CLIAMS:1. An electrochemical measuring system, the system comprising at least three electrodes; a working electrode, a reference electrode and a counter electrode, the working electrode being mounted within a first rising portion of a conduit wherein the first rising portion extends to a base portion having a second rising portion and a third rising portion extending outward from the base portion and away from the first rising portion, the second rising portion having mounted therein a reference electrode conductively connected to the working electrode or to the counter electrode, the counter electrode being mounted within the third rising portion, the working electrode and the counter electrode being in electrochemical communication with an electrolyte liquid conveyed from the first rising portion through the third rising portion.
2. The electrochemical measuring system as claimed in claim 1 wherein the electrolyte liquid comprises a cyanide salt.
3. The electrochemical measuring system as claimed in claim 2 wherein the cyanide salt is an alkali metal cyanide salt.
4. The electrochemical measuring system as claimed in any one of the claims 1 to 3 wherein the measuring system provides an output signal free from fluctuations.
5. The electrochemical measuring system as claimed in claim 4 wherein the output signal is a substantially linear function of the concentration of cyanide ions in the electrolyte liquid.
6. The electrochemical measuring system as claimed in anyone of the claims 1 to 5 wherein the inner diameter of the conduit wherein the working electrode is mounted is not more than 6 cm
7. An electrochemical measuring system wherein the working electrode 1 is mounted within a rising portion 4 of a conduit wherein the rising portion extends to a base portion 5 having a second rising portion 6 and a third rising portion7extending outward thereof and away from the rising portion, the second rising portion 6 having mounted therein a reference electrode 2 conductively connected to the working electrode 1 or to the counter electrode3, the counter electrode being mounted within the third rising portion 7, the working electrode and the counter electrode being in electrochemical communication with an electrolyte liquid conveyed from the first rising portion through the third rising portion.
8. An apparatus for analysis of cyanide ions, the apparatus comprising the electrochemical measuring system as claimed in any one of the claims 1 to 7.
9. The apparatus as claimed in claim 8 wherein the electrochemical measuring system is coupled to a treatment unit adapted to generate cyanide ions from non-ionized cyanide in an effluent.
10. The apparatus as claimed in claim 9 wherein the treatment unit is a photoreactor system
11. A method for measurement of cyanide content, the method comprising treating an effluent with an acid reagent in a photoreactor system resulting in generation of hydrogen cyanide gas, absorbing hydrogen cyanide gas in a gas absorbing unit, conveying the electrolyte liquid obtained by the gas absorption to an electrochemical measuring system comprising a working electrode mounted within a first rising portion of a conduit and transporting the electrolyte liquid from the first rising portion through a third rising portion of the conduit
,TagSPECI:FIELD OF INVENTION
The present invention relates to an electrochemical measuring system. The invention also relates to an apparatus comprising the electrochemical measuring system and to a method for measurement of cyanide content in an effluent.
BACKGROUND
Electrochemical measuring systems for qualitative and quantitative determination of electrolytic substances are known. Successful analysis of substances using such systems is dependent on a number of factors. They include the availability of conducting electrolytes, availability of suitable electrodes that can maintain measurable redox potential across them and the ability to obtain non-fluctuating and reproducible output signal. Conventional electrochemical apparatuses do not allow detection or determination of analytes in the non-ionised (complexed) form. Further, large fluctuations are observed in the output signal of conventional electrochemical measuring systems, making it difficult to obtain accurate and reproducible analysis. The cause of such signal fluctuations is not clearly understood and the nature of fluctuations varies with each measurement. Attempts made in the past to prevent or minimize such signal fluctuations had not yielded desired results. Most of the conventional electrode systems are not immune to such fluctuations, thus making them unreliable for quantitative determination of analytes. It is, therefore, desirable to have an electrochemical measuring system that is free from signal fluctuations.
OBJECTS OF INVENTION
An object of the invention is to provide an electrochemical measuring system that is free from fluctuations in the output signal.
An object of the invention is to provide a combined three electrode system that is designed to obtain high signal output.
An object of the invention is to provide an apparatus for accurate analysis of total (ionized as well as complexed) cyanide content in an effluent.
SUMMARY OF INVENTION
The invention provides an electrochemical measuring system, the system comprising at least three electrodes; a working electrode, a reference electrode and a counter electrode, the working electrode being mounted within a first rising portion of a conduit wherein the first rising portion extends to a base portion having a second rising portion and a third rising portion extending outward from the base portion and away from the first rising portion, the second rising portion having mounted therein a reference electrode conductively connected to the working electrode or to the counter electrode, the counter electrode being mounted within the third rising portion, the working electrode and the counter electrode being in electrochemical communication with an electrolyte liquid conveyed from the first rising portion through the third rising portion.
The invention also provides an apparatus comprising an electrochemical measuring system
The invention also provides a method for measurement of cyanide content, the method comprising treating an effluent with an acid reagent in a photoreactor system resulting in generation of hydrogen cyanide gas, absorbing hydrogen cyanide gas in a gas absorbing unit, conveying the electrolyte liquid obtained by the gas absorption to an electrochemical measuring system comprising a working electrode mounted within a first rising portion of a conduit and transporting the electrolyte liquid from the first rising portion through a third rising portion of the conduit.
BRIEF DESCRIPTION OF DRAWINGS
Fig 1 is a representation of an embodiment of the electrochemical measuring system of the invention
Fig 2 is a flow chart of the apparatus for determination of cyanide content using the electrochemical system of the invention
Fig 3 is a graphical representation of the output signal from the electrochemical system of the invention
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Figure 1 displays an embodiment of the electrochemical measuring system of the invention. Referring to Figure 1, the electrochemical measuring system of the invention comprises a working electrode 1 mounted within a first rising portion4 of a conduit that extends to a base portion 5having a second 6and third 7rising portions extending outward from the base portion and away from the first rising portion, the second rising portion6having mounted therein a reference electrode 2conductively connected to the working electrode 1or to the counter electrode3, the counter electrode being mounted within a third rising portion7, the working electrode 1and the counter electrode 3being in electrochemical communication with an electrolyte liquid that enters the electrochemical measuring system through an inlet 8at the first rising portion and exits through an outlet 9at the third rising portion.
Fig 2 is a schematic diagram of an apparatus comprising the electrochemical measuring system of the invention. The apparatus comprises a photoreactor system10 and a gas absorbing unit12 separated by a valve element 11 that controls communication of the photoreactor system 10 with the gas absorbing unit12.The photoreactor system 10communicates with a container containing an acid reagent 21 through a valve element 22.Thegas absorbing unit12 also communicates to the atmosphere through the gas vent 13. Further, it communicates with a container 20containing gas absorbing liquid and with the electrochemical measuring system 17through a valve element18.The valve element 18 controls the flow of the gas absorbing liquid from the container 20 to the gas absorbing unit12. The industrial effluent containing both complexed as well as free cyanide ions are first treated in a photoreactor system10 that contains an acid reagent that is pumped into the photoreactor system from a container21. After treatment of the effluent is over, the reagent solution is drained into the drain container 24. A valve element15 controls the flow of gas absorbing liquid from the gas absorbing unit 12as well as that of the electrolyte liquid from the electrochemical system 17to the drain 16with the assistance of the peristaltic pump 14The peristaltic pump 23is used to pump the effluent into the photoreactor system.10The hydrogen cyanide gas that is generated in the photoreactor system is conveyed to the gas absorbing unit 12,by operating the peristaltic pump 19,and is made to absorb into the gas absorbing liquid in the gas absorbing unit. After absorption of hydrogen cyanide, the electrolyte liquid in the gas absorbing unit is pumped into the electrochemical measuring system that records the output signal as a function of the concentration of cyanide ions in each of the injected sample.
The output signal (Current density vs concentration of cyanide ions) is recorded as in Fig 3 for a conventional electrochemical system as well as for an electrochemical system of the present invention. It is quite clear from the figure that the conventional electrochemical system provides a fluctuating signal while the output signal from the electrochemical system of the present invention if free from fluctuations.
The overall procedure of treatment of effluent in the photoreactor system and measurement of cyanide ions in the electrochemical measuring system of the present invention is described below
1. Reagent filling:
An acid reagent is pumped from a container21by a peristaltic pump though NC (normally closed) mode of a valve element 22 to the photoreactor system 10and at the same time a gas absorbing liquid is pumped from a container20by a peristaltic pump through NC (normally closed) mode of another valve element 18 to the gas absorbing unit12.
2. Baseline measurement:
The electrolyte liquid from the gas absorbing unit is conveyed by way of a peristaltic pump 14and a valve element18 by NO (normally open) mode to the electrochemical measuring system from the bottom of the gas absorbing unit. The output signal of the electrochemical measuring system is recorded as baseline.
3. Sample injection:
The effluent sample whose cyanide content is to be measured is injected to the photoreactor system 10 containing an acid reagent. Hydrogen cyanide (HCN) gas generated when the effluent liquid is contacted with the acid reagent is bubbled through the gas absorbing liquid in the gas absorbing unit.HCN gas react with the gas absorbing liquid and gets converted into a cyanide salt.
4. Measurement of cyanide ions
In this stage, the valve element18 is opened and pump 14 is switched on, the electrolyte liquid containing both the gas absorbing liquid and the cyanide salt is passed through the electrochemical measuring system and the output signal is recorded. This signal is correlated with concentration of cyanide.
In one embodiment, the electrochemical measuring system of the present invention comprises at least three electrodes; a working electrode, a reference electrode and a counter electrode, the working electrode being mounted within a first rising portion of a conduit wherein the rising portion extends to a base portion having a second rising portion and a third rising portion extending outward from the base portion and away from the first rising portion, the second rising portion having mounted therein a reference electrode conductively connected to the working electrode or to the counter electrode, the counter electrode being mounted within the third rising portion, the working electrode and the counter electrode being in electrochemical communication with an electrolyte liquid conveyed from the first rising portion through the third rising portion
The electrochemical measuring system of the invention is a three-electrode system. The working electrode used in the system is usually a metal electrode capable of maintaining a stable redox potential at the electrode-electrolyte interface. Advantageously, the working electrode is a silver electrode. More advantageously, the working electrode is a coiled silver wire The electrode is mounted within a conduit. Typically, the conduit has an inner diameter of not greater than 6cm.. Further, the conduit has a first rising portion that extends to a base portion. The electrolyte liquid that is conveyed to the conduit is transported through the rising portion to the base portion and then through the counter electrode mounted within the third rising portion. This kind of electrode design enables continuous movement of electrolyte liquid across the working electrode and the counter electrode. Surprisingly, such an electrode design ensures that a high output signal that is free from fluctuations is obtained. In contrast, in the conventional electrode system wherein the working electrode and the counter electrode are dispose adjacent to each other along the same direction, the output signal fluctuated significantly during the course of measurement.
In one embodiment, the invention provides an electrochemical measuring system, the system comprising at least three electrodes; a working electrode, a reference electrode and a counter electrode, the working electrode being mounted within a first rising portion of a conduit wherein the first rising portion extends to a base portion having a second rising portion and a third rising portion extending outward from the base portion and away from the first rising portion, the second rising portion having mounted therein a reference electrode conductively connected to the working electrode or to the counter electrode, the counter electrode being mounted within the third rising portion, the working electrode and the counter electrode being in electrochemical communication with an electrolyte liquid conveyed from the first rising portion through the third rising portion wherein the electrolyte liquid comprises a cyanide salt. The counter electrode is typically a coiled stainless steel wire. The reference electrode is, typically, an Ag/AgCl electrode.
Advantageously, the cyanide salt is an alkali metal cyanide salt. More advantageously, the cyanide salt is selected from KCN and NaCN. The gas absorbing liquid is, typically, an alkali such as NaOH or KOH.
In one embodiment, the invention provides an electrochemical measuring system, the system comprising at least three electrodes; a working electrode, a reference electrode and a counter electrode, the working electrode being mounted within a first rising portion of a conduit wherein the first rising portion extends to a base portion having a second rising portion and a third rising portion extending outward from the base portion and away from the first rising portion, the second rising portion having mounted therein a reference electrode conductively connected to the working electrode or to the counter electrode, the counter electrode being mounted within the third rising portion, the working electrode and the counter electrode being in electrochemical communication with an electrolyte liquid conveyed from the first rising portion through the third rising portion wherein the output signal is a substantially linear function of the concentration of cyanide ions in the electrolyte liquid
In one embodiment, the invention provides an electrochemical measuring system, the system comprising at least three electrodes; a working electrode, a reference electrode and a counter electrode, the working electrode being mounted within a first rising portion of a conduit wherein the first rising portion extends to a base portion having a second rising portion and a third rising portion extending outward from the base portion and away from the first rising portion, the second rising portion having mounted therein a reference electrode conductively connected to the working electrode or to the counter electrode, the counter electrode being mounted within the third rising portion, the working electrode and the counter electrode being in electrochemical communication with an electrolyte liquid conveyed from the first rising portion through the third rising portion wherein the measuring system provides an output signal free from fluctuations
In one embodiment, the invention also provides an apparatus comprising electrochemical measuring system of the invention. The electrolyte in the electrochemical measuring system of the present invention is, typically in the liquid form. The electrolyte liquid in the electrochemical measuring system of the comprise the gas absorbing liquid as the base electrolyte in addition to the cyanide salt electrolyte that is formed by the reaction between HCN gas and the gas absorbing liquid. The base electrolyte is first used to obtain the baseline for the measurement. The output signal for the electrolyte liquid (that contain both the base electrolyte and the cyanide salt) is then measured against this baseline. During measurement, the electrolyte liquid that contains the base electrolyte and the cyanide salt enters through the inlet 8 at the working electrode end and exits through the outlet 9at the counter electrode end, into the drain 16. The apparatus of the invention comprises a treatment unit for conversion of complexed cyanide into free cyanide. The treatment unit is, advantageously, a photoreactor system.
In one embodiment, the apparatus of the present invention comprises an electrochemical measuring system coupled to a treatment unit adapted to generate cyanide ions from non-ionized cyanide in an effluent.
In one embodiment, the apparatus of the present invention comprises a measuring system coupled to a treatment unit wherein the treatment unit is a photoreactor system.
In one embodiment, the apparatus of the present invention comprises a measuring system coupled to a treatment unit wherein the inner diameter of the conduit wherein the working electrode is mounted is not greater than 6 cm
In a further embodiment, the invention provides a method for measurement of cyanide content in an effluent. The method of the invention comprise treating an effluent with an acid reagent in a photoreactor system, absorbing hydrogen cyanide so obtained in a gas absorbing unit, conveying the electrolyte liquid obtained by the gas absorption to an electrochemical measuring system comprising a working electrode mounted within a first rising portion of a conduit and transporting the electrolyte liquid from the first rising portion through a third rising portion of the conduit.
The electrochemical measuring system of the invention allows measurement of cyanide content in an effluent sample with hardly any fluctuation in the output signal. Though the mechanism by which the signal fluctuations are eliminated in the electrochemical measuring system of the present invention is not clearly understood, it appears that the unique design of the electrodes in the measuring system increases the contact of the cyanide ions with the working electrode as well as eliminates the occurrence of air bubbles at the electrode-electrolyte interface. Further, the apparatus comprising the electrochemical measuring system of the present invention enables determination of total (complex and free) cyanide content in the effluent sample. Thus, the efficiency and reproducibility of measurement is improved. Further, the electrochemical measuring system of the present invention has an output signal of high intensity as compared to the signal output of conventional electrochemical systems, thereby improving the sensitivity of measurement of cyanide content in an industrial effluent.
The above description is illustrative only and is not limiting. The present invention is defined by the claims that follow and their full range of equivalents.