Measuring organic nutrients

[tatuvaaj]

Randy,

I understand that hobbyist phosphate tests only measure inorganic phosphate?

Is there any way for hobbyist to measure organic nutrients? I guess nitrogen would be difficult but what about phosphorus? Some chemical to convert org. phosphorus to inorganic and then measuring with normal phosphate test?

Also, do test kits measure all species of inorganic phosphate

TIA,

[Randy Holmes-Farley]

Tatu:

Ahhhh, what a nice question to start the forum off right!

Most hobby kits only measure inorganic orthophosphate (H3PO4/H2PO4-/HPO4--/PO4---). I use the Hach kit PO-19 for this.

The Hach kit PO-23 can measure some other inorganic forms in addition to orthophosphate, such as those forms with a P-O-P bond. These may be in some water supplies, but aren't too likely in tanks.

The Hach kit PO-24 can measure both organic forms and inorganic forms (referred to as total phosphate).

So if one was interested in organic nutrients, comparing total and orthophosphate is one way.

Total organic carbon (a send it out test) sounds like a simple and not too expensive way to me, but I've not seen anyone use it for a reef tank.

Nitrogen may be a tough way to go, as there are so many different forms of nitrogen, fron N2 in the air to nitrate to proteins.

[tatuvaaj]

Thank you very much!

I'll try to find Hach PO-24 test here in Finland.

Question about your article: "Phosphate? What is it and why should you care"

quote:
"In fact, seawater at pH 8.1 contains 0.5 percent H2PO4-, 79 percent HPO4- and 20 percent PO4--, although one should keep in mind that all of these forms interconvert many times per second."

I'm currently reading "An introduction to the chemistry of the sea" by Michael E. Q. Pilson where following amounts are given (at pH 8.0):
H2PO4- 1.2%, HPO4-- 90.3% and PO4-- 8.4%. Reference used was Atlas et al. 1976. "Phosphate association with Na+, Ca++, and Mg++ in seawater." Mar. Chem. 4: 243-254

Why the difference in numbers?

[Randy Holmes-Farley]

I don't know why they are different. I got the numbers from Table 8.4 on page 286 of "Chemical Oceanography" (1996) by Frank Millero.

The speciation will be a function of pH. Millero uses 8.1. Higher pH will shift everything toward PO4---, so that is part of the explanation, but maybe not all of it. Perhaps methods (or maybe definitions of "seawater") have simply improved in the intervening 20 years.

Temperature may play a role, but I don't know what temp. the other data was determined at.


Ignore the strange charges on those phosphate ions in that AF article. AF retyped the paper and I did not notice until a few days ago that they did it wrong.

[Gamera]

Total carbon content, as well as trace mineral content isn't difficult to establish. Either ICP or flame AA spectroscopy can establish that easily.

Given the size of most organics found in marine water, HPLC or HPGC would work quite well.

All are fairly inexpensive, and readily available spectroscopic methods.

[tatuvaaj]

Gamera,

I was thinking more like a method that average (or advanced) hobbyist might perform at home. I just might send a sample for more detailed analysis but I'm going to use the Hach PO-24 for detecting trends in my aquarium. Thanks for the advice!

Do any of you know if the Salifert Organics test has any value in detecting DOM in aquarium? From the product info:


Some organic compounds, such as phenolics/humic acids cannot be removed effectively by skimming, biological filtration or activated carbon. These compounds can become refractory (difficult to remove) and have a negative effect on the water quality.
The Salifert Organics test is a semi-quantitative measure for such compounds, and no other manufacturer offers such a test kit.

TIA,

[Randy Holmes-Farley]

Interesting, I did not know that there was such a kit.

[andy-hipkiss]

Tatu,

I can't say I really like the Salifert organic test, its very difficult to judge the endpoint. OTOH the Tropic Marin Protein test is at least very clear. Measuring different things ... maybe, but a close enough synonym for our purposes (???).

FWIW

[tatuvaaj]

andy-hipkiss,

Thanks for information! I'm going to try that test also. I already have Salifert Organics test and I agree that it is *very* difficult to tell when the water has slight yellow tint in it. But since the test doesn't give any hard numbers I guess it isn't that important if the result is off a few drops.

How many drops did your sample require when you did Salifert Org. test?

Are Tropic Marin instructions any more specific about what DOM it measures?

So hobbyist has these options for detecting DOM in aquarium water:

Salifert: "Most of the refractory organic compounds"
Tropic Marin: "Total protein ?"
Hach PO-24: "Organic phosphorous (+phosphate)"

[andy-hipkiss]

Tatu,

I have not got a Tropic Marin protein test at the moment :(

With the Salifert, I dug it out of my cupboard, brushed off the dust and did a series of tests.

With one drop I could see a difference between the control and the sample. However, following the instructions, what I would call a faint yellow came after 4 drops. However, after leaving the sample for 30 mins, it became quite obviously a yellow colour.

Sooooo, erm, I get a reading 1, 2, 3 or 4 drops! So that's either very good or problematic ... useful test kit .. I think not!

[MickAv8r]

The Tropic Marin Protein kit is most likely due for elimination. At least thats when I've been hearing from Tropic Marin USA. The kit hasn't been selling here. Randy I have a few left if you would like us to mail you one.

[Randy Holmes-Farley]

Gamera:

<< Given the size of most organics found in marine water, HPLC or HPGC would work quite well. >>

I agree that these methods would be suitable for quantifying any single organic, but since there will be hundreds (thousands?) of different organics, I'm not sure that this methodology would be very useful for getting an overall picture of what's going on.

However, since one of the main ways of detecting peaks via HPLC is via UV absorbance, why not use that alone? That will get everything all at once. Of course, some highly absorbing compounds will show up extraordinatrily strongly, and weak ones won't show up much at all, but it may be as good of an averaging system as many (refractive index would be better, but it's complicated by salt effects on refractive index).

FWIW, I'm presently tracking the UV and visible absorbance of my tank after shutting down my skimmer. That way I can see how much the absorbance rises (if any) and over what period of time.

Tom:

That would be great if you sent one to me. Too bad I didn't have (or know about) that kit before starting this experiment. I can always restart the skimmer at the end of the experiment and see how the concentrations drop (if at all). I'll send an email with my address.

[tatuvaaj]

Update:

Hach PO-24 test kit costs $320 here in Finland! :eek2:

I also called local lab and their prices seem to be more reasonable: most metals $16 per element and nutrients (incl. organic) $10 per nutrient. They use ICP.

Does Hach PO-24 cost that much in USA also ?!?

Randy,
Did you receive that Tropic Marin Protein test kit and if you did, what do you think about it?

[simonh]

I looked into the Hach PO-24 kit awhile back here in England. I beleive the price would be something equivalent to $180 ! I beleive it is substantially cheaper in the US and see to remember Craig mentioning either $50 or $80 in his original article. Maybe someone could check it out on Hach US site as I don't seem able to register for the site with been outside the US.

[Randy Holmes-Farley]

I haven't registered with them either, and my catalog is back at home, so I don't have the price handy. I'll post it Monday unless someone else posts it sooner. I've never used it, but I know that others have, and maybe they remember the price.

No, I don't have the organics test yet, but I've been away since Jan 3, so it might be sitting at the post office.

[MickAv8r]

I didn't get around to dropping it in the mail until the 4th or 5th but it should be there by now.

[RobertK]

Prices for Hach test kits in US$:

PO-19: $64.95
PO-23: $89.55
PO-24: $124.95

[Randy Holmes-Farley]

Thanks, Tom and Robert.:)

[RobertK]

You are welcome. Thank you for the info you provided. Those kits are too pricey for me. The only reason I was registered with Hach was that I bought some standardized nitrate solutions from them a while back to test out some test kits.

BTW, I agree that the Salifert organics test kit is worthless. The endpoint color change is a very pale shade of yellow that is almost indistinguishable from clear water (at least to my tired eyes), and just a couple drops of reagent makes the difference between acceptable and dangerous levels of organics. Don't waste your money on it, anyone.

[tatuvaaj]

Thank you Robert!

Hach pricing doesn't make any sense to me. I can take my water sample to local lab and have my water analyzed for total P for $18 per sample (this price includes the $10 handling fee and $8 for total P. The handling fee is the same even if I wanted to measure for n+1 elements). If I wanted to measure this parameter every two months it would take three years before the price would be the same as for the Hach test kit.

I guess the only use for Hach PO-24 is in the field where you don't have access to any other testing method.

The best solution for a hobbyist would be a method that is capable to convert all P to orthophosphate in sample. Then we could use the normal PO4 kits to measure total P.
Is this impossible?

[Randy Holmes-Farley]

Tatu:

<< The best solution for a hobbyist would be a method that is capable to convert all P to orthophosphate in sample. Then we could use the normal PO4 kits to measure total P.
Is this impossible?>>

I think that's how the Hach total phosphate kit works.

Remember on the pricing that you get many tests from each kit.


Robert:

Thanks for the input on the Salifert organics kit. I have a UV/Vis spectrometer in my basement, so I might be able to get more precise readings out of it that way. Of course, that won't help most people, and it will be difficult to know what the results really mean anyway. Nevertheless, it might be useful in conjunction with my skimmer experiment that I described earlier.

[Gamera]

Just to clarify a point I made a while ago that I should have gotten back to.

Randy: You pointed out that the HPLC uses UV-vis to measure organics as they're separated on the column. I agree that use of something like a spec-20 would be more feasible (particularly for someone who doesn't have access to a HPLC), but I was inclined to say that the overall HPLC trace would give a fair profile at any given point in time, provided that each peak in the HPLC can be correctly attributed to a particular compound. In much the same way the GCMS traces for single compounds can be used as fingerprints, I think a full HPLC 'fingerprint' can give a fair indication of what's going on in the tank chemically. I am, however, using the word fingerprint loosely as the profile would be dynamic rather than static, but I think it's possible to use it as a means of monitoring, at least, larger organics and possibly overall dissolved organics content.

[Tderasa]

Going back to the earlier question of why the differences in phosphate speciation numbers.....there may be differences between the ionic strength corrections used in each of the calculations to obtain the speciation numbers. Ka's in seawater typically are lower. i believe.....need to think about it a second.

[Randy Holmes-Farley]

tderesa:

I agree there is a huge ionic strength effect on phosphate speciation. There are also big specific effects from the presence of calcium and magnesium. I think both references that were discussed were talking about natural seawater, so those effects should be the same.

[Randy Holmes-Farley]

Gamera:

I just worry that there are too many slightly different organics in seawater to see much on a chromatogram other than a smear.

Though our tanks may be quite diifferent from seawater, here's what Millero says in "Chemical Oceanography" for natural seawater:

"In all current chromotographic methods, much of the total DOM appears as an undifferentiated peak on the chromatogram often referred to as an "unresolved complex mixture"."

Apparently, only 10-20% of the organics in seawater have even been characterized.

The other likely problem is that only about half of the organics in seawater are individual organic molecules (or very smalol aggregates). The other half are particulates (i.e., larger aggregates) bigger than 0.45 microns. These won't show much on a chromatogram.

I'd sure be happy to see someone run some tank water through an HPLC and see what results? Want to try it?

[Gamera]

I suppose I could try running a sample through an HPLC. At the very least, It'd be interesting to see what the results were.

I'll get back to you if I do run some through a HPLC.

[Randy Holmes-Farley]

Sounds good!

[tatuvaaj]

Ok, I just don't give up ;)

I have found that one can convert organic phosphates and polyphosphates into orthophosphate by microwaving (boiling) the sample with acid and an oxidizer (for organic phosphates). The sample should then be neutralized.

What could be used as an oxidizer? Iodine?
Can I use normal bicarbonate to neutralize the sample?

TIA,

[Randy Holmes-Farley]

I think one way is a digestion with perchloric acid, but I would not recommend that to anyone. Too dangerous.

I think Hach uses potassium persulfate and sulfuric acid (from looking at their reagents list).

I don't know of a good oxidizer for home use.:(

Sodium carbonate or bicarbonate is a perfectly good way to raise the pH.

[tatuvaaj]

Randy,

OK, now I give up... almost :D

Why I2 (Lugol's solution) isn't good oxidizer? Isn't it strong enough?

Also, do you think that the acid used matters (provided it is strong enough) ?

I'm also concerned about the gases formed when boiling the sample...

Anyways, thank you very much for your patience!

[Gamera]

Iodine (in its elemental form) is energetically inert as an oxidizing agent at standard temperature and pressure in solution as it can not be reduced any more than as you see it. Oxidized forms of iodine can act as oxidizing agents, but not elemental iodine itself.

Iodine containing oxidizing agents (such as periodate) are more than capable of being reduced themselves (and therefore act as oxidizing agents). Incidentally, periodate is an extraordinary oxidizer of organics and is not something you should go looking for at the hardware store to use at home. It's not a pleasant reagent.

-=-=-=-=-=-=-=-=-
It sounds like some of you may be interested in doing some home chemistry. I used to do it, and it's one of the reasons why I'm a chemist, but I've learned a lot of things in my time in the labs; and I realize that a lot of stuff I used to do was reckless and stupid. So I'm going to take a moment here to put in a small disclaimer that I don't condone home chemistry unless you know exactly what you're doing. You can get yourself into a whole heap of trouble, of the lethal kind or otherwise, if you're not properly informed of the situation beforehand. If I'm preaching to the converted, I apologize; but as someone who used to teach a lot of undergradautes, I want to make sure I cover my derierre. Sure, home chemistry is keen and a lot of fun, but in terms of safety, nothing beats a well maintained lab and a fume hood with the emergency vent button in plain view.
-=-=-=-=-=-=-=-=-=-

Possible home reagents for performing oxidations can be found under your kitchen sink. Bleach can be combined with water and mild acid to make a fairly good oxidizer. However, the fumes are rather strong and I don't recommend this. If you can get your hands on dichromate, an extremely easy oxidizing reagent is a blend of sulfuric and dichromate to give Jones reagent. However, I also don't recommend this as it is guaranteed to burn through denim in a matter of minutes (a drop of 8M solution dripped on my jeans once - one hour later, I had a dime sized hole in my jeans).

To be honest, I don't recommend doing this kind of chemistry at home, particularly in a microwave. The dilution of Jones reagent alone can be enough to crack pyrex flasks - so much excess heat is created. Moreover, controlled oxidation conditions with chromium based reagents are difficult to achieve at home. Even in undergraduate labs, I balk at allowing students to use Jones reagent out of liability (injury) issues. Moreover, chromium is a heavy metal and fairly toxic. You don't just dump it down the sink. (Coincidentally, the largest waste disposal violators on a number of campuses are art departments, specifically photography departments - not chemistry departments. :D )

Hypochlorite can be used as well (household bleach) as an oxidizing reagent and is typically marked as a household cleaning item. However you neither want to inhale the fumes, nor do you want to get it on yourself for extended periods of time (at room temperature, let alone when it's boiling hot). Additionally, perchlorates, as Randy mentioned earlier, aren't pleasant as they are highly explosive. Ten grams is enough to take off your hand. Milligrams are enough to punch a hole in jeans (which, again, I've done before - though not to myself).

That's not to say it can't be done. Given ppm concentrations, it's a safe bet that you won't kill yourself or put yourself in any danger if you work under "extremely dilute" conditions. However, as a chemist, there's simply too much wisdom in the saying that caution (whether or not induced by paranoia) is best if you want to live to see tomorrow.

Naturally, you should take my advice with a grain of salt. I've taught a lot of undergraduates in my time, and I've seen a lot of accidents; but (not to stereotype) a good 95% of them were pre-med students. :p

If you do end up performing these home experiments (which I DON'T condone), be sure to keep the following things in mind:

* Reagents that are boiling or freezing cold are extremely dangerous - most of the time more dangerous than if you pick up the bottle. It should go without saying why that's the case.

* When you handle anything that has boiling water, keep yourself at a distance, not necessarily because you could scald yourself with a spill, but because steam burns are far worse than flame burns. Do the math and you'll see why.

* If you love yourself at all, you'll wear goggles, wear latex gloves (or appropriate hand protection), and a lab coat. If you have to ask why, then you shouldn't be reading this thread.

*It's been mention that you want to neutralize a solution to bring it to an acceptable pH. When you neutralize, just as you do with dilutions, be sure you do it slowly. I can't even begin to tell the number of horror stories where someone tries to neutralize with bicarb and either gets burned by excess acid boiling over or gets hit by exploding glassware when the pressure is too much for a sealed system. Dilutions of acid can evolve a lot of heat in a short amount of time, just like neutralizations.

* Even when I do lab work in the middle of winter, I make sure the lab's well ventilated ( a window or two cracked open) and that there's both sand and a number of things (ice, water, liquid nitro, dry ice, acetone) at hand to quench a reaction.

If a reaction gets out of hand and you know what's going on, you may be forced to stop it, and stop it fast. A lot of times quenching is the only option you have. HOWEVER, that's not to say you should simply dump sand or water all over the place. I can't stress enough that you need to KNOW WHAT YOU'RE GETTING INTO AND WHAT'S GOING ON if you're going to abruptly quench a reaction. You may do more harm than good.

If it's out of control and you don't know how to stop it, don't bother. Leave it alone and get to safety. Sure, your house or apartment will go up in smoke or have to be evacuated to purge the place of fumes, but if you're doing home chemistry, that's the price you pay.

------------------------------------------------------

Randy may or may not agree with me on some of these points, particularly my rather vehement view of home chemistry; but I think any chemist reading this has to admit that we have some kind of bias, considering we already know what we do and know how to handle most situations. If you have no background in chemistry (and I don't count playing with a chemistry set or even one semester of chemistry in high school or college as any background to speak of), please don't try anything at home. It can become very dangerous, even at moderate dilution, very fast.

[Gamera]

I also forgot to mention to have a phone handy. You never know when you might need to call your siginificant other (about destroying your kitchen), a repairman (because you destroyed your kitchen), the police, paramedics, or a lawyer.

I just added the lawyer part as a joke...

[Randy Holmes-Farley]

Gamera:

You are right the bleach might be suitable. My concern with all of these possibilities is that they or their products may interfere with the phosphate assay. Excess oxidizing agent might. The persulfate of the Hach kit may have been chosen because of its temperature stability (or instability). It is completely destroyed on heating. I'm not sure most other oxidizers (e.g., bleach) are so readily destroyed.

I concur with the concerns about home chemistry.

[Randy Holmes-Farley]

Tom:

I got what I expect is the Salifert organic test kit when I got my mail from the post office. I'll try it out in the next week or so. Thanks for sending it.

[Gamera]

Persulfate is quite unstable thermally. The stuff will break down into free radicals at around 35 degrees guaranteed.

I used to use it as a polymer initiator at 3M.

Bleach won't degrade thermally under the same conditions, nor would any chromium-based oxidizer.

[simonh]

I don't have the original AF article from Craig on the PO-24 kit around. But I seem to recall that he did put a strong caution about ensuring the pan did not boil dry and just simmered otherwise you would produce some nasty things... maybe chlorine?

[MickAv8r]

Originally posted by Randy Holmes-Farley
Tom:

I got what I expect is the Salifert organic test kit when I got my mail from the post office. I'll try it out in the next week or so. Thanks for sending it.

That would be quite a trick since I sent the Tropic Marin kit LOL unless you mean they are using Salifert reagents.

As far as home chemistry goes...btdt :D it's always fun to see what you can use to aid in the "energetic disassembly" of an object.

[tatuvaaj]

Gamera,

Thank you for your great reply!

I'm am very interested in organic nutrient (and other DOM) levels in my aquarium but I guess I'm not going to do these experiments at home. Living in a apartment with wife and a two year old child makes the risks too great. I value the health of myself and other family members higher than the $18 cost of ICP analysis done by a local lab.

BTW, do you know what would the detection limit be for total P when using ICP analysis?

[Randy Holmes-Farley]

Tom:

<< That would be quite a trick since I sent the Tropic Marin kit LOL unless you mean they are using Salifert reagents. >>

Oops, my mistake.


<< As far as home chemistry goes...btdt it's always fun to see what you can use to aid in the "energetic disassembly" of an object.>>

Yes.....My favorite was to use a DC model train transformer to ............[edited out later when I worried that someone might try it].

[Gamera]

Inductively coupled plasma atomic absorbance/emission analysis can reliably detect into the ppb range for most elements.

If you can afford ICP, I say go for it. It's a unbelievably sensitive analytical method.

[TOM24]

This thread caught my interest so I took some tank water to work to see what I could find. We have headspace GC with an FID that we use for residual monomer analysis on acrylic latexes. The temperature program peaks at 240C. Limit of detection for low boiling compounds (about 100C) is in the 10-100 ppb range for water insoluble compounds. For higher boiling compounds (around 200C) the limit of detection is about 1 ppm for nonwater soluble compounds. The detection limit for water soluble compounds is increased by a factor of 10-100.

That said I ran samples from my 9 month old 30 gallon tank that has a bak pak skimmer and my two year old ten gallon eclipse. Somewhat to my surprise I did not detect anything significant. Both tanks utilize carbon 24/7.

Today I ran water from the thirty using a direct injection. This would greatly reduce the loss of sensitivity to water soluble compounds and higher boiling compounds. This time I did detect a couple of low boiling compounds ( around 50-80C). I would estimate the concentrations were in the 10 -100 ppb range. When the coloumn temperature hit 200C the baseline grew much higher than usual. It did not have any significant peaks. My guess is that something was degrading and causing the baseline to rise.

So based on my limited analytical abilities it appears my tank water is relatively clean of simple organic compounds I think it would be a different story for larger organic compounds ( fats proteins, carbohydrates etc.) that cannot be detected by a gas chromatograph.

[Randy Holmes-Farley]

Tom:

Interesting experiment. Tieing in with the iodine thread, methyliodide may be within the range of compounds that you detected (both in boiling point and typical seawater concentration (50-500 ppb)). I know it is a nasty compound (be very careful with it if you have it), but it would be great if you could report the methyl iodide concentration.

FWIW, most of the organics in natural seawater (as opposed to tanks where little data is available) are larger. Proteins, humic acids (big polyphenols), carbohydrates, etc.

[Randy Holmes-Farley]

Tatu:

<< BTW, do you know what would the detection limit be for total P when using ICP analysis?>>

I'll check at work next week. People who submitted water to Ron's study (that used ICP) may have the detection limits. For iodide and iron, the limits are not low enough to see NSW levels (as I recall from discussion with him and some participants).

[Randy Holmes-Farley]

Tom:

Polymer chemist? Some am I. I design and synthesize polymeric pharmaceuticals for a pharmaceutical company that we started about 10 years ago. (GelTex, now owned by Genzyme).

Gamera:

I recall a post from you where you also have done polymerizations, for ?Dow?. FWIW, we farmed some of our manufacturing out to DOW. Maybe you ran them for us? Does polyallylamine and/or Renagel ring any bells?

[TOM24]

We do not have methyl iodine in our lab and I don't think I will be ordering it. I will wait to see what Ron finds in his study that I many be able to look for in the future.

[Gamera]

As a RA for one of the researchers at 3M we got a million things from DOW at any point in time. :D It's difficult to remember many of the specialized materials.

With regards to methyl iodide, it is indeed fairly nasty, though I actually rank it as a much less nasty methylating agent ahn things like methyl triflate. However, I really doubt that methyl iodide would last very long in an aqueous environment such as out fishtanks - given that the overwhelming amount of water in the system would drive the formation of methanol from methyl iodide rather than allow methyl iodide to reside in the system for very long.

[Randy Holmes-Farley]

Gamera:

Methyl iodide might react in our tanks, especially near limewater addition points where hydroxide is high, but in the ocean it does seem to have a reasonable concentration that can be tracked as it cycles into the atmosphere. The pathway that you speak of, however, may be one of, or even the primary limiting pathway that keeps it from building up above ppb levels.

Actually, I mistakenly wrote earlier that the CH3I in seawater was hundreds of ppb. That would rival the iodide concentration. It is actually hundreds of ppt (parts per trillion).

[Gamera]

Randy -

Parts per trillion sounds much better than the figure you posted before. :p

[Randy Holmes-Farley]

Tom:

The Tropic Marin Protein kit is most likely due for elimination. At least thats when I've been hearing from Tropic Marin USA. The kit hasn't been selling here. Randy I have a few left if you would like us to mail you one.

OK, thanks again for sending it. I finally got around to using it as part of my skimmer experiment, and it was a total bust.

I only got as far as the first line of directions when it failed. It says pour dropper C into the vial.

Well, when I opened dropper C, a few flakes of solid fell off of the top, and it was empty inside. No liquid at all.

So, end of test........