Electrochemical sensors Amperometric

Fenomena yang terjadi pada larutan secara keseluruhan Basic principle of electroanalytical methods Fenomena yg terjadi pada interface antara permukaan elektroda dan lapisan tipis disekitar elektroda Fenomena yang terjadi pada larutan secara keseluruhan konduktometri Metode statis (I=0) Metode dinamis I>0

Basic principle of electroanalytical methods Electroanalytical methods cover a group of quantitative analytical methods that are based on the electrical properties of a solution of analyte when it is made part of an electrochemical cell. These methods have certain general advantages over other types of existing analytical procedures: electrochemical measurements are often specific for a particular oxidation state of an element, the instrumentation is relatively inexpensive.

Basic principle of electroanalytical methods Potentiometric techniques require the measurement of the potential of the working electrode with respect to a reference electrode when no current flows. The activity and hence concentration of an ion may be determined from the electrode potential. Voltammetric techniques are based on the measurement of current when a potential is applied across the electrochemical cell. Voltammetric techniques represent a wide range of methods including AC and DC polarography, linear scan and potential step voltammetry, stripping analysis and amperometry. Conductometric techniques are based on the measurement of the conductance of a solution by applying an AC potential between two electrodes in the solution. The presence of an ionic species will result in an increase in the conductance of the solution

Electrochemical sensors Amperometric Sensors Oxygen sensor Nitrate sensor Nitrous oxide sensor Methane sensor Potentiometric Sensors ISE for metal ion (P, K, Na etc) ISE for nitrogen compounds (Nitrate, Ammonia, etc)

Amperometry Kondisi khusus dari voltammetri yang hanya menggunakan satu nilai potensial polarisasi terhadap elektrode kerja B potensial arus A waktu waktu

Amperometry

Arus dalam voltammetry Arus yang terjadi ditentukan oleh: (1) laju transport massa analit dari larutan ke batas luar lapisan difusi (2) laju transport massa analit dari batas luar lapisan difusi ke permukaan elektrode

Perhitungan arus voltammetri I : arus n : jumlah mol elektron/mol analit F : bilangan Faraday A : luas permukaan elektrode DA : koefisien difusi analit A : laju transport massa A menuju permukaan elektrode

Perhitungan arus voltammetri = (cA-cA0)/ Ketika cA0 0, arus akan menjadi arus batas.

Analisis kuantitatif dg amperometri Waktu (menit) Arus (uampere) | __

Kurva kalibrasi __ __ __ __ __ __ Arus | | | | | | Konsentrasi analit 0.5 1.0 1.5 2.0 2.5 3.0 Konsentrasi analit

Cell schematic

Instrumentation schematic

Classical Amperometric Sensor Design

TRANSPORT MECHANISM OF ANALYTE transport or permeation to the surface of the permeable membrane diffusion through the membrane dissolution in the internal electrolyte further reaction-dissociation in the electrolyte diffusion to the sensing electrode surface electrochemical reaction at the sensor surface

Advanced Sensor Configuration Electronic Noses and Olfaction 2000

Advanced Sensor Configuration Analyst, 1999, 124, 871–876