What’s In My Fume Hood?

This is the 2nd post in a series of showing how I work. Today I’ll show you around my fume hood. A fume hood is a ventilated cabinet with a retractable hood where I carry out most of my chemistry to reduce my exposure to chemical fumes.

labelled fume hood
Picture caption: fume hood containing various pieces of lab equipment. Adjustable glass front, a bit like a pull-down blind.

Sometimes you have a to share a fume hood with another chemist if there’s a shortage of space but I’m lucky enough to have whole fume hood to myself in this lab, especially as this one isn’t very big. In my undergraduate studies, I was usually sharing with one or two other chemists in larger hoods – it was a bit of a squeeze! My fume hood on placement ran up to the ceiling so I could actually stand up inside it when I cleaned it at the end of my placement year, which was a rather surreal experience!

On the side of each hood are various taps for various things. One is for water, while others provide a flow of compressed gas or nitrogen gas when I need them. When reactions need to be run under unreactive conditions are stirred under a constant flow of nitrogen gas, or another unreactive/inert gas like argon to stop the usual reactive oxygen and water vapour from reacting with the chemicals.

The brown bottle, or “Winchester” as these 2.5 L glass bottles are known, is a recycled solvent bottle where I put my solvent waste. Liquid chemicals that I am finished with are poured into these bottles and once full, disposed of by our technical services.

Chemical waste in organic labs is typically separated into two classes – halogenated and non-halogenated waste – but this can vary depending on the contract a lab has with a waste disposal company. Halogenated or non-halogenated refers to group 17 of the periodic table, the halogens (chlorine, fluorine, bromine, iodine, etc.) and essentially if the major component of the reaction mixture contains one of these elements, it needs to go in the “halogenated” waste while anything without those elements goes in the “non-halogenous” waste. The reason they are separated is that combination of some halogenated and non-halogenated species, e.g. acetone (CH3COCH3) and dichloromethane (CH2Cl2) results in a chemical reaction! It’s very important to keep your waste separate.

The efficiency of a reaction can be measured in terms of how much product you get relative to the amount you calculated from the starting material, expressed as a percentage yield, but increasingly, in terms of how much waste is produced per g of material. Some reactions create very little waste but sometimes I can fill a Winchester of waste in a day if I’m running a  lot of purifications which use lots of solvents.

I have a yellow and orange sharps bin for disposing of any sharp needles I use in my reactions. Syringes are frequently used to add precise quantities of a liquid reagent to a reaction mixture.

The metal bars are used to clamp different pieces of glassware in place using all manner of knobs and handles. I like to have a portable clamp stand in my hood because my hood has fewer bars than some of my colleagues.

Any sample vials I have in my hood typically have a final product in them that I’m waiting to dry. The constant extractor fan that’s running makes it useful to transfer chemical products by dissolving them in a volatile solvent that evaporates easily. Once dry I transfer lidded samples to my bench.

Ongoing reactions tend to be in various round-bottomed flasks (RBFs). RBFs, as the name would suggest are spherical pieces of glassware with different fixtures to connect with different lab apparatus. TO hold them upright I use cork rings, made of actual cork or plastic, to store them in the hood. I typically have more than these in my hood but this was my “tidy hood” before Christmas.

Picture caption: hot plate with glass reaction vials above it. Magnetic pellet in mixture to aid stirring

When reactions need to be heated I typically use a magnetic hotplate stirrer like these two in my hood. The hotplates work very similarly to the ones used in cooking and have dials to control temperature and extent of stirring. I stir my reactions by adding a little magnetic pellet into the reaction mixture which sits atop a spinning magnet within in the hotplate. The spinning magnet causes the pellet to stir which means I don’t need to stir the reaction by hand – useful when you’re doing multiple reactions at once.

I also have a temperature probe that allows me to set a reaction at a particular temperature and keep it there. Once or twice I’ve forgotten to put the probe in my reaction mixture which causes the hotplate to continue heating up and “nuke” my reaction, which is not a good sight to come back to. Hotplates only going up to 300 °C or so.

My hood also typically contains racks of test tubes from column purifications. These racks are full of mixtures that have been separated into their components by running them through a column of silica gel – the little bags you find in new shoes and bags to absorb moisture. Much of my time is spent rinsing out these test tubes into my waste bottle when I’ve isolated the products from the test tubes I need.

My Thin Layer Chromatography (TLC) tank is where I run larger TLC analytical experiments, otherwise, I use a beaker for plates that aren’t as wide as the one pictured. You may have carried out a separation of pen inks in school using paper chromatography. TLC works by the same principle of allowing a liquid to run up a rectangular plate of silica to see how many components are in a reaction mixture, indicated by the number of spots seen on a plate after it has been run.

Finally, the manner of glass tubes in my hood is known as a Shlenk line and allows me to control the flow of nitrogen gas and vacuum into my hood. I can use the various taps to connect to my reaction mixtures and remove the air form them using the vacuum pump just to the outside of my hood, then flood them with nitrogen, and repeat a few times to make sure I’ve got rid of most of the air.

So there you have it. I hope you’ve enjoyed this tour of my fume hood and how I use everything in it. I’ve spent many hours standing at this hood during my Ph.D. and it helps to contain my spills and mini explosions to keep me safe from chemical harm.

I try to tidy my fume hood at the end of the day, cleaning up any spills, removing all unnecessary glassware as it can get pretty busy with several reactions and multiple flasks on the go at once! I give it a deep clean every so often before I go on holiday when I tend to have less stuff in it.

Picture caption: Fiona in lab coat and safety glasses working beside the fume hood

I hope that’s given you a flavour of what goes on in a fume hood. Usually, a school science classroom will have one for storing certain chemicals but in research, they’re used daily! Stay tuned for future posts about my desk and organisation system.

If you’re a chemist, what’s your fume hood like? Otherwise, what’s your main working space like? Let me know in the comments below.

 

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