Fluorescence, originally developed within the laboratory for determining concentrations of fluorescent compounds of interest, is recognised as a technique that can combine selectivity with extremely high sensitivity. The technique moved from the laboratory into the field, with in-situ fluorometers becoming available in the latter half of the 20th century, providing the benefits of instant readings of targeted fluorophors in the environment. These original in-situ fluorometers, working in the visible range, targeted to detect Chlorophyll, were initially costly and were therefore adopted mainly for scientific research in the sectors of marine biology and environmental sciences for algae studies. These in-situ visible wavelength fluorometers were also made available to detect dye tracers for time and travel studies within the water environment. Later, UV based in-situ fluorometers became available to monitor PAH (Polyaromatic Hydrocarbons) as well as CDOM (Coloured Dissolved Organic Compounds), or Gelbstoff. These original in-situ fluorometers used Xenon flash lamps for excitation, and photomultipliers were required for detection rather than photodiodes which have poor sensitivity in this region which impacted on their price to the market.
More recently the introduction of low cost LEDs to the market enabled manufacturers to offer new in-situ fluorometers that benefited from lower manufacturing costs. This has resulted in the adoption of in-situ fluorescence measurements becoming more widely used, and today, commonly being employed in large smart networked systems monitoring the aquatic environment. The scientific and environmental monitoring sectors, as well as industries involved with water processing have benefited from the use of in-situ fluorescence with the advantages of real time data and reduced requirements for laboratory analysis.
The transition from the laboratory to the field has not been so straight forward, unlike laboratory conditions, when looking to monitor specific fluorophors within natural aquatic environments, the waters under investigation can contain other non-targeted fluorophors that can contribute to the detected signal. For instance, PAH and CDOM have similar fluorescence characteristics, with CDOM ‘bleeding’ into the PAH space, as shown in Figure 1, an Excitation Emission Matrix which is obtained from a benchtop Scanning Fluorometer. Depending on levels of PAH and CDOM, this can, at best reduce the accuracy and sensitivity of the data provided for the targeted fluorophore, at worst render the data to limited use.
Fiigure 1: Fluorescence Excitation Emission Matrix (EEM) from an environmental water sample.
Another concern when monitoring PAH’s and Tryptophan-like fluorescence within the environment is the potential of signal interference from algae present within the sample, which can contribute UV fluorescence from UV excitation in these regions.
The fluorescent technique, being an optical system, can also be limited in its application where turbidity levels within the water are relatively low. High turbidity levels will cause saturation and deflection of the fluorometer excitation light, and render the resulting signal non-linear and misaligned to the instruments calibration.
Where concentrations of the targeted fluorophore are so high as to absorb the fluorometer excitation light, a similar effect occurs which curtails the use of the in-situ fluorescence technique to a limited range.
Finally, if the benefits of high sensitivity are to be gained, then the small changes in fluorescence yield from temperature changes within the environment also need to be considered, as the additional energy obtained from higher temperatures will impact on an in-situ fluorometers signal.
Contact us:Sales/Technical Contact: Justin Dunning, Sales Manager, Chelsea Technologies Group, 55 Central Avenue, West Molesey, Surrey KT8 2QZ. Tel: +44(0)20 8481 9000 , www.chelsea.co.uk
Media contact: For more information / high resolution image, please contact Ellen Keegan, Tel: +44(0) 208 481 9019.
Deployment of the new V-Lux multi-parameter fluorometer for in situ detection of either Algae, Hydrocarbons, CDOM or Tryptophan like fluorescence.
A new approach from Chelsea Technologies Group
It was these challenges that were addressed in the development of a new multiparameter in-situ fluorometer which was part funded within the EU FP7 project SenseOcean, the Chelsea Technologies Group ‘V-Lux’. It was identified that the use of fluorescence in the field could be significantly improved in relation to data reliability and range by incorporating a number of fluorescence channels into one sensor, and augmenting these with a turbidity, absorption and temperature channels. With careful design, it was recognised that a single multiparameter fluorometer could provide a flexible platform which could be easily configured to detect a number of required fluorometric parameters. Based on demand for Chelsea Technologies Group’s Lux range of fluorometers it was apparent that there would be calls for four main variants on the new instrument, detection of Algae, BTEX, Crude Hydrocarbons and Tryptophan-like fluorescence (for Bacterial monitoring and measurements of Biological Oxygen Demand (BOD)).
The new sensor provides the advantages in the latest developments in optical sensing technologies utilising sensitive yet robust solid state detectors. The sensor is packaged within a small 50mm diameter housing of 158mm length, is rated to 6000 metres, and has integrated anti-biofouling protection. It comes with an internal logger and provides real time data in a choice of data output protocols including MODBUS, SDI-12 and other digital formats and includes quality control channels.
A key driver was to provide the user with a robust measurement for the targeted fluorometric compound. This can only be done by comparing the fluorescence yield directly of both the targeted and non-targeted fluorophors. This has been achieved by a combination of techniques including use of common excitation wavelengths, reporting of data in the same units (referencing the same calibration solution), and use of Chelsea Technologies Group’s developed algorithms for reporting concentrations of the resultant targeted compound with interferences removed.
This combined use of fluorescence channels provides a significant advance in in-situ fluorescence monitoring, but in addition, the sensor also addresses the previous limitations imposed when monitoring waters of high turbidity levels. The inclusion and use of the absorption and turbidity channels provides a sensor that can provide robust fluorescence data to levels up to 1000 FNU, previously unachievable using single channel fluorescence.
These corrections also increase the useable linear range of targeted fluorophors to levels that are over ten times that of which can currently be achieved with single channel fluorometers.
These improvements in in-situ fluorometry place this relatively low cost technology into many new areas including oil and water mixes with the potential of challenging incumbent IR and GC-MS techniques in the Oil and Gas and Industrial Sectors. The new Tryptophan-like fluorescence variant is also suitable for monitoring further up the Waste Water Treatment process into secondary and primary tanks as well as WWT input.
Where can you see the new V-Lux Fluorometer? It will be on display at the Sensing in Water Conference in Nottingham (27-28 September) and at WEFTEC 2017 (2-4 October) in Chicago. Justin Dunning and his team will be at hand to give you all the information you need. Please get in touch if you'd like to set up a meeting.