Lab-On-Valve system for shipboard heavy metals measurement – Lab-on-Ship

The automated systems developed are based on an analytical protocol comprising a solid phase extraction step, followed by a detection of each metal by spectrophotometry or fluorescence after derivatization using specifically formulated reagents. Automated systems integrate various 3D printed modules for sample pre-treatment (photo-oxidation), preconcentration of targeted metals, derivatization of these metals and detection.
Several 3D printed modules have been designed :
- for the selective solid phase extraction of metals on commercial resins or on the surface of modified 3D printed modules by ligand grafting,
- for the photo-oxidation of samples by portable UV module,
- for mixing reagents and detection step.
The entire system was driven by an Arduino-type electronic interface.

Two MPFS (MultiPumping Flow System) prototypes were developed for the determination of lead and mercury in natural waters. These prototypes are based on 3D printed modules, designed to be easily exchanged. Combined with small internal volume solenoid pumps and a diode array detector, they allow the quantification of lead and mercury at concentrations as low as 0.2 and 0.3 µg.L-1, respectively. A prototype of 3D printed Lab-On-was also developed for the simultaneous determination of lead and cadmium with a detection limit of 0.2 µg.L-1 for each element. The detection limits obtained are below EQS for lead and cadmium. For mercury, the EQS has not been reached but the detection limit obtained is below the regulatory levels in drinking water.
The analytical systems developed were deployed on a boat during an analysis campaign along the Loire estuary conducted by IFREMER. The prototypes were thus tested in real field conditions under harsh conditions. This campaign also enabled the update of data on the contamination of the Loire estuary by metallic contaminants, thus confirming the improvement of the water quality of the estuary since the end of the 1990s.

The prototypes developed are a first step in the portability of complex automated analytical systems. They allow non-chemical operators to obtain rapidly a reliable result concerning the concentration levels of three of the most toxic metal trace elements that may be present at low concentrations in the environment. The 3D printed fluidic units can hardly be made more compact in the context of environmental analysis. However, improvements can be made to the detection part by using more compact illumination and detection modules (LEDs and photodiodes) or by using a smartphone detection.
Modification of the surface of a 3D printed unit by chemical grafting also opens up perspectives for new sensors. This development is an interesting alternative to the 4D printing that is developing in recent years (adding an additional property to a 3D printed object) which requires long experiments to include a compound providing the desired additional property to the 3D printing resin.

This work has been presented in national and international conferences as posters or oral communications. They have had a good reception by the international scientific community as they received twice the prize for best communication at the International Conference on Flow Injection Analysis and Related Techniques in 2016 and 2017. These presentations led to the publication of two scientific papers of rank A in Talanta journal.
The offshore analysis campaign (Lab-on-Ship mission 2018) has been referenced by IFREMER (DOI : 10.17600/18000423).

In order to significantly reduce water pollution of marine and continental waters, the European Union is now subjected to a series of measures (WFD: Directive 2000/60/EC and MSFD: Directive 2008/56/EC). A list of priority substances was established amongst those presenting a significant risk to or via the aquatic environment. Among all the 33 priority substances and 8 other pollutants concerned by the WFD, toxic metals such as Cd, Pb, Hg and their compounds are listed for “priority action”.

Only few analytical equipments allow field measurement directly in large aquatic ecosystems, such as estuaries and marine environment. Although some electrochemical or optical sensors are widely used in this context to measure some physico-chemical parameters (oxygen, turbidity, pH, organic matter,...), there is no analytical system for on-line field simultaneous measurement of toxic metals such as Cd, Pb and Hg.

The Lab-on-Ship project aims squarely at the preservation of natural aquatic resources by developing a field-deployable instrument to easily, cheaply and accurately determine environmental levels of toxic metal contaminants in various aqueous matrices. Among all the substances concerned by the Directives, we have first selected Cd, Pb, and Hg because they are the most toxic metals at low concentrations (with Environmental Quality Standards < 10 µg.L-1) and the partners involved in this project have already developed a considerable expertise on these metals quantification.

In practical terms, the objectives of the Lab-on-Ship project are to design and produce a modular, high performance and field deployable on-line analytical system by developing a lab-on-valve (LOV) system hyphenated with a MultiPumping Flow System (MPFS). This analytical system will be based on miniaturized modules directly integrated into a 3D printed LOV that will include all pre-treatment steps of sample. The LOV-MPFS will be validated by deploying the system in a progressive and interactive manner in order to i) validate the analytical performances in the laboratory and evaluate the applicability to field samples and then ii) deploy the system on-site during field campaigns.

In this project, selectivity and sensitivity will be paramount considerations. To achieve the selectivity and sensitivity necessary for such analytical systems, the developed flow analytical system will be based on a selective Solid Phase Extraction (SPE) step of Cd, Pb and Hg, followed by detection of each metal by absorptiometry or fluorescence after derivatization with a specifically formulated reagent for each one. Although selectivity is a challenging concern for sample preparation for quantification, it is difficult to achieve with commonly used materials based on ion exchange or chelating functions. In this project, solid phase extraction step will be carried out by Ion-Imprinted Polymers (IIPs). Such imprinted materials show remarkable recognition properties for a target ion because of the memory effect induced during their preparation process. On another hand, an important fraction of metals is complexed by natural or anthropogenic organic ligands in environmental samples. For total dissolved trace metal determinations, it is thus necessary to release the trace metal from the metal–organic complex prior to analysis. This pre-treatment step of samples will be carried out by photo-oxidation process with UV LEDs which will substitute to the conventional UV lamp or UV lamp/persulfate digestion method.

The last phase of the project development will be to validate the analytical LOV system by a field deployment in environments where the WFD and the MSFD are to be implemented. During this operation, uniformity of on-line data from automated method will be compared to data from reference methods. This will ensure that the project will have achieved its scientific and technical objectives.