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Title:
AN IMPROVED APPARATUS FOR MEASURING HEXAVALENT CHROMIUM IN WATER
Document Type and Number:
WIPO Patent Application WO/2016/049072
Kind Code:
A1
Abstract:
A colorimeter for measuring a concentration of a chemical in a turbid sample can include a colorimeter body having a sample chamber, a sample vessel to receive the turbid sample, where the sample vessel is disposed in the sample chamber, and a light source to emit an incident light beam. The colorimeter can further include a first photodetector configured to send a first output signal corresponding to the concentration of the chemical in the turbid sample and a first optical component arranged to direct the incident light beam through the turbid sample and to the first photodetector, where the first optical component increases a total Beer-Lambert optical path length of the incident light beam. The colorimeter can further include a second photodetector configured to send a second output signal corresponding to intensity of scattered light and a second optical component arranged to direct scattered light to the second photodetector.

Inventors:
HALL, Stephen, H. (4008 Road 104, Pasco, Washington, 99301, US)
SCHUYLER, Kimberly, Anne (1531 South Jefferson Street, Kennewick, Washington, 99338, US)
Application Number:
US2015/051533
Publication Date:
March 31, 2016
Filing Date:
September 22, 2015
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
FREESTONE ENVIRONMENTAL SERVICES, INC. (1100 Jadwin Avenue, Suite 250Richland, Washington, 99352, US)
International Classes:
G01N31/00; G01N21/78
Foreign References:
US8699025B22014-04-15
US20120212739A12012-08-23
US6654119B12003-11-25
US4995727A1991-02-26
US4758085A1988-07-19
Other References:
See also references of EP 3198268A4
Attorney, Agent or Firm:
ABEDI, Syed et al. (Seed Intellectual Property Law Group PLLC, Suite 5400701 Fifth Avenu, Seattle Washington, 98104-7064, US)
Download PDF:
Claims:
THE CLAIMS

1. A device for testing a sample, the device comprising:

a body having a chamber;

a vessel sized to hold the sample, the vessel positioned within the chamber;

a light source;

a first photodetector; and

at least one optical train positioned within the body, the at least one optical train arranged to direct light emitted from the light source through the sample and to the photodetector, the photodetector sending a first output signal to measure concentration of a chemical in the sample.

2. The device of claim 1 wherein the at least one optical train includes at least a first optical component and a second optical component, the first and second optical components arranged to direct light emitted from the light source through the sample at least twice.

3. The device of claim 1 wherein the first and second optical components are arranged to direct light emitted from the light source through the sample at least three times.

4. The device of claim 1 wherein the first and second optical components are diametrically opposed from each other across a chamber axis.

5. The device of claim 1 wherein the first photodetector comprises a photodiode.

6. The device of claim 1, further comprising:

a second photodetector positioned within the body, the second photodetector sending a second output signal corresponding to intensity of scattered light.

7. The device of claim 6, further comprising:

a second optical train positioned within the body, the second optical train arranged to direct scattered light to the second photodetector.

8. The device of claim 6, further comprising:

a third optical train positioned within the body, the third optical train arranged to direct scattered light to a third photodetector; and

the third photodetector positioned within the body, the second and third photodetectors sending output signals corresponding to the intensity of scattered light.

9. The device of claim 8 wherein the third optical train and the third photodetector are arranged in a lower portion of the body and the second optical train and the second photodetector are arranged in an upper portion of the body.

10. The device of claim 1 wherein the at least one optical train includes a first optical component, a second optical component, and a third optical component, the first, second, and third optical components arranged to direct an incident light beam of the light emitted from the light source to the first photodetector along orthogonal optical paths.

11. A colorimeter for measuring a concentration of a chemical in a turbid sample, the colorimeter comprising:

a colorimeter body having a sample chamber;

a sample vessel to receive the turbid sample, the sample vessel disposed in the sample chamber;

a light source to emit an incident light beam;

a first photodetector configured to send a first output signal corresponding to the concentration of the chemical in the turbid sample ;

a first optical component arranged to direct the incident light beam through the turbid sample and to the first photodetector, the first optical component increasing a total Beer-Lambert optical path length of the incident light beam;

a second photodetector configured to send a second output signal corresponding to intensity of scattered light; and

a second optical component arranged to direct scattered light to the second photodetector.

12. The colorimeter of claim 11 wherein the first and second photodetectors comprise photodiodes.

13. The colorimeter of claim 11, further comprising:

a third optical component diametrically opposed to the first optical component across a sample chamber axis, the first and third optical components arranged to direct the incident light beam across the turbid sample at least twice.

14. The colorimeter of claim 13 wherein the first and third optical components comprise dove prisms.

15. The colorimeter of claim 14 wherein the first and third optical components are arranged to direct the incident light through the turbid sample and to the first photodetector along orthogonal optical paths.

Description:
AN IMPROVED APPARATUS FOR MEASURING

HEXAVALENT CHROMIUM IN WATER

BACKGROUND

Field of the Invention

This invention relates in general to chemical measurements and more particularly the quantity of a chemical in a solution and in particular to the use of colorimetric instruments for measuring the concentration of hexavalent chromium in water.

Description of the Related Art

An earlier U.S. Patent No. 8,699,025 to Hall, herein noted as the parent invention, claims an apparatus and method for measuring hexavalent chromium in water based on colorimetric measurement of the chromate ion.

The present invention is an improvement upon the parent invention. This disclosure demonstrates the ability to significantly reduce the size of the colorimetric apparatus while also increasing analytical sensitivity.

BRIEF SUMMARY

The present invention comprises an optical train (50) and optional wavelength-selective photodetectors. The optical train (50) uses reflecting elements (600) including mirrors and/or prisms to fold the light path of the transmitted UV light beam to direct it through the body (100) of the instrument, through a sample vessel (200) using at least one pass but preferably two or more passes and into illumination contact with a photodetector (400). With each additional pass, the Beer-Lambert path length is effectively increased. Separate second optical train (53) and third optical train (54) exist for the detection and measurement of scattered light by illumination contact with one or more photodetectors.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE FIGURES

Figure 1 illustrates the earlier instrument of U.S. Patent No. 8,699,025 to Hall showing a sensor body (100), a sample vessel (200), a light source (300), a first photodetector (400), a second photodetector (410), a first light tunnel segment (500), a second light tunnel segment (500), and a third light tunnel segment (500). Seen is a first light tunnel segment (500) and a second light tunnel segment (500) are collinear forming a straight path from light source (300) to photodetector (400); and the said light path from light source (300) to photodetector (400) is mutually orthogonal with third light tunnel segment (500) and sample chamber axis (210).

Figure 2, Figure 2a and Figure 2b illustrates the colorimeter (1) of the present disclosure having a colorimeter body (100), sample chamber (110), outside (140), top (180), bottom (190), sample vessel (200), sample chamber axis (210) and a light source (300). Seen is a first photodetector (400), two second photodetectors (410) and two third photodetectors (420). Also seen an at least one optical train (50) and at least one light tunnel segment (500). Also seen are reflective elements (600) and reflective element spaces (700). Also seen is at least one dove prism (610) comprising two reflective elements (600).

Figure 2c illustrates cross section 2c from Figure 2 showing the colorimeter (1), colorimeter body (100), sample chamber (110), sample chamber axis (210), outside (140), sample vessel (200), sample chamber axis (210), one light source (300). Seen is at least one second photodetector (410).

Figure 2d shows section 2d from Figure 2 illustrating colorimeter (1), colorimeter body (100), sample chamber (110), sample chamber axis (210), outside (140), sample vessel (200), sample chamber axis (210), light tunnel increments (500), reflective elements (600) and reflective element spaces (700).

Figure 2e shows section 2e from Figure 2 illustrating colorimeter (1), colorimeter body (100), sample chamber (110), sample chamber axis (210), outside (140), sample vessel (200), sample chamber axis (210), reflective element (600) and reflective element spaces (700).

Figure 2f is section 2f from Figure 2 showing colorimeter (1), colorimeter body (100), sample chamber (110), sample chamber axis (210), outside (140), sample vessel (200), sample chamber axis (210), a first photodetector (400) and at least one third photodetector (420).

Figure 2g is illustrative of "n" passes of light, seen here as 3 passes, through the sample. Shown is a sample vessel (200), sample chamber axis (210), one light source (300) and first photodetector (400).

Figure 3 is a graphic comparison of the intensity of scattered light simultaneously measured at second photodetectors (410) and third photodetectors (420) for five samples of water having different levels of turbidity. Seen is the scattered light intensity measured by third photodetectors (420) is approximately 13% of the light intensity measured the second photodetectors (410). Figure 4 is a block diagram showing the relationships of the electronic, optoelectronic, and mechanical components of a cable-deployed submersible preferred embodiment designed for environmental water quality monitoring. Electrical power via the cable energizes electronic circuit board (1000) which in turn energizes and controls a sample pump (900), a light source (300), and photodetectors (400, 410, and 420). The pump (900) moves water from the surrounding environment which becomes the sample (800) within the sample vessel (200). Within the sample vessel (200) the sample (800) is illuminated by the light source (300). Voltages representing transmitted and scattered light signals are sent to circuit board (1000) and further sent to the surface from the circuit board (1000) in the form of voltages, currents, or digital data.

DETAILED DESCRIPTION

The configuration of the invention disclosed provides for two or more passes of light through a turbid sample and for simultaneous measurement of light absorption and light scatter. Those of ordinary skill in optics will recognize that this structure can, in light of the main principle of the Beer-Lambert law, increase the analytical sensitivity of a colorimetric instrument in that this sensitivity is directly proportional to the path length of the analytical light beam as it passes through a sample. Disclosed and claimed herein is the structure causing the analytical light beam to make multiple passes through the sample. Second, the near-UV wavelengths used for chromate measurement can cause materials such as certain dyes and minerals to fluoresce. The emitted fluorescent light is necessarily of longer wavelength than the near-UV light source, and is visible to the human eye. If such dyes are dissolved in a sample, or if such mineral particles are suspended in a sample as turbidity, the emitted fluorescence is an additional source of light that may become an analytical interference if it reaches the photodetectors and adds to the measured light intensities. The silicon phototransistors used in the parent patent are sensitive to visible and infrared light as well as to UV light, so sample fluorescence is an analytical interference.

Photodetectors such as the indium-gallium-nitride (InGaN) photodiodes are sensitive to the near-UV analytical wavelength, but are blind to visible light, i.e., light having a wavelength greater than approximately 400 nm. Using such photodiodes, instead of silicon phototransistors, light intensity measurements will be unaffected by fluorescence.

Having UV light transmitted through the sample at least twice and detecting scattered light at more than one point along the transmitted light path increases signal-to-noise ratio, thus improving accuracy and sensitivity. Finally, precision in the measured intensity of the scattered light is very important. Although the intensity of the scattered light is often extremely small compared to the intensity of the transmitted analytical beam, its effect on analytical accuracy can be significant.

The present invention uses a transparent cylindrical sample vessel (200) fitted into a sample chamber (110) within a supporting colorimeter body (100); the colorimeter body (100) is, in the preferred embodiment, formed of a non-reflective material such as black Delrin® polymer. Those of ordinary skills in these arts will recognize that other materials will also be available for the colorimeter body (100). The transmitted UV light beam is constrained and partially collimated by using an optical train (50) comprising at least one light source (300) emitting a light beam into the at least one optical train (50); the said light beam is directed by mirrors and/or prisms, identified here as reflective elements (600), through at least one light tunnel segment (500) formed into the body (100), reflected at each turn by a reflective element (600) and into illumination contact with at least one photodetector (400).

In the preferred embodiment the sample vessel (200) is cylindrical which, when filled with sample, acts as a lens to concentrate the light beam emitted from the light source (300) as it passes through the sample vessel (200), thus minimizing beam spread and loss of signal strength.

Figure 2, Figure 2a and Figure 2b illustrate the preferred embodiment of the invention of this disclosure. Seen is a colorimeter (1) having a colorimeter body (100), the body (100) having a sample chamber (110); a sample vessel (200) is accommodated by the sample chamber (110); a sample is contained within the sample vessel (200). At least one light source (300) is affixed to the body (100); an incident beam, from the said at least one light source (300) is directed into an optical train (50) having at least one reflective element (600) directing the incident beam through the sample vessel (200) and sample, at least once, and into illumination contact with at least one photodetector (400); and, the said at least one photodetector (400) is affixed to the body (100) and is aligned, through the said optical train (50) and is distal to the light source (300); and, an output voltage from the said at least one photodetector (400) is a factor for determining the concentration of hexavalent chromium in the sample; and, at least one second optical train (53) having at least one reflective element (600) directing the said scattered light emanating from the sample vessel (200) and sample, at least once, and into scattered light illumination contact with at least one second

photodetector (410); and, the said at least one second photodetector (410) is affixed to the body (100) and is aligned with the said second optical train (53) and produces an output voltage which is a factor for determining the concentration of hexavalent chromium in the sample.

Additional description of the preferred embodiment from Figure 2, Figure 2a and Figure 2b is realized by the disclosure. Seen is a colorimeter (1) having a colorimeter body (100), the body (100) having a sample chamber (110); a sample vessel (200) is accommodated by the sample chamber (110); a sample is contained within the sample vessel (200). At least one light source (300) is affixed to the body (100); an incident beam, from the said at least one light source (300) is directed into an optical train (50), here utilizing a hole having reflective elements (600) directing the incident beam through the sample vessel (200) and sample, at least once, and into illumination contact with at least one photodetector (400); and, the said at least one photodetector (400) is affixed to the body (100), is aligned, through the said optical train (50), is distal from the at least one light source (300) and produces an output voltage which is a factor in determining the concentration of hexavalent chromium in the sample. The indicated optical train (50) utilizes at least one reflective element (600). Those of ordinary skill in the optical and instrument arts will recognize that such an optical train (50) may turn or redirect light, whether from a light beam or scattered light, several times thus necessitating multiple bends or folds which are facilitated by mirrors and prisms.

Figures 2, 2a and 2b also illustrate the optical train (50) forming a hole with bends, folds and turns using reflective elements (600) which, in this application are preferably prisms or mirrors used to re-direct transmitted and scattered light paths through the sample vessel (200). Persons of ordinary skill in the art of optics and instruments will recognize from Figure 2 how the prisms or other reflective elements must be aligned and fixed to direct the transmitted and scattered light beams as shown in the figure. Persons so skilled will also recognize that if prisms are used as the reflective elements, clearance between the rear of the angled reflecting facet and the sensor body must be maintained to prevent optical contact between the facet and the sensor body and consequent light loss. In a preferred embodiment, a minimum of 0.25mm clearance is used and is seen as reflective element space (700). The second photodetectors (410) and third photodetectors (420) occupy the four positions representing termini of scattered light beams paths in the at least one second optical train (053) and the at least one third optical train (54). Those of ordinary skills in the optical and instrument arts will recognize that an incident beam, from for example light source (300) or from scattered light will be communicated throughout the optical train.

Figure 2a is a cross sectional plane that includes the sample chamber axis 210 and which illustrates the path of the transmitted UV light beam sequentially from the light source (300) to right angle prism or mirrors or dove prisms and to illuminate the at least one photodetector (400).

Figure 2 shows an embodiment similar to Figure 2g, but illustrating additional reflective elements (600) and multiple photodetectors. For clarity, neither the sensor body (100) nor the sample vessel (200) are fully shown. Figure 2 also depicts the instrument with two passes of the light beam through the sample instead of the three passes shown in Figure 2g. Also illustrated are reflective elements (600) which are preferably right-angle prisms or dove prisms (610) that comprise two reflective elements but may be mirrors which re-direct transmitted and scattered light paths through the respective at least one first optical train (50), the at least one second light train (53) and the at least one third optical train (54). Persons of ordinary skill in optics will recognize from Figure 2 how the prisms or other reflective elements must be aligned and fixed to direct the transmitted and scattered light beams as shown in the figure. Persons so skilled will also recognize that if prisms are used as the reflective elements (600), clearance between the rear of the angled reflecting facet and the sensor body reflective element space (700) must be maintained to prevent optical contact between the facet and the sensor body and consequent light loss. In a preferred embodiment, reflective element space (700) is at least 0.25mm.

It is also seen, in Figure 2b, that the at least one second photodetectors (410) and the at least one third photodetectors (420) occupy the four positions representing termini of scattered light beams paths.

Figure 2a is a cross sectional plane that includes sample chamber axis (210) and shows the path of the transmitted light source (300) UV light beam

sequentially from light source (300) to reflective elements (600) and to photodetector (400).

It will be understood by persons of ordinary skill in optical and measurement instrument arts that redirecting light, whether from a light source such as at least one light source (300) or from scattered light, can be done with mirrors and prisms. In this disclosure redirection of light is indicated to be redirected

"diametrically" which herein means that the light is generally redirected orthogonally and coincidentally with a diameter or cord of the sample chamber (110), through the sample chamber axis (210) and the sample vessel (200) and orthogonally and coincident to the sample chamber axis (210).

A person of ordinary skill in measuring instrument arts will recognize the following: 1. that the colorimeter body (100) will generally be made from a rigid material in order to retain alignment of the optical train such as Delrin®; 2. that the at least one light source (300), at least one photodetector (400), at least one reflective element (600) and, when there are more than at least one, that all are affixed to the body (100) so that they are immobile retaining their position in the optical train so that an incident beam or scattered light is communicated through the entirety of the optical train to make illumination contact with an at least one photodetector.

Figure 2g illustrates reflecting elements (600) used to direct the light source (300) UV light beam three times through the sample instead of once, and the view shows the at least one second optical train (53) rotated by 90°. In Figure 2g, the light path from the light source (300) is reflected two more times through the sample before it reaches the at least one photodetector (400) and hence the total Beer-Lambert path length is effectively tripled. The reflective elements (600), shown in Figure 2g, are preferably established using dove prisms (610), each of which comprises two reflective elements and offsets and reverses the light beam by 180°.

Figure 2g is illustrative of an embodiment of the invention where light from a light source (300) passes through an optical train (50), comprising light tunnel segments (500) and reflective elements (600), accomplishing three passes through a sample vessel (200) and into illumination contact with a photodetector (400).

Figure 2c through Figure 2f are cross sections further illustrating the arrangement of electro-optical and reflective components within sensor body (100).

To a person skilled in the art of colorimetric analysis, it is obvious that the reflective, optical, and electrical components within the sensor body (100) must be sealed against contact with fluid samples, and for an instrument intended for submerged deployment, the sensor body (100) must additionally include means to protect those same inner components from the external environment. It is further obvious that pump or flow processes or methods must be provided to move the fluid sample into and from the sample vessel (200) continuously or intermittently.

Figure 3 is a graph that compares signal strength in millivolts at the at least one second photodetectors (410) and the at least one third photodetectors (420) measuring light scattered within the at least one third optical train (053) and the at least one third optical train (054), respectively, for various levels of turbidity causing up to 30% signal loss detected by the at least one photodetector (400).

An embodiment of the Apparatus for Measuring the Amount of a Chemical Within a Turbid Sample comprises a colorimeter (1) having a colorimeter body (100), the body (100) having a sample chamber (110); a sample vessel (200) is accommodated by the sample chamber (110); a sample is flowed through the sample vessel (200); and, at least one optical train (50), having at least one light tunnel segment (500); said at least one light tunnel segment (500) having reflective elements (600) positioned therein directing light through the at least one optical train (50) and through the sample vessel (200) at least once and into illumination contact with at least one photodetector (400); and, an output voltage from the said at least one photodetector (400) is a factor for determining concentration of a chemical in the sample.

In a preferred embodiment of the invention the body (100) has an outside (140), a top (180) and a bottom (190); and, the body (100) and the sample chamber (110) are generally cylindrical, having a sample chamber axis (120) centrally positioned within the sample chamber (110) from the said top (180) to the said bottom (190); and the said sample vessel (200) is generally cylindrical in shape, is transparent and is sized to be friction received into the said sample chamber (110); and at least one light source (300) is affixed to the body (100); an incident beam, from the said at least one light source (300) is directed into the said at least one optical train (50); the at least one photodetector (400) is affixed to the body (100), and is aligned with the said at least one optical train (50); the said at least one photodetector (400) is distal to the light source (300); and the at least one optical train (50) is comprised of at least one light tunnel segment (500) comprising a hole; and the said at least one light tunnel segment (500) extends downwardly from the said top (180) generally parallel with the said sample chamber axis (120) and intermediate the said outside (140) and the sample chamber (110); the at least one light source (300) is proximal the said top (180) directing an incident light beam into the said at least one optical train (50); the said at least one optical train (50) is further comprised of at least one light tunnel increment (500) downwardly extending; the said at least one light tunnel increment (500) distal to the said at least one light source (300) turns diametrically, intermediate the said top (180) and the said bottom (190) ,and penetrating the said body (100) at the sample chamber (110) and continuing diametrically and penetrating the said sample chamber (110); and, intermediate the said sample chamber (110) and the said outside (140) the said at least one light tunnel segment (500) turns downwardly and the said at least one light tunnel segment (500) distal to the said sample chamber (110) and intermediate the said top (180) and the said bottom (190) turns diametrically penetrating the said body (100) at the sample chamber (110); and the said light tunnel segment (500) continuing and, intermediate the said sample chamber (110) and the said outside (140) the said at least one light tunnel segment (500) turns downwardly penetrating the said body (100) and exits the body (100) at the said bottom (190); and, the at least one photodetector (400) is proximal the said bottom (190) and is positioned in alignment with the said optical train (50) and is illuminated by the incident beam communicated by the said optical train (50) from the said light source (300); and, at each turn of the said at least one light tunnel segment (500) a reflective element (600) is immovably positioned re-directing the said incident light beam generally by 90 degrees; and, at least one second optical train (53) comprising at least one light tunnel segment (500) is formed, from at least one light tunnel segment (500) having reflective elements (600), to detect scattered light, proximal the said top (180), from within the sample vessel (200) having at least one second photodetector (410) positioned to detect scattered light; and, a signal from said at least one second photodetector (410) comprising an output signal from the said at least one second photodetector (410) which is a factor for determining the concentration of hexavalent chromium in the sample; and, at least one third optical train (54) comprising at least one light tunnel segment (500) is formed, from at least one light tunnel segment (500) having reflective elements (600), to detect scattered light, proximal the said bottom (190), from within the sample vessel (200), between the said top (180) and the said bottom (190) and proximal the said bottom (190) having at least one third photodetector (420) positioned to detect scattered light; and, a signal from said at least one third photodetector (420) comprising an output signal from the said at least one third photodetector (420) which is a factor for determining the concentration of hexavalent chromium in the sample.

Technical Specifications

A preferred embodiment as represented in Figures 2a through 2f and in

Figure 4, having an outer diameter of 39mm and a Beer-Lambert path length of 34mm comprised the following components:

Sample vessel (200)

Friedrich and Dimmock

Heraus HSQ 300 Quartz, #HA- 17201

17mm ID x 20mm OD fused quartz tubing

Pump (900)

Simply Pumps

HP Miniature Pump

#HP100S Reflecting element (600)

Thorlabs, Inc.

Right-Angle Prism, N-BK7 glass, uncoated, 5mm #PS909

Dove prism (610)

Thorlabs, Inc.

N-BK7, uncoated, 5mm

#PS990

Light source (300)

Nichia Corporation

UV LED, 375nm

#NSPU510CS

Photodetector (400. 410. 420)

Radio Shack

NPN Silicon Phototransistor

#276-0145

Electro Optical Components, Inc.

InGaN Photodiode (230 - 395nm sensitivity)

#GUVV-T10GD-L