BRPI1002571A2 - electrochemical sensor based on ceramic carbon material for determination of dissolved oxygen and the process for obtaining it - Google Patents

Abstract

ELECTROCHEMICAL SENSOR BASED ON CARBON CERAMIC MATERIAL FOR DETERMINING DISSOLVED OXYGEN AND THE PROCESS TO OBTAIN THE SAME. The present invention relates to a process for obtaining an electrochemical sensor based on ceramic carbon material for determining oxygen dissolved in water and an additional object of the present invention is said sensor. The sensor consists of a material containing SiO ~ 2 ~ / SnO ~ 2 ~, where the electroactive species is synthesized in situ in the mixed oxide. Featuring good performance, good mechanical resistance, reproducibility, selectivity, long service life and a good detection limit in the order of ppb (part per billion). The sensor has applications in several areas, in environmental monitoring, in effluent treatment plants and control of O ~ 2 ~ concentration in industrial processes.

Description

"ELECTROCHEMICAL SENSOR BASED ON CERAMIC CARBON MATERIAL FOR DETERMINATION OF DISSOLVED OXYGEN AND THE PROCESS FOR OBTAINING IT"

FIELD OF INVENTION

The invention relates to a method of obtaining a ceramic carbon based electrochemical sensor for determination of dissolved oxygen in water and a further object of the present invention is said sensor. The sensor is made of a material containing Si02 / Sn02, where the electroactive species is synthesized in situ in the mixed oxide.

The sensor has applications in several areas, in environmental monitoring, in effluent treatment plants and control of O2 concentration in industrial processes.

BACKGROUND OF THE INVENTION

Silica can be applied in admixture with other oxides to form mixed oxides. Si02 / Sn02 mixed oxide combines the structural properties of silica with the semiconductor character of SnO2. This type of material allows the immobilization of electroactive species inside the pores (Cardoso et. Al., Solid State lonics, 167 (2004) 165) and can be applied to electrochemical sensors. The silica has the silanol group Si-OH and the SnÜ2 SnOH groups on its surface, which enable modification of the oxide surface (Canevari et. Al., J. Electroanal. Chem., 609 (2007) 61).

MPc complexes (M represents transition metal and Pc represents that the molecule is a phthalocyanine) have very special properties such as high thermal stability and mechanical strength (Rajesh et. Al., Materials Letters, 51 (2001) 266.). Manganese (11) phthalocyanine has several interesting properties (Lin et. Al., Journal of Electroanalytical Chemistry, 524-525 (2002) 81) and is known primarily for electrocatalytic properties (Kraus et. Al., Chemical Physics Letters, 469). (2009) 121), especially in the reduction of molecular oxygen.

The in situ synthesis of manganese (II) phthalocyanine on the mixed oxide Si02 / Sn02, where the Mn (II) phthalocyanine is confined in the pores of the mixed oxide, results in a material with high electrocatalytic property against O2 reduction. mechanical strength and thermal stability.

Other work using manganese (II) phthalocyanine as a sensor is known from the state of the art, however, the manner in which phthalocyanine is applied differs from the manner used in this invention, in addition, they use manganese (II) phthalocyanine in other types of sensors. A microsensor has been developed to assess the quality of fish for consumption (Gupta et. Al., T. Sensors and Actuators B, 41 (1997) 199). Santos and colleagues developed a carbon paste sensor for the detection of phenols (Santos et. Al., J. Braz. Chem. Soc., 20, 6 (2009) 1180). A manganese (II) phthalocyanine-containing polymeric material was applied as an anion-selective sensor - (Arvand - et. Al., Anal. Bio Anal. Chem. 387 (2007) 1033). A sensor for thiocyanate ions was developed using manganese (II) phthalocyanine supported on a PVC membrane (Amini et. Al., Analytical Letters, 32, 14 (1999) 2737). An optical sensor for gamma radiation (γ) was developed using a thick manganese (II) phthalocyanine film on a silver surface (Arshak et. Al., Sensors, 2 (2002) 174).

Few inventions resemble the proposed invention, and those approaching the present invention differ in the application and nature of the material. US2007 / 0243449 (Sotomura, T .; Hashimoto, M.; Yamada, Y., Electrode for use in oxygen reduction, 10/18/2007) describes the use of carbon nanotube-supported colbate phthalocyanine containing carbon nanotubes. as a sensor for dissolved oxygen, differing from the proposed invention as to the metal used in phthalocyanine and in the way that phthalocyanine is used. Measurements using this electrode should be performed at pH = 13, a very limited pH range, while the proposed electrode can be used in the pH range from 4.5 to 11, without significant changes in electrode response.

The invention 5,018,380 (Zupancic, JJ et al., Dielectric sensors, 05/28/1991) consists of an isocyanate polymer combined with a nitrogenous polymer that is applied as a sensor for gaseous oxygen, while the proposed sensor is for dissolved oxygen in water. and the disadvantage is the lower stability compared to the sensor proposed in this invention.

US2005 / 0281729 A1 (Suzuki, M. et al., Method for manufacturing oxygen reduction electrode, oxygen reduction electrode and electrochemical element using same, December 22, 2005) and US2005 / 0153198 A1 (Suzuki, M. et al. , Oxygen reduction electrode and electrochemical element using same, 14/07/2005) consist of materials based on a carbon derived from the carbonization of a polymer at high temperatures. The proposed sensor has the advantage of obtaining the process under mild reaction conditions without great energy cost.

In view of the state of the art, the present invention advantageously provides a proposal for a process of obtaining a carbon-based electrochemical sensor for the determination of dissolved oxygen in water and said sensor with good performance, good mechanical strength, reproducibility and long time. lifespan. The synthesis of the mixed oxide used requires mild reaction conditions, the in situ synthesis of phthalocyanine is carried out simply and without the use of solvents. The sensor has the advantage of being very selective for oxygen. In addition, oxygen reduction reaction occurs by a mechanism involving 4 electrons, with the formation of water as a product. The sensor had a long service life and a good detection limit, in the order of ppb (part per billion).

BRIEF DESCRIPTION OF THE INVENTION

The present invention contemplates a method for obtaining a carbon-based electrochemical sensor for the determination of dissolved oxygen in water. A further object of the present invention is the ceramic carbon based electrochemical sensor for determination of dissolved oxygen in water.

The sensor has applications in several areas, in environmental monitoring, in effluent treatment plants and control of O2 concentration in industrial processes.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1: Representation of the synthesis used in the preparation of mixed oxide Si02 / Sn02;

Figure 2: Representation of the synthesis route used to prepare the Si02 / Sn02 / MnPc electrode;

Figure 3: Representation of the hard disk sensor. The sensor comprises a hard disk electrode containing Si02 / Sn02 / C / MnPc (a), graphite powder (c), a 5 mm outer diameter glass tube (b), and a metallic lead (d) ;

Figure 4: Representation of the N2 adsorption-desorption isotherm of Si02 / Sn02 mixed oxide;

Figure 5: Representation of pore size distribution of the mixed oxide Si02 / Sn02;

Figure 6: Representation of the diffuse reflectance spectrum of the Si02 / Sn02 / C / MnPc electrode and pure manganese phthalocyanine to demonstrate that manganese phthalocyanine has been successfully incorporated into the mixed oxide, as manganese phthalocyanine is the chemical species responsible. by the sensor's property of measuring dissolved oxygen concentration.

Figure 7: Infrared spectrum representation for Si02 / Sn02 / MnPc electrode, Si02 / Sn02 mixed oxide and pure manganese phthalocyanine to demonstrate presence of manganese phthalocyanine in mixed oxide

Figure 8: Demonstration of various differential pulse voltammetry measurements performed at different O2 concentrations for the Si02 / Sn02 / C / MnPc electrode in order to demonstrate the relationship between peak current and oxygen concentration, evidencing its activity as sensor.

Figure 9: Representation of the anode peak current intensity curve as a function of O2 concentration obtained by differential pulse voltammetry for the Si02 / Sn02 / C / MnPc electrode to demonstrate the linear relationship between the peak current and the O2 concentration. Dissolved oxygen.

Figure 10: Representation of anode peak current intensity values as a function of the number of cycles performed by cyclic voltammetry for the Si02 / Sn02 / C / MnRc electrode to demonstrate that even after several measurements of dissolved oxygen the electrode does not suffer loss. answer sign.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to a method of obtaining a ceramic carbon-based electrochemical sensor for the determination of dissolved oxygen in water. It is a further object of the present invention the ceramic carbon-based electrochemical sensor for the determination of dissolved oxygen in water.

Said process for obtaining a ceramic carbon-based electrochemical sensor for the determination of dissolved oxygen in water comprises the following steps:

(i) synthesis of the mixed oxide SiO2ZSnO2;

(ii) purification and drying of mixed oxide Si02 / Sn02;

iii) Incorporation of manganese (II) into the mixed oxide Si02 / Sn02;

iv) In-situ synthesis of manganese (II) phthalokinanin in the mixed oxide Si02 / Sn02;

v) Purification of Si02 / Sn02 / MnPc material;

vi) Drying of Si02 / Sn02 / MnPc material and

vii) Preparation of Si02 / Sn02 / C / MnPc electrode in hard disk form. More specifically, the process of obtaining a ceramic carbon-based electrochemical sensor for the determination of dissolved oxygen in water comprises the following steps:

(i) synthesis of mixed oxide Si02 / Sn02 by sol-gel method;

(ii) Purification and drying of mixed oxide SiO2ZSnO2:

a) Washing the mixed oxide Si02 / Sn02 with ethanol in a soxhlet system preferably for 2.5 hours; and

b) Drying of the mixed oxide in a vacuum system under heating in a water bath preferably at 100 ° C.

(iii) Incorporation of manganese (II) into Si02 / Sn02 mixed oxide:

(a) adding 2 g of the mixed oxide to 10 ml of a 0,1 ml solution of manganese acetate (II); and

b) Heating preferably at 80 ° C for solvent evaporation.

(iv) In situ synthesis of manganese (II) phthalokinanin in mixed oxide Si02 / Sn02:

(a) mixing 2 g of the solid with 2 g of phthalonitrile; and

b) Mechanical stirring of the mixture with heating in a water bath preferably at 200 ° C for 2 hours.

v) Purification of Si02 / Sn02 / MnPc material using soxhlet ethanol preferably for 2.5 hours;

vi) Drying Si02 / Sn02 / MnPc material in a vacuum system under heating in a water bath preferably at 100 ° C;

vii) Preparation of Si02 / Sn02 / C / MnPc hard disk electrode:

(a) Mechanical mixture of 15 mg Si02 / Sn02 / MnPc material with 15 mg graphite powder preferably 99.99% pure; (b) pressing the mixture into a 5 mm inner diameter steel pad under a pressure of preferably 3 tons;

c) Immersion of the disc in a candle paraffin bath, which was previously heated to melt, in a vacuum system of the order of 10-2 Pa, preferably for 1 hour;

d) Paraffin removal from the disc surface using preferably a sandpaper 1200;

e) Attaching the disc to the end of the glass tube preferably using epoxy resin; and

f) Addition of graphite powder and lead wire inside the glass tube.

It is a further object of the present invention that an electrochemical sensor for determination of dissolved oxygen in water comprises a hard disk shaped electrode 15 Si02 / Sn02 / C / MnPc, a glass tube and a metallic conductive wire. Said sensor is prepared from the process described above to be applied in the detection of dissolved oxygen.

More specifically the electrochemical sensor for determination of dissolved oxygen in water comprises:

a) A Si02 / Sn02 / C / MnPc hard disk shaped electrode thickness.

Synthesis of mixed oxide SiOzZSnO?

Synthesis of the mixed oxide Si02 / Sn02 was prepared by the sol-gel method, known in the art, (Canevari, T.; Arguello, J .; Francisco, MSP; Gushikem, Y., J. Electroanal. Chem., 609 (2007) 61) as follows containing 15 mg Si02 / Sn02 / MnPc material and 15 mg 99.9% pure graphite powder;

(b) a glass tube 5 mm in diameter and 15 cm in length, containing graphite powder inside; and

c) A 2 mm multifilament metallic conductor wire of procedure: 12 mL tetraethylorthosilicate (TEOS), 12 mL ethanol, 2.0 mL deionized water and 0.2 mL concentrated hydrochloric acid were mixed, this solution was maintained. stirring at 353 K for 3 h. After the TEOS prehydrolysis step, the solution was cooled to room temperature and then 0.8 mL of tin dibutyl diacetate solution was added and the mixture was stirred for 1h.

Deionized water (3.0 mL), concentrated HCl (0.3 mL) were then added and allowed to stir for an additional hour. The resulting solution was heated to 333 K until gelatinization began, increasing the temperature to 353 K until complete evaporation of the solvent. The obtained mixed SiO2 / SnO2 oxide was washed with ethanol and dried in a vacuum line. The flowchart of this synthesis can be seen in figure 1.

In situ synthesis of manganese (II) phthalocyanine in SiO2 / SnO2 mixed oxide

The in situ synthesis of the mixed oxide Si02 / Sn02 / MnRc was performed by. incorporation of manganese II phthalocyanine (MnPc) using phthalonitrile into the pores of the mixed oxide Si02 / Sn02- (Ganevari, T.; Arguello, J .; Francisco, MSP; Gushikem, Y., J. Electroanal. Chem., 609 (2007) 61). 10 ml of 0.1 mol.L-1 Mn (II) acetate solution was prepared in a beaker, and 2 g of the mixed oxide SiO2ZSnO2 was added to this solution. The system was stirred on a magnetic stirrer by 30 minutes, and heated on a hotplate at 80 ° C for about 2 hours, until complete evaporation of the solvent.The solid obtained was then mixed with the phthalonitrile 1: 1 by weight in a glass ampoule and placed. in a mechanical stirring system under stirring for 2 h, with heating at 200 ° C in a water bath The material obtained was then washed with ethanol in a Soxhlet system for 2.5 h to remove unconfined phthalocyanine and unconsumed phthalonitrile The reaction flowchart of this synthesis can be seen in Figure 2.

SiO2 / SnO2 / C / MnPc Electrode Construction

The present example embodiment contemplates the process of obtaining an electrochemical sensor for detection of dissolved oxygen, without, however, restricting the scope of protection and scaling of the invention. The electrode is used as a pressed disc in order to obtain an electrode with high chemical, thermal and mechanical stability. The pressed disc electrode was prepared by mechanically mixing 15 mg Si02 / SnC> 2 / MnPc material with 15 mg high purity graphite powder (99.99%) in an agate mortar. This mixture was manually macerated in mortar for about 20 minutes to homogenize the solid. The mixture was placed in a 5 mm inner diameter steel pad, applying a pressure of 3 tons, using a hydraulic press. The disk formed was then immersed in a candle paraffin bath, which was preheated to its fusion in a pressure vacuum system of the order of 10'2 Pa, to remove the gas present in the disk interstices. The resulting disk will hereinafter be referred to as SiCVSnCVC / MnPc. The disc is then sanded using 1200 sandpaper to remove the paraffin from the surface and fixed to a glass tube. Inside this tube is placed graphite powder (99.99%) and a copper wire for electrical contact (Figure 3). The electrode was able to detect dissolved oxygen at a concentration of up to 0.003 mg L "1.

X-ray fluorescence

The amount of SnO2 from the matrix could be determined by the x-ray fluorescence method, where a calibration curve was made using mechanical mixtures of SnO2 and silica gel in various proportions. The equipment used was an EDXRF spectrace model 5100 spectrometer. The amount of SnO2 found in the mixed oxide Si02 / Sn02 was 15%. A value that gives a good conductivity to mixed oxide, since SnO2 is a semiconductor, maintaining the porous character of mixed oxide, which allows the incorporation of manganese (II) phthalocyanine.

Surface area and pore volume

Porous solids are classified according to pore size as: micropores (<2 nm), mesopore (2-50 nm) or macropore (> 50 nm) (Sing et al. Puré and Appl. Chem., 57, 4 (1985) 603). The porosity of the material should be especially considered when the goal is to immobilize substances within the pores (Rouquerol et. Al., Puree and Appl. Chem., 66, 8 (1994) 1739). Another important feature is surface area, which is defined as the accessible area of the solid per unit mass of material (Lowell et al., Characterization of porous solids and powders; Surface area, pore size and / density.) Dordrecht: KIuwerAcademic Publishers , 2004).

Specific surface area measurements were performed by means of nitrogen adsorption and desorption isotherms, obtained on an Autsorb 1 - Quantachrome Instruments equipment, using the multipoint BET method.

The N 2 sorption isotherm of Si02 / Sn02 / MnPc material (Figure 4) presented a type I profile and type H4 hysteresis, characteristic of microporous materials. The surface area value obtained was As (BET) = 299 m2 g_i and the pore size distribution obtained by the BJH method showed a predominantly microporous material profile (Figure 5).

The presence of pores in the mixed oxide structure shows that it is possible to perform the synthesis of molecules within these pores, in the case of this invention the synthesis of manganese (II) phthalocyanine.

Electronic spectroscopy in the UV-Vis region

Phthalocyanines in general are highly conjugated molecules, which explains the response of these molecules to radiation in the UV-Vis region. UV-Vis measurements were performed on a Shimadzu Multispect 1501 spectrophotometer with diffuse reflectance system.

The diffuse reflectance spectrum of the material (Figure 6) showed bands similar to pure phthalocyanine bands. The band presented at 710 nm, referring to the Q band, consists of the electronic transition Homo with symmetry a1u to orbital Lumo with symmetry eg. The Q band is represented by the transfer of electrons from the pyrrol skeleton to other atoms of the molecule. The shoulder-shaped band at 360 nm, band B, represents the electron transfer from the nitrogen bridges to the pyrrol backbone carbon atoms, and consists of the transition from the Homo orbital with symmetry a2 u to the Lumo eg orbital. Another band observed is that appearing at 530 nm, this band is observed in phthalocyanines containing a central metal, referring to charge transfer from metal to ligand or from ligand to metal (Sehlotho, N .; Nyokong1 T., Journal of Electroanalytical Chemistry, 595 (2006) 161).

The technique shows that manganese phthalocyanine has been successfully incorporated into the mixed oxide, since manganese phthalocyanine is the chemical species responsible for the sensor property of measuring dissolved oxygen concentration.

Infrared (IR) vibrational spectroscopy

The infrared spectroscopy technique allows us to observe the formation of SiCVSnO2ZMnPc material and Si02 / SnC> 2 mixed oxide. Measurements of pure manganese material, mixed oxide and phthalocyanine were performed for comparison purposes. Comparative measurements between the material, mixed oxide and pure manganese phthalocyanine were obtained from 4000 to 400 cm'1 on a Bomen MB series Fourier transform (FT-IR) spectrophotometer with 2 cm "1 resolution and 64 cumulative scans The samples were dissolved in fluorolube and placed in KBr windows.

The IR spectra of Si02 / Sn02 mixed oxide, SiO2ZSnO2ZMnPc material and pure manganese (II) phthalocyanine (MnPc) were compared (Figure 7). The band at 1627 cm-1 corresponds to the silanol groups (Si-OH) of the mixed oxide surface and to the water adsorbed on the material. The Si02 / Sn02 / MnPc material did not have a band corresponding to the silanol groups. fluorolube suspension, only bands above 1380 cm-1 were observed to characterize phthalocyanine in the mixed oxide, namely: 1504 cm-1 (u C = C of the isoindole ring), 1651 cm-1 (u C = C of the benzene ring conjugate bonds). The other bands observed between 1600 and 1380 cm "1 occur due to the axial deformation vibrations of the aromatic ring (Silverstein, RM, Spectrometric identification of organic compounds. 6 ed., Rio de Janeiro: Guanabara Koogan, 2000). As well as spectroscopy In the UV-Vis1 region this technique shows the presence of manganese phthalocyanine in the mixed oxide, since manganese phthalocyanine is the chemical species responsible for the sensor property of measuring dissolved oxygen concentration.

Electrochemical characterization of the electrode

Electrochemical characterization was performed on an Autolab Eco Chemie Potentiostat model PGSTAT30. A 20 mL cell was used using a system containing three electrodes: The pressed disk electrode containing SiCVSnCVMnPc material, a platinum electrode (counter electrode) and a saturated calomel electrode (ECS) as the reference electrode.

Differential pulse voltammetry measurements were performed at different dissolved oxygen concentrations. In this type of measurement it was possible to observe the oxygen reduction in the potential of -0.31 V (Figure 8). For a material to be applied as a sensor it is important that there is a relationship between the physical response observed in the analysis and the amount of oxygen. It was observed that the increase in analyte concentration caused a linear increase in the current value (Figure 9), which enables the application of this material as a sensor. Through a linear regression calculation, it was possible to obtain a curve with the correlation coefficient 1 ^ = 0.994. The linear regression equation obtained was as follows: i (mA) = 8.0427 χ 10 "7 (± 4.05565 χ 10-7) - 4.59229 χ 10" 8 (± 1.13475 χ 10 "9) χ [O2] (mg L "1)

The limit of detection is the smallest concentration that can be distinguished with a certain level of confidence. The detection limit of this sensor was calculated, obtaining the value of LD = 3.3 ppb. These values are in the same order of magnitude as those found for Mettler Toledo InPro® 6800 and InPro® 6900 commercial sensors, which have a detection limit of 6 and 1 ppb, respectively.

Cyclic voltammetry measurements were performed ranging from 4.5 to 11 pH with a constant oxygen concentration ([02] = 8.8 mg L "1). It was observed that there was no significant change in the current value. anodic peak, showing that the sensor can be used in the pH range (4.56 to 10.99).

To evaluate the material stability, several voltammetric cycles were performed in the presence of O2. The measurements showed that even after 100 cycles, the material showed no significant reduction of the current signal (Figure 10).

The O2 reduction reaction can occur by two mechanisms: a mechanism involving two electrons resulting from the formation of H2O2, and a mechanism involving four electrons resulting in water formation. To evaluate the oxygen reduction reaction kinetics, measurements were made using a rotating disc electrode at different rotation speeds. From these measurements, it was observed that the mechanism involving four electrons is predominant in this type of electrode. The mechanism involving four electrons is preferable since water production does not cause alteration of the solution.

Claims (12)

1. Process for obtaining an electrochemical sensor comprising the following steps: (i) synthesis of SiCVSnO2 mixed oxide by the sol-gel method; (ii) purification and drying of mixed oxide Si02 / Sn02; (iii) incorporation of manganese (II) into SiCVSnO2 mixed oxide; iv) In situ synthesis of manganese (II) phthalokinanine in mixed oxide Si02 / Sn02; v) Purification of Si02 / Sn02 / MnPc material; vi) Drying of Si02 / Sn02 / MnPc material; and vii) Preparation of the Si02 / Sn02 / C / MnPc hard disk electrode. Process according to Claim 1, characterized in that step (ii) comprises the following sub-steps: a) Washing the mixed oxide Si02 / Sn02 with ethanol in a soxhlet system preferably for 2.5 hours; and (b) drying the mixed oxide in a vacuum system under heating in a water bath preferably at 100 ° C. Process according to Claim 1, characterized in that step (iii) comprises the following sub-steps: (a) adding 2 g of the mixed oxide to 10 ml of a 0,1 ml solution of manganese acetate ( II); and b) Heating preferably to 80 ° C for solvent evaporation. Process according to Claim 1, characterized in that step (iv) comprises the following sub-steps: (a) mixing 2 g of the solid with 2 g of phthalonitrile; and b) Mechanical stirring of the mixture with heating in a water bath preferably at 200 ° C for 2 hours. Process according to Claim 1, characterized in that step (vii) comprises the following sub-steps: a) Mechanical mixture of 15 mg SiCVSnCVMnPc material with 15 mg of preferably 99% pure graphite powder 99%; (b) pressing the mixture into a 5 mm inner diameter steel pad under a pressure of preferably 3 tons; c) Immersion of the disc in a candle paraffin bath, which was previously heated to melt, in a vacuum system of the order of -10-2 Pa preferably for 1 hour; d) Paraffin removal from the disc surface using preferably a sandpaper 1200; e) Attaching the disc to the end of the glass tube preferably using epoxy resin; and (f) adding graphite powder and the lead wire inside the glass tube. 6. Electrochemical sensor comprising a hard disk-shaped Si02 / Sn02 / C / MnPc electrode, a glass tube and a metallic conductive wire for application as a dissolved oxygen detector. Sensor according to claim 6, characterized in that it comprises a hard disk-shaped Si02 / Sn02 / C / MnPc electrode preferably containing 15 mg Si02 / Sn02 / MnPc material and 15 mg of 99.9% graphite powder. of purity. Sensor according to claim 6, characterized in that it comprises a glass tube of 5 mm outside diameter, 15 cm long and graphite powder inside. Sensor according to Claim 6, characterized in that it comprises a 2 mm thick multifilament metallic conductor wire. Sensor, characterized in that it is prepared from the process as defined in one of claims 1 to 5. Sensor according to Claim 10, characterized in that it is for the detection of dissolved oxygen. Sensor according to claim 11, characterized in that it is functional between pH 4.56 and 10.99.