Journal of Solid State Electrochemistry

, Volume 12, Issue 10, pp 1219–1230

Modified carbon-containing electrodes in stripping voltammetry of metals. Part II. Composite and microelectrodes

  • Natalya Yu. Stozhko
  • Natalya A. Malakhova
  • Mikhail V. Fyodorov
  • Khiena Z. Brainina
Open AccessReview Paper

DOI: 10.1007/s10008-007-0474-2

Cite this article as:
Stozhko, N.Y., Malakhova, N.A., Fyodorov, M.V. et al. J Solid State Electrochem (2008) 12: 1219. doi:10.1007/s10008-007-0474-2

Abstract

The second part of the review, which covers modified carbon-containing electrodes, describes composite and microelectrodes. Electrodes made of commercial and laboratory carbon-containing composite materials are discussed. Impregnated and thick-film electrodes and microelectrodes made of carbon fibers form a separate group. Various modifiers and methods of electrode modification are presented. Prospects for the future development of solid-state modified electrodes are considered.

Keywords

Carbon-containing electrodesModified electrodesComposite electrodesMicroelectrodesStripping voltammetryMetal ions determination

Graphitized carbon and composite electrodes

The advancement of modern engineering and the use of new principles and approaches to the synthesis of carbon materials have facilitated the development of new commercial carbon–graphite materials with assigned properties. The use of the following commercially available electrode materials is reported in the literature: pencil lead [13]; spectral [4, 5], pyrolitic [6], and felt [7] graphites; carbon glass ceramic [810]; nonwoven graphite films [11]; carbon film resistors; and switches [1216]. In most cases, electrodes of these materials are modified by metal films (mercury, copper, and bismuth), molecularly imprinted TiO2 [17]. The occurrence in the last decade of new types of carbon materials “from carbon nanotubes to edge plane pyrolytic graphite” [18, 19] has significantly changed the scope and sensitivity of electroanalytical methods for the measurement of diverse targets from metals ions to biological markers. Investigators considered in detail electrochemical characteristics [20] and practical use [21] of the “edge” plane pyrolytic graphite, which proved to have a wider interval of working potentials and a low detection limit as compared to those of the basal pyrolytic graphite and GC. For example, in situ bismuth film modified edge plane pyrolytic graphite electrode was successfully applied to the ultra trace simultaneous determination of cadmium(II) and lead(II) with detection limit 5.5·10−10 and 4·10−10 M, respectively [22].

Synthetic diamonds (nitrogen- [23, 24] and boron-doped [2549]) have come into use quite recently for electrochemical measurements. In particular, a gold-coated, boron-doped, diamond thin-film electrode was used for total inorganic arsenic detection in real water samples [50]. Unlike properties of other carbon materials, which are widely used in electroanalysis, properties of synthetic diamonds became the subject of comprehensive study just about 10 years ago. The research was hindered by two circumstances: shortage of the material and the absence of conduction. The situation radically changed with the advent of highly efficient methods for growing of polycrystalline diamond compounds.

A more efficient separation, accumulation, and determination of components is achieved with electrodes of composite materials made of graphite, carbon, glassy carbon, or diamond powders and binders such as paraffin, epoxy resins, methacrylate, silicon, styrene–acrylonitrile copolymer, polyester, and silica gel. The reviews [5154] deal with properties and applications of various composite materials. Some original papers describe the use of unmodified electrodes made of graphite [5562], glassy carbon [63], template carbon [64] -polymer composites, a composite based on natural and synthetic diamonds [65], nanocomposite made of carbon nanofibers [66], and a carbon-containing material prepared by a sol-gel technology [67, 68]. Much attention is given for the study of electrochemical properties and application of graphite-epoxy composite electrodes [6972]. Specific features of the last material are its strength, chemical inertness, absence of impurities, nonswelling in water solutions, stability in organic solvents for prolonged periods, ease and simplicity of fabrication, and secure fixing of water-soluble reagents.

Table 1 gives examples of the use of modified composite electrodes in stripping voltammetry with the composite materials made under industrial and laboratory conditions using simple sol-gel, sono-gel, spin-casting, and molding technologies [73, 7492]. The electrodes shown in the table can be divided into two groups: those made of carbon- (soot, amorphous carbon) [7379] and those made of graphite-containing [8092] materials. It should be noted that the detection limit of graphite-containing materials is somewhat higher than that of carbon-containing materials. Composite electrodes may be used to achieve the electrochemical response of ground solids, iron pigments, and insoluble samples [93, 94].
Table 1

Моdified composite electrodes

Electrode material/modifier

Manner

Analyte

Detection limit, М

Supporting electrolyte

Sweep mode

Purgea

Sample

Ref.

CC/Ag3[Fe(CN)6]

bulk

Fe (III)

7.2∙10−6

0.1 М KNO3

DP CSV

+

BGD

[73]

CC /Au

bulk

Hg (II)

1∙10−10

0.035 М H2SO4 + 2 mМ KCl

LS АSV

Waters

[74, 75]

CCSG /Hg

in situ

Cu (II), Pb (II), Zn (II)

1∙10−8 (Pb)

0.1 М HNO3 + 2∙10−5 М Hg (II) (Pb), 0.1 М NaAc (Cu, Pb, Zn)

DP АSV

Fuel

[76]

CCSG/DMG

bulk

Ni (II)

2.6∙10−6

0.1 М amm.buff. (pH 8.2)

DP CSV

Waters

[77]

CCSG /9P3F

bulk

Os (IV)

2.4∙10−9

0.15 М NaF

DP АSV

Waters

[78]

CCSG/DMPT (1); DMG (2); neocuproine (3)

bulk

Fe (II) (1); Ni (II) (2); Cu (I) (3)

7∙10−6(Fe)

NaOH + 0.5 М TFAA (pH 2) (Fe), NaAc (pH 6) (Cu), TFAA (pH 9.2) (Ni)

SQW АSV

SS of leaves

[79]

GCSG/DAN

bulk

Se (IV)

1∙10−9

0.1 М HCl

LS CSV

Waters

[80]

GCSG /RNSH

ex situ

Ag (I)

4.5∙10−14

0.1 М McIlvaine buffer (pH 5)

DP АSV

Human hair

[82]

SGC/PMTP

ex situ, on surface

Hg (II)

7∙10−9

0.2 М B-R buff. (pH 4–8)

DP АSV

Waste waters

[81]

GEC /Hg,

ex situ

Сu (II), Pb (II), Cd(II)

4.4∙10−10 (Cd)

0.05 М NaAc (рН 4.5)

SQW АSV

Waters

[83]

GEC /MBT

bulk

Bi(III), Hg (II), Cu (II)

4.2∙10−9 (Hg); 3.6∙10−9 (Bi); 9.5∙10−8 (Cu)

B-R buff. (pH 3.8) (acc.); 1 М HCl (sweep)

DP АSV

+

SS, hair

[84]

GEC /8HQ

bulk

Sn (II)

4.6∙10−10

0.1 M acetate buffer (pH 5.8) (acc.); 0.05 M HCl + 2 M CaCl2 (sweep)

DP АSV

SS, hair, juice, sea water

[85]

GCC /Ag

bulk

Pb (II)

1∙10−8

0.1 М KCl + 0.005 М HCl

DP АSV

+

Waters

[86]

GCC /Hg

in situ

Pb (II)

9.7∙10−9

0.1 М H2SO4 + 2∙10−5 М Hg(NO3)2

LS АSV

BGD

[87]

GCC /Hg

in situ

Cu (II)

1.6∙10−9

0.25 М H2SO4 + 2∙10−4 М Hg(I)

LS АSV

Waters

[88]

GCC /Hg (1); GCC/DPCO (2); GCC (3)

in situ

Cu (II) (1); Pb (II) (1); Cd (II) (1); Zn (II) (1); Cr (VI) (2); Ni (II) (3); Ag (I) (3)

7.8∙10−9 (Cu); 1.4∙10−9 (Pb); 4.4∙10−9 (Cd); 7.6∙10−8 (Zn); 9.6∙10−9 (Cr); 8.5∙10−8 (Ni); 4.6∙10−9 (Cu)

0.1 М HCl + 5∙10−5 М Hg (II) (Cu, Pb, Cd); NaAc (pH 4–5) +2∙10−4 М Hg (II) + 10−4 М Ga (III) (Zn); 0.5 М HCl + 10−6 М DPCO (Cr); FB buff. (рН 5–7) (Ni); 0.05 М H2SO4 (Ag)

LS АSV (1, 3) LS CSV (2)

Model solutions

[89]

GCC /HgO

bulk

Cu (II), Pb (II), Cd (II)

7.9∙10−10(Cu); 2.4∙10−10 (Pb); 4.4∙10−10 (Cd)

0.1 М KCl + 0.01 М HCl

LS АSV

Waters

[90]

GCC + MWN/TCC

bulk

Ag (I)

5∙10−11

0.5 М NaClO4

DP CSV

Waters

[91, 92]

CC carbon composite, CCSG carbon-containing silica gel, DMG dimethylglyoxime, 9P3F 9-phenyl-3-fluorone, DMPT 4,7-dimethyl-1,10-phenanthroline, GCSG graphite-containing silica gel, DAN diaminonaphthalene, RNSH 5-(4-dimethyl amino benzelyden)-rhodamin, SGC sonogel-carbon, PMTP poly-3-methylthiophene, GEC graphite-epoxy composite, GCC graphite-containing composite, MBT 2-mercaptobenzothiazole, 8HQ 8-hydroxyquinoline, DPCO diphenyl carbazone, MWN multi-walled nanotubes, TCC thiacrown compound, bulk modifier introduced to electrode bulk preliminary, ex situ modifier fixed on surface preliminary, in situ formation of modifying layer during deposition of substance to be determined, NaAc sodium acetate, amm.buff. ammonium buffer, TFAA trifluoroacetic acid, B-R buff. Britton-Robinson buffer, acc. stage of electrochemical accumulation, FB buff. fluoride–borate buffer, EDTA ethylenediaminetetraacetic acid, DP differential-pulse, CSV cathodic stripping voltammetry, LS linear sweep, ASV anodic stripping voltammetry, SQW square-wave, BGD supporting electrolyte, SS standard sample

a“+”, after, “−” without oxygen removal

The bulk or surface modification of composite materials by metals or organic compounds considerably reduces the detection limit for metal cations. Silicon–carbon electrodes were proposed for determination of Cu (II), Pb (II), and Zn (II) after modification by mercury [76]; Ni (II) after modification by dimethyl glyoxime [77]; Os (IV) after modification by 9-phenyl-3-fluorone [78]; and Cu (I), Fe (II), and Ni (II) after modification by neocupferron, phenanthroline derivatives, and dimethylglyoxime, respectively [79]. A satisfactory reproducibility of responses of elements to be determined, a high selectivity, and the time stability of sol-gel electrodes can be noted.

Modified electrodes of composite materials are attractive because not only their surface but also the bulk can be easily modified at the stage of the composite formation [7375, 7780, 8486, 9092], facilitating fabrication of more reproducible electrodes. Simplicity of technologies used for production of many current-conducting composite materials with preset properties makes them promising for electroanalysis applications.

Impregnated graphite electrodes

Impregnated graphite electrodes (IGE), which have found application in the electroanalytical practice, are basically of two types: those impregnated with a paraffin–polyethylene mixture and those with epoxy resins. IGE are widely used by electroanalysts in Russia. Unmodified [95, 96] and modified [97129] IGE, shown in Table 2, are used in electrochemical inorganic analysis. IGE are modified by metals (Hg, Au, Cu, Tl, Jr) [97, 98114], polymer films fixing the modifier and capable of the ion exchange [115], and Mo (IV) oxocomplexes [116, 117]. The IGE surface has good adsorbability and, hence, is readily modified by reagents specific for determined ions [118129]. The IGE surface is modified most frequently, but examples of the IGE bulk modification can be found too [118, 119]. In this case, porous graphite is first held in an acetone solution of 2-mercaptobenzoxazole and then impregnated with a two-component epoxy compound under exposure to ultrasound. IGE modified by this method were used to determine Ag (I) and Hg (II). They were additionally modified in situ by mercury and rhodamine for measurements of Bi (III) and Au (III), respectively.
Table 2

Моdified IGE

Electrode material/modifier

Manner

Analyte

Detection limit, М

Supporting electrolyte

Sweep mode

Purge

Sample

Ref.

IGE-P /Hg

in situ

Pt (IV)

1.3∙10−7

1 М HCl + 13. 4 mg L−1 Hg (II)

LS АSV

Biomaterials

[97]

IGE-P /Hg

in situ

Cu (II), Pb (II)

3.7∙10−8 (Pb); 1.2∙10−7 (Cu)

0.1 М HCl + 1∙10−4 М Hg (II) + 1.2 М NaSCN

LS АSV

Model solutions

[98]

IGE-P /Hg + Cu

in situ

Se (IV)

2.5∙10−7

0.1 М HCl + 2.5∙10−5 М Hg (II) + 3∙10−5 М Cu(II)

SQW CSV

+

Foodstuffs

[99]

IGE-R

ex situ

Au (III)

5∙10−9

0.1 М HCl

LS АSV

Rocks

[100]

IGE-R /Hg

ex situ

Tl (III)

9.8∙10−12

0.05 М EDTA (pH 4.4)

DP АSV

+

Waters

[101]

IGE-R /Hg

ex situ

Cu (II), Pb (II), Cd (II)

6.3∙10−9 (Сu); 4.8∙10−10 (Pb); 8.9∙10−10 (Cd)

0.5 М NaCl (pH 3)

LS АSV

Natural waters

[102]

IGE-R /Hg

ex situ

Pb (II), Cd (II), Zn (II)

10−10

0.02 М KNO3 + 1 mМ HCl (pH 3)

LS АSV

Model solutions

[103]

IGE-P /Au

ex situ

As (III)

2.7∙10−10

0.02–0.1 М EDТА + citrate Na (рН 4–5)

LS АSV

+

Drinking, mineral waters, strong drinks

[104]

IGE-P /Au

ex situ

As (III), Hg (II)

1.3∙10−8 (As); 2.5∙10−9 (Hg)

0.1 М HCl

LS АSV

Natural waters

[105]

IGE-P /Au

ex situ

Se (IV)

3.8∙10−8

0.3 М HClO4

LS АSV

Waters

[106]

IGE-P /Au

ex situ (1), in situ (2)

As (III) (1), Se (IV) (1), Hg (II) (2)

1.0 μg g−1 (As); 0.6 μg g−1 (Se); 0.3 μg g−1 (Hg)

0.02–0.05 М EDTA (As); 0.1–0.3 М HClO4 (Se); HClO4, HNO3, HCl + Au (III) (Hg)

LS АSV

Toys

[107]

IGE-P /Аu

in situ

Hg (II)

5∙10−10

0.02–0.05 М HClO4 (or 0.1 М HNO3) + 4∙10−6 М Au(III) + 5 mМ Cl

LS АSV

Natural waters, foodstuffs

[108, 109]

IGE-R /Au

ex situ

As (III), Сu (II)

9.3∙10−8 (As); 1.1∙10−7 (Cu)

0.01 М H3PO4 + 1 mМ EDТА

LS АSV

Model solutions

[110]

IGE-R /Au

ex situ

Hg (II)

5∙10−10

0.1 М HClO4 + 0.03 М HCl

DP АSV

+

Sea sediment

[111]

IGE-R /Au

ex situ

Hg (II)

8∙10−10

0.1 М HCl

LS АSV

Waters, foodstuffs

[112]

IGE-R /Au (1); IGE-R /Cu (2)

ex situ (1), in situ (2)

As (III)

2.3∙10−7 (1); 6.3∙10−7 (2)

0.05 М EDТА (1); 0.1 М HCl + 5∙10−6 М Cu (II) (2)

LS АSV

BGD

[113]

IGE-R/Tl or In

in situ

Hg (II)

1∙10−8

0.1 М HCl + Tl (I) or In (III) (10:1 = Hg:Tl)

LS АSV

Model solutions

[114]

IGE-P/nafion

ex situ

Ag (I)

2∙10−10

0.01 М HNO3 + 0.03 М NaCl

LS АSV

Chemicals

[115]

IGE-P/Mo(VI)-OC

in situ

As (V)

2.7∙10−9

NaCl (pH 2.5)+ 1.5∙10−3 М Mo (VI)

SQW CSV

+

Waters, foodstuffs

[116]

IGE-R or IGE-P/Mo(VI)-OC

in situ

As (V)

3∙10−9 (IGE-P); 2∙10−10 (IGE-R)

1.0 М (Na, H)Cl (pH 2.5) + 1.5∙10−3 М Mo(VI) + 30 vol. % 1,4-lioxane

DP CSV

Natural, sea waters, foodstuffs

[117]

IGE-R/MBO/Rhodamine 6G

еx situ/in situ

Au (III)

1.9∙10−10

0.1 М HCl + 1∙10−6 М Rhodamine 6G (acc.); 0.1 М HCl (sweep)

DP CVА DP CSV

Sea water

[118]

IGE-R/MBO (1); IGE-R/MBO /Hg (2)

ex situ (1), ex situ/in situ (2)

Ag (I) (1), Hg (II) (1), Bi (III) (2)

1.8∙10−10 (Ag); 1.9∙10−9 (Hg); 9.5∙10−9 (Bi)

Ag: 0.1 М NaAc (рН 4.3) (acc.); 0.07 М HCl (sweep); Hg: 0.1 М FB (рН 5.5) (acc.); 0.075 М KBr + 0.1 М HNO3 (sweep); Bi: B-R buff. (рН 3.8) + 5∙10−6 М Hg (II) (acc.); 1.0 М HCl (sweep)

DP АSV

+

Sea water, urine

[119]

IGE-R/DPCD

in situ

Сr (VI)

1∙10−9

0.15 М H2SO4 + 5∙10−6 М DPCD

LS CSV

Natural, sea waters, draw of soils

[120, 121]

IGE-R/DPCO

in situ

Mn (II)

5∙10−9

amm.buff. (рН 9.2) + 3∙10−5 М DPCO

LS CSV

SS of Ni-alloy, natural waters

[122]

IGE-P/ANTPR

in situ

Mo (VI)

5∙10−10

0.3–2.0 М HCl + 0.05 М ANTPR + 0.03 М SCN

LS АSV

Natural waters

[123]

IGE-R /DMG

in situ

Ni (II)

3∙10−9

0.2 М NaCl + 2.5∙10−4 М DMG + 0.03 М NaCl + pyridine (pH 8–10)

LS CSV

Natural, waste waters

[124]

IGE-R /CE

ex situ (1), in situ (2)

Pd (II)

5∙10−9 (1); 1∙10−8 (2)

0.1 М HClO4 (1); 0.1 М HClO4 + 1∙10−2 gL−1 CE (2)

LS АSV

BGD

[125, 126]

IGE-P/ANTPR

in situ

W (VI)

1∙10−9

1 М H2SO4 + 0.078 М NH4SCN + 0.04 М ANTPR

DP АSV

Waters

[127]

IGE-P /9P3F

in situ

Sb (III), Sn (IV)

1∙10−7

0.05 М H2SO4 + (2.5–3.0)∙10−6 М 9P3F

LS АSV

Ni, Cr, SS of steels and irons

[128, 129]

For abbreviations aside from those defined here, see Table 1

IGE-P impregnated graphite electrode soaked with paraffin and polyethylene, IGE-R impregnated graphite electrode soaked with epoxy resin, Mo(VI)-OC Mo(VI) oxocomplex, MBO mercaptobenzoxazole, DPCD diphenyl carbazide, ANTPR antipyrine, CE crown ether, EDTA ethylenediaminetetraacetic acid, FB phosphate buffer, CVA cathodic voltammetry

IGE are widely used in abrasive stripping voltammetry developed by Scholtz et al. [130]. Abrasive stripping voltammetry is a new electroanalytical technique designed for qualitative and quantitative analysis of solid materials. The essence of this method is a recording of the voltammetric response of a set of solid microparticles of the analyte immobilized on an inert electrode (most frequently paraffin-impregnated graphite) both unmodified and modified, for example, with zeolites [131] immersed in an appropriate electrolyte. Voltammetry of microparticles is a rapidly growing field of research. This scheme was previously used to analyze metals, alloys, minerals, natural and synthetic sulfosalts, sulfides, and ceramic materials [132138].

Thick-film carbon-containing electrodes

So-called “screen-printed” or “thick-film” electrodes have been used on a wide scale recently. They are reproducible and inexpensive. Thanks to their good electrochemical and metrological characteristics, these electrodes can serve for environmental monitoring and foodstuff quality control [139]. Thick-film electrodes are made of carbon- [140], graphite- [141, 142], carbon-nanotube-containing [143] inks or special current-conducting, e.g., graphite-epoxy, pastes. The design and the fabrication technology of the electrodes, as described, for example, in [144], allow easy modification of their surface by immobilizing a modifier on the electrode surface or adding it to the ink before the electrode is made.

Table 3 gives examples of the use of modified thick-film electrodes for voltammetric determination of elements [145, 146192]. Metals and their oxides are the most common modifiers [145163]. Sometimes the film electrodes are modified by inorganic [164167], metalorganic [168174], and organic substances [175180]; self-assembled layers [181184]; macrocyclic compounds [185187]; polymeric films [188, 189]; and ion-exchange resins [190, 191]. Modified thick-film electrodes provide the detection limit of elements at a level of 10−8–10−10 M.
Table 3

Моdified planar carbon containing electrodes

Electrode material

Modifier

Manner

Analyte

Detection limit, М

Supporting electrolyte

Sweep mode

Sample

Ref.

(C) ink

Ag

in situ

Pb (II)

4.8∙10−9

0.1 М HNO3 + 50 mМ NaCl + 500 μg L−1 Ag (I)

DP АSV

BGD

[145]

(C) ink

Ag nano or Au nano

ex situ

Sb (III)

6.8∙10−10(Ag nano); 9.4∙10−10 (Au nano)

B-R buff. (pH 2)

DP АSV

Sea water, PP

[146, 147]

(C) ink

Au

ex situ

Hg (II), CH3Hg+

2.5∙10−9

0.05 М HCl

SQW АSV

BGD

[148]

(C) ink

Bi

ex situ

Pb (II)

1.4∙10−9

0.01 М NaAc (pH 4.5)

SQW АSV

Waters

[149]

(C) ink

Hg

in situ

Pb (II)

2.9∙10−9

1.0 М NaBr + 1.2 М HCl + 50 μМ Hg (II) + 100 μg L−1 In (III)

SQW АSV

Blood

[150]

(C) ink

Hg

ex situ

Pb (II)

1.4∙10−11

0.02 М NaAc (pH 4.2)

DP АSV SQW АSV

Waters, urine

[151]

(C) ink

Hg

in situ

Cu (II), Cd (II), Pb (II), Zn (II)

1.9∙10−6 (Cu); 6.3∙10−7(Cd); 3.1∙10−7(Pb); 8.4∙10−7 (Zn)

0.1 М MgCl2 + 10 mМ KHPh + 120 μg L−1 Hg (II)

DP АSV

BGD

[152]

(C) ink

Hg

ex situ

Pb (II), Cd (II)

10−7

0.01 М HCl

SQW АSV

BGD

[153]

(C) ink

Hg

ex situ

Cu (II), Pb (II), Cd (II)

7.9∙10−10(Cd); 1.4∙10−10(Pb)

0.02 М NaAc (pH 4.8)

DP АSV

Urine

[154]

(C) ink

Hg

ex situ

Cu (II), Pb (II), Cd (II), Zn (II)

1.6∙10−9 (Cu); 8.9∙10−10(Cd); 4.8∙10−10 (Pb); 1.5∙10−9 (Zn)

0.1 М NaAc (рН 4.0)

SQW АSV

Waters, wine

[155]

(C) ink

Hg/Сu

ex situ

Pb (II)

3.9∙10−9

0.02 М NaAc

SQW АSV

Waters

[156]

(G-E) paste

Hg

in situ

Cu (II), Pb (II), Cd (II)

4.4∙10−9 (Cd); 1.4∙10−9 (Pb); 1.6∙10−8 (Cu);

0.1–0.5 М HCl + 1∙10−4 М Hg (II)

LS АSV, DP АSV

BGD, blood

[157, 158]

(C) paste

Hg

in situ

Cd (II), Cu (II), Pb (II)

2.5∙10−8 (Cd)

0.1 М KNO3 + 0.03 M HNO3 + 1 mM Hg(NO3)2 + 0.1 M Fe(NO3)3

LS АSV

Waters

[159]

Carbonized PAN

Hg

in situ

Pb (II); Cd (II)

3.1∙10−9 (Pb); 1.8∙10−9 (Cd)

0.1 М NaAc (pH 4.2) + 10 mg L−1 Hg (II)

SQW АSV

Blood

[160]

(G) ink

Hg

ex situ

Cu (II), Pb (II), Cd (II)

1.9∙10−9 (Pb); 8.9∙10−9 (Cd); 7.9∙10−9 (Cu)

0.1 М HCl (30 mМ NaAc) (рН 4.7)

SQW АSV

Waters, soil

[161, 162]

Soot + resin + PVC

HgO

bulk

Cu (II), Cd (II), Pb (II)

1.6∙10−8 (Cu); 8.9∙10−9 (Cd); 4.8∙10−9 (Pb)

0.10 М KNO3 + 0.024 М HCl

LS АSV

Waters

[163]

(G) ink

Hg2Cl2

ex situ

Cu (II), Pb (II), Cd (II), Zn (II)

2 10−9 (Cu); 2∙10−10 (Cd); 1∙10−10 (Pb); 8∙10−10 (Zn)

0.5 M HCl (Cu, Pb, Cd); acetic-chloride buffer (Zn)

LS АSV; SQW АSV

Waters, wines

[164, 165]

(G-E) paste

Hg2Cl2/pyrocatechin

ex situ/ in situ

Fe (III)

3.6∙10−10

0.1 M NaAc + 5 10−4 M pyrocatechin

LS CSV

Waters

[166]

(G) ink

BiPO4

ex situ

Pb (II), Cd (II), Zn (II)

2∙10−9 (Pb); 4∙10−9 (Cd); 8∙10−9 (Zn)

0.1 M acetate buffer (pH 4.5)

SQW АSV

BGD

[167]

(G-E) paste

Hg (1); DPCD (2); ANTPR (3); DPCO (4); DAN (5); DMG(6)

in situ

Cu (II), Pb (II), Cd (II), Zn (II) (1); Сr (VI) (2); Mo (VI), W (VI) (3); Mn (II) (4); Se(IV) (5); Ni (II) (6)

10−9 (Cu, Pb, Cd, Zn, Cr); 1∙10−9 (Mo); 3∙10−9 (W); 6∙10−9 (Mn); 1∙10−8 (Se); 1∙10−9 (Ni)

0.14 М NaCl + 0.04 М HCl + 1∙10−4 М Hg (II) (Cu, Pb, Cd, Zn); 0.15 М H2SO4 + 5∙10−6 М DPCD (Cr); 0.5–0.9 M HCl + 0.03–0.07 M NH4SCN + 0.02–0.05 M ANTPR (Mo, W); amm.buff. + 3∙10−5 М DPCO (Mn); 0.1 M HCl + 6.3∙10−5 M DAN (Se); 0.1 M KCl + 2.5∙10−4 M DMG (Ni)

DP АSV (Cu, Pb, Cd, Zn, Mo, W); LS CSV (Cr, Mn, Se, Ni)

Waters

[168, 169]

(G-E) paste

Hg-DDC; Hg-PDTC or HgAc + nafion (1); Au PDTC, AuCl3 + nafion or HAuCl4 (2)

ex situ

Cu (II), Pb (II), Cd (II), Zn (II), Sn (IV) (1); Hg (II) (2); As(III) (2)

10−9 (Cu, Pb, Cd, Zn); 8∙10−9 (Sn); 2.5∙10−11(Hg); 1.4∙10−8(As)

0.1 M HCl (Cu, Pb, Cd, Zn); 4.6 g L−1 NH4Cl + 9.6 g L−1 (NH4)2C2O4 + 9.4 g L−1 НСl + 10 mgL−1 МB (Sn); 0.1 М H2SO4 + 4 mM HCl (Hg); 2 M HCl (As)

LS АSV; DP АSV

Juices, waters

[170174]

(G-E) paste

NRS

in situ

Сo (II)

7.3∙10−12

0.01 M citrate buffer + 5 10−5 M NRS

LS CSV

Waters

[175]

(G) ink

SF

ex situ

Cu (II), Pb (II), Cd (II), Zn (II)

8∙10−9 (Cu); 3∙10−9(Pb); 2∙10−9(Cd); 8∙10−8 (Zn)

0.1 M NaAc + 0.35 M NaCl + 10−3 M HCl

LS АSV

Waters

[176]

(G) ink

SF

bulk

Mn (II)

1∙10−9

0.1 M NaCl + 0.1 M amm.buff. (рН 9.2)

LS CSV

Waters

[177]

(C) ink

DMG

bulk

Ni (II)

8.5∙10−8

0.1 М amm.buff. (pH 9.2)

DP CSV

Waters

[178]

(SGG) paste

DAN

ex situ

Se (IV)

1.3∙10−9

0.1 M HCl

LS CSV

Waters

[179]

(C) ink

Alizarin

bulk

Al (III)

7.0∙10−7

0.1 М amm.buff. (pH 9)

DP АSV

Soils

[180]

(G) ink

Sol-gel film + PT

ex situ

Fe (II), Fe(III)

1∙10−6

0.1 M acetate buffer

LS АSV

Waters, wines

[181, 182]

(G) ink

Ac-Phos SAMMS

ex situ

Pb (II)

4.4∙10−9

0.3–0.5 М HCl

SQW АSV

BGD

[183]

(G) ink

Sal-SAMMS

ex situ

Eu (III)

6.6∙10−8

0.05 M acetate buffer (pH 4.6–6.5) (acc.); 0.1–0.2 M NH4Cl (sweep)

SQW АSV

BGD

[184]

(G) ink

Calix[4 or 6]arene

ex situ

Pb (II), Cd (II)

2.4∙10−8 (Pb); 2.5∙10−8 (Cd)

1 М amm.buff. (рН 10.5-Pb, рН 6.5-Cd) (acc.); 0.1 М HCl (sweep)

DP АSV

Waters

[185, 186]

(C) ink

CEBM

ex situ

Pb (II), Cd (II)

0.8∙10−8 (Pb); 0.6∙10−8 (Cd)

0.01 M KNO3 (pH 2)

DP АSV

ES

[187]

(G) ink

PAN

ex situ

Pb (II)

7.2∙10−8

0.37 М amm.buff. (рН 10.5) (acc.); 0.1 М HCl (sweep)

DP АSV

Waters

[188]

(C) ink

SPE/pcPVP

ex situ

Hg (II)

1.6∙10−8

0.01 M KCl + 0.02 M H2SO4

DP АSV

CP

[189]

(C) ink

Semi chelate Q10R

bulk

Hg (II)

1.0∙10−11

0.5 М NaCl + 0.1 М NaAc (pH 4.5)

DP АSV

Waters

[190]

(G) ink

Dowex 50W-X8

bulk

Cu (II)

7.9∙10−9

5 mМ FB (рН 5.7)

DP АVA

Waters

[191]

For abbreviations aside from those defined here, see Tables 1 and 2

(G) or (C) ink graphite- or carbon-containing ink, (G-E) paste graphite-epoxy paste, PAN polyacrylonitrile, PVC polyvinylchloride, (SGG) paste sol-gel graphite paste, DAN diaminonaphthalene, NRS nitroso-R salt, Hg-DDC mercury diethyldithiocarbamate, Hg-PDTC mercury pyrrolidine dithiocarbamate, HgAc mercury(II) acetate, Au-PDTC aurum pyrrolidine dithiocarbamate, Ac-Phos SAMMS acetamide phosphonic acid self-assembled monolayer on mesoporous silica, SF hetaryl-substituted formazan, SPE/pcPVP 1,5-dibromopentane partially (7%) cross-linked poly(4-vinylpyridine), KHPh potassium hydrophthalate, MB methylene blue, PLH poly-l-histidine, CEBM crown-ether based membrane, AVA anodic voltammetry, PP pharmaceutical preparations, CP cosmetic productions, ES environmental samples

Plasma, laser, temperature, and electrochemical treatments of the surface of thick-film electrodes can influence its activity, increase the rate of electron transitions, and change the electrochemical process reversibility. Preliminary anodic polarization of an electrode [192] not only extended the range of the working potentials but also improved its sensitivity. Voltammetric, microscopic, and spectroscopic studies suggested that the reason for the favorable effect of the anodic activation on the electrochemical properties of the electrode was enrichment of its surface in new functional groups, removal of unwanted inclusions from the surface, and the increase in the surface roughness.

Carbon microelectrodes

Pioneering research into the kinetics of electrochemical reactions on microelectrodes (ME) with diameters of units to several tens of micrometers revealed that the electrodes demonstrated new properties as their diameter decreased. Specifically, capacitive currents, which are the main factor that limits fast electrochemical processes on solid electrodes, decrease to practically insignificant values, the mass transfer rate of the substance to ME increases, the electrochemical equilibrium is established much faster than on standard electrodes, and the ohmic potential drop iR is negligibly small for ME. The unique properties of ME make it possible to analyze and use solutions with a high ohmic resistance, including pure solvents, in voltammetry and extend the range of test compounds, primarily organic substances and extracts. Growing attention is given to ME because they can serve as the basis for development of simply designed and, hence, easily realizable miniature sensors and detectors for operation in flowing liquid systems and measurement of bioactive substances in vivo. The electrochemical properties, constructions, fabrication methods, and analytical capabilities of ME are described in reviews and original papers [193199].

Nonmetal ME are made of carbon, graphitized and glassy-carbon fibers, filaments, or carbon pastes. Carbon fibers are synthesized by thermal decomposition of fibers based on cellulose or polyacrylonitrile. They have large chemical resistance and good current conduction. Along with favorable properties of the carbon fiber, one should take into account its capacity for hydrogen and oxygen chemisorption especially at a potential of +1.4 V, which can lead to irreversible changes of the surface and the decrease in the detection limit of elements. In this connection, it is recommended [200] to realize the electrochemical accumulation of elements on carbon-fiber ME at potentials when the oxygen and the hydrogen adsorption is at a minimum. Unlike metal ME available in a variety of shapes (hemispherical, conical, cylindrical, disk, as a ring, or as a disk with a ring), carbon ME are generally shaped as a disk. When ME are made of the carbon fiber, the critical importance is attached to the technology used to cover the fiber with the insulating material because the insulation quality ultimately determines the mechanical strength and the operating stability of the electrode. A new technology by which ME are covered with a quartz film solves this problem to some extent. The film is deposited from the vapor phase including silicon carbide, hydrogen, and oxygen [201]. The components mutually interact to form quartz gradually precipitating on carbon fibers. Coatings made by this technology have no cracks and hermetically insulate the fibers.

The problem of measuring extremely low currents at the level of nano- and picoamperes on ME is solved by the use of up-to-date, highly sensitive electrochemical equipment or ME arrays (MEA) whose desired signal can be integrated and measured by standard electrochemical analyzers and polarographs. ME systems are made using methods of microelectronics, electron- and ion-beam technologies, X-ray and high-temperature lithography, and photolithography. It should be noted that physical methods of producing ME systems are rather expensive and laborious.

The lower detection limit of determinable concentrations on electrodes made of a single unmodified carbon or graphite fiber is 10−7–10−9 M [202–212]. Still lower detection limits of 10−8–10−10 M were achieved with mercury-, gold-, and bismuth-modified ME, MEA and CNTA [213–227]; see Table 4.
Table 4

Modified carbon micro(nano)electrodes

Electrode material/modifier

Manner

Analyte

Detection limit, М

Supporting electrolyte

Sweep mode

Purge

Sample

Ref.

GF (d = 8 μm)/Hg

in situ

Cd (II), Pb (II)

5∙10−10

0.84 mМ NaAc

SQW АSV

BGD

[213]

CF /Hg

in situ

Pb (II)

4.8∙10−10

1∙10−7 М Hg (II)

LS АSV

Natural waters

[214]

CF (d = 8 μm)/Hg

in situ

Zn (II)

1∙10−7

0.15 М FB + Hg (NO3)2

SQW АSV

Insulin

[215]

CF /Hg

in situ

Cu (II), Pb (II)

2.9∙10−9 (Pb); 3.1∙10−8 (Cu)

0.1 М KNO3 + 0.1 М HNO3 (pH 1) + 0.01 mМ Hg(NO3)2

LS АSV

+

Natural and mineral waters

[216]

CF (d = 30 μm)/Hg

in situ

Pb (II), Cd (II), Zn (II)

1∙10−10 (Zn)

0.01 М KCl + 1∙10−6 М Hg (II) + 0.033 М HNO3

LS АSV

+

Natural waters, rainfalls

[217]

CF (d = 6 μm)/Hg

ex situ

Cu (II), Pb (II)

1∙10−7

0.1 М NaAc

LS АSV

+

Natural waters

[218]

GCF (d = 10 μm)/Hg,

ex situ

Zn (II)

7.6∙10−7

10 mМ KNO3 + 10 mМ HNO3

SQW АSV

BGD

[219]

GCF (d = 8 μm)/Hg

ex situ

Cu (II); Pb (II); Cd (II)

10−8

0.01 М HCl

DP АSV, SQW АSV

+

Natural waters

[220]

CF (d = 30 μm)/Au

in situ

Hg (II)

8.1∙10−11

0.1 М HClO4 + 5 mМ HCl + 5∙10−7 М Au (III)

DP АSV

Natural waters

[221]

CF/Bi

in situ

Tl (I), Cd (II), Zn (II), Pb (II)

10−8–10−9

0.1 М NaAc (рН 4.5) + 400 μg L−1 Bi (III)

SQW АSV

BGD

[222]

CF/Bi/cupferron

ex situ/ in situ

U (VI)

1.3∙10−9

0.1 М NaAc (рН 4.6) + 7.5∙10−5 М cupferron

SQW АSV

Sea waters

[223]

CF (d = 7 μm)/Bi (1); CF/Bi/DMG (2)

ex situ (1), ex situ/in situ (2)

Pb (II) (1), Cd (II) (1), Co (II) (2), Ni (II) (2)

1.2∙10−9 (Co); 1.5∙10−9 (Ni)

0.05 М NaAc (pH 4.5) (Сd, Pb); 0.01 М amm.buff. (pH 9.2) + 5∙10−5 М DMG (Co, Ni)

SQW CSV (Co, Ni), SQW АSV (Cd, Pb)

Model solutions

[224]

CMEA /Hg

in situ

Cd (II), Pb (II)

1.4∙10−9 (Pb); 2.7∙10−9 (Cd)

0.1 М NaAc + 5∙10−5 М Hg(NO3)2

SQW АSV

+

Drinking water

[225]

CMEA (d = 7 μm)/Hg

in situ

Cd (II), Pb (II)

1∙10−6

0.1 М KNO3 (pH 1.7, HNO3) + 0.38 mМ Hg (II)

LS АSV

+

Model solutions

[226]

CMEA (d = 10 μm)/Hg

in situ

Pb (II)

1.3∙10−7

1.2 М HCl + 0.046 mМ Hg (II)

SQW АSV

Blood

[227]

CNTA/Bi

in situ

Pb (II), Cd (II)

2∙10−10 (Pb); 3.6∙10−10 (Cd)

0.1 М acetate buffer (pH 4.5) + 5∙10−4 μgL-1 Bi(III)

SQW АSV

BGD

[228]

For abbreviations aside from those defined here, see Tables 1 to 3

GF graphite fiber, CF carbon fiber, GCF glassy-carbon fiber, CFA carbon fiber array, CMEA carbon microelectrode array, CNTA carbon nanotubes array

Future trends

Having passed the point of centuries and marched into the twenty-first century, voltammetry is advancing in the direction concisely characterized by Wang [229] as “faster, cheaper, simpler and better.” This is largely because the main line of research changed from elaboration of the theory and equipment to development and application of new electrodes, sensors, and transducers in electroanalysis. Special emphasis is on the solution/electrode interface and the selective response formed on this interface. A new generation of electrodes with chemical or physical modification of the surface is under development. A great number of studies concerned with selection of modifiers, their immobilization on the solid surface, and the use of chemically modified electrodes (ChME) provide strong evidence for sincere interest paid by researchers to this problem. A wealth of experience has been accumulated in development of ChME, some features specific to fixing of modifiers on various matrices have been established, and conditions have been formulated for the electrochemical accumulation and determination of some substances on modified electrodes. However, the phenomenological stage of the ChME development is not complete because a diversity of modifiers and variants of their immobilization on electrodes will give researchers a wide scope of work for a long time to come.

It follows from the literature survey that a very promising and hopeful line of development of electrochemical sensors is the use of nanoparticles in electroanalysis [230232] and the creation of micro- and nanoelectrode arrays, which can uniquely measure the electrochemical response in nonconductive media and unstirred electrolytes. However, the technologies used for the production of ME ensembles are extremely complicated and unavailable for ordinary research laboratories, suggesting the need to develop new methods of their fabrication. The creation of ordered nanostructures by traditional methods is an impracticable task, and in this case, it is appropriate to use the “bottom to top” rather than the “top to bottom” strategy. A proven fact is that nanoparticles of similar dimensions, which are synthesized “from top” by dispersion and “from bottom” by construction from atoms, are sharply different. The structure of the initial sample is preserved in dispersion particles, whereas particles formed by aggregation of atoms can have another arrangement of atoms influencing the electronic structure and chemical properties. Furthermore, processes of self-organization and evolution of modified layers on graphite-containing electrodes are quite possible because of the high surface energy of the graphite-containing matrix.

It is reasonable to expect that the next stage of development of solid-state electrodes will include comprehensive studies of the electrode surface, elaboration of physical concepts for prediction of properties and characteristics of modified electrodes, and transition from micro- to ultramicro- and nanostructures on the electrode surface that would profoundly alter its properties. At this stage of development, study, and use of electrochemical sensors, we shall have to answer a number of questions: how the surface microgeometry influences the electrochemical activity of the modifier and the response parameters, how machining of the surface influences the electrochemical activity of the modifier and the electrode process, how the surface of the modified electrode can be made reproducible and the response stable, how to avoid formation of passivating films which impair electroanalytical performance of the electrodes, and other questions. This task will require performing a comprehensive systematic study of all links in the integral chain “electrode surface–modifier–response–SV analysis.”

Acknowledgements

Financial support of Russian Foundation for Basic Research (project No. 07-03-96070-r_ural_a) and International Science and Technology Center (projects Nos. 342, 2132 and 2897) is gratefully acknowledged.

Open Access

This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.

Copyright information

© The Author(s) 2007

Authors and Affiliations

  • Natalya Yu. Stozhko
    • 1
  • Natalya A. Malakhova
    • 1
  • Mikhail V. Fyodorov
    • 1
  • Khiena Z. Brainina
    • 1
  1. 1.Ural State University of EconomyEkaterinburgRussia