Adventures in Open Access publishing

 There is not a lot of diversity in the journals geochemists, geochronologists and hard-rock petrologists traditionally publish in.  Precambrian Research, Geochimica, Chemical Geology, Gondwana Research, and EPSL are all run by Elsevier, while the Journal of Petrology and Contributions to Mineralogy and Petrology are also published by large, for-profit corporations.  American Mineralogist is one of the few society journals still published and operated independently. And although member subscriptions and not too dear, the journal is by no means open access.

Other fields of geoscience have been making more progress in the open access revolution.  Planetary and astronomy related geophysics often finds its way into arXiv, biogeosciences can sometimes access PLOS or PeerJ, and the EGU have a variety of open access society journals which span a range of geophysical topics.

One of these journals is Geoscientific Instrumentation,Methods, and Data Systems (GI). While most of their published work appeares to relate to home-made data acquisition systems for geophysical experiments, a colleague and I decided to approach them and see if they were interested in a manuscript relating to ICP-MS, one of the mainstay bread-and-butter methods of geochemical analyses these days. So we sent in the manuscript, and, to make a long story short, it is published online here.  

Anyone reading this who is interested in new, community-based alternatives to the big scientific publishing houses should check it out- the process and handling was similar to any other journal, the timescale was similar to traditional publishing in our field (about 5 months submit to published, including Christmas, and at least 1 month of delay which was entirely my fault), and I have to say that I found the editors to be as professional and helpful as anywhere else I have submitted.

 And the work I originally blogged about here a long, long time ago is finally in print.

C. W. Magee Jr. and C. A. Norris (2015) Alkali element background reduction in laser ICP-MS Geosci. Instrum. Method. Data Syst., 4, 75-80.
www.geosci-instrum-method-data-syst.net/4/75/2015/
doi:10.5194/gi-4-75-2015

Meteorite tea, and the failures of genius

In the early 1970’s, Io, the innermost large moon of Jupiter, was somewhat of an enigma. Unlike Europa and Ganymede, it did not exhibit water ice adsorption bands it its IR spectra. Its density suggested that it was a rock and metal planet, but the surface reflectance was unlike anything known to science. This problem was addressed brilliantly in a Science paper by Fanale, Johnson, and Matson, researchers at the Jet Propulsion Laboratory. These scientists explained all the anomalous features of Io in a single stroke of genius.

By that time, it was known that meteorites were primitive condensates of the primordial solar nebula, even though the detailed work describing their subtle differences had not yet been completed. Since the outer moons of Jupiter were known to contain water, the study hypothesized that Io lost its primordial water and never accreted any ice later on. They then tested this hypothesis. Fanale et al. took a piece of the very primitive CI meteorite Orgueil, and made meteorite tea by boiling the piece of Orgueil in water. They then evaporated off the water and looked at the precipitate. What they found was mostly magnesium and sodium sulfate salts, with some halite and other elements mixed in. The reflectance spectra of these precipitates more closely matched that of Io than other hypothesized frosts, especially when treated with radiation. AS the evaporite was enriched in sodium, this process also efficiently transported sodium to the surface, where it can be ionized by ambient radiation, producing the Na ionization halo which was known around Io at the time.

So basically, the theory goes like this: during accretion, Io was too warm for ice to condense. Accretion from meteorites comprised of hydrous silicates released water as the planet grew and the interior increased in heat and pressure. This fluid then leached the rock, escaped to the surface, sublimed or evaporated, and left salts behind, which was what we see today. In other words, Io is an evaporite planet.

This theory explained everything know about Io so well that it would be another five years before Voyager one- at the time the most advanced robotic space probe ever launched- took pictures of Io as it flew past Jupiter which instantly and completely proved the evaporate hypothesis to be false.

The history of science is often taught as a series of breakthroughs generated by men of immense intellect who are smart enough to see the world as it is. But the reality is that the world doesn’t really care about genius. There are many incredibly brilliant scientific deductions- like the hypothesis of Fanale et al. of the evaporitic Io, which are spectacularly and brilliantly wrong. But science education has a powerful selection criteria that ignores all of the stunningly clever, but completely incorrect deductions. Instead, proponents of discarded theories are often depicted as dim, or close minded, or stuck in their ways. But in cases such as this one, they simply had no way of acquiring the data needed to disprove their hypothesis, as flying to Jupiter and looking at Io up close was science fiction in 1974. Five years later, it was history, and so was their wonderful model.

Fanale, F., Johnson, T., & Matson, D. (1974). Io: A Surface Evaporite Deposit? Science, 186 (4167), 922-925 DOI: 10.1126/science.186.4167.922

Choice magazine to consumers: don’t eat white dwarfs

There is a Choice Magazine report advocating for stoplight rating of foods, to help consumers eat more healthily. Their rating system uses units of 100g/mL (see figure 1, below). That is tenths of a kilogram per milliliter. I don’t know what they are eating, but the densest known substance at the surface of the Earth is osmium metal, with a density of about 22 g/mL, or 0.22 100g/mL.

Their “green light” value for sodium is 0.3 100g/mL, which is about 50% denser than anything on Earth. For comparison, a pure halite crystal 1 centimeter on a side (salt conveniently grows in cubes) will contain 2.16 g/cc x 0.39 g(Na)/g(total) = 0.85 g sodium. In units of 100g/ml, pure salt thus has a value of 0.0085 100g/mL.

Never-the-less, they rate almost every cereal as having an orange or red light rating.

There can be only one explanation. While osmium may be the densest material at surface pressures, at higher pressures many things can be more dense. As an example, consider a white dwarf star. A white dwarf is the burned out core of a star which has run out of hydrogen fuel and collapsed into a super dense state. Although calculating a diameter (and thus density) is not easy, they are generally thought to be about a million g/cc, or a ton/cc. On the Choice Magazine scale, that would weigh in at ten thousand 100g/cc.

Of course, white dwarfs are mostly carbon and oxygen, not sodium. But lets assume that they have a solar O/Na ratio. Using the Asplund et al. (2006) values, the solar O/Na ratio is about 300. But since white dwarves have carbon, silicon, etc. in them as well, we should really look at the ratio of everything except H and He to sodium. This is about 600 (in other words, carbon plus nitrogen plus all the heavier metals are about as abundant as oxygen).

So a white dwarf sodium content, using choice magazine units, is about 16.7 100g/mL.

Figure 1. The traffic light rating table from the choice magazine report.

That is more than ten times the 1.5 100g/mL “red light” value they suggest.

So eating degenerate matter from the cores of burned out stars is not recommended by Choice. It contains too much sodium, and might give you high blood pressure.

M. Asplund , N. Grevesse, A. J. Sauval; The solar chemical composition; Nuclear Physics A 777 1–4 (2006)

Mutual replacement reactions in alkali feldspars II: trace element partitioning and geothermometry

When I was taking care of the upstairs ICPMS lab back in my former university life, I would occasionally pick up stray orphan scientists who were interested in some mass spectrometry. These are people collaborating with ANU scientists on non-mass spectrometric matters, who want to get the trace element composition of something, but aren’t hooked up with one of the analytical gurus.

Ian was one such fellow. I think he was mostly here doing TEM work or something, but he came into lab one day wanting to do some laser work- something on alkali in feldspars.

Feldspars contain weight percents of alkali, so this didn’t sound terribly interesting. I set the machine up, tuned it up. OK, is there anything in particular you’re interested in?” I asked.

“I’ll need the smallest spot you can give me.”

I wasn’t a big fan of our small spot- it had 1/14th the area, and thus 1/14th the signal, of the standard size. “Why so small?” I asked.

“I’m trying to analyse exsolution lamellae. Also, I wouldn’t mind getting good numbers on rubidium, cesium and thallium.”

To make matters worse, it was a evolved unit from a layered intrusion, so the trace element compositions were way lower than from a granite.

What had been a painfully routine day had just turned into a challenge.

Fortunately, it was a challenge for which I was prepared. Rb and Cs are notorious in laser systems for having high and variable backgrounds due to reionization off the back of the skimmer cone from ejected electrons. We had a grad student who was looking at Rb and Cs in primitive, depleted melts, so I had been working on this problem for over a year. Suddenly, I had an application for all the work I had been doing.

So, I blew off everything else I had planned to do on what was supposed to be a routine out-of-the-lab-by-morning-tea day, converted everything into low detection mode, put the machine back together, tuned it up, checked the backgrounds, and off we ran. With enough trial and error, We eventually got a machine state and a run table that got most elements detectable most of the time, and by the end of the day the signals were looking semi-respectable. Cs in the albite ended up being too low for us to see, but everything else we got decent detections for. The next day was productive, and by the time we finished it was almost routine. Charlotte did the data reduction and Ian interpreted and plotted all of it up, so I never actually saw what the results meant. When I finally got the draft, I was astounded at the outcome. It’s a natural system, and yet it behaves just like it ought to. Who’d a thunk that?

Of course, the papers describes the analytical procedure used to collect the counts. But counts don't make a signal, counts in excess of background do. And while I'd love to tell you how the background was reduced, that paper just got rejected.

The abstract and word cloud are below:

Perthitic alkali feldspar primocrysts in layered syenites in the Klokken intrusion in South Greenland, underwent dissolution–reprecipitation reactions in a circulating post-magmatic aqueous fluid at *450_C, and are to a large degree pseudomorphs. These ‘mutual replacement’ reactions provide a perfect natural experiment with which to study trace element partitioning between sodium and potassium feldspars growing simultaneously. The reactant ‘phase’ was a cryptoperthitic feldspar consisting of low albite and low microcline in a coherent sub-lm ‘braid’ intergrowth and the product phases were ‘strain-free’ incoherent subgrains of low albite and low microcline forming microporous patch perthites on scales up to 200 lm. The driving force for the reaction was reduction of coherency strain energy. The mechanisms of this process are described in Part I. Five mixed braid perthite–patch perthite crystals were analysed for major and trace elements using laser ablation-inductively coupled plasma mass spectrometry with a 19 lm beam diameter. This gave bulk analyses of the braid texture, which were in the range Ab73–54Or45–27An4.3–0.8, but could resolve Ab- and Or-rich patches in patch perthite. The major element bulk compositions of the crystals were retained during the replacement reactions. Major components in patches plot on tielines in the Ab–Or–An ternary system that pass through or very close to the parent braid perthite composition and indicate local equilibrium on the scale of a few tens of mm. Many trace elements, including REE, were lost to the fluid during the deuteric reactions, but the effect is large only for Fe and Ti. Cs, Pb and Sr were added to some crystals. Plots of log distribution coefficient D for Rb, Ba, Pb, Eu2?, La and Ce between Or- and Ab-rich patches against ionic radius are straight lines, assuming eightfold coordination, and to a first approximation are independent of ionic charge. K also lies on these lines, and the smaller ions Na and Ca lie close to them. The best linear fits were obtained using ionic radii for [8]K and [8]Ca, but there is ambiguity as to whether [7]Na or [5]Na is most appropriate. The linear relationship shows that the listed trace elements are in the feldspar M-site rather than in inclusions. Tl is in M although an exact D could not be obtained. The very large Cs ion partitions strongly into the Or-rich phase but its D value appears to be less than predicted by extrapolation. The near-linearity arises because partitioning is occurring between two solids into sites which have similar Young’s moduli, so that the parabolas that normally represent trace element partitioning between crystals and liquids (which have negligible shear strength) approximately cancel out. Ga and Be are in T-sites, as well as some of the Fe and Ti present, although part is in oxide inclusions. The site of Sc is unclear, but if structural it is likely to be T. Partitioning on M-sites is a potential geothermometer but because the effective size of the irregular M-site is defined by its K and (Na ? Ca) contents, which are controlled by ternary solvus relationships, its calibration is not independent of conventional two-feldspar geothermometers. Trace elements may however provide a useful means of confirming that feldspar pairs are in equilibrium, and of recognising feldspar intergrowths produced by non-isochemical replacement rather than exsolution. Two-feldspar geothermometry for the ternary phases in the low-albite microcline patch perthites gives temperatures above the stability range of microcline, markedly so if a correction is made for Si–Al ordering. This is probably because current geothermometers are too sensitive to low concentrations of An in ordered Or-rich feldspars. This interpretation is supported by two-feldspar assemblages growing at known temperatures in geothermal systems and sedimentary basins.

Parsons, I., Magee, C., Allen, C., Shelley, J., & Lee, M. (2008). Mutual replacement reactions in alkali feldspars II: trace element partitioning and geothermometry Contributions to Mineralogy and Petrology, 157 (5), 663-687 DOI: 10.1007/s00410-008-0358-1

Why do we publish papers?

I recently had a short technical note rejected by JAAS, wrote a bitchy self-indulgent blog post about it. Then through the miracle of delayed posting came back and revisited it before it went live. So, in an attempt to create something productive (and marginally less self-indulgent) out of the experience, I’d like to look into the final comment of the first reviewer:

2g. References: I could locate but not open Geostandards Newsletter and Geostandards and Geoanalytical Research journals. I could not find ICP-MS Journal 2000 (refs 1 and 1-10). Ref. 11 is not complete. I had also no access to refs. 4-7, 12, 13. Ref. 14 is missing.

Geostandards newsletter, which became GAGR in 2001 or so, was the publication referenced in numbers 2, 3 (mostly), and 9. Number 8 referenced an article in JAAS, the journal for which this person was reviewing. How many does that leave?

In reality, of course, it doesn’t matter if anyone ever reads papers. Papers are just a way ot scorekeeping for promotion reviews of professional academics. Back in the 19th and 20th centuries, however, journals were actually used for the dissemination of scientific information. I’m not old enough to know what that was like, but it does make me wonder:

If non-academic scientists get all old-fashioned and traditional, and feel the urge to give their colleagues tips, what is the point of trying to publish papers if even the people who review the papers can’t read any of the work on which the research is based?

The reference list is attached. Observant readers may note that my likelihood to be taken seriously as a scientist might improve if I could successfully demonstrate the ability to count to three.

1 C. Tye, K. Sakata, ICP-MS Journal 2000, 8, 7.
2 S. M. Eggins 2003 Geostandards and Geoanalytical Research 2003, 27, 147–162
2 K Sakata, N. Yamada, Naoki Sugiyama Spectrochimica Acta Part B, 2001, 56, 1249-1261.
3 K. Govindaraju. Geostandards Newsletter 1994, 18, 1-158; S.M. Eggins, J. D. Woodhead, L. P. J. Kinsley, G. E. Mortimer, P. Sylvester, M. T. McCulloch, J. M. Hergt, M. R. Handler. Chemical Geology 1997, 134, 311-326; M. D. Norman, W. L. Griffin, N. J. Pearson, M. O. Garcia, S. Y. O'Reilly, Journal of Analytical Atomic Spectrometry, 1998, 13, 477-482; R. W. Hinton, Geostandards Newsletter: The Journal of Geostandards and Geoanalysis 1999, 23, 197-207; S. Gao, X. Liu, H. Yuan, B. Hattendorf, D. Günther, L. Chen, S. Hu, Geostandards Newsletter: The Journal of Geostandards and Geoanalysis 2002, 26, 181-196.
4 S.-s. Sun W. F. McDonough. 1989 Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes Geological Society, London, Special Publications; v. 42; p. 313-345
5 J. Longhi, American Journal of Science 1987, 287, 265-331.
6 D. L. Hamilton, D. M. B. Henderson, Mineralogical Magazine 1968, 36, 832-838.
7 S. Eggins, R. Grün, A. Pike, J. M. S. Shelley and L. Taylor, Quaternary Science Reviews 2003, 22, 1373–1382.
8 H. P . Longerich, S. E. Jackson and D. Gunther, Journal of Analytical Atomic Spectrometry, 1996, 11, 899-904
9 N. J. G. Pearce, W. T. Perkins, J. A. Westgate, M.P. Gorton, S.E. Jackson, C. R. Neal, S. P. Chenery, Geostandards Newsletter, 1997, 21, 115-144.
10 C. Tye, K. Sakata, ICP-MS Journal 2000, 8, 7.
11 I. Parsons, C. Magee, C. Allen, J. M. S. Shelley, M. Lee, Mutual replacement reactions in alkali feldspars II: Trace element partitioning and geothermometry. Contributions to Mineralogy and Petrology. In Press.
12 A. Kallio, T. Ireland; “Silicate melt inclusions in komatiites as potential indicators for crustal growth”. 2006 16th annual Goldschmidt conference.
13 J. D.Stopar, G. J. Taylor, and M. D. Norman 2007 Aqueous alteration in Naklite MIL 03346: LA-ICPMS and Raman spectrometry. 7th International Mars Conference.

* * UPDATE * *

Can you find the references listed above? If so, can you read them? There are polls to the right! -->

Titanium as a cathodoluminescence activator in alkali feldspars

Ian Parsons, David A. Steele, Martin R. Lee, and Charles W. Magee 2008. Titanium as a cathodoluminescence activator in alkali feldspars American Mineralogist, Volume 93, pages 875–879

Abstract:
Albite patches in coarsely mesoperthitic alkali feldspars from the Klokken syenite have oscillatory zoning seen at blue wavelengths using cathodoluminescence. Using a five-spectrometer, high-resolution elemental mapping technique in an electron probe, we show a close correspondence between CL emission intensity and Ti, present at levels up to ~200 ppm. Albite patches were analyzed for major and 16 trace elements by laser-ablation inductively coupled-plasma mass spectrometry. SEM elemental maps acquired simultaneously with the CL showed that a similar zoning pattern is exhibited by Ca, but there is no correlation between CL intensity and Ca concentration. None of the trace elements analyzed correlate with Ti. We conclude that tetrahedral Ti4+ is the most likely activator of blue luminescence in these albitic alkali feldspars possibly because of a defect associated with Al-O-Ti bridges.

word cloud:

ab-rich above activator al albite albite-rich alkali analyses blue ca cl correlation data detail detection electron elements epma et feldspars fig figure images intensity klokken la-icpms lee limits luminescence major maps nm optical parsons patches phase ppm prep present range sample showed shown strong syenite ti ti4 trace wavelengths zoning

created at TagCrowd.com

This is an example of a low marginal cost paper. The main purpose of bringing the samples to the ICP lab was a different study, but Ian figured he might as well check this out while everything was in place. The main study was big, complicated, and only just recently went off to reviewers. But this was simpler and more straightforward, so got written up and published first. So it is a great example of why research needs to be structured in a way such that investigators can veer off of their predetermined path if they see the opportunity to potentially figure something out for relatively little time, effort, and cost.

Alkali background banishment

When I started this project, the background count rates for the alkali, in ppm equivalets, were:
Li: 87
Na: 623
Rb: 0.090
Cs: 0.037

After a year of belittling the backgrounds, the machine can now generally achieve:
Li: 0.5
Na: 161
Rb: 0.022
Cs: 0.005

I'd say that result is good enough for a conference in New Zealand. I'm going to bed now.

Poster or Talk?

Which do you prefer? Which is more work? Which is more rewarding?

I used to think that posters were way more labor intensive, but I realized today that for all my previous talk, I already had figures that I just needed to slot into the talk. Having to make them up from the data just for the talk is significantly more effort.

So I don't have time to present more detailed argument for and against each format; I still have a dozen slides to finsih tonight.

Paper pause

Expect light blogging for a while, I’m trying to write up the erotic alkali stuff- the project from which I presented a data datum point at the Goldschmidt conference. As you can see from the figure below, I collected too much many data. So now I have to make sense of it them, or at least come up with good excuses to throw the crappy stuff out.



For example, excluding the days when we were running with the designated high alkali cones gives something like this- which almost looks vaguely half-under control for some of the time.



Even after I get a handle on all this, I still need to write the damn thing- and I suck bigtime at writing papers. So the lounge may be a bit quiet for a while.

Shrill smokescreens and radioactive bananas

In a dashing blaze of opportunistic fear-mongering, the New York Times op-ed page is reporting that cigarettes, in addition to their usually toxins, also contain radioactive polonium-210. This is the same isotope used to assassinate Victor Litvinenko. The article, long on analogy and short on math, even goes so far to suggest that the total polonium dosage of second hand smoke in London could equal that which killed the former Russian spy. So, how much radiation is 0.04 picocuries?

Why, 1.48x10^-3 decays per second, of course. That’s about one decay every ten minutes. You’d have to be in a very deep, shielded room to detect that sort of signal above the cosmic ray background, and if your shielded room was made of cement, sandstone, or granite, the decays from naturally occurring radioactive minerals would also dwarf your polonium signal.

For analogy lovers, here’s a more correct one that what Professor Proctor has dished out: Potassium, which is a vital nutrient, has a slightly radioactive minor isotope, ⁴⁰K. With an isotopic abundance of .01% and a half-life of 1.25 billion years, a banana with 450 mg of K will kick out 14 decays every second. So a banana is over nine thousand times more radioactive than the polonium in a cigarette.

Now, how many cigarettes would it take to get a lethal dose? Well, the LD 50 for ingestion is around 8 million becquerels (decays/sec). So with 1.48x10^-3 Bq per fag, you would need about 5.4 billion of them to accumulate a lethal dose of polonium. I reckon the nicotine would get you first.

Professor Proctor writes, “London’s smokers (and those Londoners exposed to secondhand smoke), taken as a group, probably inhale more polonium 210 on any given day than the former spy ingested with his sushi.” Can this be true? Well, with a lethal dose 5.4 billion times greater than that of a fag, and assuming that 5.4 million Londoners smoke, they’d have to suck down a thousand cigs a day (50 packs) in order for the figures to be correct. Muscovites may think a 50 pack day is cold turkey, but Londoners? I doubt it.

Professor Proctor obviously thinks that the risk of smoking justifies incorrect arithmetic and easily refutable generalizations. Hopefully, my calculations will allow all my smoking readers to rest easy tonight, secure in the knowledge that it will be the tar and the nicotine that kills them, not the ²¹⁰Po.

p.s. As a geologist, I usually work in years, not seconds, so the first time I did the banana calculation, I instinctively calculated decays per year, and assumed I had seconds. However, I quickly decided that if 17 billion Bq was the dose from a typical banana, then I had bigger things to worry about than this blog.

Tactile computing

Life in the lab is just humming along this month. I think I’ve finally licked the alkali problem, but we won’t get to test until sometime next month. Ultra low-level alkali measurements just don’t interest that many people.

I’ve also been spending time running SHRIMP I, the original Sensitive, High-Resolution Ion Micro Probe. SI is a grand old machine, built before the era of modern computing. It is manually controlled. Instead of clicking on a flat screen, it uses dials and wheels and knobs for everything. Opening the sample lock requires spinning a huge valve crank with both hands, reminiscent of diving in a U-boat, or operating a 19th century steam engine.

One of the problems with the computer age is that computer interfaces are so anti-tactile. You just click stuff on screens. There is no texture, no clutching or smashing or tasting, like in the rest of geology. Visualization only goes so far in a science where grasping concepts and feeling out hypotheses is so important.

Of course, it would be unblog-like for me to simply complain about something in this medium without attempting a solution. So I will try to interface my computer with my rock hammer. A tap seems to have no effect, but if I take a hefty swing, then-

The morning after

This is an addendum to last night’s post.

I should let everyone know that I was using an unusual definition of “my”. Usually, my is the first person possessive pronoun. But occasionally, it has other meanings. In the case on yesterday’s title, for example, I used the little known definitions of “my”, such as: my=a; my=an uncontrollable; or my = a scheming foxy, willing-to-let-me-think-I-actually-figured-her-out.

For the better part of a week, everything was perfect, blissful, the Cs barely twice the instrumental background and Rb only a few times larger. I’m still not sure exactly what happened. Perhaps I got complacent, and started taking my cps for granted. Or maybe the alkali wild spirit can never really be tamed by a lab coated man, and resumed its contaminated machine on its own schedule, without regard to the wants and desires of the laboratory staff.

Whatever the reason, in the cold light of dawn, it became evident that the Friday morning backgrounds were an order of magnitude higher than the rest of the week. I was back to square one, with no consolation or explanation to ease my loss.

Fortunately, by that time the moon people had finished their analyses. In fact, I eventually tracked down the source of the contamination. A couple of Germans from Edinburgh* had been using the machine to looks at refactory glass and carbonates. That was fine, but what ended it for me and my alkali backgrounds was their decision, late in the day, to run just a couple of volcanic sanidines (is there any other kind?). The ablation of trace element-enriched K-spar must be what brought on the contamination.

I’m not really sure what to do now. Staring at the wiggly signal lines, it feels like I’ve lost something special, something irreplaceable. The calculating pert of my mind tells me that I’ll solve the problem of getting the low backgrounds soon enough, and I think I know how to keep them, but that doesn’t stop me from worrying.

A more interesting question, however, is why the Germans are in Edinburgh. I suspect it is a result of natural selection. Researchers from Mexico, China, or Italy would not be able to survive in Edinburgh. They would starve to death. So only it is reasonable to suspect that any scientists who can thrive there must come from countries with a cuisine sufficiently bland that Scottish food is not too painful an adaptation.

Rubidium is my Bee-otch

The Alkalis are the most tempestuous of elements. Willing to drop their unfilled S shell at the drop of a hat, they shamelessly lure anions away from more respectable metals, giving up their unpaired electron like a thermal ionization source in heat.

They are also filthy little atoms, dissolving into almost any aqueous solution, and easily evaporating under fairly reducing conditions. This, along with their ubiquity, makes them infamous contaminants in ICP mass spectrometry, and their background concentrations under standard conditions can be equivalent to thousands of ppm.

Special analytical techniques, such as soft extraction, have been developed to get around the pernicious easy-going electron-induced ionization of alkali caused by premature charge separation. But these techniques lead to reduced sensitivity, uneven backgrounds, and higher detection limits.

An alternative method, which has kept me out of trouble for the past six months, is to prevent these ionic Jezebels from getting into the cones in the first place. Although this “absence-based” protocol sounds easy, actually quarantining the gas expansion region of our machine from the alkali has been a bit of a chore, and only last month (and just in time for the conference) have I had any luck getting results from this technique.

On Tuesday, I finally managed to kick some group one ass. For some planetary post-Goldschmidt visitors, I let them open fire on lunar minerals with a 15 ppb detection limit for Rb on a 70 micron spot and minimal laser power. Now, the moon isn’t exactly alkali heaven. A dry, degassed, volatile-depleted wasteland, it has one of the lowest assumed mantle K/Th ratios of any known planetary body. So even in the compatible phases Rb is going to be low. But thanks to my trusty new tuning glass, half a year of assiduous record keeping, and a bit of good old-fashioned luck, these guys have a chance at getting something other than “bdl” to put in their papers when they’re done.

Lithium drives me batty

There are all sorts of ways to categorize the 83 long-lived, naturally occurring elements. There are the physical- solids, liquids, and gasses at the STP of your favorite planetary surface, for example. There are the chemical- based on electron orbitals, valences, electronegativity, and all that other stuff that I really ought to understand better than I do. There are the behavior-based methods- lithophiles, chalcophiles, and siderophiles. And then there’s the Sergio Leone method, to which I subscribe.

Under this system, all elements fall into three well defined groups: The Good, the Bad, and the Ugly. And under this strict categorical system, the defining characteristic under which all elements are grouped is the ease with which I can set my mass spectrometer up to analyze them at 8:30 on a hungover Friday morning.

Lithium is one of the Ugly. But unlike many of the ugly, like sodium, iodine, and tellurium, which are basically set in their ways, lithium really, really wants to be good. This is fine, because the analytical community wants it to be good as well- we can’t wait to bring it into the fold. We even give it help. When lithium starts acting out or getting ornery, we try to coax it back into the light.

The heartbreaking thing about lithium is that just when you think it is finally starting to behave in a respectable and informative manner, it acts out. Call it light element rebellion, call it three-proton obstinacy, call it what you will; the fact of the matter is that just when you think the lithium problem has finally been licked, it goes out and does something really bizarre.

In ICP-MS mass spectrometry, the main problem with Lithium is that, like most alkalis, it dissolves into the skimmer cone, and then gets reionized off the back of the cone. I don’t know if this is due to cone-plasma interactions, or if it is some sort of accidental TIMS- I honestly haven’t dug into the specifics of this phenomena. I’m not paid to do that. I’m paid to make it go away.

Specifically, my aim it to get- and keep- the lithium background down to below 1000 counts per second. That may sound like a lot, but under standard operating conditions, our system runs at about 5-10 thousand cps/ppm with a 70 micron laser spot. So if I can keep the background down, we can measure tenths of a ppm concentrations, which is roughly what you can expect in a mantle olivine, for example.

The main villain in the Lithium background drama is Lithium Borate glass. Lithium borate glasses (aka “flux”) are popular for whole rock analysis for a couple of reasons. Firstly, the correct composition melts at a reasonably low temperature, so you don’t volatilize all your non-refactories when you remelt your rock. Secondly, Lithium and Boron are fairly X-ray transparent (owing to their lack of deep electron shells), so they are great for doing XRF to get the major and minor elements. This allows scientists to measure the same samples by XRF and laser ablation ICP-MS, so that they can then pull their hair out when the two methods give contradictory results.

Trouble is, if you’re ablating something that is mostly lithium oxide, it doesn’t take very long for the Li to soak into the cones to the point where the background is in the tens of millions counts per second.

So, two months ago, I set aside a special, dedicated set of “LiBO only” cones. All LiBO work is done on them, and everything else is done on “normal” cones. Since then, the Li background has been steadily declining. Last week, in fact, we were regularly under 1000 cps, and the problem appeared to be solved. We were even able to detect Li in amphiboles and quartz. Everyone was happy. Until Friday, that is.

On Friday, the background jumped by a factor of 20. So, I checked with the Thursday user, no make sure he didn’t sneak some fluxed whole rocks into the machine while I was at seminar just to piss me off. He did not; all he analyzed was natural olivine, which generally has less Li than our tuning and calibration standards. I checked the 6/7 ratio, just to make sure I wasn’t looking at a doubly charged nitrogen problem, but the Li looked real. And I have no idea where it came from.

Oh well. I have better things to worry about over the weekend, so we’ll see what it wants to do on Tuesday.