Laboratory Experiment pubs.acs.org/jchemeduc
Determining the Ibuprofen Concentration in Liquid-Filled Gelatin Capsules To Practice Collecting and Interpreting Experimental Data, and Evaluating the Methods and Accuracy of Quality Testing Nial J. Wheate,*,† Michael G. Apps,† Hazer Khalifa,† Alan Doughty,‡ and Alpesh Ramanlal Patel† †
Faculty of Pharmacy, The University of Sydney, Sydney, New South Wales 2006, Australia Chemika Pty. Ltd., Girraween, New South Wales 2145, Australia
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S Supporting Information *
ABSTRACT: A laboratory experiment to determine the concentration of the anti-inflammatory drug ibuprofen in liquid gelatin capsule dosage forms, suitable for undergraduate chemistry or pharmacy students, is described. Either individually, or in small teams, the students digest two 200 mg capsules in a KOH solution. While the capsules are digesting the students prepare a range of ibuprofen standards and determine their UV absorbance at 264 nm. Next, the students use the data to both determine the drug’s extinction coefficient using the Beer−Lambert equation and to plot a calibration graph. Using both the extinction coefficient and the calibration graph the students are then required to determine the amount of ibuprofen in each of their capsules. In undertaking the laboratory class, the students are required to complete a results data sheet, determine whether the capsules are within specification, and answer questions that prompt them to evaluate the different calculation methods and the accuracy of the tests. In their final exam, the students were asked three multiple choice questions and one multistep calculation question related to the laboratory class. The results of the students’ final exam show that the learning objectives of the laboratory were broadly met, with students being able to demonstrate an understanding behind the science of the laboratory, and an ability to undertake simple, as well as complex, calculations. KEYWORDS: First-Year Undergraduate/General, Analytical Chemistry, Laboratory Instruction, UV−Vis Spectroscopy, Drugs/Pharmaceuticals, Hands-On learning/Manipulatives
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INTRODUCTION
from the API during sample preparation are not included in the procedures. While there are published methods for the synthesis,1 resolution,2 and purification3 of ibuprofen, methods for determination of the quantity of ibuprofen in solid tablets using UV−vis4 and infrared5 spectroscopy, and studies that have looked at the rate of capsule dissolution,6 and the quantity of a drug in capsules filled with solid powders,7 there are no methods for the determination of ibuprofen in liquid capsule dosage forms. Here we have designed a basic experiment suitable for undergraduate pharmacy and chemistry students that can be used as an introduction to analytical chemistry, and quality assurance testing. The goal of the laboratory experiment is for the students to determine whether liquid capsules contain the correct amount of API, in this case the nonsteroidal antiinflammatory drug ibuprofen.8 In doing this, the students need to accurately prepare standard solutions of the drug and measure their UV absorbance. Using both the drug’s extinction coefficient and a calibration graph, the students then determine the concentration of the API in two test capsules. This experiment provides a foundation upon which the students can be taught in later years more advanced chemical instrumentation and multistep sample preparation. It is also
An important role of chemists or pharmacists working in industry is the quality assurance of manufactured pharmaceutical products. This may involve assessing the products made in house, but increasingly, this can be the assessment of products made in other countries, or by other companies, before they can be released for sale. Quality assurance testing includes determining that the medicine contains the correct active pharmaceutical ingredient (API) and that it contains the correct amount of the API. The accurate quantification of APIs in medicines is complex and can require the use of various advanced chemical instruments including high pressure liquid chromatography, mass spectrometry, and, potentially, nuclear magnetic resonance spectroscopy. These experiments are generally too advanced for early stage undergraduate chemistry and pharmacy students, but medicine quality assurance testing using simple ultraviolet (UV) spectrophotometry is practical. Another challenge in undergraduate laboratory design is selecting the correct dosage form for students to analyze. While solid oral dosage forms (tablets) are the most commonly dispensed form of medicine, they can be problematic for a number of reasons. First, other chemical ingredients (excipients) included in the tablet may absorb UV light. Second, many tablets contain excipients that do not fully dissolve in water. Both of these issues may affect the accuracy of the student’s results if additional steps to remove the excipients © XXXX American Chemical Society and Division of Chemical Education, Inc.
Received: December 14, 2016 Revised: April 17, 2017
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DOI: 10.1021/acs.jchemed.6b00955 J. Chem. Educ. XXXX, XXX, XXX−XXX
Journal of Chemical Education
Laboratory Experiment
standard samples of ibuprofen, digestion of the capsules, and the analysis of the samples using UV−vis spectrophotometry. Ibuprofen is practically insoluble in water,9 so all samples are prepared in KOH solutions to keep the drug in its salt form (see Figure 1). The standard drug solutions are prepared in 0.5 M KOH, but the capsules are digested in 1.0 M KOH so that they are fully dissolved within 30 min. In designing the experiment we found that concentrations of less than 1.0 M KOH resulted in delayed digestion of the capsules (>1 h). Further dilutions of the capsule solutions use 0.5 M KOH so that the conditions are as close to the standard ibuprofen solutions as possible. Ibuprofen has two major absorbance peaks in its UV−vis spectrum at 264 and 272 nm (Figure 2). From staff generated
suitable for institutions with only basic chemical instrumentation, or those that need to minimize costs. The learning outcomes of the laboratory experiment are the following: 1. demonstrate a practical application of the Beer−Lambert equation, 2. practice the preparation of chemical solutions and the use of spectroscopic equipment, 3. practice multistep chemical calculations and manipulate mathematical equations, 4. plot and interpret experimental data, and 5. gain an appreciation for the need for attention to detail in analytical chemistry quality assurance and testing.
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EXPERIMENTAL METHODS SUMMARY
Materials
Ibuprofen and FD&C green no. 3 (Fast Green FCF) were purchased from Sigma-Aldrich, Australia. Potassium hydroxide was purchased from ChemSupply. The liquid gelatin capsule dosage formulation used, which includes FD&C green no. 3 dye as an ingredient, was Advil Liquid Capsules (Pfizer Pty. Ltd.), batch numbers E23421/E63184. The strength of the capsules was 200 mg. The consumables, and the types and number of glassware per station, are provided in the Supporting Information. UV−vis spectra were recorded on Shimadzu UV Mini1240 spectrophotometers using plastic 1 cm cuvettes (Thermo Fisher Scientific).
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HAZARDS This is a relatively low risk laboratory class. The major hazard to staff and students is chemical burns from spilled KOH onto exposed skin. This risk can be minimized by using appropriate PPE, including laboratory coat, gloves, and safety glasses.
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Figure 2. UV−vis spectra of (purple) the FD&C green no. 3 dye (7.5 μM) in water, (red) the dye in 0.5 M KOH, and (blue) the gel capsules in 0.5 KOH at the same test concentration in the experiments undertaken by the students.
RESULTS AND DISCUSSION
data, there is a linear relationship between ibuprofen concentration and its absorbance at 264 nm, which gives a straight line when a calibration graph is created for drug concentrations between 0.5 and 2.5 mM. As well as ibuprofen, the capsules also contain a number of other chemicals: coconut oil (which comprises triglycerides, lauric and myristic acids, and low quantities of capric, caproic, caprylic, oleic, palmitic, and steric acids), gelatin, lecithin, light mineral oil, pharmaceutical ink, polyethylene glycol, KOH, water, sorbitan, sorbitol, and the dye FD&C green no. 3 (see Figure 1). Even though these chemicals can potentially interfere with the determination of the ibuprofen content, only the dye FD&C green no. 3 absorbs light in the UV−vis range (see Figure 2). This dye is used to give the capsules their green color and has a maximum absorbance in water at 625 nm. When dissolved in 0.5 M KOH, the dye’s absorbance maxima underwent a hypsochromic shift to 609 nm. While the dye does absorb at the ibuprofen detection wavelength (264 nm), the quantity of dye in each capsule is so low (
