Interrupted amperometry: the new possibilities in electrochemical

Pure Appl. Chem. 2017; 89(10): 1459–1469

Conference paper

Ekaterina Semenova, Daria Navolotskaya and Sergey Ermakov*

Interrupted amperometry: the new possibilities

in electrochemical measurements

DOI 10.1515/pac-2017-0302

Abstract: Interrupted amperometry is a new highly sensitive method for diffusion current measuring. The

main feature of the proposed technique is the use of capacitive current as the analytical signal together with

the faradaic current. The conventional electrical circuit for amperometric measurements is complemented

by a switcher that enables periodical interruption of the circuit. The technique was successfully applied for

direct amperometric determination of lead, cadmium and iron ions, phenol and hydroquinone; for determi-

nation of dichromate ion via titration; for determination of dissolved oxygen in water by Clark-type sensor.

In all the mentioned cases the achieved values of analytical characteristics are significantly better than

for conventional amperometric methods. There are limitations and perspectives of the proposed technique

considered.

Keywords: amperometry; analytical chemistry; aqueous solutions; chemical sensors; electrochemistry;

electrodes; heavy metals; iron; Mendeleev XX; oxygen; phenol; sensitivity; trace elements.

Introduction

Amperometry and voltammetry are powerful tools of analytical chemistry, including electrochemical

sensors [1–4], detection in chromatography [5–7], flow analysis [8–10], titration [11, 12], etc. Sensitivity of

these methods is defined by the signal-to-noise ratio [13, 14]. Traditionally, the signal is associated with the

diffusion controlled faradaic current produced by the charge transfer reaction of the analyte. The residual

current, consisting of the capacitance or the charging current and the faradaic currents caused by the reduc-

tion or oxidation of electroactive impurities, are conventionally referred to the noise. The capacitance current

appears to be the main interference. Thus, the increase in sensitivity in voltammetry and amperometry is

usually achieved by reduce of the capacitance current or by magnification of the faradaic current. One can

distinguish two general approaches to enhancing the signal-to-noise ratio – mathematical and instrumental

methods (see Table 1).

Mathematical techniques operate with experimentally collected data, and effectively eliminate noise-

like signals thus improving sensitivity and resolution. However, these methods do not improve the analyti-

cal signal physically. Moreover, in some cases signal processing can result in the loss of a useful part of

the current. Separation of the capacitance and faradaic currents is realized in instrumental methods based

Article note: A collection of invited papers based on presentations at the XX Mendeleev Congress on General and Applied

Chemistry (Mendeleev XX), held in Ekaterinburg, Russia, September 25–30 2016.

*Corresponding author: Sergey Ermakov, Saint-Petersburg State University, Institute of Chemistry, Department of Analytical

Chemistry, Saint-Petersburg, Russian Federation, e-mail: s.ermak[email protected]

Ekaterina Semenova and Daria Navolotskaya: Saint-Petersburg State University, Institute of Chemistry, Department of Analytical

Chemistry, Saint-Petersburg, Russian Federation

4.0International License. For more information, please visit: http://creativecommons.org/licenses/by-nc-nd/4.0/

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E. Semenova etal.: Interrupted amperometry: the new possibilities in electrochemical measurements

on time- and phase-selective current measurements. Various stripping techniques provide great sensitivity

because of the faradaic current magnification due to analyte preconcentration.

A fundamentally new approach to enhancing the signal-to-noise ratio in amperometry was first pro-

posed by Moshkin and Khustenko in 2012 [46]. The idea is to include the capacitive current in the analytically

useful part of the signal together with the faradaic current. Technically this is realized by adding a switcher

to the conventional electrical circuit for amperometric measurements. That way the measuring circuit is peri-

odically interrupted and the structure of the analytical signal becomes more complicated. The new method

was called “interrupted amperometry” (IA) [47]. Here we present a short review of its analytical applications

based on our recent studies and discuss its possibilities for analytical chemistry.

The principle of interrupted amperometry

The theoretical consideration of interrupted amperometry as well as the design of the original home-made

potentiostat “ComPot” were given in detail in our previous work [47]. Here we present only the key points of

the theory that are essential for understanding the principle of the method under consideration. The scheme

of the measuring electrical circuit for interrupted amperometry is presented on Fig. 1.

We assume that the measurement is performed under stationary diffusion of a depolarizer and the

polarizing potential difference is constant and belongs to the limiting current potential region, i.e. the dif-

fusion flow to the working electrode is constant. In this case the circuit part consisting of the serially con-

nected charge transfer resistance (R

) and the Warburg impedance (W) can be replaced by the value of direct

current:

Fig. 1:(a) General scheme of the measuring electrical circuit for interrupted amperometry. (b) Simplified circuit for the locked

state. (c) Simplified circuit for the opened state. P, potentiostat providing the polarizing voltage; R

, total ohmic resistance of

electrochemical cell; R

, charge transfer resistance; C

, double layer capacity; W, Warburg impedance; S, switcher; I

(t), meas-

ured current; I

, direct current of electrochemical reaction; I

(t), current emerging in the outer circuit path at the locked state;

(t), double layer discharging current at the opened state.

Table 1:Main approaches to enhancing the signal-to-noise ratio.

Mathematical methods Instrumental methods

– Derivative voltammetry [–]

– Fourier transformation [–]

– Wavelet transformation [–]

– Time-selective current measurements:

– Pulse voltammetry [–]

– Differential pulse voltammetry [, ]

– Square-wave voltammetry [–]

– Phase-selective current measurements:

– Alternating current [–], including sinusoidal voltammetry [–]

– Stripping techniques [–]

– Interrupted amperometry [–]

E. Semenova etal.: Interrupted amperometry: the new possibilities in electrochemical measurements

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nFAC=

(1)

where n is the number of electrons, involved in electrochemical reaction; F is the Faraday constant; A is the

surface area of the working electrode; D is the diffusion coefficient; δ is the thickness of the Nernst diffusion

layer;

is the bulk concentration of the analyte.

The switcher (S) locks the circuit for the period of time t

(µs) and then opens the circuit for the period of

time t

(ms). The sum of these times is called “the period of switching”:

Ttt

(2)

The switching is performed during the entire experiment. After several first periods the full charging of

the capacitor (C

) is achieved. Then at every locking of the circuit the capacitor is recharged by the current

(t), that emerges in the outer circuit path. At every opening of the circuit the double layer (DL) partially

discharges. This process produces the current I

(t) that supports the current of electrochemical reaction.

Recharging and discharging of the capacitor are repeated until a stationary state is achieved. This state is

characterized by the current I

(t) that can be measured in the outer circuit path when the switcher locks the

circuit. The average value of I

(t) is used as analytical signal and is proportional to the diffusion current pro-

duced by the analyte discharge:

(3)

The T/t

ratio serves as an amplification factor and usually its value is of several orders. However, this

coefficient practically amplifies not only the analytically useful diffusion current I

, but also all the noise cur-

rents I

produced by interfering processes. Therefore, the expression (3) should be written as follows:

()

mdi

∑

(4)

where I

are interfering currents depending on the experimental conditions and set up.

Experimental

Electrochemical measurements were performed using a home-built computer controlled potentiostat

“ComPot” that allows to work in direct-current and interrupted-current modes. High-performance potentio-

stat provides transition time of not more than 10 µs. The device offers the opportunity to compensate of the

initial current.

All electrodes were supplied by Metrohm (Switzerland), unless otherwise is indicated in the text below.

Measurements were carried out at room temperature in a Faraday cage. The reagents used were of analyti-

cal grade. All aqueous solutions were prepared using deionized water of resistivity 18.2 MΩ cm (25 °C, D-301

deionizer, Akvilon, Russia).

Ideal case: the determination of cadmium and lead at the static

mercury drop electrode by direct IA

Mercury electrodes are often referred to as the “ideal” working electrodes [14]. In case of an ideally polarized

electrode the applied charge is fully utilized to DL charging in a wide potential range. Usually electrochemi-

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E. Semenova etal.: Interrupted amperometry: the new possibilities in electrochemical measurements

cal reactions occurring at mercury electrodes are not affected by side reactions. Thus, the expression for the

measured current (4) in case of mercury electrode usage as a working electrode for IA measurements can be

transformed into a rather simple form:

imp

()

md tr

II I

=++

(5)

where I

imp

is the current caused by the reduction or oxidation of electroactive impurities, I

is the transition

current corresponding to the process of potential setting after switching. If the transition time of potentiostat

is at least ten times less than the locking time, the value of I

becomes negligible. The potentiostat used for

IA measurements provides the transition time of not more than 10 µs. So, the latter summand in equation (5)

can be neglected. Therefore, the interfering (or noise) current occurs only because of the presence of electro-

active impurities in case of mercury electrode. That’s why the first analytical experiments with interrupted

amperometry were performed at the fine static mercury drop electrode (SMDE). The choice of model analytes,

namely cadmium and lead, is explained by their high toxicity and abundance [49, 50], and hence, the high

relevance of their determination in environmental analytical chemistry.

Cadmium (II) and lead (II) ions were determined in aqueous solutions via interrupted amperometry

in direct mode. The measurements were carried out in a three-electrode cell of VA Computrace analyzer

(Metrohm, Switzerland) attached to the potentiostat “ComPot”. The cell consisted of the static mercury drop

working electrode (drop size ca. 0.6mm

), silver/silver chloride reference electrode with double junction and

platinum counter electrode. Stirring was provided by a mechanical rod stirrer with the speed of 1600rpm.

Supporting electrolyte was acetate buffer solution with pH 5. The following timing parameters were used:

locking time t

= 100 µs, opening time t

= 300ms. Amperometric measurements were conducted at the poten-

tial belonging to the limiting current potential region. Preliminary voltammetric experiments showed that

the proper detection potential for cadmium (II) ions is −0.60 V (vs. silver/silver chloride electrode), for lead

(II) ions – −0.40 V.

Ultrasensitive electrochemical methods of analysis require extra attention to the presence of even the

smallest amounts of electroactive impurities, primarily dissolved oxygen. In order to study the influence of

oxygen presence on IA measurements amperograms were recorded with additions of deionized water satu-

rated by atmospheric oxygen (black line of Fig. 2) and with additions of the standard solution containing

cadmium (II) ions (red line of Fig. 2).

–30

–40

–50

–60

–70

–80

100 200 300 400

Time (s)

Cathodic current (mkA)

500 600 700

800

Fig. 2:The influence of dissolved oxygen presence on IA measurements. a (black) – Amperogram obtained with additions of

deionized water saturated by atmospheric oxygen. b (red) – Amperogram obtained with standard additions of Cd

solution. c

(blue) – Amperogram obtained with standard additions of deoxygenated Cd

solution. d (pink) – Amperogram obtained with

standard additions of deoxygenated Cd

solution. The area above the solution was blown with argon during the measurement.

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As it can be seen in Fig. 2, the obtained amperograms have similar forms. This means that the standard

solution of Cd

needs to be released from oxygen. Therefore, all standard solutions used for direct IA meas-

urements were bubbled with ultrapure argon for at least 40min prior to their use.

Amperogram obtained with additions of the standard Cd

solution after the described procedure was

recorded in a more sensitive current range (see the blue “c” line of Fig. 2). However, the continuous current

drift does not allow us to identify stairs corresponding to the additions of the analyte. This stable current

decrease was caused by oxygen present in the area above the solution in the measuring cell. In order to elimi-

nate this interference the described area was blown by ultrapure argon during direct IA measurements. As

a result, amperogram was obtained with well-defined stairs each corresponding to the standard addition of

ions (the pink “d” line of Fig. 2).

The analytical possibilities of the proposed technique for determination of lead and cadmium at

SMDE were evaluated. It was found that the dependence of the measured current on Cd

concentration

is linear in the range from 1 till 200nM (y = 10

x + 17.599, r

= 0.998) and for Pb

ions – from 5 till 200nM

(y = 2*10

x + 9.2191, r

= 0.995). Practical limits of detection (LOD), calculated as three times the signal to

noise ratio, are 0.26nM and 0.79nM for cadmium (II) and lead (II) ions respectively. These LOD values are

typical for the present-day stripping techniques utilizing amalgam concentration [51], but are quite remark-

able for direct amperometry.

General case: interrupted amperometry using solid electrodes

The use of mercury electrodes in the practice of analytical chemistry is often associated with some experi-

mental manipulation difficulties. That is why it is important to consider the application of solid working

electrodes for IA measurements.

Solid electrodes are characterized by the significantly narrower region of the ideal polarizability. In this

case the applied charge is utilized not only for DL charging but also for various processes associated with

the charge transfer. In general case the residual current is related to all the processes occurring at the elec-

trode-solution interface. The following processes can appear when we use solid electrodes: electrochemi-

cal dissolution of electrode material; formation of oxide films; adsorption of solvent components (oxygen

and hydrogen for water); electrochemical instability of solvents (release of oxygen in the anodic region and

release of hydrogen in the cathodic region for water). Consequently, the sensitivity of IA measurements is

influenced by the magnitude of the current associated with non-ideal polarizability of working electrode and

the current caused by reduction or oxidation of electroactive impurities, since current types are not depend-

ent on the analyte concentration, but are dependent on the gain value. That is why the expression (4) for the

measured current in general case can be presented as following:

impnonid

()

II I

=++

(6)

where I

nonid

is the current associated with various processes occurring on the electrode surface and respon-

sible for its non-ideal polarizability. Therefore, when planning an IA experiment it is important to select the

material of the working electrode that is characterized by the minimum value of background current in the

area of analyte’s detection potential. We used solid electrodes for the direct IA determination of hydroqui-

none, phenol and iron.

The determination of hydroquinone and phenol

The determination of hydroquinone was carried out in a three-electrode cell using phosphate buffer

solution (PBS) with pH 6.9 as a supporting electrolyte. The reference electrode was silver/silver chloride

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E. Semenova etal.: Interrupted amperometry: the new possibilities in electrochemical measurements

electrode and the auxiliary electrode was a glassy carbon crucible. The following electrodes were con-

sidered as working: rotating disk electrodes made of gold, platinum, and glassy carbon (S = 0.78mm

)

and polymeric polyethylene- and carbon-based composite electrode (Tom’analit, Tomsk) (S = 1.96mm

In order to choose the optimum material of the working electrode, dependences of current density on

potential were registered using all of the mentioned electrodes. The obtained results are summarized in

Fig. 3.

These voltammograms were registered at the stepwise potential sweep. The interrupted mode of the

measurements requires the presence of at least one period of switching during a step. Consequently, the

sweep rate for the specified period of switching (100ms/100 µs) should not exceed 4mV/s. In order to

obtain sufficiently detailed voltammograms we used 1mV/s sweep rate. Three regions (roughly indicated

by two vertical solid lines on Fig. 3) can be distinguished for the four presented graphs. In the first region,

a sharp decrease and then an increase in current is observed due to the charging of DL capacitance and

also to the attainment of the initial potential value. The second region is a plateau and hence it corre-

sponds to the working region of the electrode. In the third region a smooth but considerable increase in the

background current is likely associated either with electrochemical decomposition of the solvent or with

electrochemical corrosion of the working electrode material. We compared the values of current density

in the limiting current potential range (from 0.5 till 0.9 V) of hydroquinone. As it can be found on Fig. 3

the least residual current related to non-ideal polarizability of electrode is demonstrated by the composite

electrode. Consequently, the use of this electrode can provide more sensitive determination as compared

with the other electrodes under study. The polymeric carbon-based electrode was, thus, selected as the

optimum for quantitive hydroquinone determination. The analogous experiment described in [48] was

conducted using a 1 % solution of sulfuric acid as a supporting electrolyte for selecting the most suitable

electrode for phenol determination. It was found that in this case, the composite electrode is the most

appropriate too.

Analytical characteristics of direct IA for the quantitive determination of hydroquinone and phenol

using the polymeric carbon-based composite electrode were evaluated. It was shown that the dependence of

the measured current on phenol concentration is linear in the range from 0.5 till 3 µM, and from 0.1 till 5 µM

for hydroquinone. Limits of detection calculated using the 3σ-criterion were found to be 8.8 nM for phenol

and 0.3nM for hydroquinone. It should be noted that these LOD values are characteristic for amplification

factor of 4000, i.e. for the specified period of switching. Sensitivity is defined by the slope of the linear

region of calibration curve and reached the value of 76 nA/µM for phenol determination and 75 nA/µM for

hydroquinone [48].

–50

–100

–150

0 250 500

Potential (mV)

123

Current density (mkA*mm

–2

)

750 1000

Fig. 3:Selection of the working electrode material for hydroquinone determination. Voltammograms were obtained using:

a–platinum electrode; b – gold electrode; c – glassy carbon electrode; d – polymeric carbon-based composite electrode.

E. Semenova etal.: Interrupted amperometry: the new possibilities in electrochemical measurements

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The determination of iron

The similar approach to the selection of the working electrode material was applied for the determination of

iron. Cyclic voltammograms were registered using carbon and gold RDE of the same 2mm diameter in blank

supporting electrolyte solutions and in solutions containing Fe

ions. The obtained curves are shown in

Fig.4. If we compare the values of the residual current registered on blank voltammograms in the regions of

limiting current, for example, at +0.1 V in case of carbon RDE (see the black “a” line on Fig. 4) and at +0.7 V

in case of gold RDE (see the blue “c” line of Fig. 4), we can notice the difference of about one thousand times.

On the one hand, this means that the preferable electrode for iron determination is carbon RDE. On the other

hand, the used potentiostat is able to compensate of the initial current, thus, providing additional possibili-

ties for sensitivity enhancing. Therefore, analytical characteristics were evaluated for iron determination at

both carbon and gold RDEs.

Determination of iron (III) at a carbon rotating disk electrode (RDE) in aqueous solution by direct IA

is described in [47]. It was found that the theoretical limit of detection calculated from the calibration plot

is 3 nM. The calibration curve is linear in the whole investigated concentration range from 0.02 to 0.38 µM

and gives a value of 1.22 µA µM

−1

for the sensitivity. These promising characteristics were compared with the

values obtained in conventional direct-current amperometry mode with other experimental conditions being

the same: 0.2 µM and 0.81 nA µM

−1

for LOD and sensitivity, respectively. The accuracy verification of the pro-

posed technique showed that it does not produce any significant systematic errors.

Similar experiment was performed at gold RDE as a working electrode for iron (III) determination. Silver/

silver chloride reference electrode and platinum counter electrode were used. Supporting electrolyte was

0.1M HCl prepared by the dilution of concentrated ultrapure hydrochloric acid with deionized water. Detec-

tion potential was held at +0.70 V. Locking time was 100 µs and the period of switching was 300ms. Calibra-

tion plot (y = 10

x + 36.947, r

= 0.9995) obtained under stated conditions by the method of standard additions

was found to be linear in the concentration range from 0.01 till 1 µM of Fe

ion. The practical LOD reached the

value of 2.5 nM, which is very close to the theoretical LOD obtained at carbon RDE. The proposed technique

was tested on real samples of Baltic Sea bottom water. After acidic microwave-assisted sample preparation

these 11 water samples were analyzed by IA and electrothermal atomic absorption spectroscopy (ETAAS)

using AA-7000 spectrophotometer (Shimadzu). Results obtained by these two methods are presented in

Table2 and show good agreement with each other. This means that direct IA can be successfully applied in

practical analytical chemistry.

6000

4000

2000

–2000

–4000

–6000

–8000

0 200 400

Potential (mV)

Current (nA)

600 800

Fig. 4:Selection of the working electrode material for iron determination. a – Cyclic voltammogram obtained using a carbon

RDE in 0.1M nitric acid as supporting electrolyte without any additions, b – voltammogram registered after a standard addition

of Fe (III) ion. c – Background voltammogram obtained using gold RDE in 0.1M hydrochloric acid, d – voltammogram registered

after a standard addition of Fe (III) ion. The sweep rate in all cases is 50mV/s.

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Interrupted amperometric titration: the determination

of dichromate ion

In amperometric titration the influence of the working electrode material is not as significant as in direct

amperometry, because the value of the measured current is of interest only as an indicator. The shape of titra-

tion curve depends on the role of electrochemically active substance, which can be analyte, titrant or their

reaction product [14]. One of the assumptions made for theoretical consideration of IA in our previous work

[47] stated that the concentration of a depolarizer is so low, that the current of electrochemical reaction is

much lower than the DL charging current. This condition is easily fulfilled when an electrochemically inac-

tive substance is titrated by electrochemically active titrant.

A well-known technique for determination of dichromate ions based on their reduction by iron (II) ions

[52] was used as a model system in order to investigate the possibilities of IA in titration mode. The measur-

ing electrochemical cell consisted of platinum RDE (diameter 2.0mm, rotation speed 2000rpm) as a working

electrode, platinum rod as a counter electrode and a silver/silver chloride reference electrode. The potential

was held at +1.0 V (vs. silver/silver chloride electrode) and amplification factor was 1000. A standard 0.01M

solution of ammonium iron (II) sulfate served as titrant. Both titrant and model analyte solutions were deoxy-

genated by argon prior to measurements.

The end point is found graphically as the point of intersection of the “residual current” line before the

end point and of the anodic diffusion current line of the ferrous iron after the end point (see Fig. 5b). Prelimi-

nary studies showed that the acceptable value of the error (±0.7 %) is achieved when the concentration of

dichromate ion is not less than 1.68 µM.

Table 2:Concentration (C) of Fe

ion determined by ETAAS and IA in the samples of Baltic Sea bottom water (n=2, P=0.95).

Sample # ETAAS results, (C±ΔC) µg L

−

IA results, (C±ΔC) µg L

−

LLA .±. .±.

F .±. .±.

LL .±. .±.

P .±. .±.

NAR .±. .±.

F .±. .±.

LL .±. .±.

GF .±. .±.

F .±. .±.

LL .±. .±.

LL .±. .±.

Current (mkA)

0 250 500 750

Time (s) Volume (mL)

0.0 0.5 1.0 1.5 2.0 2.5

1000 1250

Fig. 5:Typical amperogram (a) and the corresponding titration curve (b) obtained with IA detection.

E. Semenova etal.: Interrupted amperometry: the new possibilities in electrochemical measurements

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Using of direct interrupted amperometry in a Clark-type sensor

The use of direct IA for detection in electrochemical sensors is of particular interest. This approach was

applied to determine concentration of dissolved oxygen in water by Clark-type sensor. The problem of the

ultrasensitive determination of dissolved oxygen in high-purity aqueous media is topical, for example, in

thermal and nuclear power industry [53]. Therefore, ultrapure water obtained by the ion-exchange deioniza-

tion of distilled water, being in equilibrium with atmospheric air, was taken as a model sample to be ana-

lyzed. Changing the concentration of dissolved oxygen was achieved by adding fixed amounts of sodium

sulfite. This procedure provided decrease in O

concentration to the required value due to a redox reaction.

The experimental setup was assembled as follows. Two sensors were immersed in a 300mL beaker filled with

deionized water. The first was Clark-type oxygen sensor AKPM-02 (“Al’fa BASSENS” Company OOO, Russia)

attached to “ComPot” potentiostat. The second sensor was a part of commercially produced MARK-302T

oxygen meter (“VSOR” Company OOO, Russia) that was used as a reference device. The beaker was placed on

a magnetic stirrer and covered with laboratory film “Parafilm” (“Pechiney Plastic Packaging”) that did not

allow oxygen inflow. Additionally, the area above the water in the beaker was blown with ultrapure argon.

Amplification factor of 1000was used in direct IA-mode and detection potential was −0.7 V. After a constant

response was achieved from both MARK-302T oxygen meter and “ComPot” potentiostat, we started to lower

the concentration of dissolved oxygen by successively adding 10mg portions of sodium sulfite. As a result

a chronoamperogram presented on Fig. 6a was registered and a calibration plot (see Fig. 6b) was obtained.

350

300

Decreasing O

IC-mode

Concentration

250

200

Current (mkA)

Current (nA)

150

100

300

200

100

300

200

100

200 400 600 800

Time (s)

Sensitivity = 30.31 mkA (mg/dm

)

Y = –8.10 + 30.31x

= 0.996

Y = –12.43 + 36.88x

= 0.995

Sensitivity = 36.88 nA (mg/dm

)

1000 1200

0.0 2.5 5.0 7.5

Concentration of oxygen (mg dm

–3

)

Concentration of oxygen (mg dm

–3

)

10.0 12.5

0 2468

350

300

Decreasing O

DC-mode

Concentration

250

200

Current (nA)

150

100

1000 1200 1400 1600

Time (s)

1800

2000

Fig. 6:Comparison of IA- and conventional DC-mode for detection in Clark-type oxygen sensor. (a) Chronoamperogram regis-

tered in IA mode. (b) Calibration plot obtained for IA mode. (c) Chronoamperogram registered in DC mode. (d) Calibration plot

obtained for DC mode.

1468



E. Semenova etal.: Interrupted amperometry: the new possibilities in electrochemical measurements

The slope of the calibration curve gave a value of 30.31 µA/(mg/dm

) for the sensitivity of IA technique.

The similar experiment was carried out in conventional DC amperometric mode in order to compare the sen-

sitivity of the proposed technique with this of a common method (see Fig. 6c and d). It was found that the

use of IA mode for detection in Clark oxygen sensor provides a significant gain in sensitivity. The proposed

technique is approximately a thousand times more sensitive than conventional one.

Conclusions and perspectives

The principle of interrupted amperometry can be briefly represented by depicting the scheme of excitation

factor (Fig. 7a) and the structure of analytical signal (Fig. 7b). As it follows from Fig. 7b, sensitivity of IA meas-

urements depends on the material of the working electrode and on the amount of electroactive impurities.

Thus, the development of the sensitive and selective IA methodology requires the selection of the appro-

priate supporting electrolyte solution and of the optimum working electrode material, just like it is in con-

ventional amperometry.

Interrupted amperometry provides significantly better analytical characteristics as compared with those

typical for conventional amperometric techniques. This is confirmed by the obtained LOD values in direct IA

mode for cadmium (0.26 nM) and lead (0.79 nM) divalent ions at the static mercury drop electrode, for phenol

(8.8 nM) and hydroquinone (31 nM) at the polymeric carbon-based electrode, and for iron (III) at the carbon

RDE (3 nM) and at the gold RDE (2.5 nM). The lowest concentration of dichromate ion estimated by IA titra-

tion was 1.68 µM with the error of 0.7 %. The sensitivity of the Clark-type sensor with IA detection of dissolved

oxygen reached 30.31 µA/(mg/dm

). The mentioned experimental results show good prospects of the use of

IA in analytical chemistry. In addition to expanding the range of analytes, we expect the future development

of IA in its application for detection in HPLC, flow injection analysis and biosensors. Possibilities of IA for

coulometry and electroanalysis with ultramicroelectrodes are also of great interest.

Acknowledgements: Scientific researches were performed at the Educational Resource Center of Chemistry

of Research park of St. Petersburg State University. The authors are very grateful to Larisa Khustenko and

Vladimir Moshkin for providing the original potentiostat “ComPot”.

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For solid electrodes: I

+ I

imp

nonid

For mercury electrodes:

Theoretically:

>> t

Time

nonid

imp

Current

Potential

Fig. 7:The principle of interrupted amperometry: excitation factor (a) and analytical signal (b).

E. Semenova etal.: Interrupted amperometry: the new possibilities in electrochemical measurements

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