JPS6027376B2 - Measuring method of refractive index of pharmaceuticals, etc. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for easily and highly accurately measuring the refractive index of crystalline pharmaceuticals, etc. using an immersion method.

The method of measuring the refractive index of crystalline substances using a polarizing microscope using the immersion method has long been used in fields such as petrology and mineralogy, but this method has also been applied to the field of organic compounds such as pharmaceuticals. The poem I am trying to write is the one published by the present inventor in Pharmaceutical Journal, Volume 59, Page 131 (1939).

In the immersion liquid method, an immersion liquid series with a refractive index of approximately 1.45 to 1.75 is prepared, and the crystal is treated with the immersion liquid to observe differences in refractive index. However, when trying to measure the refractive index of organic pharmaceuticals using this method, crystals may dissolve in the immersion liquid depending on the type of immersion liquid. In order to increase the accuracy of measurement to an accuracy of about 0.001, for example, it would be necessary to create more than 100 different types of immersion liquid and observe the extremely weak movement of Becke lines, and the number of experiments would also increase. As a result, the measurement operation was considered to involve an extremely large number of overflows.

In this way, despite the drawbacks of the immersion method, measurements using this method are limited to only a small amount (for example, 0.2 to 2
It is possible to confirm the identity of the molecular species using the sample in step 9), and to identify several types of polymorphisms and pseudopolymorphisms (pseudopoMmor) in the same molecular species.
phism), the identification of each form can be carried out without using complex mechanical equipment, such as X-ray diffraction, infrared absorption spectrum measurement, etc.
It has the advantage that even when two or more substances are mixed, they can be differentiated without separating them from each other. This method is considered to be widely used in pharmacies, dispensing pharmacies, etc.

Based on this idea, the present inventor developed a method for precise refractive index measurement to accurately and quickly evaluate and determine the crystal type of pharmaceuticals, etc., in situations where equipment such as X-ray diffraction or infrared absorption measurement cannot be used. As a result of examining various methods, the method of the present invention was completed.

That is, the present invention provides a method for measuring the refractive index of a crystalline drug by an immersion method using a polarizing microscope, in which a series of immersion liquids are used so that the refractive index difference is at intervals of 0.004 to 0.00 competitive degrees. Create a chart, evaluate the Becke line intensity for each immersion liquid of the test drug, plot it on a chart with the refractive index of each immersion liquid as the vertical axis and the Becke line intensity as the axis, and connect each plot. This is a method for measuring the refractive index of pharmaceuticals, etc., which is characterized in that the refractive index at the intersection of a straight line and the center line with Becke line intensity of 0 is taken from the vertical axis. In the method of the present invention, the refractive index difference is 0.
A series of immersion liquids with intervals of about 0.004 to 0.006 are used, and any immersion liquid that is normally used for measuring refractive index by the immersion method can be used as appropriate.

For example, normal decane (2 for the sodium D line)
Refractive index at 0qo (n volume) 1.420), olive oil (n color ol. 470), cedar wood oil (n volume 1
．． 522), Q-promonaphthalene (n answer 1.6 spots),
A series having a refractive index difference of 0.004 to 0.00 specularity is prepared by suitably mixing methylene iodide (n color 01.703), sulfur, etc., and their adjacent immersion liquids. If you try to obtain a precision of 0.001 using the conventional method of measuring the refractive index using the immersion method, the refractive index will be 1.450.
200-30 for measuring samples between 1.750 and 1.750
It was necessary to prepare an immersion liquid of type 0 with a refractive index between 0.001 and 0.002, but with the method of the present invention, it is sufficient to prepare an immersion liquid with a refractive index of 4 to 1/5 of that. . In measuring the refractive index, a method commonly used when measuring by an immersion method using a polarizing microscope is conveniently applied.

That is, the light source used in the measurement may be white light or monochromatic light. As the monochromatic light, for example, sodium D line is often used, but it goes without saying that other monochromatic light may be used. However, when measuring with white light, the accuracy may be slightly lower than when using monochromatic light, so it is desirable to measure using monochromatic light in a room as dark as possible, such as a dark room or semi-dark room. In the measurement, a small amount of the sample whose refractive index is to be measured is placed on a slide glass, 1 to 2 drops of immersion liquid is added thereto, the sample is held down with a cover glass, and the sample is first observed under crossed Nicols of a polarizing microscope. Next, the upper Nicol is removed at the extinction point of the sample to be measured, and the linearly polarized light is passed through the lower Nicol with an aperture to observe the bright lines (Becke lines) appearing at the periphery of the crystal. Furthermore, move the lens barrel or stage up and down slightly to remove the focus, and at this time observe the direction in which the Becke lines move in or out of the crystal periphery. When the distance between the microscope objective lens and the sample increases, the Becke lines move to a medium with a higher refractive index. That is, when the refractive index of the immersion liquid is higher than that of the sample, the Becke line moves toward the immersion liquid, and in the opposite case, it moves toward the sample. In measuring the refractive index using the follow-up method, the refractive index of the sample was determined by following this movement to determine the refractive index of the sample relative to the refractive index of various types of immersion liquid, and the refractive index of the sample was determined from the refractive index of the closest immersion liquid. Therefore, in order to improve measurement accuracy, it was necessary to prepare a large number of immersion liquids with slightly different refractive indexes. On the other hand, many organic compounds can hardly be identified when the difference in refractive index with the immersion liquid is about ±0.002.

However, the inventor's research has revealed that the intensity or brightness of the Becke line is approximately proportional to the difference in refractive index between the sample and the immersion liquid in a certain weak range.

Therefore, by knowing the intensity of the Becke line observed as described above, even if an immersion liquid with a relatively large difference in refractive index, such as 0.004 or 0.006, is used, the intensity of the Becke line and each ±0, which can be considered practically accurate based on the refractive index of the immersion liquid.
．． It became possible to know the refractive index of a sample with an error of about 0.001. In other words, the refractive index difference with the sample is ±0.
Although it is difficult to identify the Becke line, which has a relatively weak intensity in the range of about 0.003 to 0.010, the refractive index difference between the sample and the sample can be determined by utilizing the fact that its intensity (or brightness) is proportional to the refractive index difference. Using an immersion liquid with a refractive index difference (greater or smaller than 0.002) on both sides of the immersion liquid of 0.002, the difference in refractive index between the sample and the immersion liquid is, for example, 0.008 to 100. The refractive index of the sample can be determined by enlarging it to .003. The Becke line intensity is 110 when the refractive index of the crystal is larger than the refractive index of the immersion liquid.
It is best to score from 0 to 0, and vice versa from 0 to -10. Of course, this score does not have to be between 110 and 110, and may be 5 on each positive or negative side or 100, but in practice, the refractive index difference between the immersion liquid and the sample is 0.010. It is sufficient to set the Bezke line strength to about 10 for each of the positive and negative directions, and even if the score is finer than that, the accuracy will not improve even though it is time-consuming. Furthermore, if the score is too rough, the accuracy will naturally decrease. It is best to evaluate the intensity of the Betzke line between immersion liquids of 3 to 8 types that are close to the refractive index of the crystal, and in most cases, 5 or 6 types of immersion liquids are used in the present invention. desirable for the purpose of the method. For example, if the refractive index of the immersion liquid and one of the crystals are approximately equal, as the stage is slowly rotated from a position where the Becke line is not visible, the intensity of the Becke line will gradually increase, so the relationship between the rotation angle and the intensity is For example, the Becke line intensity of the refractive index difference between the immersion liquid and the sample of ±0.010 or 0.005 can be memorized and used as a reference for scoring.
Roughly dividing the shapes of crystalline pharmaceuticals observed under a microscope, there are approximately six types, as shown in FIG. 1, for example.

Among these, if (b) it is thin plate-like or scaly-like, or (e) it is long and thin, the plane of the crystal will be perpendicular to the direction of the lens barrel axis. Since the two types of refractive indexes are measured with an accuracy of ±0.001 at two extinction positions, it is possible to determine the molecular species, polymorphic or condensed polymorphic crystal form in this type of crystal. can be identified. Two types of refractive indexes are used for identification of these crystal forms, so these are called key refractive indexes (key refractive indexes).
We will call it ``dice''. Crystals having shapes c and d in FIG. 1 may rotate about the long axis direction shown by the dotted line during immersion treatment. When a crystal in the form c or d is directly quenched, the refractive index in the long axis direction does not change even when the crystal rotates, so the refractive index can still be measured with an accuracy within ±0.001, and this is the key refraction. It can be used as a percentage to confirm the identity of crystalline pharmaceuticals, etc. In the case of plate crystals such as a or pyramidal crystals such as f, the crystals are usually crushed using an agate mortar or other convenient means and examined under a microscope. In crystals with b,
It becomes a crystal belonging to c, d, or e, etc., and the key refractive index can be measured, but it is generally difficult to measure the key refractive index when it does not have an interlocking property and shows irregular fractures.
Furthermore, even if the crystal form is intended to be c or d, it may be difficult to measure the key refractive index if oblique extinction occurs. In this way, if the key refractive index of the specimen is measured, it will be extremely easy to fix, confirm, and differentiate the specimen by comparing it with the refractive index of the specimen decoupled by the method of the present invention. Can be done.

In addition, even if the sample is contained in a mixture of pharmaceutical preparations, etc., the contained pharmaceuticals can be identified by microscopic examination with a polarizing microscope and the immersion method of the present invention without separating them, and if the sample is polymorphic, etc. It is also possible to confirm the fo blood.
In such cases, for example, the National
Using a table of principal refractive indices of pharmaceuticals listed in formularies, etc., if the key refractive index corresponds to a part of the principal refractive index, compare this with the refractive index of the sample measured by the method of the present invention. By comparison, the sample can be authenticated. The method of the present invention will be explained in more detail below using the measurement of the refractive index of thiamine hydrochloride as an example. The immersion liquids used in this example were: olive oil (n. = 1.470), cedar wood oil (n. = 1.522), Q-fromonaphthalene (n. =
1.658) and methyl iodide (no=1.703
) and a mixture thereof, with a refractive index difference of 0.003 and 0.006, were prepared and used. In addition, a chart for measuring the refractive index was prepared, as shown in FIG. 2, in which the refractive index was taken as the vertical axis, the intensity of the Becke line was taken as the horizontal axis, and the refractive index of the immersion liquid was shown as a line parallel to the horizontal axis. In this chart, for example, a difference in refractive index of 0.010 is 10 on the vertical axis, a difference in Becke line strength of 5 is on the horizontal axis, and the difference in Becke line strength can be scored in the range of 110 to 110. There are two scale marks on each side of the center line where the intensity is 0. This is explained in detail in Part 4
As shown in the figure.

In FIG. 4, AB corresponds to 10 squares on the vertical axis and represents a refractive index difference of 0.010, BC corresponds to 1 square on the horizontal axis, and CD
corresponds to the axis extended by one additional length. Axis B
Since CD has 20 ribs, it corresponds to a difference in intensity of Betzke lines of 10, and point D is on the center line. Each refractive index no. at point A and point B shown in the figure. 550 and nol
．． 540 shows an example. If a line is drawn parallel to the horizontal axis through point A and its intersection with the center line is E, then the angle x of the diagonal line in a right triangle ABE or DEB is nxniAB/AEniDE/BDni1/2× =26.5o.

(Similarly, if we use the refractive index difference 0.010 on the vertical axis 5 and the difference 5 in Becke line intensity on the horizontal axis 1 scale, the angle of the diagonal line is similar to ta = 1/4, x = (14.036o.) Therefore, if we draw a diagonal line at an angle of 26.5o with respect to the horizontal axis, the refractive index indicated by the intersection of this line and the center line will be the Becke line intensity of each immersion liquid that intersects with the diagonal line, and therefore It corresponds to the difference in refractive index. In other words, all the points on the diagonal line show the same refractive index when converted to Becke line intensity (hereinafter, this line will be referred to as the equirefractive index line). In this case, the angle that the diagonal line makes with the machine axis is 26.5
0, but if the refractive index on the vertical axis is, for example, 0.005 equal to IQ, it becomes 450, which can of course be changed as desired. Now, in this case, for convenience, the chart shows 2
If parallel lines of 6.50 are drawn at a spacing between two sides, measurement of the refractive index becomes more convenient as will be described later. for example,
Figure 5 shows a part of the chart based on the diagonal line method (angle of diagonal line 2650), but it is difficult to identify the Bekke lines in the parallel diagonal line areas on both sides of the center line (within a refractive index difference of ±0.002). .

Now, the refractive index (true value al) of a certain sample shows Bezke line intensity x (approximately 1.7) in immersion liquid a. However, x is extremely weak and difficult to identify. Therefore, when we measured the strength and direction of movement of the Becke line using immersion liquids b and c on both sides, we found that the Becke line was clear as shown in the figure at point B (approximately 17) and point C (
Approximately 13) was obtained. Therefore, the refractive index of the sample is the intersection point al between the horizontal line that crosses the intersection m between the diagonal line BC and the center line and the vertical axis.
It is required as. For convenience, the above explanation assumes the case of 20 and 0. When thamine hydrochloride (commercial product, monohydrate) was observed under a polarizing microscope using a cedarwood oil immersion solution, the light was obliquely quenched with thin plate-like crystals belonging to b to e in Figure 1, and two key refractions were observed. It seemed possible to measure the rate. Based on the observation of the Becke line, the immersion liquid was sequentially changed to one with a refractive index close to that of thiamine hydrochloride, and the Becke line strength was approximately +6 with the immersion liquid having no. of 1.685. 1.685 16 on the horizontal line
Mark , and look at the intersection with the horizontal line of 1.695 immersion liquid on the equirefractive index line passing through this point, it is -4.

When microscopically examined using 1.695 immersion liquid, the intensity of the Becke line was 1. It was stronger than the 16 I got at Iso 5, and I didn't get the 14.

Therefore, if we correct the Becke line intensity of 1.685 to 14 and find the intersection with the Fuji line of 1.695 on the equirefractive index line again, -6
It was found that the results were in agreement with the actual measurement results. Just to be sure, I measured it with an immersion liquid of 1.6791.690, and all values were on the above-mentioned equirefractive index line, so from the intersection of this line and the center line, one key of thiamine hydrochloride can be determined. The refractive index is 1. Demon 9 and neck. It was done. Next, another key refractive index of the same thiamine hydrochloride is no=1.59&1.
Using immersion liquids such as 613, 1.604, 1.607 in sequence,
Evaluate the intensity of the Betzke line, select the immersion liquid on the opposite side of ± on the equirefractive index line that creates the point marked by the rating, and make corrections if necessary as a result of the actual measurement.In the end, the value of nD = 1.605 is obtained. Obtained. Note that the room temperature at the time of measurement was adjusted to the standard temperature of 20°C, so there was no need for temperature correction of the refractive index of the immersion liquid, and in places where the Becke line intensity was weak within ±5, the sodium D line was used to It was carried out in a room. Commercially available thiamine hydrochloride (
In addition to thiamine hydrochloride anhydride (b), which is obtained by recrystallization, the key refractive index of this crystal was similarly measured to be 1.617 and 1.6.

FIG. 2 shows the results of measurement using the iso-refractive index line on the chart of anhydride (0). Thiamin hydrochloride exists in the world market as monohydrate (1) and anhydride (0), both of which are coagulated polymorphs, and have different molecular weights, which naturally poses a problem in terms of trade. It has been found that the immersion method of the present invention allows for relatively easy identification. When the key refractive index of fromvalerylurea and ampicillin was measured using the same method as in this example, the results shown in FIG. 3 were obtained.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of crystal forms of pharmaceutical products whose refractive index is measured by the method of the present invention, FIGS. 2 and 3 show experimental results in Examples, and FIG. 4 is an embodiment of the chart of the present invention. of,
FIG. 5 is for explaining the measuring method of the present invention. Multi leg * Juzuko 2 Kyouta; Shigeru * Go■

Claims (1)

[Claims] 1. In a method of measuring the refractive index of crystalline drugs by the immersion method using a polarizing microscope, a series of immersion liquids are created so that the refractive index difference is approximately 0.004 to 0.006, and the test drug is Score the Betzke line intensity for each immersion liquid, plot it on a chart with the vertical axis as the refractive index of each immersion liquid and the horizontal axis as the Betzke line intensity, and compare the straight line connecting each plot with the center line of the Betzke line intensity of 0. A method for measuring the refractive index of pharmaceuticals, etc., characterized in that the refractive index of the intersection point of is taken from the vertical axis.