Sitting Down with a Chromatography Icon:
Dr. Robert Sternberg
Dr. Robert Sternberg received his PhD in electrochemical biosensors and worked on the development of a glucose sensor in an artificial pancreas for 10 years before joining an emerging field of astrobiology. This started a 37-year career in analytical chemistry that would play a critical role in the success of the Cassini-Huygens, Curiosity, ExoMars, and most recently the Rosetta mission. His areas of interests are in the characterization for organic molecules in extraterrestrial environments. He is currently a senior lecturer of chemistry at University of Paris and is head of the GC space instrumentation group at Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA). Dr. Sternberg and the European Space Agency (ESA) have been working with Restek, using our columns and Pro ezGC software on their missions, for over 15 years. With the Rosetta spacecraft and its Philae lander making the news recently, we caught up with Dr. Sternberg to discuss his work.
Q: Can you tell us more about your background?
A: I did my PhD on electrochemical biosensors, and I worked 10 more years in this field more particularly on a glucose sensor for artificial biopancreas. Then I went from the liquid phase to the gas phase, still remaining in analysis with gas chromatography and always related to life, but this time working on its origin and not on its functioning. The origin and the distribution of life in the universe is a field of research that started with space exploration in the '60s and is named exobiology or astrobiology.
Q: What chromatographic techniques have you performed?
A: Essentially gas chromatography coupled, or not, to mass spectrometry, with all the compatible various sample processing methods.
Q: How did you become a specialist of chromatography in space missions?
A: By joining a team of the Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA) that worked on the chromatographic columns of the GC-MS of the Cassini-Huygens mission.
Q: We know that you and the LISA were involved in several space missions, including the Cassini-Huygens, Curiosity, and ExoMars. Can you explain how these collaborations evolved?
A: You know, it is easy to say, but you have to be at the right place at the right moment, and once you have started, you stay more and more in the right place because your experience is growing, and at the same time, those of the teams you are working with. And each developed instrument is the result of a fruitful collaboration, which also improves and becomes more and more efficient with years.
Q: How was your lab chosen for these missions?
A: We were involved in the interpretation of the GC data of the Venera mission’s onboard gas chromatograph, and, therefore, we answered a request proposal of the European Space Agency (ESA) for the development of the GC columns of the GC-MS onboard the Huygens probe. After having been selected, we followed the same procedure for the following missions: Rosetta, MSL, and ExoMars.
Q: How many labs worldwide are involved in similar works?
A: A very limited number because of the very limited space exploratory missions. I would say about three to six for the chromatographic part.
Q: Why is chromatography important in exobiology?
A: Because of the compatibility of gas chromatography with space constraints: low energy consumption, easy automation, columns aging, etc.
Q: You have used our GC optimization software known as Pro ezGC. Can you tell us how Pro ezGC has helped you optimize your GC conditions and column selection?
A: We used this software at the very beginning of the columns selection of the COSAC instrument of the Rosetta mission. A coupled experimental and theoretical approach was taken in order to predict chromatographic data. We used a four-point experimental calibration (0 to 65% diphenyl group) in conjunction with the Pro ezGC modeling software, and we were able to predict with a mean error less than 5% for each compound the retention times of a complex mixture of target molecules irrespective of the stationary phase's diphenyl content and column physical parameters. Therefore, with the help of this software, we showed that with a small number of well-tuned DP-DMPS columns, the separation and identification of most of the targeted compounds can be achieved with a minimum amount of coelutions and within the experiment requirements . And, this work was used for missions such as MSL 2011 and ExoMars 2018.
Q: What is the most challenging part about developing a chromatographic system for space?
A: It is quite different from developing a “terrestrial” chromatographic system. Because of the space constraints, you have to consider, as your first objective, whether you say it or not, is to get an unambiguous signal of a targeted compound. And, only then one cares of quantification. The challenge is to certify the presence of a new or awaited interesting compound.
Q: What does the composition of Saturn’s largest moon Titan tell us?
A: The Cassini-Huygens mission showed that Titan hosts subsurface liquid water ocean, probably deep enough to not be frozen. It allowed us also to discover the presence of cryovolcanoes, which do not discharge lava but instead discharge liquid materials at low temperatures. All these findings have improved significantly our knowledge of this satellite, which as we know could host life. And, above all, the numerous data delivered by this mission confirmed and validated all those modeling and experimental simulations had predicted.
Q: What was your contribution to the Mars Curiosity mission?
A: My personal contribution was to participate in the selection of the six chromatographic columns of the Sample Analysis at Mars GC system and to the design and validation of the Sample Processing System used. This SPS used derivatization (MTBST and thermochemolysis) for the extraction and volatilization of the molecules of interest included in the sample. But, the total contribution of LISA was the construction of the GC subsystem (box) with chemical traps, columns, and nanoTCDs, and, of course, the in situ experiments and their interpretation.
Q: How is COSAC (COmetary SAmpling and Composition experiment) different from other chromatographic systems designed for space?
A: Since the rendezvous with the comet Tchouri took 10 years (in fact, 11 because the mission was delayed one year because of the problems encountered with the launcher Ariane 5), the GC subsystem was developed long before those of the current MSL and the coming ExoMars missions. Nevertheless, there have been some improvements over the GC of the GC-MS of the Huygens atmospheric probe. First of all, what is different is the number of columns. There are eight columns (instead of three for the Huygens GC-MS), and all of them capillary. In order to prevent problems encountered on the Huygens probe, each column has its own thermal conductivity detector. What is new also is the use for the first time of chiral stationary phases (three columns) with an SPS for the nonvolatile molecules using derivatization in gaseous phase. And, of course, the mass of COSAC (4.5 kg), which is about four times less than that of the Huygens GC-MS.
Q: How long have you been working on the Rosetta mission with the ESA (European Space Agency)?
A: Six years, from 1996 to 2002. During the 11 years of transfer, we studied the chromatographic performances of the columns stored under vacuum, and, of course, now we are taking care of the measurement strategy, the recuperation of the in situ data and their treatment and interpretation.
Q: Four Restek columns were chosen to be fitted on the Philae lander now situated on the comet. Why did you choose Restek columns? How did you choose these specific phases?
A: We have been working with the Restek company since the Cassini-Huygens mission. The first capillary column that has ever flown in space was a Restek MXT-1701. For COSAC we had a very close collaboration with Restek, which developed custom-made columns with specific ID and film thicknesses particularly for the Plot column one. Once an agreement was obtained on the molecules to be searched for, we did an exhaustive work on the stationary phases available [3,4,6] (especially work described above) and matched them with the target molecules.
Q: You have visited Restek facilities in Pennsylvania prior to starting the project. What was your overall impression?
A: My colleague David Coscia and I visited Restek facilities some years ago. We were extraordinary well received both in the beautiful visitor house and in the company itself where we met the founder Paul Silvis and many Restek employees to whom we could express our problems and needs. We were very impressed by the ambience, setting, and working conditions.
Q: Has the Philae lander been able to transmit any data?
A: Yes, on November 12, during the first rebound of Philae, a sniffing of the cometary dust on the surface was directly analyzed by mass spectrometry. And then, drilling was attempted and a GC-MS analysis with a chiral column carried on. The data of these two analyses were processed and are currently being published. Then, because of battery problems, Philae went into hibernation for seven months and just woke up. The operating status of Philae is being checked and all instruments will be restarted .
Q: Restek columns have been “flying” in space for more than 10 years. Are they still performing well?
A: Except for the PLOT column, the efficiency (HETP) of which decreased less than 15% in 10 years, the three others kept their performance (H, r) intact [2,5].
Q: Based on your experience, what chromatographic advancements will help you with future missions?
A: I am not sure that the future is miniaturization (lab on chips), whatever the analysis system (LC, CE, or GC) used because the main problem will always remain sample processing, especially when the sample is solid. You can use some microliters or nanoliters for the mobile phase but not for extracting target molecules. Therefore, I think for future missions, efforts need to be focused primarily on the sample processing and mostly on the extraction to make it easily coupled to whatever chromatographic techniques are compatible with space constraints.