diamond ph electrode improving on

Transcription

1 Development of a boron doped diamond ph electrode improving on current ph sensing technologies Zoë J Ayres University of Warwick

2 ph sensing: industrial and environmental importance ph = - log ah+ Environmental monitoring Clinical medicine Waste management3 Oilfield services4 Biopharmaceuticals P. Arquint et al., Sensor. Actuat. B-Chem., 993, 3, G. Helmlinger et al., Nat. Med., 997, 3, K. Komonweeraket et al., Waste Management, 205, 38, M. Abdou et al., Oilfield Rev., 20, 23,

3 Current technologies Most prevalent ph sensor is the glass ph sensor Potentiometric measurement

4 E ph sensing: industrial and environmental importance Open circuit potential 7 4 ph () Issues with Alkali errors (2) Fragility (3) Subject to drift glass fouls

5 The ideal ph sensor Wide dynamic range No interferences Robust Does not foul Operates across a range of temperatures Reagentless Ion selective field effect transistors ISFETs devices Improved robustness Wide dynamic range BUT Suffers from interferences Fluorescent sensors Improved robustness Little interference BUT Very restricted range Requires addition of reagents Metal Oxide devices Improved robustness Wide dynamic range BUT Not necessarily robust Requires addition of reagents

6 Current Quinone-based ph sensing technologies Based on the redox potential of the quinone Can be surface bound or in solution Peak position moves with ph Can use voltammetry Voltage

7 Current voltammetric ph sensors Quinones can be inherently part of the electrode surface Sp 2 carbon OR chemically/mechanically bound to the electrode surface Dropcast or chemically added to any electrode surface + Simple to manufacture + High pka - Requires degassing - No control of surface density + Can design molecule properties + High pka - Complicated synthesis - Not robust

8 Current Issues with current quinone based technologies () Need to degas solution not ideal for in-situ monitoring (2) If quinones are added to an electrode surface they can be inherently unstable 7 (3) In unbuffered (low buffer capacity solutions) by making the measurement, you actually change the local ph 2 2 Voltage Aim: to overcome these issues to make the ultimate ph electrode

9 Boron doped diamond as a starting material. Conductive sp 3 carbon material 2. Highest Knoop hardness (robust) 3. Resilient to fouling 4. Excellent electrochemical properties (no need to degas) Low Capacitance Widest Solvent Window Works under HPHT HOWEVER No intrinsic quinone groups on the BDD surface = not ph sensitive Reduced Fouling Diamond Can apply extreme potentials Corrosion Resistant

10 Laser ablation of BDD to create quinone groups High T acidic treatment Strongly attached sp2 carbon + Robust + High pka + Simple manufacture + Fine control of surface coverage Figure credit: J.C. Newland

11 Manufacturing a diamond ph sensor Laser micromachined array of ph active sp 2 containing regions

12 The diamond ph sensor Produces linear potential response to a change in ph (~59 mv/ ph unit T= 298 K) Advantages Ayres, Z. J. et. Al. Anal. Chem. 206, 88 (), Robust Not subject to alkali errors No O2 interference 3 s per scan Can be stored dry

13 Stability Repeat measurements over a 3 month period

14 Application to real-world samples Seawater from Cornwall ph 8.42 (glass ph probe) Equates to ph 8.40

15 Conclusions BDD ph sensor developed by controlled, localised sp 2 incorporation By laser micromachining the surface of BDD gains quinone groups that are ph sensitive Advantages include: No influence from O 2 - does not need to be degassed Uses voltammetry - does not experience alkali errors No fragility issues Works at high temperatures Potential range means common electroactive species do not interfere Can accurately measure ph in buffered AND unbuffered solutions

16 Acknowledgements Prof Julie Macpherson Sam Cobb Mareike Herrmann EPSRC Element Six Warwick Electrochemistry and Interfaces Group 6