Method and apparatus for optical measurement of concentration and temperature of liquids

A method for determining a change in concentration of a given component in a sample of a multi-component liquid mixture from an initial concentration of the given component corresponding to an initial refractive index of the sample at an initial temperature, said method comprising the steps of:

• (a) determining the refractive index of the sample of the multi-component liquid mixture by:
• (a-1) causing the sample of the liquid mixture to be contained in a vessel having a planar entrance side and a planar exit side, with a known angular relationship therebetween, said vessel being immersed in known surroundings;
• (a-2) causing a beam of light to impinge on said entrance side at an angle θi with respect to a normal to an outer surface of said entrance side, to pass through the sample of the multi-component liquid mixture, and to then pass through said exit side, from which it exits at an angle θe with respect to a normal to an outer surface of said exit side;
• and
• (a-3) calculating the refractive index of the sample of the multi-component liquid mixture, based on said angles θi and θe, by applying Snell's law at:
• an interface between the surroundings and said entrance side;
• an interface between said entrance side and the given sample of the multi-component liquid mixture;
• an interface between the sample of the multi-component liquid mixture and said exit side;
• and
• an interface between said exit side and the surroundings:
• (b) determining a change in refractive index, Δn, by subtracting from the initial refractive index the refractive index determined in step (a-3);
• (c) measuring the temperature of the sample of the multi-component liquid mixture;
• and
• (d) determining the change, ΔC, in the concentration of the given component in the sample of the multi-component liquid mixture from the initial concentration according to the approximate formula:
• ΔC≅(Δn−(∂n/∂T)ΔT)(∂n/∂C)−1,
• where:
• ∂n/∂T is partial derivative of index of refraction, n, with respect to temperature, determined from known data,
• ΔT is the difference between the temperature measured in step (c) and the initial temperature, and
• ∂n/∂C is partial derivative of index of refraction, n, with respect to concentration, evaluated from known data in a region near the initial concentration.

A method for determining the temperature of a sample of a liquid, the liquid being one of a pure liquid and a multi-component liquid mixture having a substantially constant concentration of its components, said method comprising the steps of:

• (a) determining the refractive index of the sample of the liquid by:
• (a-1) causing the given sample of the liquid to be contained in a vessel having a planar entrance side and a planar exit side, with a known angular relationship between said entrance side and said exit side, said vessel being immersed in known surroundings;
• (a-2) causing a beam of light to impinge on said entrance side at an angle θi with respect to a normal to an outer surface of said entrance side, to pass through the sample of the liquid, and to then pass through said exit side, from which it exits at an angle θe with respect to a normal to an outer surface of said exit side;
• and
• (a-3) calculating the refractive index of the given sample of the liquid, based on said angles θi and θe, by applying Snell's law at:
• an interface between the surroundings and said entrance side;
• an interface between said entrance side and the sample of the liquid;
• an interface between the sample of the liquid and said exit side;
• and
• an interface between said exit side and the surroundings;
• and
• (b) comparing the refractive index of the given sample of the liquid determined in step (a) to predetermined data relating different temperatures of the liquid to corresponding values of the refractive index of the liquid, so as to determine the temperature of the sample of the liquid corresponding to the refractive index of the sample determined in step (a).

An apparatus for determining the concentration of a given component in a sample of a multi-component liquid mixture, said apparatus comprising:

• (a) a vessel which contains said sample, said vessel having a planar entrance side and a planar exit side, with a known angular relationship between said entrance side and said exit side, said vessel being immersed in known surroundings;
• (b) a light source which is located so as to cause a beam of light to impinge on said entrance side at an angle θi with respect to a normal to an outer surface of said entrance side, to pass through said sample, and to then pass through said exit side, from which it exits at an angle θe with respect to a normal to an outer surface of said exit side;
• (c) a sensor which determines said exit angle θe, thereby permitting the refractive index of said sample to be determined, based on said angles θi and θe, by applying Snell's law at:
• an interface between the surroundings and said entrance side;
• an interface between said entrance side and the sample;
• an interface between the sample and said exit side;
• and
• an interface between said exit side and the surroundings;
• and
• (d) a computer programmed to compare a refractive index of said sample determined using said angles θi and θe with predetermined data relating different concentrations of the given component of the multi-component liquid mixture to corresponding values of the refractive index of the multi-component liquid mixture so as to determine the concentration of the given component in the sample of the multi-component liquid mixture.

An apparatus for determining the temperature of a sample of liquid, said apparatus comprising:

• (a) a vessel which contains said sample, said vessel having an entrance and an exit side, with a known angular relationship, between said entrance side and said exist side, said vessel being immersed in known surroundings;
• (b) a light source which is located so as to cause a beam of light to impinge on said entrance side at an angle θi with respect to a normal to an outer surface of said entrance side, to pass through said sample, and to pass through said exit side, from which it exits at an angle θe with respect to a normal to an outer surface of said exit side;
• (c) a sensor which determines said exit angle θe thereby permitting the refractive index of said sample to be determined, based on said angle θi and θe, by applying Snell's law which:
• an interface between the surrounding and said entrance side;
• an interface between said entrance side and the sample;
• an interface between the sample and said exit side;
• and
• an interface between said exit side and the surroundings;
• (d) a computer programmed to compare a refractive index of said sample determined using said angles θi and θe with predetermined data relating different temperatures of the liquid to corresponding values of the refractive index of the liquid so as to determine the temperature of the sample of the liquid.