FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
COMPLETE SPECIFICATION
(See Section 10)
"CHEMICAL OXYGEN DEMAND MEASUREMENT METHOD AND
APPARATUS"
We, UNITED PHOSPHORUS LIMITED,
a company incorporated under the Companies Act,
1956 and having its registered office at 3-11, GIDC,
Vapi-396195,
State of Gujarat, India,
INDIAN.
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:-

FIELD OF INVENTION
The present invention relates to an apparatus and a method for measuring the chemical oxygen demand of an aqueous sample. More particularly, the present invention relates to a spectrophotometric method and an apparatus for measuring the chemical oxygen demand of an aqueous sample.
BACKGROUND OF THE INVENTION
The regulatory restrictions prescribed in almost all the countries require waste water and other industrial aqueous discharge to be monitored to determine their suitability for disposal into large bodies of water such as lakes, rivers and seas. One of such requirements is the determination of the carbon content of the aqueous samples that are generated from industrial and other units.
Chemical oxygen demand, hereinafter referred to as COD, is a measure of the oxygen equivalent of the organic matter content of an aqueous sample that is susceptible to oxidation by a strong chemical oxidant. According to the known conventional method for calculating the chemical oxygen demand of an aqueous sample, the aqueous sample is digested using a combination of primary and secondary digestion catalysts. The primary digestion catalyst conventionally used in the art is concentrated sulfuric acid while the secondary catalyst is preferably silver sulfate. The secondary digestion catalyst is generally used to assist the oxidation of straight chain hydrocarbons such as diesel fuel and motor oil.
The aqueous sample to be tested is mixed with the abovesaid catalysts and the sample is allowed to digest at about 150°C in the presence of a strong oxidizing agent such as potassium dichromate. The dichromate anion containing hexavalent chromium ions oxidizes the organic sample present in the aqueous sample and in turn gets reduced to trivalent chromium ions releasing oxygen atoms which bond with carbon atoms to generate carbon dioxide.

The chemical reaction occurring during the oxidation of organic content present in an aqueous sample can be presented as follows:
Cr6++ Organic compound Acid C02 + H20 +Cr3+
|
3 Oxygen atoms have been released
The test method essentially determines the total carbon content in an aqueous sample by measuring the amount of oxygen consumed during the chemical reaction with the aqueous sample.
In the conventional titrimetric method for the determination of chemical oxygen demand, a known volume of the aqueous sample is taken in a container, preferably a conical flask with a round glass neck fittable with a condenser for refluxing. Subsequently, a predetermined quantity of mercuric chloride is added followed by a solution containing the primary and secondary digestion catalysts. A known quantity of potassium dichromate solution is added to the sample. The sample is then boiled for two hours and thereafter cooled down to the room temperature, and then diphenylamine indicator is added. The resultant mixture is titrated against ammonium ferrous sulfate and the quantity thereof consumed recorded. The above titrimetric procedure is repeated for a blank clear aqueous sample and the quantity of ammonium ferrous sulfate consumed is recorded.
The chemical oxygen demand of the provided aqueous sample is thereafter calculated using the following formula:
Calculation
C.O.D = (A-B)x 8000x Normality of AFS mg/L Equation no :1
Volume of COD sample in mL.
where A = Volume of AFS consumed for titration of blank in mL; and
B = Volume of AFS consumed for titration of sample after digestion in mL.

An alternative known method comprises vaporizing the water present in the aqueous sample and burning the organic material present therein. However, this method has a disadvantage that the inorganic nitrogen content of water in the form of ammonium and nitrate are concurrently oxidized along with the carbonaceous material, which therefore requires an additional ammonium and nitrate concentrations measurement and subsequent recalculation.
Another disadvantage of the known titrimetric method for the determination of chemical oxygen demand is that the known methods are all time-consuming requiring at least 2-4 hours for completion and are expensive costing the water industry and local government bodies exorbitant amounts worldwide annually.
These and other problems existing within the art are solved by way of the invention described hereinafter.
OBJECTS OF THE INVENTION
The various embodiments of the present invention may, but do not necessarily, achieve one or more of the following advantages and/or objects:
It is an object of the present invention to provide a method and an apparatus for the measurement of the chemical oxygen demand of an aqueous sample which significantly reduces the time required for the measurement of the chemical oxygen demand of the aqueous sample.
Yet another object of the present invention is to provide an apparatus and a method for the measurement of the chemical oxygen demand of an aqueous sample which does not require an additional ammonium and nitrate concentrations measurement and subsequent recalculation.
Yet another object of the present invention is to provide a cost-effective and convenient method for the measurement of the chemical oxygen demand of an aqueous sample.

Another object of the present invention is to provide a portable and reliable apparatus for the measurement of the chemical oxygen demand of an aqueous sample.
Yet another object of the present invention is to provide an apparatus and a method for the determination of the chemical oxygen demand of an aqueous sample that enables the calculation of the chemical oxygen demand of a provided aqueous sample within about 10 to about 20 minutes.
These and other advantages may be realized by reference to the remaining portions of the specification and abstract.
SUMMARY OF THE INVENTION
An apparatus for measuring the chemical oxygen demand of an aqueous sample comprising:
(a) a sample holder adapted to hold at least one provided aqueous sample;
(b) a light source placed on one side of said sample holder and adapted to generate light of a predetermined wavelength and illuminate said aqueous sample held within said sample holder;
(c) a photodetector placed on another side of said sample holder opposite to said illumination source such that the light generated by the light source, passing through the aqueous sample held in said sample holder, is received by the photodetector and is converted into an electrical signal corresponding to an optical property of the aqueous sample held within the sample holder;
(d) an analog to digital converter which receives the electrical signal generated by the photodetector and converts the received electrical signal into digital signal corresponding to an optical property of said aqueous sample held within the sample holder;
(e) a microcontroller comprising a storage means having stored therein a plurality of chemical oxygen demand values of a plurality of random samples matched to a plurality of digital signals corresponding to an optical property of said random samples, said microcontroller being adapted to (i) receive the digital signal

generated by said analog to digital converter for a provided aqueous sample, (ii) generate a chemical oxygen demand value matching the received digital signal, and (iii) output the generated chemical oxygen demand value; and (f) a display means capable of receiving the generated chemical oxygen demand value from said microcontroller and displaying the received chemical, oxygen demand.
A method for measuring the chemical oxygen demand of an aqueous sample comprising:
(a) selecting a first vial and a second vial;
(b) adding a first predetermined volume of a first reagent to said first and second vials;
(c) adding a second predetermined volume of distilled water to said first vial;
(d) adding a third predetermined volume of a provided aqueous sample to said second vial;
(e) adding a fourth predetermined volume of a second reagent to said first and second vials;
(f) digesting the contents of said first and second vials in a provided digester for a first predetermined amount of time;
(g) providing an apparatus for measuring the chemical oxygen demand of an aqueous sample comprising a sample holder, a light source, a photodetector, an analog to digital converter, a microcontroller and a display means;
(h) illuminating the aqueous sample held within the sample holder with light of predetermined wavelength generated from the light source, such that the light generated by the light source, passing through the aqueous sample, is received by the photodetector;
(i) causing the light incident on a subsequently placed provided photodetector to be converted into an electrical signal corresponding to an optical property of the aqueous sample held within the sample holder;

(j) causing the generated electrical signal to be converted into a digital signal corresponding to an optical property of the aqueous sample held within the sample holder using the provided analog to digital converter;
(k) communicating the generated digital signal to a provided microcontroller, said microcontroller comprising a storage means having stored therein a plurality of chemical oxygen demand values matched to a plurality of digital signals corresponding to an optical property of a plurality of random samples;
(1) causing the microcontroller to generate a chemical oxygen demand value matching the digital signal corresponding to an optical property of the provided aqueous sample; and
(m)displaying the generated chemical oxygen demand on said provided display means.
A kit-of-parts for chemical oxygen demand measurement of an aqueous sample comprising:
(a) a plurality of sample vials, each said sample vial having a cap;
(b) a first reagent comprising a predetermined amount of potassium dichromate and another predetermined amount of mercuric sulfate in a liquid mixture comprising water and sulfuric acid;
(c) a second reagent comprising a predetermined amount of silver sulfate in sulfuric acid;
(d) a digester for completely or partially oxidizing the carbonaceous content of a plurality of aqueous samples;
(e) an apparatus for measuring the chemical oxygen demand of an aqueous sample comprising a sample holder,, a light source, a photodetector, analog signal conditioning circuit, an analog to digital converter, a microcontroller and a display means; and
(f) an instruction manual comprising instructions for chemical oxygen demand measurement according to a predetermined method.
The above description sets forth, rather broadly, a summary of one embodiment of the present invention so that the detailed description that follows may be better

understood and contributions of the present invention to the art may be better appreciated. Some of the embodiments of the present invention may not include all of the features or characteristics listed in the above summary. There are, of course, additional features of the invention that will be described below and will form the subject matter of the present invention. In this respect, before explaining at least one preferred embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of the construction and to the arrangement of the components set forth in the following description or as illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in connection with the drawings described hereinafter.
Figure 1 represents a schematic representation of the apparatus for measuring chemical oxygen demand according to the present invention.
Figure 2 is a flowchart depicting the operation of the apparatus according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Accordingly, in one aspect, the present invention provides an apparatus for measuring the chemical oxygen demand of an aqueous sample. The apparatus comprises a sample holder, a light source, a photodetector, signal conditioning circuit, an analog to digital converter, microcontroller and a display means.
The sample holder is adapted to hold a vial containing an aqueous sample. Accordingly, in an embodiment, a vial containing an aqueous sample may be placed in the sample

holder for a time such that the apparatus may measure the chemical oxygen demand corresponding to the placed aqueous sample. Subsequently, the measured sample may be removed and a second sample may be placed for measurement. In an embodiment, a plurality of aqueous samples may be placed in the sample holder successively allowing the chemical oxygen demand of the placed samples to be measured sequentially.
The apparatus comprises a light source which is placed on one side of the sample holder. The light source generates light of a selected wavelength and illuminates the aqueous sample placed within the sample holder.
In an embodiment, the illumination source comprises an interference filter that is adapted to allow a specific wavelength of light to pass through it thereby enabling a specific wavelength of light to be selected for analysis of the aqueous sample. In another embodiment, said interference filter is powered by a provided motor allowing the filter to be changed enabling a predetermined wavelength of light to be selected.
In another embodiment, the illumination source illuminates the aqueous sample at 420 nm light. In yet another embodiment, the illumination source illuminates the aqueous sample at 600 nm light. In yet another embodiment, the light source is preferably a light emitting diode. The light emitting diode preferably emits light at a wavelength of 420 nm or 600 nm. The semiconductor materials used to fabricate light emitting diodes capable of emitting light specifically at 420 nm and/or 600 nm are known in the art and do not particularly limit the scope of the present invention.
The apparatus further comprises a photodetector which is placed on another side of the sample holder such that it is disposed opposite to the light source. The light having a predetermined wavelength generated by the light source illuminates and passes through the aqueous sample held in the sample holder and is received by the photodetector placed opposite to the light source. The photodetector generates an electrical signal in response to the incident light passing through the aqueous sample. The light passing through aqueous samples having different chemical oxygen demand values is absorbed or transmitted to a different degree. A difference in absorbance or transmittance between

different aqueous samples causes different light power to be incident upon the photodetector triggering the generation of electrical signals having different amperages.
In an embodiment, the preferred photodetector may be a photodiode although other photodetectors are not excluded, which are capable of generating an electrical signal in response to the incident light passing through the aqueous sample. Such other photodetectors may be conveniently selected from optical detectors, chemical detectors such as photographic plates, light dependent resistors, photovoltaic cells, photomultipliers comprising photocathodes, phototubes, phototransistors, pyroelectric detectors, Golay cells, cryogenic detectors, charge-coupled devices and reverse-biased LEDs.
In another embodiment, a plurality of light sources and photodetectors may be positioned equidistant around the sample holder. Preferably, three light sources illuminating at the same selected wavelength and three photodetectors are placed equidistant from the aqueous sample holder. It has been found that such an arrangement substantially improves the reproducibility of the apparatus readings and the standard deviation of the individual readings. In this embodiment, the apparatus is adapted to simultaneously measure the absorbance from said plurality of positions at which said photodetectors are placed and the average of the said plurality of absorbance readings is utilized for the measurement of the chemical oxygen demand value of an aqueous sample.
In an embodiment, the photodetector generates electrical signal corresponding to a predefined optical property of the aqueous sample. The predefined optical property may be either absorbance or transmittance of the aqueous sample.
The apparatus of the present invention comprises an analog to digital converter which receives the electrical signal generated by the photodetector and converts the received electrical signal into a digital signal, which measures the optical property of the aqueous sample held within the sample holder.
In an embodiment, the preferred analog to digital converter is a 12-bit MCP3204. These devices are successive approximation 12-bit analog to digital converters with on-board sample and hold circuitry. The specifications of the preferred converter MCP3204 are

available from Microchip Technology Inc., which may be accessed via the internet at http://wwl .microchip.com/downloads/en/DeviceDoc/21298e.pdf. The contents of the specifications are incorporated herein in its entirety.
The zero drift is inherent in the design of a photodetector and remains constant throughout the life cycle of the photodetector. It results from physical changes within the photodetector such as change in resistance etc. within the photodetector. The span drift results from a decrease in the signal magnitude when the photodetector becomes catalytic active site-limited with the passage of time.
In a preferred embodiment, the apparatus of the present invention comprises a drift compensation means which compensates the span and zero drifts in the digital signal generated by the analog to digital converter. In another embodiment, the drift compensation means may be adapted to compensate the span and zero drifts in the electrical signal generated by the photodetector.
The apparatus of the present invention comprises a microcontroller. The microcontroller comprises a storage means having stored therein a plurality of chemical oxygen demand values of a plurality of random samples matched to a plurality of digital signals corresponding to an optical property of said random samples.
In an embodiment, the optical property of the aqueous samples may be absorbance. In this embodiment, the microcontroller has stored therein a plurality of chemical oxygen demand values of a plurality of random samples matched to a plurality of digital signals corresponding to the absorbance of the random samples.
In this embodiment, the microcontroller is adapted to receive the digital signal corresponding to the measured absorbance of a digested sample. The measured absorbance corresponds to the concentration of Cr ions, which is produced when the aqueous sample to be tested is digested with a known amount of potassium dichromate. The hexavalent chromium ions oxidize the organic sample and in turn get reduced to the trivalent chromium ions. The microcontroller correlates the measured absorbance to the

concentration of the trivalent chromium ions in the digested sample, which is directly proportional to the chemical oxygen demand of the sample.
In another embodiment, the optical property of the aqueous samples may be percentage transmission of light through the aqueous sample. In this embodiment, the microcontroller has stored therein a plurality of chemical oxygen demand values of a plurality of random samples matched to a plurality of digital signals corresponding to the percentage transmission of the random samples.
The microcontroller according to the present invention is adapted to receive the digital signal generated by the analog to digital converter for an aqueous sample and generate a chemical oxygen demand value matching the received digital signal.
In an embodiment, the microcontroller receives the digital signal corresponding to an aqueous sample, searches the stored values of digital signals to locate the instance wherein the received digital signal matches exactly with the stored digital signal and generates the chemical oxygen demand value matching the stored digital signal.
In another embodiment, the microcontroller plots the stored digital signals against the corresponding chemical oxygen demand values in a graph. In the event of the microcontroller receiving a digital signal, it calculates the corresponding chemical oxygen demand value by plotting the received digital signal on the stored graph.
In another embodiment, the microcontroller is adapted to calculate the slope of the plotted graph and calculate the chemical oxygen demand value of the aqueous sample from said calculated slope.
In this embodiment, the microcontroller thereof calculates the sample COD value from the corresponding calibration plot. In a preferred embodiment, the sequence of calculating the COD value from the input digital signal identifying the absorbance of a particular sample may be automated.

In this embodiment, software sub-routines designed to control the device functions automatically may be provided within the microcontroller. Some exemplary functions according to the preferred embodiment may be sample COD measurement and system calibration using blank and reference standards. Preferably, each function may be subdivided into separate sub-functions, which may be each be automated by a different subroutine. Some exemplary sub-functions according to a preferred embodiment may be sample and reagents loading, heating, measuring, loading etc.
In an embodiment, the apparatus of the present invention allows one or more parameters associated with each of these sub-functions to be modified, which enables the apparatus to be adapted to specific characteristics of water samples available from different regions or sources such as sea water, fresh water etc. Therefore, in this embodiment, the present invention allows the apparatus to measure the COD values of different aqueous samples by correspondingly modifying one or more parameters associated with one or more sub-functions.
In another embodiment, the microcontroller is adapted to record the "zero" reading of a blank sample and the standard "maximum" reading of a known sample having a known chemical oxygen demand value. In this embodiment, a blank distilled water sample is placed in said sample holder and the chemical oxygen demand value corresponding to said sample is set as "zero". Further, a standard reference having known chemical oxygen demand value e.g. an oxalic acid solution having a known concentration is placed in said sample holder and the chemical oxygen demand value corresponding to this standard sample is calibrated as the standard.
In a preferred embodiment, aqueous oxalic acid solution at a concentration of 1000 mg/L is taken an standard solution with chemical oxygen demand measurement of 1000 mg/L. The chemical oxygen demand value corresponds to the number of reducible oxygen present in a known amount of oxalic acid.

The apparatus of the present invention comprises a display means. The display means receives a calculated chemical oxygen demand value from the microcontroller and visually displays the received chemical oxygen demand value.
In another embodiment, the apparatus of the present invention may include a communication means which receives the calculated chemical oxygen demand of a predetermined sample and stores the received chemical oxygen demand value into a memory provided on an authorized computer. Preferably, the authorized computer is a pre-defined central server located at a predetermined location.
In another embodiment, the communication means of the present invention is capable of transmitting the calculated chemical oxygen demand values to a plurality of predetermined remote locations over a communication network.
The communication means may be a wireless communication means such as a GSM module. The wireless communication means transmits the stored real-time chemical oxygen demand values to a wireless data receiving device in real time. In a further preferred embodiment, the wireless communication means may be a GSM module which transmits the stored chemical oxygen demand values via SMS to a pre-defined mobile phone registered in the GSM module. The apparatus of the present invention may thus enable a real-time monitoring of the chemical oxygen demand values of aqueous samples at a specified location by a user placed at a remote location.
In another embodiment, the stored chemical oxygen demand value may be simultaneously transmitted to a remote location over a communication network where it may be accessed by authorized personnel. The communication network may be radio transmission network, telephone line, optical fiber transmission line, cable line and internet.
In another preferred embodiment, the communication means may cause the chemical oxygen demand values measured at a specified location to be transmitted to a predetermined website in real-time. The website allows authorized personnel to access the transmitted data and to communicate corrective instructions to the microcontoller via the

internet. In a preferred embodiment, the website authorization means prompting the personnel to enter the given login and password and allowing personnel access to the chemical oxygen demand values subsequent to successful authorization.
In another aspect, the present invention provides a method for measuring the chemical oxygen demand of an aqueous sample.
The method of the present invention comprises selecting a first vial and a second vial. Preferably, the first vial may be labeled as "blank sample" while the second vial may be labeled as "aqueous sample". However, it should be understood that selection of two vials is only exemplary and does not limit the present method in any manner. In an embodiment, a plurality of vials may be selected.
The method of the present invention comprises adding a predetermined volume of a first reagent to the selected first and second vials. Preferably, the predetermined volume added to the selected vials is about 1 mL though lower or greater volumes are also possible without limitation.
In a most preferred embodiment, first reagent preferably comprises about 12 g/L of potassium dichromate, about 96 g/L of mercuric sulfate in about 880 mL of water and about 120 mL of sulfuric acid. However, these specified amounts are exemplary and appropriate amounts may be arrived at by a skilled addressee without undue experimentation.
A predetermined amount of distilled water is thereafter added to the first vial. Preferably, about 1 mL of distilled water is added though lesser and greater amounts of distilled water may also be.added without limitation. Thereafter, a predetermined volume of the provided aqueous sample to be tested is added to the second vial. In an embodiment, about 1 mL of the provided aqueous sample may be added although lesser and greater amounts may also be added without limitation.

Thereafter, a known volume of a second reagent is added to both the selected vials. In an embodiment, about 1 mL of the second reagent may be added although lesser and greater amounts may also be added without limitation.
Most preferably, though without limitation, the second reagent comprises about 14 g/L of silver sulfate in about 1 L of concentrated sulfuric acid.
The method of the present invention thereafter comprises digesting the contents of the first and second vials in a provided digester for a predetermined amount of time. Preferably, a plurality of aqueous samples may be placed simultaneously within the digester. The digester completely or partially oxidizes the carbonaceous content of the plurality of aqueous samples placed within it.
In a preferred embodiment, the contents of the first and second vials are preferably digested for about two hours.
In an embodiment of the present invention, the digestion time of the aqueous samples is significantly reduced by microwave heating the aqueous samples for a substantial period during digestion.
In a preferred embodiment, the aqueous samples are digested for a period ranging from about 5 minutes to about 2 hours. Preferably, the aqueous samples are digested for a period of about 20 minutes in the presence of microwave heating.
The method according to the present invention comprises providing an apparatus for measuring the chemical oxygen demand of an aqueous sample comprising a sample holder, a light source, a photodetector, signal conditioning circuit , an analog to digital converter, a microcontroller and a display means. Preferably, the provided apparatus according to this aspect of the invention is the apparatus as described in the preceding aspect of the present invention or according to any embodiment thereof.

The method of the present invention further comprises selecting a wavelength of light for analysis of the aqueous sample. The light source is thereafter adapted to illuminate the aqueous sample held within the sample holder at the selected wavelength.
In an embodiment, the illumination source comprises an interference filter that is adapted to allow a specific wavelength of light to pass through it thereby enabling a specific wavelength of light to be selected for analysis of the aqueous sample. In another embodiment, said interference filter is powered by a provided motor allowing the filter to be changed enabling a predetermined wavelength of light to be selected.
In yet another embodiment, the light source is preferably a light emitting diode. The light emitting diode preferably emits light at a wavelength of 420 nm or 600 nm.
In another embodiment, the method of the present invention additionally comprises receiving the calculated chemical oxygen demand of a predetermined sample and storing the received chemical oxygen demand value into a memory provided on an authorized computer via a provided communication means. Preferably, the authorized computer is a pre-defined central server located at a predetermined location.
In another embodiment, the method of the present invention may additionally comprise transmitting the calculated chemical oxygen demand values to a plurality of predetermined remote locations via the provided communication means.
The communication means may be a wireless communication means such as a GSM module. The wireless communication means transmits the stored real-time chemical oxygen demand values to a wireless data receiving device in real time. In a further preferred embodiment, the wireless communication means may be a GSM module which transmits the stored chemical oxygen demand values via SMS to a pre-defined mobile phone registered in the GSM module. The method of the present invention may additionally comprise a real-time monitoring of the chemical oxygen demand values of aqueous samples at a specified location by a user placed at a remote location.

In another embodiment, the method of the present invention may additionally comprise simultaneously transmitting the chemical oxygen demand values to a remote location over a communication network where it may be accessed by authorized personnel. The communication network may be radio transmission network, telephone line, optical fiber transmission line, cable line and internet.
In another preferred embodiment, the method of the present invention may additionally comprise transmitting the chemical oxygen demand values measured at a specified location to a pre-determined website in real-time. The website allows authorized personnel to access the transmitted data and to communicate corrective instructions to the microcontroller via the internet. In a preferred embodiment, the website authorization protocol may include prompting the personnel to enter the given login and password and allowing personnel access to the chemical oxygen demand values subsequent to successful authorization.
In a preferred embodiment of the method according to the present invention, the volumes of sample and reagents are placed in provided vials. Preferably, the volume of each component is predetermined and that the total volume is the same for the sample vial as well as the blank vial.
In an embodiment, the digested samples are diluted to a known volume such that the volume of the blank sample and the aqueous samples are same. The samples are thereafter cooled to room temperature slowly to avoid precipitation. Preferably, the method comprises venting the cooled samples to relieve any pressure generated during the digestion. The contents of the digested vials are combined with condensed water to settle or dislodge insoluble matter. The suspended matter may be allowed to settle till the optical path through the samples becomes clear. The absorption of blank and aqueous samples may thereafter be measured at a selected wavelength of either 420 nm or 600 nm.
In an embodiment, the method of the present invention comprises measuring the chemical oxygen demand of an aqueous sample at 600 nm. In this embodiment, an

undigested blank is used as a reference solution. The method comprises analyzing the digested blank to determine the chemical oxygen demand of the blank sample. The measured chemical oxygen demand of the blank sample is subtracted from the chemical oxygen demand of the aqueous sample.
In an alternate embodiment, the method of the present invention comprises using a digested blank sample as the reference solution.
In another embodiment, the method of the present, invention comprises measuring the chemical oxygen demand of an aqueous sample at 420 nm. In this embodiment, the method comprises using distilled water as a reference solution.
In this embodiment, the method comprises calculating the initial dichromate absorption by measuring the absorption of an undigested blank sample wherein the aqueous sample is replaced with distilled water. The method of the invention additionally comprises calculating the difference between absorbance of a digested aqueous sample and the digested blank, which corresponds to the chemical oxygen demand of the aqueous sample.
In another aspect of the present invention, there is provided a kit-of-parts for chemical oxygen demand measurement of an aqueous sample. The kit comprises a plurality of sample vials, a first reagent, a second reagent, a digester, a chemical oxygen demand measuring apparatus and an instruction manual.
The plurality of sample vials have a cap provided at the top portions thereof for enclosing the aqueous samples placed within said samples from the external environment.
The kit according to the present invention comprises a first reagent. In a preferred embodiment, the first reagent preferably comprises about 12 g/L of potassium dichromate, about 96 g/L of mercuric sulfate in about 880 mL of water and about 120 mL of sulfuric acid.

The kit according to the present invention further comprises a second reagent. More preferably, the second reagent comprises about 14 g/L of silver sulfate in about 1 L of concentrated sulfuric acid.
The kit according to the present invention additionally comprises a digester. The digester is provided to either completely or partially oxidize the carbonaceous content of a plurality of aqueous samples.
The kit according to the present invention comprises an apparatus for measuring the chemical oxygen demand. The apparatus comprises a sample holder, a light source, a photodetector, an analog to digital converter, a microcontroller and a display means.
In an embodiment, the apparatus comprised in the kit according to the present invention is in accordance with any preceding aspect relating to the apparatus or an embodiment thereof.
The kit according to the present invention further comprises an instruction manual comprising instructions for chemical oxygen demand measurement according to a predetermined method. Preferably, the instructions included within the instruction manual causes the method of the present invention recited in any preceding aspect or embodiment to be carried out.
In an embodiment, the kit according to the present invention comprises a plurality of pipettes. The provided pipettes facilitate quantitative transportation of a sample from one vial or container to another during the measurement of the chemical oxygen demand according to the present invention.
A verification of the performance of the apparatus of the present invention was compared vis-a-vis the conventionally known apparatus. The result of the verification protocol followed is brought out as hereunder:
S No. Reading of the Conventional Percentage
apparatus according apparatus deviation

to the present invention
1 466 460 1
2 424 455 -7
3 350 320 9
4 279 268 4
5 342 312 9
6 529 500 5
7 418 410 2
8 485 518 -7
9 377 401 -7
10 393 425 -8
The result of another verification protocol is tabulated as hereunder:

SNo. Reading of a Reading of the Percentage
competitive apparatus according deviation
apparatus to the present invention
1 1582 1446 +8.5
2 6059 5530 +8.7
3- 2126 2230 -4.8
It was surprisingly found that the apparatus according to the present invention provided comparable results in a significantly reduced time period of about 20 minutes as compared to about 2 to 4 hours required for the conventional apparatuses known in the art.
Turning now to figure 1, illustrated is a representation of the apparatus for measuring chemical oxygen demand according to the present invention. The apparatus (1) comprises a sample holder, a light source, a photodetector, signal conditioning circuit, an analog to digital converter, ,microcontroller and a display means.

The sample holder (2) is adapted to hold a vial containing an aqueous sample. The apparatus further comprises a light source (3) which is placed on one side of the sample holder. The light source generates light of a selected wavelength and illuminates the aqueous sample placed within the sample holder. A photodetector (4) is placed on the other side of the sample holder (2) such that it is disposed opposite to the illumination source (3). The light having a predetermined wavelength generated by the illumination source illuminates and passes through the aqueous sample held in the sample holder and is received by the photodetector placed opposite to the illumination source. The photodetector generates an electrical signal in response to the incident light passing through the aqueous sample.
A digital to analog converter (5) is connected to signal conditioning circuit having the photodetector and receives the electrical signal generated by the photodetector in response to the incident light. The apparatus optionally comprises a drift compensating means (6) according to the present invention.
The apparatus of the present invention comprises a microcontroller (7). The microcontroller comprises a storage means having stored therein a plurality of chemical oxygen demand values of a plurality of random samples matched to a plurality of digital signals corresponding to an optical property of said random samples. In an embodiment, the optical property of the aqueous samples may be absorbance. In this embodiment, the microcontroller has stored therein a plurality of chemical oxygen demand values of a plurality of random samples matched to a plurality of digital signals corresponding to the absorbance of the random samples. In another embodiment, the optical property of the aqueous samples may be percentage transmission of light through the aqueous sample. In this embodiment, the microcontroller has stored therein a plurality of chemical oxygen demand values of a plurality of random samples matched to a plurality of digital signals corresponding to the percentage transmission of the random samples. The microcontroller according to the present invention is adapted to receive the digital signal generated by the analog to digital converter for an aqueous sample and generate a chemical oxygen demand value matching the received digital signal. In an embodiment, the

microcontroller receives the digital signal corresponding to an aqueous sample, searches the stored values of digital signals to locate the instance wherein the received digital signal matches exactly with the stored digital signal and generates the chemical oxygen demand value matching the stored digital signal. In another embodiment, the microcontroller plots the stored digital signals against the corresponding chemical oxygen demand values in a graph. In the event of the microcontroller receiving a digital signal, it calculates the corresponding chemical oxygen demand value by plotting the received digital signal on the stored graph. In another embodiment, the microcontroller is adapted to calculate the slope of the plotted graph and calculate the chemical oxygen demand value of the aqueous sample from said calculated slope. The calculated chemical oxygen demand is displayed on a display means (8).
Turning to figure 2, illustrated is a flowchart depicting the operation of the apparatus according to the present invention. At the start of the apparatus, the display means displays a welcome note, name and purpose of the apparatus along with absolute measurable range, resolution and the mode of operation of the apparatus. The apparatus then prompts the user to select either the calibration mode or the sampling mode. In response to a calibration mode input received from the user, the apparatus prompts the user to enter a password and upon a successful password authorization, receives a known concentration of a reference sample and self-calibrates the chemical oxygen demand apparatus accordingly. In response to a sampling mode input received from the user, the apparatus prompts the user to place a blank sample into the sample holder and actuate a provided enter key on the apparatus. The apparatus thereafter prompts the user to place an aqueous sample to be analyzed into the sample holder and actuate the provided enter key on the apparatus. The apparatus calculates the chemical oxygen demand of the aqueous sample on actuating the enter key and displays the concentration of the organic material present in the sample on the provided display means.
It is understood that the systems and methods described herein can be implemented in hardware, software, functions and means or a combination of hardware, software, functions and means to attain those functions. They may be implemented by any type of computer system or other devices adapted for carrying out the methods described herein.

A typical combination of hardware and software could be a general-purpose computer system with a computer program that, when loaded and executed, controls the computer system such that it carries out the methods described herein. Alternatively, a specific use computer, containing specialized hardware for carrying out one or more of the functional tasks of the invention could be utilized.
The present invention can also be embedded in a computer program product, which comprises all the features enabling the implementation of the methods and functions described herein, and which--when loaded in a computer system--is able to carry out these methods.
Wherein the aforegoing reference has been made to integers or components having known equivalents, then such equivalents are herein incorporated as if individually set forth accordingly will be appceciated .that change may be made to the ab?re described embodiments of the invention without departing from the principles taught herein. Additional advantages of the present invention will become apparent for those skilled in the art after considering the principles in particular form as discussed and illustrated. Thus, it will be understood that the invention is not limited to the particular embodiments described or illustrated, but is intended to cover all alterations- or modifications which are within the scope of the present invention.

WE CLAIM
1. An apparatus for measuring the chemical oxygen demand of an aqueous sample comprising:
(a) at least one sample holder adapted to hold at least one provided aqueous sample;
(b) at least one light source placed on one side of said sample holder and adapted to generate light of a predetermined wavelength and illuminate said aqueous sample held within said sample holder;
(c) at least one photodetector placed on another side of said sample holder opposite to said illumination source such that the light generated by the light source, passing through the aqueous sample held in said sample holder, is received by the photodetector and is converted into an electrical signal corresponding to an optical property of the aqueous sample held within the sample holder;
(d) at least one analog to digital converter which receives the electrical signal generated by the photodetector and converts the received electrical signal into digital signal corresponding to an optical property of said aqueous sample held within the sample holder;
(e) at least one microcontroller comprising a storage means having stored therein a plurality of chemical oxygen demand values of a plurality of random samples matched to a plurality of digital signals corresponding to an optical property of said random samples, said microcontroller being adapted to (i) receive the digital signal generated by said analog to digital converter for a provided aqueous sample, (ii) generate a chemical oxygen demand value matching the received digital signal, and (iii) output the generated chemical oxygen demand value; and

(f) at least one display means capable of receiving the generated chemical oxygen demand value from said microcontroller and displaying the received chemical oxygen demand.
2. The apparatus as claimed in claim 1, wherein said sample holder is adapted to simultaneously hold a plurality of aqueous samples.
3. The apparatus as claimed in claim 1 or claim 2, wherein said light source illuminates said aqueous sample at 420 nm or 600 nm light.
4. The apparatus as claimed in any preceding claim, wherein said light source is a light emitting diode.
5. The apparatus as claimed in any preceding claim, wherein the photodetector is selected from optical detectors, chemical detectors such as photographic plates, light dependent resistors, photovoltaic cells, photomultipliers comprising photocathodes, phototubes, phototransistors, pyroelectric detectors, Golay cells, cryogenic detectors, charge-coupled devices, reverse-biased LEDs and photodiodes.
6. The apparatus as claimed in claim 5, wherein said photodetector is a photodiode.
7. The apparatus as claimed in any preceding claim, wherein at least three light sources and photodetectors are positioned equidistant from the sample holder.
8. The apparatus as claimed in any preceding claim, wherein said photodetector generates electrical signal corresponding to either absorbance or transmittance of the aqueous sample.
9. The apparatus as claimed in any preceding claim, wherein said analog to digital converter is MCP3204.
10. The apparatus as claimed in any preceding claim, wherein said microcontroller has stored therein a plurality of chemical oxygen demand values of a plurality of

aqueous samples matched to a plurality of digital signals corresponding to the absorbance of the samples. -
11. The apparatus as claimed in any preceding claim, wherein said microcontroller, upon receipt of a digital signal corresponding to an aqueous sample, searches the stored values of digital signals to locate the instance wherein the received digital signal matches exactly with the stored digital signal and generates the chemical oxygen demand value matching the stored digital signal.
12. The apparatus as claimed in claims 1-10, wherein said microcontroller plots the stored digital signals against the corresponding chemical oxygen demand values in a graph and upon receipt of a digital signal corresponding to an aqueous sample, calculates the corresponding chemical oxygen demand value by plotting the received digital signal on the stored graph.
13. The apparatus as claimed in claim 12, wherein said microcontroller calculates the slope of the plotted graph and calculates the chemical oxygen demand value of the provided sample from said calculated slope.
14. The apparatus as claimed in any preceding claim comprising a communication means.
15. The apparatus as claimed in any preceding claim capable of generating the chemical oxygen demand values of a provided aqueous sample within about twenty minutes.
16. A method for measuring the chemical oxygen demand of an aqueous sample comprising:

(a) selecting a first vial and a second vial;
(b) adding a first predetermined volume of a first reagent to said first and second vials;
(c) adding a second predetermined volume of distilled water to said first vial;
(d) adding a third predetermined volume of a provided aqueous sample to said second vial;

(e) adding a fourth predetermined volume of a second reagent to said first and second vials;
(f) digesting the contents of said first and second vials in a provided digester for a first predetermined amount of time;
(g) providing an apparatus for measuring the chemical oxygen demand of an aqueous sample comprising a sample holder, a light source, a photodetector, an analog to digital converter, a microcontroller and a display means;
(h) illuminating the aqueous sample held within the sample holder with light of predetermined wavelength generated from the light source, such that the light generated by the light source, passing through the aqueous sample, is received by the photodetector;
(i) causing the light incident on a subsequently placed provided photodetector to be converted into an electrical signal corresponding to an optical property of the aqueous sample held within the sample holder;
(j) causing the generated electrical signal to be converted into a digital signal corresponding to an optical property of the aqueous sample held within the sample holder using the provided analog to digital converter;
(k) communicating the generated digital signal to a provided microcontroller, said microcontroller comprising a storage means having stored therein a plurality of chemical oxygen demand values matched to a plurality of digital signals corresponding to an optical property of a plurality of random samples;
(1) causing the microcontroller to generate a chemical oxygen demand value matching the digital signal corresponding to an optical property of the provided aqueous sample; and
(redisplaying the generated chemical oxygen demand on said provided display means.

17. The method as claimed in claim 16, wherein said first reagent comprises about 12 g/L of potassium dichromate and about 96 g/L of mercuric sulfate in about 880 mL of water and about 120 mL of sulfuric acid.
18. The method as claimed in claim 16 or claim 17, wherein said second reagent comprises about 14 g/L of silver sulfate in about 1 L of concentrated sulfuric acid.
19. The method as claimed in claims 16-18 comprising analyzing a digested blank to determine the chemical oxygen demand of the blank sample and subtracting the measured chemical oxygen demand of the blank sample from the chemical oxygen demand of a provided aqueous sample.
20. The method as claimed in claims 16-18 comprising calculating the difference between absorbance of a digested aqueous sample and distilled water.
21. A kit-of-parts for chemical oxygen demand measurement of an aqueous sample comprising:

(a) a plurality of sample vials, each said sample vial having a cap;
(b) a first reagent comprising a predetermined amount of potassium dichromate and another predetermined amount of mercuric sulfate in a liquid mixture comprising water and sulfuric acid;
(c) a second reagent comprising a predetermined amount of silver sulfate in sulfuric acid;
(d) a digester for completely or partially oxidizing the carbonaceous content of a plurality of aqueous samples;
(e) an apparatus for measuring the chemical oxygen demand of an aqueous sample comprising a sample holder, a light source, a photodetector, an analog to digital converter, a microcontroller and a display means; and
(f) an instruction manual comprising instructions for chemical oxygen demand measurement according to a predetermined method.

22. The kit-of-parts as claimed in claim 21, wherein said first reagent comprises about 12 g/L of potassium dichromate, about 96 g/L of mercuric sulfate in about 880 mL of water and about 120 mL of sulfuric acid.
23. The kit-of-parts as claimed in claims 21-22, wherein said second reagent comprises about 14 g/L of silver sulfate in about 1 L of concentrated sulfuric acid.
24. The kit-of-parts as claimed in claims 21-23 comprising a plurality of pipettes.
25. An apparatus for measuring the chemical oxygen demand of an aqueous sample substantially as described herein with reference to the accompanying drawings.
26. A method for measuring the chemical oxygen demand of an aqueous sample substantially as described herein with reference to the accompanying drawings.
27. A kit-of-parts for measuring the chemical oxygen demand of an aqueous sample substantially as described herein with reference to the accompanying drawings.