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[Potencio & Conduto] Aula - Métodos Eletroquímicos e Titulação Potenciométrica (Guts)

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containing fixed sites and membranes containing mobile ion-exchangers or ionophores (carriers). The binding sites are incorporated in the membrane matrix, which determines the internal polarity, lipophilicity, transport and other mechanical properties of the membrane. 
Técnicas Eletroanalíticas – Bibliografia
Nomeclatura: IUPAC (consulta on-line)
http://www.iupac.org/publications/analytical_compendium/TOC_cha8.html
8. ELECTROCHEMICAL ANALYSIS 
8.1 Introduction 8.2 Electrochemical cells and their operations 
8.3 Electrodes 
8.3.1 Classification of electrodes 8.3.2 Ion-selective electrodes 8.3.2.1 Terms related to ion-selective electrodes 8.3.2.2 Classification of ion-selective electrodes 8.3.2.3 Constants and symbols 8.3.2.4 Ion-selective field effect transistor (ISFET) devices 8.3.3 Chemically modified electrodes 8.4 General terms, symbols and definitions used in electroanalytical chemistry 
8.5 Classification of electroanalytical techniques 
8.5.1 Potentiometric and related techniques 8.5.2 Amperometric and related techniques 8.5.3 Voltammetric and related techniques 8.5.4 Impedance or conductance and related measurements 8.6 References 
Técnicas Eletroanalíticas – Bibliografia
Nomeclatura: IUPAC (consulta on-line) termos específicos – Gold book
http://www.iupac.org/publications/compendium/index.html
Exemplos:
polarography
A measure of current as a function of potential when the working electrode is a dropping mercury (or other liquid conductor) electrode and unstirred solutions are used.
 faradaic current
A current corresponding to the reduction or oxidation of some chemical substance. The net faradaic current is the algebraic sum of all the faradaic currents flowing through an indicator or working electrode.
adsorption
An increase in the concentration of a dissolved substance at the interface of a condensed and a liquid phase due to the operation of surface forces. Adsorption can also occur at the interface of a condensed and a gaseous phase.
Técnicas Eletroanalíticas – Classificação
8.5 Classification of electroanalytical techniques
8.5.1 Potentiometric and related techniques (Techniques Involving Electrode Reactions and Employing Constant Excitation Signals)
Técnicas Eletroanalíticas – Classificação
8.5 Classification of electroanalytical techniques
8.5.1 Potentiometric and related techniques (Techniques Involving Electrode Reactions and Employing Constant Excitation Signals)
Técnicas Eletroanalíticas – Classificação
Eletrodo de vidro - calibração
Eletrodo de vidro - calibração
ISEs de dimensões reduzidas
http://www.rothamsted.bbsrc.ac.uk/cpi/nut_acq/plantele_ise.php#types
 Composição do material íon-seletivo para nitrato:
 * MTDDA.NO36% (w/w) (3)
 * 2-nitrophenyl octyl ether 65% (w/w) (Fluka 73732)
 * methyltriphenyl phosphonium bromide 1% (w/w) lipophilic cation (Sigma M7883)
 * nitrocellulose 5% (w/w) (Whatman 7184002)
 * PVC 23% (w/w) high molecular weight polymer (Fluka 81392)
 * Tetrahydrofuran, THF (Sigma T5267)
Ver modo de preparação e de enchimento do ISE em:
Potencial de Eletrodos de Referência
Hg/Hg2Cl2
Ag/AgCl
Tl/TlCl
Efeito da força iônica
*
Figure 18.2 (a) A galvanic cell that uses oxidation of zinc metal to Zn2+ions and reduction of Cu2+ions to copper metal. Note that the negative particles (electrons in the wire and anions in solution) travel around the circuit in the same direction. The resulting electric current can be used to light a light bulb. (b) An operating Daniell cell. The salt bridge in part (a) is replaced by a porous glass disk that allows ion flow between the anode and cathode compartments but prevents bulk mixing, which would bring Cu2+ions into direct contact with zinc and short-circuit the cell. The light bulb in part (a) is replaced with a digital voltmeter (more about this in Section 18.3). 
*
Figure 18.2 (a) A galvanic cell that uses oxidation of zinc metal to Zn2+ions and reduction of Cu2+ions to copper metal. Note that the negative particles (electrons in the wire and anions in solution) travel around the circuit in the same direction. The resulting electric current can be used to light a light bulb. (b) An operating Daniell cell. The salt bridge in part (a) is replaced by a porous glass disk that allows ion flow between the anode and cathode compartments but prevents bulk mixing, which would bring Cu2+ions into direct contact with zinc and short-circuit the cell. The light bulb in part (a) is replaced with a digital voltmeter (more about this in Section 18.3). 
*
Ceramic plug and the asbestos wick and fiber (Figure 70.4(a) and (d)) have relatively slow
flow rates of about 0.01 to 0.1 mL per 5 cm head of bridge solution per day, ground sleeve junctions of
type (b) have a flow rate of 1 to 2 mL. On the other hand, the flow rates of different asbestos wick
junctions may vary by a factor up to 100 and the liquid junction potential may have a day-to-day
(in)stability of ±2 mV under the favorable conditions of a junction between strong potassium chloride
solution and an intermediate pH buffer. Under the same conditions, ground glass sleeve junctions of
type (b) and the little-used palladium annulus junction show stabilities of ±0.06 mV and ±0.2 mV,
respectively.
*
4.4 Cleaning
If the behavior of the measurement setup indicates an electrode malfunction,
the most effective way to clear the fault is by cleaning. The cleaning agent
used basically depends on the type of contamination. In most cases, warm
water with some household washing-up liquid is sufficient to remove grease
and oil. Lime or iron oxide deposits can be removed with vinegar, citric acid or
dilute hydrochloric acid.
Never mechanically clean the membrane. Even wiping or drying the membrane
can lead to faults in the measurement function.
After cleaning, rinse the electrode with deionized (distilled) water.
4.5 Calibration
It is recommended that calibration is carried out after each maintenance operation
(e.g. cleaning or changing the electrode), at the latest after about 3 to 4
weeks operating time.
4.6 Storage of the electrode
Electrodes have only a limited shelf-life. Stocks on hand should be used up
within about a year.
Do not leave an electrode connected to a switched-off instrument for a long
period. Thoroughly clean the used electrode and store it.
To store the
electrode
❏ close off the filler opening if there is one
❏ fill the protection cap with electrolyte solution
❏ insert the cleaned electrode into the protection cap
❏ during longer storage times, check regularly that there is sufficient electrolyte
in the protection cap.
Store the electrode in such a way that no moisture can enter the connector.
ISFET stands for ion selective field effect transistor. These sensors differ not
so much as a result of the membrane material but rather because of their construction.
For the high-impedance pH measurement with glass electrodes, a high-performance
instrumentation amplifier (transistor) is required. Normal instruments
have a resistance of at least 1012Ω. One of the reasons for this is the high
resistance of the glass membrane. The amplifier is often mounted in the instrument,
in the fitting, or in a separate unit installed between the electrode and
the instrument. The greater the distance between membrane and amplifier, the
more sluggish and unresponsive is the signal transmission. With a long transmission
path, each change in pH value means a time-consuming generation
and movement of electric charges.
With an ISFET sensor, the membrane forms a single unit with the amplifier.
One advantage of this arrangement is the good response and reduced susceptibility
to interference. As miniaturization of transistors does not present a
problem, ISFET sensors are an interesting alternative in the field of biological
and medical applications.
Depending on the membrane material, ISFET sensors have a limited range,
worse linearity, shorter service live, reduced reliability, and are sensitive to light
in some cases. These are without doubt some of the