|Marilyn and hydrogen isostope glass vacuum line, circa 1980|
Isotope camps are good for people who want to learn the very basics about isotope chemistry. But for those of us who build a career on this technique, training is a life-long process. In every major university in the United States, for example, there will probably be one, if not two, stable isotope ratio mass spectrometers at each one! Typically, it’s in a geoscientist’s laboratory, rather than in chemistry, anthropology, or biology, but that’s only a general observation. I estimate that in California alone, there are 70 of these instruments at universities. I am sure there are others in business and government laboratories. If there are 70 instruments in California’s academic labs, there are probably at least 25 professors whose research programs use stable isotope techniques at the heart of their work. How did these 25 academics get their training? They’ve mastered their work by learning from their professors, trial-and-error, reading and studying others.
The trial-and-error period never seems to end. Every week, I hear about something someone tried that resulted in some form of “failure” or “error” or just plain “disaster.” I’ll be the first to say that I’ve learned a significant amount through this method, as have others. We learn a lot from our mistakes. Following are some good examples of trial-and-error that I’ve personally experienced as well as some good stories from my colleagues.
Today, many of the stable isotope methods that we use are fully automated. Some students think that they’ve accomplished something major after weighing 40 some samples into little tin capsules. We older generation isotopists roll our eyes at this. Read on for some isotope entertainment.
|Marilyn's son Evan preparing samples for isotope analysis; he was in high school, 2009|
Even before samples are analyzed in mass spectrometers, they all need to be dried, then often chemically extracted to either remove potential contaminants or to concentrate a portion of the sample that is of interest. In my laboratory, we are interested in examining the protein fraction of organisms in order to understand metabolism or an animal’s diet. The first part of getting at the protein is to heat the sample in a special test tube with strong acid. Our analyses are very sensitive and we can pick up very small amounts of contamination—perhaps from a test tube. Accordingly, we take great pains to make sure all of the tubes, spatulas, and anything that touches the sample are extremely clean.
|One colleague put in samples in reverse order; another forget a plastic cover was in place.|
All of our glassware is “muffled” in a hot furnace at 500-550°C for 1-2 hours before we use it. For the United States folks, 500-550°C is about 1,000°F, well above anything a commercial kitchen oven can reach. Most of us realize that only glass and metal can survive such high temperatures. But, some of us, usually those in training, don’t really know what 500°C means.
The test tubes we use have caps—made of plastic with Teflon liners on the insides of the caps. Plastic and Teflon can’t survive at 500°C and melt around 250°C, then at higher temperatures start to combust!
One well-meaning postdoc was instructed on how to muffle his test tubes to analyze protein in fossil bones. I assumed he understood that he was to muffle the glass tubes, not the caps. The next day, he started the process. It wasn’t long before the lab was filled with an acrid smell. I rushed into the room with the furnace and was confronted with a wall of smoke.
“Who has stuff in the muffle furnace?” I shouted into the lab.
“I do,” the postdoc answered.
“What’s in there?”
“The hydrolysis tubes,” he answered.
“Did you put the caps in there?” I shouted back.
“Yes, but they have Teflon on them,” he said.
I grabbed a metal bucket filled it with water, ran into the furnace room, and switched off the furnace. The door was opened carefully, and using a heavy-duty oven mitt, grabbed the smoldering caps out and into the bucket.
“Get this outside,” I shouted to the trembling postdoc. Fortunately, I have a sensitive nose and found the problem before a real disaster happened.
The same scenario happened three more times! The second time, a very senior colleague of mine made the same mistake—he did not figure that plastic and Teflon could not withstand high temperatures. We were prepared with the metal bucket nearby, the thick mitt, and a calmer response having gone through this once before. The third time it happened was probably due to a language issue. A Japanese postdoc did not fully understand all the potential sources of plastic. In that instance, the building was filled with acrid smoke and evacuated. Fortunately, my nose smelled this before the smoke set off the fire alarms.
That was not the case the fourth time. I had already moved from UC Merced down to UC Riverside, but my lab in Merced was still being used. My nose was useless 300 miles away.
A text message: There is a funny smell in the lab.
Me: Sometimes truck exhaust comes through the ventilation system.
Response: It’s getting stronger.
Me: What room is it in? Main lab or chemistry lab?
Response: Seems to be the chem lab.
Me: Anything going on in the hood?
My phone now rings.
“There’s smoke in the lab.”
“Is there anything in the muffle furnace?” I asked.
“I’ll call you later.”
The smoke alarms went off in the Science and Engineering 1 Building housing over 75 labs with professors, students, and staff. The building was evacuated. Firemen arrived to find the smoldering furnace with plastic caps inside.
Plastered on the front of the furnace was a big sign: NO PLASTICS!
One of the firemen smugly said, “Someone can’t read.”
The furnace was put on a cart and hauled out to the center of the campus Quad for all to see. Finally, my phone rang again.
“I muffled the caps,” the guilty person admitted.
“And what is that about?” I asked.
“I guess I wasn’t thinking at the time.”
All four of these folks have gone on to become competent in their fields—some of them perhaps relying more on technical assistants. Lessons were learned.
Other problems happened when we used liquid mercury in our glass vacuum lines. A visiting graduate student at the Geophysical Laboratory insisted on working at night. We arrived one morning to find Steve Macko’s glass vacuum line in pieces and a sheepish student with an injured hand.
I learned—no working alone at night!
Another visiting postdoc, a cocky fellow, broke my hydrogen isotope line that included hot uranium along with hot mercury. It was a big mess that Tom Hoering and I had to clean up. He was not invited back.
|One of Doug Rumble glass vacuum lines with mercury, 2001|
One of my best postdocs (well, they’ve all been great) was experiencing some personal family issues. We shared an office in the old Geophysical Lab with a mass spectrometer that used a mercury-based glass vacuum line to admit nitrogen gas into the instrument. He was performing a very delicate part of the analysis with liquid mercury surging carefully up into a small fragile opening into the mass spectrometer. His phone rang and he sprang for it—momentarily forgetting the mercury.
I was in the adjacent lab at the time and heard the glass explode and the vacuum pump chug loudly. There was the postdoc with the phone still in his hand and his mouth open staring at the destruction. I moved swiftly to turn off the vacuum pump and the ion source on the mass spec. Both of us were shaking—no one was injured.
Eventually, Tom Hoering came down to view the damage. He shook his head. Later in the day he met with the postdoc.
“I think you’re destined for administration,” he said, a verdict that was akin to research failure for us technically savvy folks.
It took several weeks to fix the instrument and was a mess to clean up all the mercury in our office. The postdoc, indeed, did go into administration later in his career and turned out to be a very successful science research administrator.
Another postdoc had a scare on that same mass spectrometer with its frightening mercury pistons. She had been working in Australia and had put some plants into plastic bags while they were still fresh. Long story short, the plants molded by the time they came to the lab. Were they any good for isotope analysis? A resourceful person, the postdoc decided to conduct an experiment with molded Ramen noodles that one of my other colleagues left in a bowl in my office sink. She knew the noodles would have very little nitrogen in them, so she weighed out more than twice the normal amount. When she put the noodle sample into the mercury-piston glass vacuum line, her heart leapt! The mercury piston shot down perilously bubbling out the bottom. Turns out she had produced a substantial amount of carbon monoxide from all those carbon-rich noodles. Fortunately, nothing was broken.
|Postdoc Jeff Silfer, Marilyn, Postdoc Bev Johnson in front of isotope line, circa 1995|
Other innocent mistakes happened that I would never have thought of. This story is a bit different. Once, during travel, my colleague had a graduate student who was quite strong in the lab, meaning the student could be trusted not to harm the expensive equipment. He felt confident that this student could keep things running while he was attending a meeting. At some point the mass spectrometer needed to be turned off, vacuum pumps off and vented to the atmosphere. Eventually the student was able to turn the instrument on again. Using the vacuum pump system, the student starting evacuating the instrument.
“The student realized that it was taking too long and panicked – torn between patience (during which maybe the leak would turn out to be water degassing, or perhaps the turbo would heat up and stop functioning) and immediately shutting everything down to wait for my return, the student decided to call me on my cell phone and ask for a video call. I was pretty sure I knew what the problem was, I just needed to see the screen on the control computer. A quick video call would get the student going again. Sure. We connected. We had 30 seconds of small talk, laughed at the faux pas, and the student apologized.
I smiled, and said, 'OK let’s get to work.'
The student started to walk over the mass spec. I recognized with satisfaction as he swung his laptop computer on the brief transit to the mass spec that the components in my lab were still roughly in place while I was gone.
There was a quick spin, a lift of his laptop, and my student said, 'OK, let me put this down and show you…'
Before I could scream, 'NOOOOOOOO!!!!!!' the screen went blank--disconnected.
I knew my student didn’t intentionally hang up on me. I also knew it was not worth calling back. The mass spec would have to await my return. My very bright and capable graduate student had put the laptop computer on top of the mass spectrometer’s magnet.”[thereby destroying its hard drive.]
Two other senior isotopists shared an experience I had with a postdoc—mixing up the gases we use for transferring our samples into the mass spectrometers. Helium—the gas that fills birthday party balloons—is used in many of our instruments as a “carrier gas”—a gas that propels the gases that we analyze, carbon dioxide, nitrogen gas, and hydrogen gas, into the mass spectrometers. Helium, an ultralite gas, flows through our mass spectrometers swiftly. One of my lab folks put a tank of argon on our mass spectrometer because the tank had been mistakenly painted the same color as a helium tank. A rookie mistake!
|Mark Woodworth: master of fixing complicated instruments, UC Merced 2014|
Another very senior isotopist reports tearing his hair out over why he was mysteriously only able to measure vastly reduced amounts of hydrogen gas than he thought he should have. He’d checked everything and it all seemed fine. Eventually, with less hair on his head, he remembered having purged all of his carrier gas lines with ultrapure nitrogen gas to remove moisture and contamination. Nitrogen gas is much heavier than helium and hydrogen—of course. Helium wasn’t strong enough to push through the nitrogen, thus preventing any hydrogen from making its way through.
Turns out that helium, although rare and expensive does the trick for our analyses. Another bright isotope geochemist had a “better idea.” He intentionally used argon gas on purpose. He thought other scientists with similar but different instruments use it all the time. He did some fine-tuning and was able to find nitrogen and carbon dioxide gases. Precision was not as good as he was used to. He briefly thought he was going to save the research field from helium shortages!
A week later, the delicate ion source—the heart of the mass spectrometer--blew and was filthy when he opened it up to see what had happened. Oh, the colors he saw when he disassembled it. And it smelled horrible. That ended his “experiment,” and he switched back to using helium as a carrier gas. That didn’t end the “experiment” completely, however. Even with helium, there were still residual effects and the new source blew again shortly thereafter and needed to be cleaned again. We’re stuck with using helium.
|A dirty ion source with colors|
Those not in the stable isotope chemistry field might think we’re a bunch of cowboys—but that is not the case. Our work demands, not just needs, but demands 100% concentration. Sometimes, for whatever reason, we operate at 95%. For the tens of thousands of isotope analyses I’ve made with my lab group over 40+ years, we’ve done a pretty good job of keeping within the rigorous boundaries of safe and sensible lab practice.
|When we needed to channel intelligence we donned the Arkansas razorback Pig Hat. It worked!|