Short Stories - Mass Spec

It was a quiet evening in the analytical chemistry laboratory. Although I was supposed to have clocked off and gone home some time ago, I was busily finishing off the last few samples left for me to run through the mass spectrometer. That was one of the problems: the postgrads spent all day playing with their chemistry set and considered the day to be a total failure if they didn't leave me a tiny amount of reddish-brown powder or sticky black gunge in a sample tube. If I ran them through the machine, they would have a chance to work out what they had made, and get on with their chemistry game in the morning.

Now, I'm not talking about one of those modern fully automated namby pamby computerised quadrupole magnet jobs. This was the manual version with a big quadrant and two chunky magnetic coils. It was a bit touchy and required a regular dose of TLC. I hadn't calibrated the magnet for a while, so I dispensed a tiny drop of clear liquid into the cut length of sample tube. The tube had to be small or it would take too long to heat up, evaporating the sample into the machine. That just made the job more fiddly. It was not a good idea to tell someone that you'd dropped the fruit of their labours because the tube was too small to hold.

The liquid was PerFluoroKerosene, PFK, a long-chain carbon polymer molecule that conveniently lost one Carbon, with its attached Fluorine and Hydrogen atoms, at a time as you heated it up in the injector. The trick was to use just enough, and the scanner gave a nice pattern, with regular spikes across the trace, corresponding to the molecular weights of the fragments. Too little and it could be relied on to fade out at the most interesting region. Too much, and you couldn't see anything else for a day while the pumps slowly sucked it out!

That made the calibration process a bit risky, so it was better to do it just after an important sample, rather than before. Mind you, if you did it before and got it exactly right, there would be tiny traces of PFK left in the machine, leaving those spikes all the way up, intermingled with those from the unidentified molecules. It made it much easier to work out the molecular weights of all those fragments.

I went through the usual sequence: Open the port; slide the sample holder through the vacuum seal into the heavy stainless steel block of the injection port; open the port seal, exposing the sample to the vacuum inside the spectrometer; push it fully home; connect up the heater wires; and lastly check the vacuum pressure. Just after I looked away from the gauge and turned to watch the oscilloscope screen on the instrument rack, there was a sharp Crack! I was pretty sure it came from behind me, low down on the bulky tower of the mass spectrometer, near the pressure gauge, where the neon lamp that usually glowed bright orange to show it was switched on was dark. Then I noticed the silence. Even the chug chug chug of the mercury vacuum pumps was missing. The whole instrument rack had lost power. The fuse must have blown.

I had my boss's phone number, so I called for instructions. It rang a few times and then the answering machine cut in. "We're not home right now. Please leave a message." Why can you never find an academic when you need one? I left a message but the machine was holding me up.

I looked at the electrical power feed. The power for the entire rack came from an isolation switch on the wall behind the bulky magnetic coils. If the fuse had gone, I would need an electrician to fix it and they went home at five o'clock. I didn't have a works order, so there wasn't much chance of help. There wasn't enough time before the heavy steel apparatus cooled enough for the vacuum seals to start leaking, and that meant days of downtime while they were replaced and the vacuum circuit purged. I was already on borrowed time.

In my day job as electronics technician, I had tools to make a temporary connection. I dashed down two floors to the lab and grabbed screwdrivers, wire cutters and strippers, and a fused plug. I ran up again with my booty and after catching my breath, set about opening up the isolation switch and disconnecting the armoured cable. Fortunately it was long enough to reach a panel of wall sockets on the other side of the electronics rack. It wasn't what you could call an approved standard connection, but when I plugged it in and switched on, the chugging of the pump told me I was at least on the right track. Maybe the seals had survived. However, the pressure gauge neon light was still dark, showing no friendly orange glow.

That was about as much as I could do. Without the gauge, I couldn't finish the calibration run: It was too risky to run the electronics. I phoned the number again, and this time I got an answer. I relayed the situation and the steps I had taken, but it looked as though the machine would be out of action for some time. He told me to pack up and go home. Those samples and the steady trudge of science would have to wait.