In the Laboratory
Constructing a LabVIEW-Controlled HighPerformance Liquid Chromatography (HPLC) System: An Undergraduate Instrumental Methods Exercise Eugene T. Smith* and Marc Hill Harriet L. Wilkes Honors College, Florida Atlantic University, Jupiter, Florida 33458, United States *
[email protected] LabVIEW software for computer-assisted data acquisition is ubiquitous in academic and industrial laboratory settings (1). In the past decade, a number of chemical education articles have been published describing the use of LabVIEW in the general(2), analytical, and physical chemistry (3-5), and advanced chemistry course curricula (6, 7). Articles have also described the incorporation of LabVIEW throughout the entire undergraduate chemistry sequence (8, 9). LabVIEW is considered an important tool for chemists, and many chemical educators rightfully feel that it is worth exposing students to this visual programming language. Nonetheless, using LabVIEW in the undergraduate laboratory does have drawbacks due to the time it takes for students to become proficient programmers. With this problem in mind, we developed a set of integrated exercises appropriate for an instrumental methods course that provides instructors with flexibility in incorporating LabVIEW instruction in the laboratory. Students develop a high-performance liquid chromatography (HPLC) system, suitable for large-scale separations, consisting of LabVIEW-controlled pumps, detector, and fraction collector. Experimental Overview Students working in small groups use different programming strategies for controlling and monitoring the various HPLC components, including serial control, analog-to-digital conversion, and digital input-output control. For example, the pumps are controlled through serial communication. Monitoring the signal from the detector involves a classic LabVIEW problem whereby an analog voltage is monitored. Acquiring an analog signal from an instrument is a fundamental application of LabVIEW, and nearly all the previous chemical education articles describe such an exercise (2-4, 6-10). Finally, a fraction collector is controlled using a simple circuit and digital output from a data aquisition (DAQ) device. It is explained to students that the fraction collector is used to collect samples eluting off of a chromatography column, such as proteins in a biochemical separation. This entire LabVIEW project can be completed in a single laboratory period if the various tasks (controlling the pump, acquiring the detector signal, and controlling the fraction collector) are assigned to individual groups. For each instrumental component, exercises can be broken down into manageable tasks with varying degrees of difficulty (see the supporting information for details). Thus, projects can be easily adapted to the ability of the student. The exercise provides great flexibility in the curriculum because the tasks can
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be completed through individually assigned projects that each student completes or as a class project whereby a small group of students are responsible for a given task. We typically carry out this exercise in a single laboratory period as a set of group projects. Toward the end of the laboratory period, the students explain their project to the rest of the class, and then they are shown how to incorporate their individual virtual instruments (VIs) into a single program. Students are graded on their LabVIEW program and oral presentation. If they cannot complete their task in the 3-h period, they are allowed to finish their program outside of the scheduled laboratory time. Although the integrated exercises are designed to cover as little as one lab period, the projects can be modified to span multiple weeks. In a more advanced exercise, students write a program for two pumps to generate a linear solvent gradient (see a partial block diagram illustrated in Figure 1). There are additional LabVIEW-based signal processing exercises that have also been described in the literature, including programming for ensemble and boxcar averaging (5) as well as peak detection and integration (11). We found that it requires an additional laboratory period for students to program a linear solvent gradient utilizing two HPLC pumps. Similarly, it takes an entire laboratory period to incorporate and debug all three VIs into a single operational program. We recognize that it is important for students to be able to demonstrate the functionality of an HPLC system they constructed. In the supporting information, we suggest two additional simple experiments that demonstrate both the generation of a solvent gradient and a preparatory-scale chromatography. Both of these exercises demonstrate tasks
Figure 1. Partial block diagram illustrating LabVIEW programming for an HPLC pump resulting in the formation of a linear gradient.
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r 2010 American Chemical Society and Division of Chemical Education, Inc. pubs.acs.org/jchemeduc Vol. 88 No. 3 March 2011 10.1021/ed100078k Published on Web 11/29/2010
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required of a preparatory-scale HPLC controller without significantly adding laboratory time. Discussion The exercise described in this article has the added advantage of exposing students to instrumentation involved in preparative-scale separations, which typically utilize fraction collectors. We developed the preparative-scale HPLC for future use in the biochemistry curriculum, where there is a need for inexpensive instrumentation with gradient-control capabilities for large-scale protein purification. The HPLC systems will run columns previously controlled by gravity or peristaltic pumps in the biochemistry labs, although some institutions may want to use the HPLC as a part of their instrumental methods laboratory. Most courses in instrumental methods, including ours, focus on analytical methods and, therefore, are likely to incorporate a laboratory exercise utilizing an analytical-scale HPLC. The overall cost for the preparative-scale HPLC system is about $14,000, including $4,000 for each pump (alternative programmable pumps under $2,000 are available from Lab Alliance). Although this is expensive for a single laboratory experiment, the HPLC system can be used for preparative-scale separations in other courses as discussed above, including organic and biochemistry laboratories. An integrated HPLC system capable of solvent gradients would be far more expensive, and with the system we describe, the individual components can be acquired over time as budgets allow. Alternatively, an isocratic single-pump system could be used in this assignment. We have also written LabVIEW programs to control peristaltic pumps through RS-232 ports. Thus, an integrated low-pressure LC system could be constructed with existing laboratory equipment for far less money. In our particular application, we utilize a group approach to generating a single LabVIEW program for controlling the entire HPLC in a single laboratory period. This laboratory exercise occurs at the beginning of the term to correspond to the lecture material on data acquisition and signal processing. Chromatographic methods, which have been used in other courses, are only briefly described so students understand the significance of their programming task. The handout found in the supporting information was developed with sufficiently detailed instructions to enable all of the subroutines to be completed in the allotted time of 3 h. Students are able to find various creative programming solutions to these exercises, and they are encouraged to do so. They typically need guidance with LabVIEW case structures for them to be able to successfully incorporate multiple subroutines into an integrated program. Most of the students have some experience in MatLab programming, and visual programming is a new experience for them. We typically do not obtain evaluations for individual laboratory exercises, so feedback from students was obtained by directly asking students about the exercise. On the basis of discussions with students, they enjoy the experience of controlling instrumentation through computers. Because of limited experience with LabVIEW, some students perceive visual programming as difficult.
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Vol. 88 No. 3 March 2011
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It is generally recognized by chemical educators, particularly in analytical and physical chemistry disciplines, that students should understand something about instrument control and data acquisition. Teaching LabVIEW, however, presents challenges because it requires time for students to become efficient programmers. Like many programs that have evolved over the years, LabVIEW has become increasing complex and sophisticated. The number of programming options has steadily risen, and the context help has been enhanced with new, unique, and more complex jargon. Students, as well as instructors, can become frustrated looking for specific functions, deciphering options, and trying to execute seemingly straightforward tasks. Moreover, an important aspect of an undergraduate laboratory course in instrumental methods is to provide students with a working knowledge of a wide range of chemical instrumentation, including theory, practice, and applications. Most curricula for such courses center on the collection and analysis of spectral, chromatographic, and electrochemical data. Devoting an entire laboratory course to LabVIEW-based projects may not be practical. Conclusion The HPLC exercise described above allows for flexibility in incorporating LabVIEW into an instrumental methods course. These tasks introduce students to LabVIEW, and they allow instructors flexibility in the level of difficulty and time devoted to programming. The exercise encompasses a number of computer interfacing tasks, including serial communication, analog-todigital conversion, and digital input-output control, in a single project. Lastly, an additional advantage to this exercise is that students are introduced to instrumentation that is traditionally covered in an instrumental methods course (e.g., DAQ devices and HPLC systems). Literature Cited 1. Kirkman, I. W.; Buksh, P. A. Rev. Sci. Instrum. 1992, 63, 869–872. 2. Allerhand, A.; Dobie-Galuska, A. Chem. Educator 2000, 5, 71–76. 3. Belletti, A.; Borromei, R.; Ingletto, G. J. Chem. Educ. 2006, 83, 1353–1355. 4. Ogren, P. J.; Jones, T. P. J. Chem. Educ. 1996, 73, 1115–1116. 5. Jensen, M. B. J. Chem. Educ. 2009, 86, 525–527. 6. Gostowski, R. J. Chem. Educ. 1996, 73, 1103–117. 7. Algar, W. R.; Massey, M.; Krull, U. J. J. Chem. Educ. 2009, 86, 68–71. 8. Drew, S. M. J. Chem. Educ. 1996, 73, 1107–1111. 9. Muyskens, M. A. J. Chem. Educ. 1996, 73, 1112–1114. 10. Ogren, P.; Nelson, S.; Henry, I. J. Chem. Educ. 2001, 78, 353–355. 11. Lan, K.; Jorgenson, J. W. Anal. Chem. 1999, 71, 709–714.
Supporting Information Available Student handout; two experiments that demonstrate the generation of a solvent gradient and a preparatory-scale chromatography. This material is available via the Internet at http://pubs.acs.org.
pubs.acs.org/jchemeduc
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r 2010 American Chemical Society and Division of Chemical Education, Inc.
