Field of the invention:
The invention relates to detection of low concentration of phosphine gas in air using a chemiluminescence method.
Background Of the invention:
Phosphine or hydrogen phosphide is a highly reactive and toxic gas. It is flammable and explosive in air and can auto-ignite at ambient temperatures. Phosphine may occur naturally in the anaerobic degradation of phosphorous containing organic matter such as in the production of marsh gas.
Phosphine has multiple industrial uses, for example it is used in the production of organophosphorous compounds, in semiconductor processing as a dopant. Phosphine is also a powerful fumigant for disinfecting food grains and for pest control.
Despite its wide industrial use, safety is still a concern with phosphine. The calculated LD50 value in rats for phosphine is 0.055 mg/L for 4 hours, making it highly toxic. According to the 2009 US National Institute for Occupational Safety and Health (NIOSH) pocket guide and US Occupational Safety and Health Administration regulations, the 8 hour respiratory average for phosphine should not exceed 0.3ppm. NIOSH recommends that the short term exposure to phosphine gas should not exceed 1 ppm.
Inhalation of phosphine may cause severe pulmonary irritation leading to acute pulmonary oedema, cardiovascular dysfunction, CNS excitation, coma and death. Other symptoms may include nausea, vomiting, diarrhoea, headache, fatigue and dizziness. Gastrointestinal disorders, renal damage and leucopenia may also occur. Initial clinical manifestation of mild phosphine inhalation mimics an upper respiratory tract infection.
Considering the health hazards associated with even a low concentration of phosphine, it becomes necessary to monitor the level of the phosphine gas in the environment and especially in places where the likelihood of enhanced levels is higher. Various devices and methods of detection of phosphine have been used. These devices include infrared spectrometers, colorimeters, semiconductor detectors etc. GB1001160 (Drager) describes an invention which comprises a reagent for detecting gases including phosphine, the said reagent comprising a mixture of a salt of gold, palladium, platinum or silver and mercuric chloride, precipitated on a granular carrier, and the use thereof in testing gases. The use of precious metals for detection of gases is also mentioned in US5997706 (Kiesele et.al), which describes an electrochemical measuring apparatus with gold electrodes and silver sulfide as the electrolyte additive along with sulphuric acid for detection of gases such as phosphine and arsine. The electrolyte chamber is closed off with respect to the gas to be detected by a diffusion membrane.
JP 8105879 (Yoshiaki et. al) discloses the use of Bismuth chloride as a discoloration agent for detection of hazardous gases like phosphine or arsine. Bismuth chloride which is chemically stable and non toxic turns black when it contacts volatile inorganic hydride such as phosphine.
US6251244 (Kiesele et.al) discloses an electrochemical measuring cell for detecting hydride gases such as arsine and phosphine. The measuring cell includes at least one working electrode made up of a catalytically inactive material and a reference electrode in an electrolyte chamber filled with an electrolyte.
US 5171536 (Evers) discloses an improved measuring apparatus for the colorimetric indications of gases such as phosphine. The apparatus comprises a carrier that is impregnated with a solution of a moisture retainer and a detection indicator. To measure gases like phosphine the indicator consists of palladium tetramine chloride.
US2009098655 (Brokenshire et. al) describes an apparatus for detecting the presence of phosphine or arsine in a sample gas ,the apparatus including a detection unit (which can include an Ion mobility Spectrometer) having a gas inlet, the detection unit being relatively unresponsive to the presence of arsine or phosphine within the unit, wherein the apparatus includes a chemical cell having an inlet connected to receive the sample gas and an outlet connected with the gas inlet of the detection unit, and that the chemical cell is operative to produce a chemical that can be detected more readily by the detection unit when arsine or phosphine is supplied to the cell.
JP8129009 (Takashi et. al) describes a method of detection of hydride gas by supporting at least one molybdic acid and molybdate on an inorganic carrier as a discoloring component and can be used in the detection of hydride gas such as arsine or phosphine most generally contained in semiconductor exhaust gas. By the contact of detection agent with hydride gas, the discoloring component is sharply changed from lemon yellow to bluish-green-black.
The various methods and devices meant for detecting phosphine in the prior art have their own disadvantages. For example, although colorimetric tubes detect phosphine with good reliability they cannot be adapted to a continuous monitoring system. Semiconductor detectors are sensitive to many compounds, particularly gases which are normally present in the air such as water vapour, carbon dioxide or carbon monoxide etc. because of which they may not exhibit sufficient specificity. Moreover most of these methods and devices are not equipped to detect phosphine in concentrations as low as parts per billion.
Considering the toxicity of phosphine, there is a need for devices and methods which can detect phosphine at very low concentrations. Also, the methods in the prior art use components such as gold, silver, platinum and palladium which are not cost effective or environmentally friendly and may result in formation of by products which would need to be discarded after further treatment which can be cumbersome.
The present invention aims to overcome the problems in the prior art, namely the need for a device and method that detects phosphine in very low concentrations.
Summary of the invention:
It is therefore an aspect of the present invention to provide an apparatus for detecting phosphine gas in the ambient air using chemiluminescence, said apparatus comprising at least a reaction cup and a photosensitive device, wherein said reaction cup allows a reaction between ozone and phosphine to occur and said photosensitive device being capable of detecting the reaction.
In another aspect, the present invention provides an apparatus for detecting phosphine gas in the ambient air, said apparatus comprising:
a. at least a reaction cup;
b. at least a photosensitive device;
c. at least an ozone generator;
d. at least an ozone scrubber; and
e. at least an analytical module.
In another aspect, the present invention provides a method of detecting phosphine gas in the ambient air by reacting phosphine with ozone, said method comprising:
a. introducing an air sample and in-situ generated ozone into a reaction cup and causing the introduced air sample to react with the generated ozone, said reaction generating photons;
b. amplifying the generated photon signal in a provided photosensitive device; and
c. measuring the amplified photon signal and calculating the phosphine concentration in the sampled air by correlating the photon signal in a provided analytical module.
Object of the invention:
It is therefore an object of the present invention to provide a method of detecting phosphine gas in very low volumes.
It is another object of the present invention to provide an apparatus to detect phosphine gas in very low volumes.
It is yet another object of the present invention to provide a method and apparatus for detecting phosphine gas using chemiluminescence.
It is yet another object of the present invention to provide an apparatus that detects phosphine gas when present in parts per billion.
Brief Description of the drawings:
Figure 1 is a block diagram of the process for detection of phosphine gas.
Figure 2 is a cross section of the reaction cup
Figure 3 is a cross section of the reaction cell and photosensitive device.
Figure 4 is a graph exhibiting the correlation between the generated electrical signal and the measured concentration of the phosphine gas.
Detailed description of the invention:
The present invention relates to a method of detecting phosphine gas when present even in very low concentrations. Since there is no antidote for phosphine poisoning, early detection and management is essential. The low LD50 values indicate that even concentration in parts per million will be harmful. It is therefore essential that phosphine leaks be detected at an early stage when concentrations are as low as parts per billion.
Therefore one aspect of the present invention relates to using chemiluminescence for detecting phosphine gas in the ambient air by measuring the chemiluminescence within an apparatus. The method, in general comprises the use of ozone gas as a reactant, wherein, the phosphine gas in the air sample reacts with the ozone to form a product that is in an excited stage. The molecule then releases a photon which is captured by a photosensitive device which in turn measures the intensity of light emitted to determine the quantity of phosphine in the sample. Such a reaction and detection, according to the present invention may be carried out in a compact handheld device of the present invention.
In one embodiment the ozone gas may be produced within the apparatus by an ozone gas convertor, which converts oxygen taken from the air sample itself and converts it to ozone. There are many methods which can be used to covert oxygen to ozone, such methods include but are not limited to use of ultra violet light, corona discharge, electrolytic ozone generation etc. Since the phosphine gas is detected in extremely low concentrations there must be enough ozone in the reaction cell so as to react with the low volumes of phosphine in the air sample. Thus, ozone may be added in excess into the reaction cell, so as to ensure absolute reaction and thus detection of phosphine even in very low concentrations.
In one embodiment a photosensitive device may be used to detect the release of the photon during the reaction between ozone and phosphine. Such photosensitive devices include but are not limited to photodiodes, silicone based photodiodes, photomultipliers etc. The most preferred being photomultiplier tubes which have a fast response and high sensitivity. The photomultiplier tube may detect the photon emitted and report the intensity of the light emitted in the visible spectrum as well as infrared spectrum based on the concentration of phosphine gas present in the sample. The photosensitive device may be placed next to the reaction cell, where phosphine reacts with ozone, so as to measure the intensity of light emitted during the reaction, thereby determining the quantity of phophine in the sample. The intensity of chemiluminescence varies according to concentration of phosphine in the air sample.
The photo-multipliers tubes generally comprise a photocathode and a series of dynodes in an evacuated glass enclosure. T he photons generated during the reaction between ozone and phosphine gas strike the photoemissive cathode, which releases electrons due to the photoelectric effect. A plurality of provided anodes is maintained at a very positive potential. The released electrons are accelerated towards these dynodes, each of which dynodes generates additional electrons in response to the electrons incident thereon, thereby producing a cascade of electrons. Typically, about 105 to 107 electrons are released for each electron that hits the cathode. The number of electrons generated in this manner depends primarily on the number of dynodes and the accelerating voltage. The amplified signal is thereafter collected at the anode, where the current generated is measured.
Therefore, according to an embodiment of the invention, the photomultiplier tube generates and amplifies an electric signal in response to a chemical reaction occurring between the quantity of phosphine in the air sample and ozone. The air samples having different concentrations of phosphine react with ozone in different degrees to produce different intensities of photons, which are received and amplified by the photomultiplier tube to produce electric signals of different amperages.
In an aspect, the apparatus of the present invention comprises a photomultiplier tube for generating an electrical signal in response to the detection of a reaction between phosphine and ozone although other photosensitive devices are not per se excluded.
In an embodiment, the photosensitive device according to the present invention is capable of generating an electric signal in response to an incident light. The incident light is generated due to the reaction between the phosphine concentration present in the sampled air and ozone.
In an embodiment, the photosensitive device may be selected from photomultiplier tubes, optical detectors, chemical detectors such as photographic plates, light dependent resistors, photovoltaic cells, photocathodes, phototubes, phototransistors, pyroelectric detectors, Golay cells, cryogenic detectors, charged-coupled detectors and reverse-biased LEDs.
In an embodiment, the photosensitive device is adapted to generate an electric signal corresponding to the intensity of the generated light.
In an embodiment, the apparatus of the present invention includes an analytical module comprising an analog to digital converter which receives the electrical signal generated by the photosensitive device and converts the received electrical signal into a digital signal. The digital signal therefore measures the concentration of phosphine gas present within the sampled air.
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://ww1.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 photosensitive device and remains constant throughout the life cycle of said photosensitive device. It results from physical changes within the photosensitive device such as change in resistance etc. within the photosensitive device. The span drift results from a decrease in the signal magnitude when the photosensitive device becomes catalytic active site-limited with the passage of time.

In a preferred embodiment, the analytical module 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 photosensitive device.

The analytical module of the present invention comprises a microcontroller. The microcontroller comprises a storage means having stored therein a plurality of phosphine concentration values of a plurality of random air samples matched to a plurality of digital signals values corresponding to said random samples.

In an embodiment, the microcontroller has stored therein a plurality of phosphine concentration values of a plurality of random air samples matched to a plurality of digital signals corresponding to the phosphine concentrations in the random air samples.

In this embodiment, the microcontroller is adapted to receive the digital signal corresponding to the phosphine concentration in the tested air samples. The microcontroller correlates the measured digital signal values to the concentration of phosphine gas in the tested air sample.

The microcontroller according to the present invention is adapted to receive the digital signal generated by the analog to digital converter for an air sample and generate a phosphine concentration value matching the received digital signal.

In an embodiment, the microcontroller receives the digital signal corresponding to an air 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 phosphine concentration value matching the stored digital signal.

In another embodiment, the microcontroller plots the stored digital signals against the corresponding phosphine concentration values in a graph. In the event of the microcontroller receiving a digital signal, it calculates the corresponding phosphine concentration 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 phosphine concentration value of the air sample from said calculated slope.

According to an exemplary embodiment of the present invention, the apparatus of the present invention was used to measure the concentration of phosphine gas in different air samples. The concentration of phosphine gas measured was plotted against the electrical signal generated in voltage, which is tabulated hereunder:

Table 1

S No. Output in mV Concentration of PH3 in ppm
1 0 0
2 2 2.7
3 4.6 5.4
4 7.5 8.1
5 16.1 13.5

It was found that the apparatus of the instant invention was capable to detecting the phosphine has concentration in the tested air samples for as low as 2.7 ppm. In one of the provided air samples, zero concentration of phosphine gas was also recorded. The corresponding graph arrived at by plotting the intensity of the generated electrical signal versus the concentration of the measured phosphine gas accompanies this specification as figure 4.

In a further preferred embodiment, the microcontroller is programmed to calculate the phosphine concentration at a locus after the lapse of a predetermined time interval. In an exemplary embodiment, the microcontroller may be programmed to repeat the measurement of phosphine concentration after every five hours.

In an embodiment, the microcontroller is adapted to periodically monitor the concentration of phosphine gas at selected locations at predetermined time intervals and store each measured concentration data in a memory provided in the apparatus of the present invention.

In a preferred embodiment, the microcontroller is programmed to compare each measured phosphine gas concentration with a pre-selected threshold concentration value and is capable of initiating corrective action if the measured concentration value falls below the pre-selected threshold value.

In a further preferred embodiment, the corrective action includes generating and sending warning signals to a remote location reporting the phosphine gas concentration along with the pre-selected threshold value.

In another embodiment, the corrective action includes allowing a calculated amount of the phosphine gas to the locus, when the measured phosphine gas concentration value falls below the selected lower threshold value.

In yet another embodiment, the corrective action includes allowing a calculated amount of fresh air into the treated locus when the measured phosphine gas concentration value exceeds the pre-selected upper threshold value.

In a preferred embodiment, the measured phosphine gas concentration value stored in a memory provided in the apparatus of the present invention is downloaded onto an authorized computer where it is accessed by authorized personnel. Preferably, the authorized computer is a pre-defined central server located at a predetermined location.

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.

In an 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 phosphine concentration measurement and system calibration using blank and reference standards. Preferably, each function may be sub-divided into separate sub-functions, which may each be automated by a different sub-routine. Some exemplary sub-functions according to a preferred embodiment may be sample and reagents loading, heating, measuring, loading etc.

In another embodiment, the microcontroller is adapted to record the “zero” reading of a blank air sample having no phosphine and the standard “maximum” reading of a known air sample having a known phosphine concentration value.

In this embodiment, a blank air sample is fed to the apparatus and the phosphine concentration value corresponding to said sample is set as “zero”. Further, a standard reference having known phosphine concentration is fed to the apparatus and the phosphine concentration value corresponding to this standard sample is calibrated as the standard.

The apparatus of the present invention comprises a display means. The display means receives a calculated phosphine concentration value from the microcontroller and visually displays the received phosphine concentration value.

Thus, in another embodiment, the present invention provides an apparatus for detecting phosphine gas in the ambient air, said apparatus comprising:
a. at least an ozone generator capable of receiving a first air sample and converting the oxygen content of said first air sample to ozone;
b. at least a reaction cup adapted to receive the generated ozone and a second air sample and allowing a reaction between the received air sample and ozone to occur thereby generating light of a predetermined wavelength;
c. at least a photosensitive device disposed proximal to said reaction cup and adapted to receive said light of predetermined wavelength generated in the reaction cup and converting the received light into electrical signal, said photosensitive device being adapted to further amplify the generated electrical signal;
d. an analytical module comprising at least one analog to digital converter and at least one microcontroller, said analog to digital converter being adapted to receive the electrical signal generated by the photosensitive device and converting the received electrical signal into digital signal, said microcontroller comprising a storage means having stored therein a plurality of phosphine concentration values of a plurality of random air samples matched to a plurality of digital signals, said microcontroller being adapted to (i) receive the digital signal generated by said analog to digital converter for said second air sample, (ii) generate a phosphine concentration value matching the received digital signal, and (iii) output the generated phosphine concentration value;
e. at least one display means capable of receiving the generated phosphine concentration value from said microcontroller and displaying the received phosphine concentration; and
f. at least one ozone scrubber.
In another embodiment, the microcontroller, upon receipt of a digital signal corresponding to the second air 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 phosphine concentration value matching the stored digital signal.

In another embodiment, the microcontroller plots the stored digital signals against the corresponding phosphine concentration values in a graph and upon receipt of a digital signal corresponding to the second air sample, calculates the corresponding phosphine concentration value by plotting the received digital signal on the stored graph. In this embodiment, the microcontroller calculates the slope of the plotted graph and calculates the phosphine concentration value of the provided second air sample from said calculated slope.

In another embodiment, the apparatus of the present invention may include a communication means which receives the calculated phosphine concentration of a predetermined air sample and stores the received phosphine concentration 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 phosphine concentration 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 phosphine concentration 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 phosphine concentration 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 phosphine concentration values of air samples at a specified location by a user placed at a remote location.

In another embodiment, the stored phosphine concentration 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, internet and the like.

In another preferred embodiment, the communication means may cause the phosphine concentration values measured at a specified location to be transmitted 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 means prompting the personnel to enter the given login and password and allowing personnel access to the phosphine concentration values subsequent to successful authorization.

Upon the sample being tested the ozone gas needs to be properly disposed without damage to the environment. Therefore, in one embodiment an ozone scrubber may be added to the device, wherein, the ozone is let into a scrubber, wherein, special catalyst may be used to remove all traces of ozone from the reaction cell. The preferred catalyst may be such that it does not produce any byproducts when converting ozone to oxygen. There are several commercially available catalysts, for this purpose, one of which is Carulite 200. Once the ozone is converted to oxygen it may be released into the atmosphere.
The air sample taken from the ambient air may not react if moisture is present in the sample therefore, it may be passed through a dehumidifier so as to remove all traces of moisture from the air sample. The dehumidifier may be heat pump dehumidifiers or chemical absorbent dehumidifiers. The preferred dehumidifier is a heat pump dehumidifier such as a Peltier cooler. The air sample is passed through the dehumidifier where the air is cooled to 2 Deg C using a Peltier cooler designed for the purpose. At 2 deg C, the saturated vapor pressure of water is so low that a negligible amount of water vapor will be left in the sample air (10 ppm.)
In another aspect, the present invention provides a method for measuring the phosphine concentration present in an air sample.

The method of the present invention comprises introducing an air sample and in-situ generated ozone into a reaction cup and causing the phosphine gas present within the introduced air sample to react with the generated ozone. The reaction between ozone and phosphine generates photons having a predetermined wavelength and intensity.

The generated light signal is amplified in a provided photosensitive device. The amplified light signal is thereafter correlated with the concentration of phosphine gas using a provided analytical module.

Therefore, in one aspect, the present invention provides a method of detecting phosphine gas in the ambient air by reacting phosphine with ozone, said method comprising:
a. introducing an air sample and in-situ generated ozone into a reaction cup and causing the introduced air sample to react with the generated ozone, said reaction generating photons;
b. amplifying the generated photon signal in a provided photosensitive device; and
c. measuring the amplified photon signal and calculating the phosphine concentration in the sampled air by correlating the photon signal in a provided analytical module.

In an embodiment, the ambient air or air at a locus to be tested is collected into the apparatus using an air pump provided in the apparatus. The collected air sample is passed through a dehumidifier. The flow rate of air within the apparatus is reduced by a rotameter adapted for such a purpose. The air stream is thereafter split using a splitter to obtain a first air stream and a second air stream.

The first air stream is communicated to a reaction cup. The second air stream is communicated to an ozone generator. The generated ozone is communicated to the reaction cup wherein it contacts the first air stream.

The reaction occurring between ozone and the phosphine comprised within the first air stream generates light of a predetermined wavelength and intensity. The generated light is incident upon a provided photosensitive device, preferably a photomultiplier tube. The generated light is amplified and the amplified light signal is communicated to an analytical module.

The analytical module receives the transmitted light signal and generates a corresponding phosphine concentration value as described hereinabove. The calculated phosphine concentration is thereafter displayed on a provided display means such as an LCD screen.

The air remaining in the reaction cup after the completion of the calculation is communicated to an ozone scrubber. The ozone scrubber is adapted to convert the unreacted ozone to oxygen, which is released into the environment.

Therefore, in another embodiment, the present invention provides a method of determining phosphine gas at a locus, said method comprising:
a. absorbing an air sample into the apparatus by means of a provided air pump;
b. passing the air sample through a provided dehumidifier;
c. reducing the flow rate of the air within the apparatus by means of a splitter and/or a rotameter such that the air sample divides into a first stream and a second stream;
d. introducing said second stream into an ozone generator;
e. simultaneously introducing said first stream and the ozone generated in step d into a reaction cup, wherein, the reaction cup is placed besides a photosensitive device;
f. causing the second air sample and the ozone to react in the reaction zone so as to release photons of light;
g. capturing the light released in the visible and infra red spectrum by means of the photosensitive device, wherein, the photosensitive device amplifies the signal;
h. measuring the signal to find the amount of phosphine gas in the first air sample by means of a analytical module;
i. displaying the detected quantity of gas on a LCD screen on the device.
j. evacuating the gases from the said reaction chamber into a ozone scrubber, wherein, the ozone from the reaction is converted into oxygen; and
k. releasing the converted oxygen in step I into the atmosphere

The process for carrying out the invention can therefore be best illustrated by referring to process flow chart in Figure 1. Air sample from the ambient air may be let in through inlet 1 and may pass through dehumidifier A, where the sample may be stripped off all moisture. From dehumidifier A the air sample may pass through a splitter 2, wherein, the air sample may split into two parts. A first part may move towards flow meter C1 and a second part may move towards ozone generator B. The first part may be measured through the flow meter C1 and released into the reaction cup (not shown) placed within the reaction and detection cell D via inlet 5. The second part may move into ozone generator B, where the oxygen maybe converted to ozone and then transferred to reaction cell D via inlet 6. After the reaction within reaction and detection cell D, the remaining ozone from the reaction cell may be transferred via outlet 7 into flow meter C2 and pump E into ozone scrubber F where the ozone is converted to oxygen and may then be released into the atmosphere via outlet 8.
Figure 2 is a cross section of the reaction cup within the reaction and detection cell within the phosphine measuring apparatus. The reaction cell may be an elongated tubular closed chamber with inlet 5 placed at right angle to inlet 6 at the proximal end of the reaction cell such that when the phosphine gas enters from inlet 5 and ozone enters from the inlet 6 the gases react immediately in the reaction zone G and the light emitted is directly detected by the photosensitive device. Outlet 7 is placed at the distal end of the chamber to let out towards the ozone scrubber once the reaction has been completed.
Inlets 9 and 10 may be extended such that there may be a gap of a few milli meters between them where the two meet in reaction zone G. The inlets 9 and 10 may have tapered opening inside the reaction cell.
The placement of the reaction cup R and the photomultiplier tube T within the reaction and detection box is shown in Figure 3. As shown in Figure 3, the reaction cup may be supported within the apparatus by means of a supporting stand S. The photosensitive device may be connected to a power supply cord P and an analytical module M (not shown). The analytical module comprises an analog to digital converter, a microprocessor and an LCD display to relay the quantity of phosphine gas in the sir sample taken.
The reaction cup placed next to the photosensitive device is placed in an acrylic box which is black on the inside and a silver mirror coating on the inside, so as to reflect the chemiluminescent light falling on its surface to the photomultiplier tube. The black colour prevents any light entering into the reaction cell.
In one embodiment the reaction cup of the present invention may have a dimension of 1 to 10 mm in diameter and a depth of 1 mm to 15mm carved into a metal block of appropriate dimensions so as to fit the cup shaped reaction cell within the block. The photosensitive device may be placed in the open side of the reaction cup so as to detect light emitted during the reaction within the reaction cell. Ozone from the ozone generator and the sample air may enter the reaction cup from two 1 mm diameter holes drilled through the block on opposite side of the cup. A third hole in the cup may be placed at 90 degrees to the axis joining the first two holes and may be used to evacuate the reactant gases from the reaction cell. The cup may be silver coated to reflect the chemiluminescence light falling on its surface to the photosensitive tube.
Figure 4 illustrates the apparatus of the present invention used to measure the concentration of phosphine gas in different air samples. The concentration of phosphine gas measured was plotted against the electrical signal generated in voltage. The apparatus of the instant invention was capable to detecting the phosphine has concentration in the tested air samples for as low as 2.7 ppm. In one of the provided air samples, zero concentration of phosphine gas was also recorded.
In one embodiment a pump may be used for drawing the sample of ambient air into the reaction cell. A pump such as a Schwarz pump may be used for this purpose. The sample with the aid of the pump may be drawn at flow rate of 1000 mL/minute, in order to reduce the flow rate to 50 to 500mL/min a splitter and a flow meter may be used. The flow rate meter in one embodiment is a rotameter.
The reaction cup and the photosensitive device may be placed in an acrylic box or in a light weight metal box. The metal for the box must be non corrosive and light weight for example aluminum, titanium etc.
In an embodiment, the method of the present invention further comprises selecting a wavelength of light for analysis of the air sample. The photosensitive device is thereafter adapted to detect and amplify light of the selected wavelength.

In another embodiment, the method of the present invention additionally comprises receiving the calculated phosphine concentration value of a predetermined air sample and storing the received phosphine concentration 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 phosphine concentration 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 phosphine concentration 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 phosphine concentration 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 phosphine concentration values of air 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 phosphine concentration 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 phosphine concentration 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 phosphine concentration values subsequent to successful authorization.

In another aspect of the present invention, there is provided a kit-of-parts for phosphine concentration measurement of an air sample at a predetermined location. The kit comprises an apparatus for measuring the phosphine concentration at a predetermined location and an instruction manual.

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 phosphine concentration 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.

Therefore, in this aspect, the present invention also provides a kit-of-parts for the measurement of phosphine gas in an air sample, said kit-of-parts comprising:
(a) an apparatus for measuring the phosphine concentration of an air sample comprising a photosensitive device, an analog to digital converter, a microcontroller and a display means; and
(b) an instruction manual comprising instructions for phosphine concentration measurement according to a predetermined method.

The apparatus and method of the present invention have many distinct advantages over the prior art. The sensitivity of the apparatus is very high and can detect phosphine in the air at quantities as low as parts per billion. This is especially essential in places such as factories where semi conductors are manufactured as well as in other confined spaces where fumigation may have been carried out using phophine gas.
The apparatus is light weight and portable which means it can be easily carried around and placed at convenient locations so as to alert occupants in the room or premises about the presence of phosphine.
The apparatus is cost efficient as it does not require expensive material for its manufacture. It is also environmentally friendly as it has a leak proof ozone scrubber that converts ozone to oxygen which is released back into the atmosphere.

These and other advantages of the invention may become more apparent from the examples set forth herein below. These examples are provided merely as illustrations of the invention and are not intended to be construed as a limitation thereof.
Although the present invention has been disclosed in full, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention. Wherein the foregoing reference has been made to components having known equivalents, then such equivalents are herein incorporated as if individually set forth.
Accordingly, it will be appreciated that changes may be made to the above described aspects and 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 invention.

WE CLAIM:
1. An apparatus for detecting phosphine gas in the ambient air, said apparatus comprising at least a reaction cup and a photosensitive device, wherein said reaction cup allows a reaction between ozone and phosphine to occur and said photosensitive device being capable of detecting the reaction.

2. An apparatus for detecting phosphine gas in the ambient air, said apparatus comprising:
(a) at least a reaction cup;
(b) at least a photosensitive device;
(c) at least an ozone generator;
(d) at least an ozone scrubber; and
(e) at least an analytical module.

3. The apparatus as claimed in claim 1 or claim 2, wherein said photosensitive device is a photomultiplier tube.

4. The apparatus as claimed in claim 3, wherein said photomultiplier tube is capable of generating and amplifying an electric signal in response to an incident light generated due to the reaction between the phosphine concentration present in the sampled air and ozone.

5. The apparatus as claimed in claim 2, wherein said analytical module comprises an analog to digital converter adapted to receive the electrical signal generated by the photosensitive device and convert the received electrical signal into a digital signal.

6. The apparatus as claimed in claim 2 or claim 5, wherein said analytical module comprises a microcontroller.

7. The apparatus as claimed in claim 6, wherein said microcontroller comprises a storage means having stored therein a plurality of phosphine concentration values of a plurality of random air samples matched to a plurality of digital signals values corresponding to said random samples.

8. The apparatus as claimed in claim 6 or claim 7, wherein said microcontroller receives the digital signal corresponding to an air 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 phosphine concentration value matching the stored digital signal.

9. The apparatus as claimed in claim 6, wherein said microcontroller plots the stored digital signals against the corresponding phosphine concentration values in a graph, calculates the slope of the plotted graph and calculate the phosphine concentration value of the air sample from said calculated slope.

10. The apparatus as claimed in any preceding claim comprising a display means.

11. An apparatus for detecting phosphine gas in the ambient air, said apparatus comprising:
(a) at least an ozone generator capable of receiving a first air sample and converting the oxygen content of said first air sample to ozone;
(b) at least a reaction cup adapted to receive the generated ozone and a second air sample and allowing a reaction between the received air sample and ozone to occur thereby generating light of a predetermined wavelength;
(c) at least a photosensitive device disposed proximal to said reaction cup and adapted to receive said light of predetermined wavelength generated in the reaction cup and converting the received light into electrical signal, said photosensitive device being adapted to further amplify the generated electrical signal;
(d) an analytical module comprising at least one analog to digital converter and at least one microcontroller, said analog to digital converter being adapted to receive the electrical signal generated by the photosensitive device and converting the received electrical signal into digital signal, said microcontroller comprising a storage means having stored therein a plurality of phosphine concentration values of a plurality of random air samples matched to a plurality of digital signals, said microcontroller being adapted to (i) receive the digital signal generated by said analog to digital converter for said second air sample, (ii) generate a phosphine concentration value matching the received digital signal, and (iii) output the generated phosphine concentration value;
(e) at least one display means capable of receiving the generated phosphine concentration value from said microcontroller and displaying the received phosphine concentration; and
(f) at least one ozone scrubber.

12. The apparatus as claimed in claim 11, wherein said microcontroller, upon receipt of a digital signal corresponding to the second air 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 phosphine concentration value matching the stored digital signal.

13. The apparatus as claimed in claim 11, wherein said microcontroller plots the stored digital signals against the corresponding phosphine concentration values in a graph and upon receipt of a digital signal corresponding to the second air sample, calculates the corresponding phosphine concentration value by plotting the received digital signal on the stored graph.

14. The apparatus as claimed in any preceding claim, said apparatus comprising a communication means which receives the calculated phosphine concentration of a predetermined air sample and stores the received phosphine concentration value into a memory provided on an authorized computer.

15. The apparatus as claimed in any preceding claim, wherein said apparatus includes a communication means capable of transmitting the calculated phosphine concentration values to a plurality of predetermined remote locations over a communication network.

16. A method of detecting phosphine gas in the ambient air, said method comprising:
(a) introducing an air sample and in-situ generated ozone into a reaction cup and causing the introduced air sample to react with the generated ozone, said reaction generating photons;
(b) amplifying the generated photon signal in a provided photosensitive device; and
(c) measuring the amplified photon signal and calculating the phosphine concentration in the sampled air by correlating the photon signal in a provided analytical module.

17. The method as claimed in claim 16 comprising splitting the input air stream into a first and a second air stream, conveying the first air stream to a reaction cup and the second air stream to a provided ozone generator whereby the oxygen content of said second air stream is converted to ozone and conveying the generated ozone to said reaction cup.

18. The method as claimed in claim 16 or claim 17 further comprising transmitting the amplified light signal to a provided analytical module and generating a corresponding phosphine concentration value.

19. A method of determining phosphine gas at a locus, said method comprising:
(a) absorbing an air sample into the apparatus by means of a provided air pump;
(b) passing the air sample through a provided dehumidifier;
(c) reducing the flow rate of the air within the apparatus by means of a splitter and/or a rotameter such that the air sample divides into a first stream and a second stream;
(d) introducing said second stream into an ozone generator;
(e) simultaneously introducing said first stream and the ozone generated in step d into a reaction cup, wherein, the reaction cup is placed besides a photosensitive device;
(f) causing the second air sample and the ozone to react in the reaction zone so as to release photons of light;
(g) capturing the light released in the visible and infra red spectrum by means of the photosensitive device, wherein, the photosensitive device amplifies the signal;
(h) measuring the signal to find the amount of phosphine gas in the first air sample by means of a analytical module;
(i) displaying the detected quantity of gas on a LCD screen on the device;
(j) evacuating the gases from the said reaction chamber into a ozone scrubber, wherein, the ozone from the reaction is converted into oxygen; and
(k) releasing the converted oxygen in step I into the atmosphere

20. The method as claimed in claim 16-19 comprising transmitting the phosphine concentration values to a remote location over a communication network where it may be accessed by authorized personnel or transmitting the phosphine concentration values measured at a specified location to a pre-determined website in real-time.

21. A kit-of-parts for the measurement of phosphine gas in an air sample, said kit-of-parts comprising:
(a) an apparatus as claimed in claims 1-15 for measuring the phosphine concentration of an air sample comprising a photosensitive device, an analog to digital converter, a microcontroller and a display means; and
(b) an instruction manual comprising instructions for phosphine concentration measurement according to a predetermined method as claimed in claims 16-20.

ABSTRACT

Disclosed is an apparatus for detecting phosphine gas in the ambient air comprising at least a reaction cup and a photosensitive device, wherein said reaction cup allows a reaction between ozone and phosphine to occur and said photosensitive device being capable of detecting the reaction. Also disclosed is a method for the detection of phosphine gas and a kit-of-parts thereof.