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MEASUREMENTS OF HEAVY METALS IN FLUIDS WITH VOLTAMMETRIC METHODS Øyvind Mikkelsen and Knut H. Schrøder Norwegian University of Science and technology Department.

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Presentation on theme: "MEASUREMENTS OF HEAVY METALS IN FLUIDS WITH VOLTAMMETRIC METHODS Øyvind Mikkelsen and Knut H. Schrøder Norwegian University of Science and technology Department."— Presentation transcript:

1 MEASUREMENTS OF HEAVY METALS IN FLUIDS WITH VOLTAMMETRIC METHODS Øyvind Mikkelsen and Knut H. Schrøder Norwegian University of Science and technology Department of Chemistry N TRONDHEIM, NORWAY Mikkelsen 2000

2 Voltammetry In voltammetry the information about the analyte is achieved by measure the current as a function of a applied potential. The current is proportional to the concentration. Mikkelsen 2000

3 Cross section of the dental amalgam (or somewhat related material) electrode. Mikkelsen 2000

4 Working electrode Metal ions are deposited on the electrode surface. Me n+ Me Mikkelsen 2000

5 Voltammetric cell Counter electrode Working electrode Reference electrode Mikkelsen 2000

6

7 KILDE: Mikkelsen 2000

8 Signal Source & Measuring Unit (SMU) - Control UNIT, Microcontroller unit that controls the card in the SMU (voltammetric analyzer). Communicates with a external PC via a RS232 interface. - Signal Source UNIT, this unit consists of two electronic boards; Signal Source ControlER Board and the D/A Converting Unit. Digital numeric values of the voltage signal to the cell are generated by the microcontroller and placed in this unit. When a scan is started the values is cloked out from the D/A converter as analog voltage steps. - Converter/Measure UNIT, consists of one electronic board ref. as the A/D converting unit. This board receives the current feedback from the Ampl. Int. UNIT as a voltage signal from a I/E converter, and converts the signal from the cell to digital words, which the processor can read and place into a buffer for transmission to the PC. Mikkelsen 2000

9 Ampl. Int. UNIT Amplifier / Interface UNIT for both the applied and the received signal, to/from the spesific cell in use. Takes the asserted potential from the SMU and puts it to the cell. It also converts the current from the cell to a voltage wich can be converted to digital values in the voltammetric analyzer and send it to a PC.

10 Mikkelsen 2000 Signal Source & Measuring Unit Control UNIT Signal Source UNIT Convert/ Measure UNIT Sync Ampl. Int. UNIT Ext. rec. connect. Cell UNIT Ext. trig. Cntrl. Recording, analysing, presentation and documentation UNIT (PC)

11 Mikkelsen 2000 Voltammetric equipment

12 Mikkelsen 2000 Linear-scan voltage generator A  + B  + C  + Recorder Current-to-voltage converter Potensiostatic control circuit Referance electrode Counter electrode Working electrode Signal source E out Operational amplifier potentiostat (OP AMP) Cell I

13 Mikkelsen 2000 Some typical signalmodulations in voltammetry Linear scanDifferential pulse scan Cyclic scanSquare wave

14 Mikkelsen 2000 Typical controlled parameters in voltammetri

15 Mikkelsen 2000 Apparatus for voltammetric analyses

16 Mikkelsen 2000 Software for setting/loading parameters to control unit LabVIEW

17 Background of dental amalgam electrode in acetatbuffer pH=4,6. Scan from -1.2 to -0.2 V Mikkelsen 2000

18 Zinc, cadmium and lead (25, 50 and 75 ppb) detected by DPASV on dental amalgam electrode. All scan in NH4Ac (non-buffered) pH=6,4 also containing nickel and copper and gallium (75 ppb). Deposition time 60 s at -1.2V. Scan from -1.2 to -0.4V, pulse height 50 mV. Mikkelsen 2000

19 Plot of a typical scan at silver electrode before and after lead addition. Scan performed by DPASV using a sine oscillating working silver electrode. Deposition time 60 s, scan rate 15mV s -1, pulse height 40 mV. Mikkelsen 2000

20 Soilwatch Project Mikkelsen 2000


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