WO2003048766A2

WO2003048766A2 - Colorimetric artemisinin and artemisinin derivatives assay and assay kit

Info

Publication number: WO2003048766A2
Application number: PCT/US2002/037987
Authority: WO
Inventors: Michael D. Green
Original assignee: The Government Of The United States Of America, As Represented By The Secretary, Department Of Health And Human Services, Centers For Disease Control And Prevention
Priority date: 2001-11-29
Filing date: 2002-11-26
Publication date: 2003-06-12
Also published as: WO2003048766A3; AU2002365753A1; AU2002365753A8

Abstract

Disclosed are methods and kits that enable visual detection of the presence of atemisinin and/or an artemisinin derivative in a sample. The method involves a colorimetric assay that includes contacting the sample with a least one reagent to form an analyte and observing the analyte for a color change that occurs in the presence of artemisinin and/or artemisinin derivative, but not in the absence of artemisinin and/or an artemisinin derivative.

Description

COLORIMETRIC ARTEMISININ AND ARTEMISININ DERIVATIVES ASSAY AND ASSAY KIT

Field

The disclosed methods and diagnostic kits relate to an assay for detecting or measuring the presence of antimalarial therapeutic substances.

Background

Artemisinin and artemisinin derivatives (e.g., artemether, artesunate, and dihydroartemisinin) are being increasingly used in antimalarial therapeutic formulations due to their effectiveness against multi-drug resistant malaria. This family of therapeutic agents is derived from artemisinin (also known as qinghaosu), a naturally occurring product that can be isolated from Artemisia annua L. (also known as qinghao or sweet wormwood). The recent and widespread appearance of counterfeit artesunate tablets in Southeast Asia poses a serious health threat to this region. Although distribution of other counterfeit artemisinin derivatives has not been documented to date, these drugs are similar in cost and appearance to artesunate and it is likely they will become targets of counterfeiting.

The standard method for determining the authenticity of artemisinin and artemisinin derivative tablets involves high performance liquid chromatography. In many countries, resources to purchase and maintain such equipment are not always available; therefore, such countries are particularly vulnerable to the growing problem of counterfeit drugs. Thus, a need exists for a relatively easy to use and inexpensive test to confirm the presence of artemisinin or an artemisinin derivative in a purported pharmaceutical formulation.

Summary of the Disclosure

Disclosed herein are relatively easy to use and inexpensive methods and diagnostic kits for detecting or measuring the presence of artemisinin and/or an artemisinin derivative in a sample. One aspect of the disclosed method is a colorimetric assay that includes contacting the sample and at least one reagent to form an analyte and observing the analyte for a color change that occurs in the presence of artemisinin and/or an artemisinin derivative, but not in the absence of artemisinin and/or an artemisinin derivative. According to one embodiment, an acid reagent is contacted with the sample to form an intermediate analyte that is then contacted with at least one indicator reagent to form a detection analyte such that the presence of an artemisinin derivative is indicated by a difference in color between the intermediate analyte and the detection analyte. It has been found that the use of an acid reagent allows for the detection of a range of artemisinin derivatives such as, for example, artemether, arteether, artesunate (sodium), artesunic acid, artelinic acid, artelinate (sodium), dihydroartemisinin, and mixtures thereof.

According to a second embodiment, a base reagent is substituted for the acid reagent. However, it has been found that only artemisinin and/or artesunate can be detected when using a base reagent. In other words, unlike the acid reagent, the base reagent is specific for only a single artemisinin derivative - artesunate. Thus, the base reagent method lacks the versatility of the above-described acid reagent method.

A diagnostic kit is also described for detecting or measuring the presence of artemisinin and/or an artemisinin derivative in a sample that includes at least one acid reagent (or base reagent) and at least one indicator reagent. According to a particular embodiment, the kit is a colorimetric assay kit wherein the indicator reagent is a color indicator reagent.

The disclosed methods and diagnostic kits will become more apparent from the following detailed description of several embodiments.

Detailed Description of Several Embodiments

Various artemisinin derivatives that may be useful in connection with the disclosed methods are described, for example, in U.S. Patent No. 6,306,896 and U.S. Patent No. 6,297,272. It is well known that one method for making such derivatives involves chemically modifying artemisinin, typically by reducing artemisinin to form dihydroartemisinin that is then converted to other derivatives via techniques described, for example, in U.S. Patent No. 6,297,272. In particular, as used herein, "artemisinin derivatives" includes, but is not limited to, artemether, arteether, artesunate (sodium), artesunic acid, artelinic acid, artelinate (sodium), and dihydroartemisinin.

The described methods and kits can be used to determine the authenticity of purported artemisinin or artemisinin derivative tablets by detecting the presence and/or amount of any artemisinin or artemisinin derivatives in the tablets. As described below in more detail, the disclosed methods and kits provide an on-the-site assay capability. As used herein, an "on-the-site" assay means a test that can be performed in the field. It does not require transport of the samples, the need for organic solvent extraction or the use of sophisticated equipment. The test procedure may be performed without the assistance of qualified laboratory personnel. Moreover, the results of a qualitative test can be visually determined (i.e., with an unaided human eye) within about one hour for the acid reagent method and within about 10 minutes for the base reagent method. The methods are sufficiently sensitive so that only about 1% to about 5% of the total tablet mass (assuming 50 mg per tablet) is required. Therefore, the remaining tablet can still be used as an effective antimalarial treatment.

Artemisinin and artemisinin derivatives do not include any particular chemical moieties that easily react with certain reagents to yield colored products, but they can be transformed by acid or base treatment to produce more reactive intermediate compounds. These reactive intermediate compounds react readily with diazonium salts.

In particular, the acid reagent may be any acidic material that could react with the sample to form an intermediate product that is reactive with the color indicator reagent. Illustrative acid reagents include strong acids (i.e., acids having protons that substantially completely disassociate when placed in aqueous solution) such as, for example, hydrochloric acid, hydrobromic acid, hydroiodic acid, nitric acid, perchloric acid, and sulfuric acid. According to certain examples of the disclosed methods, the intermediate product typically is an acid decomposition product such as, for example, an , β-unsaturated decalone compound. In the case of artemether, dihydroartemisinin, and artesunate, the α, β- unsaturated decalone would be 8-methyl-5-(2-propanalyl)decalin-4-ene-3-one. Such , β- unsaturated decalone compounds then react with a diazonium salt via an azo coupling reaction resulting in a color change.

The base reagent may be any basic material that could react with the sample to form an intermediate product that is reactive with the color indicator reagent. Illustrative base reagents include ammonia, sodium metasilicate, trisodium phosphate, Group IA metal hydroxides (e.g., lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide), and heavy Group HA metal hydroxides (e.g., calcium hydroxide, strontium hydroxide, and barium hydroxide). According to certain examples of the disclosed methods, the intermediate product typically is a base decomposition product such as, for example, an enolate/carboxylate compound. Such enolate/carboxylate compounds then react with a diazonium salt via an azo coupling reaction resulting in a color change.

The color indicator reagent may by any material that when contacted with the sample causes the sample to change color if artemisinin or an artemisinin derivative is present in the sample. In most embodiments of the disclosed method, the color change will occur only if artemisinin or an artemisinin derivative is present. The color change may occur in the detection analyte or final solution prepared during the assay procedure. The color change may be from colorless to a color or it may be from a first color to a second color. For example, in embodiments with Fast Red TR salt as the color indicator reagent the sample typically undergoes a change from colorless to yellow.

Illustrative color indicator reagents include diazonium salts, for example, diazo dyes such as Fast Red TR salt ("FRTR") (also known as 4-chloro-2-methylbenzene/diazonium chloride or 4-chloro-o-toluidine hydrochloride), Fast Corinth V, Diazo Red RC, Fast Blue B, Fast Black K, Fast Violet B, Varamine Blue RT, and Fast Yellow GC.

As described above, the acid reagent or base reagent is contacted with a sample of desired test material (e.g., a purported antimalarial drug). For example, if the purported antimalarial drug is in the form of a tablet, then the sample could be a portion of the tablet or a whole tablet. A mixture of acid or base reagents could be used. The minimum sample amount can range down to about 0.5 mg of the active ingredient(s) in the test material. For example, a whole antimalarial tablet typically weighs about 270 mg. Assuming that the tablet includes about 50 mg of active ingredient(s), the minimum tablet sample amount can range down to about 2.7 mg. If the test material is a solid such as a tablet, the sample may be mixed with an appropriate solvent under conditions sufficient to form a precursor analyte solution. Illustrative solvents include organic solvents miscible with water such as, for example, methanol, ethanol, isopropanol, acetone, and acetonitrile. The amount of solvent may be sufficient to dissolve at least a portion of the solid sample. Alternatively, the purported pharmaceutical formulation could be offered on the market in the liquid phase rather than as a solid. In such a case, the acid agent or base reagent could be mixed directly with the liquid purported pharmaceutical formulation. The acid or base reagent may be contacted with the sample by any suitable method, such as by vortex mixing.

After the acid or base reagent is contacted with the sample, the resulting mixture typically is incubated for a time period sufficient for formation of the intermediate product or analyte. Suitable incubation periods may range widely and depend upon the acid or base reagent used as well as the temperature of the intermediate analyte during the incubation period. Use of a more concentrated acid or base reagent and/or a higher temperature will decrease the incubation period. For example, at room temperature the minimum incubation time period may be about five minutes for the base reagent assay to about an hour or less for the acid reagent assay. The minimum incubation period for the acid reagent assay may be decreased if the amount of the analyte sample is increased. The maximum incubation time period may range widely, for example, from up to about 30 minutes for the base reagent assay and up to about four hours for the acid reagent assay. The amount of acid or base reagent contacted with the sample also may range widely. For example, with an acid reagent at a concentration of about 5 N about 1 ml of acid per 1 mg solid sample may be mixed together.

A buffering solution may be added to adjust and/or maintain the pH of the analyte at any point of the procedure. For example, the buffering solution can be added after the acid reagent or base reagent addition. In the acid reagent assay embodiments, the pH of the intermediate analyte prior to addition of the color indicator reagent may range from about 3 to about 9, with an optimal pH of about 8. In the base reagent embodiments, the pH of the intermediate analyte prior to addition of the color indicator reagent may range from about 3 to about 9, with an optimal pH of about 4 to about 6. Buffering solution formulations are generally known and any such solution may be suitable in the presently disclosed methods. In the case of an acid reagent assay, a basic buffering solution typically would be used such as any alkaline reagent (e.g., a borate-containing solution) that when combined with a strong acid can raise the pH of the mixture to the desired value, hi the case of a base reagent assay an acidic buffering solution typically would be used to lower the pH to the desired value.

The intermediate product or analyte formed by addition of the acid or base reagent is contacted with the color indicator reagent to form a detection analyte. A mixture of color indicator reagents may be used.

According to one variant, a solution of the intermediate product solution is mixed with a solution of the color indicator reagent. The amount of color indicator reagent mixed with the intermediate product should be sufficient to induce a color change if artemisinin or an artemisinin derivative is present in the sample. The color change may occur soon after addition of the color indicator reagent. For example, a yellow color may develop within about five minutes when FRTR is the color indicator reagent.

According to another variant, the color indicator reagent may be incorporated into, or coated onto, a solid substrate to make a test strip. For example, the color indicator reagent could be dissolved in a solvent such as water or methanol and the test strip substrate (e.g., filter paper) could absorb the color indicator reagent. Alternatively, the color indicator reagent could be adsorbed into a solid substrate matrix by direct application of the color indicator reagent to the solid substrate matrix. The solid substrate may be made from any suitable material such as, for example, a paper, plastic, metallic, or glass material. The test strip is contacted with a liquid sample of the intermediate analyte in any manner. For ■ example, the liquid intermediate analyte could be delivered to the substrate surface via a dropper. The resulting liquid on the test strip or the test strip itself (i.e., the detection analyte) would be observed for the indicative color change. Alternatively, the test strip containing the color indicator reagent could be dipped into a container holding the liquid intermediate analyte and the liquid in the container (i.e., the detection analyte) would be observed for the indicative color change.

The disclosed methods can also be used to quantify the amount of artemisinin or an artemisinin derivative in a sample. According to one embodiment, quantification can be performed via spectrophotometric analysis due to a positive correlation between absorbance intensity and artemisinin derivative concentration. In general, the spectrophotometry embodiment involves obtaining absorbance values at a wavelength corresponding to the absorbed wavelength for the particular color of the color indicator reagent/intermediate product mixture (e.g., 420 nm for FRTR/artemisinin derivative-acid reagent reaction product). Linear regression analysis of absorbance vs. concentration data from a standard curve then is performed to calculate the concentration of artemisinin or the artemisinin derivative. Extraction of the colored product formed upon addition of the color indicator reagent may improve the accuracy of the spectrophotometric analysis.

According to another embodiment, a relative quantitative assessment can be determined visually (i.e., without the need for a spectrophotometer) by comparing the color intensity of the analyte to standard solutions of known artemisinin or artemisinin derivative content. For example, a reference or key could be provided with a range of color intensities corresponding to those obtained for a range of concentrations of standard solutions. The color intensity of a tested analyte then could be compared to this reference to determine where the concentration in the analyte falls compared to the ranges in the reference. The reference also could include markings that indicate the therapeutically effective amounts of artemisinin or the various artemisinin derivatives so that one could determine whether a purported pharmaceutical formulation has, in fact, been diluted to a concentration less than the therapeutically effective amount.

The diagnostic or test kit enables a user to perform the above-described detection methods. Such kits could include a first container for the acid or base reagent, a second container for the color indicator reagent, and instructions for performing the assay.

Alternatively, the kit could include a test strip that includes the color indicator reagent as described above. The kit also could include a reference or key member having colorimetric standards on it in order to comparatively quantify the amount or concentration of artemisinin or the artemisinin derivative as described above. Such a reference member may be, for example, a paper or plastic substrate or a container having different colored regions on its surface. Optional components that could be included with the kit include buffering solutions and solvents similar to those described above, a container(s) or transfer pipette(s) for holding and bringing into contact the various assay mixtures and/or reagents, and any applicators or sampling tools as necessary. Each component of the kit could be packaged together or separately.

An illustrative example of a kit with the base reagent could include a container of Fast Red TR salt with a dye content of 15% available from Sigma Aldrich Fine Chemicals, a container of 4% sodium hydroxide, a container of glacial acetic acid, circular filter paper, a pestle, a spatula, a microspoon, a graduated test tube, and a transfer pipette. The kit can be used as described below.

About 50 to 100 mg of Fast Red TR salt is placed into a first test tube. About 5 ml of water and one drop of glacial acetic acid then are added to the first test tube and shaken until all the solids are dissolved.

The tablet is placed on the circular filter paper and ground into a fine powder by the pestle. The resulting fine powder is placed into a separate, second test tube. Five ml of the sodium hydroxide is added to the second test tube, the second test tube is shaken, and the resulting solution is allowed to sit for 15 minutes at room temperature. About 0.6 ml of glacial acetic acid then is added to the second test tube. About 0.5 ml of the Fast Red TR salt solution previously prepared in the first test tube is added to the second test tube. If artesunate is present in the tablet, a vivid lemon color is instantly produced.

An illustrative example of a kit with the acid reagent could include a container of solvent (e.g., an alcohol) to dissolve the purported active ingredient(s), a container of the acid reagent, a container of the buffering solution, a container of dry color indicator reagent, and a positive control sample of the active ingredient(s). The amount of the various kit components would vary depending upon how many tests could be practically performed with the kit. For example, the buffer solution likely would require the most volume (e.g., 10 tests might require at least about 22 ml). Of course, the buffer solution could be concentrated so that a specific volume of water could be added to achieve the desired concentration. The reagents typically are stable in tropical environmental conditions and there is no need for sterilization. Other possible components may include filter paper to remove any excipients to provide a clear solution for possible absorbance readings. A device to scrape the tablet (e.g., a scalpel) would be useful as well as a measuring spoon for a more quantitative test. The acid reagent assay kit could be used in a manner similar to that described above for the base reagent assay kit. The specific examples described below are for illustrative purposes and should not be considered as limiting the scope of the disclosure.

Example 1 - Assay with Acid Reagent

Listed below in Table 1 are an assortment of antimalarial tablets that were tested to determine if the acid reagent assay could (1) detect the presence of an artemisinin derivative compound and (2) measure the amount of the artemisinin derivative compound if present. Artesunate was produced by Mepha (Aesch-Basel, Switzerland); Arenax® tablets (100 mg β-artemether per tablet) were manufactured by Arenco Pharmaceutica, Belgium; Malaxin® (60 mg dihydroartemisinin) tablets were manufactured by Dongsan Pharmaceutical Co., Ltd. South Korea; Arsumax® (50 mg artesunate) was produced by Guilin Pharmaceutical Works, China; artemisinin was manufactured by Sigma Chemical Co.; Aralen® tablets were manufactured by Winthrop Labs; Larium® tablets were manufactured by Hoffman- LaRoche; Falcidin® tablets were manufactured by Hoffman-LaRoche; and co-trimoxazole tablets were manufactured by Schein Pharmaceutical. All the assay steps described below were performed at room temperature (22-27°C) with exposure to air.

About 5% of the tablet mass was scraped into a glass tube. Methanol (0.4 ml) was mixed with the sample in the tube for about 10 seconds to dissolve the purported active ingredient. Hydrochloric acid (0.4 ml, 5 N) was mixed with the dissolved purported active ingredient and incubated at room temperature (22-27°C) for at least one hour to form an intermediate analyte. A buffering solution (2.2 ml of a 0.1 M borate in 5% ammonia solution) was added to the intermediate analyte. A Fast Red TR salt (FRTR) solution (0.1 ml) was added to the intermediate analyte to form a detection analyte. The FRTR was reagent grade with a dye content -20% that was purchased from Sigma-Aldrich Fine

Chemicals (Milwaukee, WI, USA). The FRTR solution (5 or 10 mg/ml water) was prepared immediately before addition to the intermediate analyte. A distinct yellow color in the liquid developed within about five minutes after addition of the FRTR solution if artemether, dihydroartemisinin, or artesunate was present in the sample. A faint orange color appeared in the presence of acetaminophen, and the other tested antimalarial pharmaceuticals appeared colorless.

For a quantitative assessment, insoluble tablet excipients were centrifuged (500xg; 10 min) and 0.4 ml of the supernatant was transferred to a clean glass tube. Weighing the tablet and scrapings, and centrifuging the insoluble excipient was done to perform the quantitative analysis. Standard curves were prepared from artemether, dihydroartemisinin, and artesunate at concentrations of 0.5, 1, and 2 times the concentration determined for 5% of Arenax® (100 mg artemether), Malaxin® (60 mg dihydroartemisinin), or Arsumax® (50 artesunate) in 0.5 ml of methanol. Absorbance (420 nm) values measured by a spectrophotometer were recorded for the standard curve and tablet samples. Linear regression analysis of absorbance vs. concentration data from the standard curve samples was used to calculate the concentration of the active ingredient for each tablet. Two ml of ethyl acetate was added to the detection analyte solution and the sample thoroughly shaken. After addition of the ethyl acetate, the entire yellow reaction product migrated into the organic phase. Quantitative analysis of the yellow reaction product extracted into the organic phase was assessed.

Quantitative analysis using absorbance measurements showed the artemether content of Arenax® and the dihydroartemisinin content of Malaxin® to be within 15% from the expected values, while the artesunate content of Arsumax® showed a much greater deviation of 65% (see Table 1). The extraction with ethyl acetate was employed in an effort to improve accuracy. From absorbance measurements, the active ingredients for each tablet were calculated and are shown in Table 1. The results showed the ethyl acetate extraction improved accuracy (% deviation from expected value) of artesunate content in the Arsumax® tablet from 65 to 11%, while the Malaxin® tablet showed a greater deviation (46%) of dihydroartemisinin from the expected value. Thus, the disclosed method can provide a relatively quick and straightforward approximate quantitative assessment of the artemisinin derivative content of. a sample.

Table 1

"Percent accuracy" is defined as the difference between the expected value and calculated value divided by the expected value times one hundred. Calculated amount of active ingredient (mg/tablet) and percent accuracy are given before and after (*) ethyl acetate extraction.

Example 2 - Assay with Base Reagent

An assortment of antimalarial tablets was tested to determine if the base reagent

10 assay could (1) detect the presence of an artemisinin derivative compound and (2) measure the amount of the artemisinin derivative compound if present. The tested antimalarial formulations were: artesunate (those produced by Mepha (Aesch-Basel, Switzerland) were used for the standard control and Arsumax^® (50 mg artesunate, produced by Guilin Pharmaceutical Works, China) was used to test the amount of artesunate in a tablet);

15 artemisinin; artemether; chloroquine phosphate (available from Winthrop Laboratories); quinine (available from Sigma Chemical Co.); primaquine phosphate (available from Sigma Chemical Co.); and sulfadoxine/pyrimethamine (Fansidar® available from Hoffman- LaRoche). All the assay steps described below were performed at room temperature (22- 27°C) with exposure to air.

20 Approximately 1 % of the total mass of each tablet was scraped from the tablet using a scalpel. The scrapings were weighed and transferred to 13 x 100 mm borosilicate glass tubes. A standard curve was prepared with samples containing 0 (blank), 0.25, 0.5, 1.0 mg of analytical grade artesunate. One-half millimeter of 1 N NaOH was added to form an intermediate analyte, the tubes gently swirled and the samples were allowed to sit at room

25 temperature for 20 minutes. Then 1.34 ml of FRTR (5.6 mg/ml in 0.2 M boric acid /0.2 M acetic acid/0.2 M phosphoric acid) was added to form a detection analyte and the tubes were gently swirled. Final pH of the solution was 6. After 5 minutes, a distinctive yellow color appeared in the detection analyte for the genuine artesunate tablet samples. If the pH is adjusted to be greater than 6, artemisinin develops a yellow color while primaquine develops an intense orange color. When pH is increased to 8, sulfadoxine exhibits a strong yellow color. Although less intense at lower pH, artesunate is the only compound tested that developed a yellow color at pH 4.

For quantitative analysis, the yellow reaction product was extracted from the water insoluble tablet excipients by adding 2 ml of ethyl acetate and vigorously shaking the capped tubes. After phase separation, the upper organic phase was transferred to 13 x 100 mm borosilicate glass tubes and the absorbance measured at 420 nm. Artesunate content for each tablet was determined from the standard curve.

The artesunate content for each tablet was verified using HPLC and diode array detection. A portion of material from each tablet was weighed and dissolved in 3.75% sodium bicarbonate. The sample solution was centrifuged and the supernatant was injected directly into the HPLC system. Using HPLC and diode array detection, each genuine tablet was verified to contain 50 ± 5 mg of artesunate while no artesunate was detected in the counterfeit tablets. The colorimetric assay method was then applied to these tablets to assess artusenate content. The method was also applied to sulfadoxine/pyrimethamine and chloroquine phosphate tablets since these drugs would be more likely substituted for artesunate. The average artesunate concentration for the six genuine artesunate tablets as determined by the colorimetric assay was 50.8 ± 2.9 mg per tablet. The quantitative analysis was performed with the ethyl acetate extract. A pH of 6 was chosen because sulfadoxine does not react at this pH and the intensity of artesunate is stronger than observed at pH 4. A negative result (colorless, absorbance <0.01) was observed when the method was applied to alleged counterfeit artesunate tablets, sulfadoxine/pyrimethamine and chloroquine phosphate tablets.

Having illustrated and described the principles of the disclosed methods and diagnostic kits with reference to several embodiments, it should be apparent that the disclosed methods and diagnostic kits may be modified in arrangement and detail without departing from such principles.

Claims

What is claimed is:

1. A method for visually detecting the presence of at least one compound selected from artemisinin and an artemisinin derivative in a sample, comprising: contacting the sample and at least one reagent to form an analyte; and observing the analyte for a color change that occurs in the presence of artemisinin or an artemisinin derivative, but not in the absence of artemisinin or an artemisinin derivative.

2. The method according to claim 1, comprising contacting the sample and a first reagent to form an intermediate analyte and then contacting the intermediate analyte and a color indicator reagent to form the analyte that is observed for a color change.

3. The method according to claim 1, wherein the color change occurs in the presence of at least one of artemether, dihydroartemisinin, and artesunate.

4. The method according to claim 1, wherein the reagent comprises a diazonium salt.

5. A method for detecting or measuring the presence of at least one artemisinin derivative in a sample, comprising: contacting the sample and at least one acid reagent to form an intermediate analyte; and contacting the intermediate analyte and at least one indicator reagent to form a detection analyte such that the presence of an artemisinin derivative is indicated by a difference in color between the intermediate analyte and the detection analyte that does not occur in the absence of an artemisinin derivative.

6. The method according to claim 5, wherein the method can detect or measure the presence of more than one artemisinin derivative.

7. The method according to claim 5, wherein the method can detect or measure the presence of at least one of artemether, dihydroartemisinin, and artesunate.

8. The method according to claim 5, wherein the acid reagent comprises at least one acid selected from hydrochloric acid, hydrobromic acid, hydroiodic acid, nitric acid, perchloric acid, and sulfuric acid.

9. The method according to claim 5, wherein the indicator reagent comprises a diazonium salt.

10. The method according to claim 5, further comprising dissolving the sample in a solvent prior to contacting the sample with the acid reagent.

11. The method according to claim 5, wherein the intermediate analyte is contacted with the indicator reagent at a pH of about 3 to about 9.

12. The method according to claim 5, wherein about one hour lapses between initial contact of the sample with the acid reagent and any initial difference in color between the intermediate analyte and the detection analyte.

13. The method according to claim 5, further comprising performing the method at room temperature.

14. The method according to claim 5, wherein the method is used for quantitatively measuring the amount of an artemisinin derivative and further comprises spectrophotometric analysis.

15. The method according to claim 5, wherein the method is used for quantitatively measuring the amount of an artemisinin derivative and further comprises comparing a color intensity of the detection analyte to a standard solution of a known artemisinin derivative concentration.

16. The method according to claim 8, wherein the indicator reagent comprises a diazonium salt.

17. A method for detecting the presence of at least one artemisinin derivative in a sample, comprising: contacting the sample and at least one acid reagent to form an intermediate analyte; and contacting the intermediate analyte and fast red TR salt to form a detection analyte such that the presence of an artemisinin derivative is indicated by appearance of a yellow color in the detection analyte.

18. The method according to claim 17, wherein the method can detect or measure the presence of more than one artemisinin derivative.

19. The method according to claim 17, wherein the method can detect or measure the presence of at least one of artemether, dihydroartemisinin, and artesunate.

20. The method according to claim 17, wherein the acid reagent comprises at least one acid selected from hydrochloric acid, hydrobromic acid, hydroiodic acid, nitric acid, perchloric acid, and sulfuric acid.

21. A method for determining the presence of at least one artemisinin derivative ingredient in a purported antimalarial tablet, comprising: contacting at least a portion of the purported antimalarial tablet with at least one acid reagent and at least one color indicator reagent to form a detection analyte; and observing the detection analyte for a color change that occurs only in the presence of artemisinin derivative ingredient.

22. The method according to claim 21 further comprising preparing a sample of the purported antimalarial tablet and then contacting the sample and the acid reagent.

23. The method according to claim 22, wherein preparing the sample comprises dissolving at least a portion of the purported antimalarial tablet in a solvent.

24. The method according to claim 21, wherein the color indicator reagent comprises a diazonium salt.

25. The method according to claim 21, wherein the method can detect or measure the presence of at least one of artemether, dihydroartemisinin, and artesunate.

26. The method according to claim 21, wherein the acid reagent comprises at least one acid selected from hydrochloric acid, hydrobromic acid, hydroiodic acid, nitric acid, perchloric acid, and sulfuric acid.

27. A diagnostic kit for detecting or measuring the presence of at least one artemisinin derivative in a sample, comprising: at least one acid reagent; at least one indicator reagent; and instructions for detecting or measuring the presence of at least one artemisinin derivative in a sample.

28. The diagnostic kit according to claim 27, wherein the acid reagent comprises at least one acid selected from hydrochloric acid, hydrobromic acid, hydroiodic acid, nitric acid, perchloric acid, and sulfuric acid.

29. The diagnostic kit according to claim 27, wherein the indicator reagent comprises a diazonium salt.

30. The diagnostic kit according to claim 29, wherein the diazonium salt comprises Fast Red TR salt.

31. The diagnostic kit according to claim 27, further comprising at least one of a solvent and a buffering solution.

32. The diagnostic kit according to claim 27, further comprising at least one colorimetric comparison reference member.

33. A colorimetric assay kit for detecting the presence of at least one artemisinin derivative in a purported antimalarial tablet, comprising: at least one acid reagent; at least one color indicator reagent; and instructions for detecting or measuring the presence of at least one artemisinin derivative in a purported antimalarial tablet.

34. The colorimetric assay kit according to claim 33, further comprising at least one colorimetric comparison reference member.

35. A method for detecting or measuring the presence of at least one of artemisinin or artesunate in a sample, comprising: contacting the sample with at least one base reagent to form an intermediate analyte; and contacting the intermediate analyte with at least one indicator reagent to form a detection analyte such that the presence of artemisinin or artesunate is indicated by a difference in color between the intermediate analyte and the detection analyte that does not occur in the absence of artemisinin or artesunate.

36. The method according to claim 35, wherein the base reagent comprises at least one base selected from ammonia, sodium metasilicate, trisodium phosphate, Group IA metal hydroxides, and Group HA metal hydroxides.

37. The method according to claim 35, wherein the indicator reagent comprises a diazonium salt.

38. The method according to claim 35, wherein about ten minutes lapse between initial contact of the sample with the base reagent and any initial difference in color between the intermediate analyte and the detection analyte.

39. The method according to claim 35, further comprising performing the method at room temperature.

40. A diagnostic kit for detecting or measuring the presence of at least one of artemisinin or artesunate in a sample, comprising: at least one base reagent; at least one indicator reagent; and instructions for detecting or measuring the presence of artesunate in a purported antimalarial tablet.

41. The diagnostic kit according to claim 40, wherein the indicator reagent comprises a diazonium salt.

42. The diagnostic kit according to claim 41, wherein the diazonium salt comprises Fast Red TR salt.

43. The diagnostic kit according to claim 40, further comprising at least one of a solvent and a buffering solution.

44. The diagnostic kit according to claim 40, wherein the diagnostic kit comprises a colorimetric assay kit that includes at least one color indicator reagent.

45. The diagnostic kit according to claim 40, further comprising at least one colorimetric comparison reference member.