Celebrating 40 Years of Spectroscopy with “Molecular Spectroscopy Workbench” Columnist Fran Adar

As part of celebrating the 40^th year of Spectroscopy magazine, we sat down with our “Molecular Spectroscopy Workbench” columnist Fran Adar to talk about the advancements in spectroscopy during the lifetime of the publication, as well as how, in her view, Spectroscopy magazine has evolved. We note that Emil W. Ciurczak was the first author and editor of this column for many years and published a Wiley book by the same name in 1996.

What would you say are some of the most transformative advancements in Raman spectroscopy and other spectroscopies in the ultraviolet-visible (UV-vis) part of the spectrum over the last 40 years?

The changes in Raman instrumentation have definitely been transformative and are a result of the introduction of the digital camera as detector; the notch and edge filters that enable collection of spectra on a single mono rather than a double or triple; the implementation of a microscope for sampling; and the availability of low cost computers, which enabled the development of software for a multitude of things, but especially imaging and multivariate analysis (MVA) to extract information from the spectra.

I can make some remarks about another technology. Absorbance, transmittance, and fluorescence excitation-emission-matrix acquisition (A-TEEM) spectroscopy has been introduced in recent years for characterizing materials that exhibit UV-vis absorbance and fluorescence signatures. In addition to simultaneously acquiring absorbance and transmission spectra, the technique produces three-dimensional (3D) fluorescence excitation-emission-matrix (EEM) plots that are corrected for the inner filter effect. Even though the spectra themselves are quite broad (compared to Raman spectra), the 3D molecular fingerprints provide exquisite detail at very low concentrations, enabling detection of biopharmaceuticals, contaminants in water, and phenolic profiles of wine and other food products.

What technologies do you think will have a transformative impact on the industry moving forward? How do you think spectroscopy will evolve over the next decade?

When I was hired in 1978, the feeling that my managers had for the Raman microscope was that there would be a big market in biomedical and life sciences. At that time, we were using water cooled gas lasers, single channel detectors, and a strip chart recorder for detection. I like to say that if the pen went dry, you had to redo your experiment! I had come from a biophysics department, and it was clear to me that getting information from spectra that represented multiple very large molecules whose spectra could change with pH, interactions, or concentration, would be near impossible. In those days, the Raman action would be in semiconductor analysis (even though the physicists in this country didn’t recognize it for some years), but now the action will be in the life sciences. The reason that information can be extracted today is because the acquisition of the spectra is faster, the instruments are smaller and easier to use, and there is software to assist with the information extraction. In particular, multivariate techniques applied to the Raman maps in the life sciences have enabled what was previously impossible. Raman microscopy, in combination with MVA, has been elucidating metabolic changes and disease diagnosis. Although the number of clinical researchers that are using the technology is limited, as the number of successful studies increases, more researchers are certain to come asking to understand what can be done for their problems. In a way, the situation will be like what it is today with industrial analysts who come to us having heard that Raman microscopy can be helpful but do not know where or how to start getting the needed information. It will be our job to continue to work with them on their problems and to understand what innovations in the hardware and software can help so that we can prod our engineers to innovate in ways that will enable new applications.

Are there any emerging techniques or hybrid approaches that you believe will define the future of the field?

We have been working for many years with Israel Wachs, G. Whitney Snyder Professor, Chemical and Biomolecular Engineering Director, Operando Molecular Spectroscopy and Catalysis Research Lab at Lehigh University, who has been systematically studying catalysis by combining his Raman measurements with Fourier transform infrared (FT-IR) and mass spectrometry (MS) to understand what the catalyst is doing so that new catalysts can be designed in a rational way. The catalyst world calls this “Operando,” a term initially coined by Professor Miguel Banares in Madrid who had been post-docking with Wachs.

Using the same idea to study a system while it is undergoing chemical change can be applied to life sciences, chemical reactions such as polymerization and corrosion, and mineral transformations under controlled conditions of pH, stress, and temperature. All these applications will require the design of sampling cells to control the atmosphere and/or solvent environment, and the chemistry and/or physics of the process.

What advice would you give to folks who are just starting out their career in spectroscopy?

One thing that we all see is that people who know or have heard that Raman spectroscopy or microscopy can help them with their research often have little knowledge about spectral interpretation. I am acutely aware of how challenging this can be, especially because my formal background was in solid state physics and I can’t even remember what the names of the various organic functional groups mean. But this knowledge is necessary to solve problems of analytical spectroscopy. About 20 years ago, I took the course on Vibrational Spectroscopy at Bowdoin College because we had just introduced an FT-IR “accessory” to our Raman microscopes. I knew nothing about FT-IR spectroscopy and not much more about the Raman behavior of organic materials. Bruce Chase asked what I was doing in the course. My response was that I had been faking it. When I had to work on a particular material (such as polyethylene terephthalate fibers) I would figure out what I needed to know. That meant that I had to have a picture of the molecular structure. I have to say that even after all these years I still cannot remember the names of many organic functional groups, but I have learned to look them up when needed. The real issue is what can be the chemical changes during a reaction or degradation. That is what vibrational spectroscopy can elucidate but without a strong chemical background it is difficult to explain what is happening.

So, my advice is to learn all that is possible. I believe that many application fields are still in their infancy so there will be many breakthroughs.

On the other hand, for those who are looking for simple spectral identification, there are now tools that were not available 20 years ago. With an adequate spectral library, one can perform a spectral search and determine what is the identity of material from which a spectrum was acquired. This makes using a Raman microscope for routine analysis much less formidable.

In your view, how has Spectroscopy changed or grown over time?

In the past, I have referred to Spectroscopy as a trade magazine. But today, it is much more. There are articles that are quite sophisticated. And the editorial staff is working hard to understand what is happening in the analytical community and to publicize it appropriately. This is quite beneficial to the analytical spectroscopy community who, I know from comments to me personally, are following the field with this magazine because it presents complicated material in an accessible manner.

What has been your favorite part about writing your column for Spectroscopy?

Just as getting this job in 1978 was a gift, the opportunity to write the column has also been a gift. Because the articles are short and don’t have to have the rigor of a refereed publication, I am able to select a topic and write casually with the goal of making the material easy to understand. At the beginning, I felt like I was sitting in my living room and talking to a friend. My goal is to select a topic that is relevant to evolving technologies with practical and commercial relevance, to describe a problem that Raman spectroscopy can answer, and to show measurements that present an answer. I have often been shocked by utter strangers approaching me to tell me how much they learn from my articles. It is not even clear what this says about refereed publications. I find writing refereed articles quite painful. And when I get a review that seems to be nitpicking for the reviewer’s agenda, my feelings are only enforced.

What do you hope readers take away from your writing?

I hope that my columns inspire people to do what I do. To use the spectroscopy to solve their own problems. I hope that in couching my explanations in simplistic terms I have helped the readers to appreciate some tips and tricks that I have used which are obvious to me but not necessarily obvious to the novice.

Which column or topic you’ve written about has excited you the most, and what made it so compelling for you?

Wow, this is an impossible one to answer. I have written several articles on carbon, including a recent one on the formation of carbon from degrading organic materials. This is surprising because the spectra of carbons are quite simple, but making systematic measurements and correlating the spectroscopic characteristics with physical or chemical properties makes deriving information possible. I can’t say that it is more exciting than other topics, but the fact that it keeps coming up means that it is important.

Having thought about the range of topics that I have covered, I see that there are quite a few on polymers which is itself interesting because when I started, I didn’t know what the word “polymer” meant. One of my recent columns on polymers shows the results analyzing layers. I compared the results doing a depth profile, which does not require cutting and preparing the material, to a cross-sectional profile. I was really surprised to see how well the layers matched up. I have also done polarization studies to document orientation trends. Early on, I studied how orientation in polyester fibers reflected prior treatment including orientation from the spinning operation and from drawing (stretching) at room temperature. But I think that the polarization study of spherulites of polyhydroybutyrate hydroxyhexaonate (PHA) confirmed the conjecture that the rapid growth crystal axis is rotating around the spherulite radius. These measurements of PHA spherulites were studied with two-dimensional correlation spectroscopy (2D-COS), which I have enjoyed learning to use in some of my studies. When a system is changing systematically, 2D-COS enables one to extract information that cannot be “seen” in the data, because of the significant overlap of spectral features. For sure, this will be important when studying reacting systems because it enables determining the order in which changes occur! There is also now freeware available (to academia, with a minimum charge to industry for six months) to make the implementation of 2D-COS accessible to the non-programmer. It was developed by Higeyuki Shinzawa, who had been a student of Yukihiro Ozaki and a post-doc of Sergey Karzarin. If interested, one can contact h-shinzawa@aist.go.jp.

Is there anything else you’d like readers to know about your work?

The most important impact that I can have on the field in which Raman microscopy is used to understand materials and to solve problems is that I have inspired others to “think outside of the box.” I remember about 10 years ago while giving a talk at a conference, I made a comment that I am inspired by the “mysteries of the universe.” I am sure that this sounds odd for an analyst, but this curiosity and wonder at what I see is what keeps me going. If I can inspire my readers with the same curiosity and wonder, they will also be motivated to delve into the problems confronting them, doing the background research necessary to understand the problems, that will enable finding the solutions. With the world changing as fast as it is, there will be much to study to support these challenges.

Fran Adar is the Principal Raman Applications Scientist for Horiba Scientific in Piscataway, New Jersey. Direct correspondence to: SpectroscopyEdit@mmhgroup.com. ●