raw materials and average values for the sum of phenolic compounds and flavonoids. There are observed a significant increase in the content of particles with the size <1000 nm for "ultrasonic" lingonberry leaf extracts is compared to the traditional method, however this pattern is not fulfilled for other types of raw materials. All heather herb extracts have a high polydispersity and the greatest tendency to sediment formation during the storage.

Advanced multichannel submersible probe for autonomous high-resolution in situ monitoring of the cycling of the potentially bioavailable fraction of a range of trace metals

We report here on the development and application of a submersible, compact, low power consumption, integrated multichannel trace metal sensing probe (TracMetal). This probe is unique in that it allows high-resolution, simultaneous in-situ measurements of the potentially bioavailable (so-called dynamic) fraction of Hg(II), As(III), Cd(II), Pb(II), Cu(II), Zn(II). The TracMetal incorporates nanostructured Au-plated and Hg-plated gel-integrated microelectrode arrays. In addition to be selective to the fraction of metal potentially bioavailable, they offer protection against fouling and ill-controlled convective interferences. Sensitivities in the low pM for Hg(II) and sub-nM for the other target trace metals is achieved with precision ≤ 12%. The TracMetal is capable of autonomous operation during deployment, with routines for repetitive measurements (1-2 h−1), data storage and management, data computer visualization, and wireless data transfer. The system was successfully applied in the Arcachon Bay, to study the temporal variation of the dynamic fraction of the trace metals targeted. The in situ autonomous TracMetal measurements were combined with in situ measurements of the master bio-physicochemical parameters and sample collection for complementary measurements of the dissolved metal concentrations, organic matter concentrations and proxy for biological activities. The integration of all data revealed that various biotic and abiotic processes control the temporal variation of the dynamic fractions of the target metals (Medyn). The difference in the percentage of the dynamic forms of the metals studied and the short-term processes influencing their variation highlight the TracMetal potentiality as metal bioavailability-assessment sentinel to achieve comprehensive environmental monitoring of dynamic aquatic systems.

Diel vertical movements determine spatial interactions between cod, pelagic fish and krill on an Arctic shelf bank

Predator-prey spatial interactions are essential to understand ecosystem processes like predation rates and trophic interaction strength. In marine systems, such spatial interactions are highly dynamic and difficult to observe, as predators, prey and resources are mobile and responsive to each other, and also since shifting vertical light gradients strongly affect the space use of visual predators and their prey. We visited a bank area in the northern Barents Sea with cold bottom waters (~1°C), and combined conventional trawl and acoustic sampling with broadband hydroacoustics to obtain long-range, fine-scale observations of interactions between cod, their planktivore prey (capelin and polar cod) and krill. We caught cod in demersal trawl hauls but could not detect them with the vessel acoustics. However, broadband acoustics mounted on a submersible probe allowed us to track individual cod, revealing that they remained mostly within 10 m of the bottom throughout the diel cycle. In the morning, cod lifted slightly from the seabed indicating feeding activity, which corresponded with more fresh prey in cod stomachs in the morning. During daylight, krill pushed towards the bottom, sharing habitat with cod, while the planktivores aggregated in pelagic schools at the cost of lost feeding opportunities, overlapping with their krill prey only during twilight hours. The diel light cycle was an important driver of the spatial movements and aggregations, and krill appear to hide from capelin among the cod near bottom, while cod take advantage of descending pelagic fish after dawn to feed with a minimum of effort.

Submersible probe type microbial electrochemical sensor for volatile fatty acids monitoring in the anaerobic digestion process

Abstract: Microbial electrochemical sensor with a more simplified architecture is required in the anaerobic digestion (AD) process for in situ on-line volatile fatty acids (VFAs) monitoring. In this study, a submersible probe type microbial electrochemical sensor was constructed, and the current signal showed a linear relationship with the VFAs concentration (0–200 mM) at the specific reaction time from 10 to 120 min (R2 > 0.96), with the slope increased from 0.87 × 10−3 to 1.70 × 10−3 mA mM −1. The sensor showed a good selectivity when VFAs were co-existed with 2 g/L of additional organic matters (cellulose, yeast extract, peptone, and potassium oleate), and 0.1% formaldehyde. Particular attention should be paid when additional electroactive matter such as Cu(II) as well as high concentration of TAN (above 200 mg/L) was co-existed with VFAs in the digestate. When amending the artificial AD digestate with extra 50 mM NaCl to increase the ionic strength, the current generation increased from 0.064 ± 0.002 to 0.185 ± 0.001 mA (50 mM VFAs at 60 min). The sensor was successfully applied for actual digestate samples detection and the results did not show significance differences with the total VFAs measured by GC. The submersible probe type sensor depicted a good repeatability during one-month operation. This study provides a direct approach based on microbial electrochemical technology for VFAs monitoring in the AD process.

In Situ Detection of Macronutrients and Chloride in Seawater by Submersible Electrochemical Sensors

A new submersible probe for the in situ detection of nitrate, nitrite, and chloride in seawater is presented. Inline coupling of a desalination unit, an acidification unit, and a sensing flow cell containing all-solid-state membrane electrodes allows for the potentiometric detection of nitrate and nitrite after removal of the key interfering ions in seawater, chloride and hydroxide. Thus, the electrodes exhibited attractive analytical performances for the potentiometric detection of nitrate and nitrite in desalinated and acidified seawater: fast response time ( t95 < 12 s), excellent stability (long-term drifts of <0.5 mV h-1), good reproducibility (calibration parameter deviation of <3%), and satisfactory accuracy (uncertainties <8%Diff compared to reference technique). The desalination cell, which can be repetitively used for about 30 times, may additionally be used as an exhaustive, and therefore calibration-free, electrochemical sensor for chloride and indirect salinity detection. The detection of these two parameters together with nitrate and nitrite may be useful for the correlation of relative changes in macronutrient levels with salinity cycles, which is of special interest in recessed coastal water bodies. The system is capable of autonomous operation during deployment, with routines for repetitive measurements (every 2 h), data storage and management, and computer visualization of the data in real time. In situ temporal profiles observed in the Arcachon Bay (France) showed valuable environmental information concerning tide-dependent cycles of nitrate and chloride levels in the lagoon, which are here observed for the first time using direct in situ measurements. The submersible probe based on membrane electrodes presented herein may facilitate the study of biogeochemical processes occurring in marine ecosystems by the direct monitoring of nitrate and nitrite levels, which are key chemical targets in coastal waters.

In Situ Detection of Species Relevant to the Carbon Cycle in Seawater with Submersible Potentiometric Probes

We report on the development of a submersible probe for the simultaneous potentiometric detection of carbonate, calcium, and pH in seawater. All-solid-state electrodes incorporating nanomaterials provide an adequate response time (<10 s), stability (drifts of <0.9 mV h–1), reproducibility (calibration parameter deviation of <0.7%), and accuracy (deviation of <8% compared to reference techniques) for real-time monitoring of seawater using a flow system. The functioning of the deployable prototype was checked in an outdoor mesocosm and via long-term monitoring in Genoa Harbor. The electrodes worked properly for 3 weeks, and the system demonstrated the capability to autonomously operate with routines for repetitive measurements, data storage, and management. In situ profiles observed in Genoa Harbor and Arcachon Bay were validated using on site and ex situ techniques. The validation of in situ-detected carbonate is a challenge because both re-equilibration of the sample with atmospheric CO2 and the use of ap...

Analysis of dissolved metal fractions in coastal waters: An inter-comparison of five voltammetric in situ profiling (VIP) systems

This paper presents the results of an inter-comparison exercise undertaken to test the reliability and performance of a voltammetric in situ profiling system (VIP system) and carried out by partners based in Italy, Sweden, Switzerland and the UK. The VIP system was designed to allow in situ simultaneous monitoring of the dynamic fractions (i.e. the maximum potentially bioavailable fractions) of Cu(II), Pb(II) and Cd(II) in natural waters at a frequency of 2–3 analyses h − 1 . The four participating groups used the VIP systems under laboratory conditions to determine dissolved concentrations of Cu, Pb and Cd in river, estuarine and coastal water reference materials (SLRS-3/4, SLEW-2/3 and CASS3/4, respectively). The accuracy of the VIP method was comparable to that of established methodologies, including inductively coupled plasma mass spectrometry and voltammetric methods using mercury-electrodes. The VIP systems were also applied to determine the dynamic fractions of the target analytes in freshly collected samples ex situ, as well as in situ in contrasting European marine waters. There was good agreement between the concentrations of the dynamic metal fractions determined in laboratory analyses, and observed during the simultaneous deployment of up to five VIP instruments for periods of several hours in coastal waters. The simultaneous in situ deployment of two VIP instruments in an estuary showed a consistent analytical performance over several days of continuous operation. The results of this inter-comparison exercise show that the VIP system is a reliable submersible probe for accurate, sensitive and high resolution in situ monitoring of dissolved metal fractions in the picomolar (Cd, Pb) and nanomolar (Cu) concentration ranges.

In situ determination of organic compounds in liquid samples using a combined UV-Vis/fluorescence submersible sensor

In order to improve the in situ evaluation and quantitative analysis of complex contaminations of liquid media such as ground-, surface, and wastewaters, an integrated submersible sensor probe has been developed. It is especially characterized by the option of simultaneously measuring ultraviolet/visible (UV/Vis) and fluorescence spectra. Owing to the compact construction with light sources, flow cell, detection system, and data acquisition/processing unit in the waterproof case, the data transfer to the surface can be realized electrically, and the operation depth is practically not limited. The variability in the measuring techniques allows a wide variety of chemical compounds to be analysed within a broad concentration range. The performance of the new submersible sensor probe was tested ex situ in laboratory scale, and the performance was comparable with that of stationary measuring instruments. As an example for an in situ application, the sensor probe was successfully used to monitor the migration of chemical substances during a tracer experiment in groundwater. The concentration of the tracer compound uranin (sodium fluorescein) was measured in the range of 5–500 µg L−1 using fluorescence spectroscopy, while at the same time the contents of toluene were continuously detected in the same groundwater wells using the UV/Vis sensor channel.

A phycocyanin probe as a tool for monitoring cyanobacteria in freshwater bodies

In many countries, the presence of cyanobacteria in freshwater bodies used for both drinking water and recreational purposes is under increasing public health attention. Water managers are considering how to implement monitoring that leads to a minimization of the risks incurred by the users of potentially contaminated sites. To address this question, this study involved assessing the performance of a submersible probe for measuring phycocyanin-specific fluorescence as a function of cyanobacterial biomass, with the aim of applying it as a tool for surveillance management. Its advantages and limits compared to more traditional analyses are discussed. The monitoring of cyanobacteria in the water bodies of western France was carried out using a minifluorimeter specific to the fluorescence of phycocyanin, a pigment specific to cyanobacteria. The results are compared with the analyses recommended by the World Health Organisation (chlorophyll a and cell counting). This study based on nearly 800 samples shows a significant correlation between the phycocyanin content and the cyanobacterial biomass, expressed as the number of cells per mL (R2 = 0.73). This submersible probe is simple and rapid to use, making it possible to take into account horizontal and vertical heterogeneities in the proliferation growth. In this way, we are able to detect at an early stage the conditions that could potentially lead to a risk, in order to start sampling. Due to its sensitivity, this tool proves suitable for monitoring aimed at reducing the risks incurred by the users of contaminated sites and launching preventative actions. The use of the phycocyanin probe provides an effective tool to complement traditional analyses of cyanobacterial presence. It is suggested that a surveillance protocol based on phycocyanin concentration can significantly improved the accuracy of the extent of cyanobacterial bloom development in the light of spatial and temporal variabilities associated with these occurrences.

Freshwater phytoplankton quantification by chlorophyll a: a comparative study of in vitro, in vivo and in situ methods

Standard ISO method for chlorophyll a quantification (extraction into ethanol, spectrophotometrical quantification at 665 and 750 nm), spectrofluorometry (reader for 96 wells, excitation 410 nm, emission 670 nm), and a submersible fluorescence probe for in situ phytoplankton quantification (excitation 410, 525, 570, 590, and 610 nm, emission 685 nm) were compared in different freshwater environments—reservoirs and rivers. The ISO method is accepted as a standard method but requires sample handling and transport to the laboratory. Spectrofluorometry is a sensitive method, even for natural phytoplankton populations. Nevertheless, it cannot be recommended for the quantification of cyanobacterial water blooms because colonial and filamentous species such as Microcystis, Anabaena, or Aphanizomenon display unacceptable variability (18–33%). The submersible probe featured high correlation with a standard ISO method ( r=0.97, P<0.05). This probe can provide the selective measurement of technologically important phytoplankton groups like cyanobacteria, diatoms, green algae, and cryptophytes in lake vertical profiles of up to 100 m. The limitation of this instrument is the possible reabsorption of the light signal, e.g. in the presence of humic substances, or dense algal blooms. The use of submersible probes for in situ phytoplankton quantification can be recommended as a sensitive tool for water management, especially in the case of drinking water resources.

Submersible Online Oxygen Removal System Coupled to an in Situ Voltammetric Probe for Trace Element Monitoring in Freshwater

A new online oxygen removal system specifically built to allow in situ deoxygenation of freshwater before in situ voltammetric detection of trace elements using a submersible probe is described. It is based on the permeation of oxygen through a silicone tubing surrounded by an enzymatic cross-linked O2 scavenging gel. The main advantages of the enzyme cross-linked gel compared to the chemical O2 reducing solutions proposed in the literature for laboratory online deoxygenation coupled to other devices are as follows: (i) ease of preparation and storage under normal room condition, (ii) good long-term stability (maximum time tested 1 month), (iii) no formation of insoluble oxidized chemical compounds adsorbed on the external silicone tubing wall that may interfere with the O2 diffusion, and (iv) easy in situ applications thanks to the convenience of chemical gel for transport and pressure compensation. Detailed description of the construction of the system as well as the systematic laboratory tests performe...

Submersible voltammetric probes for in situ real-time trace element measurements in surface water, groundwater and sediment-water interface

A summary of the state of the art in the development of two submersible voltammetric probes performed by us to allow continuous, real-time monitoring of trace elements (Cu(II), Pb(II), Cd(II), Zn(II) and Mn(II), Fe(II)) in natural aquatic ecosystems is given. The first one, called the voltammetric in situ (VIP) profiling system, allowed in situ measurements in surface water and groundwater down to 500 m. Its construction required the development of: (i) a gel-integrated, either single or interconnected, array microsensor, (ii) a submersible probe and (iii) hardware, firmware and software for control of the whole system: i.e. data transmission and acquisition, data processing and maintenance operations. The second system, called the sediment-water interface voltammetric in situ profiling (SIVIP) system, has been developed to allow real-time, high spatial resolution trace elements concentration profile measurements at the sediment-water interface. Its construction required the development of: (i) a gel-integrated microsensor array with 64 individually addressable lines, (ii) a voltammetric probe based on powerful double multiplexing system and single potentiostat allowing simultaneous measurements over the 64 sensor lines, and (iii) hardware, firmware and software for control of the whole system. A general description of both systems as well as examples of laboratory characterization and/or field applications are reported.

Flow probe for in situ electrochemical monitoring of trace chromium

A submersible electrochemical probe for in situ monitoring of trace chromium is described. The new flow probe relies on the coupling of an ultrasensitive adsorptive–catalytic stripping voltammetric procedure with a submersible operation. Such in situ monitoring involves a continuous delivery of an internal (ligand–catalyst, DTPA–NO3–) reagent solution, a microdialysis collection of the target chromium ion, transport of the Cr–DTPA complex and nitrate-ion catalyst to the working-electrode compartment and adsorptive–catalytic stripping detection of the complex. The optimization of various parameters resulted in a detection limit of 0.10 µg l–1 (with 10 min accumulation), good precision and stability (RSD 6% for n=80 at 25 µg l–1 chromium) and a rapid response to sudden changes in the chromium level. A stable response was obtained for both Cr(VI) and Cr(III) species. The attractive performance of the submersible probe holds great promise for environmental and industrial monitoring.

Electrochemical flow sensor for in-situ monitoring of total metal concentrations

An electrochemically-based submersible probe for in-situ monitoring of the total content of dissolved metal species is described. The flow-through sensor relies on the coupling of an internal on-line acidification of the collected samples with potentiometric stripping detection of the metals released from their complexes. The optimisation and characterisation of the new remote sensor have been carried out with trace measurements of cadmium and lead in the presence of EDTA and NTA. Elevated levels of these ligands (e.g. 0.05 and 1.0 mM EDTA and NTA, respectively) had no effect upon the cadmium and lead peaks, as compared to the complete disappearance of the response without the internal acid delivery. Such real-time measurements of the total form of dissolved heavy metals hold great promise for environmental and industrial monitoring. Other in-situ speciation sensing schemes are anticipated based on the versatility of the renewable-reagent flow probe.

Electrocatalytic modified electrode for remote monitoring of hydrazines

A remote electrochemical sensor for field monitoring of hydrazine compounds is described. The new submersible probe relies on the coupling of an effective electrocatalytic modified electrode to a 50 ft long shielded cable. The catalytic surface, based on an electorpolymerized film of 3.4-dihydroxybenzaldehyde, offers low-potential detection of hydrazine compounds. Such catalytic activity results in high sensitivity and selectivity, and hence offers convenient measurements of micromolar hydrazine concentrations in untreated groundwater, river water or lake water samples. Coexisting sample constituents do not contrubute to the response. Operational conditions have been optimized to meet the spacific requirements of remote operation. The concept seems suited for the remote monitoring of other contaminants via the judicious choice of the surface modifier.

Remote electrochemical biosensor for field monitoring of phenolic compounds

A submersible probe for monitoring of phenolic compounds at large sample/instrument distances is described. A specially designed device, comprising a specially designed tyrosinase enzyme electrode coupled to a 50-ft long shielded cable (via environmentally sealed connectors), is used. Challenges associated with the adaptation of enzyme electrodes to remote sensing are addressed. Variables relevant to field operations are explored and discussed. The combination of biocatalytic recognition and amperometric transduction offers highly selective measurements of micromolar concentrations of phenolic substrates in untreated river and groundwater samples. The concept seems suited for the remote monitoring of other environmentally relevant compounds via a judicious selection of the biorecognition element.