JPH0442040A - Absorbance measuring cell - Google Patents

Abstract

PURPOSE:To enhance the measuring limit of high absorbance material and to make it possible to perform the accurate measurement by providing a constitution wherein external light is not transmitted through plastic tubes for linking a measuring part and external apparatuses. CONSTITUTION:In a cell 1, tubes 4 are provided at the input side and the output side of a holding container 3 having a measuring part 2. In this tube 4, the main body of the tube which is molded of Teflon is covered with heat contracting-type plastic tube which does not transmit ultraviolet rays, the tube is heated and the covering is accomplished. Connecting tools 5 which are con nected to external apparatuses such as liquid chromatography apparatuses are provided at the tip parts of the tubes. Since the tubes 4 which are to become the exposed parts when the cell 1 is connected to the external apparatuses are covered, ultraviolet rays hardly intrude into the measuring part 2 from the outside. Thus, the absorbance characteristic can be measured even for mate rial having high OD value. The measurable density can be remarkably improved for the material whose OD value is very high.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a cell for measuring absorbance.

[Prior Art] An absorbance measurement cell is a container for measuring the light absorption characteristics of a substance. Measurement light is transmitted through this cell, and the amount of light absorption is measured from the difference in light intensity between the entrance and exit sides. It is (
OD measurement).

It is used for OD measurement, analysis of mixed solutions, and fractionation, and its absorption characteristics are determined by comparing it with known curves. That is, the absorbance of the liquid introduced into the cell is continuously measured to determine the substance and amount thereof.

This cell usually consists of a measuring section and a tube, the measuring section being a container through which measurement light passes, and the tube being a pipe for connection to external equipment.

The measuring part is often made of glass, and the tube is made of stainless steel or Teflon. This is because it does not react with the substance to be measured.

[Problem to be solved by the invention] This conventional cell had the following drawbacks.

First, for substances with high absorbance, the amount of light transmitted is very small, sometimes less than 1/1000. This is a value specific to the substance, and substances that absorb ultraviolet rays very well (for example, nitrobenzene and anthracene) will have such a value.

Usually, in this field, absorbance is expressed as an OD value, and the incident light (
Here, it is the logarithm of the reciprocal of the ratio between the amount A of ultraviolet rays and the amount B of transmitted light.

OD = l o g (B/A) For substances whose OD value exceeds 3, the measuring section must measure a very small amount of transmitted light, so the measurement accuracy must be high ( Of course, no matter how high the measurement accuracy is, if ultraviolet rays or visible light from the outside enters the measuring section, even a small amount will cause a large error in the measurement.This external light (stray light) Most of the intrusion is through the tube, so if you use a stainless steel one, there will be no problem, but depending on the substance, the metal may elute, which is not preferable.

Stray light becomes a problem when the amount of transmitted light is small compared to the amount of stray light, and the amount of transmitted light is large (the amount of light absorbed is low).
This is not a problem with materials.

Therefore, it is conceivable to reduce the influence of stray light by adopting a method of increasing the amount of transmitted light as much as possible even in a material with a small amount of transmitted light. This method is as follows.

- Absorbance is proportional to the optical path length (distance that ultraviolet rays pass through the material), so shorten the optical path length.

■ Decrease the concentration of the substance Among these methods, the limit of the method (■) of shortening the optical path length is 0.1 mm from the viewpoint of pressure loss and processing accuracy, and this method cannot measure the high absorbance substances mentioned above, and the method (■) shortens the optical path length. The method of lowering the concentration makes the chromatographic peaks broader (poor peak separation) and increases the amount of liquid, so it is not actually carried out.

Therefore, methods of increasing the amount of transmitted light are not realistic.

In addition, it has been possible to measure substances with an OD value of 3 or more if the concentration is low, but there is a measurement limit depending on the concentration, and at present it is almost impossible to use in practice.

Therefore, in this industry, there has been a long-awaited desire to increase the measurement limit of such a highly absorbent substance as much as possible (so as to be able to measure as high a concentration as possible), and to have a cell that can accurately measure it.

[Means for Solving the Problems] In view of the above-mentioned current situation, the present inventor has conducted intensive research and has discovered the following.
The cell of the present invention has been completed, and its characteristics include a container for measuring the absorbance of a liquid,
A holding container that holds a measurement section that transmits measurement light, and a plastic tube that connects the measurement section directly or indirectly to an external device, where the tube transmits external light. The point is that it is configured so that it does not.

Here, the measuring part is generally a disc-shaped plate having an oblong through hole made of Teflon sandwiched between glass plates, or a container made of glass, but is not particularly limited.

Furthermore, the holding container is a metal container that houses the measurement section described above and fixes the measurement section at the position where the measurement light passes, and this container has tubes at the entrance and exit for connection with external equipment. ing.

The measurement light is light used for measurement, and although it differs depending on the substance to be measured, it is usually ultraviolet light, but may also be visible light or infrared light.

Outside 1? 'ts equipment includes liquid chromatography equipment, pumps, valves, other piping such as tubes, etc.

The tube is made of Teflon or other plastic.
It has a structure that hardly transmits ultraviolet rays and visible light.

External light refers to stray light that enters the measuring section, and is usually sunlight or illumination light. From its components, ultraviolet rays, visible light,
This includes infrared rays, etc.

A structure that does not transmit external light means that when manufacturing the tube, a pigment (substance that does not transmit external light) is mixed and molded, or
Either an internal coloring method, such as mixing and polymerization, or an external coating method, such as coating the outside with a coating material or coating the outside with a light blocking agent after manufacturing the transparent tube, is acceptable. A simple method is to place a light-shielding heat-shrinkable plastic tube outside the tube and heat it to coat the transparent tube.

Of course, it is clear from the purpose of the present invention that it is not necessary to strictly block 100% of both ultraviolet rays and visible light, and it is sufficient that it does not affect the measurement. However, it is desirable to block 90% or more of both.

In this way, when the tube is shielded from external light, stray light does not enter the measuring section from the outside, and the measurement error due to the above-mentioned stray light does not occur.

The cell of the present invention can be used both as an analytical device and a preparative device.

[Embodiments] The present invention will be described in more detail below based on embodiments shown in the drawings.

FIG. 1 is a perspective view showing an example of a cell 101 of the present invention, in which tubes 4 are provided on the inlet and outlet sides of a holding container 3 having a measuring section 2.

This tube 4 is made by covering a tube body made of Teflon with a heat-shrinkable plastic tube that does not transmit ultraviolet rays, and heating the tube body to cover the tube body. A connector 5 for connecting to an external device (not shown) such as a liquid chromatography device is provided at the tip of the tube 4. Therefore, since the tube 4, which is a portion exposed when the cell 1 is connected to an external device, is covered, almost no ultraviolet rays enter the measuring section 2 from the outside.

[Effects of the Invention] According to the cell of the present invention, almost no external stray light enters, so that even substances with high OD values can be measured for light absorption characteristics. Furthermore, in the case of a substance with a very high OD value, its measurable concentration is significantly improved.

Furthermore, the present invention itself has the advantage that it is simple in structure, inexpensive, and can be easily implemented in already completed cells.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing one embodiment of the cell of the present invention. 1...Cell 2...Measuring part 3... Holding container 4...Tube 5... Connection tool

Claims (1)

[Claims] 1. A holding container that holds a measurement part that is a container for measuring the absorbance of a liquid and is a part that transmits measurement light;
A cell for measuring absorbance, comprising a plastic tube for directly or indirectly connecting the measuring section to an external device, wherein the tube is configured so as not to transmit external light. . 2. The absorbance measurement cell according to claim 1, wherein the tube is coated with a colored heat-shrinkable plastic.