Title of Invention

A GAS DOSIMETER FOR DETECTING PHOSPHINE DURING FUMIGATION

Abstract

Abstract The present invention describes a simple method of measuring the cumulative dose of phosphine to which a commodity is exposed to during fumigation using a dosimeter which comprises of a pre-calibrated glass tube filled with a diffusing medium like silica gel impregnated with gold chloride. The dosimeter gives a visual indication of the phosphine concentration by the colour stain which develops as the phosphine diffuses into the medium through the open end of the tube.

Full Text

FORM 2 THE PATENTS ACT 1970 (39 Of 1970) And THE PATENT RULES, 2003 (See Section 10, rule 13) Improved method for monitoring fumigation UNITED PHOSPHORUS LIMITED, a company incorporated under the Companies Act, 1956 having its registered office at 3-11, GIDC, Vapi-396 195, State of Gujarat, India and its corporate office at Uniphos House, 11th Road, C. D. Marg, Khar (West), Mumbai - 400 052, State of Maharashtra, India, an Indian Company. The following specification particularly describes the invention and the manner in which it is to be performed:- FIELD OF INVENTION: The invention relates to a method of measuring cumulative dose of a gas during fumigation. More particularly the invention relates to measuring phosphine concentration by a visual reaction using a dosimeter. BACKGROUND OF THE INVENTION : It is a common practice to use fumigation to destroy pests such as insects, worms and rodents which might damage grains, cereals, spices and other agricultural products stored in bulk compartments or chambers. Phosphine is currently the most preferred fumigant because of its relative safety and reported lack of serious health hazards associated with other fumigants such as methyl bromide, ethylene oxide and ethylene dibromide and sulphur oxide. Unlike other fumigants, phosphine leaves minimum toxic residues, relatively inexpensive and does not accumulate in the food chain. Any residue of phosphine will be lost or oxidized to a harmless phosphate when the grain is processed to produce a food. During fumigation, phosphine is generated in situ using aluminium phosphide or other metal phosphides by slow action of atmospheric or grain moisture. A1P + H20 ► PH3+Al(OH3) A modification of this technique involves the placement of pellets of a metallic phosphide in the head-space of a grain silo and allowing the phosphine produced when the phosphide reacts with moisture in atmosphere above the grain to be circulated through the stored grain by the natural convection currents that are present in the silo. Phosphine cyclinders or generators have also been used for this purpose. For the total elimination of insects / pests, it is necessary to maintain a certain concentration of phosphine for a stipulated period of time. Successful fumigation 2 depends on phosphine dose i.e. which is the concentration - time product expressed in ppm hrs or ppm days. Phosphine dose = C x T (Concentration x Time) Fumigation has to be performed in air tight enclosures to maintain necessary concentration of the phosphine in the chamber throughout the period of the treatment. A small opening or crack in the compartment may lead to leakage of the gas resulting in inadequate fumigation inspite of the longer duration of treatment; low concentration can lead to eggs and pupae surviving the fumigation. In fact US Patent No. 5063771 describes the method of testing for leaks in compartments intended to contain goods specially cereals, in bulk, in which disinfection or insecticidal action by fumigation with gases like phosphine is to be performed. Hence, there is a critical need for a method to monitor dose of phosphine during fumigation. There are eletronic instruments with sensors for measuring phosphine concentration at any instant of time at a chosen location in the fumigation enclosure. There are also detector tubes available for the measurement of phosphine at any given time. The phosphine detector tubes which are available have the following drawbacks : 1. Most of them need the use of pump for drawing the samples, which could be cumbersome and if not used properly may lead to erroneous results. 2. Detector tubes with pumps vitiate the measuring environment. 3. Not suitable for continuous monitoring; can provide information regarding the level of gas at the specific time and not the total dose to which the commodity is exposed. 3 The phosphine dose can only be evaluated by measuring the phosphine concentration at every 1 - 5 hours interval over the entire period of fumigation of 200 hours and computing the area under curve. This involves several measurements using either detector tubes or electronic instruments. It is a cumbersome, time consuming and costly process. There are no instruments available which can directly measure the phosphine dose or the phosphine concentration time product - which is essential for ensuring successful fumigation. The main object of the present invention is to provide a simple method which can measure the phosphine dose, in a single measurement - using a dosimeter during fumigation without vitiating the environment at the point of measurement. Another object of the present invention is to provide a method which can be used for determining the phosphine concentration distribution in an enclosure. SUMMARY The present invention discloses a method for measuring the total dose of phosphine to which a commodity is exposed during fumigation through visual indication using a pre-calibrated dosimeter comprising of a transparent tube preferably made up of glass with both the ends sealed, with a means at one end for opening before use and the tube filled with at least one gas diffusing porous medium containing at least one gas detecting sensor capable of reacting with the target gas diffusing into the medium through the open end of the tube. In one embodiment of the invention , the gas diffusing medium is silica gel and the gas detecting sensor is gold chloride , the concentration of gold chloride approximately around 7000 ppm. 4 In yet another embodiment, the glass tube is sealed at both the ends with a predetermined scratch mark for breaking the tube at one end. Another embodiment of the invention discloses gas dosimeter comprising of a pre-calibrated transparent tube preferably made up of glass with both the ends sealed having a means at one end for opening the tube before use and the tube filled with at least one gas diffusing medium containing at least one gas detecting sensor capable of reacting with the target gas diffusing into the medium through the open end of the tube. Still another embodiment discloses that the gas to be measured is phosphine. BRIEF DESCRIPTION OF THE DRAWING : The Fig 1. is an enlarged schematic representation of the dosimeter used for measuring the phosphine concentration according to the invention. Fig 1. (Dosimeter Phosphine) 1, 2- sealed ends of the dosimeter. 3 - diffusing medium containing sensor. 4 - Scratch mark for breaking of the tube at one end. 5 - Calibration DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT : The aims and objects of the invention are achieved in accordance with he invention by providing a phosphine dosimeter. The dosimeter consists of a narrow glass tubing of 15 cm length filled with phosphine sensing chemical. Both the ends of the tube are sealed with round tips. The sensing chemical i.e. the gas diffusing medium silica gel with gas detector gold chloride - 5 occupies 8-10 cms of the tube beginning from one end. At the other end of the sensing chemical a plug is placed to hold the sensing chemical in position. There is a scratch mark at the edge of the plug meant for facilitating breaking of the tube while using. The preparation of the diffusion medium with the detector chemical involves the following steps : 1. The silica gel is thoroughly washed with distilled water till the pH of the suspension reaches to 7. 2. The supernatant liquid was removed by filtration and transferred into an air oven maintained at a temperature of 120 C. It as dried for a period of 8 hours. 3. After cooling to room temperature, the silica gel is activated by heating to 500 C for a period of 4 hours in a muffle furnace and then allowed to cool to room temperature in nitrogen atmosphere. 4. A solution of gold chloride is prepared in a beaker by dissolving the required amount of gold chloride in distilled water. 5. It is stirred thoroughly, filtered into a flat bottom flask and the pretreated silica gel of 60-100 mesh of required quantity is added into this solution. 6. The mixture of gold chloride and silica gel is mixed thoroughly for an hour by shaking and the mixture is allowed to stand for 16 hours in soaked condition. 7. The powder is then dried in nitrogen atmosphere at a temperature of 100 C or it is vacuum dried. The mixture is shaken intermittently during the drying process till the solvent content reaches to 10 -15 %. 6 8. The powder prepared is stored in an airtight container and this sensing chemical is used for fabrication of dosimeter tube. 9. The sensing chemical concentration is in ppm i.e. approximately 7000 ppm of gold chloride in silica gel. While using, the tube after breaking at the scratch mark provided on it, is to be kept at a representative place inside the fumigation enclosure at the beginning of fumigation. After the fumigation is over, stain length developed on it is directly proportional to the total phosphine dose received by the commodity. The dosimeter is designed and calibrated to read the phosphine dose on the tube scale. The tube scale is marked showing the time in hours. The reading taken at the demarcation line between reacted and unreacted chemical is to be multiplied by 1000 ppm to obtain the dose in ppm hours. Calibration: The dosimeter tube has been calibrated by exposing the tube at a constant concentration of 1000 ppm for a period of 200 hours and determining the stain length, at various time intervals. The stain length is a direct measure of dose in ppm hours = 1000 ppm x time in hours. In actual experiment dose is calculated by the following formula. Dose = Reading on the tube (hrs.) x 1000 ppm hours. The average concentration can be also calculated using the formula given below. Average confiltered = Dose measured on dosimeter tube in ppm. Hrs. Actual time of exposure in hours 7 The operating principle of the phosphine dosimeter tube is the chemical reaction of phosphine with the phosphine detector sensor present in the diffusing medium. Phosphine diffuses into the tube according to the Ficks law of diffusion and the resultant reaction with the sensing chemical produces a coloured stain. The length of stain on the tube is dependent both on concentration in ppm and time in hours and is a measure of concentration of the time product or dose in ppm hours. For e.g. if a reading of 70 hours is obtained on the dosimeter tube at the end of fumigation, the phosphine dose received by the commodity is 70 hours x 1000 ppm = 70,000 ppm hrs. 8 WE CLAIM: 1. A method for measuring the total dose of phosphine to which a commodity is exposed during fumigation through visual indication using a pre-calibrated dosimeter comprising of a transparent tube preferably made up of glass with both the ends sealed, with a means at one end for opening before use and the tube filled with at least one gas diffusing porous medium containing at least one gas detecting sensor capable of reacting with the target gas diffusing into the medium through the open end of the tube. 2. A method as per claim 1 wherein the gas diffusing medium is silica gel and the gas detecting sensor is gold chloride. 3. A method as per claim 2 wherein the concentration of gold chloride is approximately 7000 ppm. 4. A method as per claim 1 and claim 2 where in the glass tube is sealed at both the ends with a predetermined scratch mark for breaking the tube at one end. 5. A method as per claim 1 and claim 2 wherein the gas diffusing medium containing the colour sensor occupies preferably two third of the tube beginning from one end with a plug to hold the medium in place in the other end. 6. A gas dosimeter comprising of a pre-calibrated transparent tube preferably made up of glass with both the ends sealed having a means at one end for opening the tube before use and the tube filled with at least one gas diffusing medium containing at least one gas detecting sensor capable of reacting with the target gas diffusing into the medium through the open end of the tube. 7. A dosimeter as per claim 6 wherein the gas to be measured is phosphine. 9 8. A dosimeter as per claim 7 wherein the diffusing medium is silica gel and the colour sensing detector is gold chloride. 9. A dosimeter as per claim 8 wherein the concentration of gold chloride is approximately 7000 ppm. 10. A dosimeter as per claim 6 wherein the glass tube is sealed at both the ends with scratch mark provided at one end for breaking the tube before use. Dated this 11th day of October 2006 For UNITED PHOSPHORUS LIMITED M.B. TRIVEDI (COMPANY SECRETARY) UNIPHOS HOUSE, 11TH ROAD, C. D. MARG, KHAR (WEST), MUMBAI-400 052. 10 Abstract The present invention describes a simple method of measuring the cumulative dose of phosphine to which a commodity is exposed to during fumigation using a dosimeter which comprises of a pre-calibrated glass tube filled with a diffusing medium like silica gel impregnated with gold chloride. The dosimeter gives a visual indication of the phosphine concentration by the colour stain which develops as the phosphine diffuses into the medium through the open end of the tube. 11

Documents:

1694-mum-2006-abstract(13-10-2006).doc

1694-mum-2006-abstract(13-10-2006).pdf

1694-mum-2006-abstract-1.jpg

1694-mum-2006-abstract.doc

1694-mum-2006-abstract.pdf

1694-mum-2006-cancelled pages(13-10-2006).pdf

1694-mum-2006-claims(granted)-(13-10-2006).doc

1694-mum-2006-claims(granted)-(13-10-2006).pdf

1694-mum-2006-claims....doc

1694-mum-2006-claims.pdf

1694-mum-2006-correspondance-received-ver-111006.pdf

1694-mum-2006-correspondance-received-ver-291206.pdf

1694-mum-2006-correspondence(28-08-2007).pdf

1694-mum-2006-correspondence(ipo)-(07-03-2008).pdf

1694-mum-2006-description (complete).pdf

1694-mum-2006-drawing(13-10-2006).pdf

1694-mum-2006-drawings.pdf

1694-mum-2006-form 1(13-10-2006).pdf

1694-mum-2006-form 13(29-08-2007).pdf

1694-mum-2006-form 18(29-12-2006).pdf

1694-mum-2006-form 2(granted)-(13-10-2006).doc

1694-mum-2006-form 2(granted)-(13-10-2006).pdf

1694-mum-2006-form 3(13-10-2006).pdf

1694-mum-2006-form 5(13-10-2006).pdf

1694-mum-2006-form 9(29-12-2006).pdf

1694-mum-2006-form-1.pdf

1694-mum-2006-form-2.doc

1694-mum-2006-form-2.pdf

1694-mum-2006-form-3.pdf

1694-mum-2006-form-5.pdf

1694-mum-2006-form-9.pdf

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