Laboratory Experiment pubs.acs.org/jchemeduc
Determining the Mass and Time of Release of Acetaminophen from Gel Capsules K. Christopher Smith* and Diana Cedillo Department of Chemistry, University of Texas-Pan American, Edinburg, Texas 78539-2999, United States S Supporting Information *
ABSTRACT: A laboratory experiment is described in which students spectrophotometrically determine the mass of acetaminophen in a gel capsule as well as how quickly the acetaminophen is released from the gel capsule. The experiment involves converting acetaminophen into a colored complex through a series of reactions, generating a calibration curve, and making a series of measurements at specific time intervals. Students gain hands-on experience with the spectrophotometer and engage in graphical analysis of data while analyzing a common pharmaceutical compound.
KEYWORDS: High School/Introductory, First-Year Undergraduate/General, Laboratory Instruction, Physical Chemistry, Hands-On Learning/Manipulatives, Drugs/Pharmaceuticals, Oxidation/Reduction, UV−Vis Spectroscopy
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investigate while also providing experience with chemical instrumentation and the graphical analysis of data. This laboratory experiment is suitable for advanced high school or college general chemistry students.
harmaceutical compounds are common chemicals that can be the central focus of interesting analyses in teaching laboratories. One such compound, acetaminophen, has been the subject of several experiments appearing in this Journal. Some of these experiments have focused on separating and identifying acetaminophen in pharmaceuticals using thin-layer chromatography1−5 and high-performance liquid chromatography (HPLC).6−8 Other experiments quantified acetaminophen in pharmaceuticals using ultraviolet spectrophotometry,9−11 liquid chromatography−mass spectrometry,12 nuclear magnetic resonance,13 capillary electrophoresis,14 and HPLC.14 In addition, experiments focused on reactions involving acetaminophen15,16 have appeared in this Journal. These reports focus largely on chromatographic separation and identification of acetaminophen. The activity described in this paper, however, is unique in that it involves visible spectrophotometric analysis to determine the quantity of acetaminophen in a gel capsule as well as to measure the rate at which it is released from the gel capsule. The analytical and pharmaceutical chemistry literature contains several reports of methods of visible spectrophotometric analysis of acetaminophen. Each of these methods involves the reaction of acetaminophen with a reagent system to produce a colored species, which is then quantified using spectrophotometry. The reagent systems used include HCl and K2Cr2O7;17 HCl, phenol, and NH4OH;18 HCl and pdimethylaminobenzaldehyde;19 and Fe3+ and 1,10-phenanthroline.20,21 In this laboratory experiment Fe3+ and 1,10phenanthroline are used to react with acetaminophen as it is released from the gel capsules over time. Thus, this experiment affords an engaging, real-world problem for students to © 2014 American Chemical Society and Division of Chemical Education, Inc.
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EXPERIMENTAL OVERVIEW In this experiment students spectrophotometrically determine the mass of acetaminophen in a gel capsule as well as how quickly the acetaminophen is released from the gel capsule. The experiment involves converting acetaminophen into a colored complex through a series of reactions, generating a calibration curve, and making a series of measurements at specific time intervals. Acetaminophen undergoes a reduction−oxidation reaction with Fe3+ in which the acetaminophen is oxidized and the Fe3+ is reduced to Fe2+.22 Then, Fe2+ reacts with 1,10-phenanthroline to form the complex ferroin,21 Fe(Phen)32+ (Scheme 1). Ferroin is an intensely red colored complex23 with an absorbance maximum at 508 nm.24 As such, it is possible to obtain the quantity of acetaminophen in a sample using visible spectrophotometric analysis. This experiment was carried out by students in three sections of an introductory general chemistry college laboratory course, with each section having 7 students completing the experiment. There were 4−5 spectrophotometers per laboratory, and students worked in groups of 2−3. The first group of students finished in 2 h and 50 min, whereas the last group finished in 4 h and 5 min. As such, the lab can be completed in one threePublished: February 18, 2014 437
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Laboratory Experiment
eye and skin irritation and may be harmful if absorbed through the skin, ingested, or inhaled. If contact with these chemicals occurs, the affected area should be washed with plenty of cold water for at least 20 min. Proper laboratory clothing, gloves, and eye protection should be worn at all times.
Scheme 1. Reaction of Acetaminophen To Form the Color Complex
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RESULTS AND DISCUSSION The ferroin calibration curve gave a linear plot, with a representative calibration curve obtained by one group of students shown in Figure 1. The graph of absorbance of ferroin
hour laboratory session, but could extend to a second laboratory session.
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EXPERIMENTAL PROCEDURES Students begin this experiment by preparing ferroin standard solutions using stock solutions of acetaminophen, Fe3+, and 1,10-phenanthroline. They then measure the absorbances of these standards at 508 nm and construct an absorbance versus concentration calibration curve. To measure the rate of release of acetaminophen from the gel capsules, a gel capsule is placed into 750 mL of a 0.1 M HCl(aq) solution at 40 °C (to approximate stomach acid at an elevated body temperature) and 1.0 mL aliquot samples are withdrawn every 3 min for 30 min. Samples are treated with Fe3+ and 1,10-phenanthroline to produce ferroin. Students then plot absorbance versus time to determine how quickly the acetaminophen was released from the gel capsule. Finally, students determine the total mass of acetaminophen contained in the gel capsule using their calibration curve and their absorbance versus time plot. In the experiments, students used a Spectronic GENESYS 20 spectrophotometer, which has a grating-based optical system, a wavelength range of 325−1100 nm, and an accuracy of ±2.0 nm.25 The experimental details are given in the Supporting Information. The gel capsules used contain acetaminophen, as well as one or both of doxylamine succinate and phenylephrine HCl, as gel capsules containing only acetaminophen could not be located. However, experiments using doxylamine succinate and phenylephrine HCl independently showed that they did not reduce Fe3+ to Fe2+, so the only source of Fe2+ in the experiments was due to reduction of Fe3+ by the acetaminophen.
Figure 1. Calibration curve for ferroin; slope is 0.0273 μM−1, yintercept is −0.0456, R2 = 0.9948.
solution from the gel capsule versus time gave a roughly asymptotic plot, with a representative plot obtained by one group of students shown in Figure 2.
Figure 2. Plot of absorbance of ferroin solution from a gel capsule versus time.
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HAZARDS Pharmaceuticals used in laboratory experiments should never be consumed, inside or outside the laboratory. Sulfuric acid (used to help dissolve the iron salt) and hydrochloric acid fumes or mist can cause severe irritation of the respiratory tract; these compounds should be used in a well-ventilated area. Contact with hydrochloric acid or sulfuric acid can cause burns and irritation to the skin and eyes. Skin contact with ferroin results in red stains. Phenanthroline causes eye and skin irritation, may be harmful if inhaled or absorbed through the skin, and is harmful if swallowed. Iron(III) sulfate may cause
In determining the length of time taken for the acetaminophen to be completely released from the gel capsules, students generally reported the time corresponding to the maximum absorbance of the ferroin solution or the time at which the gel capsule completely disappeared. This length of time typically ranged from 15 to 25 min. The students generating the data for the plot in Figure 2 reported that their gel capsule dissolved completely after 21 min, corresponding to an absorbance of the ferroin solution of 0.650. This absorbance yielded a total mass of 289 mg of acetaminophen in the gel capsule. This mass corresponded to 89% of the 325 mg of 438
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(10) Yarnelle, M. K.; West, K. J. Modification of an Ultraviolet Spectrophotometric Determination of the Active lngredients in APC Tablets. J. Chem. Educ. 1989, 66, 601−602. (11) Williams, J. P.; West, K. J.; Erickson, K. L. Separation of Aspirin from Acetaminophen and Caffeine in an Over-the-Counter Analgesic Tablet: A Solid-Phase Extraction Method. J. Chem. Educ. 1992, 69, 669−670. (12) Fenk, C. J.; Hickman, N. M.; Fincke, M. A. Identification and Quantitative Analysis of Acetaminophen, Acetylsalicylic Acid, and Caffeine in Commercial Analgesic Tablets by LC-MS. J. Chem. Educ. 2010, 87, 838−841. (13) Schmedake, T. A.; Welch, L. E. The Quantitative Analysis of an Analgesic Tablet: An NMR Experiment for the Instrumental Analysis Course. J. Chem. Educ. 1996, 73, 1045−1048. (14) Thompson, L.; Veening, H.; Strein, T. G. Capillary Electrophoresis in the Undergraduate Instrumental Analysis Laboratory: Determination of Common Analgesic Formulations. J. Chem. Educ. 1997, 74, 1117−1121. (15) Volker, E. J.; Pride, E.; Hough, C. Drugs in the Chemistry Laboratory: The Conversion of Acetaminophen into Phenacetin. J. Chem. Educ. 1979, 56, 831. (16) Mirafzal, G. A.; Summer, J. M. Microwave Irradiation Reactions: Synthesis of Analgesic Drugs. J. Chem. Educ. 2000, 77, 356−357. (17) Guha, B. Estimation of Active Ingredients of Formulations of Paracetamol. J. Inst. Chem. (India) 2001, 73, 157−158. (18) Frings, C. S.; Saloom, J. M. Colorimetric Method for the Quantitative Determination of Acetaminophen in Serum. Clin. Toxicol. 1979, 15, 67−73. (19) Usifoh, C. O.; Adelusi, S. A.; Adebambo, R. F. Colorimetric Determination of Paracetamol in Raw Material and in Pharmaceutical Dosage Forms. Pak. J. Sci. Ind. Res. 2002, 45, 7−9. (20) Carmona, M.; Silva, M.; Pérez-Bendito, D. Stopped-Flow Kinetic Determination of Acetaminophen by Oxidation with a 1,10Phenanthroline/Iron(III) Complex. Anal. Chim. Acta 1989, 218, 313− 322. (21) Zarei, A. R.; Afkhami, A.; Sarlak, N. Simultaneous Spectrophotometric Determination of Paracetamol and Salicylamide in Human Serum and Pharmaceutical Formulations by a Differential Kinetic Method. J. AOAC Int. 2005, 88, 1695−1701. (22) Issa, M. M.; Nejem, R. M.; El-Abadla, M. S.; Al-Kholy, M.; Saleh, A. A. Novel Atomic Absorption Spectrometric and Rapid Spectrophotometric Methods for the Quantitation of Paracetamol in Saliva: Application to Pharmacokinetic Studies. Indian J. Pharm. Sci. 2008, 70, 344−350. (23) Bellér, G.; Lente, G.; Fabián, I. Central Role of Phenanthroline Mono-N-oxide in the Decomposition Reactions of Tris(1,10phenanthroline)iron(II) and -iron(III) Complexes. Inorg. Chem. 2010, 49, 3968−3970. (24) Fortune, W. B.; Mellon, M. G. Determination of Iron with oPhenanthroline: A Spectrophotometric Study. Ind. Eng. Chem. 1938, 10, 60−64. (25) Thermo Electron Corporation. Spectronic GENESYS 20 Visible Spectrophotometer. http://www.thermo.com/eThermo/CMA/ PDFs/Product/productPDF_2487.pdf (accessed February 2014).
acetaminophen in the capsule, as listed on the capsule’s active ingredient information. The results of the mass of acetaminophen from the different groups ranged from 272 mg to 344 mg, with an average value of 301 ± 38 mg.
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CONCLUSION The spectrophotometric experiment described provides students with hands-on experience with the spectrophotometer and gives them experience in graphically analyzing data. It is also an interesting and relevant experiment incorporating acetaminophen, a common pharmaceutical, and students seemed to enjoy the idea of working with the gel capsules. This experiment could be extended by analyzing and comparing other forms of delivery of acetaminophen including tablets, caplets, and extended release formulations.
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ASSOCIATED CONTENT
S Supporting Information *
Experimental handout for students and notes for the instructor. This material is available via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We thank the students in the general chemistry laboratory courses for participating in the experiment. We also thank Dr. Deborah Herrington and Dr. Brian Postek for their helpful comments and insight on the manuscript. Finally, we acknowledge the HHMI Science Education Grant 52007568 for financial assistance.
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REFERENCES
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