Detector-cell adapted for continuous-flow absorption detection

• US 5,407,638 A
• Filed: 04/28/1993
• Issued: 04/18/1995
• Est. Priority Date: 04/28/1993
• Status: Expired due to Term

• Current Assignee: Shell Oil Company (Shell Plc)
• Original Assignee: Shell Oil Company (Shell Plc)
• Inventors: Wang, Priestley J.
• Primary Examiner(s): Housel, James C.
• Assistant Examiner(s): Ludlow, Jan M.
• Application Number:
  US08/053,785
• Time in Patent Office: 720 Days
• Field of Search: 422/81, 422/82.05, 422/82.06, 422/82.09, 422/91, 436/164, 436/52, 356/213, 356/246, 356/436, 356/440, 250/432 R, 250/435, 250/576
• US Class Current: 422/82.09
• CPC Class Codes: G01N 2030/027 Liquid chromatography
• CPC Class Codes: G01N 21/05 Flow-through cuvettes G01N21/09 takes precedence; handling fluid samples G01N1/10
• CPC Class Codes: G01N 30/74 Optical detectors measurement of intensity, velocity, spectral content, polarisation, or phase of infrared, visible or ultraviolet light G01J

Abstract

A continuous-wavelength absorption detector adapted for continuous-flow detection is provided. The detector includes an electronics section, a bifurcated optical guide and a detector-cell. Each branch of the optical guide has a plurality of fibers, and at one end the branches are separated and connected to different portions of the electronics section. One of the branches is terminated next to a source for producing illumination to irradiate sample material and the other branch is terminated next to a detector for producing an absorption spectrum signal. At the opposite end of the optical guide the fibers of the two branches are combined to form a common end which is connected to the detector-cell. The detector-cell includes an approximately vertically aligned continuous-flow sample cell which is connected to a sample line and also includes a concave mirror. Within the detector-cell, the common end'"'"'s fiber ends are held at a fixed location on one side of the sample cell with the concave mirror being located on the opposite side. Illumination is guided from the electronics section through its respective branch of the optical guide to the common end where the light is transmitted from the fixed location across the sample cell to irradiate the sample material. The sampling material absorbs optical energy of certain wavelengths to a greater extent than other wavelengths to provide an absorption spectrum. Portions of the illuminations are reflected back across the sample cell by the concave mirror to the fiber ends at the fixed location. Reflected light which strikes the branch fiber ends associated with the detector for producing the absorption spectrum signal is then guided to the electronics section. There, an absorption spectrum signal is produced which is proportional to the illumination intensity of the wavelengths striking the fiber ends.

Claims

1. A detector-cell for use in continuous-flow chemical analysis which uses a single location to both irradiate sample material with electromagnetic radiation and collect the radiation which has been subjected to sample material, the detector-cell having the additional attributes of providing for inspection, cleaning and replacement of detector-cell components to improve detector-cell performance when the response of the detector-cell components has been reduced by contact with the sample material or by a change in the characteristics of the sample material and being substantially free of bubble induced noise, the detector-cell being adapted to connect to a sample line having the capability of providing a continuous stream of material for sampling, the sample line including an inlet sample line, an outlet sample line and a means for flowing sampling material into the inlet sample line, the detector-cell comprising:

a detector-cell body, the body having four openings connecting to a central cavity within the body, the four openings including a top opening and a bottom opening located opposite each other and a third opening and a fourth opening located opposite each other and approximately transverse to the top and bottom openings;

a means for connecting the top opening to the outlet sample line;

a means for connecting the bottom opening to the inlet sample line wherein flow from the sample line is from bottom to top through the detector-cell;

a longitudinal sample cell having two flat parallel sides, the sample cell being located within the central cavity such that its longitudinal length is aligned approximately vertical, the sample cell including a bottom inlet and a top outlet which are functional to allow sample material from the sample line to flow through the sample cell, wherein bubbles are swept out of the sample cell by an upward flow of the sample material thereby preventing entrapment of bubbles within the sample cell and reducing the ability of the sample cell to cause the bubble induced noise;

wherein the means for connecting the top opening to the sample line includes a means for removing the sample cell through the top opening for inspection, cleaning and replacement;

a multi-branched optical guide having a common end, the guide being attached to the third opening such that the common end is located at a fixed location within the body and adjacent to one of the flat parallel sides of the sample cell, wherein a first branch of the optical guide is functional for guiding irradiating electromagnetic radiation from outside the detector cell to the common end, and wherein a second branch of the optical guide is functional for guiding collected radiation from the common end to the outside of the detector-cell;

a concave mirror located within the fourth opening and adjacent to the other flat parallel side of the sample cell such that the mirror is on the opposite side of the sample cell from the fixed location;

a means for securing the mirror within the fourth opening so that the mirror is removable to allow the mirror to be inspected and replaced and to allow inspection of the sample cell through the fourth opening;

wherein the common end at the fixed location is functional for transmitting the electromagnetic radiation across the sample cell'"'"'s width such that the radiation diffuses as it crosses the sample cell and encounters the mirror; and

wherein the concave mirror is functional to reflect and to focus portions of the diffused radiation back across the sample cell to the common end such that it is concentrated at the fixed location for collection, wherein the portions of the diffused radiation striking the common end are collected and guided outside the detector-cell, thus the detector-cell is functional for subjecting the collected radiation to the sample material within the sample cell twice, thereby doubling the detector-cell'"'"'s optical path length within the sample material without increasing the sample material'"'"'s volume within the sample cell.

2. The detector-cell of claim 1 also including an o-ring and wherein the sample cell has a tapered top, the tapered top having a round exterior top surface such that the o-ring may provide a pressure seal between the tapered top and the means for connecting the top opening to the sample line.

3. The detector-cell of claim 1 wherein the central cavity and the sample cell have dimensions which are sized such that when the sample cell is positioned within the central cavity the cavity'"'"'s dimensions confine the sample cell in such a manner that the sample cell is aligned within the cavity to ensure a proper alignment of the sample cell with respect to the fixed location, the mirror and the means for connecting the top opening to the sample line.

4. The detector-cell of claim 3 also including a second sample cell having an optical path length which is approximately the same as said sample cell, an external exterior size which is the same as said sample cell and a different sample material volume than said sample cell, and wherein the sample material volume within the detector-cell may be changed by exchanging the sample cell within the detector-cell with the second sample cell.

5. The detector-cell of claim 1 wherein the concave mirror is a spherical mirror and the fixed location is located at the center of curvature of the spherical mirror.

6. The detector-cell of claim 1 wherein the sample cell is made of annealed quartz.

7. The detector-cell of claim 1 wherein the detector-cell body is made of polyetheretherketone.

8. The detector-cell of claim 1 wherein the means for connecting the top and bottom openings to the sample line includes screw connectors which allow connection to the sample line to be made by hand.

9. A continuous-wavelength absorption detector for use in continuous-flow chemical analysis, the detector being adapted to both irradiate a species with radiation over a bandwidth of interest and collect an absorption spectrum of the irradiated species from a single location, the detector also being adapted to connect to a sample line having the capability of providing a continuous stream of sampling material containing the species for sampling, the sample line including an inlet sample line, and outlet sample line and a means for flowing sampling material into the inlet sample line, the absorption detector also having the additional attributes of providing for inspection, cleaning and replacement of certain detector components to improve detector performance when the response of these certain components has been reduced by contact with the sample material or by a change in the characteristics of the sample material and of being substantially free of bubble induced noise, the detector comprising:

a means for producing radiation having the bandwidth of interest for irradiating the species;

a means for producing an absorption spectrum signal from an absorption spectrum which results from irradiating the species with the radiation;

a detector-cell, the detector-cell includes a detector-cell body having four openings connecting to a central cavity within the body, a longitudinal sample cell and a mirror;

the four openings include a top opening and a bottom opening located opposite each other and a third opening and a fourth opening located opposite each other and approximately transverse to the top and bottom openings;

a means for connecting the top opening to the outlet sample line;

a means for connecting the bottom opening to the inlet sample line wherein flow from the sample line is from bottom to top through the detector-cell;

the longitudinal sample cell has two flat parallel sides and is located within the central cavity such that its longitudinal length is aligned approximately vertical, the sample cell also including a bottom inlet and a top outlet which are functional to allow sample material containing the species to flow from the sample line through the sample cell, wherein bubbles are swept out of the sample cell by an upward flow of the sample material thereby preventing entrapment of bubbles within the sample cell and reducing the ability of the sample cell to cause the bubble induced noise;

wherein the means for, connecting the top opening to the sample line includes a means for removing the sample cell through the top opening for inspection, cleaning and replacement;

a multi-branched optical guide having a common end, the optical guide being attached to the third opening such that the common end is located at a fixed location within the body and adjacent to one of the flat parallel sides of the sample cell, the multi-branched optical guide including a first branch and a second branch, wherein the first branch of the optical guide has a distal end which is terminated near the means for producing radiation, the first branch being functional for guiding the radiation from the means for producing radiation to the common end, and wherein the second branch of the optical guide has a distal end which is terminated near the means for producing the absorption spectrum signal;

the concave mirror is located within the fourth opening and adjacent to the other flat parallel side of the sample cell such that the mirror is on the opposite side of the sample cell from the fixed location;

a means for securing the mirror within the fourth opening so that the mirror is removable to allow the mirror to be inspected and replaced and to allow inspection of the sample cell through the fourth opening;

wherein the common end at the fixed location is functional for transmitting the radiation to irradiate the species, the radiation being transmitted into and across the sample cell such that the radiation diffuses at it emerges from the common end; and

wherein the concave mirror is functional to reflect and focus portions of the diffused radiation back across the sample cell such that some of these portions of the reflected radiation are concentrated near the fixed location such that they strike the common end thereby providing the absorption spectrum at the common end, and wherein the common end is also functional to collect the absorption spectrum and guide the absorption spectrum outside the detector-cell on the second branch of the guide to the means for producing the absorption spectrum signal, whereby the absorption spectrum is converted into an absorption spectrum signal.

10. The continuous-wavelength absorption detector of claim 9 also including an o-ring and wherein the sample cell has a tapered top, the tapered top having a round exterior top surface such that the o-ring may provide a pressure seal between the tapered top and the means for connecting the top opening to the sample line.

11. The continuous-wavelength absorption detector of claim 9 wherein the central cavity and the sample cell have dimensions which are sized such that when the sample cell is positioned within the central cavity the cavity'"'"'s dimensions confine the sample cell in such a manner that the sample cell is aligned within the cavity to ensure a proper alignment of the sample cell with respect to the fixed location, the mirror and the means for connecting the top opening to the sample line.

12. The continuous-wavelength absorption detector of claim 11 also including a second sample cell having an optical path length which is approximately the same as said sample cell, an external exterior size which is the same as said sample cell and a different sample material volume than said sample cell, and wherein the sample material volume within the detector-cell may be changed by exchanging the sample cell within the detector-cell with the second sample cell.

13. The continuous-wavelength absorption detector of claim 9 wherein the concave mirror is a spherical mirror and the fixed location is located at the center of curvature of the spherical mirror.

14. The continuous-wavelength absorption detector of claim 9 wherein the sample cell is made of annealed quartz.

15. The continuous-wavelength absorption detector of claim 9 wherein the detector-cell body is made of polyetheretherketone.

16. The continuous-wavelength absorption detector of claim 9 wherein the means for connecting the top and bottom openings to the sample line includes screw connectors which allow connection to the sample line to be made by hand.