Authentic Performance in the Instrumental Analysis Laboratory

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

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classrooms from the high school level to the upper-division undergraduate level.3−23 The purpose of such instruments is to (1) demystify the “black box” of spectroscopic instrumentation by providing instruments with components that can be seen and manipulated and (2) provide instruments for students to use at a reduced cost compared to commercially available options. These hand-built instruments have varied widely in design from simple LED → sample → light detector photometers7−9,11−18 to diodearray-like cell-phone spectrophotometers,3,19,20 dual beam instruments with lock-in detection,10 and scanning instruments incorporating monochromators.4−6,21−23 Likewise, they vary widely in construction materials from salt shakers and digital picture frames3 to 3-D printed construction14,17,19 and sophisticated circuitry.10−12,21,22 Hand-built spectrophotometers have largely been presented as short-term projects for instructors or students to build from provided instructions and use to make absorbance or simple kinetics measurements.3−14,16 In a few cases, students were asked to perform critical analysis of the performance of specific components or the overall instrumental design.15−23 In several projects, students explored the effects of altering individual components of the instrument, such as the light source, grating, or detector, on overall instrument performance.16−19 Scheeline had students choose important placement parameters for instrument components to help them understand the fundamental origins of limitations in instrument performance, such as stray light versus light throughput.20 Similarly, the

odern UV−vis spectroscopy instrumentation continues to evolve, becoming more capable, robust, and userfriendly with each generation. Spectrophotometers are now produced that can operate from the UV through the NIR wavelength range, read up to eight absorbance units, and achieve better than 0.05 nm resolution.1,2 These and other advances make UV−vis−NIR spectroscopy, already a widely applied analysis technique, useful for an expanded range of applications, and therefore even more important for future scientists to understand. Unfortunately, one side effect of advances in spectrophotometer design has been to make the internal construction and operation of these instruments more of a “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 without risking damage to an expensive instrument. This trend has been extended to the software as well. Modern software often defaults to settings such as “speed of scan” or “resolution” without indicating what instrumental parameters are adjusted with the different options. There is often no direct way to change hardware settings such as slit width. User-friendly software also performs much of the data analysis automatically, particularly for common applications such as water quality analysis and protein or DNA/RNA analysis. Thus, improvements in UV−vis instrumentation have made teaching and learning these instruments in a hands-on way more challenging. As instruments have become more difficult to examine and manipulate directly, do-it-yourself spectrophotometers have become increasingly popular as a way to introduce students to this important instrumental method. A variety of hand-built visible single- or multiple-color colorimeters and spectrophotometers have been reported in the literature for use in © XXXX American Chemical Society and Division of Chemical Education, Inc.

Received: July 12, 2016 Revised: October 17, 2016

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DOI: 10.1021/acs.jchemed.6b00515 J. Chem. Educ. XXXX, XXX, XXX−XXX

Journal of Chemical Education

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SpecUP is a spectrophotometer kit that students assemble.22 Students choose the placements of different components in the optical path to optimize the experimental results. A different level of student engagement occurs when students design and build instruments themselves. Tavener and ThomasOates help students build a photometer and then ask them to design and build a working spectrophotometer.21 Likewise, Wang et al. designed a four-week guided inquiry project to introduce the principles of spectroscopy and allow students to design, build, and test a submersible photometer.15 Recently, Bougot-Robin et al. reported a problem-based learning course in which students used materials provided to build and optimize the performance of spectrophotometers.23 These projects are examples of authentic performance tasks, in which students must apply knowledge to a complex task in order to produce a tangible product.24−26 The products in these cases are an optimized instrument and the performance data that demonstrate its capabilities. Authentic performance tasks frame large problems in “realworld”-like contexts.24−27 Students are responsible for dividing a large and complex goal into small subproblems and applying their knowledge to solve them. The outcome of an authentic performance task is a finished product that reflects not only the body of knowledge a student has acquired, but also the student’s ability to transfer and apply that knowledge in context. The final outcome need not be a single “correct” solution, but can be a range of solutions incorporating a diversity of perspectives, creativity, and innovation. Authentic assessment tasks directly address the “Integrative and Applied Learning” learning outcome for undergraduates published by the Liberal Education and America’s Promise (LEAP) initiative in 2007.28 This is defined in the report as (ref 15, p 7): synthesis and advanced accomplishment...demonstrated through the application of knowledge, skills, and responsibilities to new settings and complex problems. In the authentic performance task reported here, students designed and built a visible spectrophotometer, determined its performance and performance limitations, and revised and optimized their design. The emphasis was for students to combine a knowledge set gained in classroom study of UV−vis instrumentation, performance data, and available literature on 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 performance. In this project students demonstrated their knowledge of spectrophotometer components and design as well as their many technical and creative talents.

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lecture/discussion course in which the principles and instrumentation of UV−vis spectroscopy were discussed. Early iterations of the project were carried out in 2010 and 2012; it is the 2014 project that we will primarily describe here. Spectrophotometer Assignment

According to a recent work by Frey et al.,27 some of the key features of an authentic performance assessment are that it is realistic and cognitively complex, that it includes formative assessment, that it requires a defense of the final product or answer, that it is collaborative, and that multiple measures are used to evaluate it. In the spectrophotometer project, student groups (2−3 students) acted as research and development teams for a start-up instrument manufacturer developing an inexpensive visible spectrophotometer for simple applications. Students were provided with a range of choices of light sources, detectors, dispersion elements, lenses, and mirrors, all necessary circuit components, and multimeters, as well as a range of construction materials and a budget of $20. See Table S1 in Supporting Information for a list of components provided. They were given a list of desirable performance characteristics (Table 1). This project is cognitively complex and collaborative, Table 1. Performance Characteristics for Hand-Built Spectrophotometers Specified in the Project Assignment with Method for Assessing Each Characteristic Performance Characteristic Adjustable wavelength in visible region Acquisition of absorbance spectrum of chromophore (absorbance characteristics, wavelength calibration) Linear absorbance vs concentration response Reproducible

User-friendly Detection limit

Linear range

Assessment Method Visual, movement of rainbow across exit slit Comparison with spectrum acquired for same sample using Cary 50 spectrophotometer Linear calibration curve of chromophore Multiple student-generated measurements and instructorgenerated measurements Instructor measurements using instrument Student determination of detection limit compared to Cary 50 detection limit Student determination of linear range compared to Cary 50 linear range

requiring students to work together to break a large project down into discrete and manageable steps and address these steps by applying knowledge gained in the classroom and from other sources. On the first day of the project, students individually built a light-detection circuit and made a simple photometer with guidance from the instructor.21 By the end of day one, every student had produced a working photometer. The photometers were used to practice converting the voltage output of the detector circuit to % transmittance and absorbance values according to

THE SPECTROPHOTOMETER PROJECT

Cohort and Course Context

The purpose of this work is not to describe a hand-built spectrophotometer, which has been done by others, but to describe how we have used hand-built instrument design and construction as a deep learning experience through authentic performance pedagogy. The spectrophotometer project was conducted in a 300-level Instrumental Analysis laboratory course at Doane College, a small liberal arts college in rural Nebraska. Students enrolled in this alternate-year course are primarily Junior and Senior Chemistry and Biochemistry majors (three cohorts of 9−14 students from 2010 to 2014). The 3 h laboratory session met once per week, complementing a traditional 50 min

%T =

(V − Vd) × 100 (Vo − Vd)

A = −log T

(1) (2)

where T is transmittance, A is absorbance, V is the output voltage from the detector circuit for the sample of interest, Vo is the output voltage for a blank, and Vd is the “dark” output voltage in B



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which the optical path at the sample holder is blocked with opaque material. Weeks 2−4 of the project were devoted to designing, building, calibrating, and testing the performance of the spectrophotometers. Measurable milestones served as formative feedback as parts of the optical train were assembled and, later, as absorbance measurements were obtained. For example, the first challenge faced by all groups was choosing dispersion elements and aligning them with light sources, entrance slits, and collimating lenses to produce rainbows. The outcome required was the production of a high-intensity and well-dispersed visible spectrum of light. By week 4, groups produced a functional spectrophotometer including a spectrum and calibration curve of a chromophore of their choice. They analyzed their performance data to improve upon their instrument designs in weeks 5−7, and documented their success with a second round of performance testing. The final products of the spectrophotometer project were the instrument and performance data obtained with it. Each student also kept a logbook to record detailed schematics of their spectrophotometer, evidence used in making design decisions, raw and worked-up data, and analysis of spectrophotometer performance. Finally, each group presented their design to the “upper-management” of the fictitious company in which they presented an analysis of their design and its performance characteristics.29−31 These served as multiple measures of student performance in this project.

Table 2. Summary of Components, Mechanism of Wavelength Selection, and Construction Materials Used in the Spectrophotometers of Six Individuals and Groups Group/ Individual

Optical elements

A

White LED Transmission grating Convex lenses Planar mirror Exit slit White LED Entrance slit DVD Convex lenses Rotating planar mirror White LED

B

C

D

E

Spectrophotometer Design

Instrument designs bore several similarities across groups and individuals. These similarities were imposed by general spectrophotometer design principles as well as the range of materials available. Students typically chose to use DVDs or 1000 line/mm transmission gratings to maximize light dispersion, although some used CDs or 500 line/mm transmission gratings to yield greater light throughput at the cost of resolution. Students universally chose to use the CdS LDR detectors over photodiodes, citing from experimental evidence, vendor specifications, or literature research the greater sensitivity of the LDR in the visible region.18,32 Spectrophotometers typically included a convex lens to collimate light from the LED or entrance slit and a fixed exit slit/sample holder/detector assembly. Despite these general similarities, the designs varied widely in optical elements, optical path, instrument features, and construction. A characteristic feature of authentic performance assessments is that there are multiple ways to solve the problem. Each group and individual brings unique knowledge, skills, and background to the table, and the collaboration of individuals can produce new innovations. This is abundantly reflected in the spectrophotometers produced through the project. A summary of the features of selected spectrophotometers is shown in Table 2. Schematics or photographs of spectrophotometers produced by individuals or teams of 2−3 students in Instrumental Analysis from 2010 to 2014 are shown in Figure S1. Some instruments used in-line optical paths with only transmission elements while others contained one or more reflective elements to increase optical path length/reduce the total bench footprint of the instrument (groups A and E, Figure S1). Some groups housed detectors in enclosures designed to minimize stray light (Figure S2A). Wavelength selection was achieved by rotating reflective gratings, rotating mirrors (Figure S2B), or moving the exit slit/sample holder/detector assembly

F

Transmission grating Convex lenses White LED Entrance slit CD Convex lenses Exit slit 100 W light bulb Adjustable entrance slit Transmission grating Convex lenses Exit slit 100 W light bulb Entrance slit Transmission grating Convex lenses Exit slit

Wavelength Selection

Construction

Rotation of planar mirror

LEGO bricks

Rotation of planar mirror

PVC pipe

Linear movement of sample/ detector assembly

Wood/PVC pipe

Rotation of CD

LEGO bricks


Wood


Metal mailbox

across the visible spectrum. One group lined the light source housing with mirrors to increase light output (Figure S2C), a concept similar to that used by Perkin-Elmer in the construction of its high-end spectrophotometers.33 Special features included doors for easy access to the sample holder, a nut-and-bolt assembly for reproducible wavelength adjustment (Figure S2D), and a variable entrance slit size (Figure S2C). Construction strategies varied widely as well and included LEGO bricks, PVC pipe housing, wood, or combinations of materials. Students in the 2010 and 2012 cohorts were not provided with sample designs, although they were free to do their own research. One advantage of not providing ideas is the creative designs that emerge, such as the highly unique mailbox-housed spectrophotometer (individual F, Figure S1). Some students from these cohorts struggled to produce a functional design without initial design guidance; however, this may have been alleviated by allowing collaboration as in 2014. Students in the 2014 cohort were provided with a selection of literature articles from which to generate initial ideas.4,5,10,18,20 Although at least four out of five groups started with one of these or an independently researched alternative source, all groups ultimately arrived at unique designs. For example, group B enclosed their optical train in PVC pipe C



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based on an Internet resource, but incorporated a rotating mirror rather than a set of fixed mirror positions to expand their wavelength sampling (Figure S1). Group C initially attempted to reflect light into their sample from a rotating mirror as in Knagge and Raftery,5 but encountered problems with the angle of light into their exit slit. Ultimately they used a slit/sample/detector assembly and moved it linearly across their dispersed rainbow for wavelength selection.

D−1 =

Δλ Δx

(3)

where D−1 is inverse dispersion, Δλ is the change in wavelength, and Δx is the change in position along the dispersed visible light. While we are aware that light dispersion is not linear, it served as a good approximation for our purposes. Inverse dispersion was multiplied by exit slit width to yield effective bandwidth BWeff = D−1w

Student-Generated Results

In order to evaluate the performance of their spectrophotometers, students made solutions of available chromophores (Table S2). They acquired visible absorbance spectra of a chromophore solution, constructed a calibration curve, and determined the limit of detection (LOD). Some cohorts also found the effective bandwidths of their instruments. Nearly all student spectrophotometers yielded a linear increase in absorbance with increasing concentration of chromophore (Figure 1), although sensitivity varied (Figure S3). Hand-built

(4)

where BWeff is effective bandwidth, in nanometers, of light going through the exit slit and w is the exit slit width. Effective bandwidths were between 3.2 and 8.4 nm for student spectrophotometers, with slit widths generally between 0.25 and 1.0 mm. Overlaid spectra of student-selected chromophores from hand-built spectrophotometers and a Cary 50 spectrophotometer are shown in Figure 2. It can be seen in this figure that the

Figure 2. Overlaid visible absorbance spectra acquired by students of malachite green (top) and methyl orange (bottom). Error bars for student instrument-derived data show one standard deviation based on multiple measurements (n = 2 for malachite green, top, and n = 3 for methyl orange, bottom). Reproduced with permission.

Figure 1. Calibration curve of indigo carmine (top) and cobalt(II) chloride (bottom) generated by students using a Varian Cary 50 spectrophotometer (circles) and their own hand-built spectrophotometers (squares). The sensitivities achieved were 63% (top) and 48% (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 presented where available and represent one standard deviation (n = 3, bottom). Reproduced with permission.

total number of spectral points acquired varied depending on the width of the dispersed visible light and the ability to finely control 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 light, effective bandwidth, wavelength calibration, and mechanical stability of instrument construction. High levels of stray light or a lack of a sufficiently narrow effective bandwidth led to poor absorbance response (∼10−15% compared to a Cary 50 spectrophotometer). Stray light in particular was a challenge in the early iterations of this project, when dark voltage was measured with the light source off. See Figure S3 for a representative spectrum and calibration curve. Dramatic improvement was observed when dark voltage was measured instead with the light source on using an opaque cuvette. Finally, physical construction of a mechanically robust instrument was a

photometers and spectrophotometers have proven to be fairly robust in that regard, both in our experience and for previously reported instruments. R2 values for linear regressions have typically been >0.9, and in some cases >0.98. Figure 1 shows two of the best student-produced calibration curves plotted with the corresponding curve produced using a Varian Cary 50 spectrophotometer. The effective bandwidths of the hand-built spectrophotometers in the 2010 and 2012 cohorts was determined by using a linear regression of wavelength calibration data to determine the average inverse dispersion according to D



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Table 3. Items on the UV−Vis Spectrophotometry Assessment Instrument and Project Activities Designed To Address Each Topic, as Applicable Item 1 2−3

Primary Learning Goal

Question Type

Task within Project

4

Principle of molecular absorbance Beer’s Law, path length and molar absorptivity Transmittance and absorbance

Identification of phenomena on Jablonski diagram Beer’s Law calculations and concept question testing understanding of relationships in Beer’s Law Transmittance/absorbance conversions

5−6

Ideal absorbance working range

7−8

Sensitivity and range

9−10

Instrumental reasons for differences in sensitivity and range Identification of instrument components from schematic drawing Alternative designs of spectrophotometers Diffraction grating properties

Concept question on underlying reason for ideal working absorbance range Identification of calibration curve with greatest sensitivity and linear range Free response question asking for possible instrumental causes of low sensitivity and poor linear range Labeling of components indicated on an unlabeled simplified instrument schematic Free response question asking for alternative spectrophotometer designs Concept question on relationships between line spacing and light dispersion

11 12 13

Students converted raw voltage data from instruments to absorbance none Students determined sensitivity and range of instruments Part of student analysis of and revision of instruments Designing and building instrument; producing schematic drawings of instrument Designing and building instrument; exposure to other hand-built spectrophotometers Evaluating different dispersive elements

colored LEDs or laser pointers in a way that was consistent with the white light source proved to be an intractable problem for many instrument designs. Acceptable calibration was typically achieved by determining λmax values of several chromophore solutions and assigning the wavelength values by comparison with spectra acquired using a Cary 50 spectrophotometer.

challenge, particularly when components such as mirrors and lenses could not be permanently mounted due to the need to recover and reuse them at the end of the project. Slight changes in the angle of a mirror or slight hysteresis in the wavelength selection mechanism led to significant problems obtaining reproducible results. Despite these challenges, several groups obtained high-quality spectra using their hand-built instruments. In the absorbance spectrum of malachite green shown in the top panel of Figure 2, wavelength calibration and reproducibility were very good, and the maximum absorbance recorded with the hand-built instrument was ∼70% that of the commercial instrument. The spectrum of methyl orange shown in the bottom panel of Figure 2 shows excellent absorbance response and wavelength calibration; however, there was large variation in absorbance response from trial to trial. Limits of detection were obtained using the following equation ALOD = A blank + 3s

none none

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ASSESSMENT AND OUTCOMES

Assessment of the Spectrophotometer Project

The spectrophotometer project was assessed in a variety of ways; final instruments, logbooks, and presentations were all used as artifacts for evaluation. Spectrophotometers were assessed directly by the course instructor following final submission for quality of design, construction, performance, and user-friendliness (see rubric included in Supporting Information). Each student group prepared a one-page instruction manual for their instrument. The instructor used each instrument to obtain a spectrum and calibration curve for solutions of thymol blue in methanol. While the resulting spectra and calibration curves were generally not very different from student-reported results, this process was valuable in other ways. It allowed first-hand evaluation of the functionality of the spectrophotometer design, the robustness of construction, and the methods reported by students. In one case, it revealed an error in data workup that had been consistently made by a group of students. In another case, a spectrophotometer proved to be impossible to operate with a single user. In contrast, robust wavelength selection and convenience features like sample compartment doors improved ease-of-use and reproducibility of results. Student log books were used as a measure of the process used by students to arrive at their final spectrophotometer design (see rubric included in Supporting Information). Log books were assessed after week 4 of the project to provide some formative feedback as well as at the conclusion of the project. Log books were evaluated for the presence of detailed instrument schematics at each stage of construction and revision, as well as a record of evidence-based decision-making throughout the design of the instrument. For example, one group compared the performance of the LDR detectors with that of the photodiodes experimentally, documenting the superior performance of the LDRs in the visible range as justification for choosing the LDR for their instrument. Another group analyzed the angle of light

(5)

where ALOD is the signal limit of detection, Ablank is the average absorbance of the blank after a minimum of seven measurements, and s is the standard deviation of the absorbance of a lowconcentration sample after a minimum of seven measurements. For the blank measurements, a single initial measurement of Vd and Vo were recorded and used for all other measurements of the blank. Limits of detection were reported ranging from ∼6−200× the corresponding limits of detection determined for the same chromophore using a Cary 50 spectrophotometer. Limits of detection determined for substances with λmax values >600 typically yielded the best response compared to the commercial instrument. This is most likely due to the wavelength dependence of the CdS LDRs, which are most sensitive at 520 nm, and which have significantly attenuated responses at short visible wavelengths.32 Students used three basic strategies to calibrate the wavelength scales of their spectrophotometers: a holmium oxide reference cell, a series of solutions having λmax values across the visible region, or the use of colored LEDs or laser pointers. Of these methods, the use of a series of colored solutions was both the most popular and the most universally practicable. While some groups reported successful calibration using the holmium oxide cell, many instruments did not have narrow enough effective bandwidths or sufficiently small wavelength change increments to record its narrow absorbance bands. Likewise, aligning the E



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into their exit slit at different wavelengths to justify a change in wavelength selection mechanism. Finally, log books contained complete records of all data collected as well as the workup of data into spectra, calibration curves, and limits of detection. This allowed the instructor to easily verify that students were correctly collecting voltage outputs, converting them to absorbance values and performing appropriate analysis. Student presentations, initiated in the 2014 spectrophotometer project, served primarily as the venue for students to provide a final analysis of the design and performance of their spectrophotometers. This assessment was based on the students’ performance in identifying the strengths and weaknesses in their instruments. Most critically, students were expected to analyze the instrumental reasons for performance limitations.

sketch an alternative to a provided spectrophotometer schematic, achieving 88% correct responses for an item on which the pretest had a 38% correct response rate. Significant improvement was also observed on items asking students to diagnose instrumental causes of limited sensitivity and range as well as assessing their knowledge of instrument components. Although a significant improvement in score was observed in an item asking students to convert between transmittance and absorbance, only a 38% correct response rate was achieved in the post-test. We suspect that groups assigned one member to handle most of the data workup, so that other group members never engaged in that task. Instrument items not tied directly to project tasks but covered in class (or in a previous course) experienced a more modest, and generally not statistically significant, improvement.

Evidence of Student Learning

Student Engagement

A 13-item UV−vis spectrophotometry assessment was administered on the first day of class and readministered during final exam week for comparison. The assessment instrument was designed to address the learning outcomes of the project as well as aspects of UV−vis spectroscopy not specifically targeted in the project. Different items assessed basic understanding of molecular spectroscopy, skill with using the Beer−Lambert Law, knowledge of instrument components, and knowledge of overall spectrophotometer design (Table 3). The assessment instrument was not used in determining student grades beyond a small number of extra credit points for volunteering to complete it. Pre- and post-test results of the 13-item assessment instrument are shown in Figure 3. The assessment was administered on the

The spectrophotometer project generated a high level of student engagement each time it was implemented. In all cohorts, students and groups self-reported or were observed working on the project outside of the scheduled laboratory time, often for many hours. This engagement also showed in the time and effort students devoted to making the final product attractive and userfriendly, including painting/staining/decorating the outer cases and including features such as a hinged lid for loading and unloading cuvettes. Students also reported believing the project to be beneficial to their understanding of UV−vis spectrophotometry. The following comments were made by students about the project, and are reproduced anonymously here with permission: 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 frustrations that came with building and calibrating my own instrument as well as the satisfaction of seeing something that I had made work consistently and accurately. I feel that the spectrophotometer project helped me learn the importance of each different component that was picked and how by changing one thing it affects the whole thing. I now understand what exactly it takes to make an instrument. I felt like this was a good experience because it made me realize how much work it is to run UV−vis by hand. I will not be mad or impatient at the Cary 50 in the lab with the time it takes to run the sample.

Figure 3. Pretest (gray) and post-test (black) correct response rates for 12 students completing the spectrophotometer project in the 2014 Instrumental Analysis cohort. A single star indicates significant improvement in proportion of correct responses at the 90% C.I., while a double star indicates a significant improvement at the 95% C.I. using the Fisher’s Exact Test. Student assessment data shown here with permission.

first day of class as well as during the final exam period, 6 weeks after the end of the project. Twelve students took both the preand post-test. Students scored significantly higher on the posttest (70 ± 10%) than the pretest (42 ± 20%) as evaluated in R34 using a paired t test (p < 0.00005). The pre- and post-test differences for individuals were normally distributed. In addition, an item-by-item analysis performed using the Fisher’s Exact Test35 revealed that most of the significant gains occurred on items directly addressed in the spectrophotometer project (items 4 and 9−13 in Table 3). Students largely used their own instrument designs to respond to an item asking students to

Instrument Design as an Authentic Performance Task

There are many examples in recent literature of using hand-built instruments to demonstrate how photometers and spectrophotometers operate and to allow students to use these instruments in a hands-on fashion. However, most of these laboratory activities involve students assembling an instrument according to an existing design, followed by the use of the instrument to make F



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typical measurements to determine concentration or obtain a kinetic rate constant. While this approach clearly and cleanly addresses a limited set of content learning outcomes, its limitations are similar to those of “cookbook” laboratory activities. Students are able to follow the instructions and arrive at the correct result with little or only shallow engagement with the material and no opportunity for higher-order thinking such as synthesis of knowledge and application of knowledge in a new setting. The approach described here is significantly different due to the complexity of the task, the lack of specific instructions to get to a solution, and the requirement for students to justify decisions based on knowledge and evidence. Students independently synthesized and used knowledge presented in class or gleaned from research to make design decisions such as increasing optical path length to increase light dispersion, creating a closed compartment for the detector to prevent stray light from reaching it, and using a long lever to achieve finer control of wavelengths passing through the exit slit. Students applied their knowledge to solve problems in unique and creative ways, leading to as many spectrophotometer designs as there were student groups, each addressing the same design challenges differently. Often students drew on and used skills and talents from other arenas, such as wookworking, machining, or even just a talent for 3-D visualization. This approach also allowed for initial failures and subsequent analysis and revision, with an emphasis on process as well as outcome. Instrument performance was tested and used as evidence to track down the reasons for the failure so that better solutions could be found. This process mimics the kinds of tasks students can expect to encounter in the workforce, and prepares them by developing “soft skills” like critical thinking, problem solving, and working collaboratively. Finally, completion of the project involved not only a functional instrument, but also an explicit record of how knowledge of spectroscopy, spectrophotometer design, and instrumental components led to the final product. This record, as well as other assessments, served as evidence of learning.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Present Address †

Division of Biological, Chemical and Environmental Sciences, Westminster College, 319 S. Market St., New Wilmington, PA 16172, United States. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors acknowledge Mark Plano Clark for the interdepartmental loan of materials, technical assistance, and helpful discussions. The authors acknowledge Peggy Hart for advice on statistical analysis of assessment data. Purchase of components was generously supported by the Doane College Chemistry Department.

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REFERENCES

(1) Bradley, I. Technical Note: Linearity Measurements in the Visible Region on a LAMBDA 850/950/1050 Using Hellma Linearity Filters; Perkin-Elmer, Inc.: Waltham, MA, 2009. https://www.perkinelmer. com/lab-solutions/resources/docs/TCH_ LinearityMeasurementsLAMBDAHellmaFilters.pdf (accessed Sep 2016). (2) Padera, F. Application Note: High Resolution Scanning Performance with the PerkinElmer LAMBDA 1050; PerkinElmer, Inc.: Waltham, MA, 2011. https://www.perkinelmer.com/lab-solutions/resources/docs/ APP_LAMBDA_Scanning_Performance.pdf (accessed Sep 2016). (3) Quagliano, J. M.; Marks, C. A. Demystifying Spectroscopy with Secondary Students: Designing and Using a Custom-Built Spectrometer. J. Chem. Educ. 2013, 90 (10), 1409−1410. (4) Albert, D. R.; Todt, M. A.; Davis, H. F. A Low-Cost Quantitative Absorption Spectrophotometer. J. Chem. Educ. 2012, 89 (11), 1432− 1435. (5) Knagge, K.; Raftery, D. Construction and Evaluation of a LEGO Spectrophotometer for Student Use. Chem. Educ. 2002, 7 (6), 371−375. (6) Lema, M. A.; Aljinovic, E. M.; Lozano, M. E. Using a Homemade Spectrophotometer in Teaching Biosciences. Biochem. Mol. Biol. Educ. 2002, 30 (2), 106−110. (7) Delgado, J.; Quintero-Ortega, I. A.; Vega-Gonzalez, A. From Voltage to Absorbance and Chemical Kinetics Using a Homemade Colorimeter. J. Chem. Educ. 2014, 91 (12), 2158−2162. (8) Kvittingen, E. V.; Kvittingen, L.; Sjursnes, B. J.; Verley, R. Simple and Inexpensive UV-Photometer Using LEDs as Both Light Source and Detector. J. Chem. Educ. 2016, 93, 1814. (9) Clippard, C. M.; Hughes, W.; Chohan, B. S.; Sykes, D. G. Construction and Characterization of a Compact, Portable, Low-Cost Colorimeter for the Chemistry Lab. J. Chem. Educ. 2016, 93 (7), 1241− 1248. (10) Hamilton, J. R.; White, J. S.; Nakhleh, M. B. Development of a Low-Cost Four-Color LED Photometer. J. Chem. Educ. 1996, 73 (11), 1052−1054. (11) Matsuo, T.; Muromatsu, A.; Katayama, K.; Mori, M. Construction of a Photoelectric Colorimeter and Application to Students’ Experiments. J. Chem. Educ. 1989, 66 (4), 329−333. (12) Matsuo, T.; Muromatsu, A.; Katayama, K.; Mori, M. Construction of a Photoelectric Colorimeter and Application to Students’ Experiments (Part 2). J. Chem. Educ. 1989, 66 (10), 848−851.

Project Extension

While the students in Instrumental Analysis had little to no programming experience, our long-term goal is to incorporate programming to automate absorbance measurements using the student instruments. This could be done, for example, using an Arduino.36 All modern spectrophotometric instrumentation incorporates software to convert raw detector output to transmittance and absorbance values. Instrumental Analysis students would need to understand how to process raw voltage data from samples, blanks, and dark readings to produce % transmittance and absorbance values in order to program these functions. Ambitious students might also seek to include userfriendly “bells and whistles” such as automated absorbance to concentration computation, automatic generation of calibration curves, calculation of detection limits, or automated kinetic measurements. In each case, students would need to demonstrate facility with these skills in order to plan and execute a successful program.

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instructors with associated hazards, schematics or photographs of student-built instruments, student-generated data showing the effects of stray light, the spectrophotometer assessment rubric, and the log book assessment rubric (PDF)

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.6b00515. List of spectrophotometer components provided to students, a list of chromophores used by students and G



Article

(35) McDonald, J. H. Handbook of Biological Statistics, 3rd ed.; Sparky House Publishing: Baltimore, MD, 2014. (36) Arduino Home Page. https://www.arduino.cc/ (accessed Sep 2016).

(13) Asheim, J.; Kvittingen, E. V.; Kvittingen, L.; Verley, R. A Simple, Small-Scale Lego Colorimeter with a Light-Emitting Diode (LED) Used as Detector. J. Chem. Educ. 2014, 91 (7), 1037−1039. (14) Mendez, J. D. An Inexpensive 3D Printed Colorimeter. Chem. Educ. 2015, 20, 224−226. http://chemeducator.org/bibs/0020001/ 20150224.html (15) Wang, J. J.; Rodríguez Núñez, J. R.; Maxwell, E. J.; Algar, W. R. Build Your Own Photometer: A Guided-Inquiry Experiment To Introduce Analytical Instrumentation. J. Chem. Educ. 2016, 93 (1), 166−171. (16) Vanderveen, J. R.; Martin, B.; Ooms, K. J. Developing Tools for Undergraduate Spectroscopy: An Inexpensive Visible Light Spectrometer. J. Chem. Educ. 2013, 90 (7), 894−899. (17) Porter, L. A.; Washer, B. M.; Hakim, M. H.; Dallinger, R. F. UserFriendly 3D Printed Colorimeter Models for Student Exploration of Instrument Design and Performance. J. Chem. Educ. 2016, 93 (7), 1305−1309. (18) Thal, M. A.; Samide, M. J. Applied Electronics: Construction of a Simple Spectrophotometer. J. Chem. Educ. 2001, 78 (11), 1510−1512. (19) Grasse, E. K.; Torcasio, M. H.; Smith, A. W. Teaching UV−Vis Spectroscopy with a 3D-Printable Smartphone Spectrophotometer. J. Chem. Educ. 2016, 93 (1), 146−151. (20) Scheeline, A. Teaching, Learning, and Using Spectroscopy with Commercial, Off-the-Shelf Technology. Appl. Spectrosc. 2010, 64 (9), 256A−268A. (21) Tavener, S. J.; Thomas-Oates, J. Build Your Own Spectrophotometer. Educ. Chem. (London, U. K.) 2007, 151−154. http://www.rsc. org/education/eic/issues/2007Sept/ BuildYourOwnSpectrophotometer.asp (22) Forbes, P. B. C.; Nö t hling, J. A. Shedding Light on Spectrophotometry: The SpecUP Educational Spectrophotometer. S. Afr. J. Sci. 2014, 110 (1-2), 1−5. (23) Bougot-Robin, K.; Paget, J.; Atkins, S. C.; Edel, J. B. Optimization and Design of an Absorbance Spectrometer Controlled Using a Raspberry Pi To Improve Analytical Skills. J. Chem. Educ. 2016, 93 (7), 1232−1240. (24) Wiggins, G. The Case for Authentic Assessment. Pract. Assess. Res. Eval. 1990, 1−5. (25) Wiggins, G. P.; McTighe, J. Understanding by Design, Expanded, 2nd ed.; Association for Supervision and Curriculum Development: Alexandria, VA, 2005. (26) Mueller, J. The Authentic Assessment Toolbox: Enhacing Student Learning through Online Faculty Development. J. Online Learn. Teach. 2005, 1 (1). (27) Frey, B. B.; Schmitt, V. L.; Allen, J. P. Defining Authentic Classroom Assessment. Pract. Assess. Res. Eval. 2012, 17 (2), 1−18. (28) Liberal Education and America’s Promise (Program); Association of American Colleges and Universities. The LEAP Vision for Learning: Outcomes, Practices, Impact, and Employers’ Views; Association of American Colleges and Universities: Washington, DC, 2011. (29) Walters, J. P. Role-Playing Analytical Chemistry Laboratories. Part I: Structural and Pedagogical Ideas. Anal. Chem. 1991, 63 (20), 977A−985A. (30) Walters, J. P. Role-Playing Analytical Chemistry Laboratories. Part II: Physical Resources. Anal. Chem. 1991, 63 (22), 1077A−1087A. (31) Walters, J. P. Role-Playing Analytical Chemistry Laboratories. Part III: Experiment Objectives and Design. Anal. Chem. 1991, 63 (24), 1179A−1191A. (32) Technical Datasheet: CdS Photoconductive Photocells; Advanced Photonix, Inc.: Camarillo, CA, 2006. http://www.advancedphotonix. com/wp-content/uploads/PDV-P9203.pdf (accessed Sep 2016). (33) Technical Specifications for the LAMBDA 1050 UV/Vis/NIR and LAMBDA 950 UV/Vis/NIR Spectrophotometers; PerkinElmer, Inc.: Waltham, MA, 2007. http://camcor.uoregon.edu/site/wp-content/ uploads/2012/11/Lambda-1050-spec.pdf (accessed Sep 2016). (34) R Core Team. R: A Language and Environment for Statistical Computing; R Foundation for Statistical Computing: Vienna, Austria, 2013. H


Authentic Performance in the Instrumental Analysis Laboratory

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