Source: Bartlett Group SOPs, University of Michigan Department of Chemistry
Tags: solvent purification, hydrothermal vessel, Parr bomb, centrifuge, vacuum oven, tube furnace, compressed gas cylinders, hydrofluoric acid, HF, FTO, Ag/AgCl electrode, lab safety
Difficulty: Intermediate | Prerequisites: Schlenk line and glovebox notes, basic PPE knowledge
This set of notes covers the remaining standard equipment and specialised procedures in the Bartlett Group labs: the solvent purification system for dispensing dry, oxygen-free solvents; hydrothermal reaction vessels (Parr bombs) for high-temperature sealed reactions; centrifuge and vacuum oven operation; tube furnace use under controlled atmospheres; compressed gas cylinder handling; hydrofluoric acid safety (the most dangerous acid in the lab); fluorinated tin oxide (FTO) glass cutting; and Ag/AgCl reference electrode preparation. Each has its own hazard profile, but common threads run through all of them: inspect equipment before use, know the pressure and temperature limits, use the correct PPE, and never work alone with the most dangerous materials.
Solvent purification system
A bench-top apparatus that stores, dries, and degasses solvents (using molecular-sieve columns and inert-gas sparging) so they can be dispensed directly into evacuated receiving flasks. Solvents must circulate through the purifier for at least 16 hours before use.
Hydrothermal reaction vessel (Parr bomb)
A sealed metal vessel with a PTFE (Teflon) liner used for reactions at elevated temperatures and pressures. Aqueous reactions may use up to 80% of the vessel volume; organic solvent reactions are limited to 5 mL and 120 °C.
Centrifuge
A machine that separates solids from liquids by spinning at high speed. Must always be loaded with a counter-balanced sample of equal weight opposite the sample of interest. Warped tubes must be discarded.
Vacuum oven
An oven that dries samples under reduced pressure. Vessels inside must not be tightly capped, or the pressure differential between the vessel and the oven interior could cause an implosion or explosion.
Tube furnace
A furnace built around a quartz tube, used for annealing, calcining, and sintering materials under a controlled gas atmosphere. The tube must be purged with the working gas for 20 minutes before heating.
Hydrofluoric acid (HF)
A highly corrosive liquid and contact poison. HF penetrates tissue rapidly due to its low dissociation constant and neutral, lipid-soluble molecular form. It dissolves calcium from bone. Burns may not be painful initially because HF interferes with nerve function. Requires prior PI approval, online training, and the presence of a second trained person.
In simple terms, HF is the one acid that can pass straight through skin without you feeling it, dissolving bone underneath. Burns may only become evident a day later.
Calcium gluconate gel
The first-aid treatment for HF skin burns. Applied with a gloved hand immediately after 5 minutes of water rinsing. Must be checked for expiry before each HF session.
Fluorinated tin oxide (FTO)
A transparent conductive coating on soda-lime glass, used as an electrode substrate. Cut with a diamond cutter; the conductive side is identified by multimeter.
Circulate the desired solvent through the purifier overnight (at least 16 hours) before dispensing.
Dry the receiving flask (RF) in the glass oven for at least 30 minutes, preferably overnight. Inspect for cracks, especially at joints and the chem-thread neck.
To dispense: start the vacuum pump, purge the dispensing spout for 3 minutes, attach the RF, evacuate and refill three times (total vacuum time: 15 minutes), then dispense by turning V1 to off and V2 to the solvent position. Monitor the flask every 5 to 10 minutes.
Refilling the reservoir: turn off the circulator, open the vent valve, turn on sparge gas, add unstabilised OmniSolv solvent through a funnel, reseal, and circulate for at least 16 hours. Log everything.
Monthly: check reservoir levels (refill when about 1 L remains). Quarterly: inspect all lines, valves, fittings, and O-rings.
Safety: always have a filling buddy nearby, especially with anesthetic solvents (ether, chloroform). Inspect all receiving flasks for cracks.
Three types of vessel in the lab. Check you have the correct setup for your brand.
Aqueous reactions: max fill is 80% of vessel volume. Temperature limits: Parr bomb up to 240 °C; other PTFE vessels up to 200 °C.
Organic solvent reactions: max 5 mL, max 120 °C.
Acid digestion (Parr bomb 4745, 23 mL): max inorganic sample 1.0 g, max organic sample 0.1 g, nitric acid 2.5 to 3.0 mL with organic samples. Recommended temperature 150 °C, absolute max 250 °C.
Assembly: keep the bomb upright, check the bottom disc orientation, slide the liner in, add the pressure plate, spring, upper plate, and screw cap (hand-tight, MoS2 lubrication). No wrench needed below 100 °C.
Let vessels cool in the oven after reaction. Do not place hot bombs on bench tops.
Clean PTFE liner walls immediately after reaction. Do not run highly exothermic reactions or reactions that release large gas volumes in the autoclave.
Centrifuge
Always counter-balance: place a tube of equal weight directly across from your sample.
Cap tubes tightly; wear gloves for non-aqueous solvents.
Ramp speed gradually; do not exceed 3200 rpm to avoid damaging the rotor.
If rattling occurs, stop immediately and rebalance.
Wait for complete stop before opening the lid.
Warped tubes must be discarded; they can explode during centrifugation.
Mechanical failure: turn off and unplug immediately; do not reuse until inspected.
Vacuum oven
Do not tightly cap materials inside the oven (pressure differential hazard).
Use cold traps in-line for high vapour loads.
Release vacuum slowly (to avoid dispersing powders). Open the knob on top of the oven gently.
Ensure your sample is not completely liquid to minimise solvent entering the vacuum system.
Consult labmates before changing temperature settings.
Cover vials with a Kimwipe and rubber band to contain powders.
Mechanical failure: turn off, unplug, vent to atmosphere if safe.
The tube furnace anneals, calcines, and sinters materials under controlled gas atmospheres in a quartz tube.
Power off (red button) before loading. Load the sample at the centre of the heating zone (use the thermocouple as your guide). Place alumina insulating blocks at both ends of the heating zone.
Purge the tube with working gas at about 10 bubbles per second for 20 minutes before heating. For hydrogen: purge with an inert gas for 20 minutes first, then hydrogen for an additional 20 minutes.
During the reaction, flow gas at a slow rate (1 to 2 bubbles per second).
After the reaction, power off, remove the outlet phalange and insulating block, and extract the crucible with the hooked steel rod.
For air-sensitive work: use the inline purifying columns (P2O5 for water removal, Cu/Cu2O heated to 185 °C in a sand bath for oxygen removal). These purifiers are compatible with nitrogen and argon only. Check columns before use (P2O5 should be white powder, not black goo; Cu/Cu2O should not be fully black/CuO). After finishing, leave gas flowing through the Schlenk line to blanket the purifiers.
Transport only on a cylinder cart with securing chains. Never drag, roll, or lift by the cap.
Secure cylinders upright with wall or bench restraints at all times.
Use the correct regulator for each gas type. Never interchange regulators.
To set up: remove cap, briefly crack the valve to clear debris (aim away from people), attach the correct regulator, open the main valve first, then adjust the regulator.
To shut down: close the main cylinder valve first, wait a few minutes, then close the regulator.
Empty cylinders (below 25 psi) go to room 2626 with the tag reading "Empty."
Leak detection: soapy water or a flammable gas detector, never a flame. If a leak cannot be stopped by tightening, call emergency services.
Storage: dry, well-ventilated area with caps on. Oxidisers stored at least 20 feet from fuel gases.
This is the most dangerous acid in the lab. Prior approval from the PI, online training (course BLS026w), and review of the OSEH SOP are all mandatory before any HF work.
Why HF is uniquely dangerous
HF is a weak acid by dissociation, which means it exists largely as a neutral, lipid-soluble molecule that penetrates tissue far more rapidly than strong mineral acids. It dissolves calcium from bone. Burns may not be painful initially because HF interferes with nerve function. Symptoms can be delayed by a day or more.
Controls
All work in a chemical fume hood. Eyewash/drench hose and safety shower available.
Never work alone. A second person trained in HF first aid must be present.
PPE: splash goggles, nitrile gloves under neoprene gloves, lab coat.
Stock calcium gluconate gel (check expiry) and Calgonate Emergency Eyewash (single use, 120 mL).
Use only polyethylene or other HF-compatible containers. Never glass or ceramic.
Do not heat HF. Add acid to water, not the reverse.
Decontaminate surfaces with 10% sodium carbonate solution after use.
First aid
Skin: rinse 5 minutes with water, then apply calcium gluconate gel with a gloved hand. Seek medical treatment.
Eyes: use Calgonate Emergency Eyewash immediately. Call 911.
Inhalation: evacuate the area, contact OSEH-HMM.
Spills
Over 5 mL on campus: call OSEH-HMM at (734) 763-4568.
Under 5 mL in the hood: absorb with magnesium sulfate, soda lime, or sodium carbonate. Never use silica-based absorbents (Floor-Dri, kitty litter, sand), as HF reacts with silica to produce toxic silicon tetrafluoride gas.
Large spills: leave the lab, call 911, post a warning, do not attempt cleanup.
Storage
Polyethylene containers in secondary containment. Below eye level, in a cool, ventilated area, away from bases and incompatible metals.
FTO cutting
Identify the FTO (conductive) side with a multimeter. Place FTO side face-down for cutting.
Score with a diamond cutter along a ruler, then snap. Wear goggles and gloves; cut edges are sharp.
Clean cut pieces by sonicating in ethanol and acetone (10 minutes), then water.
Ag/AgCl electrode preparation
Sand the silver wire with 600-grit emery paper to bare metal. Rinse with distilled water.
Coat by inserting into 0.1 M HCl and passing 10 mA/cm2 for about 1 minute using a platinum counter electrode. A black deposit forms.
Rinse with water, dry with N2, insert into a glass tube with a Vycor frit tip filled with saturated KCl.
Equilibrate in saturated KCl for a few hours before use. Store in saturated KCl. Accuracy: within plus or minus 1 mV of expected value.
"HF burns hurt immediately, so I would know if I was exposed." HF interferes with nerve function. Burns may be completely painless at first and only become visible a day later. This is what makes HF so dangerous: exposures go unnoticed until serious tissue damage has occurred.
"Any spill absorbent works for HF." Silica-based absorbents (Floor-Dri, kitty litter, sand) react with HF to produce silicon tetrafluoride, a toxic gas. Only magnesium sulfate, soda lime, or sodium carbonate should be used.
"The centrifuge does not need to be balanced for small samples." An unbalanced load at high RPM creates asymmetric forces that can damage the rotor, the machine, and potentially injure nearby personnel. Always counter-balance.
"You can just put the hydrogen on and start heating the tube furnace." Hydrogen must be preceded by a 20-minute inert-gas purge to displace all air. Starting with hydrogen while air is still in the tube creates an explosive mixture.
"Glass containers are fine for HF since we use them for other acids." HF dissolves glass. Only polyethylene or other HF-compatible materials may be used.
⚠️ HF's mechanism of injury (lipid-soluble neutral molecule, tissue penetration, calcium sequestration, delayed symptom onset) is a commonly tested topic.
⚠️ Know the first-aid protocol for HF skin exposure: 5 minutes water rinse, then calcium gluconate gel applied with a gloved hand.
⚠️ The hydrogen purging sequence for the tube furnace: inert gas first for 20 minutes, then hydrogen for 20 minutes. Starting hydrogen with residual air creates an explosion risk.
⚠️ Centrifuge balancing is a standard lab-safety exam question: always counter-balance with equal weight opposite your sample.
⚠️ Compressed gas regulator rule: never interchange regulators between gas types. Explosions can occur if flammable gases contact oxidiser-contaminated regulators.
⚠️ Hydrothermal vessel fill limits: 80% for aqueous, 5 mL max for organic solvents at no more than 120 °C.
Q: Why is hydrofluoric acid more dangerous than other mineral acids of comparable concentration?
A: HF has a low dissociation constant, so it exists largely as a neutral, lipid-soluble molecule that penetrates tissue rapidly, unlike fully dissociated strong acids that are stopped by the skin surface. Once inside tissue, HF sequesters calcium from bone and interferes with nerve function, meaning burns may be painless and go unnoticed until serious damage has occurred.
Q: Describe the correct first-aid procedure for HF skin exposure.
A: Remove contaminated clothing. Rinse the affected area with water for 5 minutes. Immediately after rinsing, apply calcium gluconate gel to the skin using a gloved hand and rub it in. Seek medical treatment. For eye exposure, use Calgonate Emergency Eyewash immediately and call 911.
Q: Why must you purge the tube furnace with an inert gas before introducing hydrogen?
A: Hydrogen is flammable and forms explosive mixtures with oxygen. Purging with an inert gas (nitrogen or argon) for 20 minutes displaces all residual air from the tube, ensuring that when hydrogen is introduced there is no oxygen present to form an explosive mixture.
Q: What are the maximum fill and temperature limits for organic solvent reactions in the hydrothermal vessels?
A: Maximum volume of 5 mL, maximum temperature of 120 °C.
Q: Why should you never use silica-based absorbents (Floor-Dri, kitty litter, sand) for an HF spill?
A: HF reacts with silica (SiO2) to produce silicon tetrafluoride (SiF4), a toxic gas. Only non-silica absorbents such as magnesium sulfate, soda lime, or sodium carbonate should be used.
Q: What is the minimum solvent circulation time in the purification system before dispensing?
A: 16 hours (overnight) to reach the desired purity level.
The solvent purification system feeds directly into the Schlenk line and glovebox workflows: purified solvents are dispensed into Schlenk flasks and transferred to the glovebox for air-sensitive reactions. The tube furnace, when used for air-sensitive work, relies on the same Schlenk-line infrastructure (inert gas, vacuum, purifying columns).
HF safety principles (delayed injury, calcium sequestration, tissue penetration) connect to toxicology and pharmacokinetics concepts. The compressed gas cylinder SOP overlaps with the tube furnace and Schlenk line SOPs wherever controlled-atmosphere work is involved.
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