Novel photometric system

• US 4,276,475 A
• Filed: 04/16/1979
• Issued: 06/30/1981
• Est. Priority Date: 10/20/1976
• Status: Expired due to Term

• Current Assignee: Waters Technologies Corporation (Waters Corporation)
• Original Assignee: Waters & Associates PLC
• Inventors: Nelson, Kenneth E.
• Primary Examiner(s): Willis, Davis L.
• Application Number:
  US06/030,312
• Time in Patent Office: 806 Days
• Field of Search: 250/372, 250/373, 250/365, 250/343, 250/344, 250/345, 250/346, 250/432 R, 250/435, 356/181, 356/246, 356/427, 356/130
• US Class Current: 250/373
• 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

Novel photometric apparatus advantageously having a conical shaped flow-cell comprising a light source proximate the narrow end and a photosensitive detector at the wider end of the cell. The flow-cell adequately compensates for a lens effect that has been discovered to be a substantial factor in electro-magnetic energy absorption studies on liquid streams.

Claims

1. Apparatus for measuring the amount of light absorbed by a portion of a flowing liquid, comprising:

a sample cell for transporting said flowing liquid along the longitudinal dimension of said cell, said cell including

a wall extending generally longitudinally,

a light entrance window at one longitudinal end of said cell, and

a light exit window at the other longitudinal end of said cell;

a light source for generating a light beam;

masking means including a mask with an aperture positioned between said light source and said entrance window of said cell for optically shaping said beam so that the portion of said beam that enters said cell through said window is transmitted through said cell without contacting said cell wall for a predetermined maximum liquid-lensing condition, thereby assuring that wall contact does not occur under any expected condition,

said maximum condition corresponding to when the liquid in said cell has a distribution of refractive index that causes the greatest expected divergent spreading of said beam by refraction,

detection means positioned beyond said exit window for measuring substantially all of the light emerging from said window, said detection means including a photoelectric element onto which said emerging light beam is incident,

whereby the amount of light detected by said apparatus is independent of the amount by which said beam is bent by refraction within said cell because all of said beam entering said cell and not absorbed by said liquid also emerges from said cell and is detected, thereby making said apparatus independent of variations in the refractive index of said liquid.

2. The apparatus of claim 1 further comprising a second cell for holding a reference liquid, said second cell including a wall and entrance and exit windows, said masking means including means to shape said beam so that the portion of the beam entering said second cell is transmitted therethrough without contacting the cell walls, and said detection means including means for measuring substantially all light emerging from said second cell.

3. The apparatus of claim 1 wherein said sample and reference cells have parallel longitudinal axes and said light entrance windows of said cells each include a lens surface for bending said beam emerging from said mask into the general direction of parallel cell axes.

4. The apparatus of claim 3 wherein said entrance windows comprise a single element and said lens surfaces are a common surface on said element.

5. The apparatus of claim 1 wherein

said mask is positioned with respect to said light source and said aperture is sized so that light emerges from said aperture at less than a predetermined angle with respect to the longitudinal centerline of said cell and

said cell is shaped so that light entering said cell with an inclination of no more than said predetermined angle passes through said cell without contacting said cell wall, for said predetermined liquid-lensing condition.

6. The apparatus of claim 5 wherein said mask is substantially closer to said light source than to said cell.

7. The apparatus of claim 1 wherein said masking means includes means for shaping said beam so that light of a pre-selected wavelength that enters said cell through said window is transmitted through said cell without contacting said cell wall for said predetermined liquid-lensing condition.

8. A photometer as defined in claim 1 wherein said light source and said measuring means are so selected that said photometer is an ultra-violet absorbance detector.

9. A photometer as defined in claim 1 wherein said sample has a volume of less than 32 microliters and a maximum diameter of less than 2 millimeters.

10. A photometer as defined in claim 8 wherein said sample cell has a volume of less than 32 microliters and a maximum diameter of less than 2 millimeters.

11. A photometer as defined in claim 8 wherein said flow cell comprises walls devergent at an angle of at least 1°

from the axis of said flowpath.