JPH0711487B2 - Real-time determination method of colloid titration end point - Google Patents

Description

TECHNICAL FIELD The present invention relates to determination of a titration end point in a colloid titration method using a color change indicator which is one of quantitative analysis methods.

[Conventional technology]

FIG. 1 shows a conventional method for determining the end point of titration in the titration method. After determining the relationship between the measured amount (the amount of transmitted light in FIG. 1) and the amount of titrant added, a point corresponding to any of the following definitions is calculated or drawn to be the titration end point.

a) A point at which the measured value starts to change rapidly-an inflection point method b) A point at which the difference in the measured amount before and after the point at which the measured value suddenly changes is divided into two equal parts-bisect method c) Amount of titrant added The difference between the measured value and the measured value is differentiated, and the differential value becomes maximum-differential method [Problems to be solved by the invention] The conventional titration end point determination method has the following drawbacks.

1) Since the titration end point is determined by calculation or drawing after the titration operation is completed, the end point cannot be determined in real time.

2) Due to the reason 1), the analytical operation is a batch method,
It is difficult to make it continuous.

3) Since the inflection point and the like of the measured value cannot be easily automatically determined, the software for determining the end point becomes complicated, and the analysis equipment becomes expensive.

4) There are factors that interfere with the color change reaction, and the accuracy of the titration end point decreases. For example, the dissolved salts obscure the discoloration of the indicator.

On the other hand, as one method for solving the above-mentioned problems, the present applicant first measured the amount of transmitted light at the time of addition of the indicator before the start of titration, and gave a transmitted light amount of a value obtained by multiplying the amount by a predetermined constant. A real-time determination method has been proposed in which the addition amount of is determined as the end point of titration (see JP-A-1-116447).

However, in this method, the end point of titration is set at the initial stage of the inflection area of the titration curve, and therefore, there is a small change in the amount of transmitted light with respect to the amount of the titrant added, and the accuracy is somewhat poor.

The present invention overcomes the above problems in colloid titration,
(EN) An extremely simple method for determining a titration end point in real time without being disturbed by dissolved salts and the like.

[Means for solving problems]

The idea for solving the above problems is to predefine and set the change status of the color change indicator at the end point of titration. That is, it is a real-time determination method in which the titration end point is detected when the sample changes with the addition of the titrant, and when the change state is defined and set in advance.

Examples of the color change indicator used in the present invention include chalcone and toluidine blue.

That is, the present invention is a colloid titration method in which the test water to which a color change indicator is added is titrated using a reagent, and the colloidal charge amount of the test water is calculated by determining the titration end point from the color change reaction of the color change indicator. In the colloidal titration method and the real-time determination method of the colloidal titration end point, when the irradiation is performed, the titration end point is the time when the transmitted light amounts at the two wavelengths in the wavelength region in which the change in the transmitted light quantity is caused by the color change reaction of the color change indicator are changed. When the test water is irradiated with light and any two of the transmitted light amounts of the two detection bands in the color change reaction of the color change indicator and the transmitted light amount of the isosbestic point existing between them are detected, and the transmitted light amounts of both become equal. Is a real-time method for determining the colloid titration end point.

Two detection zones having isosbestic points between them mean that one of wavelengths shorter than the wavelength of isosbestic points is within the wavelength range of substantially visible light that causes a change in the amount of transmitted light corresponding to the amount of titrant added. The other one means a region having a wavelength longer than the wavelength of the isosbestic point. That is, the detection zone specifically includes a wavelength region in which two types of absorption peaks are formed before and after titration.

In the present invention, it is preferable to select an arbitrary wavelength in each of the two wavelength regions, determine the transmitted light amount of the two types, or to determine the wavelengths of the isosbestic point and the wavelengths of the two types.
It is carried out by determining one of the wavelengths of one detection band, but the two wavelengths for the assay can be selected from only one detection band.

In the selection of the two wavelengths, it is desirable to have a wavelength width (difference) in a range that does not hinder the accuracy in practical use, and it is appropriately determined according to the purpose, but preferably 1 nm or more,
Particularly preferably, the difference is 10 nm or more.

In the present invention, when the amount of transmitted light becomes equal does not necessarily mean only when the difference between the amounts of transmitted light of two types is 0, and the time when the value becomes close to 0 is defined as the titration end point. However, there is no problem.

The apparatus used in the present invention includes a container for receiving test water, which is provided with a reagent supply pipe as a titrant and an indicator supply pipe,
It is composed of a light emitting unit that irradiates the test water with light and a light amount detector that receives the light of the predetermined two types of wavelengths that has passed through the test water and converts them into electric signals as transmitted light outputs.

Specific embodiments of the present invention will be described below with reference to FIGS. 2 to 4.

FIG. 2 is a transmitted light output curve of a predetermined test water using toluidine blue as a discoloration indicator and a predetermined concentration of polyvinyl potassium sulfate (PVSK) as a titrant.

The test water was assayed by a back titration method by adding a predetermined cation colloid standard solution to a sample having a negative colloidal charge and adjusting the colloidal charge of the entire sample to be positive.

After the addition of the indicator to the test water and before the addition of the titrant, the test water has a blue color and has an absorption peak with a central wavelength near 640 nm (in the figure, a line of 0 μl titrant). On the other hand, after the end of the titration, the test water turns pink, but it has an absorption peak with a central wavelength near 520 nm (in the figure, a line of the titrant 200 μl). Further, in the middle of both absorption peak wavelengths, there exists an isosbestic point (near 550 nm) where the amount of transmitted light is substantially constant even with different titration amounts. Therefore, one of the detection bands in the present invention is 400n
The range is from m to 550 nm, and the other is from 550 nm to 700 nm. Although there is an isosbestic point near 700 nm, it is obvious that this is not adopted in the present invention because the transmitted light amounts may not be equal. That is, the line giving the titration end point exists in the area of the figure eight formed by both lines.

Although there are as many lines as previously defined that may give the titration end point, in the present invention, two wavelengths corresponding to the figure-eight region including the wavelength giving the isosbestic point, particularly , The amount of transmitted light at two wavelengths selected from the wavelengths selected from each of the two detection bands and the wavelength giving an isosbestic point [preferably, the wavelength near the center of the main absorption peak before titration (640 nm Near), the wavelength near the center of the main absorption peak after the titration (near 520 nm) and the wavelength near the isosbestic point existing between them (near 550 nm). A line that passes through points where the light outputs are equal can be defined as a line that gives a titration end point, and the amount of titrant added when the line is formed may be the titration end point. The reason for this will be described with reference to FIG. Also, as the wavelengths of the two types, two types may be selected from the detection band of the one type (for example, the selection range is 520 nm to 550 nm, 550 nm to 640 nm).
Each range of nm range is mentioned).

The titration endpoint defined above need not coincide with the titration endpoint defined by the conventional method.

The reason for this is that in colloid titration, a blank test is carried out separately during measurement, the measured value is subtracted from the measured value of the main test, and the difference is quantified. Therefore, if the method of taking the titration end point on the titration curve in this test and the way of taking the titration end point on the titration curve in the blank test are the same, the value of the difference between the conventional method and the method of the present invention is the inflection of the titration curve. It will be the same regardless of where it is taken in the area (preferably at the rising straight line or near it). The value of the difference is, as shown in FIG. 3, the titration agent addition amount at the titration end point of the main test and the titration agent addition amount at the titration end point of the blank test when the above-mentioned conventional bisection method is used. Difference (Δb) and the difference when the titration end point defined in the present invention is applied to the main test and the blank test (for example, Δp, Δp ′) are equal (that is, Δb = Δp = Δp ′). The same result is obtained without taking the required bisection method.

In terms of wavelength selection, it is practically preferable that the combination with the largest rate of change before and after the titration end point is maintained in order to maintain accuracy, and in the present embodiment, the wavelength is in the vicinity of 640 nm and in the vicinity of 520 nm. That is, the greater the gradient of the transmitted light output difference (I ₆₃₀ -I ₅₂₀ ) at the two wavelengths with respect to the amount of titrant added, the higher the accuracy.
Also, the point where the difference becomes 0 gives the titration end point.
In this case, even if the difference is not 0 mV and a value of ± several mV is used as the end point of titration, no problem is caused practically. This state is shown in FIG. 4 together with I ₅₂₀ -I ₅₅₀ and I ₆₃₀ -I ₅₅₀ .

In this embodiment, an anion (PVSK) is selected as a titrant so that the color change reaction of toluidine blue changes from blue to purple. It is used when measuring cationic raw water. On the contrary, it is possible to use a cation (MGCh) as the titrant and use it so that the color change reaction of toluidine blue changes from purple to blue, but in that case, the direction of increase and decrease of the measured value becomes opposite as the titration proceeds. As for the accuracy of the analysis, it is said that using the discoloration reaction of toluidine blue in the blue → purple direction (disappearance of blue) is better than using it in the purple → blue direction.

Further, chalcone can be used for titration of anion colloid as an indicator utilizing the color change reaction. In this case, a positively charged polydiallyldimethylammonium chloride (registered trademark: CATFLOC, manufactured by Calgon Inc., USA) is used as a titrant, and an absorption peak near 510 nm or around 665 nm, near isobaric point near 560 nm is used as a detection wavelength. Good.

As described above, when the titration end point is determined by comparing the two wavelengths, variations in the turbidity of the sample, the light amount of the light source, the added amount of the indicator, etc.
It will be canceled and the measurement accuracy will be improved.

〔Example〕

Hereinafter, the present invention will be specifically described with reference to examples. The invention is not limited to these examples only.

Example 1 A cationic polymer was added to sewage sludge to cause coagulation, and the filtrate obtained by dehydration with a belt press was used as a sample, and toluidine blue was used as an indicator, and potassium polysulfate (PVSK) was used as a titrant to perform colloid titration. The amount of titrant added at the end of titration was determined. The absorption peak wavelengths of 635 nm and 520 nm were used as the measurement wavelengths of the present invention. In addition, a comparison was made with the conventional method using the same sample. The results are shown in Table-1.

From Table-1, it can be seen that the present invention has better accuracy and shorter measurement time than the conventional method.

Example 2 Colloidal titration using chalcone as an indicator and CATFLOC as a titrating agent using an anionic polymer [Ebagrose A110 (trade name: manufactured by Ebara Infelco), dissolution concentration 10 mg / l] as a sample, and a titration agent at the titration end point The amount added was determined. As the measurement wavelength of the present invention, the absorption peak wavelength of 51
A wavelength of 0 nm and an isosbestic point wavelength of 560 nm were used.

In addition, a comparison was made with the conventional method using the same sample. The results are shown in Table-2.
Shown in.

According to the present invention, the titration point can be output in a short time with higher accuracy than the conventional method.

〔The invention's effect〕

According to the present invention, the end point of colloid titration can be obtained with higher accuracy than the conventional method and in real time. Therefore, the measurement time required for analysis can be shortened. In addition, since software required for determining the titration end point is not particularly required, there is an effect that an analytical instrument can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a conventional titration method, FIGS. 2, 3, and 4 are diagrams for explaining the present invention, and FIG. 2 is a case where toluidine blue is used as an indicator. PVSK
It is a figure which shows the difference of the transmitted light output curve with respect to the wavelength by the addition amount difference, and FIG. 3 is a figure which shows the titration curve of the transmitted light amount with respect to the titrant addition amount for explaining the titration end point defined by this invention. FIG. 4 is a diagram in which the transmitted light output of two wavelengths used in the present invention is plotted against the amount of titrant added.

Claims (2)

[Claims] 1. A colloidal titration method in which a test water containing a color change indicator is titrated with a reagent, the end point of titration is determined from the color change reaction of the color change indicator, and the colloidal charge of the test water is calculated. A method for real-time determination of a colloidal titration end point, wherein the titration end point is when the transmitted light amounts at two wavelengths within the wavelength region that cause a change in the transmitted light amount due to the color change reaction of the color change indicator are equal. 2. A colloid titration method in which the test water to which a color change indicator is added is titrated with a reagent, the end point of the titration is determined from the color change reaction of the color change indicator, and the colloidal charge of the test water is calculated. However, the colloid whose titration end point is when either of the two transmitted light amounts in the two detection zones in the color change reaction of the color change indicator and the transmitted light amount at the isosbestic point existing between them is detected, and when both transmitted light amounts become equal Real-time determination method of titration end point.