I didn't see any links to this, sorry if I missed it. Curious what people think about the article. Randy?
Reefs Magazine - Skeptical Reefkeeping XII:
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Awesome! Thanks for your comments Randy, it's very interesting. Could one make a standard to test using very pure lab grade chemicals to make NSW levels from scratch so to speak? Wouldn't that remove the issue of having a standard that was examined using the same process. Would that be accurate if using an extremely sensitive balance and/or making a large amount so the trace elements could be added accurately - or would there be issues getting everything in solution correctly?
It is an interesting paper and such tests are worth doing, but I have a few comments.
1. For most of major and minor ions, it seems plenty accurate to me, and that is good to see since I had a lot of trouble getting a highly accurate number for calcium using the same basic method.
Iodine seems off significantly, which is somewhat of a concern since many reefers target iodine. The acidification of the standard by the manufacturer might have an impact on iodine since iodate (the predominant form in seawater) has a pKa around 1. Acidification to near that level or lower (which is done in the author's standard but not in normal tank samples sent to Triton) might cause some loss of HIO3 to the air before the sample gets to the ICP plasma. If so, that issue won't reproduce in tank samples, but I have no idea if it is the reason or not (or even if the standard sample contained iodate). The article's analysis and comment on acidification does not address the potential for this element to go into the gas phase and leave the sample when the pH was dropped to near or below the pKa.
2. For the trace elements, being off by up to a factor of 2 (what they'd call 100%) seems not optimal, but is likely accurate enough for any reef husbandry purpose. Take copper as an example. The standard claims 10 ppb. The test gave 13 ppb. That's "33%" error, but the way we'd use that number is exactly the same, no matter what the value was with that same % error. Either too high, about right, or too low. 33% error won't change that for a trace element (IMO). A few are off by more than that (Cd, Mn, Zn, Ni). That deviation of more than a factor of two is a concern if those elements give a result that deviates from NSW in a way that is important to the user. Several of these are elements are those which aquarists have been concerned with, either because there's too much or too little, and having a better handle on these values would be highly desirable, IMO.
3. The "guaranteed standard" was evaluated by the manufacturer using the same basic method that Triton used (although the details might be very different). Without further testing, one might properly assume the guaranteed analysis is more likely to be correct, but that isn't a certainty in the case of the trace elements, IMO.
4. There has been some discussion about the sample supplied being acidified with nitric acid by the manufacturer. Such a "matrix" effect might impact the results for some elements (the effect is well known, but usuallyn smaller than the large discrepancy for some of the trace elements; the paper shows a small subset of data from the literature, but shows no data for the elements most off in the Triton study). Hence a dispute between Ehsan of Triton and the authors of the study. Interestingly, the acidification is supposed to prevent binding of ions to the sides of the containers and equipment used in the study. Since Triton doesn't acidify, there may possibly be some inherent loses of some ions in normal tank samples, but not in acidified ones. So if Triton's method inherently has some loses in normal samples (and their own standards) that are not present in the acidified samples sent to them by the authors, then that might possibly be why they got higher values for some elements: because Triton's method "assumed" there would be losses in their equipment that didn't happen in the standard. Or it may just be a faulty method.
IMO, the only way to answer the acidification issue with certainty is to measure a normal seawater sample, acidify it, and measure it again.
Triton hasn't released an official statement regarding the article yet. Triton only claims accuracy of tests when performed on the matrix of seawater, not on an acid. The preparation, calibration, and method all rely on starting with actual seawater. This is absolutely a must according to Ehsan. Like Randy mentioned above, Iodine for example will test differently when in an acid vs seawater according to Ehsan. He accounts for this loss through calculations and customized methodology.
If any one else reading this or the article thinks that purchasing and sending a certified acidified sample would be a fun thing to do please consider that the ph in the sample is <2 and extremely dangerous to eyes, skin, etc. These samples SHOULD have been labeled for the safety of Triton-US and Trition GMBH who regularly handle the samples. They were sent disguised as seawater samples to Triton. On the msds sheet for CRM-SW it is listed as a hazardous material so the fun fact in the article is false.
I suspect that the actual concentrations of trace metals in most sea surface water samples will be below the limit of quantification for this method, so that test might not be as revealing as you think, unless both samples were spiked to bring up the levels to the quantifiable range. Since we aren't supposed to send acidified samples to Triton, the test is impossible to perform. Unless they revise their opinion on that issue, I will never be able to have a high degree of confidence in this method. Period.
Thanks for the comments, Craig.
What I meant by a normal sample, was a tank sample. Sorry for not making that clear.
A tank sample that did show some trace elements, before and after acidification (or a split sample, one half of which is acidified on collection). That should help clarify the issue.
Regarding the safety of shipping the standard, I've read the SDS. I review SDS's almost daily for various reasons, and this one strikes me as no more dangerous than most household products you all pick up at the grocery store (and use with no protective gear). If you are not used to reading these documents I could see how it would look scary dangerous, but if you compare it to a smattering of normal laboratory materials, it raises no flags.
Good Laboratory Practices would have all sample handlers wearing protective gear anyway (coat/gloves/glasses) especially with unknowns.
I agree that evaluating standards is appropriate, as long as they fit the requirements of the expected analytical process. I just don't know what those are at the moment.
Hey Craig, I did a big bacteriological survey of a bunch of aquaria a few years back. Know what I found, aside from Vibrio? Salmonella. Staph. Other pathogens. So yeah, acidified water would be a safer thing (assuming no PPE)