Authentic Performance in the Instrumental Analysis Laboratory: Building a Visible Spectrophotometer Prototype Mark V

Article

pubs.acs.org/jchemeduc

Authentic Performance in the Instrumental Analysis Laboratory: Building a Visible Spectrophotometer Prototype Mark V. Wilson† and Erin Wilson*,†

Department of Chemistry, Doane College, 1014 Boswell Avenue, Crete, Nebraska 68333, United States

*S Supporting Information

ABSTRACT: In this work we describe an authentic performance project for Instrumental Analysis in which students designed, built, and tested spectrophotometers made from simple components. The project addressed basic course content such as instrument design principles, UV−vis spectroscopy, and spectroscopic instrument components as well as skills such as evidence-based decision-making, seeking and applying knowledge, teamwork, and breaking down complex problems. Over the course of the seven-week project, students produced unique, functional spectrophotometers with creative designs. Students reported a high level of engagement and learning during the project. Student performance on a UV−vis spectroscopy assessment instrument improved signiﬁcantly (28%) from a pretest to a post-test, with the greatest gains occurring in items aligned to the project learning outcomes. KEYWORDS: Upper-Division Undergraduate, Analytical Chemistry, Laboratory Instruction, Problem Solving/Decision Making, Collaborative/Cooperative Learning, Inquiry-Based/Discovery Learning, Hands-On Learning/Manipulatives, Instrumental Methods, UV−Vis Spectroscopy

odern UV−vis spectroscopy instrumentation continues classrooms from the high school level to the upper-division − M to evolve, becoming more capable, robust, and user- undergraduate level.3 23 The purpose of such instruments is to friendly with each generation. Spectrophotometers are now (1) demystify the “black box” of spectroscopic instrumentation produced that can operate from the UV through the NIR by providing instruments with components that can be seen and wavelength range, read up to eight absorbance units, and achieve manipulated and (2) provide instruments for students to use at a better than 0.05 nm resolution.1,2 These and other advances reduced cost compared to commercially available options. These make UV−vis−NIR spectroscopy, already a widely applied hand-built instruments have varied widely in design from simple − − analysis technique, useful for an expanded range of applications, LED → sample → light detector photometers7 9,11 18 to diode- and therefore even more important for future scientists to array-like cell-phone spectrophotometers,3,19,20 dual beam ff instruments with lock-in detection,10 and scanning instruments understand. Unfortunately, one side e ect of advances in − − spectrophotometer design has been to make the internal incorporating monochromators.4 6,21 23 Likewise, they vary construction and operation of these instruments more of a widely in construction materials from salt shakers and digital “ ” picture frames3 to 3-D printed construction14,17,19 and black box than ever before. There is no longer an easy way to lift − the lid on most instruments to see and explore what is inside sophisticated circuitry.10 12,21,22 without risking damage to an expensive instrument. This trend Hand-built spectrophotometers have largely been presented as has been extended to the software as well. Modern software often short-term projects for instructors or students to build from defaults to settings such as “speed of scan” or “resolution” provided instructions and use to make absorbance or simple 3−14,16 without indicating what instrumental parameters are adjusted kinetics measurements. In a few cases, students were asked with the different options. There is often no direct way to change to perform critical analysis of the performance of specific 15−23 hardware settings such as slit width. User-friendly software also components or the overall instrumental design. In several performs much of the data analysis automatically, particularly for projects, students explored the effects of altering individual common applications such as water quality analysis and protein components of the instrument, such as the light source, grating, 16−19 or DNA/RNA analysis. Thus, improvements in UV−vis or detector, on overall instrument performance. Scheeline instrumentation have made teaching and learning these instru- had students choose important placement parameters for ments in a hands-on way more challenging. instrument components to help them understand the As instruments have become more difficult to examine and fundamental origins of limitations in instrument performance, 20 manipulate directly, do-it-yourself spectrophotometers have such as stray light versus light throughput. Similarly, the become increasingly popular as a way to introduce students to this important instrumental method. A variety of hand-built Received: July 12, 2016 visible single- or multiple-color colorimeters and spectropho- Revised: October 17, 2016 tometers have been reported in the literature for use in Published: November 11, 2016

SpecUP is a spectrophotometer kit that students assemble.22 lecture/discussion course in which the principles and instru- Students choose the placements of different components in the mentation of UV−vis spectroscopy were discussed. Early optical path to optimize the experimental results. iterations of the project were carried out in 2010 and 2012; it Adifferent level of student engagement occurs when students is the 2014 project that we will primarily describe here. design and build instruments themselves. Tavener and Thomas- Spectrophotometer Assignment Oates help students build a photometer and then ask them to 27 According to a recent work by Frey et al., some of the key design and build a working spectrophotometer.21 Likewise, features of an authentic performance assessment are that it is Wang et al. designed a four-week guided inquiry project to realistic and cognitively complex, that it includes formative introduce the principles of spectroscopy and allow students to assessment, that it requires a defense of the final product or design, build, and test a submersible photometer.15 Recently, answer, that it is collaborative, and that multiple measures are Bougot-Robin et al. reported a problem-based learning course in used to evaluate it. In the spectrophotometer project, student which students used materials provided to build and optimize the groups (2−3 students) acted as research and development teams performance of spectrophotometers.23 These projects are for a start-up instrument manufacturer developing an inex- examples of authentic performance tasks, in which students pensive visible spectrophotometer for simple applications. must apply knowledge to a complex task in order to produce a − Students were provided with a range of choices of light sources, tangible product.24 26 The products in these cases are an detectors, dispersion elements, lenses, and mirrors, all necessary optimized instrument and the performance data that demon- circuit components, and multimeters, as well as a range of strate its capabilities. construction materials and a budget of $20. See Table S1 in Authentic performance tasks frame large problems in “real- − Supporting Information for a list of components provided. They world”-like contexts.24 27 Students are responsible for dividing a were given a list of desirable performance characteristics (Table large and complex goal into small subproblems and applying 1). This project is cognitively complex and collaborative, their knowledge to solve them. The outcome of an authentic performance task is a finished product that reflects not only the ’ Table 1. Performance Characteristics for Hand-Built body of knowledge a student has acquired, but also the student s fi ability to transfer and apply that knowledge in context. The final Spectrophotometers Speci ed in the Project Assignment with outcome need not be a single “correct” solution, but can be a Method for Assessing Each Characteristic range of solutions incorporating a diversity of perspectives, Performance Characteristic Assessment Method creativity, and innovation. Authentic assessment tasks directly Adjustable wavelength in visible region Visual, movement of rainbow across address the “Integrative and Applied Learning” learning outcome exit slit for undergraduates published by the Liberal Education and Acquisition of absorbance spectrum of Comparison with spectrum acquired ’ 28 fi chromophore (absorbance characteristics, for same sample using Cary 50 America s Promise (LEAP) initiative in 2007. This is de ned in wavelength calibration) spectrophotometer the report as (ref 15, p 7): Linear absorbance vs concentration response Linear calibration curve of synthesis and advanced accomplishment...demonstrated chromophore through the application of knowledge, skills, and responsi- Reproducible Multiple student-generated bilities to new settings and complex problems. measurements and instructor- generated measurements In the authentic performance task reported here, students User-friendly Instructor measurements using designed and built a visible spectrophotometer, determined its instrument performance and performance limitations, and revised and Detection limit Student determination of detection optimized their design. The emphasis was for students to limit compared to Cary 50 combine a knowledge set gained in classroom study of UV−vis detection limit Linear range Student determination of linear range instrumentation, performance data, and available literature on compared to Cary 50 linear range spectrophotometer construction to make well-justified design decisions for their hand-built instruments. The final products included a visible spectrophotometer, a set of performance characteristics for the instrument, and an analysis of instrument requiring students to work together to break a large project performance. In this project students demonstrated their down into discrete and manageable steps and address these steps knowledge of spectrophotometer components and design as by applying knowledge gained in the classroom and from other well as their many technical and creative talents. sources. On the first day of the project, students individually built a ■ THE SPECTROPHOTOMETER PROJECT light-detection circuit and made a simple photometer with guidance from the instructor.21 By the end of day one, every Cohort and Course Context student had produced a working photometer. The photometers The purpose of this work is not to describe a hand-built were used to practice converting the voltage output of the spectrophotometer, which has been done by others, but to detector circuit to % transmittance and absorbance values describe how we have used hand-built instrument design and according to construction as a deep learning experience through authentic ()VV− performance pedagogy. The spectrophotometer project was %T = d × 100 conducted in a 300-level Instrumental Analysis laboratory course ()VVod− (1) at Doane College, a small liberal arts college in rural Nebraska. A =−log T (2) Students enrolled in this alternate-year course are primarily Junior and Senior Chemistry and Biochemistry majors (three where T is transmittance, A is absorbance, V is the output voltage − cohorts of 9 14 students from 2010 to 2014). The 3 h laboratory from the detector circuit for the sample of interest, Vo is the “ ” session met once per week, complementing a traditional 50 min output voltage for a blank, and Vd is the dark output voltage in

45 DOI: 10.1021/acs.jchemed.6b00515 J. Chem. Educ. 2017, 94, 44−51 Journal of Chemical Education Article which the optical path at the sample holder is blocked with Table 2. Summary of Components, Mechanism of opaque material. Wavelength Selection, and Construction Materials Used in Weeks 2−4 of the project were devoted to designing, building, the Spectrophotometers of Six Individuals and Groups calibrating, and testing the performance of the spectropho- Group/ Optical tometers. Measurable milestones served as formative feedback as Individual elements Wavelength Selection Construction parts of the optical train were assembled and, later, as absorbance A White LED Rotation of planar mirror LEGO bricks measurements were obtained. For example, the first challenge Transmission faced by all groups was choosing dispersion elements and grating aligning them with light sources, entrance slits, and collimating Convex lenses lenses to produce rainbows. The outcome required was the Planar mirror production of a high-intensity and well-dispersed visible Exit slit spectrum of light. By week 4, groups produced a functional B White LED Rotation of planar mirror PVC pipe spectrophotometer including a spectrum and calibration curve of Entrance slit a chromophore of their choice. They analyzed their performance DVD data to improve upon their instrument designs in weeks 5−7, and Convex lenses documented their success with a second round of performance Rotating planar testing. mirror The final products of the spectrophotometer project were the C White LED Linear movement of sample/ Wood/PVC detector assembly pipe instrument and performance data obtained with it. Each student Transmission also kept a logbook to record detailed schematics of their grating spectrophotometer, evidence used in making design decisions, Convex lenses raw and worked-up data, and analysis of spectrophotometer D White LED Rotation of CD LEGO bricks performance. Finally, each group presented their design to the Entrance slit “upper-management” of the fictitious company in which they CD presented an analysis of their design and its performance Convex lenses 29−31 characteristics. These served as multiple measures of Exit slit student performance in this project. E 100 W light Linear movement of sample/ Wood bulb detector assembly Spectrophotometer Design Adjustable Instrument designs bore several similarities across groups and entrance slit individuals. These similarities were imposed by general Transmission grating spectrophotometer design principles as well as the range of Convex lenses materials available. Students typically chose to use DVDs or 1000 Exit slit line/mm transmission gratings to maximize light dispersion, F 100 W light Linear movement of sample/ Metal although some used CDs or 500 line/mm transmission gratings bulb detector assembly mailbox to yield greater light throughput at the cost of resolution. Entrance slit Students universally chose to use the CdS LDR detectors over Transmission photodiodes, citing from experimental evidence, vendor grating specifications, or literature research the greater sensitivity of Convex lenses the LDR in the visible region.18,32 Spectrophotometers typically Exit slit included a convex lens to collimate light from the LED or entrance slit and a fixed exit slit/sample holder/detector across the visible spectrum. One group lined the light source assembly. housing with mirrors to increase light output (Figure S2C), a Despite these general similarities, the designs varied widely in concept similar to that used by Perkin-Elmer in the construction optical elements, optical path, instrument features, and of its high-end spectrophotometers.33 Special features included construction. A characteristic feature of authentic performance doors for easy access to the sample holder, a nut-and-bolt assessments is that there are multiple ways to solve the problem. assembly for reproducible wavelength adjustment (Figure S2D), Each group and individual brings unique knowledge, skills, and and a variable entrance slit size (Figure S2C). Construction background to the table, and the collaboration of individuals can strategies varied widely as well and included LEGO bricks, PVC produce new innovations. This is abundantly reflected in the pipe housing, wood, or combinations of materials. spectrophotometers produced through the project. A summary Students in the 2010 and 2012 cohorts were not provided with of the features of selected spectrophotometers is shown in Table sample designs, although they were free to do their own research. 2. Schematics or photographs of spectrophotometers produced One advantage of not providing ideas is the creative designs that by individuals or teams of 2−3 students in Instrumental Analysis emerge, such as the highly unique mailbox-housed spectropho- from 2010 to 2014 are shown in Figure S1. tometer (individual F, Figure S1). Some students from these Some instruments used in-line optical paths with only cohorts struggled to produce a functional design without initial transmission elements while others contained one or more design guidance; however, this may have been alleviated by reflective elements to increase optical path length/reduce the allowing collaboration as in 2014. Students in the 2014 cohort total bench footprint of the instrument (groups A and E, Figure were provided with a selection of literature articles from which to S1). Some groups housed detectors in enclosures designed to generate initial ideas.4,5,10,18,20 Although at least four out of five minimize stray light (Figure S2A). Wavelength selection was groups started with one of these or an independently researched achieved by rotating reflective gratings, rotating mirrors (Figure alternative source, all groups ultimately arrived at unique designs. S2B), or moving the exit slit/sample holder/detector assembly For example, group B enclosed their optical train in PVC pipe

46 DOI: 10.1021/acs.jchemed.6b00515 J. Chem. Educ. 2017, 94, 44−51 Journal of Chemical Education Article based on an Internet resource, but incorporated a rotating mirror −1 Δλ fi D = rather than a set of xed mirror positions to expand their Δx (3) wavelength sampling (Figure S1). Group C initially attempted to − fl where D 1 is inverse dispersion, Δλ is the change in wavelength, re ect light into their sample from a rotating mirror as in Knagge Δ and Raftery,5 but encountered problems with the angle of light and x is the change in position along the dispersed visible light. into their exit slit. Ultimately they used a slit/sample/detector While we are aware that light dispersion is not linear, it served as a good approximation for our purposes. Inverse dispersion was assembly and moved it linearly across their dispersed rainbow for ff wavelength selection. multiplied by exit slit width to yield e ective bandwidth −1 Student-Generated Results BWeff = D w (4) In order to evaluate the performance of their spectrophotom- ff where BWeff is e ective bandwidth, in nanometers, of light going eters, students made solutions of available chromophores (Table through the exit slit and w is the exit slit width. Effective S2). They acquired visible absorbance spectra of a chromophore bandwidths were between 3.2 and 8.4 nm for student solution, constructed a calibration curve, and determined the ff spectrophotometers, with slit widths generally between 0.25 limit of detection (LOD). Some cohorts also found the e ective and 1.0 mm. bandwidths of their instruments. Overlaid spectra of student-selected chromophores from Nearly all student spectrophotometers yielded a linear increase hand-built spectrophotometers and a Cary 50 spectrophotom- in absorbance with increasing concentration of chromophore eter are shown in Figure 2. It can be seen in this figure that the (Figure 1), although sensitivity varied (Figure S3). Hand-built

Figure 2. Overlaid visible absorbance spectra acquired by students of Figure 1. Calibration curve of indigo carmine (top) and cobalt(II) malachite green (top) and methyl orange (bottom). Error bars for chloride (bottom) generated by students using a Varian Cary 50 student instrument-derived data show one standard deviation based on spectrophotometer (circles) and their own hand-built spectrophotom- multiple measurements (n = 2 for malachite green, top, and n = 3 for eters (squares). The sensitivities achieved were 63% (top) and 48% methyl orange, bottom). Reproduced with permission. (bottom) of the sensitivity obtained using the Cary 50 spectrophotometer. R2 values obtained with student instruments were 0.99 (top) and 0.98 (bottom). Error bars for hand-built instrument data are total number of spectral points acquired varied depending on the presented where available and represent one standard deviation (n =3, width of the dispersed visible light and the ability to finely control bottom). Reproduced with permission. wavelength selection (e.g., length of lever for a rotating element). This performance task proved more challenging than obtaining a calibration curve at a single wavelength. Spectrophotometer performance in acquiring spectra depended on four factors: stray photometers and spectrophotometers have proven to be fairly light, effective bandwidth, wavelength calibration, and mechan- robust in that regard, both in our experience and for previously ical stability of instrument construction. High levels of stray light 2 reported instruments. R values for linear regressions have or a lack of a sufficiently narrow effective bandwidth led to poor typically been >0.9, and in some cases >0.98. Figure 1 shows two absorbance response (∼10−15% compared to a Cary 50 of the best student-produced calibration curves plotted with the spectrophotometer). Stray light in particular was a challenge in corresponding curve produced using a Varian Cary 50 the early iterations of this project, when dark voltage was spectrophotometer. measured with the light source off. See Figure S3 for a The effective bandwidths of the hand-built spectrophotom- representative spectrum and calibration curve. Dramatic eters in the 2010 and 2012 cohorts was determined by using a improvement was observed when dark voltage was measured linear regression of wavelength calibration data to determine the instead with the light source on using an opaque cuvette. Finally, average inverse dispersion according to physical construction of a mechanically robust instrument was a

47 DOI: 10.1021/acs.jchemed.6b00515 J. Chem. Educ. 2017, 94, 44−51 Journal of Chemical Education Article

Table 3. Items on the UV−Vis Spectrophotometry Assessment Instrument and Project Activities Designed To Address Each Topic, as Applicable

Item Primary Learning Goal Question Type Task within Project 1 Principle of molecular absorbance Identification of phenomena on Jablonski diagram none 2−3 Beer’s Law, path length and molar Beer’s Law calculations and concept question testing none absorptivity understanding of relationships in Beer’s Law 4 Transmittance and absorbance Transmittance/absorbance conversions Students converted raw voltage data from instruments to absorbance 5−6 Ideal absorbance working range Concept question on underlying reason for ideal working none absorbance range 7−8 Sensitivity and range Identification of calibration curve with greatest sensitivity and Students determined sensitivity and range of linear range instruments 9−10 Instrumental reasons for differences in Free response question asking for possible instrumental Part of student analysis of and revision of sensitivity and range causes of low sensitivity and poor linear range instruments 11 Identification of instrument Labeling of components indicated on an unlabeled simplified Designing and building instrument; producing components from schematic drawing instrument schematic schematic drawings of instrument 12 Alternative designs of Free response question asking for alternative Designing and building instrument; exposure to spectrophotometers spectrophotometer designs other hand-built spectrophotometers 13 Diffraction grating properties Concept question on relationships between line spacing and Evaluating different dispersive elements light dispersion challenge, particularly when components such as mirrors and colored LEDs or laser pointers in a way that was consistent with lenses could not be permanently mounted due to the need to the white light source proved to be an intractable problem for recover and reuse them at the end of the project. Slight changes many instrument designs. Acceptable calibration was typically λ in the angle of a mirror or slight hysteresis in the wavelength achieved by determining max values of several chromophore selection mechanism led to significant problems obtaining solutions and assigning the wavelength values by comparison reproducible results. Despite these challenges, several groups with spectra acquired using a Cary 50 spectrophotometer. obtained high-quality spectra using their hand-built instruments. In the absorbance spectrum of malachite green shown in the top ■ ASSESSMENT AND OUTCOMES panel of Figure 2, wavelength calibration and reproducibility Assessment of the Spectrophotometer Project were very good, and the maximum absorbance recorded with the hand-built instrument was ∼70% that of the commercial The spectrophotometer project was assessed in a variety of ways; fi instrument. The spectrum of methyl orange shown in the nal instruments, logbooks, and presentations were all used as bottom panel of Figure 2 shows excellent absorbance response artifacts for evaluation. and wavelength calibration; however, there was large variation in Spectrophotometers were assessed directly by the course fi absorbance response from trial to trial. instructor following nal submission for quality of design, Limits of detection were obtained using the following equation construction, performance, and user-friendliness (see rubric included in Supporting Information). Each student group ALOD=+As blank 3 (5) prepared a one-page instruction manual for their instrument. The instructor used each instrument to obtain a spectrum and where ALOD is the signal limit of detection, Ablank is the average calibration curve for solutions of thymol blue in methanol. While absorbance of the blank after a minimum of seven measurements, the resulting spectra and calibration curves were generally not and s is the standard deviation of the absorbance of a low- very different from student-reported results, this process was concentration sample after a minimum of seven measurements. valuable in other ways. It allowed first-hand evaluation of the For the blank measurements, a single initial measurement of Vd functionality of the spectrophotometer design, the robustness of and Vo were recorded and used for all other measurements of the construction, and the methods reported by students. In one case, blank. Limits of detection were reported ranging from ∼6−200× it revealed an error in data workup that had been consistently the corresponding limits of detection determined for the same made by a group of students. In another case, a spectropho- chromophore using a Cary 50 spectrophotometer. Limits of tometer proved to be impossible to operate with a single user. In λ detection determined for substances with max values >600 contrast, robust wavelength selection and convenience features typically yielded the best response compared to the commercial like sample compartment doors improved ease-of-use and instrument.Thisismostlikelyduetothewavelength reproducibility of results. dependence of the CdS LDRs, which are most sensitive at 520 Student log books were used as a measure of the process used nm, and which have significantly attenuated responses at short by students to arrive at their final spectrophotometer design (see visible wavelengths.32 rubric included in Supporting Information). Log books were Students used three basic strategies to calibrate the wavelength assessed after week 4 of the project to provide some formative scales of their spectrophotometers: a holmium oxide reference feedback as well as at the conclusion of the project. Log books λ cell, a series of solutions having max values across the visible were evaluated for the presence of detailed instrument region, or the use of colored LEDs or laser pointers. Of these schematics at each stage of construction and revision, as well as methods, the use of a series of colored solutions was both the a record of evidence-based decision-making throughout the most popular and the most universally practicable. While some design of the instrument. For example, one group compared the groups reported successful calibration using the holmium oxide performance of the LDR detectors with that of the photodiodes cell, many instruments did not have narrow enough effective experimentally, documenting the superior performance of the bandwidths or sufficiently small wavelength change increments LDRs in the visible range as justification for choosing the LDR to record its narrow absorbance bands. Likewise, aligning the for their instrument. Another group analyzed the angle of light

48 DOI: 10.1021/acs.jchemed.6b00515 J. Chem. Educ. 2017, 94, 44−51 Journal of Chemical Education Article into their exit slit at different wavelengths to justify a change in sketch an alternative to a provided spectrophotometer schematic, wavelength selection mechanism. Finally, log books contained achieving 88% correct responses for an item on which the pretest complete records of all data collected as well as the workup of had a 38% correct response rate. Significant improvement was data into spectra, calibration curves, and limits of detection. This also observed on items asking students to diagnose instrumental allowed the instructor to easily verify that students were correctly causes of limited sensitivity and range as well as assessing their collecting voltage outputs, converting them to absorbance values knowledge of instrument components. Although a significant and performing appropriate analysis. improvement in score was observed in an item asking students to Student presentations, initiated in the 2014 spectrophotom- convert between transmittance and absorbance, only a 38% eter project, served primarily as the venue for students to provide correct response rate was achieved in the post-test. We suspect a final analysis of the design and performance of their that groups assigned one member to handle most of the data spectrophotometers. This assessment was based on the students’ workup, so that other group members never engaged in that task. performance in identifying the strengths and weaknesses in their Instrument items not tied directly to project tasks but covered in instruments. Most critically, students were expected to analyze class (or in a previous course) experienced a more modest, and the instrumental reasons for performance limitations. generally not statistically significant, improvement. Evidence of Student Learning Student Engagement A 13-item UV−vis spectrophotometry assessment was admin- The spectrophotometer project generated a high level of student istered on the first day of class and readministered during final engagement each time it was implemented. In all cohorts, exam week for comparison. The assessment instrument was students and groups self-reported or were observed working on designed to address the learning outcomes of the project as well the project outside of the scheduled laboratory time, often for as aspects of UV−vis spectroscopy not specifically targeted in the many hours. This engagement also showed in the time and effort project. Different items assessed basic understanding of students devoted to making the final product attractive and user- molecular spectroscopy, skill with using the Beer−Lambert friendly, including painting/staining/decorating the outer cases Law, knowledge of instrument components, and knowledge of and including features such as a hinged lid for loading and overall spectrophotometer design (Table 3). The assessment unloading cuvettes. Students also reported believing the project instrument was not used in determining student grades beyond a to be beneficial to their understanding of UV−vis spectropho- small number of extra credit points for volunteering to complete tometry. The following comments were made by students about it. the project, and are reproduced anonymously here with Pre- and post-test results of the 13-item assessment instrument permission: are shown in Figure 3. The assessment was administered on the I feel the spectrophotometer project helped me learn how intricate spectrophotometer design must be to balance the inherent trade-offs of the instrument (such as dispersion vs light intensity). I now understand how spectrophotometers work at a much deeper level. This project taught me more about spectrophotometers than a class lecture ever could. I feel the spectrophotometer project helped me learn a lot more about UV−vis and how the components work individually as well as collectively. I sure am glad that I am not a spectrophotometer engineer, because that is a lot of components to have to worry about! I really enjoyed the spectrophotometer project. It gave me the hands on experience that every student should have before they graduate college as it was both mentally exhausting and exhilarating. It made me take what I had learned in class and apply it to a real-world scenario. I experienced the Figure 3. Pretest (gray) and post-test (black) correct response rates for frustrations that came with building and calibrating my own 12 students completing the spectrophotometer project in the 2014 fi instrument as well as the satisfaction of seeing something that Instrumental Analysis cohort. A single star indicates signi cant I had made work consistently and accurately. improvement in proportion of correct responses at the 90% C.I., I feel that the spectrophotometer project helped me learn the while a double star indicates a significant improvement at the 95% C.I. ’ importance of each different component that was picked and using the Fisher s Exact Test. Student assessment data shown here with ff permission. how by changing one thing it a ects the whole thing. I now understand what exactly it takes to make an instrument. I fi fi felt like this was a good experience because it made me rst day of class as well as during the nal exam period, 6 weeks realize how much work it is to run UV−vis by hand. I will after the end of the project. Twelve students took both the pre- fi not be mad or impatient at the Cary 50 in the lab with the and post-test. Students scored signi cantly higher on the post- time it takes to run the sample. test (70 ± 10%) than the pretest (42 ± 20%) as evaluated in R34 using a paired t test (p < 0.00005). The pre- and post-test Instrument Design as an Authentic Performance Task differences for individuals were normally distributed. In addition, There are many examples in recent literature of using hand-built an item-by-item analysis performed using the Fisher’s Exact instruments to demonstrate how photometers and spectropho- Test35 revealed that most of the significant gains occurred on tometers operate and to allow students to use these instruments items directly addressed in the spectrophotometer project (items in a hands-on fashion. However, most of these laboratory 4 and 9−13 in Table 3). Students largely used their own activities involve students assembling an instrument according to instrument designs to respond to an item asking students to an existing design, followed by the use of the instrument to make

49 DOI: 10.1021/acs.jchemed.6b00515 J. Chem. Educ. 2017, 94, 44−51 Journal of Chemical Education Article typical measurements to determine concentration or obtain a instructors with associated hazards, schematics or photo- kinetic rate constant. While this approach clearly and cleanly graphs of student-built instruments, student-generated addresses a limited set of content learning outcomes, its data showing the effects of stray light, the spectropho- limitations are similar to those of “cookbook” laboratory tometer assessment rubric, and the log book assessment activities. Students are able to follow the instructions and arrive rubric (PDF) at the correct result with little or only shallow engagement with the material and no opportunity for higher-order thinking such as ■ AUTHOR INFORMATION synthesis of knowledge and application of knowledge in a new Corresponding Author setting. * The approach described here is significantly different due to E-mail: [email protected]. the complexity of the task, the lack of specific instructions to get Present Address † to a solution, and the requirement for students to justify Division of Biological, Chemical and Environmental Sciences, decisions based on knowledge and evidence. Students Westminster College, 319 S. Market St., New Wilmington, PA independently synthesized and used knowledge presented in 16172, United States. class or gleaned from research to make design decisions such as Notes increasing optical path length to increase light dispersion, fi creating a closed compartment for the detector to prevent stray The authors declare no competing nancial interest. fi light from reaching it, and using a long lever to achieve ner ■ ACKNOWLEDGMENTS control of wavelengths passing through the exit slit. Students applied their knowledge to solve problems in unique and creative The authors acknowledge Mark Plano Clark for the ways, leading to as many spectrophotometer designs as there interdepartmental loan of materials, technical assistance, and were student groups, each addressing the same design challenges helpful discussions. The authors acknowledge Peggy Hart for differently. Often students drew on and used skills and talents advice on statistical analysis of assessment data. Purchase of from other arenas, such as wookworking, machining, or even just components was generously supported by the Doane College a talent for 3-D visualization. This approach also allowed for Chemistry Department. initial failures and subsequent analysis and revision, with an emphasis on process as well as outcome. Instrument perform- ■ REFERENCES ance was tested and used as evidence to track down the reasons (1) Bradley, I. Technical Note: Linearity Measurements in the Visible for the failure so that better solutions could be found. This Region on a LAMBDA 850/950/1050 Using Hellma Linearity Filters; process mimics the kinds of tasks students can expect to Perkin-Elmer, Inc.: Waltham, MA, 2009. https://www.perkinelmer. encounter in the workforce, and prepares them by developing com/lab-solutions/resources/docs/TCH_ “ ” LinearityMeasurementsLAMBDAHellmaFilters.pdf (accessed Sep soft skills like critical thinking, problem solving, and working 2016). collaboratively. 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51 DOI: 10.1021/acs.jchemed.6b00515 J. Chem. Educ. 2017, 94, 44−51