The LCGC Blog: What Can Analytical Chemists Do for Chemical Oceanographers, and Vice Versa?
It did not take long for us outsiders to realize that chemical oceanographers are already really good analytical chemists. There are myriad real challenges that were quickly brought to light as the workshop began with presentations by a number of renowned oceanographers. First, all measurements must deal with a background matrix of 0.6 M NaCl and a lot of dissolved and undissolved organic and inorganic matter. For example, there is strong interest in measuring the concentration of iron throughout the ocean system, because this can tell you where organisms can and cannot grow, but currently there appears to be a real lack of understanding of how the iron is distributed among organic and inorganic forms. To make this more difficult, the distribution of forms is likely to change depending on proximity to the coast or the depth at which the information is desired.
Speaking of depth, probably the most desirable technologies for oceanographers would be those that could make measurements at specific depths in situ, for the wide range of elemental, nutrient, and physical parameters desired to be known, and simply radio that information back. If such a system could operate unattended for as many as five years, then all the better. We heard descriptions of long scientific voyages across the Atlantic and Pacific, north and south, which initially sounded intriguing to try to join. Then, as the notion of sample collection and shipboard analysis were considered, the limitations in space, environmental stability, and time became apparent. In some cases, radiometric dating elements, such as thorium and protactinium isotopes, need to be measured at ultratrace (attomolar or lower) levels. We heard stories of how literally as much as 12 tons of seawater would be delivered from a voyage to one lab to make these measurements — because the time and resources simply were not available to reduce this collection volume on the ship, during the voyage. Such a situation, where the capacity of a 150-ft-plus long scientific research vessel to hold collected ocean water on deck must be considered, gives a new meaning to the term “sample limited.”
Of course, much progress has been made in recent years, with the use of unmanned vehicles and sophisticated sensors, to achieve the analysis of some key parameters, such as salinity, dissolved oxygen, and temperature in situ and at different depths. Interestingly, pH is still an issue – at least at the level of precision desired to be measured by oceanographers. It was shocking to hear that measuring pH to a precision of ±0.002 units was just not quite good enough. I suppose that when the goal is to monitor small changes that result in large environmental impacts, over long time periods, you want your measurements to be as precise as possible. With regard to elemental analysis, a nice summary was given by Prof. Gary Hieftje when he said, “Okay, I guess you just need an ICP-MS that fits in a shoebox, can operate underwater, and consumes no power and gases.” It falls into that category of things that are funny because they are true.
The analytical chemists were not without some new solutions to offer, however. Microfluidic lab-on-a-chip and lab-on-a-valve platforms were presented for various applications, both oceanography-related and otherwise-to-be-adapted. Flow injection analysis appeared to be a strong player for development in shipboard measurements, given its small footprint and versatility. The main challenge in this area appeared to be a greater degree of multiplexing — to minimize the number of individual methods that would be needed to simultaneously measure different analytes. Electrochemistry, perhaps even in combination with spectroscopic measurements, showed significant promise. Few could help but be enamored by the future possibilities afforded by nanosubs driven by electrochemical motors that appeared to be well suited to perform a variety of tasks. Perhaps two areas that were not as heavily considered as one might think (at least that was my, perhaps biased, assessment) were chromatography and mass spectrometry (MS). These techniques appear to have their place in the traditional laboratory setting, except for some on-board gas chromatography (GC) measurements for chlorofluorocarbons that were discussed. Yet, miniaturized chromatography and MS platforms, and perhaps even other contemporary techniques, such as ambient ionization MS, do not have a place in shipboard measurements. To get there, they are certainly going to have to be made more robust and sensitive. For chromatography, perhaps some systems that are currently being developed to send to Mars could have the performance capabilities necessary for shipboard operations. In the end, it was not lost on the analytical chemists that there is certainly an inherent limitation with MS — the transfer efficiency from source to detector is a major source of loss of analyte signal. It is hard to expect to be able to detect species that only have 10,000 atoms in a given sample, if you are going to throw away 9800 of them just getting them to the detector.
So, in my more limited analytical chemistry experience, compared to some others that I was honored to spend time with at this workshop, I can honestly say that oceanographic measurements represent a real challenge for our discipline. When routine measurements of elements present in nano- to picomolar levels in the presence of a huge background are desired to be determined on a ship that travels from the subfreezing arctic to the tropics and costs $40,000/day to operate (not including the science), then some special considerations have to be made. But it’s difficult to make choices that sacrifice information. As one oceanographer said, “Ocean chemistry is always underdetermined, so you can never have too much data.” Despite their costs, these efforts are important; the oceans hold a great deal of history, but more importantly, they are our barometer for how climate change and human activity may drastically affect the world as we know it in the near future. A report from the workshop, prepared by its organizers and other contributors (including yours truly), will soon be submitted to the National Science Foundation. I assume that this report will be made available to the public, and when it is, I urge you to give it a read. I think you will find it fascinating. More such collaborative assessments should be undertaken to understand where new advances can be applied to solve challenging problems in different areas of science and engineering. In this case, my only regret is that I did not get more time to enjoy the outdoors in Hawaii. And I am sure you feel bad for me.
Previous blog entries from Kevin Schug: