JPH04244948A - Method for measuring moisture content over wide range in flow injection analysis - Google Patents

Abstract

PURPOSE:To measure concn. over a wide range without changing the length of a cell by spectrally diffracting incident light after the transmission through the cell and extracting the wavelength showing absorbancy optimum to measurement. CONSTITUTION:A predetermined amount of a solution to be tested is added to the reagent flowing through a cell 2 and light of a multi-wavelength is projected on the cell 2 from a light source 1 and the transmitted light thereof is spectrally diffracted into many wavelengths by a spectroscope 3. The respective lights are respectively inputted to many photodetectors arranged to a multi- wavelength simultaneous photometric detector 40. The outputs from the respective photodetectors are inputted to an amplifying signal processing circuit 4 and a required wavelength showing measurable absorbancy is extracted and concn. is calculated on the basis of said absorbancy and outputted to be displayed on an indication part 5. By this constitution, concn. can be measured over a wide range without changing the size of the cell.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method for measuring moisture concentration using a Karl Fischer reagent in flow injection analysis, and more particularly to a method for measuring moisture over a wide range of concentrations in which the measurement range can be automatically set.

0002

2. Description of the Related Art FIG. 4 shows a conceptual diagram of concentration measurement using an absorbance method. A test liquid colored according to the concentration of the target substance (usually by adding a reagent to cause a coloring reaction) is filled into a cell 2 of a predetermined length L, and a spectrometer is applied to the cell 2 from a light source 1. When light of a predetermined wavelength λ is incident on the light receiving element 4 through the light receiving element 3, an output corresponding to the transmittance is obtained.

[0003] In the above concentration measurement method using the absorbance method,
The absorbance M at the wavelength λ is M=logIr/I=εCL... (1) Ir
: Standard transmittance at wavelength λ (transmittance of pure water) I
: Transmittance ε at wavelength λ : Molar extinction coefficient C at wavelength λ : Concentration L : Given by cell length.

On the other hand, FIG. 5 is a principle diagram showing an outline of the flow injection analysis method to which the present invention is applied. A reagent is caused to flow from one end of a thin tube (for example, 1 mmφ) 10 at a constant rate, for example, 1 ml/min, and the reagent flows into an absorptiometer 30 via a mixer 20 and is then discharged. A predetermined amount of the test liquid is injected into this reagent using a metering cock 11 provided at the front stage of the mixer 20, and is mixed with the above reagent in the mixer 20 to cause a predetermined coloring reaction or fading reaction. 30. As a result, the absorbance meter 30 shows an output absorbance corresponding to the concentration of the target substance. Here, if the relationship between concentration and absorbance is measured in advance using a standard solution, the concentration can be determined from the absorbance shown by the test solution. Here, for example, if Karl Fischer reagent is used as a reagent, the water concentration in the test liquid can be measured.

The concentration measurement method based on the flow injection analysis method is advantageous in that, unlike the potentiometric titration method or the amperometric titration method, which is a batch method, it has the advantage of being able to perform continuous measurements by repeating injections. Furthermore, in concentration measurement using the absorbance method, the absorbances M0 and M corresponding to light of two adjacent wavelengths λ0 and λ1 are
1 are respectively M0 = logI00/I0 = ε0 CL... (2
) M1 = logI10/I1 = ε1 CL...
(3) ε0, ε1: Wavelength λ0, λ1, respectively
molar extinction coefficient C: concentration L of the substance to be measured
:Measurement cell length I00, I10: Can be expressed by the reference transmittance at wavelengths λ0 and λ1, respectively. From equations (2) and (3),
S=M0 −M1 =(ε0 −ε1)CL…
(4) is obtained, and from this, the absorbance difference S between both wavelengths λ0 and λ1 is obtained, and the concentration C can be determined. This method is based on the change in absorbance due to reagent deterioration (curve α0
Even if the absorbance difference S changes to α1 or α2), the absorbance difference S itself remains the same (that is, if
= M0 - M1 , S of curve α1 = M01-M11 or S of curve α2 = M02-M12), so
This method is advantageous in that an accurate concentration C can be obtained without performing a blank test.

Furthermore, considering the influence of suspended particles,
Absorbance M0, M1 at the above wavelengths λ0, λ1
are respectively M0 = ε0 CL + ΔA0 [ΔA0: wavelength λ
0 scattering component] M1 = ε1 CL + ΔA1 [ΔA1: Wavelength λ
The scattering amount at 1 is as follows. Here, if ΔA0 ≒ ΔA1, then the above (4
) When calculating the equation, it can be seen that the influence of suspended particles is almost eliminated.

[0007]

FIG. 7 shows the relationship between wavelength (nm) and absorbance when the cell length is the same, using concentration as a parameter. The range of wavelengths that exhibit measurable absorbance differs significantly depending on the concentration. Conversely, the concentration range that can be measured with a single wavelength is extremely limited. Therefore, when trying to widen the measurable concentration range by fixing the wavelength, the only way to do so is to change the cell length L according to equation (1) above when the Karl Fischer reagent concentration is the same. In extremely small ranges, absorbance cannot be measured unless the cell length is significantly increased. However, in the case of the flow injection method, changing the cell length means changing the tube diameter. However, changing the tube diameter means changing the mixing state due to the dispersion of the test liquid and reagent, which has the disadvantage that it is difficult to ensure the same measurement conditions, and the structure that allows changing the tube diameter is also complicated. , measurement work is also troublesome.

The present invention has been proposed in view of the above-mentioned conventional circumstances, and it is an object of the present invention to provide a method capable of obtaining a wide concentration measurement range without changing the cell length.

[0009]

[Means for Solving the Problems] The present invention employs the following means to achieve the above object. In other words, in the flow injection analysis method, in which a predetermined amount of test liquid is added to a reagent flowing in a thin tube of a predetermined diameter, and the concentration is detected by an absorbance meter, the multi-wavelength components of light transmitted through the absorbance meter cell are In this method, light having a wavelength that exhibits a measurable absorbance is extracted, and the concentration is measured based on the absorbance that the light exhibits.

It is also possible to use a differential absorbance method in which two adjacent wavelengths are used as wavelengths exhibiting measurable absorbance and the concentration is measured based on the difference in absorbance between the two wavelengths.

[0011]

[Operation] When an absorbance cell is irradiated with multiple wavelengths in a wide wavelength range, a measurable absorbance is exhibited in a specific region within the cell. Therefore, the measurement range can be freely determined by splitting the incident light into multiple wavelengths after passing through the cell and extracting the wavelength exhibiting the most suitable absorbance for measurement from the absorbance corresponding to each wavelength. When this method is applied to a differential absorbance method, two wavelengths exhibiting a differential absorbance suitable for measurement are extracted instead of the absorbance described above.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a conceptual diagram showing an outline of the optical system of the present invention. Multi-wavelength light (for example, white light) is incident on a cell 2 from a light source 1, and the transmitted light from the cell 2 is split into multiple wavelengths by a spectrometer 3. Each light is multi-wavelength simultaneous photometry using a large number of light-receiving elements arranged. The light is input to each light receiving element of the detector 40. The output from each light-receiving element is input to an amplification/signal processing circuit 4, which will be described below, and then displayed on an instruction section 5.

FIG. 2 is a block diagram showing the electrical system of the present invention. The following description will be made according to the differential absorbance method shown in the above equations (2), (3), and (4). The output from each element of the multi-wavelength simultaneous photometry detector 40 is input to a preamplifier 41 constituting the amplified signal processing circuit 4 and amplified there. The number of preamplifiers 41 corresponding to each wavelength may be provided, or the preamplifiers 41 may be configured to time-divisionally amplify the light receiving element output corresponding to each wavelength. The output of this preamplifier 41 is input to the transmittance converting means 42, and the transmittance I of each wavelength is obtained according to the output of the preamplifier 41, and the output of the preamplifier 41 is also input to the reference transmittance generating means 43, Here, the reference transmittance I0 (transmittance of pure water) corresponding to each wavelength is obtained. From the above transmittance I and the reference transmittance I0, the absorbance calculation means 44 calculates the absorbance of each wavelength according to the above equation (1). Then, in the next stage measurement wavelength determination means 45, the absorbance at each wavelength is compared, and two adjacent wavelengths showing absorbance suitable for measurement are compared.
Two wavelengths λ0, λ1 are selected, and the wavelengths λ0, λ1 are selected.
The absorbances M0 and M1 corresponding to 1 are output. At this time, each absorbance M0, M1 is read out from the calibration memory 46 as the absorbance in the standard solution (calibration solution with known water concentration) at the two wavelengths λ0, λ1, and the absorbance M0 at each of the wavelengths λ0, λ1 is read out from the calibration memory 46. , M1
Calibration is applied to. after that,
A difference absorbance calculation means 47 calculates the difference between the two absorbances, and a concentration calculation means 48 calculates the concentration C from the difference absorbance S, which is displayed on the display section.

The concentration calculating means 48 stores the relationship between the absorbance difference S at two wavelengths λ0 and λ1 obtained from, for example, a standard solution (calibration solution with known water concentration), as shown in FIG. 3, for example. memory can be used. Table 1 shows examples of the present invention for three samples (■■■) in which the water concentration in 15 μl of methanol was measured. The concentration of each sample is the average value of the results of 5 measurements. The standard deviation in Table 1 is the standard deviation of each measurement value five times, and the coefficient of variation is the standard deviation/
The value is the concentration average value x 100%. According to Table 1, it can be seen that both the standard deviation and the coefficient of variation are small, indicating almost satisfactory values regardless of the concentration.

[0015]

[Table 1]

Although only the differential absorbance method has been described above, the present invention can of course be applied to cases other than the differential absorbance method, that is, to the conventional absorbance method using one wavelength. In this case, the measurement wavelength determination means 45 determines only one wavelength that shows appropriate absorbance, and the difference absorbance calculation means 47 becomes unnecessary. Further, as the concentration calculating means 48, a memory storing the relationship between the absorbance M and the concentration C is used.

[0017]

Effects of the Invention As explained above, the present invention allows light of multiple wavelengths to be transmitted through a cell when measuring concentration using the absorbance method, and uses the absorbance of a wavelength that exhibits absorbance suitable for measurement to measure concentration. Therefore, the concentration can be measured over a very wide range, and there is an advantage that it does not include structurally complicated elements such as changing the cell length and elements that are likely to cause measurement errors.

[Brief explanation of the drawing]

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

FIG. 2 is a conceptual diagram of the electrical system of the present invention.

FIG. 3 is a graph showing the relationship between concentration and absorbance.

FIG. 4 is a conceptual diagram of the absorbance method.

FIG. 5 is a conceptual diagram of a flow injection analysis method.

FIG. 6 is a graph showing the relationship between absorbance and wavelength due to reagent deterioration.

FIG. 7 is a graph showing the relationship between absorbance and wavelength.

[Explanation of symbols]

2 Cell 30 Absorbance meter

Claims (2)

[Claims] Claim 1: A flow injection analysis method in which a predetermined amount of reagent or test solution is added to the test solution or test solution flowing in a thin tube of a predetermined diameter, and the concentration is detected by an absorbance meter, and a Karl Fischer reagent is used. In the moisture measurement using flow injection, light with a measurable absorbance is extracted from the multi-wavelength component light that has passed through the cell of the absorbance meter, and the concentration is measured based on the absorbance shown by the light. Method for measuring moisture over a wide range of concentrations in analytical methods. 2. The wide range concentration in the flow injection analysis method according to claim 1, wherein two adjacent wavelengths are used as wavelengths exhibiting measurable absorbance, and the concentration is measured based on the absorbance difference between the two wavelengths. Moisture measurement method.