JP3269757B2 - Temperature compensation method for refractive index - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a refractive index, and more particularly, to a method for temperature compensating a refractive index.

[0002]

2. Description of the Related Art In general, the refractive index fluctuates according to the temperature of a substance. Therefore, it is necessary to keep the sample temperature constant in order to secure required measurement accuracy.

FIG. 6 is a block diagram showing an example of a refractive index measuring apparatus to which the above-mentioned total reflection method is applied. A light source 103 is arranged on one side of the prism 101, and a light detecting device CCD licensor 107 is arranged on the other side.
4 is fixed inside. The Peltier element 105 is attached to the constant temperature block 104, and the prism 10
The control circuit controls the Peltier element 105 based on the temperature detected by the temperature sensor 106 built in
The constant temperature block 104 and the prism 101 are controlled at a constant temperature.

In this apparatus, a sample is dropped on an interface 102 between the sample and the prism, and light is incident from the back of the prism.
By totally reflecting the light to the sample, the refractive index of the sample is measured from the incident angle and the reflection angle. When the refractive index of the sample is measured in this way, the physical and chemical values of the sample derived from the refractive index, such as the sugar concentration (Brix) in the sample, can be calculated immediately.

Since the refractive index changes depending on the temperature, the temperature of the refractive index measuring device is strictly controlled as described above. However, when the sample temperature is different from the set temperature of the refractive index measuring device, for example, After dropping, the measurement is performed after waiting for a predetermined time until the temperature at the interface between the prism and the sample reaches an equilibrium state. In addition, since this method takes time, temperature compensation is performed by measuring the prism temperature at the time of measuring the refractive index.

[0006]

In the method of obtaining the refractive index by performing the temperature compensation as described above, it is assumed that the measured temperature represents the correct interface temperature. However, as shown in FIG. 2, the interface position 102 and the position of the temperature sensor 106 do not match. Therefore, the temperature sensor 106
Will not necessarily represent the exact interface temperature.

In fact, even if the measured refractive index is temperature-compensated using the actually measured value of the prism temperature as described above, the measured refractive index does not coincide with an accurate refractive index as described later. The present invention has been proposed in view of the above-mentioned conventional circumstances, and provides a refractive index temperature compensation method that can accurately measure a refractive index even when an interface temperature and a prism temperature measured by a temperature sensor are different. It is intended to do so.

[0008]

[Means for Solving the Problems] The interface between the prism and the sample
Temperature T₁And the measured temperature T of the prism temperature by the temperature sensor _Two
Has a correlation as shown in FIG. 3, for example. Obedience
The measured temperature T_TwoReferring to the correlation shown in FIG.
Interface temperature T₁And the interface temperature T₁Actual measurement based on
Temperature compensation is performed for the folding ratio.

Thus, an accurate refractive index can be obtained even in a temperature imbalance state immediately after dropping a sample. The interface temperature T ₁ can be determined from the refractive index measured when a standard substance whose relationship between the temperature and the refractive index is known is dropped on the prism.

[0010]

FIG. 1 is a conceptual diagram of one embodiment of the present invention.
FIG. 2 is a conceptual diagram showing a positional relationship between an interface (prism interface) 102 on which a sample is arranged and a temperature sensor 106.

First, when, for example, 0.1 to 1.0 ml of a sample is dropped on the prism interface 1 of the refractive index measuring device set at a predetermined temperature, the measured temperature T _{2 of the} prism is changed as shown in FIG. Changes under the influence of the initial temperature, and converges to the set temperature T ₀ with the passage of time. Along with the change in the measured temperature T _2, the refractive index N ₁
Is also measured.

The position of the temperature sensor 106 of the prism 101 and the position of the interface 102 with the sample are usually different. Accordingly, since the measured temperature T ₂ does not accurately represent the interface temperature T ₁ , even if the measured refractive index N ₁ is temperature compensated using the measured temperature T ₂ , the obtained refractive index Dn _{2 is} obtained. It cannot be said that represents the true value N ₀ of the refractive index as shown in FIG.

On the other hand, from the measured temperature T ₂ , the interface temperature T ₁
Cannot be asked directly. Here, if a standard substance whose relationship between the temperature and the refractive index is already known is used, the interface temperature T ₁ can be determined conversely to the refractive index N ₁ .

Considering the relationship between the measured temperature T ₂ and the interface temperature T ₁ thus obtained, it can be understood that there is a correlation as shown in FIG. In FIG. 3, the horizontal axis represents the difference between the measured temperature T _{2 of the} prism and the set temperature T _0, and the vertical axis represents the difference between the interface temperature T ₁ and the set temperature T ₀ obtained as described above. And the correlation is a straight line in this example.

If the correlation between the actually measured temperature T ₂ and the interface temperature T ₁ is determined in advance for a specific substance in this way,
If the measured temperature T ₂ is seen from the next time can be determined interfacial temperatures T ₁ with reference to FIG. 3, when the surface temperature T ₁ is known, the refractive index N _1, which is the measurement refers to the interfacial temperature T ₁ of Temperature compensation, and the true value of the refractive index N ₀ can be obtained.

FIG. 4 shows an embodiment of the present invention when the sample is water and the sample initial temperature is 35.degree. When temperature compensation of the actually measured refractive index N ₁ is performed based on the measured temperature as in the conventional method, an accurate value of the refractive index N ₂ cannot be obtained until one minute or more has elapsed from the start of measurement. It can be seen that the true value N _{0 of the} refractive index is already obtained in about 20 seconds.

FIG. 5 shows another embodiment of the present invention. The sample was a 20% sucrose solution, and the initial temperature of the sample was 30 ° C. The result is the same as in the case of FIG.

[0018]

As described above, according to the present invention, even when the sample temperature immediately after dropping the sample is different from the set temperature of the apparatus, the refractive index can be accurately obtained, and the measurement time can be greatly reduced. Can be.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of the present invention.

FIG. 3 is a graph showing a correlation between an actually measured temperature and an interface temperature according to the present invention.

FIG. 4 is a graph showing one embodiment of the present invention.

FIG. 5 is a graph showing another embodiment of the present invention.

FIG. 6 is an apparatus configuration diagram to which the present invention is applied.

[EXPLANATION OF SYMBOLS] 101 prism T ₁ interface temperature T ₂ actually measured temperature

Continuation of the front page (56) References JP-A-6-273329 (JP, A) JP-A-6-273328 (JP, A) JP-A-1-17038 (JP, A) JP-A-64-68637 (JP) , A) JP-A-62-12840 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 21/00-21/01 G01N 21/17-21/61 JICST file (JOIS )

Claims (2)

(57) [Claims] In a method of measuring a refractive index by a total reflection method using a prism, a correlation between an interface temperature of a prism onto which a sample is dropped and an actually measured temperature of the prism is determined in advance, and the correlation is referred to from the measured temperature. A temperature compensation method for a refractive index, wherein temperature compensation of a refractive index is performed based on an interface temperature. 2. The temperature compensation of the refractive index according to claim 1, wherein the interface temperature is obtained from a refractive index measured when a standard substance having a known relationship between the temperature and the refractive index is dropped on the prism. Method.