Recent Advances in Ion-Selective Membrane Electrodes for In Situ Environmental Water Analysis
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igures Captions Figure 1. Illustration of typical sampling procedure in a natural reservoir for subsequent centralized analyses. A discrete number of samples are extracted at different depths by with a mechanical pump. Once the samples are on the platform (or shipboard), preservatives are aggregated in clean hermetic vessels. Thereafter, refrigerated samples are transported to a laboratory unit equipped with centralized instruments, such IC, ICP, AAS and ISEs and ion-analysers to finalize the analysis. Certain samples require special pretreatments, such as digestion, filtration, centrifugation, etc. Figure 2. ISE principles and features for water research. Key ISE components, such as membranes, transducers and receptors, are described with the triangle, whereas the analytical performance features that make ISEs an attractive platform for decentralized water research are illustrated in the vertices of the hexagon. Figure 3. Three decentralized paths for water analysis (a) on-board, (b) on-site and (c) in situ . The red points indicate the sampling at different longitudinal and vertical positions. P: corresponds to an operational sensing probe. Figure 4. Left: On-site potentiometric detection of Ca 2+ in a water reservoir. Samples are discretely extracted by a pump and directed to a flow cell attached to an inner-filling solution Ca 2+ -selective electrode. Concentrated KCl solution is pumped through the detection cell, allowing the potentiometric readout by establishing a liquid junction between the ISE and the RE. Right: Potentiometric time trace for the extracted samples (inset indicates the depth) accompanied with the profile concentration of Ca 2+ as a function of depth. Figure 5. Top: In situ high profiling concentration of ammonium as a function of depth in natural waters by the deployment of a sensing probe mainly composed of different kinds of sensors, electronics and syringes. Bottom: Portrayal of setup of the profiling device: (1) pressure housing (containing computer, electronics and batteries); (2) CTD probe; (3) optode module; (4) impedance converter for potentiometric channels (pH, redox, S 2 – ); (5) O 2 preamplifier; (6) S 2 – preamplifier and amperometric S 2 – microsensor; (7) syringe sampler; (8) O 2 sensor (microoptode embedded within a syringe); and (9) Ammonium- selective electrode and RE with galvanically separated amplifiers. Figure 6. (a) Illustration of the electrochemical mechanism upon application of a positive potential to the working electrode. Cl – present in the sample is reversibly deposited onto Ag (WE) as AgCl with the concomitant release of Na + to the outer solution. The opposite reaction takes place in the counter/reference electrode (CE/RE = coiled Ag/AgCl element). (b) Calibration curves for nitrate obtained with 1 mM and 600 mM NaCl background. (c) Working principle for the in-line acidification cell based on a cation exchange process between the sample and the membrane. Reconditioning of the membrane occurs through backside contact with an acid reservoir. (d) Calibration curves for nitrite obtained with 1 mM and 600 mM NaCl background. PUMP CENTRALISED DEVICES Figure 1 SAMPLING + PRESERVATIVES TRANSPORTATION LABORATORY UNIT S A M P L E IC ISEs ICP PRETREATMENT AAS RES E R AR E T C A H W ISE RECEPTOR MEMBRANE TRANSDUCER ISE ROBUSTNESS PORTABILITY STABILITY SELECTIVITY LIMIT OF DETECTION IP RESSURE/LIGHT Figure 2 INSENSITIVITY TO PUMP a) ON-BOARD D E P T H b) ON-SITE PUMP D E P T H c) IN SITU PROBE D E P T H P P Figure 3 ANALYSIS ANALYSIS PUMP Figure 4 PORTABLE DEVICE KCl 2+ Ca / mM 1 3 5 7 D E P T H / m 0.7 0.8 0.9 KCl 9 SIGNAL RE ISE 20mV 1 2.5 4 5.5 7 8.5 2 HOURS 12 10 8 6 4 2 D E P T H / m + - NH (? M) 4 20 60 100 140 Figure 5 P tải về 1.01 Mb. Chia sẻ với bạn bè của bạn:
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