Quantitative Determination of Aluminum in Deodorant Brands: A

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Quantitative Determination of Aluminum in Deodorant Brands: A Guided Inquiry Learning Experience in Quantitative Analysis Laboratory Victoria Sedwick, Anne Leal, Dea Turner, and A Bakarr Kanu* Department of Chemistry, Winston-Salem State University, Winston-Salem, North Carolina 27110, United States S Supporting Information *

ABSTRACT: The monitoring of metals in commercial products is essential for protecting public health against the hazards of metal toxicity. This article presents a guided inquiry (GI) experimental lab approach in a quantitative analysis lab class that enabled students’ to determine the levels of aluminum in deodorant brands. The utility of a GI experimental lab introduced in the quantitative analysis lab class as part of an active learning hands-on-experience approach enhances student learning, improves students’ critical thinking and problem solving skills, and motivates underrepresented students to work independently in solving a real-world scenario-type problem. Students were required to develop certain lab skills at the start of the semester and apply these skills toward the end of the semester to investigate the GI project. The GI project that analyzes for aluminum improves the overall student engagement, enthusiasm for the quantitative analysis laboratory course, and even the overall success rate in scientific report writing. KEYWORDS: Upper-Division Undergraduate, Hands-On Learning/Manipulatives, Inquiry-Based/Discovery Learning, Laboratory Instruction, Interdisciplinary/Multidisciplinary, Problem Solving/Decision Making, Consumer Chemistry, Quantitative Analysis

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INTRODUCTION Guided inquiry (GI) method of instruction in the laboratory1−8 has been shown to be effective for enhancing students’ achievement9 in the classroom. GI lab approach can be considered as an active learning strategy10−13 capable of advancing critical-thinking and problem-solving skill sets for science, technology, engineering, and mathematics (STEM) education.14−22 In this article, a GI experimental lab designed to investigate aluminum content in deodorant brands was incorporated in a quantitative analysis lab class. At the beginning of the semester, the instructor designed and introduced targeted laboratories geared toward improving the skill set for each student. The skills sets incorporated in the targeted laboratories were the following: safety practices in the lab, best practices for maintaining laboratory notebook, sample preparation techniques, processing data using Microsoft Excel, statistical analysis of experimental data, experimental design, proper use of equipment, interpretation of experimental data to reach a valid conclusion, and writing detailed scientific reports. At the end of the skills enhancement period, students’ break away from their teams and worked independently to investigate the GI problem presented to them. Aluminum is the most abundant metal in the earth’s crust. It is a very reactive metal and is capable of combining with several other elements. Aluminum metal is light in weight and silverywhite in appearance. Aluminum is found in many consumer © XXXX American Chemical Society and Division of Chemical Education, Inc.

products including antiperspirant and deodorants. Oral administration of Al is not harmful. However, some studies have shown that people exposed to high levels of aluminum may develop Alzheimer’s disease, but other studies have not found this to be true.23 People with kidney disease store a lot of Al in their body. Kidney disease causes less aluminum to be removed from the body in the urine.23 These individuals may developed bone or brain diseases that doctors think may be linked to excess aluminum. Aluminum containing over-thecounter oral products are considered safe in healthy individuals at recommended doses. However, some adverse effects have been observed following long-term use in some individuals. Children with high levels of Al in their body and suffering from kidney disease have been shown to suffer from brain and bone diseases. The bone damage may have been caused by aluminum in the stomach preventing the absorption of phosphate, a chemical compound required for healthy bones.23 With all these problems, it may be necessary to develop a method for evaluating Al in commercial products. A deodorant or antiperspirant is a common commodity in every household. It is typically used once or twice a day depending on how much a person sweats, but is it actually safe? Received: May 22, 2017 Revised: December 10, 2017

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DOI: 10.1021/acs.jchemed.7b00336 J. Chem. Educ. XXXX, XXX, XXX−XXX

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chlorohydrate (ACH) compound (Al2Cl(OH)5, FW = 174.45 g/mol)23,26,27 were investigated as follows; 10 mL of deodorant sample, 30 mL of EDTA, and 5.00 mL of pH 4 buffer were added to a 150 mL Erlenmeyer flask. The mixture was heated on a hot plate at 250−300 °C for approximately 15−20 min or until the solution began to boil. The mixture was then allowed to cool at room temperature. To start the titration, 5−6 drops of Eriochrome Black T indicator was added to the solution to give it a purple color. The mixture was titrated with 0.01 M ZnSO4 until it turned a permanent shade of pink. The shade varied with the temperature of the solution and the amount of indicator added. Seven replicate titrations were performed for each deodorant.

The primary purpose of deodorant or antiperspirant is to keep the areas applied to in the body dry, thus the name. The primary ingredient that contributes to this purpose is aluminum in the form of either aluminum zirconium trichlorohydrex GLY24 (AZG) or aluminum chlorohydrate (ACH).23 To block perspiration, aluminum clogs sweat ducts in the areas to which it is applied. This makes the ducts swell as they are filled with water. Aluminum is not an element that resides naturally in the human body. Therefore, analytical methods should be developed to determine its content in commercial products such as deodorants. The purpose of this GI experimental lab was to determine the presence and quantity of aluminum in different brand deodorants. To address this problem, ethylene diamine tetraacetic acid (EDTA) was employed in a back-titration approach with Zn2+ ions. The back-titration approach was chosen by the students because Al is capable of blocking the indicator if a direct titration is employed. In this study, we measured the levels of Al in deodorant brands to see if actual Al content matches the label.

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HAZARDS Undergraduate students were initially shown the American Chemical Society (ACS) safety video before conducting any experimental work in the laboratory. The students wore safety goggles and gloves at all times in the laboratory and were instructed to handle concentrated acids with great care because of their corrosive nature. For activities involving these concentrated acids, including sample preparation, it was recommended that undergraduate students work in pairs and under close supervision.

EXPERIMENTAL SECTION

Experimental Lab Design

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The student enrollment in the quantitative analysis laboratory course, fall 2015, was made up of 12 African American and 1 Caucasian, a total of 13 students, 18−27 years old. Female enrollment for the fall 2015 class accounts for 70% of the class. At the start of the semester, students were divided into five groups of two and one group of three. This was necessary to promote teamwork among the students. The teams worked on ten targeted laboratories designed by the instructor to improve the analytical skills set of each student. Skills developed during the targeted laboratories period includes: safety practices in the lab, best practices for maintaining laboratory notebook, sample preparation, processing data in Microsoft Excel, statistical analysis of experimental data, experimental design, proper use of equipment, interpretation of experimental data to reach a valid conclusion, and writing detailed scientific reports. At the end of the skills enhancement period, the groups were dissolved and each student was encouraged to work independently to complete the GI project. Before groups were dissolved, the entire class conducted literature review on the GI project and brainstormed on how to analyze deodorants for aluminum. The discussions led to the decision that sodium ethylene diamine tetraacetic acid (Na2EDTA) should be used to conduct the analysis through back-titration with zinc sulfate. After the deliberation, each student chose a deodorant brand and designed the experiment on their own to complete the analysis. The entire project including scientific report writing lasted for 5 weeks, and students were required to meet with the instructor each week to discuss their progress. The students’ requested all supplies they needed, designed their buffer solution, and prepared their own samples. At the end of the project, each student was required to submit a detailed scientific report for her or his analysis.

RESULTS AND DISCUSSION

Aluminum Content in Deodorant Brands

Several EDTA titration techniques exist. The titration procedure employed for this investigation was designed to follow a back-titration approach because Al under investigation has a capability of blocking the indicator in the titration process.28 Back titration may also prevent precipitation of Al. For example, Al(OH)3 precipitates at pH = 7 in the absence of EDTA. Boiling the solution was also necessary for the titration process to ensure complete formation of stable, soluble Al(EDTA)− complex. The metal ion for back-titration must not also displace Al from EDTA.28 This was the reason why Zn2+ was chosen for the back-titration. Table S-1 (see Supporting Information) shows information for each deodorant which includes the total mass for each deodorant brand and the percent of AZG or ACH present in the sample. For example, Dove Powder deodorant has a total mass of 74 g, 18.20% AZG, and 0.00% ACH. Only one of the deodorant samples (soft and dri) contained 0.00% AZG and ACH. Table S-2 (see Supporting Information) shows the mass of deodorant measured to prepare each stock solution and the total volume of solution of stock solution for each deodorant brand. Table S-3 (see Supporting Information) summarizes the result for the titration (n = 7) and shows the moles of EDTA, moles of ZnSO4 required to react with excess EDTA, the moles of Al3+ present in the stock solution of each deodorant brand, and the mass of Al3+ present in the total deodorant brand. As an example, 2.1152 g of Lady Speed Stick deodorant was measured and prepared as a stock solution of 250 mL (Table S2). This solution contained 9.30 × 10−4 moles Al3+ (Table S-3). The total mass of Lady Speed Stick was 39.6 g (Table S-1). This mass of Lady Speed Stick deodorant contained 0.47 g of Al3+ (Table S-3). Table 1 summarizes the weight percent (% wt) Al3+ from each deodorant brand, the 99.9% confidence interval (CI), the theoretical % wt of Al3+ in each deodorant brand and the

Titration Analysis

The titration process was performed as follows: deodorants that contained aluminum zirconium tetrachlorohydrex Gly (AZG) compound (Al2Cl7H7O7Zr2, FW = 603.64 g/mol)24,25 were investigated as follows; 15 mL of deodorant sample, 30 mL of 0.01 M EDTA, and 5.00 mL of pH 4 buffer were added to a 150 mL Erlenmeyer flask. Deodorants containing the aluminum B

DOI: 10.1021/acs.jchemed.7b00336 J. Chem. Educ. XXXX, XXX, XXX−XXX

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Table 1. Comparative Analysis of Weight Percent of Al3+ from Different Deodorant Samples Sample Source

Experimental Al3+ % wta

99.9% CIb

Theoretical Al3+ % wtc

Error, %d

1.54 0.00 1.19

±0.37

5.52

±0.61

1.63 0.00 1.38

13.77

8.85

±1.86

5.57

58.89

1.72 1.60 1.73

±0.65 ±0.59 ±0.35

1.61 1.63 1.63

6.83 1.84 6.13

5.80 1.39

±0.72 ±0.33

6.19 1.43

6.30 2.80

Dove Powder Soft and Dri Lady Speed Stick Ban Powder Free Old Spice Men Degree Women Degree Mitchum Right Guard a

Experimental weight percent of Al3+ obtained for the deodorant brand (n = 7). b99.9% confidence interval (CI, n = 7). cTheoretical weight percent of Al3+ calculated using either Al2Cl7H7O7Zr2 (AZG) or Al2Cl(OH)5 (ACH) in deodorant sample (n = 7). dCalculated using eq S-10.

Figure 1. Example image of students working on a guided-inquiry project in a quantitative analysis lab class, fall 2015.

in situations where they have to apply skills developed early on in the semester. In addition, efforts were made to assess the impact of the experiment on students’ perception, attitudes, and overall success in the GI project. In the past few years, the instructor teaching this course has collaborated with undergraduate students by encouraging them to suggest analytical problems they would like to investigate. Thus, a student initially suggested the GI project reported in this article. At the conclusion of the project, all students were required to write and submit a full scientific report for assessment by the instructor. The data from submitted reports for the GI laboratories shows that students’ results demonstrated consistency between replicate measurements. The reports were assessed and the results are shown in Figure 2. In general, for

percent error for the analysis. The steps used to calculate these values are shown in the Supporting Information. The experimental % wt values of Al3+ for Dove Powder, Soft and Dri, Lady Speed Stick, Ban Powder Free, Old Spice, Degree Men, Degree Women, Mitchum, and Right Guard were 1.54 ± 0.37%, 0.00 ± 0.00%, 1.19 ± 0.61%, 8.85 ± 1.86%, 1.72 ± 0.65%, 1.60 ± 0.59%, 1.73 ± 0.35%, 5.80 ± 0.72%, and 1.39 ± 0.33%, respectively. A higher CI was used (99.9%, n = 7, t = 5.959) to provide more reliability on the range of the true % wt Al3+. For example, the % wt Al3+ in men degree was 1.60 ± 0.59%. This tells us that we are 99.9% confident that the true Al3+ %wt falls between 1.01 to 2.19%. To determine the percent error for the analysis, the theoretical Al3+ % wt was calculated using eq S-9 (see Supporting Information for all other equations) and information from the deodorant product. This information was then used to calculate the percent error according to eq S-10 (see Supporting Information), and shown below. percenterror =

|E% wt − T% wt | × 100% T% wt

(S−10)

where E%wt is the experimental % wt and T%wt is the theoretical % wt. The percent errors for the titration process are shown in Table 1. For the Ban Powder Free deodorant, Old Spice, and Degree Women, the results shows that the amount of Al content from the titration process exceeded that reported on the label. In addition, the high percent error shown for Ban Powder Free was a result of the experimental % wt Al3+ was much higher than the theoretical % wt Al3+. These results further demonstrates that GI projects in laboratory settings proved to be effective for improved student achievements.9 The approach used here required students to solve a real-world problem and they have to demonstrate understanding of skills developed earlier on in the semester to be successful with the project.

Figure 2. Comparison of students’ lab grades for GI and non-GI laboratories.

fall 2015 GI lab (n = 13), 46% of the students scored between 90 and 100%, 31% scored between 80 and 90%, and 23% scored between 70 and 80%. To use fall 2015 non-GI lab (n = 13) as an example, 8% of the students scored between 90 and 100%, 23% scored between 80 and 90%, 23% scored between 70 and 80%, 15% of the students scored between 60 and 70%, and 8% of the students scored between 50 and 60%. A similar data summary showing improvement in scientific report writing grades for fall 2016 is also shown in Figure 2. These GI lab grades were a significant improvement when compared to the

Evaluation and Informal Feedback

The student feedback from the quantitative analysis class was generally very positive. Figure 1 is an example picture of students working on their project in the quantitative analysis class, fall 2015. The experiment ensured students were placed C

DOI: 10.1021/acs.jchemed.7b00336 J. Chem. Educ. XXXX, XXX, XXX−XXX

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Figure 3. Comparison of survey results concerning anxiety due to using chemicals, preskills enhancement for GI lab, recording experimental data, and overall experience in a GI lab.

Implementing techniques in quantitative analysis type settings such as hand-on-experience, problem solving, critical thinking, independence, and communication skills in GI laboratory experience are highly desirable to advance and sustain learners’ academically and professionally in future science careers.

majority of other laboratories where a GI approach was not implemented. The perception of students toward GI lab was further evaluated by administering a survey designed around the Dalgety’s et al. Chemistry Attitude and Experiences Questionnaire (CAEQ). Completion of the survey was voluntary, and written informed consent was obtained from all participants. Figure 3 shows the results of four questions posed to the students. The survey also allowed participants in the quantitative analysis class to provide open-ended feedback on their GI lab approach compared to traditional “cookbook” experiments where students simply followed a laboratory procedure. Some of the specific comments from two participants include: “At first, the GI lab investigation was difficult and the concept did not solidify completely with me. After reviewing the concept and the connection between the targeted lab reports and the GI project, the way forward becomes clearer to me.” “The GI experiment helped me to view things from a scientific perspective because what we may have worked on with previous labs may not work for you, so it causes you to think of other ways to get better results.” The students further identified the five-week GI lab in which they analyzed for Al in a commercial product as their best experience for the semester and identified the approach as being very different form other laboratories. Majority of the students particularly liked the idea they were in charge of their experiment and enjoyed the freedom to review the literature and think through most of the problems they encountered with minimum supervision. They were also very excited to have played a role in the GI topic selection for the semester. They reported that this motivated them to be accurate and made their experience more worthwhile. Some students reported that the GI lab experience in quantitative analysis motivated their interest in a research career.

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CONCLUSION This manuscript reports on the introduction of a GI lab in a quantitative analysis class that analyzed for Al contents in deodorant brands. The GI lab approach used here required students to solve a problem encountered in their everyday lives. This article demonstrated that utilizing GI lab approach has a direct relationship to improving students’ critical thinking, and problem solving skills. Most students enrolled in the quantitative analysis class had no previous knowledge on how to develop an experimental strategy and execute the strategy to solve a real-life problem. The results communicated in this article demonstrated that students can develop as well as apply skills to solve problems if the right scenario is setup for them. By offering a lab course that allowed students to develop specific skills during the semester, it may prove beneficial when these students are placed in situations where they can apply their knowledge. Other studies have documented that teamwork in a chemistry laboratory has advantages such as promoting individual responsibility from students, ensuring collective responsibility in a laboratory setting, as well as allowing students to learn from their group members. However, other students have reported they did not like group work especially in situations where all responsibility is left to one member of the group. We have noted that the approach used in this GI lab; improving students’ skill sets and encouraging them to participate individually in situations where they can apply skill sets learned previously may promote critical thinking, D

DOI: 10.1021/acs.jchemed.7b00336 J. Chem. Educ. XXXX, XXX, XXX−XXX

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(11) Wenzel, T. J. General chemistry: expanding the learning outcomes and promoting interdisciplinary connections through the use of a semester-long project. CBE Life Sci. Educ. 2006, 5 (1), 76−84. (12) Bishop, M. A. Creating tools to prepare students for active learning in the classroom. Abstracts of Papers, 248th ACS National Meeting & Exposition: San Francisco, CA, August 10−14, 2014. (13) Wenzel, T. J. Active learning in the classroom and laboratory of undergraduate analytical chemistry courses. Abstracts of Papers, 251st ACS National Meeting & Exposition: San Diego, CA, March 13−17, 2016. (14) Kazerounian, K.; Green, W. P.; Trotochaud, A.; Sherman, J.; Faraclas, E. W. Using LEDs and phosphorescent materials to teach high school students quantum mechanics. A guided-inquiry laboratory for introductory high school chemistry. J. Chem. Educ. 2009, 86, 340− 342. (15) Dwyer, T. M.; Fillo, J. D. Assaying α-dicarbonyl compounds in wine. A complimentary GC-MS, HPLC, and Visible Spectrometric analysis. J. Chem. Educ. 2006, 83, 273−276. (16) Hooker, P. Mineral analysis of whole grain total cereal. J. Chem. Educ. 2005, 82, 1223−1225. (17) Walker, E. B.; Davies, D. R.; Campbell, M. Quantitative measurement of trans-fat by infrared spectroscopy. J. Chem. Educ. 2007, 84, 1162−1164. (18) Correia, P. R. M.; Oliveira, P. V. Simultaneous atomic spectrometry for cadmium and lead determination in wastewater. A laboratory exercise. J. Chem. Educ. 2004, 81, 1174−1176. (19) Arnold, R. J. The water project: a multi-week laboratory project for undergraduate analytical chemistry. J. Chem. Educ. 2003, 80, 58− 60. (20) Selco, J. I.; Roberts, J. L., Jr.; Wacks, D. B. The analysis of seawater: a laboratory-centered learning project in general chemistry. J. Chem. Educ. 2003, 80, 54−57. (21) Karukstis, K. K. Reinvigorating the undergraduate experience with a research-supportive curriculum. J. Chem. Educ. 2004, 81, 938− 939. (22) Shiland, T. W. Constructivism: the implications for laboratory work. J. Chem. Educ. 1999, 76, 107−109. (23) Agency for Toxic Substances and Disease Registry (ATSDR). Toxicology Profile for Aluminum; ATSDR, 2008. https://www.atsdr.cdc. gov/toxprofiles/TP.asp?id=191&tid=34 (accessed December 9, 2017). (24) World of Chemicals. Aluminum Zirconium Tetrachlorohydrex GLY; World of Chemicals, 2017. http://www.worldofchemicals.com/ chemicals/chemical-properties/aluminum-zirconiumtetrachlorohydrate.html (accessed December 9, 2017). (25) World of Chemicals. Aluminum Zirconium Tetrachlorohydrex GLY; Wikipedia, 2017. https://en.wikipedia.org/wiki/Aluminium_ zirconium_tetrachlorohydrex_gly (accessed December 9, 2017). (26) Lukacs, V. A.; Korting, H. C. Antiperspirants & deodorants − ingredients and evaluations. Dermatosen in Beruf Und Umwelt (in German) 1989, 37 (2), 53−57. (27) World of Chemicals. Aluminum Chlorohydrate; Wikipedia, 2017. https://en.wikipedia.org/wiki/Aluminium_chlorohydrate (accessed December 9, 2017). (28) Harris, D. C. Quantitative Chemical Analysis, 9th ed.; W.H. Freeman and Company: New York, 2016.

problem solving, and independence of each student in a classroom environment. Students’ feedback to the approach was overwhelmingly positive. The GI lab introduced herein used an approach that initially introduced skills enhancement with structured assessments to develop the theoretical and technical skills set of the students. Applying learned skill sets to solve real-life problems in a GI-type lab approach may assist students in informed choices for their future career in the sciences.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.7b00336. Materials and reagents; preparation of standards; calculations; supporting tables; notes to students and faculty (PDF, DOCX)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: +1 336-750-3199. ORCID

A Bakarr Kanu: 0000-0002-0869-3310 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge the support of the Research Initiation Program and Professional Development Committee at Winston-Salem State University for their support of this work. The authors also thank David Pollard and the Analytical Sciences Digital Library (ASDL) Active Learning Workshops for their support during this investigation.

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DOI: 10.1021/acs.jchemed.7b00336 J. Chem. Educ. XXXX, XXX, XXX−XXX