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iSchlenk: Portable Equipment for Hands-On Instruction in Air-/Moisture-Sensitive Syringe, Cannula, and Schlenk Techniques Louis Messerle* Departments of Chemistry and Radiology, The University of Iowa, Iowa City, Iowa 52242, United States S Supporting Information *

ABSTRACT: iSchlenk, a portable instructional cart with equipment for hands-on student experience in safe handling of air-sensitive, moisture-sensitive, toxic, pyrophoric, and/or radioactive chemical materials, is described. The cart, for use by ≤4 students, has compressed air and vacuum from a diaphragm vacuum pump supplied to 4 three-port Schlenk lines with double-oblique glass stopcocks. Air pressure is adjusted by a pressure-release mineral oil bubbler. The cart’s drawers contain glassware and equipment (polypropylene and glass syringes, deflected-point needles, cannula, rubber septa, Schlenk flasks, Schlenk fritted funnels, pour tubes, gas-inlet adapters) for instruction in liquid transfer (syringe, cannula, pour tube) and basic Schlenk techniques. Water serves as the simulant for pyrophoric liquids, compressed air for inert gases, and fine sand for insolubles. The results of anonymous (coded by student) written assessments, before and after student use of iSchlenk, are presented. iSchlenk design criteria and construction, classroom/ laboratory implementations in an undergraduate advanced inorganic chemistry laboratory course and in a graduate lecture course in organometallic chemistry, and an assessment instrument for undergraduate and graduate student mastery of safe Schlenk, cannula, and syringe techniques is discussed. KEYWORDS: Upper-Division Undergraduate, Graduate Education/Research, Laboratory Instruction, Inorganic Chemistry, Organic Chemistry, Nuclear/Radiochemistry, Safety/Hazards, Hands-On Learning/Manipulatives, Laboratory Equipment/Apparatus, Organometallics, Synthesis

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of her body after accidental exposure on December 29, 2008, to highly pyrophoric tert-butyllithium solution and nearby ignited solvent.2 Despite the efforts of nearby researchers, she died 18 days later in a hospital burn unit. She was able to communicate a few details about the accident before her death. A consensus has emerged that she tried to transfer a large amount (3 × 50 mL) of tert-butyllithium solution with a 60 mL plastic syringe coupled to a short, small-gauge needle, leading to accidental plunger removal while filling the syringe from a tilted, septum-sealed storage bottle without makeup inert gas. Subsequent, lengthy legal proceedings3 have pointed to inadequate precautions (e.g., absence of flameproof lab coat) and safety training (Ms. Sangji was shown a technique for handling organolithium solutions that was counter4 to safety recommendations5 supplied by the manufacturer). This tragedy has been the subject of numerous articles in the media and scientific news journals.6 This and other accidents, many unreported, involving pyrophoric or water-reactive compounds and elements in academic, governmental, and industrial research laboratories have led, for safety and legal reasons, to the development of instructional literature, videos, and online training that demonstrate techniques for handling air- and moisturesensitive materials and of alternative solvent-drying methods.7 Chemical and radiochemical synthesis involves manageable personnel risks, provided that there is effective instruction and

ioxygen-sensitive, moisture-sensitive, toxic, and/or radioactive reactants are used frequently in organic and inorganic synthesis, organometallic chemistry, radiochemistry, and materials chemistry. Examples of the first two include organolithium, Grignard, organozinc, organoaluminum, and organotransition metal reagents. Their reactivity is a benefit, but also a liability: what makes them effective at activating reactant chemical bonds or forming new bonds may make them moisture-sensitive, air-sensitive, and even pyrophoric. Personnel need protection from pyrophoric and/or toxic reagents. Unfortunately, there remain few safe, general, or green replacements for these reagents in synthesis. At best, manipulation of these reagents or toxic chemicals by inexperienced students and technicians results in lower reaction yields. At worst, personal injuries, laboratory fires, and/or radiation exposure can occur. Students are shown procedures, depending on the university or college, for handling air-/moisture-sensitive reagents (e.g., alkyllithium solutions) in research by upper-level undergraduate students, graduate students, postdoctoral researchers, and moreadvanced researchers, and by training videos,1 with the expectation that such training is adequate. This leads to variable levels of expertise, poor or no documentation of training, little or no assessment of effectiveness, potential propagation of poor technique, potential injuries from accidents, and potentially significant liabilities. Ms. Sheharbano Sangji, a research associate in the Department of Chemistry and Biochemistry at the University of California at Los Angeles, received second- and third-degree burns over 40% © XXXX American Chemical Society and Division of Chemical Education, Inc.

Received: February 23, 2018 Revised: May 2, 2018

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DOI: 10.1021/acs.jchemed.8b00141 J. Chem. Educ. XXXX, XXX, XXX−XXX

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iSchlenk construction and equipment costs total ∼$7900 (2017 prices). Figure 1 shows a front view of the folded cart, from the

Integrated Safety Management in protection of personnel from these reagents and conceivable accidents, guidance via written and experiment-specific protocols, and postinstruction assessment. Lab experiments in the chemical education literature8 can be used to teach selected Schlenk techniques to undergraduate students but may not be feasible for technical staff outside of academia. While there are articles in the safety literature9 and books10 with information on Schlenk, syringe, and cannula techniques, the author is unaware of reports on methods or approaches to teaching Schlenk and syringe/cannula techniques in a systematic, hands-on manner and with post-training assessment. This is perhaps the result of the understandable institutional fear that hands-on handling of pyrophoric substances by inexperienced undergraduate or graduate students is not safe, leaving such training to the responsibility of Chemistry departments, faculty research mentors, and/or research supervisors. The author has taught a junior-level inorganic chemistry laboratory course at the University of Iowa over three decades, with multiday experiments involving glovebox, Schlenk techniques (inert-gas purging and evacuation/backfill methods for apparatus assembly, pressure-equalizing addition funnel use, and filtration), and cannula and syringe needle liquid transfers of solvents. The author has expended considerable time and effort in collecting and assembling Schlenk equipment in a lecture room for instruction prior to each experiment. This time cost led the author to conceive a dedicated, portable instructional cart, termed iSchlenk, for use by 1−4 students. The cart includes four compact Schlenk lines, pressure-regulating mineral oil bubbler, oil-free diaphragm vacuum pump to supply vacuum and compressed air, lattice rod supports, clamps, glassware, syringes, needles, and secure storage. This article describes iSchlenk design criteria, sources of components/glassware (Supporting Information), specific techniques taught to students, and preand postassessment of instructional effectiveness. iSchlenk portability also means that research groups, outside of a formal classroom environment, can use the cart for handson group instruction on a regular basis for new researchers.

Figure 1. Front view of iSchlenk cart with back table folded down. Rubber hoses for back pair of Schlenk lines removed for clarity. Back table legs with casters stored on bottom shelf. Storage drawers shown below top table edge, with keyed locking mechanism on right side.

side with the lockable storage drawer, without hoses for the back pair of Schlenk lines (in order to simplify view). Figure 2 shows the back table raised and supported by easily installed legs with casters, also showing the vacuum pump on the lower shelf. Figure 3 shows one of the four Schlenk lines with hoses for two separate operations. On the left, a septum-sealed Schlenk flask with colored aqueous solution and Luer-lock plastic syringe (with long deflected-point needle) is used to teach syringe purging and liquid withdrawal with makeup gas supplied by the Schlenk line. The right side shows a cannula transfer of solution from a storage bottle to a septum-sealed Schlenk flask. The solution in the bottle is first purged with gas via the middle Schlenk line port, using a Luer-lock-to-hose adapter to a long deflected-point needle and a dual deflected-tip cannula, inserted only into the bottle septum, to allow escape of purging gas and to purge the cannula. The other end of the purged cannula is inserted into the septum-sealed Schlenk flask (previously glass stoppered, evacuated, and backfilled three times, and stopper replaced with a septum under countercurrent of gas). A second deflected-point needle is then inserted into the Schlenk flask septum in order to allow for gas displacement by solution about to be transferred. The first cannula end is then pushed into the bottle’s solution for liquid transfer by differential pressure. The cannula is finally removed from the bottle solution level to drain the cannula, followed by removal from the Schlenk flask along with the pressure-release needle, and then from the bottle septum. Figure 4 shows a close-up view of the syringe and cannula transfer equipment setups. Figure 5 shows a Schlenk filtration on the right-side Schlenk line, after the mixture of water and insoluble colored inorganic salt (copper carbonate, in place of fine sand, for the picture) has

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ISCHLENK DESIGN CRITERIA Key criteria for a portable cart for hands-on instruction in Schlenk and syringe techniques include the following: 1. usability in laboratory and lecture rooms, requiring only 110 V ac electrical power, 2. capacity for hands-on instruction of up to four students at a time, 3. portability, with lockable casters, 4. dimensions that allow transport through standard classroom doors, 5. secure storage of glassware and equipment such as needles and cannulas, 6. marine-edge table top to contain liquid (water in this case) spills, 7. stainless steel construction for corrosion resistance and ease of cleaning, and 8. diaphragm vacuum pump to provide compressed air and vacuum, replacing both a cryogenic trap to protect an oil vacuum pump and a compressed inert-gas tank with regulator. A dual-sided, 6 foot-long cart with four Schlenk stations, with the hinged back table used for two of the four Schlenk lines and folded down for transport, was constructed. The list of components and student-use items can be found in Supporting Information; B

DOI: 10.1021/acs.jchemed.8b00141 J. Chem. Educ. XXXX, XXX, XXX−XXX

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Figure 4. Closeup views of the syringe transfer setup (left) and cannula transfer setup (right).

Figure 2. Side view of iSchlenk with back table opened and legs installed. Rubber hoses for back pair of Schlenk lines removed for clarity. Diaphragm pump visible on bottom shelf.

Figure 5. Schlenk filtration of a mixture of water and insoluble metal salt, after transfer via pour tube to Schlenk frit but before actual filtration with static vacuum. Three Schlenk ports are needed for apparatus assembly under countercurrent of gas and for evacuation of the receiving flask. The pressure-release bubbler is visible at top left.

This minimizes formation of solid product under the frittedglass surface. While air, water, and sand are used as simulants for inert gas, solvent or air-sensitive solution, and crystals or precipitate, respectively, the undergraduate students use their iSchlenk experience in a later experiment to prepare and transfer moderately air-sensitive reagents (e.g., in-situ-generated sodium cyclopentadienide solution, whose color is indicative of the degree of exposure to dioxygen during its preparation). The author later takes the students to an open parking lot near the building and, wearing protective equipment and flame-proof lab coat and carrying a fire extinguisher, uses a 5 mL syringe with needle, initially capped with a septum, to shoot a stream of 1 mL of either trimethylaluminum or diethylzinc, both highly pyrophoric, downwind into the air. Students are, to put it mildly, very impressed by this demonstration.

Figure 3. iSchlenk equipment for hands-on instruction in syringe (left) and cannula (right) liquid transfers. The three-port, dual gas, and vacuum line Schlenk line with double-oblique glass stopcocks is at top of figure. On upper far right is the pressure-adjusting bubbler, and on far left is a bubbler as a simple trap between the diaphragm vacuum pump and the vacuum distribution lines to the Schlenk lines.

been transferred via a pour tube from the reaction flask to the Schlenk frit, before actual filtration. Students are taught to perform the filtration using a static vacuum in the receiving flask, i.e., with the receiving flask’s stopcock closed to the Schlenk line after evacuation, in order to minimize evaporation of solvent (here, water) from solution after passage through the fritted funnel.

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SPECIFIC HANDS-ON TECHNIQUES AND CLASSROOM INSTRUCTION Students are introduced to turnover rubber septa, deflectedpoint cannulas, outer Luer-lock deflected-point syringe needles C

DOI: 10.1021/acs.jchemed.8b00141 J. Chem. Educ. XXXX, XXX, XXX−XXX

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In the following questions, assume that you do not have access to a glovebag/glovebox, are working in a fume hood in air, and want to do so safely. Assume that the air-sensitive liquid is either a liquid reagent or a solution of an air-sensitive reagent in a flammable organic solvent. Air-sensitivity implies reactivity toward dioxygen, dinitrogen (e.g., in case of lithium metal), carbon dioxide, and/or water vapor. 1. Describe your current experience in lab courses and/or prior research, other than using a glovebag, in handling air-sensitive compounds. 2. How would you transfer 10 mL of an air-sensitive liquid from a sealed bottle to a flask? Give the steps. 3. How would you transfer 50 mL of an air-sensitive liquid from a sealed bottle to a flask? 4. How would you transfer 10 mL of an air-sensitive solution from one flask or bottle to another flask? 5. How would you transfer 100 mL of an air-sensitive solution from one flask to another flask? 6. How can you pour an air-sensitive solution from one flask into another? 7. How would you filter an air-sensitive solution to either remove an insoluble byproduct or recover an air-sensitive solid product, while protecting the filtrate? 8. What is a cannula? A deflected-point syringe needle? A Luer-lock fitting? A septum? 9. Define an inert gas. Give an example. The rubric for scoring these anonymous, pre- and postiSchlenk use assessment instruments was the following for Q1: 0 No experience; 1 Experience

for septum penetration, Luer-lock syringes, syringe stopcocks, and rubber tubing-to-inner Luer-lock connectors. The advantages and contraindications for use of argon vs dinitrogen blanketing gases for various chemistries are presented, with a discussion of the importance of knowing levels of impurities in inert gases for long vs short purging times. After a discussion of silicone, hydrocarbon, and fluorocarbon greases, the best method for greasing a stopcock with minimal grease is shown. The general concept of counterstreams of inert gas for connecting previously evacuated and then purged Schlenk glassware is demonstrated. The various stopcocks (straight-bore, T-bore, and doubleoblique), and the reason that the latter are used on Schlenk lines, are discussed. The specific Schlenk, syringe, and cannula techniques, in order of increasing complexity, are 1. degassing water in a Schlenk flask or bottle closed with a septum 2. purging air from a syringe and attached needle by multiple withdrawals of air from a septum-closed Schlenk vessel under slight air pressure, each followed by injection into the air 3. withdrawing water from a septum-closed vessel by syringe, with an explanation of the types of volumes that can be safely transferred by syringe (no more than half of the syringe’s maximum volume) and the specific dangers of using large volume syringes (from accidental withdrawal of the plunger, especially with small-gauge needles); the technique for accurately adjusting water volume in the syringe, followed by blanketing the volume with air by inversion of the syringe, and emptying all water into the receiving vessel, is then demonstrated 4. cannula transferring of larger volumes from storage vessel to a Schlenk flask, via a purged graduated-cylinder with septum and makeup air supply, and from there to Schlenk flask by switching and inserting the emptied supply end of the cannula into the Schlenk flask septum

For Q2−Q9: 5 Expert-level technique; complete understanding 4 Some minor improvements in technique needed; excellent understanding 3 Some improvements in technique needed; good understanding 2 Major improvements in technique needed; some understanding 1 Simplistic answer 0 No answer, or no experience −1 Danger to self or others

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HAZARDS AND SAFETY PRECAUTIONS There are no chemical hazards from the use of water, lowpressure air, and sand. Goggles are mandatory because of the use of vacuum and the possibility that a cannula can spring out of a septum and cause eye injury. Deflected-point cannulas and syringe needles can penetrate skin, so finger pokes are a hazard that can be lessened by glove use; we have not experienced finger pokes over the time periods reported here. The application of vacuum to a closed glass vessel can result in implosion, particularly if a Schlenk flask or a fritted funnel has scratches on the inside or outside or has star cracks, so glassware needs to be inspected before reuse.

Table 1 shows the composite assessment results, pre- and post-iSchlenk use, for Questions 1−9 over three semesters (48 students total) of the undergraduate student inorganic chemistry laboratory course. Table 2 shows the corresponding results over two semesters (17 students total) of the graduate student organometallic chemistry lecture course. The assessment instrument results, averaged over 3 semesters for undergraduate students, showed significant improvements in undergraduate student median scores from pre- to postassessment for question 1 (possible answers yes or no experience) and for questions 2−9. The results averaged over 2 semesters for graduate students (generally, those involved in organic, inorganic, and organometallic synthesis, and thus with some possible experience in Schlenk and cannula/syringe techniques) showed significant improvements, pre- vs post-iSchlenk use, in median scores for questions 2−9 While the sample sizes for the assessment instrument results are small from a statistical perspective, as shown by the standard deviations, it is clear from the increases in pre- vs postassessment instrument median scores that iSchlenk use has improved the competence, and confidence, of undergraduate and graduate

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ASSESSMENT INSTRUMENT AND OUTCOMES Students were given questionnaires to assess their knowledge of syringe and Schlenk techniques prior to use (pre) and after use (post) of syringes, Schlenk lines, needles, cannulas, septa, and glassware. The assessment instrument was anonymous, with a student-selected code (in absence of instructor) for correlation of pre- and postassessments. The assessment instrument appears below (extra space was provided between each question): Pre/Post-Assessment of Knowledge of/Experience with Air-Sensitive Techniques

Student code number: XX (randomly chosen by students with instructor outside of classroom for preassessment; this number is then used for postassessment). D

DOI: 10.1021/acs.jchemed.8b00141 J. Chem. Educ. XXXX, XXX, XXX−XXX

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Table 1. Undergraduate Pre- and Post-iSchlenk Assessment Composite Scores, over Three Semesters, for Q1−9 (48 Students)a Pre Q1 avg SD med avg SD med a

0.21 0.41 0.00 Pre Q6

Post Q1

Pre Q2

0.96 0.20 1.00

0.77 1.19 0.00 Post Q6

0.15 0.65 0.00

2.04 1.38 2.00

Post Q2 3.02 0.92 3.00 Pre Q7

Pre Q3

Post Q3

0.40 1.08 0.00 Post Q7

0.19 0.56 0.00

2.85 0.89 3.00 Pre Q8

2.27 1.27 2.00

Pre Q4

Post Q4

0.60 0.97 0.00

2.60 0.84 2.00 Post Q8

0.77 1.08 0.00

3.58 1.26 4.00

Pre Q5 0.31 0.96 0.00 Pre Q9 2.52 1.49 2.00

Post Q5 2.46 1.14 2.00 Post Q9 3.77 1.26 4.00

avg = average, SD = standard deviation, med = median.

Table 2. Graduate Pre- and Post-iSchlenk Assessment Composite Scores, over Two Semesters, for Q1−9 (17 Students)a Pre Q1 avg SD med avg SD med a

0.88 0.32 1.00 Pre Q6

Post Q1

Pre Q2

0.94 0.24 1.00

2.41 1.19 3.00 Post Q6

0.88 1.18 0.00

2.65 1.23 3.00

Post Q2 3.59 1.03 4.00 Pre Q7

Pre Q3

Post Q3

1.82 1.58 2.00 Post Q7

0.88 1.18 0.00

3.24 0.88 3.00 Pre Q8

2.82 1.46 3.00

Pre Q4

Post Q4

2.29 1.23 2.00

3.29 0.96 3.00

2.53 1.29 2.00

Post Q8 4.29 1.18 5.00

Pre Q5 1.53 1.46 2.00 Pre Q9 3.82 1.34 4.00

Post Q5 2.88 0.90 3.00 Post Q9 4.47 1.19 5.00

avg = average, SD = standard deviation, med = median.

students in toxic and air-/moisture-sensitive reagent manipulation in a laboratory environment.

ORCID

SUMMARY A new, documentable approach to teaching air- and moisturesensitive synthesis techniques, including Schlenk and (especially, from safety perspectives) needle/cannula methods, to undergraduate and graduate students via a mobile iSchlenk cart has been developed. An anonymous assessment instrument for gauging and documenting student knowledge of Schlenk and cannula/syringe techniques, pre- and postuse of the iSchlenk cart, has been designed and implemented in an undergraduate student inorganic chemistry laboratory class and in a graduate student organometallic chemistry lecture class over several semesters. Positive increases in pre- vs postassessment medians have been demonstrated. While iSchlenk use is focused on training students in handling pyrophoric and air- and moisture-sensitive reagents, the equipment and techniques are invaluable for any scientist requiring isolation from toxic (chemically, biologically, radiologically) reagents.

Notes

Louis Messerle: 0000-0002-7636-122X

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The author declares no competing financial interest.

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ACKNOWLEDGMENTS The author thanks graduate teaching assistants Justine Olson, Nathaniel Coleman, Anthony Montoya, Nicholas Schnicker, Madeline Basile, Nathan Black, Taylor Fetrow, Kyounghoon Lee, and Kyle Spielvogel for their help in demonstrating iSchlenk in the advanced undergraduate inorganic chemistry laboratory course, and thanks Kyle Spielvogel for his help in one graduate organometallic chemistry lecture class. The author also thanks Frank Turner for excellent machining work in assembling crucial mechanical portions (e.g., the back table folding mechanism), Peter Hatch for glassblowing of the Schlenk lines and glassware, Renée Cole for helpful discussions and an explanation of approaches to searching the chemical education literature other than by CAS’s SciFinder, and Johnathan Culpepper for artistic advice and excellent editing of the artwork and photographs. The author acknowledges financial support from the University of Iowa (Office of the Provost, Council on Teaching) for financial assistance via an Instructional Improvement Award, and the University of Iowa Department of Chemistry for matching funds and services.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.8b00141. List of iSchlenk construction and student-use components and suppliers with 2017 pricing, tables showing individual responses to pre- and post-iSchlenk assessment instruments per anonymous student over 3 semesters (undergraduate) and 2 semesters (graduate), picture of underside of iSchlenk, showing hinge/spring assembly for back table surface elevation or storage, with table surface folded down in this view (PDF)

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REFERENCES

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. E

DOI: 10.1021/acs.jchemed.8b00141 J. Chem. Educ. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.jchemed.8b00141 J. Chem. Educ. XXXX, XXX, XXX−XXX