Rapid detection method of minoxidil

Abstract

The present invention relates to a method for rapid detection of minoxidil, which can be used for a method for rapid detection of minoxidil in a preparation, comprising the following steps: (1) taking a liquid preparation sample to be tested, evaporating it, re-dissolving it with an extraction solvent, filtering it with filter paper, and obtaining an extract; (2) mixing the extract obtained in step (1) with a bismuth potassium iodide reagent to obtain a mixed solution; (3) observing the clarity of the mixed solution obtained in step (2) and making the following judgment: if the solution becomes turbid and accompanied by the formation of an orange-red precipitate, it is judged that the sample may contain minoxidil; if the solution does not see the formation of an orange-red precipitate, it can be judged that the sample does not contain minoxidil. The method of the present invention can quickly identify a pharmaceutical hair growth agent liquid preparation or a cosmetic hair growth liquid preparation that may be added with minoxidil.

Description

Technical Field

[0001] The present invention belongs to the field of pharmaceutical detection technology, and relates to a method for detecting chemical substances, and in particular to a method for detecting 6-(1-piperidinyl)-2,4-pyrimidinediamine, 3-oxide, namely minoxidil. In particular, the method of the present invention can quickly detect minoxidil in a minoxidil raw material or composition. The composition can be a pharmaceutical external preparation for treating hair loss or a cosmetic hair product, etc. Background Art

[0002] Minoxidil, namely 6-(1-piperidinyl)-2,4-pyrimidinediamine, 3-oxide, has a molecular formula of C 9 H 15 N 5 O, molecular weight is 209.25, its chemical structure is as follows:

[0003] .

[0004] Minoxidil is a white or off-white crystalline powder. Clinically, it is used as a potassium channel opener. It can directly relax vascular smooth muscle and has a strong dilation effect on arterioles, which reduces peripheral vascular resistance and blood pressure, but has no obvious effect on capacitance vessels, so it can promote venous return. At the same time, due to reflex regulation and positive frequency effects, it can increase cardiac output and heart rate, increase plasma renin activity and water and sodium retention, but does not cause orthostatic hypotension. The increased heart rate is also related to the direct positive inotropic effect of minoxidil on the heart. Its water and sodium retention effect is partly due to increased renin secretion and partly due to a direct effect on the renal tubules, which makes the renal tubules sensitive to Na + The mechanism of action may be that it is metabolized into minoxidil NO sulfate in the body, which increases the vascular smooth muscle cell membrane's ability to resist K. + permeability, promoting intracellular K + Outflow causes hyperpolarization of the vascular smooth muscle cell membrane, thereby relaxing the vascular smooth muscle and lowering blood pressure. Minoxidil is used clinically as a blood pressure-lowering drug for refractory, primary or renal hypertension. In addition, it can also be used to prevent oily hair loss and is used topically for male scarring alopecia (alopecia areata).

[0005] The mechanism by which minoxidil promotes hair growth is still unclear. Studies have shown that it may be carried out through the following pathways. 1. Stimulate the proliferation and differentiation of hair follicle epithelial cells. Normal human hair follicle epithelial cells were cultured in minoxidil solutions of different concentrations. Minoxidil can stimulate the proliferation of hair follicle epithelial cells at micromolar concentrations. Minoxidil sulfate is an active metabolite that stimulates hair growth, and the activity of sulfotransferase is higher in hair follicles than in the epidermis and dermis. In vitro histological culture of rat vibrissa follicles and experiments using 35S-labeled cysteine ​​to synthesize hair keratin have confirmed that minoxidil and its sulfate both have a hair growth effect. In vitro experiments have shown that the effect of minoxidil sulfate is 14 times that of minoxidil. If a sulfotransferase inhibitor or sulfate scavenger is added, the hair growth effect of minoxidil can be inhibited, but it has no effect on the effect of sulfate metabolites. Animal experiments have shown that minoxidil can increase the number of dermal papillae, hair matrix, outer root sheath and hair surrounding fiber cells, thereby prolonging the hair growth period. 2. Promote angiogenesis and increase local blood supply. Hair growth relies on the vascular network of the hair papilla to supply nutrition. In different growth cycles of hair, the mRNA expression of vascular endothelial growth factor is different. In the growth phase, vascular endothelial growth factor mRNA is strongly expressed in dermal papilla cells, but less expressed in the regression phase and resting phase. Experiments have shown that minoxidil increases the expression of vascular endothelial growth factor mRNA and its protein in a dose-dependent manner, thereby promoting dermal papilla blood vessel formation and increasing local blood supply. 3. Open potassium channels: Potassium channel opening is an important step in regulating hair growth. In vitro and in vivo experiments on animal models have shown that minoxidil is a potassium channel activator that can increase the permeability of potassium ions and prevent calcium ions from flowing into cells, resulting in a decrease in the concentration of free calcium ions in cells. When calcium ions are present, epidermal growth factor inhibits hair growth.

[0006] Therefore, those skilled in the art are eager to provide a method that can simply and quickly detect and determine whether minoxidil exists or may exist in a composition. Summary of the invention

[0007] The object of the present invention is to provide a method for simply and quickly detecting and judging whether minoxidil exists or may exist in a composition.

[0008] To this end, the present invention provides a method for quickly detecting minoxidil in a preparation, the method comprising the following steps:

[0009] (1) Take the liquid preparation to be tested, evaporate it to dryness, then re-dissolve it with the extraction solvent, filter it with filter paper, and obtain the extract;

[0010] (2) mixing the extract obtained in step (1) with a bismuth potassium iodide reagent to obtain a mixed solution;

[0011] (3) Observe the clarity of the mixed solution obtained in step (2) and make the following judgment:

[0012] If the solution becomes turbid and an orange-red precipitate is formed, it is judged that the test sample may contain minoxidil;

[0013] If no orange-red precipitate is seen in the solution, it can be determined that the test sample does not contain minoxidil.

[0014] According to the method of the present invention, the preparation is selected from: pharmaceutical liquid preparations of hair growth agents and cosmetic liquid preparations of hair growth liquids.

[0015] According to the method of the present invention, the preparation is a preparation selected from the following groups, which is claimed not to contain minoxidil: a pharmaceutical liquid hair growth agent preparation, a cosmetic liquid hair growth liquid preparation.

[0016] According to the method of the present invention, the evaporation is performed by placing the preparation in an evaporating dish and evaporating it in a boiling water bath.

[0017] According to the method of the present invention, the extraction solvent is 0.1 M hydrochloric acid solution.

[0018] According to the method of the present invention, the bismuth potassium iodide reagent is prepared as follows: take a bismuth subnitrate solution and a potassium iodide solution, mix them in a volume ratio of 5:2 and use them, and mix them freshly before use.

[0019] According to the method of the present invention, the bismuth subnitrate solution is prepared as follows: 0.85 g of bismuth subnitrate is added with 10 ml of glacial acetic acid and 40 ml of water, and then ultrasonicated for 30 minutes, and filtered with filter paper to obtain the solution.

[0020] According to the method of the present invention, the potassium iodide solution is prepared as follows: take 8g of potassium iodide, add 20ml of water to dissolve, and shake well to obtain the solution.

[0021] The method according to the present invention comprises the following steps:

[0022] (1) Place an appropriate amount of the sample in an evaporating dish and evaporate in a boiling water bath.

[0023] (2) Add 5 ml of 0.1 M hydrochloric acid solution to dissolve, filter through filter paper, and transfer the filtrate to a conical colorimetric tube;

[0024] (3) Add 10 drops of potassium bismuth iodide reagent, let it stand, observe the clarity of the solution and make the following judgments:

[0025] If the solution becomes turbid and an orange-red precipitate is formed, it is judged that the test sample may contain minoxidil;

[0026] If no orange-red precipitate is seen in the solution, it can be determined that the test sample does not contain minoxidil.

[0027] According to the method of the present invention, the step (1) of taking an appropriate amount of the test sample is to speculate that the test sample contains an amount equivalent to 1-3 mg of minoxidil, for example, an amount equivalent to 1.5-2.5 mg, for example, an amount equivalent to about 2 mg. Generally speaking, for a liquid preparation labeled as a pharmaceutical hair growth agent, the volume of the test sample can be 0.05-0.2 ml, for example, 0.075-0.15 ml of the test sample, for example, 0.1 ml of the test sample. Or, generally speaking, for a liquid preparation labeled as a cosmetic hair growth liquid, the volume of the test sample can be 0.5-2 ml, for example, 0.75-1.5 ml of the test sample, for example, 1 ml of the test sample.

[0028] In the above-mentioned various operation steps of the present invention, although the specific steps described therein are different from the steps described in the various examples in the specific implementation section below in some details or language descriptions, those skilled in the art can fully summarize the above-mentioned method steps based on the detailed disclosure of the full text of the present invention.

[0029] Any embodiment of any aspect of the present invention can be combined with other embodiments, as long as they do not conflict. In addition, in any embodiment of any aspect of the present invention, any technical feature can be applied to the technical features in other embodiments, as long as they do not conflict. The present invention is further described below.

[0030] All documents cited in the present invention are incorporated herein by reference in their entirety, and if the meanings expressed in these documents are inconsistent with the present invention, the description of the present invention shall prevail. In addition, the various terms and phrases used in the present invention have the general meanings known to those skilled in the art. Even so, the present invention still hopes to provide a more detailed description and explanation of these terms and phrases. If the terms and phrases mentioned are inconsistent with the known meanings, the meanings expressed in the present invention shall prevail.

[0031] The present invention exhibits excellent effects as described in various aspects herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 : Comparison of precipitation produced by adding different concentrations of minoxidil reference solution to negative samples.

[0033] Figure 2 : Comparison of negative samples with positive samples.

[0034] Figure 3 : Comparison of precipitation produced by minoxidil reference solution with different concentrations.

[0035] In the above figures, regardless of whether precipitation or turbidity occurs in the test tube, the liquid in the tube is orange-yellow in different shades. DETAILED DESCRIPTION

[0036] The present invention can be further described by the following examples, however, the scope of the present invention is not limited to the following examples. It will be appreciated by those skilled in the art that various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. The present invention provides general and / or specific descriptions of the materials and test methods used in the test. Although many materials and operating methods used to achieve the purpose of the present invention are well known in the art, the present invention is still described in as much detail as possible herein. The following examples further illustrate the present invention, rather than limiting the present invention.

[0037] Example 1: Method for rapidly detecting and determining whether minoxidil is present in a test sample

[0038] 1. Reagent preparation:

[0039] 0.1M hydrochloric acid solution: Take 9ml of hydrochloric acid and add appropriate amount of water to make 1000ml.

[0040] Bismuth subnitrate solution: Take 0.85 g of bismuth subnitrate, add 10 ml of glacial acetic acid and 40 ml of water, ultrasonicate for 30 minutes, and filter with filter paper to obtain the solution.

[0041] Potassium iodide solution: Take 8g of potassium iodide, add 20ml of water to dissolve, shake well, and you have it.

[0042] Bismuth potassium iodide reagent: Take bismuth subnitrate solution and potassium iodide solution, mix them in a volume ratio of 5:2 and use them. Mix them freshly before use.

[0043] 2. Detection method

[0044] (1) The test product is a drug that may contain minoxidil or a minoxidil API

[0045] Take an appropriate amount of the test sample (equivalent to 1-3 mg of minoxidil, 2 mg in this example),

[0046] Add 5 ml of 0.1 M hydrochloric acid solution to dissolve, filter through filter paper, and transfer the filtrate to a conical colorimetric tube;

[0047] Add 10 drops of potassium bismuth iodide reagent, let it stand, observe the clarity of the solution and make the following judgments:

[0048] If the solution becomes turbid and an orange-red precipitate is formed, it is judged that the test sample may contain minoxidil;

[0049] If no orange-red precipitate is seen in the solution, it can be determined that the test sample does not contain minoxidil.

[0050] (2) The test product is a liquid preparation of a pharmaceutical hair growth agent

[0051] Take an appropriate amount of the test sample (presumably equivalent to 1-3 mg of minoxidil, usually the volume of such pharmaceutical hair growth liquid preparations is 0.05-0.2 ml, and 0.1 ml is taken in this embodiment) and place it in an evaporating dish, evaporate it in a boiling water bath,

[0052] Add 5 ml of 0.1 M hydrochloric acid solution to dissolve, filter through filter paper, and transfer the filtrate to a conical colorimetric tube;

[0053] Add 10 drops of potassium bismuth iodide reagent, let it stand, observe the clarity of the solution and make the following judgments:

[0054] If the solution becomes turbid and an orange-red precipitate is formed, it is judged that the test sample may contain minoxidil;

[0055] If no orange-red precipitate is seen in the solution, it can be determined that the test sample does not contain minoxidil.

[0056] (3) The test product is a cosmetic hair growth liquid preparation

[0057] Take an appropriate amount of the test sample (presumably equivalent to 1-3 mg of minoxidil, usually the volume of such pharmaceutical hair growth agent liquid preparations is 0.5-2 ml, and 1 ml is taken in this embodiment) and place it in an evaporating dish, evaporate it in a boiling water bath,

[0058] Add 5 ml of 0.1 M hydrochloric acid solution to dissolve, filter through filter paper, and transfer the filtrate to a conical colorimetric tube;

[0059] Add 10 drops of potassium bismuth iodide reagent, let it stand, observe the clarity of the solution and make the following judgments:

[0060] If the solution becomes turbid and an orange-red precipitate is formed, it is judged that the test sample may contain minoxidil;

[0061] If no orange-red precipitate is seen in the solution, it can be determined that the test sample does not contain minoxidil.

[0062] 3. Specificity of method validation

[0063] According to the "9101 Guidelines for Validation of Analytical Methods" of the "Chinese Pharmacopoeia" (Volume 4 of the 2020 Edition), when the test item is identification, the indicators to be verified are specificity and durability.

[0064] Specificity refers to the ability of the analytical method to correctly determine the substance being tested in the presence of other components (such as impurities, degradation products, excipients, etc.). For identification reactions, it is required to be able to distinguish substances that may coexist or compounds with similar structures. Test samples that do not contain the tested component, as well as compounds with similar structures or related components, should all show negative reactions.

[0065] Distinguish between substances or structurally similar compounds that may coexist:

[0066] In the experiment, a negative sample of cosmetic hair growth solution (negative sample 1, confirmed by liquid chromatography that minoxidil was not added, and the detection standard was "Technical Specification for Safety of Cosmetics" (2015 Edition) Chapter 4 Physical and Chemical Test Methods 2 Prohibited Component Test Method 2.5 Minoxidil and other 7 components) (referred to as #15 standard method in the present invention) was used as a blank matrix, 1 ml was aspirated into an evaporating dish, six portions were operated in parallel, 0, 50, 100, 150, 200, 300 µl of 10 mg / ml minoxidil reference substance stock solution were added respectively, shaken well, evaporated in a boiling water bath, 5 ml of 0.1 M hydrochloric acid solution was added for re-dissolution, filtered through filter paper, transferred to a conical colorimetric tube, 10 drops of potassium bismuth iodide test solution were added, and the solution was allowed to stand to observe the clarity of the solution. Figure 1 The figure shows the comparison of precipitation produced by adding different concentrations of minoxidil reference solution to negative samples.

[0067] In addition, the test sample that does not contain the tested component, as well as the related compounds with similar structure or in the components, should all show negative reactions. For this reason, in one experiment, a negative sample (negative sample 1) and a positive sample (positive sample 1) of a cosmetic hair growth liquid were used and operated according to "2. Test method". The results are shown in Figure 2 , which shows the comparison between negative samples and positive samples.

[0068] 4. Sensitivity of method validation

[0069] Prepare a 10 mg / ml minoxidil reference stock solution using 0.1 M hydrochloric acid solution as the dilution solvent.

[0070] Pipette 0, 50, 100, 150, 200, 300 µl (equivalent to 0, 0.5, 1.0, 1.5, 2.0, 3.0 mg minoxidil) of 10 mg / ml minoxidil reference stock solution into conical graduated colorimetric tubes, dilute to 5 ml with 0.1 M hydrochloric acid solution, shake well, add 10 drops of potassium bismuth iodide test solution, let stand, and observe the clarity of the solution.

[0071] Figure 3 The results are shown in Table 1. Figure 3 As can be seen from the results in the figure, a clear positive result is shown in the addition amount range of 1~3mg).

[0072] 5. Durability of method validation

[0073] Durability refers to the degree to which the test results are not affected by small changes in the test conditions, which provides a basis for the established method to be used for daily inspection. The amount of indicator used (number of drops (d)) is a typical factor that characterizes the durability of the method. The test results are detailed in Table 1 below.

[0074] The test results show that even small changes in the measuring conditions can meet the test requirements and the method is reliable.

[0075] Table 1: Number of drops of indicator used (d)

[0076]

[0077] Note: Blank - 5 ml of 0.1 M hydrochloric acid solution; Positive sample - Minoxidil concentration is 2 mg / ml, added amount is 2 mg; The precipitate in the positive samples in the table is orange-red precipitate.

[0078] In the above table, negative samples 1 to 8 are all pharmaceutical hair growth liquid preparations or cosmetic hair growth liquid preparations that are not labeled as containing and confirmed by the inventor using the #15 standard method to not contain minoxidil, and positive samples are cosmetic hair growth liquid preparations that are not labeled as containing but confirmed by the inventor using the #15 standard method to contain 2 mg / ml minoxidil. Negative samples 1 and 3 are cosmetic hair growth liquid preparations sampled on the market and labeled as produced in a certain province in East China, negative sample 6 is a pharmaceutical hair growth liquid preparation sampled on the market and labeled as produced in a certain province in East China, negative samples 2, 4~5 are cosmetic hair growth liquid preparations sampled on the market and labeled as produced in a certain province in South China, negative samples 7~8 are pharmaceutical hair growth liquid preparations sampled on the market and labeled as produced in a certain province in South China, and positive sample 1 is a cosmetic hair growth liquid preparation sampled on the market and labeled as produced in a certain province in South China.

[0079] It can be seen from the usage (number of drops) of the indicator in the above table that at 4 days, a large amount of precipitation can be visually observed in the positive sample, and a negative sample can still be identified at 10 days, so the indicator usage is preferably selected for 10 days. In the "2. Detection method" of the above embodiment 1, after adding the potassium bismuth iodide reagent, it has been found that although a large amount of precipitation is visually visible in the suspension of the positive sample 1 in Table 1 with more than 4 drops of the indicator, these precipitations usually take more than seven minutes to present an easily observable deposition (for example, at 10 days in Table 1, it takes seven and a half minutes to present a visually observable precipitation deposition, and the verification of specificity and sensitivity also presents these two types). If the precipitation deposition rate can be increased, it is very necessary and meaningful for the method of rapid detection of minoxidil of the present invention, because the method of rapid detection of minoxidil is applicable to the rapid sampling of market-related products by market supervision departments. Therefore, one purpose of the present invention is to further improve the method on the basis of the above embodiment 1, especially to increase the precipitation deposition rate so as to improve the efficiency of observation and judgment. It has been unexpectedly found that when 2% propylene glycol and 0.5% acetone are added to the 0.1M hydrochloric acid solution used, all of the suspensions of positive sample 1 in Table 1 with more than 4 drops of indicator added can show easily observable large amounts of precipitation within three minutes. The present invention provides some examples for comparison. The various results mentioned in the present invention that require more than seven minutes for precipitation to occur refer to precipitation occurring within seven to nine minutes. Example 1a: The method was carried out in accordance with Example 1, except that 2% propylene glycol and 0.5% acetone were added to the 0.1M hydrochloric acid solution used, and the other reagents and operating conditions remained unchanged. In the validation of specificity and sensitivity, the positive test tubes all showed a large amount of easily observable precipitation within two to three minutes. In the durability validation of reference Table 1, all the suspensions of positive sample 1 to which more than 4 drops of indicator were added showed a large amount of easily observable precipitation within two to three minutes (for example, from 10d to two and a half minutes, visually observable precipitation was shown). Example 1b: The method was carried out in accordance with Example 1, except that 2% propylene glycol was added to the 0.1M hydrochloric acid solution used, and the other reagents and operating conditions remained unchanged. The test tubes for the validation of specificity and sensitivity all need more than seven minutes to show a large amount of easily observable precipitation. In the durability verification of Table 1, the positive sample 1 needs more than seven minutes to show a large amount of easily observable precipitation in the suspension with more than 4 drops of indicator. Example 1c: Refer to Example 1, except that 0.5% acetone is added to the 0.1M hydrochloric acid solution used, and the other reagents and operating conditions remain unchanged. The test tubes for the validation of specificity and sensitivity all need more than seven minutes to show a large amount of easily observable precipitation. In the durability verification of Table 1, the positive sample 1 needs more than seven minutes to show a large amount of easily observable precipitation in the suspension with more than 4 drops of indicator.For this purpose, in any embodiment of any method of the present invention, 2% propylene glycol and 0.5% acetone are also added to the 0.1M hydrochloric acid solution used. "(1) The test sample is a drug that may contain minoxidil or a minoxidil API" in "2. Detection method" of Example 1 and Example 1a of the present invention can be conveniently used to detect drugs containing minoxidil or minoxidil APIs, while "(2) The test sample is a pharmaceutical hair growth agent liquid preparation" and "(3) The test sample is a cosmetic hair growth liquid preparation" can be conveniently used to detect minoxidil in mixed products such as cosmetics or drugs, so as to determine whether such mixed products clearly do not contain minoxidil (qualitative result) or may contain minoxidil (qualitative result) so as to further use a more accurate method such as HPLC to determine whether minoxidil is contained and the amount of minoxidil (quantitative result).

[0080] Example 2: Method for rapidly detecting and determining whether minoxidil is present in a test sample

[0081] In this embodiment, there are 6 batches of pharmaceutical liquid hair growth preparations sampled from market supervision work, which are respectively referred to as samples 11 to 16, and 9 batches of cosmetic liquid hair growth preparations sampled from market supervision work, which are respectively referred to as samples 21 to 29.

[0082] In Example 2, the method and conditions of Example 1a were used to test the above-mentioned samples 11-16 and samples 21-29, a total of 15 samples. The results showed that all four samples with positive results showed a large amount of easily observable precipitation within two to three minutes. In addition, these samples were also verified by HPLC according to the #15 standard method, and the results are shown in Table 2 below.

[0083] Table 2: Two methods for detecting minoxidil in hair growth / hair maintenance products

[0084]

[0085] It can be seen from the above results that the method for rapid detection of minoxidil of the present invention is accurate, reliable and has high detection efficiency.

[0086] The above-described embodiments are only preferred embodiments for fully illustrating the present application, and the protection scope of the present application is not limited thereto. Equivalent substitutions or changes made by technicians in the technical field based on the present application are all within the protection scope of the present application. The protection scope of the present application shall be subject to the claims.

Claims

1. A method for rapidly detecting minoxidil in a preparation, the method The following steps are involved: (1) Take the liquid preparation to be tested, evaporate to dryness, re-dissolve it with an extraction solvent, and filter it with filter paper to obtain an extract; the extraction solvent is 0.1 M hydrochloric acid solution. (2) mixing the extract obtained in step (1) with a bismuth potassium iodide reagent to obtain a mixed solution; (3) Observe the clarity of the mixed solution obtained in step (2) and make the following judgment: If the solution becomes turbid and an orange-red precipitate is formed, the test sample is judged to contain minoxidil; If no orange-red precipitate is formed in the solution, it can be determined that the test product does not contain minoxidil; The preparation is a preparation selected from the following: a pharmaceutical liquid hair growth agent preparation, a cosmetic liquid hair growth liquid preparation and is claimed not to contain minoxidil, and 2% propylene glycol and 0.5% acetone are also added to the 0.1M hydrochloric acid solution.

2. The method according to claim 1, wherein the evaporation is performed by placing the preparation in an evaporating dish and evaporating it in a boiling water bath.

3. according to the method for claim 1, wherein said bismuth potassium iodide reagent is prepared as follows: get bismuth subnitrate solution and potassium iodide solution, use after mixing by volume 5: 2, and mix newly before using.

4. according to the method for claim 3, wherein said bismuth subnitrate solution is prepared as follows: take 0.85g of bismuth subnitrate, add 10ml of glacial acetic acid and 40ml of water ultrasonically for 30min, filter with filter paper, and obtain.

5. The method according to claim 3, wherein the potassium iodide solution is prepared as follows: take 8g of potassium iodide, add 20ml of water to dissolve, and shake well to obtain.

6. The method according to claim 1, comprising the steps of: (1) Place an appropriate amount of the sample in an evaporating dish, evaporate in a boiling water bath, add 5 ml of 0.1 M hydrochloric acid solution to dissolve, filter through filter paper, and transfer the filtrate to a conical colorimetric tube; 2% propylene glycol and 0.5% acetone are also added to the 0.1 M hydrochloric acid solution; (2) Add 10 drops of potassium bismuth iodide reagent and let stand; (3) Observe the clarity of the solution and make the following judgments: If the solution becomes turbid and an orange-red precipitate is formed, the test sample is judged to contain minoxidil; If no orange-red precipitate is seen in the solution, it can be determined that the test sample does not contain minoxidil.

7. The method according to claim 6, wherein the amount of the test sample taken in step (1) is an amount equivalent to 1-3 mg of minoxidil in the test sample.

8. The method according to claim 6, wherein the amount of the test sample taken in step (1) is an amount equivalent to 1.5-2.5 mg of minoxidil in the test sample.

9. The method according to claim 6, wherein the appropriate amount of the test sample in step (1) is an amount equivalent to 2 mg of minoxidil in the test sample.

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