Fluid flow cell and method for photometric analysis
A flow cell and method for photometric transmission measurements are disclosed in which a folded optical path provides for co-located, collinear fiber optic read and illumination cables that can be bundled together. Light passes through a fluid sample, is reflected off a pair of right-angle turning mirrors and returns through the fluid for a second pass. A center divider separates fluid passages on the first pass of the light through the fluid and the second pass of the light through the fluid to block any undesired backscattered light from reaching a detector.
1. A flow cell for taking transmission measurements in a fluid, comprising a body having a substantially fluid measurement cavity having a bight portion and tip portions, co-linear fiber optic ports operatively arranged at one side of the body, fluid ports arranged at another portion of the body such that the fluid being measured enters at a first of the tip portions adjacent one of the fiber optic ports operative as an illumination port and exits at a second of the tip portions adjacent another of the fiber optic ports operative as a read port, a turning mirror system located adjacent the bight portion of the cavity, and a divider arranged in the cavity between the tip portions and configured to prevent light back-scattered off the fluid or off particles suspended in the fluid from reaching the read port.
2. The flow cell of claim 1 , wherein the turning mirror system is comprised of a pair of right-angle prism mirrors.
3. The flow cell of claim 2 , wherein the mirrors are provided with at least one of an anti-reflective coating and a broadband coating selected to reflect light externally incident on a hypotenuse of the prism mirrors.
4. The flow cell of claim 1 , wherein a fiber optic cable is associated with each of the ports, and a collimating lens is arranged between each of the cables and the ports.
5. The flow cell of claim 4 , wherein each collimating lens is a plano-convex lens.
6. The flow cell of claim 4 , wherein the fiber optic cable associated with the port operative as the illumination port is selected to have a diameter smaller than the fiber optic cable associated with the port operative as the read port so that an illumination beam entering through the illumination port approximates a point collimated light source.
7. The flow cell of claim 4 , wherein an optical window is operatively arranged between the lenses and the fluid ports.
8. The flow cell of claim 1 , wherein an optical window is operatively arranged between the bight portion and the mirror system.
9. The flow cell of claim 8 , wherein a second optical window is operatively arranged between the lenses and the fluid ports.
10. The flow cell of claim 9 , wherein seals are provided between the optical windows and the body.
11. The flow cell of claim 1 , wherein the mirror system includes an end cap operatively connected with the body.
12. The flow cell of claim 11 , wherein an optical window is operatively arranged in the end cap between the bight portion and a pair of right-angle prism mirrors comprising the mirror system.
13. A method for taking measurements of a fluid, comprising flowing the fluid being measured into a fluid port of a flow cell body having a bight portion, tip portions and co-linear fiber optic ports operatively arranged at an end of the body such that the fluid being measured enters at a first of the tip portions adjacent a first of the fiber optic ports operative as one of an illumination port when a second of the fiber optic ports is operative as a read port or the read port when the second fiber optic port is operative as the illumination port, and flows toward a first location on the body at which a collimated beam is directed to travel through the fluid and be reflected off right-angle prism mirrors located adjacent the bight portion of the cavity to create incident light, having the fluid exit at another of the tip portions adjacent the second fiber optic port operative as one of the read port when the first fiber optic port is operative as the illumination port or the illumination port when the first fiber optic port is operative as the read port and directing the incident light to a second location adjacent the first location on the body via a substantially U-shaped path, wherein the collimated beam and incident light are divided at the bight portion to prevent back-scattered light or light reflected off fluid particles from reaching the second location.
14. The method of claim 13 , wherein the collimated beam is directed to the body from a fiber optic cable through a focusing lens.
15. The method of claim 13 , wherein the incident light is focused and transmitted through a fiber optic cable.
16. The method of claim 15 , wherein the incident light is focused by a lens and then transmitted through a second fiber optic cable co-linear with the first-mentioned fiber optic cable.
17. A flow cell for taking transmission measurements in a fluid, comprising a body having a substantially fluid measurement cavity having a bight portion and tip portions, co-linear fiber optic ports operatively arranged at one side of the body, fluid ports arranged at another portion of the body such that the fluid being measured enters at a first of the tip portions adjacent a first of the fiber optic ports operative as one of an illumination port when a second of the fiber optic ports is operative as a read port or the read port when the second fiber optic port is operative as the illumination port and exits at a second of the tip portions adjacent the second fiber optic port operative as one of the read port when the first fiber optic port is operative as the illumination port or the illumination port when the first fiber optic port is operative as the read port, a turning mirror system located adjacent the bight portion of the cavity, and a divider arranged in the cavity between the tip portions and configured to prevent light back-scattered off the fluid or off particles suspended in the fluid from reaching the read port.
18. The flow cell of claim 17 , wherein the turning mirror system is comprised of a pair of right-angle prism mirrors.
19. The flow cell of claim 18 , wherein the mirrors are provided with at least one of an anti-reflective coating and a broadband coating selected to reflect light externally incident on a hypotenuse of the prism mirrors.
20. The flow cell of claim 17 , wherein a fiber optic cable is associated with each of the ports, and a collimating lens is arranged between each of the cables and the ports.