JP2003207442A - Long light path cell for spectrophotometer utilizing optical fiber tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a long light path cell for spectrophotometers that can sensitively analyze the concentration of a sample in a liquid phase containing a case where the liquid phase, especially solution, is used by utilizing an optical fiber principle, can be retrofitted to an existing spectrophotometer as needed, and can be manufactured compactly. <P>SOLUTION: In a light path cell for spectrophotometers, a flexible tube whose inner wall has a lower refractive index as compared with a liquid phase to be measured is set to be a cladding, and the inside of the tube is filled with the liquid phase containing a sample and light is transmitted into a core as the core. The preferable example of the flexible tube is a Teflon (registered trademark) tube and a compact long light path cell can be manufactured. Expecially, by sticking Teflon or the like having a smaller refractive index as compared with water to an inne wall, the long light path cell for analyzing nearly all liquid phases containing a solution base with high sensitivity can be obtained. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of spectroscopic analysis, and in particular, a novel optical path cell for a spectrophotometer capable of performing highly sensitive analysis by applying the principle of an optical fiber, and a method for producing the same. Regarding

[0002]

2. Description of the Related Art A spectrophotometer (for example, an ultraviolet / visible spectrophotometer) is a spectrophotometer for measuring the concentration of a sample by measuring the absorbance when monochromatic light is transmitted through a sample solution. Is measured. At this time,
As is well known, I
Assuming that the intensity of light after passing ₀ is I, the absorbance A (= lo
gI ₀ / I) is Lambert-Beer
(A = εCL). Here, ε is the molecular extinction coefficient of the sample (medium), C is the concentration of the sample, and L is the optical path length.

Therefore, in order to increase the sensitivity in the absorptiometry, it is necessary to increase the absorbance (A) by some means when the concentration C is constant, as is clear from the above Lambert-Beer law. For this purpose, the extinction coefficient (ε) must be increased or the optical path length L must be increased. In order to increase ε, it is necessary to somehow react the target molecule or ion in the sample with other molecule or ion to convert it into a compound having a larger ε (for example, using a porphyrin compound). Is not a method that can be used for any molecule or ion, but it is a very limited method.

Therefore, a general means for increasing the absorbance A is to increase the optical path length (L). At present, there is a multiple reflection cell as a commercially available product having an extended optical path length. This is 2
Light is passed through a single mirror (the surface of which is plated with gold or aluminum), and reflection is repeated many times to gain distance. Although there are various types depending on the application, they mainly deal with substances in the gas phase (gas) and are not used in the liquid phase (liquid or solution). Also, the price is generally expensive.

On the other hand, the optical path cell used for the measurement of the liquid phase sample in the absorptiometry is usually a glass rectangular cell having a length of about 1 cm. In addition to these, there are also cylindrical cells, which have an optical path length of 5 cm to 10 c.
Most of them are m. As described above, since the optical path cell currently used in the spectrophotometer is made of glass or the like having a fixed optical path length, the optical path length (L) can be extended only to about 10 cm.

In recent years, various ideas have been made to improve the sensitivity and accuracy in the field of analytical chemistry by applying the principle of optical fiber. The use of optical fibers in the field of analytical chemistry includes (a) a method of using an optical fiber as a medium for transmitting light, a method of transmitting light from a light source and collecting a signal generated in an analysis target, and (b) an optical fiber. There are three possible methods: use as a light-splitting element that utilizes the light dispersion characteristics of the above, and (c) the core of the optical fiber itself as the target of the spectroscopy. Fujiwara et al. Are conducting "research on a long-light capillary absorption tube" according to the third method (c) (for example, Fujita Futao: Analytical Chemistry (general essay), Vol. 34, pp. 737-756). (19
85)). That is, by dissolving the sample to be measured in a solvent with a high refractive index such as carbon disulfide and introducing this into a capillary (capillary tube) to form the core and the inner wall of the capillary as the cladding, optical transmission is possible in the long optical path. It is said that it could be utilized as a simple waveguide type optical path cell. Then, it is proposed to use a commercially available coiled tube for gas chromatography as a hollow fiber (capillary), for example, a length of 50 m.
Absorbance using a capillary of 3
It is said that it was able to amplify up to 10,000 times.

The method proposed by Fujiwara et al. Is a small number of long optical path cells for a spectrophotometer for measuring a liquid phase sample by applying the principle of an optical fiber, but it is solved for practical use. There are some problems left to be addressed. One of them is that Pyrex (registered trademark) or quartz tube is selected as the material forming the optical path. Pyrex and quartz have a large refractive index (for example, the refractive index n = 1.474 of Pyrex at room temperature). As will be explained later, in order to transmit light while totally reflecting it according to the principle of the optical fiber, as the liquid that becomes the core,
It is necessary to use a liquid larger than Pyrex or quartz that forms the clad. In fact, the liquids they used were highly toxic liquids such as carbon disulfide (n = 1.628), harmful liquids such as benzene (n = 1.4744), and acetophenone (n = 1.534). ) And 1-bromonaphthalene (n = 1.659) and the like, and the total reflection condition is examined using these, but no investigation using an aqueous solution, which is most important in practical use in liquid phase analysis, has not been conducted. An example used in actual absorbance analysis is the determination of iodine in carbon disulfide (K. Fujiwara et al. Anal. Che.
m., 56, 1640 (1984)), carbon disulfide is not only highly toxic, it is highly flammable and explosive, and it has a strong malodor (however, in the case of ultra-high purity products, it is malodorous). There is no)). In the case of carbon disulfide, 319 nm and 3
Since it has an absorption band (vapor) at 55 nm, it is not preferable as a solvent for the absorption spectrum. Furthermore, the materials such as Pyrex and quartz presented by Fujiwara et al. As the material for the optical path cell are poor in flexibility, and even if a tube having a diameter as small as possible is used and a radius of curvature is small, only about 10 cm can be obtained. , It is not possible to make a compact long-path cell,
In addition, since it is glassy, it is easily broken.

[0008]

The object of the present invention is to solve the above problems and to apply the principle of an optical fiber to highly sensitively detect the concentration of a sample in a liquid phase, particularly in the case of using an aqueous solution. It is an object of the present invention to provide a new type of long-path cell for a spectrophotometer which can be analyzed in a compact manner and can be retrofitted to an existing spectrophotometer if necessary and can be made compact.

As a result of repeated studies, the inventor of the present invention has found that a long optical path cell for a spectrophotometer capable of achieving the above-mentioned object can be realized by using a flexible tube typified by a Teflon tube. Thus, according to the present invention, first, an optical path cell for a spectrophotometer for measuring the concentration of a sample contained in a liquid phase by transmitting light, It consists of a flexible tube with a low refractive index, and this flexible tube is used as a clad,
An optical path cell for a spectrophotometer is provided, wherein the flexible tube is filled with a liquid phase containing the sample to serve as a core so that light can pass through the core.

According to the invention, there is further provided an optical path cell for a spectrophotometer for transmitting light into the liquid phase to measure the concentration of a sample contained in the liquid phase, the optical path cell comprising: A flexible tube in which a film having a low refractive index is fixed to the inner wall, and the inner wall of the flexible tube serves as a clad,
An optical path cell for a spectrophotometer is provided, wherein the flexible tube is filled with a liquid phase containing the sample to serve as a core so that light can pass through the core.

Further, the present invention is a method for producing an optical path cell for a spectrophotometer as described above, wherein the flexible tube portion is made of a substance having a refractive index lower than that of the liquid phase containing the sample to be measured. A method is provided which comprises a step of fixing a film of the low refractive index substance to the inner wall of the flexible tube by injecting a solution and repeating heating and drying and depressurizing operation. Another aspect of the present invention is also directed to a spectrophotometer using the above-described optical path cell.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The principle of an optical fiber, which is the theoretical background of the present invention, will be described below with reference to the accompanying drawings.
Embodiments of the present invention will be described in detail with respect to the configuration of the optical path cell of the present invention, the method of manufacturing the optical path cell according to the present invention, application to a spectrophotometer, and the like.

[0013]The principle of optical fiber First, using a simple principle diagram, why light is totally reflected?
In addition, under any condition, the optical path cell of the present invention is preferable.
Light is completely reflected inside the hollow coil-shaped optical fiber
Explain whether to shoot and proceed. Figure 1 shows the direction of light
(Snell's law that governs reflection, refraction, refraction, etc.)
law). Refractive index is n₁N of the medium
₂When a ray enters the medium of₁The angle of
When incident₂Enters at an angle of (refraction phenomenon). This
The opposite is also true. That is, the refractive index is n₂The medium of
N₁When a ray enters the medium of₂Angle of
Incident at θ₁Enter at the angle. However,
The following relationship exists between the folding rate and the angle.     sin (θ₁) / Sin (θ₂) = (N₂/ N₁) = (C₂/ C₁) (1) Where c₁, C₂Is the medium n₂And n₁Light passing through
Is the speed of. This is called Snell's law. θ₁Is (π
/ 2) θ when rad = 90 °₂Is called the critical angle θ_cTable
You The light ray has a refractive index n₂From the medium of θ (> θ_c)It is
That is, if the incident angle is larger than the critical angle,
, Refractive index n₁Cannot enter the medium of
It reflects like a mirror at the (horizontal line). This is all
It is a shooting phenomenon.

In FIG. 1, α (= (π / 2) −θ) is a boundary line.
They are at an angle. This relationship is wound into a coil
Flexible tubes such as Teflon
Figure 2 when applied to a bull tube)
There is. In FIG. 2, r is the average value of the radius of curvature (ρ).
Where d is the inner diameter (optical path width) of the tube. Now θ is
It is the incident angle when the condition of total internal reflection is satisfied, and φ is the glancing angle.
(Π / 2 = θ + φ). These as Snell's law
If applied, sin (θ) ≥ sin (θ_c) = (N / n _s), Si
n (θ) = 2r / (2r + d). However, here, n
Is the refractive index of the inner wall of the tube to be the cladding,_sIs the core
The refractive index of the liquid phase is water. From now on, the total reflection condition
Then, the following relational expression is obtained.     2r ≧ d (n / [n_s-N]); θ_c= Sin^-1(n / n_s) (2) As a specific example, measure an aqueous solution as shown in the examples below.
Of Teflon with a refractive index of 1.31 or 1.29
If the film is fixed, n_s= 1.333
3, n = 1.29 or 1.31, d = 0.1 cm
When entered, r (n
= 1.29) ≧ 1.50 cm, r (n = 1.31) ≧ 2.
81 cm is obtained. The critical angle of incidence is θ
_c(n = 1.29) = 75.4 ° and θ_c(n = 1.3
1) = 79.3 °. Therefore, the critical angle of the irradiation angle
Is φ_c(n = 1.29) = 14.6 ° and φ_c(n =
1.31) = 10.7 °. That is, φ_c(n =
1.29) = 14.6 ° and φ_c(n = 1.31) = 1
It can be seen that total reflection occurs at 0.7 °. like this
The principle of optical fiber (total reflection of light: Snell's law)
And Lambert-Beer's law in both theoretical aspects of the present invention
is there.

[0015]Long optical path constructed directly from flexible tube
cell An optical path cell for a spectrophotometer of the present invention is, as a first aspect,
It can be constructed directly from a flexible tube. Sanawa
It has sufficient flexibility and can be
Made of a material with a lower refractive index than the liquid phase containing the sample
Using a tube that is wound into a coil.
The flexible tube of
As a core filled with a liquid phase, light is transmitted through this core.
By doing so, it is possible to
The optical path length is much longer than that of optical path cells made of lath or quartz.
A long long path cell is obtained. According to the present invention
Most suitable for constructing optical path cells for spectrophotometers
Teflon (polytetrafluoroethylene) tube
Depending on the purpose, a commercially available Teflon tube (FE
P spaghetti tube; inner diameter: 0.4 mm or more, 90 m
Wide range up to about m, with various lengths and properties
[Available from Universal, Inc.])
Buy from inside or prepare. For example, commercially available low refractive index
(Refractive index n = 1.34) Use Teflon tube
Enables analysis of liquid phase samples with a higher refractive index
An optical path cell is obtained. Of course, similar to Teflon tube
In addition, it has flexibility and chemical resistance, and has excellent tensile strength and bending strength.
Other tubes can be applied as long as they have them.

[0016]Long optical path cell with low refractive index film fixed The optical path cell for a spectrophotometer of the present invention comprises the second aspect, and
As a preferred embodiment of the present invention, a low refractive index film (thin film) is
Consists of a flexible tube fixed (coated) to the inner wall
You can also That is, a chew with sufficient flexibility
The inner wall of the tube has a higher refractive index than the liquid phase containing the sample to be measured.
Stick or coat a film of low material, which can be
It is wound into a coil and the inner wall film of this flexible tube is clad.
And fill the tube with the sample-containing liquid phase as the core,
By allowing light to pass through this core
Also has a significantly longer optical path length than conventional optical path cells.
An optical path cell can be obtained. This type of long-path cell
Enables highly sensitive analysis especially in aqueous solution samples
Excellent in terms. From the perspective of total internal reflection conditions,
If it is possible to measure an aqueous system under the conditions of
Generally, measurement is possible. Because it refracts more than water at room temperature
This is because there is almost no liquid with a low rate (normal conditions
Is smaller than the refractive index of water (n = 1.3333).
The liquid is methanol (CH₃OH: n = 1.330
0) and acetaldehyde (CH₃CHO: n = 1.33
16) only. Moreover, its value is slightly smaller than that of water.
Only).

When an optical path cell is constructed from a flexible tube according to the above-mentioned first embodiment and the inner wall of the tube is used as a clad, the refractive index is smaller than that of water for commercial use or for research (n = 1.33333). I can't find any of the tubes below) that are easily available. Therefore, according to a preferred embodiment of the present invention, a film of a substance having a refractive index lower than that of water is fixed (coated) on the inner wall of a flexible tube that is easily available as a commercial product. For example, a Teflon-containing solution (6% solution) having a refractive index n = 1.31 or a Teflon-containing solution (1% solution) having n = 1.29 (both can be obtained from Mitsui DuPont Fluorochemical Co., Ltd.) is used. , These are fixed (coated) on the inner wall of the flexible tube. These low-refractive-index substances can be obtained as solids (resin form), and in this case, they can be purchased at a relatively low cost, but they will be dissolved in an appropriate solvent separately before use. The long-path cell of the present invention thus produced is applicable to the spectroscopic analysis of any liquid phase sample handled in a normal range, because the refractive index of the inner wall serving as the clad is smaller than that of methanol or acetaldehyde as described above. it can. As the flexible tube, various flexible tubes such as a polyvinyl chloride tube and a polyethylene tube can be used in addition to the Teflon tube.

[0018]Fabrication of long optical path cell with low refractive index film fixed For high-sensitivity analysis of a wide range of liquid-phase samples including the above-mentioned aqueous systems
The long optical path cell for spectrophotometer of the present invention that enables the present invention is
According to the flexible tube, especially with sufficient flexibility and resistance
It is also excellent in chemical resistance and physical strength,
Teflo, which has high oil repellency and difficulty in fixing to other substances
A material with a low refractive index on the inner wall of the tube (for example,
Teflon with a refractive index of 1.31 or 1.29)
It can be made by fixing or coating the membrane
it can. This method is better than the liquid phase containing the sample to be measured.
Injection of a solution of a substance with a low refractive index inside a flexible tube
Then, heating and drying and depressurizing operation are repeated,
If necessary (especially as a flexible tube, Teflon tube
Tube), inner wall cleaning process and etching
A pretreatment consisting of steps is applied. Below the low refractive index thin on the inner wall
A detailed description will be given of a method of manufacturing a flexible tube having a membrane fixed thereto.
It The following description describes a Teflon tube as a flexible tube.
This is mainly done when using a probe, but other flexible cables are used.
Tube, for example polyvinyl chloride tubing or polyethylene
Even when using a tube, a low refractive index thin film
It is possible to wear (cover) it, and moreover it is a Teflon tube.
It doesn't require strict manipulation.

First-stage pretreatment : When a low refractive index is fixed to a flexible tube, especially a Teflon tube, it is necessary to perform pretreatment in order to improve the fixing property inside the flexible tube. The first step of pretreatment is to thoroughly clean the inside of the tube (inner wall). That is, for example, after thoroughly cleaning the inside and outside of the tube with a glassware detergent or pure water,
Further, the tube is filled with a detergent having an appropriate concentration and shaken in the ultrasonic cleaner for a certain period of time. Then, after thoroughly cleaning the inside with pure water or the like, a volatile solvent such as alcohol or acetone is repeatedly passed through. Finally, the solvent is completely expelled with a heat dryer such as a dryer (if stains and moisture remain, uneven processing tends to occur).

Second Stage Pretreatment : It is desirable that the flexible tube (particularly Teflon tube) is then subjected to another stage of pretreatment. That is, in order to firmly fix or coat Teflon resin or the like in the Teflon tube, it is not enough to wash the inner wall of the tube, and the inner surface of the tube must be etched in advance. I won't. Although various methods can be applied as the etching treatment, the following two methods can be exemplified as preferable methods. The first method is the simplest method and utilizes the chemicals at hand. Teflon is generally very resistant to chemicals and is not attacked by most chemicals. It is said to be stable in all organic solvents. Chloroform (CHCl3) and ether (C2H5OC2H5), which are considered to have the strongest effect on Teflon among ordinary organic solvents, are slightly affected, but they are said to be sufficiently durable for use. It is known that this Teflon is also the only one that is significantly affected by bromine, so bromine is effective from the viewpoint of etching action, but in actuality, from the viewpoint of experimental safety, for example, it was cleaned. Chloroform is filled in a Teflon tube, both ends are sealed, and after leaving it for about 3 months, the liquid is extracted, washed with alcohol, and further vacuum and heat dried. In this case, the dried surface is slightly etched. The second method uses the established means that the surface of Teflon can be etched. For example,
After filling with Teflon etching agent Tetra Etch (trade name: manufactured by Junkosha Co., Ltd., an etching agent containing petroleum as a main component), it is contacted for a certain time (about 5 seconds). After confirming that the treatment is finished (dark green changes to brown when treated), the liquid is extracted and the treated surface is washed with alcohol or the like. Next, pure water is washed to completely remove the remaining tetra-etch. Further, in order to dry the inside, vacuum drying, heat drying and the like are performed as in the first method.

Fixing (coating) method : After the completion of the two-step pretreatment as described above, the fixing or coating in the flexible tube is performed using the low refractive index substance-containing liquid as follows. The following operation is a specific example of fixing (coating) a thin film of low refractive index Teflon on the inner wall of the Teflon tube, but basically the same applies when using other flexible tubes or low refractive index substances. The operation may be performed. Commercially available Teflon tubes have some elasticity and flexibility, and are usually curved in a large circular shape. Therefore, in order to manufacture a Teflon fixing film having a uniform film thickness, it is necessary to perform the fixing operation with the inner surface of the Teflon tube being straight. For example, when using a commercially available Teflon tube having an inner diameter of 1 mm and an outer diameter of 1.8 mm, a thick glass tube having an inner diameter of 2 mm is used, and as shown in FIG. Inject. It is possible to heat dry while rotating the glass tube containing the Teflon-containing liquid sideways (in a horizontal state), and at the same time evaporate the solvent while depressurizing it, but it takes a little longer than when vertical, so Here, only the vertical case is shown as an example. Inject a small amount of low refractive index Teflon liquid into the Teflon tube in the glass tube with a syringe to keep the glass tube at the same height (position),
Dry with a dryer while rotating at a constant speed. The amount of liquid to be injected should be such that it completely finishes drying from the inlet to the outlet (excessive amount of solution drops into the lower container if too much). It is advisable to perform vacuum (pressure reduction) drying every two to three passes to ensure volatilization of the solvent vapor (pressure may be reduced simultaneously with heating and drying). Also, at this point, the glass tubes are switched upside down and the same operation is performed. The above operation is generally repeated 4 to 5 times so as to obtain a fixed film with the uniformity kept as a whole.

[0022]Application to spectrophotometer Consists of a flexible tube typified by Teflon tube
Since the optical path cell of the present invention is excellent in flexibility and elasticity,
It can be formed in any shape. Practically good in general
A coil shape is preferable, but other shapes are also possible.
Wear. In particular, winding in a coil with a radius of curvature of 10 cm or less
You can also do it. Thus, the bending of the inner wall of the tube used
Folding rate, refractive index of liquid phase containing sample to be measured, tube inner diameter
From the (optical path width), from the above-mentioned equation (2), the curvature half to be wound
Estimate the diameter, and based on the value,
The flexible tube may be wound so as to be compact.
However, in practice, all the antithesis as estimated from equation (2)
Curvature considered to be smaller than the radius of curvature that satisfies the shooting condition
It is possible to increase the sensitivity by adopting a radius.
(See Example 1 below).

The optical path cell of the present invention is basically assembled as a device as shown in FIG. 4 and applied to a spectrophotometer. As shown in FIG. 4, an optical path cell made of a flexible tube made of a flexible tube wound in a coil is supported by two supporting plates, and a sample inlet and a sample outlet are attached. There is. As shown in the figure, the optical path cell is preferably movable in the XZ direction by an appropriate slide means arranged on the support plate. The incident light passes through a condenser lens (which is also preferably movable in the XZ direction), passes from the entrance of the optical path cell enlarged in a trumpet shape into the optical path filled with the sample, and then the transmitted light is detected. Is transmitted to the vessel.

This device can be roughly classified into two types. One is the optical path length L = 50 of the optical path cell.
This is a type that can be retrofitted to an existing spectrophotometer, that is, a type that can be used as it is without modifying the cell chamber of a normal spectrophotometer cell chamber (about 15 cm x 20 cm). It is a popular type. The other type is for a slightly special purpose, and is used when the sensitivity is to be increased to several times to several tens of times that of the normal type. For example, optical path length L = 5 m or more and 20 m
It is about 600 to 3000 times as a whole.
The amplification rate is about double. In this case, since it is difficult to put the optical fiber type cell inside the cell chamber of a normal spectrophotometer for measurement, the optical fiber type cell is attached to the outside for implementation. In this second mold, since the sample amount increases, it is necessary to use a Teflon tube having an inner diameter reduced to about 0.4 mm (in this case, the maximum sample amount is 2.5 mm).
cm ³ ). However, since the sample injection pressure also increases, it is necessary to devise a method such as applying a high pressure with a liquid feed pump or introducing the sample under a reduced pressure.

[0025]

EXAMPLES The features of the present invention will be more specifically described below.
However, the present invention is not limited to these examples.
Is not limited.Example 1: A solution having almost no absorption in the ultraviolet / visible region
Measurement results with long optical path cell when liquid is used This example has almost no absorption in the ultraviolet / visible region.
Long-path cell consisting of flexible tubing using different solutions
The relationship between the size and the intensity of transmitted light is investigated. use
The prepared solution was a water-ethanol (47%) mixed solution (refractive index
n = 1.350), and the ultraviolet-visible region (wavelength: 20
It has no absorption maximum at 0 nm to 800 nm (however,
Excess rate is not 100%, so it is almost constant over the entire area
Has a weak absorption). For the experiment, the device as shown in FIG.
Was used. Place the He-Ne laser transmitter on the right side, 2
Laser bee with beam diameter narrowed to about 00-300 μm
Signal (wavelength: 632.8 nm). curvature radius
In consideration of (ρ), the inner diameter (light
(Width) 1 mm, outer diameter 1.8 mm, refractive index 1.338
Wrap a Teflon tube of fixed length in a coil
At the tip of the tube (light entrance: widened like a trumpet)
The laser beam was launched and the beam passed through the tube.
Light is received by an optical power meter placed at the tube outlet,
Intensity I (in mW) was measured. Total tube length L
(Cm) was changed in the range of 100 cm to 600 cm.
In addition, the radius of curvature ρ is in the range of 1.0 cm to 8.0 cm.
Experiment with changing. Results are shown in FIG. In this figure,
The horizontal axis represents the optical path length L, and the vertical axis represents the transmitted light intensity. However
However, since the range of change in light intensity is wide here,
It is logarithmic (log 10 [I / mW]). Within experimental range
For all radii of curvature (1.0 cm ≤ ρ ≤ 8.0 cm),
When the optical path length L is 600 cm or less, log_Ten[I / mW] and length
Relationship between the length L, that is, -log_Ten[I / mW] =
A relationship of αL + β was obtained (α and β are constants). This is my first
Luminous intensity I₀Organized using (mW), -log_Ten[I /
I₀] = ΑL, which is equivalent to Lambert-Beer's law
Value. This relationship can theoretically be calculated using a simple model.
Can also be explained. There is one between the slope (α) and the radius of curvature (ρ).
Constant relationship is recognized, and this relational expression is approximated as
did it. α = P (ρ) = − 0.63 coth (0.19ρ) −4.4 When 4 cm ≤ ρ, α is almost constant, and all incident light is
It is considered to be reflected. Curvature radius ρ is 4 cm or less
Since the total internal reflection is incomplete, the light is partially reflected in the tube.
It will leak out. That is, assuming total reflection,
The attenuation of light that exceeds the absorption value due to the passage of light
It will be observed by mouth. However, this phenomenon
On the contrary, if you decide to use it aggressively, from a practical point of view
Can be used to further increase sensitivity, in other words
The same effect as increasing the optical path length.
Become.

[0026]Example 2: Having absorption in the ultraviolet / visible region
Measurement result by the long-path cell when the compound solution is used Next, using an apparatus similar to the example,
For substances with absorption, perform concentration measurement experiments by absorbance
went. That is, in 50% ethanol aqueous solution,
The electronic spectrum of dephenol has a first absorption band of 400
It exists in the vicinity of ~ 800 nm and has an absorption maximum of 620 n.
It is near m. On the other hand, He-Ne laser is
Is 632.8 nm, near the absorption maximum and the laser wavelength
Almost overlap. Figure 7 shows the measurement results, and the horizontal axis shows India.
Phenol concentration (ppm unit: mg / L), absorption on the vertical axis
Indicates the absorbance. Conventional for comparison
According to the invention, as measured in a normal 1 cm cell of the mold
L = 100 cm (N = 4 rolls) and L = 200 cm
(N = 9 turns) long optical path cell (inner diameter 1 used in Example 1
mm Teflon tube; radius of curvature ρ = 3c
m; straight line portion = 25 to 30 cm)
Shows. As is clear from the figure, the long light according to the present invention
The tract cell shows overwhelmingly high absorption, which is usually 1 cm.
Based on the cell, it is about 140 times as large as a 100 cm cell.
A sensitivity increase of about 260 times has been obtained with a 00 cm cell.
It

[0027]Example 3: Optical fiber having a lower refractive index than water
Measurement results using a fiber-type long optical path cell In this example, a low refractive index Teflon solution (6% solution: n
= 1.31; Mitsui DuPont Fluorochemical Co., Ltd.
Teflon tube (L = 60cm; half curvature)
Diameter ρ = 3 cm; inner diameter d = 1.0 mm)
When a long-path cell made by fixing Teflon is used
It shows the experimental results of. As already mentioned,
And Teflon etching
After pre-processing the tube, follow the method described above with reference to FIG.
In a Teflon tube fixed in a glass tube,
The solution was injected with heating. I left it until the end of the fall
Then, a suction device was used to accelerate the drying. Do this operation 5
Tef with a bending rate of 1.31 Teflon stuck repeatedly
A long-path cell consisting of a long tube was prepared. Preliminary experiment
From the results of (3), pure water (n = 1.3333) was used for light
Laser light) through the coiled tube.
Since it was confirmed that it had passed, the first absorption of the electronic spectrum
The band (500-700 nm; λmax = 654 nm) is H
Met overlapping with e-Ne laser wavelength (632.8 nm)
The experiment was conducted using an aqueous solution of renblue. Measured in Figure 8
The resulting calibration curve is shown. Methylene blue concentration on the horizontal axis
And the vertical axis is the absorbance. As shown in the figure,
Blue concentration up to around 0.8 μmol / L.
Then, the absorbance increases linearly. This is 1 cm
Sensitivity is about 70 times higher than the standard
(A simple calculation assuming that the cell is linear is 6
It becomes 0 times).

[0028]

As is apparent from the above description, according to the present invention, by using the principle of an optical fiber to extend the optical path length, a glass cell or a quartz cell which has been generally used conventionally can be obtained. An optical path cell for a spectrophotometer having a significantly increased measurement sensitivity can be obtained. The optical path cell for a spectrophotometer according to the present invention is a spiral tube (coil-shaped) or the like using a flexible tube having sufficient flexibility represented by a Teflon tube and having excellent physical strength and chemical resistance. It can be formed in any shape and size, for example, a shape and size that can be used as a compact long-path cell that can be retrofitted into an existing spectrophotometer as it is. The optical path cell for a spectrophotometer of the present invention is configured such that a tube inner wall having a refractive index lower than that of a liquid phase to be measured is a clad, a liquid phase is filled in the tube as a core, and light is transmitted to the core. Therefore, spectroscopic analysis of the liquid phase is possible. In particular, a low refractive index material having a refractive index lower than that of water (for example, a refractive index of 1.3
By fixing 1 or 1.29 Teflon), almost all liquid phase samples including aqueous systems can be measured, and liquid phase (solution) restrictions are extremely small, and a wide range of samples are targeted for measurement. A high-sensitivity long-path cell for a spectrophotometer. The spectrophotometer optical path cell of the present invention can be easily manufactured at low cost by using commercially available or existing materials, devices, instruments, and the like.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining Snell's law.

FIG. 2 is a schematic diagram for explaining the traveling of light in a long optical path cell wound in a coil shape according to the present invention.

FIG. 3 is a view showing a typical example of a method for fixing a low refractive index substance to the inner wall of a flexible tube according to the present invention.

FIG. 4 shows a typical example of an optical path cell device using the long optical path cell of the present invention.

FIG. 5 is a diagram of an experimental apparatus used in the examples.

FIG. 6 shows the relationship between the length of a Teflon tube constituting the long optical path cell of the present invention and the transmitted light intensity.

FIG. 7 shows the relationship between the concentration of indophenol and the absorbance measured using the long-path cell of the present invention and an ordinary cell.

FIG. 8 shows the relationship between the concentration of methylene blue and the absorbance measured using the long-path cell of the present invention to which low refractive index Teflon is fixed.

Claims (21)

[Claims] 1. An optical path cell for a spectrophotometer for transmitting light into a liquid phase to measure the concentration of a sample contained in the liquid phase, the optical path cell having a refractive index lower than that of the liquid phase. It is composed of a flexible tube, and the flexible tube serves as a clad, and the flexible tube is filled with a liquid phase containing the sample to serve as a core so that light can be transmitted through the core. The optical path cell for the spectrophotometer. 2. The optical path cell for a spectrophotometer according to claim 1, wherein the flexible tube is a Teflon tube. 3. The optical path cell for a spectrophotometer according to claim 1, wherein the flexible tube is wound in a coil shape. 4. The optical path cell for a spectrophotometer according to claim 3, wherein the flexible tube is wound in a coil shape having a radius of curvature of 10 cm or less. 5. The total length of the flexible tube is 50 cm to 50.
The optical path cell for a spectrophotometer according to claim 1, which is 0 cm. 6. The optical path cell for a spectrophotometer according to claim 1, wherein the flexible tube has a total length of 5 m to 20 m. 7. A spectrophotometer optical path cell for transmitting light into a liquid phase to measure the concentration of a sample contained in the liquid phase, the film having a refractive index lower than that of the liquid phase. Consists of a flexible tube fixed to the inner wall, the inner wall of the flexible tube serves as a clad, and the flexible tube is filled with a liquid phase containing the sample to serve as a core, and a light is introduced into the core. An optical path cell for a spectrophotometer, which is characterized in that it transmits light. 8. The flexible tube is a Teflon tube,
The optical path cell for a spectrophotometer according to claim 7, which is a polyvinyl chloride tube or a polyethylene tube. 9. The optical path cell for a spectrophotometer according to claim 8, wherein the flexible tube is a Teflon tube. 10. The inner wall of the flexible tube has a refractive index of 1.
31 or 1.29 Teflon thin film is fixed,
An optical path cell for a spectrophotometer according to any one of claims 7 to 9. 11. The spectrophotometer optical path cell according to claim 10, wherein the sample-containing liquid phase is an aqueous solution. 12. The optical path cell for a spectrophotometer according to claim 7, wherein the flexible tube is wound in a coil shape. 13. The optical path cell for a spectrophotometer according to claim 12, wherein the flexible tube is wound in a coil shape having a radius of curvature of 10 cm or less. 14. The total length of the flexible tube is from 50 cm to 5 cm.
The optical path cell for a spectrophotometer according to claim 7, which is 00 cm. 15. The flexible tube has a total length of 5 m to 20 m.
The optical path cell for a spectrophotometer according to any one of claims 7 to 13. 16. A method for producing an optical path cell for a spectrophotometer according to claim 7, wherein a solution of a substance having a refractive index lower than that of a liquid phase containing a sample to be measured is injected into a flexible tube. By repeating the heat drying and depressurizing operation,
A method comprising: affixing a film of the low refractive index material to an inner wall of the flexible tube. 17. The spectrophotometer according to claim 16, further comprising a step of cleaning the inner wall of the flexible tube and then etching the inner wall before the step of fixing the film of the low refractive index material. Optical path cell fabrication method. 18. The method for producing an optical path cell for a spectrophotometer according to claim 17, wherein the flexible tube is a Teflon tube. 19. The method for producing an optical path cell for a spectrophotometer according to claim 16, wherein the low refractive index substance is Teflon having a refractive index of 1.31 or 1.29. 20. A spectrophotometer using the optical path cell according to claim 1. Description: 21. A spectrophotometer using the optical path cell according to claim 7.