Upload
ricardo-patrick
View
18
Download
1
Embed Size (px)
DESCRIPTION
ooioioioioioio
Citation preview
Aula 3- Breve histórico dos eletrodos, conceitos fundamentais e potenciometria
IntroductionHistoric overview, Classification of (bio)chemical electrodes, definitions of sensors andbiosensors and basic measuring techniques
Fundamental ConceptsElectrical conduction, electrodes, electrolytic cells, faraday’s law of electrolysis, Voltaic orGalvanic cells, The Nernst equation, reference and indicator electrodes, standard electrodepotentials, liquid-junction potentials
Potentiometric Methods and ElectrodesPrinciples of potentiometric electrodes, experimental set-up and instrumentation (Galvanic
ll) I di t l t d 1) t lli l t d fi t ( ti d l t d ) d dcell), Indicator electrodes: 1) metallic electrodes: first (cation or redox electrode), second andthird class or specie; 2) membrane electrodes: glass electrodes, polymer (liquid membranes)electrodes, crystalline and pressed powder solid electrodes, gas electrodes, enzymaticelectrodes (biosensors) practical aspects and applicationselectrodes (biosensors), practical aspects and applications
References1)R. W. Cattrall, Chemical Sensors, Oxford, Oxford Press, 1997
2) A. Evans, Potentiometry and Ion Selective Electrodes, Chichester, Wiley, 1987
3) F. Scholz, Electroanalytical methods-guide to experiments and applications, Berlin,Springer-Verlag, 2009
4) V. A. Gault, N. H. McClenaghan, Understanding Bioanalytical Chemistry- Principles andApplications, Oxford, Wiley-Blackwell, 2009
5) A. P. F. Turner, I. Karube, G. S. Wilson, Biosensors- Fundamentals andapplications,Oxyford, Oxyford University Press, 1987
6) G. G. Guilbault, A. A. Suleiman, O. Fatibello-Filho, M. A. Nabirahni, ImmobilizedBioelectrochemical Sensors, In: D. L. Wise, Bioinstrumentation and Biosensors, New York,Dekker, 659-692,
7) O. Fatibello-Filho et al, Chapter 17 - Electrochemical biosensors based on vegetabletissues and crude extracts for environmental, food and pharmaceutical analysis, In: S.p yAlegret & A. Merkoçi, Comprehensive Analytical Chemistry, Vol. 49-Electrochemical SensorAnalysis”, Amsterdam, Elsevier , 355-375, 2007
Breve histórico sobre os sensoresTabela- Breve histórico sobre o desenvolvimento dos sensores
Ano Tipo de sensor Investigadorquímicos
1888 Eletrodos metálicos/íons W. Nernst1906 Eletrodo de vidro M. Cremer1922 Eletrodo gotejante de Hg J. Heyrovsky1930 Eletrodo de vidro/Corning 015 D. Innes & M. Dole1934 El t d d id N (I) B L l & E Bl1934 Eletrodo de vidro para Na(I) B. Lengyel & E. Blum1936 Eletrodo c/ CaF2 para Ca(II) H.J.C. Tenderloo1956 Eletrodo para Oxigênio L C Clark1956 Eletrodo para Oxigênio L.C. Clark1958 Eletrodo para CO2 W. Severinghaus & A. Bradley1958 Eletrodo de pasta de carbono R.N. Adams1958 Eletrodo de pasta de carbono R.N. Adams1959 Sensor piezelétrico G.Z. Sauerbrey
3
Ano Tipo de Sensor InvestigadorAno Tipo de Sensor Investigador1961 Sensor AgI(s) parafina p/ I- E. Pungor1962 Biossensor para glicose L.C. Clark & W. Lyonsp g y1964 Sensor piezelétrico W.H. King1966 Sensor de LaF3/EuF2 para F- M.S. Frant & J.W. Ross1967 Sensor de membrana liq. p/ Ca2+ J.W. Ross1970 Sensor de membrana de PVC p/ Ca2+ G. Moody et al1970 ChemFET P. Bergveld1974 Calorimétrico (enzimático) K. Mosbach & B. Danielson1975 ENFET J. Janata1979 Biossensor PC c/ ADH e LDH T. Yao & S. Musha1979 Biossensor de tecido Rechnit et al1979 Biossensor de tecido Rechnitz et al1980 Sensor de fibra-óptica J.I. Peterson et al1997 Eletroantenograma J Pickett et al1997 Eletroantenograma J. Pickett et al
? Pâncreas artificial implantável J Jaremko & O. Rorstad
Electrical energElectrical energyNon-electrolytic Electrolytic cellsNon-electrolytic cells (gavanic)
Electrolytic cells
Non-Spontaneous Spontaneous process
pprocess
ΔG 0ΔG < 0ΔE > 0
ΔG > 0ΔE < 0
Chemical energyΔE > 0
PotenciometryI 0
Electrolysis CoulometryP l h /V l
5I ~ 0 Polarography/Voltammetry
Electrogravimetry
Electroanalytical methods
Interfacial methods
Bulkmethodsmethods methods
Static methodsI 0
Dinamic methodsI 0
Conductometry(G 1/R)
Conductometric Ti iI=0 I > 0 (G = 1/R) Titrations
Potentiometry Potentiometric ConstantPotentiometry(E)
Potentiometric titrations
Constant current
Coulometric Titrations(Q = It)
Electrogravimetry(wt)
Controlled potentialConst.
electrode ( )
ElectrogravimetryAmperometric i i
Voltammetry[ I f (E) ]
electrode potential
coulometry (Q = ∫ 1 idt
6
titrations[ I = f (E) ](Q = ∫01 idt
Esquema de (Bio)sensor químico
7
Detectores eletroquímicos
Potenciométricos Amperométricos
Medidas realizadas sem a passagem de corrente
Medidas de corrente elétrica realizadas sob a aplicação passagem de corrente
elétrica
Baseada na mudança de t i l d fí i d
de um potencial elétrico constante
Baseada nas reaçõespotencial da superfície do eletrodo de trabalho
Baseada nas reações oxidação e redução que ocorrem na superfície do
eletrodo
8
eletrodo
2 Fundamental Concepts2. Fundamental Concepts
11
Electrical conduction
Materiais
Isolantes
Eletrô nicos Iô nicos
Condutores
Metais, Óxidos Inorgâ nicos,Polí meros Condutores
Soluç õ es de Eletró litosCristais Dopados
I = dQ/dt
e-
Electronic conductor
12Ionic conductor
Condutores Eletrônicos e Iônicos
Eletrônicos: Obedecem a lei de Ohm (E = IR)E = Diferença de Potencial (volts) devido ao movimento f ç ( )
de elétronsR = Resistência (ohms) do condutor à passagem de Correntep gI = Corrente (amperes)
Iônicos: Obedecem a lei de Ohm para pequenos l d valores de corrente
E Dif d P t i l ( lts) d id i t E = Diferença de Potencial (volts) devido ao movimento de íons
R = Resistência (ohms) do eletrólito à passagem de corrente13
R = Resistência (ohms) do eletrólito à passagem de correnteI = Corrente(amperes)
Reações de Oxi-Redução
Transferência de elétrons de um reagente para outro
2 Ag+ + Cu(s) 2Ag(s) + Cu2+2 Ag + Cu(s) 2Ag(s) + Cu
Esta reação pode ser realizado por dois caminhos fi i t dif tfisicamente diferentes
Caminho 1: Colocar os reagentes em contato diretoCaminho 1: Colocar os reagentes em contato direto
Cuo CuoCu
Ag+ Ag+
A o
14
Ago Cu2+
Célula Eletroquímica
Caminho 2: Separar os reagentes em um arranjo apropriado
e- e-
Eletrodo de Cobre Eletrodo de PrataPonteSalina
(KCl sat.)
[Cu2+] = 1.00 mol/L [Ag+] = 1.00 mol/L
Componentes de uma Célula Eletroquímica
Cu(s) Cu2+ + 2e- Ag+ + e- Ag(s) Ânodo (oxidação) Cátodo (redução)
C p C q• 2 condutores imersos em uma solução contendo eletrólitos (eletrodos)• 1 condutor eletrônico externo para permitir o fluxo de elétrons
15• 1 condutor iônico para evitar o contato direto dos reagentes e permitir o fluxo de íons
Célula Eletroquímica – Movimento de cargas
e-e-
e-
e- e-
e
e e
e- Cu2+ NO3 e-
Oxidação Redução
Cl-
e-
Cu2+SO4
2-
SO42-
-Ag+
Ag+
NO3e-
e-
e
e-
e-
e-AgNO3CuSO4
K+
K+Cl-
Cu2+ NO3e e
Interface Eletrodo/solução Interface Eletrodo/solução
g 34
16Voltaic or Galvanic Cell
17
E ll = E t E + EjEcell Ecat – Ean + Ej
18
Schematic diagram showing the t d d h d l t dstandard hydrogen electrode
19
20Voltaic or Galvanic Cell
21
2 2
22Galvanic Cell: Zno + Cu2+ Cuo + Zn2+
Schematic diagramshowing the saturatedcalomel electrode
Schematic diagram showing a Ag/AgCl electrode.
23
calomel electrode
24
25
26
27
Relationship between the potential of an Fe3+/Fe2+ half cell relativeRelationship between the potential of an Fe3+/Fe2+ half-cell relativeto the reference electrodes. The potential relative to a standardhydrogen electrode is shown in blue, the potential relative to ay g , psaturated silver/silver chloride electrode is shown in red, and thepotential relative to a saturated calomel electrode is shown ingreen.
28
Junction Potentials
Fig Origin of the junction potential between a solution of 0 129
Fig. Origin of the junction potential between a solution of 0.1 M HCl and a solution of 0.01 M HCl.
Potential of Junction
Potencial de Junção Líquida: Origem e Cálculos
Devido a diferença de mobilidade dos íons que transportam pelajunção (ponte salina)junção (ponte salina)Max Planck (Ann. Phys., 39, 161 (1890); 40, 561 (1890)
sendo Zi = número atômico
ti = número de transporte
bilid d iô i ( 2 1V 1)31
µi = mobilidade iônica (cm2 s-1V-1)
Caso 1Caso 1P Henderson (Z Physik Chem 59 118 (1907); 63P. Henderson (Z. Physik. Chem., 59, 118 (1907); 63,325 (1908)): Cálculo da junção líquida entre 2soluções com concentrações diferentes (C1 e C2) massoluções com concentrações diferentes (C1 e C2), masde mesma valência
Ag │ AgCl │ MCl(C1)│ │ MCl(C2) │AgCl │Ag
Ej = 0,0591 (2 t+ -1) log C1/C2
32
Caso 2Caso 2Lewis & Sargent (J. Am. Chem. Soc., 31, 363 (1909)):Cálculo do potencial de junção líquida entre 2eletrólitos univalentes diferentes de mesma
Ag │AgCl │ M Cl(C)│ │ M Cl(C) │AgCl │Ag
concentração com um íon comum
Ag │ AgCl │ M1Cl(C)│ │ M2Cl(C) │AgCl │Ag
Onde Λ é a condutância iônica equivalente a diluiçãoinfinita de cada eletrólitoa de cada e e ó o
34
3. Potentiometric Methods and Electrodes
35
Potentiometric Methods and electrodes: Principles
In potentiometry the potentialp y pof an electrochemical cell ismeasured under staticconditions. Because no currentor only a negligible currentflows through theflows through theelectrochemical cell.
36
Potenciometria
E = E* + 0,059 / n log [ox] / [red] Equação de Nernst
Metallic Indicator Electrodes
1a)Electrodes of the First Kind or Class responds to theactivity of Mn+activity of Mn+
Examples: Ag, Hg, Cu, Pb in contact with Ag+, Hg2+, Cu2+, Pb2+Pb2+
Cu2+(aq) + 2 e Cuo Eo = 0.34 V
ECu2+/Cu = EoCu2+/Cu + 0.0592/2 + log [Cu2+]
Ecell = Eind – Eref + Ej
39
1b) Redox Electrodes
Pt, Au and Pd electrodes
40
Potentiometric Methods: Redox Electrodes
The platinum electrode generally form a monolayer of PtO on its surface that causes
Treatment of platinum electrode
The platinum electrode generally form a monolayer of PtO on its surface that causes
changes in its potential and also delay its response,
Th l d b k d bThe electrode can be attacked by:
a) Oxidizing solutions containing Cl- with formation of PtCl4-;
b) Natural waters or other oxidant solutions with formation of PtO;
c) Cr(II) in acid medium reduces H+ by formation of adsorbed H2 on Pt
Pre-treatment of Pt electrode
a) Mechanical with Al2O3 or CeO2 or diamond powder;
b) Chemical (alcoholic KOH , sulphochromic, aqua regia or Ce(SO4)2 solution) ;
c) Electrolytic: a) Cathodic - remove the oxide layer; b) Anodic - remove adsorbed H2
41
Potentiometric Titration
42
Potentiometric Methods and electrodes: Electron activity and pE
43
Potentiometric Methods and electrodes: Electron activity and pE
Continuing...
44
Potentiometric Methods and electrodes: Principles Electron activity and pE
Table. Standard EMF`s and pEO for some common redox couplesp p
45
Potentiometric Methods: Electrodes of the Second kind
The electrode of the second kind responds to the activity of another specie in
equilibrium with Mn+ (precipitate or stable complexes) Generally this species areequilibrium with Mn+ (precipitate or stable complexes). Generally this species are
anions.
h i l f A l d i l i f A + iEx: the potential of a Ag electrode in a solution of Ag+ is:
This first kind electrode in presence of AgI has the following half-cell equation:
Where:
46
Potentiometric Methods: Electrodes of the Second kind
Another examples: Ag/AgCl(s), Ag/AgBr(s), (Hg/HgY2-).
Where:
47
Potentiometric Methods: Electrodes of the Second kind
Electrode of the second kind: metal-metal oxide electrodes
Ex: Ti, Pb, Nb, Sb, W when passivated chemically responses to H3O+ (pH).
Ex:
Ex:
Potentiometric Methods: Electrodes of the third kind
Electrode of the third kind responds to the activity of another Cation in specific
conditions Some times when an electrode of the second kind is subjected to a redoxconditions. Some times when an electrode of the second kind is subjected to a redox
reaction and another reaction, such as a solubility reaction (involving more than two
reactions) an electrode of the third kind is foundreactions) an electrode of the third kind is found.
Ex:
Where :
Electrode Membranes
50
Origin of a membrane potential
If the smaller ions are able to diffuse through the membrane butthe larger ions cannot, a potential difference will develop betweenthe two solutions. This membrane potential can be observed byintroducing a pair of platinum electrodes.
5151
52
Potentiometric Methods: Membrane potential
A typical potentiometric electrochemical cell equipped with an ion-selectiveelectrode.
The electrochemical cell includes two reference
electrodes: one immersed in the ion-selective
electrode’s internal solution and one in the
sample. The cell potential, therefore, is:Variable
K- Constant
The analyte’s interaction with the membrane generates a membrane potential if
K Constant
53
The analyte s interaction with the membrane generates a membrane potential if
there is a difference in its activity on the membrane’s two sides.
Potentiometric Methods: Glass Selective Electrodes
Fritz Haber (1901): discovered that there is a change in potential across a
glass membrane when its two sides are in solutions of different acidity.g y
Harber & Klemensiewicz (1909): First glass electrode + Nernst equation;Harber & Klemensiewicz (1909): First glass electrode + Nernst equation;
Mc-Innes & Dole (1930): Corning 015 (commercial);
Lengyel & Blum (1934): Na+ electrode;
Nikolsky & Eisenman (1960-1975): Alkaline and alkaline-earth
electrodes;54
electrodes;
Potentiometric Methods: pH Glass Electrode
Reference electrolyteelectrolyte
Inner solution
Sample solution
E1 = Outer potential of the glass membrane (a1);E2 = Asymmetry potential:
solution
glass thickness;
asymmetry;
wearing;E3 = Inner potential of the membrane (a1‘);E = Inner reference electrode potential (a -);
Glass membrane (0.2-0.5 mm)Gel layer (10-4 mm)
55
E4 = Inner reference electrode potential (aCl-);
E5 = Outer reference electrode potential;E6 = Junction potential;
Potentiometric Methods: Glass Selective Electrodes
Schematic representation of the
reactions in a glass membrane
aq = aqueous solution;
sg = surface gel ;g g
g = gel layer;
v = dry glass layerv dry glass layer.
56
Potentiometric Methods: Glass Selective Electrodes
57Schematic representation of the atomic structure of (a) soda silica glass; (b) soda aluminosilica glass
Potentiometric Methods: Combined pH Glass Electrode
Screw Cap
Filling port
Connecting plugConnecting plug
Reference elementLead-off electrode
Reference electrolyte
Diaphragm
58Internal buffer
Membrane
An early Beckman pHmeter
Arnold Beckman59
Arnold Beckman (1934 -1939)
Potentiometric Methods: Glass Selective Electrode
Asymmetry potential and pHmeter calibration
61
Potentiometric Methods: Glass Selective Electrodes
pHmeter calibration Dependence of the factor pre-Nernstian with T
K is found using buffer solutions
62
63
64
65
Potentiometric Methods: Glass Ion-Selective Electrodes
Corning 015 (first commercial) = 22% Na2O, 6% CaO and 72% SiO2. When
immersed in an aqueous solution for 7 h, the outer approximately 10 nm of the
membrane’s surface becomes hydrated, resulting in negatively charged sites, —SiO–.
Na+, serve as counter ions. H+ displace the Na+, giving rise to the membrane’s
selectivity for H+.
Corning 015 obeys the following equation:
Ideal application: a pH range of approximately 0.5 to 9;
At more basic pH levels the glass membrane is more responsive to other cations66
At more basic pH levels the glass membrane is more responsive to other cations,
such as Na+ and K+ (alkaline error).
Potentiometric Methods: Selectivity of Membranes
Most membranes are not selective toward a single analyte. Instead, the membrane
potential is proportional to the concentration of each ion that interacts with thepotential is proportional to the concentration of each ion that interacts with the
membrane’s active sites.
zA and zI = charges of the analyte and the interferent;
KA I = selectivity coefficient.KA,I selectivity coefficient.
(aA)e and (aI)e = activities of analyte and interferent;
67If KA,I is 1.0, the membrane responds equally to the analyte and the interferent;
If a membrane shows good selectivity, KA,I << 1.0.
68
Nikolsky’s equation:Nikolsky s equation:
S l ti id dNAS 11-18 from Na+
Na2O 11% (mol)
Seletividade:pH > 7 KNa,K = 10-3
H 7 K 3 3 10 3Al2O3 18%
SiO2 71%
pH = 7 KNa,K = 3.3.10-3
pH < 7 KNa,H > 1
NAS 27-4 from K+
N O 27% ( l)Seletividade:H+ > Ag+ > K+ = NH + > Na+ >Li+ >> Ca2+Na2O 27% (mol)
Al2O3 4%
H+ > Ag+ > K+ = NH4+ > Na+ >Li+ ....>> Ca2+
70SiO2 69%
Potentiometric Titration
Solid-based graphite-epoxy electrodes for potentiometric measurements of pH and acid-base titration
Graphite-epoxy composite
pH range Slope /mV pH-1
Lifetime /mon (det)
Ref.
40% m/m PbO2 1.0 – 11 -58.7 + 0.3 > 8 (> 1200) 1
30% m/m silica gel 2.0 – 13 -40.5 + 0.4 > 12 (> 6000) 2
30% m/m λ-MnO2 2.0 – 13 -53.6 + 0.5 > 4 (1500) 3
30% m/m Fe2O3 1.7 – 12.5 -39.7 + 0.6 > 6 (2000) 4-6
20% magnesium silicate
1.0 – 12.0 -39.2 + 0.3 > 8 (1500) 7
74Cu/Cu2S film acid-base
titrations-59.0 + 0.5 > 3 (400) 8
Potentiometric Methods: Liquid-Based Selective Electrodes
This class of ISEs uses a hydrophobic membrane containing a liquid organic
complexing agent that reacts selectively with the analyte. Three types of organic
complexing agents have been used:
Cation exchangers;
Anion exchangers;Anion exchangers;
Neutral ionophores.
One example of a liquid-based ion-selective electrode is that for Ca2+, which
l ti b t t d ith th ti h di ( d l)uses a porous plastic membrane saturated with the cation exchanger di-(n-decyl)
phosphate.
75
Potentiometric Methods: Kind of ionic exchangersCationic exchangers:Cationic exchangers:
Calcium di-(n-decyl) phosphate: (Ca[PO2 (CH3(CH2)9O)2];Sodium tetraphenylborate: (NaBØ4);Sodium tetraphenylborate: (NaBØ4);
Anionic exchangers:g
Tricaprylylmethylammonium chloride (Aliquat 336) : CH3N[(CH2)7CH3]3Cl ;
Protonated tertiary amine (tri-n-octylamine);y ( y );
Tri-n-benzylamine;Tetraphenylarsonium chloride ((AsPh4)Cl)Tetraphenylarsonium chloride ((AsPh4)Cl)
Neutral exchangers:
Valinomycin;
Crown ether.
76
Preparation of the ionic pair and polimeric membrane
P ti f th ti t i l
a)Cationic Species:
Preparation of the active material
) p
Ionic Pair
a)Anionic Species:
Ionic Pair
Preparation of the polimeric membrane with the active material
2 10 % ( / ) f i i i2 - 10 % (m/m) of ionic pair;60 – 68 % (m/m) of plasticizer DBP (dibutylphtalate), DOP (dioctylphtalate), or
2-nitrofeniloctileter (o-NPOE);30 % (m/m) PVC;dissolve the mixture in 10 mL THF (tetrahydrofuran)
Potentiometric Methods: Liquid-Based Selective Electrodes
First L-ISE selective to Ca2+ developed by Ross (Science, 156, 1378 (1967).
The membrane is placed at the end of a non-conducting cylindrical tube, and is in
p y ( , , ( )
contact with two reservoirs. The outer reservoir contains di-(n-decyl) phosphate in
di-n-octylphenylphosphonate, which soaks into the porous membrane. The inner
78reservoir contains a standard aqueous solution of Ca2+ and a Ag/AgCl reference
electrode.
79
Potentiometric Methods: PVC membrane electrode
PVC b l t dElectric conection
Silicone rubber
PVC membrane electrodedeveloped by Moody et al(Analyst, 95, 910 (1970).
Glass junction
Ag/AgCl electrode
0.1 mol L-1 CaCl solution
PVC tubePVC tube
PVC membrane
80
Potentiometric Methods: Polymeric membrane
Experimental arrangement for casting PVC membrane
81
82
83
84
Fi t C t d i PVC i l ti l t d
Potentiometric Methods: Polymeric membrane with ionic exchanger
First Coated-wire PVC ion-selective electrode
Coaxial cable
Outer conductor
Inner cond ctorInner insulation
Outer conductor
Inner conductor ParaffinPolymeric membrane
ith i i h85Cattrall, R. W. & Freiser, H.; Anal. Chem.; 43, 1905 (1971).
with ionic exchanger
Coated graphite ion-selective electrode
Coated graphite ion-selective electrode
88
Tubular electrode made of graphite-epoxy with a PVC film
Potentiometric Methods: Tubular electrodeTubular electrode made of graphite-epoxy with a PVC film
P ti f th t b l l t d A li ld ith 8 d 10 f iPreparation of the tubular electrode. A = acrylic mold with 8 and 10 mm of innerand outer diameters, respectively, 7 mm of length, a = 1mm diameter hole. B =adaptation of the central conductor of coaxial cable with welded copper plate. C =
8989mold filled with graphite-epoxy paste. D = view of the electrode showing thechannel where it was deposited the PVC membrane.
Potentiometric Methods: Tubular electrode
l
acrylic mold
graphite-epoxy paste
copper plate
coaxial cable
Details of the tubular electrode based
Shielded Connector
on graphite-epoxy PVC film
A = View of the support; B = View of the tubular electrode holder on the
9090support. 1 = Acrylic holders. 2 = Screws, 3 = rings of silicone rubber, 4 =coaxial cable, 5 = polyethylene tubes (input and output of fluid).
Potentiometric determination of saccharin using coated-carbon rod ISEs and a graphite-epoxy ISE
Toluidine blue O saccharinateNH3C OToluidine blue O-saccharinate Ion-pair: 5:30:65 % m/m ion-pair:DBPh:PVC
SH2N N+(CH3)2 SO2
N-
1 21
2 31
m
2 3
6 cm3
4
2 cm
0 5 cm
5
91Coated-carbon rod ISEs (1 and 2) and graphite-epoxy ISE (3)
0.5 cm
FI-Potentiometric determination of saccharin using a tubular ISE
RE
pH R
WC 6 mm
3 2
1
1 mm
TISEW
coatingS
L6 mm 1 mm
2-3 cm
Schematic diagram of the flow system and tubular ISE of carbon rod: 1) PVC membrane with ionic pair; 2) epoxy resin coating;
3) electric connection.
FIA1.0 x 10-4 – 1.0 x 10-2 mol L-1,
Manual 8.1 x 10-5 – 1.4 x 10-2 mol L-1
DL = 8.0 x 10-5 mol L-1
Slope = 53.1 + 0.4 mV dec-1
DL = 6.3 x 10-5 mol L-1
Slope = 58.9 + 0.9 mV dec-1
92Sampling frequency = 40 h-1Lifetime = 9 months (over 1000
determinations)
Transient potentiometric signals for saccharin determination
1 0 x 10-2 1 0 x 10-4 mol L-11.0 x 10 2 – 1.0 x 10 4 mol L 1,DL= 8.0 x 10-5 mol L-1
Slope= 53.1 + 0.4 mV dec-1
Sampling frequency = 40 h-1
Fatibello-Filho, O.; Aniceto, C. Lab. Rob. and Autom., 11, 234 (1999).
Eletrodo para gases (Severinghaus e Bradley)
9494