Papes for the Peeps – Analysis of Antioxidants in Fuels

This is the latest in a series of posts where I attempt to translate my published research into a format suitable for a non-specialist audience.

My paper “Synthetic Phenolic Antioxidants in Conventional and Alternatively-Derived Middle Distillate Fuels Analysed by Gas Chromatography with Triple Quadrupole and Quadrupole Time of Flight Mass Spectrometry” was recently published in the ACS journal Energy and Fuels (paywalled).

This piece of work describes two new methods for determining antioxidant compounds in jet and diesel fuels. Antioxidants are added to some fuels to stop the fuel reacting with oxygen while in storage. When fuels react with oxygen, they can become unsuitable for use and cause engine problems. Although these antioxidants serve an important purpose, they are only permitted to exist in the fuel up to a certain concentration. Sometimes, if a fuel is suspected to be reacting with oxygen, the users might want to add antioxidant to stop the fuel from going bad – but if they don’t know how much antioxidant is in there (if any), how will they know how much to add without going over the limit?

The antioxidants are present in the fuel at very low concentrations, which makes it difficult to measure them without the bulk of the fuel interfering in the analysis. It’s possible to extract the antioxidants from the fuel, which then makes the measurement easier, but the extraction process is often long, resource intensive (uses lots of solvent) and frequently doesn’t work well enough. My laboratory recently acquired two new GC-MS (gas chromatography – mass spectrometry) instruments with advanced detection systems so I decided to see how these instruments would go at detecting antioxidants in fuels at low levels, and without any sample treatment.

SPA1

Left: generic structure of these antioxidants, where ‘R’ can represent a methyl or tertiary butyl group in 1-3 of these R positions. Right: BHT, a common antioxidant used in fuels, foods and other products, where the R group opposite the OH is a methyl and the two R groups adjacent to the OH are tertiary butyl.

 

I have posted before about how gas chromatography and mass spectrometry work, and in this study it is the mass spectrometers that play a key role in the detection of the antioxidant compounds. The two different instruments I used are able to exploit different characteristics of the target molecules, in order to detect them at low levels, without interference.

Triple Quadrupole (QQQ) MS

The QQQ achieves excellent sensitivity by fragmenting molecules in the mass spectrometer more than once. For example, using the antioxidant shown in the picture above, the spectrum for this compound is

 qqq1

Which means that ordinarily, I would use the strong signal from the ion with a mass of 205 to look for this compound. But fuels have so many other moelcules in them, that there are loads of other compounds that also generate a signal at 205 and these swamp the signal from the target compound. So I can program the QQQMS to collect the strong ions, and perform another fragmentation on it. This generates a new mass spectrum with a new set of fragment ions. In this case, the fragmentation of 205 produces a signal at 145. So I can get the QQQMS to monitor these specific fragmentations, and keep track of the transition of each ion into another ion as it is broken apart in the spectrometer. So while there may be many compounds that have a signal at 205, there is only one molecule which has a signal of 205 fragmenting to 145. By using this approach, I can be very specific in my identification and measurement of my target compounds and this specificity brings with it excellent sensitivity and low detection limits.

Quadrupole Time of Flight (QTOF) MS

The QTOF is able to detect very specific compounds because it can measure their mass very accurately. The other mass spectrometers in our lab are able to measure the weight of ions to one atomic mass unit (amu). Using the example above, the most accurate mass of the main ion we can obtain with these instruments is 205 amu. And again, there will be many other compounds with fragment ions of the same molecular weight. However, if we calculate the mass of this fragment (C14H21O) accurately, it comes out as 205.1587. Another possible ion with the same molecular weight is C13H19NO, but the accurate mass of this ion is 205.1461. This difference of 0.0127 amu is enough for the QTOF to distinguish between these two molecules, so I can program the instrument to look only for the accurate mass ion I’m interested in and discard the other closely matching, but interfering compounds.

Exploiting the strengths of these two mass spectrometers has allowed me to detect and measure low levels of antioxidant compounds in very complex  fuel mixtures.

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Aliquots of the #chemophobia blogversation

10 days is a long time in internetland, this fickle place where memes flap in and out of our lives like disoriented cartoon birds attempting to navigate between vertical pipes. In the time since I posted the first part of the chemophobia blogversation, there have been many fantastic contributions to the discussion.

Chemtacular put forth three contributions, the first of which began with calling me a superstar so naturally, everything she said in the rest of the post was flawless. NEXT.

In the second post, Chemtacular used a recent twitter interaction as an example to make her case. She argues that the label chemophobia is a gateway to ad hominem attacks and bullying of those who fear or misuse chemistry.

Chemtacular’s third offering was posted at Chemistry Blog and asked ‘where to from here?’. If the chemists of the internet can’t agree on how to use the term chemophobia (herding cats anyone?), does it really matter? (yes, it does) We all want the same thing, to see chemistry appreciated amongst the wider community, and how can we as professional chemists help to make that happen?

Luke expressed his concern that chemists are losing ownership of the word ‘chemical’ and suggests taking concerns about false labelling of products as ‘chemical-free’ to the relevant authorities. He asserts that we as chemists are ‘brand ambassadors’ for chemistry, and this is an attitude that we can adopt in our everyday lives amongst our families, friends and colleagues.

Chad* made references to things like dolphins and jazz music in the beehive state, which appear to somehow relate to some strange North American cultural phenomena that I in the land down under found utterly puzzling. However, he also said some good things that I did understand. Namely, that chemophobia is not an insurmountable problem. Together with organisations like the ACS, we can make a concerted effort to change the way the public responds to chemistry. Also, keep an ear out for an upcoming episode of Chad’s Chemjobber’s podcast, in which he, Chemjobber, Chemtacular and ScienceNotScary will explore these issues further.

Dorea tells us that she is ahead of the curve, and ditched using chemophobia in favour of ‘chemical misconceptions’. Dorea’s emphasis is on increasing understanding of chemistry in everyday life, with a splendid example of this in her follow up post.

Edit 1: Feb 13 2014 8:30 PM AEDST

Thanks to commenter Chad below, I’m pleased to add two more posts to the roundup.

Jen at Experimentalitea pointed out that chemophobia almost certainly isn’t technically the right word to use, as people’s fear is not an involuntary, irrational response. Rather, it is the product of years of conditioning to the false dichotomy of natural=good/synthetic=bad which is perpetuated through the media.

Tyler at Science Borealis took the example of polyaromatic hydrocarbons to demonstrate the complexities and nuance of the chemicals we experience in our daily lives. PAHs are ubiquitous in the modern world, found in cigarettes, outer space, burned food, and the atmosphere. Some of them are known carcinogens, yet we generally go about our lives breathing and eating PAHs without giving it a second thought – what does this mean for our understanding of chemicals and the risks associated with them?

Edit 2: Feb 13 2014 10:40 PM AEDST

Shawn at Chemistry Reflux suggests that it might be time for chemists to eat a little humble pie, and accept that the ‘defend and debunk’ model of combatting chemical wrongs is not going to get us very far. The last paragraph of Shawn’s post in particular is really ace and you should go and read it right now.

End Edits

It seems the chemists of the internet have well and truly spoken on this issue, but it has also become clear that we are only speaking amongst ourselves. The question of how we should best approach the problems of chemistry’s bad reputation in the public sphere is what remains.

Go forth, fellow champions of the chemical sciences and react.

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*Chad recently let me in on the fact that Chad is short for Chadmium. Actually, maybe we are long lost siblings because I use Renée as the short version of my full name, Rhenéenium.

** If I have missed any other contributions, please let me know.


A Discussion of #chemophobia on Twitter: in Blogversation with @chemtacular

Over the last few months, there has been an ongoing conversation between some chemists on twitter discussing the use of the word, and hashtag, (#)chemophobia, kicked off (I think) by this post from @mustlovescience. One of the main drivers behind this dialogue is @chemtacular, who led a charge to replace the use of #chemophobia, which is described in this post from her blog Tales from the Critical State. Feeling a little stifled by twitter’s 140 character limit, @chemtacular and I (@reneewebs) have decided to go long-form and discuss this over a few posts on our respective blogs, a ‘blogversation’ if you will (I love terrible portmanteaux, go ahead and judge me I don’t care!).

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To break down and expand upon some points that @chemtacular raised in her post:

My issue is that this term [chemophobia] is used by chemists to describe a negative portrayal of chemistry.

This I agree with, and I can provide a couple of examples here where chemistry has been misused or misunderstood, but there is not necessarily a fear element involved.

bogus

Left image source: Reddit Chemistry .Right image source: also Reddit Chemistry I think but I couldn’t find the original thread, if anyone has the link please let me know so I can add it

Cases like these is where the hashtag #boguschem is perfect.

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I also have a hard time with this word [chemophobia] because it is used in such a way that it strengthens the rift between the public and chemistry when there doesn’t have to be one

This I believe it the strongest argument against using the word chemophobia, especially on twitter. Consider this Totally 100% Real* twitter interaction I captured earlier:

 chemophobia1

*not actually any % real

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When the chemtwitosphere jump on some dodgy chemistry in the media (which we often do), what do we hope to achieve by tweeting about it, whether we include the hashtag #chemophobia in the discussion or not? I suggest there would usually be two reasons;

  1. We want to point out that the individual or organisation in question has made a scientific error, ideally in a polite and civil way that would educate them and encourage them to think about making a change their marketing or labelling. Climb On Products is an example of one company who did make such a change, although I’m not sure of the circumstances in which this came about.
  2. We want to have a joke or commiserate amongst our community, to laugh and cry together about crimes against ‘our’ chemistry. We’re a passionate bunch of chemists, and to bond (pun intended) over these shared frustrations is something that helps to connect us.

What do you think @chemtacular, are there other situations you can think of where we might need to frame things differently again?

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I spent an afternoon tweeting with chemists … and the best we could do to come up with a term that wasn’t dismissive, punching down, or dissing chemistry was #BogusChem

@chemtacular, I would love if you could expand upon this – why is the choice of wording in the phrase so important? On twitter you’ve talked about being wary of using certain words like ‘abuse’ and ‘exploitation’, or derivations of these. And finally, is it possible that maybe there just isn’t an English word or short phrase that exists to perfectly convey what we’re trying to say?

I look forward to your response.